HARDNESS TESTERS TECHNICAL CONTENT

Tech Round Up: Helpful, Readable, and Applicable Content

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On just about any given Tuesday, Heat Treat Today features an article that aims to educate our heat treating readers — be it in a process, equipment, metals, analysis, critical parts, or more. On this Thursday, enjoy this sampling of Technical Tuesday articles from the past several months. 

Case Study: Heat Treat Equipment Meets the Future Industry Today 

How has one heat treat furnace supplier contended with modern challenges of manufacturing? In this case study about a shift away from traditional forms of heat treat, explore how vacuum furnace technology has more technological horizons to bound. 

Figure 1. Construction and schematic furnace cross-section CMe-T6810-25 

Several key features discussed are the various challenges that characterize modern industry; the differences between historical heat treat furnaces and vacuum furnaces; furnace features that can meet these obstacles; and a close look at what one equipment option from SECO/WARWICK can offer. Additionally, explore the case study of a process that resulted in the following assessment: All technological requirements have been met, obtaining the following indicators of efficiency and consumption of energy factors calculated for the entire load and per unit net weight of the load (700 kg).” 

Read the entire article at “Case Study: Heat Treat Equipment Meets the Future Industry Today”

How Things Work: Thermocouples 

How do thermocouples work? How would you tell if you had a bad one? Those ever-present temperature monitors are fairly straightforward to use, but when it comes to how it works — and why — things get complicated.  

Figure 2. Eric Yeager of Cleveland Electric Laboratories explaining the 101 of all things thermocouple

This transcript Q&A article was published in a print edition, but there was too much information to fit the pages. Click below to read the full-length interview, including the final conversation about how dissimilar metals create electromotive force (EMF). Included in the discussion is proper care of T/C and guidance on when it’s time to replace. 

Read the entire article at “How Things Work: Thermocouples”

A Quick Guide to Alloys and Their Medical Applications 

Figure 3. Sneak peak of this medical alloys resource 

If you’re pining for a medical heat treat quick resource in our “off-season,” we have a resource for you. Whether you are a seasoned heat treater of medical application parts or not, you know that the alloy composition of the part will greatly determine the type of heat treat application that is suitable. Before you expand your heat treat capabilities of medical devices, check out this graphic to quickly pin-point what alloys are in high-demand within the medical industry and what end-product they relate to. 

The alloys addressed in this graphic are titanium, cobalt chromium, niobium, nitinol, copper, and tantalum.  

Check out the full resource at “A Quick Guide to Alloys and Their Medical Applications”

Resource — Forging, Quenching, and Integrated Heat Treat: DFIQ Final Report 

How much time and energy does it take to bring parts through forging and heat treatment? Have you ever tried integrating these heat intensive processes? If part design, forging method, and heat treat quenching solutions are considered together, some amazing results can occur. Check out the report findings when Direct from Forge Intensive Quenching (DFIQTM) was studied. 

Figure 4. Examples of DFIQ equipment

Forgings were tested, in three different locations, to see if immediate quenching after forging made a difference in a variety of steel samples. The report shares, “The following material mechanical properties were evaluated: tensile strength, yield strength, elongation, reduction in area, and impact strength. Data obtained on the mechanical properties of DFIQ forgings were compared to that of forgings after applying a conventional post-forging heat treating process.” 

Read the entire article “Forging, Quenching, and Integrated Heat Treat: DFIQ Final Report”

3 Top Tips for Brinell and Rockwell Hardness Tests 

Figure 5. Testing hardness 

Accurate hardness testing is a critical business for numerous industries, not least heat treatment. In this guide, evaluate “best practice” for getting the best possible reading for your hardness test with the most efficiency. These comprehensive tips include proper set up for test equipment and need-to-know information regarding the preparation and execution of both Brinell and Rockwell hardness tests. 

In fact, while there are some practices that overlap, knowing the differences is critical to determine whether or not a piece has reached the appropriate hardness. For Brinell, grease may skew a reading so that “at 300 HBW the material may appear 20 HBW softer than it actually is.” On the other hand, the precision in measuring indentation depth (versus indentation width) makes it imperative to keep the surfaces clear of any contamination.  

Read the entire article at “3 Top Tips for Brinell and Rockwell Hardness Tests”

Trending Market Insights for Aluminum Thermal Processing 

Figure 6. State of the North American aluminum industry

In this survey on recent and developing changes in the aluminum market, we asked industry players about the impact of trending technology and the overall state of the industry. Their responses to our questions in August 2023 described a steady and increasing melters’ demand; a limited, or lack of, business increase from additive manufacturing and 3D printing; the impact of — and response to — slow supply chains; the status of sustainability in the aluminum market; and how they plan to meet future market demand. 

Read the entire article at “Trending Market Insights for Aluminum Thermal Processing”

Find heat treating products and services when you search on Heat Treat Buyers Guide.Com

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How To Tell If You Really Have an Abrasion Problem

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Understanding abrasion can be the key to extending the life of your refractory lining. The following article provided by Plibrico Company examines abrasion resistance, its role in choosing a refractory solution, and what factors to take into consideration when assessing counter-measures.

Refractory material is designed to be very durable, withstand extreme service conditions and defy mechanical abuse in many different types of thermal-processing operations. However, severe conditions that cause abrasion in the form of high levels of mechanical scraping and airborne particulate matter can challenge refractories, shortening their service lives. 

Abrasion resistance is one of the most critical and possibly the most misunderstood considerations when choosing a refractory solution. A clear understanding of what abrasion is and, perhaps more importantly, what it is not can prevent needless repair costs and lead to significant savings. This is especially important when evaluating refractory designs for a new application or when considering upgrades for an existing one. 

What Abrasion Is 

Abrasion is the destructive process that causes a material to wear away through mechanical scraping or scratching. Anyone who has ever grated cheese or sanded wood has experienced the abrasion encountered in everyday life. As abrasion continues, thin layers of the abraded material are removed, leaving the object thinner and usually making its surface smoother. 

The same process can be observed in the refractory world. Refractory linings are abraded by high-velocity airborne particulate, cleaning tools and fuel/process materials that pass through the unit and come into contact with the lining. The telltale sign of abrasion is a refractory lining that has steadily become thinner while its surface has become smoother. The surface may even shine as if it had just been polished, which is not surprising when we consider that polishing is another common form of abrasion. 

Fig. 1. Abrasion damage to the refractory bottom of a choke ring of a thermal-oxidizer unit

What Abrasion is Not 

Abrasion is considered a type of mechanical abuse, but it is not the only type of mechanical abuse to which refractory linings are subjected. Equally common is impact: the sudden, forceful collision between the refractory lining and a moving object. Impact can come from a variety of sources. The moving object may be a cleaning tool, a piece of process material, a chunk of fuel or a dislodged mass of refractory or slag, depending on the application. Impact with such objects typically results in chips and cracks in the refractory lining. 

Refractory materials designed for abrasion resistance tend to have increased strength and hardness compared to those found in traditional refractories, and these abrasion-resistant materials may provide some resistance to impact. Abrasion-resistant properties can also lead to increased brittleness. This is because if the impact exceeds the strength of the material, chipping and cracking could potentially be worse than in traditional refractories. 

Compression and tension are also forms of mechanical abuse and can be caused by changes in the shape of the refractory lining as it is heated or cooled or by movements of the furnace shell itself – by intentional design or otherwise. Here again the increased strength and corresponding brittleness of the material could potentially result in a negative effect on the refractory lining. 

All types of mechanical abuse can cause thinning of the refractory lining, so it is important to conduct a detailed investigation into the destructive mechanism before drawing any conclusions. Refractory solutions designed to resist abrasion may not be helpful against damage caused by impact, compression or tension. 

Similarly, solutions designed to address other types of mechanical abuse may be ineffective against abrasion. For example, stainless steel needles are commonly incorporated into refractory linings to extend service life when impact resistance is required. The needles bridge cracks formed as a result of the impact, making it more difficult for these cracks to grow and connect. This helps the refractory lining hold together longer. The bridging provided by needles has no effect in an abrasion situation, however, since crack growth is not caused by the abrasion process. 

Meeting Abrasion-Resistance Demands 

Once abrasion is identified as the main mode of failure, there are several options to counter it. Selecting a refractory material based on a raw material hard enough to resist the abrasion is a common technique. For one material to abrade another it must be harder than the material being abraded. For instance, a diamond can be used to scratch glass, but glass cannot be used to scratch a diamond. 

It follows that refractory materials based on very hard raw materials, like silicon carbide, can be used to resist abrasion and extend the life of the lining. It should be remembered, however, that a refractory lining is made up of many different materials, not just the main constituent raw materials. Clay, cement, silica and other softer components will still be exposed and abraded even if abrasion of the main aggregate is stopped completely. 

Another option is to investigate the source of the abrasion and make adjustments to the process. Can a less-abrasive cleaning tool be used? Is there a way to limit the contact of the abrading process materials with the refractory lining? Is it possible to adjust the angle between the refractory lining and the incoming airborne particulate? 

A seemingly minor change in the process, with minimal cost and no downsides to the operation, can save in refractory replacement costs. When changes to the process are not an option, it is best to consider the abrasion resistance of the lining as a whole and select a specifically designed abrasion-resistant solution. A qualified, knowledgeable refractory solution expert with genuine experience will help you make the best decision for your specific application, taking into consideration the following: 

  • Speed of installation 
  • Service life 
  • All-in price 
Fig. 2. Airborne particle matter has contributed to the abrasion damage seen in the refractory of a thermal-oxidizer choke ring. Notice on the left side of the photo how the abrading of the refractory lining becomes worse.

Abrasion-Resistance Testing 

The most common measure of holistic abrasion resistance used to compare refractory solutions is the ASTM 704 test. This test exposes refractory lining materials to a stream of abrasive particulate that cause a portion of the sample to be abraded over time. By keeping sample size and shape constant – along with particle velocity, particle material and test duration – various refractory materials can be compared on an apples-to-apples basis. 

This testing can be performed by any qualified refractory testing lab and most reputable refractory manufacturers. Test results are recorded based on the volume of material lost from the sample during the test and are reported in cubic centimeters. Products with excellent abrasion resistance consistently test at 5 cc of loss or less, while elite materials can score less than 3 cc of loss. 

Products designed specifically for abrasion resistance will report ASTM 704 results on their material technical data sheets. It is important to remember that the abrasion-loss numbers reported on material technical data sheets are based on samples prepared in a lab under controlled conditions. Achieving these same properties in the field under real-world, job-site conditions would require a high-quality refractory installer partnered with a world-class refractory manufacturer. 

Fig. 3. Severe conditions lead to abrasion damage in the refractory lining of this dry-ash hopper. Notice the abrasion damage goes past the anchor line, leaving the bottom-left anchors exposed. 

Conclusion 

The thinning of a refractory lining due to abrasion is a source of frustration for many thermal-processing operations and is one of the most common modes of failure encountered in the refractory world. But, by taking the time to understand the failure mechanism and learn about the options available, you can realize significant savings by avoiding needless costs in the future. 

Learn more at www.plibrico.com. 

This article was initially published in Industrial Heating. All content here presented is original from the author.

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Automating the Brinell Hardness Tester In-House

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Automating Brinell hardness testing could mean saving on expensive laboratories, as was the case for one oil tool industry manufacturer. Learn the basics of Brinell hardness testing, its strengths and weaknesses, and options for automation.

This Technical Tuesday article, written by Alex Austin, managing director of Foundrax Engineering Products Ltd., was originally published in Heat Treat Today’s December 2023 Medical and Energy Heat Treat print edition, both in English and in Spanish.

Brinell Hardness Testing: Strengths and Weaknesses

Alex Austin, Managing Director, Foundrax Engineering Products Ltd.

In many steelworks producing large forgings and billets, in numerous heat treatment companies, and near many factory lines producing components for safety-critical applications, you’ll find a Brinell hardness tester. These machines have been used all over the world for more than a century (the test was first demonstrated by its inventor, the Swedish metallurgist August Brinell, in 1900), determining metal hardness by means of a tungsten carbide indenter ball that leaves a dish-shaped indentation in the surface of the test material.

Figure 1. Brinell equation (Source: Foundrax Engineering Products Ltd.)

In the test, the material sample is placed on a rigid anvil, and the indenter descends onto it under loads ranging from 1 kg up to 3,000 kg, depending on the material. Indenters vary in diameter from 1 mm to 10 mm. Most tests use a 3,000 kg load and a 10 mm ball, and the standards always refer to this as “HBW 10/3000.” HBW stands for Hardness Brinell Wolfram, Wolfram being another name for the tungsten carbide the indenter ball is made from. After the (approximately) fifteen second indenting cycle, the indentation is measured across both its x and y axes, as a minimum, by a special calibrated microscope. The mean of the diameter readings is then fed into the Brinell equation.

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Naturally, most technicians would rather not use that equation, so they look the indentation diameter up on a chart and “read across” to the derived hardness.

The great advantage of the Brinell test, when considered alongside other metal hardness testing methods, is that the large indentation diameter (typically between 2.4 mm and 6 mm) means the test result is generally unaffected by the grain structure of the metal. It also means that the surface of the test sample can be adequately prepared in just a few seconds with an angle grinder. For these reasons, the test is regarded by many as the “default” one for rough-surfaced and/or coarse-grained samples.

On the block in image (Figure 4), the distortion around the indentations can be seen very clearly.

That seems pretty simple, but there are inherent weaknesses in the Brinell test: measuring the indentation. In our previous article (read it in Heat Treat Today’s August 2023 Automotive Heat Treat print edition), we used this image (Figure 2) to illustrate how difficult it could be to work out exactly where an indentation edge begins and ends.

You might look at Figure 2 and think, “I’m pretty confident about where that indentation edge is,” but it’s trickier than it looks, because the process of indenting doesn’t just push material downwards; it also spreads it sideways, and you get a “pile up” around the rim of the indentation. The pile up may be difficult to see on hard material, or there may be a subtle “lip” inside the pile up that represents the true edge, but considered in cross-section, indentations look roughly like this simple sketch above (Figure 3).

Figure 2. Measurement of Brinell hardness test indentation (Source: Foundrax Engineering Products Ltd.)
Figure 3. Sketch of cross-section of indentation (Source: Foundrax Engineering Products Ltd.)

The overhead light illuminates the “pile up” rim very clearly on some of those indentations as a highlight around the edge. Where, exactly, does the pile up end and the true edge of the indentation begin? Bear in mind that 0.2 mm can equal 20 hardness points. You could show an indentation to three experienced workshop technicians and receive three different answers to the diameter question, and this problem has been a challenge of the Brinell test from its inception. Special blocks are available for training technicians in measurement, but the problem of operator interpretation was such that, in some quarters, the Brinell test was regarded as a bit “rough and ready.” “Ok for the workshop but not for the lab,” was perhaps how it was once seen.

Why Automate the Brinell?

The first question to consider when looking at the automation of the Brinell test is the measurement system because this is the inherent weakness. There are, of course, applications where only narrow tolerances are acceptable, and disagreements can arise between customers and suppliers.

Over the years, certain manufacturers, who mill heat treated materials for the oil tool industry, confided to us that they were regularly using expensive testing laboratories because of clients disputing the hardness figures of their products. They had previously been using manual microscopes. Obviously, this has reputational, as well as financial, consequences. If a manual microscope is employed on raw materials at the goods-in-process stage and there’s an error reading the hardness, you could find at final machining that you have put a lot of time and effort into a part that, in the end, is too hard or soft for the intended application.

Manually manipulating the microscope may not be worth the effort, especially when even a diligent operator may read the result incorrectly. With an automatic Brinell microscope, however, there is the possibility of major time and cost savings.

4 Levels of Automation

#1 Beginnings of Brinell Automation

The first step in automating Brinell hardness testing began 40 years ago when the world’s first automatic measurement microscope hit the market. The system, still being regularly refined, was able to measure the diameter of the indentation across over 100 axes, calculate the mean, and determine the hardness in a split second. It can handle most surface irregularity, operate in poor lighting, and warns operators of unacceptable surface preparation. Additionally, its precision adjusts for spatial error when lining up with a graticule. Within a few years of launch, a major oil tool manufacturer’s quality chief recommended its use to his suppliers, and user uptake was rapid.

#2 Integrated Microscope Model

A further step in automation is to dispense with operator handling of the microscope entirely by the acquisition of a tester with an integrated microscope. The microscope mentioned above, for example, is a feature on several hardness testing machines. The heavy-duty indenter holder pivots away from its normal line of thrust at the end of the indenting cycle, allowing a supra-mounted camera to view the indentation. This is hugely advantageous: no separate apparatus near the test machine, reduced handling time, and thus, much faster testing overall. Results from such machines are displayed next to the control panel and quickly uploadable to company quality systems.

Figure 4. Block with distortion around indentations (Source: Foundrax Engineering Products Ltd.)

#3 Dispensing of Manual Operations

Another automation option is to dispense with a hand-cranked anvil capstan and purchase a tester with a fixed anvil and movable test head. The technician is not required to manually raise and lower the anvil to allow for variations in the size of sample. Instead, the test head automatically “takes up” the space and also clamps the test piece very securely in place during the test cycle.

#4 Incorporate Custom Hardness Tester in Production Line

The fourth, and obviously most dramatic, automation step to consider is incorporating a custom-designed hardness tester into the production line. In some industries, this is essential. Large billets and forgings can’t be lifted into the jaws of a benchtop or floor-standing Brinell tester; so, for highly accurate testing of such items, a larger machine is required (Figure 5).

Figure 5. A custom-designed production line hardness tester. This machine is now in Texas. (Source: Foundrax Engineering Products Ltd.)

The whole gantry moves on one axis of travel while the test head moves perpendicular to that and, of course, up and down. This provides the full x, y, z movement. Large samples are maneuvered on and off by crane. The test head assembly incorporates the automatic microscope and results are displayed on a screen beside the control panel. Test results can be instantly uploaded to factory quality systems. The head assembly can also incorporate a milling tool for surface preparation!

With any decision to purchase plant and machinery equipment, some form of cost-benefit analysis is worthwhile. Clearly, if you’re doing a significant amount of business annually with a customer who is threatening to cease contracting with you because your hardness measurements are wrong too often, then the decision to buy an automatic microscope is not a difficult one. If staff are on overtime because mandatory hardness testing is adding too much time to production schedules, then a heavy-duty production machine with automatic microscope, movable test head, and sample clamp will pay for itself easily.

One thing is certain: Every automation option in Brinell testing increases accuracy and saves time.

About the Author

Alex Austin has been the managing director of Foundrax Engineering Products Ltd. since 2002. Foundrax has supplied Brinell hardness testing equipment for 60+ years and is the only company in the world to truly specialize in this field. Alex sits on the ISE/101/05 Indentation Hardness Testing Committee at the British Standards Institution. He has been part of the British delegation to the International Standards Organization advising on the development of the standard ISO 6506 “Metallic materials – Brinell hardness test” and is the chairman and convenor for the current ISO revision of the standard.

For more information: Visit www.foundrax.co.uk

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3 Top Tips for Brinell and Rockwell Hardness Tests

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OC

Accurate hardness testing is a critical business for numerous industries, not least heat treatment. In this guide, we will offer our “best practice” list for getting the best possible reading for your hardness test with the most efficiency.

This Technical Tuesday article was written by Alex Austin, the managing director at Foundrax Engineering Products Ltd.  

1. Tip for All Tests 

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Alex Austin
Managing Director
Foundrax Engineering Products Ltd.
Source: Foundrax

Make sure the test equipment is properly set up. In most instances, this involves keeping the test machine serviced and calibrated in accordance with the international standards (ASTM E-10 for Brinell and ASTM E-18 for Rockwell) or the manufacturer’s instructions — whichever are more strict — along with mounting it on a level, vibration-free surface. The absence of vibration is crucial if you are using a lever and weight machine, but still desirable for hydraulic and motor-driven types, and it is mandated by the standards. 

It is worth noting that for tests made using portable Brinell hardness testers that apply the full test load (albeit without the ability to maintain it uninterrupted for the full ten seconds), while it might not always be possible to mount the machine on a solid and level surface, the rest of the above still applies.  

If the anvil is mounted on a leadscrew, ensure that it is properly secured. Similarly, jigs should be in good condition, correctly mounted and hold the test piece securely. It is easy to become very relaxed about the amount of energy that goes into applying 3000 kg to a 10 mm ball, but if the component shatters under load the results can be dramatic and, potentially, very dangerous. 

Don’t forget your safety boots!  Also, as fingerprint residue is corrosive, always wear gloves.

2. Brinell Hardness Testing 

Preparation 

Before performing a Brinell hardness test, make sure both the test area and the indenter ball are clean and free of all lubricants. Oil or grease on the test surface or indenter could wreck the test by lubricating the path of the indenter, making a very significant difference to the apparent hardness level. For example, at 300 HBW the material may appear around 20 HBW softer than it actually is. Moreover, it can change the appearance of the indentation edge, causing a false diameter measurement. In any case, the hardness standards are clear that test pieces must be clean and lubricant-free. 

Prepare the area of the component surface where the test is to be carried out so that the indenter comes into direct contact with the core material. For this, the skin must be removed, including any decarburized layer, using a hand grinder with 60 grit abrasive (or finer, if appropriate) in 3–5 seconds, if a good automatic Brinell microscope will measure the indentation, or 10–15 seconds for a good manual microscope. This time differential is on the basis that a good automatic system will measure hundreds of diameters and ignore grinding “noise” when identifying the true edge of the indentation. On the other hand, use of a manual microscope is limited to the number one can reasonably measure by the time available and the equipment at hand. However, in the case of both automatic and manual testing, the better the surface, the better the result.    

Next, place the material on the test machine’s table or anvil. Ensure that it is stable and cannot move under the test load (machines with an integral clamp are preferable from this point of view). The clamp should be holding the material so that the test surface is perpendicular to the indenter’s line of operation.  

Carrying Out the Brinell Hardness Test

Table A. Force-diameter indexes for different materials

Use the correct force-diameter index (F/D²) for the material being tested; see Table A.

Apply the test force in accordance with ISO6506 or ASTM E-10, as appropriate. While the indenter is in downward motion and in contact with the material, avoid doing anything that might create vibrations that could reach the machine. When the indenter has withdrawn, measure the resulting indentation in a minimum of two diameters perpendicular to each other and convert the mean measurement into an HBW number.  

If using a portable Brinell hardness tester, exercise caution when removing the machine from the component so that the edge of the indentation is not accidentally damaged when the machine is released.  

3. Rockwell Hardness Testing

Preparation 

Figure 1. Close-up of Rockwell indentation

Cleanliness is everything in Rockwell testing. The indenters are much smaller than those used in Brinell testing and (as you would expect) so are the indentations (see Figure 1). And because the Rockwell test measures indentation depth, not width, any contaminant or particle that gets between the indenter and the material is a problem. Underside contamination is almost as important. There have been instances of clients finding that the testing block seemed to render two hardness points lower than we stated, yet in every instance, we found a buildup of soft contaminants (e.g., grease, oxides, micro-swarf) on the underside of the block. These contaminants “give” as the indenter is driven into the block, thereby permitting further indenter travel than would occur in the block material alone.

Lubricant contamination on the block surface is obviously extremely problematic. All blocks should be cleaned with a cloth and a liquid solvent that leaves minimal residue (e.g. isopropyl alcohol). Tissue paper can be used for cleaning but can scratch aluminum and brass easily; untreated cotton wipes are preferable. The anvil should also be cleaned by gentle application of a lint-free cloth dampened with solvent, and the indenter itself should be gently wiped at intervals throughout the test session. Another place where contaminants can build up (easily producing an error in excess of one Rockwell point) is the mating face where the indenter holder is inserted into the test head of the machine (see Figure 2). 

Figure 2. Importance in preparation

It is obviously also essential that the anvil mount cannot budge under the indenting load. If it is mounted on a vertical threaded column, the column should be free of excess grease and tightened to the point of no movement. Column “give” is another area where we have detected consequential erroneous readings.  

A further notable check worth performing is that the block, or test piece, has not been dropped and landed on a corner of the underside, which would leave a burr. This would prevent the piece from sitting flush on the anvil and probably negate the possibility of correct readings, as the piece would move under the indenter load. 

Procedure 

Figure 3. Softer block placed over test material during Rockwell test

If the first indentation on a block suggests a lower hardness than the remainder, there is a chance that air was trapped underneath it. The first indentations usually drives any air out, but in the case that air remained trapped beneath the indenter, the hardness reading will be falsely soft; the block will have moved downwards as it displaced the air, and the indenter will, therefore, have travelled further than if the block were truly sitting flush on the anvil. Placing a block that is softer than the test material on top of the test block and putting one indentation into it before commencing the tests will eliminate this problem (see Figure 3). 

Have an aerosol duster to hand during indenting to keep the block surface clear. 

Test blocks should, ideally, be stored in airtight cases to reduce the rate at which oxides form on their surfaces. Better still, wrap them in rust-reducing paper as well.   

(Photo Source: Foundrax Engineering Products Ltd.) 

About the Author: Alex Austin has been the managing director of Foundrax Engineering Products Ltd. since 2002. Foundrax has supplied Brinell hardness testing equipment for 60+ years and is the only company in the world to truly specialize in this field. Alex sits on the ISE/101/05 Indentation Hardness Testing Committee at the British Standards Institution. He has been part of the British delegation to the International Standards Organization advising on the development of the standard ISO 6506 “Metallic materials – Brinell hardness test” and is the chairman and convener for the current ISO revision of the standard.

For more information:

Contact www.foundrax.co.uk

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El ensayo de dureza Brinell para principiantes

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Cuáles son las características más deseables de un probador de dureza Brinell? Esta reseña del equipo le permitirá evaluar si debe o no incorporarlo a su departamento de tratamiento térmico.

Read the Spanish translation of this article in the version below or read the English translation when you click the flag to the right. Both the Spanish and the English versions were originally published in Heat Treat Today's August 2023 Automotive Heat Treat print edition.

Toda empresa dedicada al tratamiento térmico deberá practicar ensayos de dureza, algunos de ellos utilizando la medición Brinell que data desde el año 1900, lo que lleva a que se amerite el análisis de tan perdurable técnica. La prueba en mención requiere de un penetrador de bola de carburo de tungsteno que impacte de manera vertical sobre la superficie del material a ser ensayado, previamente ubicado éste sobre un yunque fijo. Paso seguido, se mide el diámetro de la “huella” generada por la bola, mínimo por los ejes “x” y “y,” y se toma el promedio de estas mediciones como cifra operativa de la que se pueda valer el técnico para establecer la dureza, bien sea alimentando una ecuación o mediante la lectura de una tabla de valores en la que se relacione diámetro frente a dureza.

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Para el ensayo Brinell se dispone de una amplia gama de cargas de fuerza, al igual que de diámetros de penetradores, reflejando la gran variedad de metales a ser probados; no obstante, en la mayoría de ensayos se implementa una bola de 10mm bajo una carga de 3.000 kg. En las grandes máquinas de apoyo a suelo por lo general el penetrador es motorizado, aunque otras operan a partir de palancas y pesas, mientras que también las hay hidráulicas o neumáticas.

Existen tres razones principales por las que la prueba Brinell no deja de ser el método más opcionado para la medición de la dureza en muchas industrias de tratamiento térmico.

1. Preparación de la superficie

La preparación de la superficie de una muestra para las pruebas Brinell toma solo unos segundos con una amoladora. Siempre que la muestra esté firmemente asentada sobre el yunque presentando la cara superior en dirección perpendicular a la dirección de la fuerza del penetrador, de acuerdo a lo exigido por las normas, no es necesario lograr una superficie demasiado lisa.

Figura 1. Robusto probador Brinell in situ

2. Contaminación de la superficie

Es poco probable que los contaminantes diminutos en una superficie generen una “prueba errónea” bajo un penetrador Brinell, a diferencia de la prueba de dureza Rockwell (el método más común en la industria). En esta prueba un pequeño indentador de diamante penetra menos de una centésima de pulgada, arrojando como resultado el que cualquier contaminante o anomalía en la superficie que pueda impedir o favorecer el progreso del penetrador (incluído el paralelismo) represente un problema, y obligando a que las muestras para la prueba Rockwell se deban preparar cuidadosamente antes de realizar la misma.

3. Portabilidad

Quizás el factor más significativo es que los robustos equipos portátiles de mano Brinell, con cabezales de prueba hidráulicos, permiten probar, in situ, piezas grandes, pesadas, de superficies rugosas o formas irregulares. Esta característica es de tal utilidad en la industria que ha motivado a que los órganos de normalización internacional otorguen una dispensación especial, una excepción si se quiere, a las máquinas portátiles, pese a que la ejecución de las mismas no sea susceptible de verificación directa como sí lo es la de sus equivalentes, las máquinas fijas.

Con fuerzas que van desde los 3000 kg hasta 1 kg, y bolas penetradoras tan pequeñas como 1 mm, las pruebas Brinell se pueden usar en una amplia gama de metales, pero los lugares en los que existiría la mayor probabilidad de encontrar un equipo de 10mm/3000kg son las forjas, las fundiciones, las plantas de tratamiento térmico, los laboratorios y las áreas de control de calidad. Previamente mencionamos que no se requiere que la superficie de las muestras de prueba sea absolutamente lisa; de hecho, es posible medir con un grado importante de precisión las superficies irregulares en materiales de configuración gruesa ya que el diámetro de la hendidura es tan grande en relación con cualquier irregularidad en la superficie.

Figura 2. Probador de Brinell, grado calibrador, en primer plano

En la Figura 2 se puede apreciar cómo un probador Brinell de grado calibrador introduce la bola de carburo de tungsteno en la muestra de prueba. Se mantiene la bola en posición para estabilizar la deformación plástica.

Las normas que rigen de manera detallada las pruebas Brinell son la ASTM E-10 y la ISO 6506, pero el procedimiento práctico para los técnicos es muy sencillo, tanto que el entrenamiento no debería tardar más de una hora. Para ensayar piezas forjadas, palanquillas y otras muestras, una hendidura debería bastar aunque, desde luego, en ciertas aplicaciones de extrema importancia se podrá utilizar más de una para mayor seguridad.

Saber si analizar o no cada muestra en un lote determinado deberá decidirse con base en la inconsistencia de las muestras mismas, más no responde a problemática alguna con las pruebas de Brinell en sí. En ciertas industrias se prueba cada pieza que se produce debido a que el riesgo de error es demasiado alto. Un buen ejemplo lo encontramos en la producción de los componentes de los eslabones para las orugas utilizadas en tanques y maquinaria pesada (retroexcavadoras y demás). Cada eslabón de cada oruga de un tanque en uso en el ejército británico ha sido probado por Brinell en una máquina totalmente automática, de alta velocidad, que cuenta con una poderosa abrazadera integral para mantener el componente absolutamente rígido durante la prueba. Por cierto, esa máquina es la de la primera foto. Con un cuidado adecuado y razonable, un probador Brinell robusto podrá generar cientos de miles de pruebas; de hecho, el probador de la Figura 1 ha realizado varios millones.

Las pruebas duran aproximadamente quince segundos ya que el penetrador se debe dirigir hacia el material de manera uniforme sin permitir la posibilidad de un “rebote” y evitando por completo llegar a golpear el material. Por otro lado, el metal debe recibir la presión por un período de tiempo suficiente que garantice que la hendidura se deforme de la manera más plástica posible, es decir, minimizando al máximo el riesgo de la más ligera contracción de la hendidura una vez retirado el penetrador.

Figura 3. Medición de una hendidura de prueba de dureza Brinell

Sin embargo, es en este punto que se presentan las complicaciones. Después de generar cuidadosamente la hendidura y retirar la muestra de prueba de la “boca” de la máquina probadora, es necesario medir la hendidura en al menos dos diámetros. Dado que las hendiduras de Brinell tienen como máximo 6 mm de ancho y que una diferencia de 0,2 mm en el diámetro podría equivaler a 20 puntos de dureza, obtener la medición correcta es esencial y de alta complejidad. La mayoría de los técnicos usan un microscopio iluminado para lograrlo, pero aún así puede ser un desafío. Considere la Figura 3.

Los microscopios de medición manual han mejorado a lo largo de los años, y cuando se obtiene una hendidura relativamente “limpia” con una retícula nítidamente iluminada, se le puede facilitar al técnico experimentado realizar una medición precisa. La Figura 4 presenta un escenario menos complejo que el anterior pero, aun así, ¿cómo podemos saber si realmente se ha juzgado con precisión la posición del borde?

Figura 4. Medición con microscopio mejorado y retícula bien iluminada.

Al crearse la hendidura se genera un cordoncillo en el perímetro de la misma debido a que el metal no solo presiona hacia abajo, sino también hacia los lados. Este cordoncillo puede difi cultar la ubicación del punto en el que comienza realmente la hendidura, y tres técnicos diferentes pueden hacer fácilmente tres estimaciones diferentes de su lugar de inicio. Es esta variación en la interpretación de los resultados por parte de los operadores la que ha llevado a que, durante más de 80 años, la prueba Brinell se haya considerado un poco “ordinaria”, apta tal vez para el maquinista en el taller, pero de dudoso valor para el científi co en el laboratorio.

En 1982 llegó a los mercados el primer lector automático, siendo éste la culminación de años de investigación, y valiéndose de software privado que llevó a las computadoras de la época a sus límites. El equipo podía hacer cientos de mediciones de un lado a otro de la hendidura y calcular el diámetro medio en una fracción de segundo. Poco después llegó a ser parte integral de una máquina de prueba Brinell. La noticia de la aparición de este equipo pronto llegó a algunos usuarios importantes en la industria de las herramientas petroleras quienes exigieron a sus proveedores valerse de él; quince años más tarde se había diseminado ampliamente el uso de esta tecnología generando la transformación de la percepción que se tenía de la prueba Brinell. Podríamos decir que la prueba Brinell había llegado a la mayoría de edad.

Figura 5. La última versión de ese microscopio automático en acción

Desde luego, como con cualquier equipo de medición importante, la calibración y el mantenimiento regulares son aconsejables, si no obligatorios. Los fabricantes mismos suelen estipular un cronograma de mantenimiento que se debe tener en cuenta junto con las reglas de calibración establecidas por las agencias internacionales.

Al considerar las opciones para la prueba de dureza en muestras con tratamiento térmico, en última
instancia existen tres métodos: Brinell, Rockwell y Microdureza (Vickers o Knoop).

Pese a que no es adecuada para muestras muy pequeñas o demasiado delgadas, la prueba Brinell es relativamente “inmune” a los contaminantes pequeños, los penetradores no son costosos, y, gracias al ancho de la hendidura, las pruebas de superficies con acabado áspero e irregular no presentan dificultades. Con el desarrollo, hace 40 años, de la medición automática de la hendidura, se superó la única deficiencia grave de la prueba Brinell, proporcionando las garantías que tan vital importancia revestían para los proveedores de piezas esenciales en industrias de toda índole, incluídas las de petróleo y gas, aeroespaciales y de defensa y transporte.

Sobre el autor: Alex Austin se viene desempeñando desde 2002 como gerente de Foundrax Engineering Products Ltd. Foundrax es proveedor de equipos de prueba de dureza Brinell desde1948, siendo en realidad la única compañía en el mundo especializada en el campo.

Alex funge en el Comité de Prueba de Dureza por Hendidura ISE/101/05 del British Standards Institution. En su calidad de miembro de la delegación británica de la Organización Internacional de Normalización, ha aportado como consultor para el desarrollo de la norma ISO 6506 “Materiales metálicos–prueba de dureza Brinell” y preside en la actualidad la revisión ISO de dicha norma.

Mayor información en www.foundrax.co.uk

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Brinell Hardness Testing 101

/ AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, FEATURED NEWS, HARDNESS TESTERS TECHNICAL CONTENT

What are the most desirable attributes of a Brinell hardness tester? Does it belong in your heat treat department? Read this equipment overview to decide. 

Read the English translation of this article in the version below or read the Spanish translation when you click the flag to the right. Both the Spanish and the English versions were originally published in Heat Treat Today's August 2023 Automotive Heat Treat print edition.

Alex Austin
Managing Director
Foundrax Engineering Products Ltd
Source: Foundrax

All heat treatment companies must test hardness; many with a Brinell tester. Existing since 1900, a review of this time-tested method is in order.

Contact us with your Reader Feedback!

The Brinell test requires a tungsten carbide ball indenter to be forced vertically into the surface of the test material, placed on a rigid anvil. The diameter of the indentation made by the ball is then measured across both its x and y axes as a minimum, and the average of these measurements is taken as the working figure. The technician can then either feed that figure into an equation to determine the hardness or read from a “diameter-to-hardness” chart.

There are various forces and indenter diameters available for Brinell testing reflecting the very wide range of metals that need to be assessed, but most tests involve a 10 mm ball under a 3,000 kg load. In large, floor standing machines, the indenter is usually motor-driven, but some machines use levers and weights, while others are hydraulic or pneumatic. The Brinell test remains the default method for hardness measurement in many heat treatment facilities, for three primary reasons.

1.  Surface Preparation

Preparing the surface of a sample for Brinell testing takes just a few seconds with a grinder. Provided the sample is sitting steadily on the anvil and the top face of the sample is perpendicular to the direction of force of the indenter — as mandated by the standards — the surface does not need to be particularly smooth.

Figure 1. Heavy-duty Brinell tester in situ

2. Surface Contamination

Minute surface contaminants under a Brinell indenter are unlikely to cause a “mis-test.” By comparison, during Rockwell testing, the most widely used method across all industries, a tiny diamond indenter penetrates the surface by less than one hundredth of an inch, and any contaminants or surface abnormalities (including parallelism) that could impede or assist the progress of the indenter are a problem, which means that Rockwell samples must be carefully prepared before testing.

3. Portable

Perhaps most significant, rugged, hand-held portable Brinell testers with hydraulic test heads enable large, heavy, and awkwardly shaped components of rough surface finish to be tested in situ. This feature is of such utility in industry that the international standards authorities give a dispensation — a special designation — to portable machines, although their performance cannot be directly verified like their floor-standing cousins.

With forces ranging from 3000 kg down to 1 kg and indenter balls as small as 1 mm, Brinell testing can be used on a vast range of metal, but forges, foundries, heat treatment plants, quality control areas, and laboratories are the places one would most likely find a test machine working at 10 mm/3000 kg. It was mentioned earlier that the surface of test samples doesn’t need to be particularly smooth, in fact roughly- ground surfaces on materials with a coarse grain structure can be measured quite safely because the diameter of the indentation is so large relative to any irregularities on the surface.

Figure 2. Close-up of a calibration-grade Brinell tester

In Figure 2, a calibration-grade Brinell tester drives the tungsten carbide ball into the test sample. The ball is being held in position to stabilize plastic deformation. ASTM E-10 and ISO 6506 — the authoritative documents for Brinell testing — lay out standards in detail, but the practical procedure for workshop technicians is very straightforward; training should not take longer than an hour. When testing forgings, billets, and other samples, one indentation should suffice but in certain critical applications more than one indentation may be used for assurance.

The question of whether to test every sample in a batch will depend on how inconsistent those samples might be; it has nothing to do with any issues with Brinell testing itself. In certain industries, every single product is tested because the risk of failure is too high. A good example of this is the production of links for the tracks used on tanks and other armored vehicles. Every link in every tank track in use by the British Army has been Brinell tested on a high-speed, fully automatic machine that features a powerful integral clamp to keep the component rigid during the test. You can view the machine in Figure 1 on page 44. Subject to reasonable care, a heavy-duty Brinell tester will perform many hundreds of thousands of tests. The machine in Figure 1 has performed several million.

Tests take approximately fifteen seconds. The indenter must be driven uniformly into the material with no possibility of either a rebound or a speed that would “punch” the indenter into the material. Also, the metal must be loaded for a sufficient length of time to ensure the indentation is properly (plasticly) deformed, that is, the risk of an indentation shrinking very, very slightly after the indenter is withdrawn is kept to a minimum.

Figure 3. Measurement of Brinell hardness test indentation

Measuring the indentation is more challenging. After carefully making the indentation and withdrawing the test sample from the “jaws” of the test machine, one must measure the indentation across at least two diameters. Given that Brinell indentations are at most 6 mm across and that 0.2 mm difference in diameter might equal 20 hardness points, getting the measurement right is critical — and tricky. Most technicians will use an illuminated microscope to do this, but even then it can be a challenge. Consider Figure 3 on the next page.

Making an indentation leaves a “ridge” at the indentation perimeter because metal is not just pushed downwards, but also sideways. This ridge can obscure where the real indentation begins, and three different technicians can easily make three different estimates of where that is. And this variation in operators’ interpretation of results is why, for over 80 years, the Brinell test was seen as a little “rough and ready,” for the workshop machinist, perhaps, but probably not for the laboratory scientist.

Manual measurement microscopes have improved over the years, and a relatively “clean edged” indentation with a crisply illuminated graticule can be less challenging for the experienced technician to make an accurate measurement. Figure 4 is a less difficult scenario than the one above. Even so, how can we know if we have really judged the position of the edge precisely?

Figure 4. Measurement with improved microscope and well-illuminated graticule

In 1982, the first automatic reader hit the markets. This was the culmination of years of research and used proprietary software that pushed the computers of the day to their limits. The equipment could make hundreds of measurements across the indentation and calculate the mean diameter in a split second. Not long afterwards, it was available as an integral part of a Brinell test machine. Word of this equipment soon reached critical users in the oil tool industry, and they mandated its use to their suppliers. Within 15 years, the use of this technology was widespread and the perception of the Brinell test’s accuracy had been transformed. The Brinell test, in a sense, had come of age. See Figure 5 for the latest version of that automatic microscope in action.

Finally, like any important measuring equipment, regular calibration and servicing is desirable, if not compulsory. Manufacturers typically stipulate a service schedule which must be considered alongside the calibration rules dictated by international agencies.

When considering options for hardness testing of heat treated samples, there are ultimately three test methods: Brinell, Rockwell, and Microhardness (Vickers or Knoop).

Figure 5. Latest version of the automatic microscope in action

While Brinell testing isn’t suited to very small or very thin samples, it is relatively “immune” to small contaminants, the indenters are not expensive, and the width of the indentation means that testing of coarse grained and roughly finished surfaces is not problematic. With the development of reliable automatic indentation measurement, the one serious deficiency of the Brinell test was overcome, providing the assurance that was vital to critical components suppliers in all types of industries such as oil and gas, aerospace, defense, and transportation.

About the Author:

Alex Austin has been the managing director of Foundrax Engineering Products Ltd. since 2002. Foundrax has supplied Brinell hardness testing equipment since 1948 and is the only company in the world to truly specialize in this field. Alex sits on the ISE/101/05 Indentation Hardness Testing Committee at the British Standards Institution. He has been part of the British delegation to the International Standards Organization advising on the development of the standard ISO 6506 “Metallic materials – Brinell hardness test” and is the chairman and convenor for the current ISO revision of the standard.

For more information:
Contact www.foundrax.co/uk.

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Tips #13 – 23 – 33 – 43

/ HARDNESS TESTERS TECHNICAL CONTENT, HEAT TREAT NEWS INDUSTRIES

One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks from some of the industry’s foremost experts.

Heat Treat Today’s latest round of 101 Heat Treat Tips is featured in Heat Treat Today 2020 fall issue (also featuring the popular 40 Under 40).

Today’s selection includes four tips from Leybold Vacuum USA, Young Metallurgical Consulting, Dr. Valery Rudnev, and Chiz Bros. Increase output, decrease production costs, hit target temperature, and avoid thermal shock with these four tips.

Heat Treat Tip #13

New Diffusion Pump Technology Increases Production Output

Gain immediate positive net cash flow with a lease to own finance option by upgrading your diffusion pumps with the new immersion heater technology. The new style heater will extend oil life and reduce energy consumption. New heater technology can increase production by eliminating the need of dropping your pump every time you change oil for faster maintenance turn around. Drop in place pump design with improved performance.

NEW-DIJ Diffusion Pumps with smart heater technology by Leybold Vacuum
Source: Leybold Vacuum USA

(Leybold Vacuum USA)

Heat Treat Tip #23

Inspection Mistakes That Cost

Rockwell hardness testing requires adherence to strict procedures for accurate results.  Try this exercise to prove the importance of proper test procedures.

  • A certified Rc 54.3 +/- 1 test block was tested three times and the average of the readings was Rc 54 utilizing a flat anvil.  Water was put on the anvil under the test block and the next three readings averaged Rc 52.1.
  • Why is it so important that samples are clean, dry, and properly prepared?
  • If your process test samples are actually one point above the high spec limit but you are reading two points lower, you will ship hard parts that your customer can reject.
  • If your process test samples are one point above the low spec limit but you are reading two points lower, you may reprocess parts that are actually within specification.
  • It is imperative that your personnel are trained in proper sample preparation and hardness testing procedures to maximize your quality results and minimize reprocessing.

Properly preparing a hardness sample can save time and money.

Source: Young Metallurgical Consulting

(Young Metallurgical Consulting)

Heat Treat Tip #33

Not Able to Hit Target Temperature — What To Do

Situation: Customer had an available 100kW/1kHz inverter and needed to heat 1-in.-diameter carbon steel bar to hot working temperature (2000°F). It was a low production application and cycle time was not critical. However, regardless of the heat time and irrespective of using maximum available output power, it was not possible to reach required target temperature. Actually, after reaching about 1470o°F there was no noticeable temperature rise regardless of increased heat time.

Solution: Severe eddy current cancellation was responsible for a failure to reach target temperature. The use of frequencies 6 kHz and greater can easily help to accomplish the goal. As a simple “rule-of-thumb,” in order to provide an efficient heating and avoid eddy current cancellation in through heating applications (e.g., through hardening or hot working), it is necessary to choose a frequency that will guarantee that the “bar diameter-to-penetration depth” ratio exceeds 3.6 at a target temperature.

(Dr. Valery Rudnev, FASM, Fellow of IFHTSE/Professor Induction/Director Science & Technology, Inductoheat Inc., An Inductotherm Group company)

Heat Treat Tip #43

Brick to Fiber to Avoid Thermal Shock

Thermal shock is a regular issue with hard refractory and brick-lined furnaces due to the constant changes in temperature for batch annealing. Switching an old furnace over to ceramic fiber is an easy process that can save time and money.

(Chiz Bros)

Tips #13 – 23 – 33 – 43 Read More »

Understanding Heat Treatment Specifications

/ FEATURED NEWS, HARDNESS TESTERS TECHNICAL CONTENT, MANUFACTURING HEAT TREAT

Metallurgists need accurate specifications in order to correctly perform the necessary heat treatment of parts. This helpful guide, written by William Rassieur, Sales Leader at Paulo Heat Treating, is a useful tool to identify what details ought to be communicated to the heat treating expert. Read below to understand the terms to pass along.

William Rassieur, Sales Leader, Paulo Heat Treating

Too often, metallurgists receive inadequate heat treatment specifications. Some specs contain too little information. Some are unclear. Some are just plain wrong.

In any case, inadequate specs mean heat treaters don’t have the information they need to deliver finished parts that can stand up to the applications intended by their manufacturers. Avoiding the confusion and delays that follow comes down to understanding what heat treaters need to see in heat treatment specifications so that the right treatment is applied.

Make certain your parts get the appropriate treatment by including the following information:

Clearly identified materials

The chemical makeup of a part is one of the most critical determinants of how it is heat treated. It’s not enough to state on the spec that a piece is steel alloy. Consult materials standards and use the correct material designation on the spec.

For example, if you want to treat a carbon steel or an engineering alloy, using those terms (or known trade names for a specific material) isn’t adequate. Good heat treatment specifications include the material as expressed in the standards—AISI 1040 for a carbon steel, for example, or SAE 4140 for an engineering alloy.

Specific process required

It’s not enough to tell a heat treater you’d like a harder part because there are many ways to do that. Does it need to be through hardened? Case hardened? Does it require stress relief via annealing?

Specs that dictate which process is to be used help heat treaters shape the rest of the heat treatment steps that follow.

Hardness tolerance

For through hardened parts, a prescribed hardness should be included on the spec and expressed as a range. Tolerances are always more useful than uniform hardness levels because parts can have different hardness values in different regions due to material thickness or closeness to an edge.

Engineers should note that the materials and dimensions of a part affect how well it hardens out. As these variables change, so does the acceptable hardness tolerance that should appear on a spec.

Case depth tolerance

For case hardened materials (i.e., those that are carburized or carbonitrided), specs should indicate whether the desired hardness is expressed as effective case depth or total case depth.

Case Hardening (photo source: Paulo.com)

Total case depth refers to the distance carbon has diffused into the part. This is usually specified for parts that have thinner case depths after treatment. Effective case depth applies to parts with generally thicker cases. This is measured as the distance from the surface through the case to a specific hardness level. Usually, that hardness is effective based from 50 or 52 HRC. This should always be stated on specs.

Heat treatment specifications should also identify the case tolerance, or the range of depths the prescribed hardness should reach. For example, a good spec for the heat treatment of a theoretical gear might state the effective case depth should be between 0.007 and 0.012 inches at the prescribed hardness.

As with through hardening, it’s more useful and realistic to specify minimum and maximum case depths rather than to write specs with a single case depth. Specs that include only minimum or maximum case depths still leave too much to interpretation and should be avoided.

Avoid too much information

Sometimes, though, too much specificity can lead to trouble. Specs that include too much process information can paint metallurgists into a corner, forcing them to abide by strict requirements that can end up thwarting their efforts to deliver improved parts.

For example, if a tempering spec includes both a specified temperature and a specified hardness, the hardness may not be possible to achieve due to differences in equipment. In such a scenario, metallurgists advise that specs be amended to call for a minimum temper as long as the part’s configuration and material hardenability are capable of achieving it.

Correct hardness scales

The scale on which a part’s hardness is determined depends on the heat treatment applied to the part. In the U.S., we typically use the following four hardness scales: Rockwell Hardness, Brinell Hardness, Microhardness, and Leeb Hardness. Become familiar with each scale and which parts and processes should be tested with each.

Also note that conversions between hardness scales should be avoided unless it’s absolutely necessary. That’s because hardness values are approximate; converting from one approximation to another compounds variation and could lead heat treaters and owners to incorrectly assume the prescribed hardness has been achieved.

Inspection points

Heat treatments are carefully designed to achieve specific results on specific areas of parts, so owners need to clearly identify those areas on which hardness tests are to be conducted.

For example, the critical part of the theoretical gear mentioned above is its teeth; case hardening is designed to strengthen that part of the gear while leaving other areas relatively soft and ductile. Applying a hardness test anywhere else but the teeth won’t inform heat treaters of whether the treatment was successful.

Be prescriptive with heat treatment specifications

Problems with heat treatment specifications are one of the biggest —and perhaps the most avoidable— pain points in the relationship between a manufacturer and heat treater. Manufacturers need finished parts that perform as promised. Armed with accurate and descriptive heat treatment specifications, heat treaters can deliver that performance.

For more information, contact the quoting team at Paulo or download Paulo's guide for in-house versus out-source handling of heat treatment needs.

 

(photo source: original article)

 

 

 

 

 

 

Understanding Heat Treatment Specifications Read More »

Manual Versus Automated Hardness Testing

/ AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT NEWS, FEATURED NEWS, HARDNESS TESTERS TECHNICAL CONTENT

When it comes to hardness testing nowadays, the process does not have to be done manually; automation has taken much of the burden away from operators. But which way produces the better result?

In this Heat Treat Today Original Content feature, Buehler recently published the results of a time study that compared case hardness testing of automotive crank pins and journals using both automation and manual testing. Find out which method showed a definite edge over the other in terms of time saved, less part manipulation, fewer errors in data transcription, and lower variability between performing tests.

EXECUTIVE SUMMARY

A study shows an operator time savings of 86% for making and measuring indents in three locations of crank pins and journals when using automation compared to manual testing. There was less part manipulation, fewer errors in data transcription and lower variability between operators performing tests.

INTRODUCTION

A large automotive manufacturer wanted to investigate the potential time savings of using automation for hardness testing crank pins and journals. Their existing process required two skilled operators per shift, two shifts per day, seven days per week. Tests were performed in three specified locations, two at forty-five degrees off axis and one perpendicular to the axis. Specified locations are critical, as missed locations could lead to manufactured parts being held in quarantine until further confirmation can be performed. Also of concern are failed parts that were inadvertently passed being installed and ultimately being prone to catastrophic failures. Data transcribing error was also a concern; if part information was entered incorrectly in a separate database it would cause mismatched data to lot number. When this occurs, it causes parts to become quarantined until the part information can be verified. With the total scrap cost being a considerable factor, skilled trained operators are needed for testing. Round robin testing is also used to determine the variability between operators. Qualifying new lines put into production increased testing by a factor of three to five times the normal operation analysis rate.

OBSERVATION

Current Process Observation

An evaluation of time to make and measure Vickers indentations on automotive crank pins and journals was established to determine a baseline of time for the existing process. Testing was done on a standalone manual system and required operator time for alignment, making and measuring of indents. The operators would fixture parts in similar orientation to ensure that measurements of the forty-five degree axis were in close proximity to expedite testing and reduce errors in testing. A high degree of manipulation for part alignment is necessary prior to physical testing to ensure accuracy.

It was observed that the operators’ set up time for location took the largest amount of testing time at 60%, measuring indents taking the second largest amount of time at 30% and making indents the third largest amount at 10%. The total amount of indents per pin and journal varied but averaged eighteen indents per section; six in each location. Total amount of indents for a crankshaft, pins being measured top dead center and bottom dead center and journals being measured along split, was 216 indents on average. The total analysis time for making and measuring indents at the specified locations on a crank was nine hours with 8 hours of operator interaction.

Implemented Process

For the implemented process a Wilson VH3100 series Vickers Microhardness Tester with DiaMet software was used. Parts were clamped in a machinist vice and placed on the stage without manipulation of orientation.

Figure 1.1 – Crank pin held in machinist vice (source: Buehler)

Trace function was used with the overview camera to create a template of the part to be tested; minimizing the set up time for the indent locations. The use of the template reduced the location set up time to 45 seconds in the three areas; two at forty-five degrees and one perpendicular to case.

Figure 1.2 – Trace function template for ease of indent locations (source: Buehler)

The DiaMet software snapped the template to the part at the specified location and the operators confirmed location. Observation of the set up time, making and measuring indents was 10, 50 and 40 percent respectively. Total amount of indents for a crankshaft was 216 indents on average with of time 1.25 hours with 15 minutes of operator interaction.

Figure 1.3 – Indent make and measure being performed automatically (source: Buehler)

Visual high and low threshold warnings were added to each program giving the operator the ability for quick assessment of parts versus the confirmation after all crank pins and journals were analyzed as it was in previous methodology.

Figure 1.4 – Visual high low threshold warnings to alert operators of
hardness thresholds (source: Buehler)

For reporting, metadata was set up to prevent operator errors in transcribing data.

Figure 1.5 – Metadata setup to reduce operator input transcription
errors (source: Buehler)

SUMMARY

The time study evaluation shows automation saves a significant amount of time with setup as well as the time required to make and measure the Vickers indents. The total amount of time that the operators spend setting the indent profile, measuring and compiling data is reduced by 86% as well as avoiding any errors in transcribing data. Repeatability of testing is increased operator to operator, as variability between operator judgement is eliminated. The combination of using trace function and templates eliminated the need for operators to spend time aligning parts on the stage as well as mitigated the risk of a misplaced indent profile. The increase of visibility of part failure is evident at time of measurement and gives the operator the ability to recheck either an area or total part without the need for extended quarantine of parts for re-examination. Using metadata fields within the Vickers testing program removed transcribing issues which would hold up batches of cranks until records could be reviewed.

(source: Buehler)

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In-Situ Hardness Testing of Large Aerospace Structures – A Case Study

/ AEROSPACE HEAT TREAT, AEROSPACE HEAT TREAT NEWS, FEATURED NEWS, HARDNESS TESTERS TECHNICAL CONTENT

This article originally appeared in Heat Treat Today’s March 2019 Aerospace print edition.

How a Custom Designed Fixture and Hardness Testing Unit Solved a Major Aerospace Engine Manufacturer’s Hardness Testing Dilemma

Situation: A major aerospace engine manufacturer wanted to ensure the appropriate hardness of a specific section of a heat-treated engine housing. They wanted to non-destructive test the actual housing and not test shims. They wanted to do the test in-house so as to not stall production by having to ship the part out for testing. Another reason they did not want to ship the parts out for testing was the size of the parts. Some of the parts had a diameter as large as 40 inches (102 cm), 20 inches (51 cm) high, and 900 lbs (400 kg). The aerospace company also wanted an automated, full-proof system that reduced the chance of human error.

Figure 1

Solution: The solution came in the form of a custom-built hardness testing machine and an innovative fixture to hold the engine housing. As can be seen in Figure 1, AFFRI USA, located in Illinois, designed a fixture to hold both a custom-designed hardness testing machine as well as a fixture to hold the engine housing.

The Hardness Testing Machine

The specific hardness testing unit chosen for the job was DAKOMASTER 300. Typically, this unit is a tabletop unit as shown in Figure 2. For this specific aerospace application, the unit was modified so that it could be securely attached to the steel

Figure 2

construction holding fixture. Additionally, the custom-built unit was adapted so that the measuring head had a much greater vertical and horizontal range to accommodate varying height engine housings. The engine housings varied in size from as large as 110 inches (2.8m) in diameter and 39 inches (1m) high to the smallest being approximately 16 inches (400mm) in diameter and 9 inches (250mm) tall. The typical vertical working distance range on the tabletop unit is approximately 12 inches (300mm) while the custom unit has a vertical working distance range of 39 inches (100cm). The measuring and loading head of the unit was designed so that no misalignment would occur with the engine housing. If effective, the machine utilized what can be considered a self-clamping technology that structural deflection is absorbed ensuring an accurate and absolute reading in varying test conditions. Finally, to eliminate potential operator error, once in place, the test is initiated by a single button eliminating the need for operator engagement.

The Fixture Table

Since part and machine stability is critical for accurate hardness tests, providing a stable base for the large aerospace parts was a critical part of the solution. The company wished to execute multiple tests in multiple locations around the flange face of the engine housing. Some tests were to be conducted on the outer edge of the housing and some tests were to be conducted on the inner edge of the housing. To do this, the fixture holding the engine housing was designed so that the entire housing could move closer to or further away from the test machine. Additionally, the housing had to be rotated so that the machine could test completely around the perimeter of the housing flange face. To accomplish this, the part fixture was equipped with heavy-duty bearings so that the entire engine housing was able to be easily rotated. Once rotated to the desired location, the table would move closer to or further away from the test machine to pinpoint the exact spot for the test.

The Results

Simply stated, the results were excellent. Hundreds of tests have been run on a wide range of engine housing diameters, all with success – all well within the 1% tolerance. Being able to conduct in-house testing has helped smooth production. Having hardness testing equipment that is flexible enough to handily negotiate large or small engine housings saved the company money from needing to purchase several hardness testing machines and fixtures. Tests can be run quickly and simply by rotating the part fixture table and operator error has been virtually eliminated with the single push-button equipment. The hardness testing equipment provided for this aerospace company is capable of performing HRC, HRB, HRT, HRN measurements all in conformance with ASTM E-18. HTT

About the Author: AFFRI is an Italian-based international designer and manufacturer of state-of-the-art hardness testing systems for over 60 years. The company’s North American headquarters is located in Wood Dale, Illinois. This article originally appeared in Heat Treat Today’s March 2019 Aerospace print edition and is published here with the author’s permission.

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