Hardness Testing

This is an attempt to briefly explain the mechanics of how a hardness tester works.  Hardness testing can be done with many different tools.  There are simple hardness files, Rockwell hardness testers, and also Micro-hardness testers.  I will briefly describe and tell the uses for each one.

A hardness file is just what it sounds like.  These files are created at different hardness levels.  When you try to file the surface of the specimen that you are testing, if the file scratches the surface then the material is softer than the file that you used.  Likewise, if the file that you use does not scratch the surface of the specimen then the material is harder than the file.  These tools are useful when the specimen that you are testing cannot be placed into one of the other types of hardness testers.  It is also good for quick checks on materials where the exact hardness value is not critical.

The second tool is probably the most familiar tool to people.  The Rockwell hardness tester (shown below) uses a penetrator, usually a diamond or steel ball, to check hardness.  The penetrator is pressed into the specimen with a predefined weight or load.  This load is defined by the scale in which you have chosen to do your test.  For example, if you wish to test your specimen on the Rockwell C Scale, then you would set your load on the tester to 150kg and would choose the correct size penetrator.  Once the load is presented to the specimen the machine is then released from the load.  The machine then measures how deep the penetrator went into the specimen.  This measurement is then displayed as a relative hardness reading.  As I mentioned earlier this is the most commonly used tester for measuring hardness.

 

Finally, the Micro hardness tester is the most accurate measurement for hardness.  This is used when precise hardness measurements are required.  The basic operation of this machine is the same as the Rockwell testers except the loads and the actual depth measurements are different.  The penetrator is pressed into the load at a predetermined weight.  Then the specimen is viewed through a microscope (see below).  In the microscope you can see the impression left by the diamond.  This impression is then measured in two directions when using a Vickers diamond.  These measurements will then correspond to a specific hardness value.

 

Bob Puls

President

Zion Industries, Inc.

Use of Flux Field Intensifiers with Induction Heating

Induction heating is the process of heating a conductive material by generating a circulating flow of electrons or eddy currents in the material. This effect can be intensified or in some cases shielded by using materials that control the magnetic flux field generated by the induction coil. These materials are called magnetic flux concentrators or flux intensifiers. 

Flux concentrators are made from high permeability, low power loss materials. The most common examples are a molded material consisting of iron powders in a compacted non-conductive binder, or lamination style concentrators. Both will have similar results but specific applications or geometries may dictate the use of one or the other style. 

Most applications calling for flux intensifiers require the field to be compressed or intensified in certain area. Under normal conditions the field of the coil is drawn to the load side closest to the work piece. Some of the field naturally flows around the other sides of the coil. This is where flux intensifiers can be used to help focus more the energy towards the work piece. By wrapping the sides of the coil and creating an opening towards the work pieces, the additional flux field is focused into a smaller area and results in improved coil to work piece coupling. 

The same materials that are used to focus the flux fields towards a work piece can also be used to protect certain areas from undesired hardening. If for example, a coil is wrapped around a shaft with a flange, the natural tendency will be for most of the field to be attracted towards the shaft area. As the coil gets closer the flange, a certain amount of the energy is drawn towards the mass area next to the coil, by the proximity effect. If that area is required to remain soft, flux intensifiers can be used on the face of the coil in between the coil and the flange to prevent heating in that area. Conversely if the area is required to be heated, the effect can be intensified by placing the intensifier material on the side opposite the flange so that the coil is between the flange and the concentrator.

The use of flux concentrators can make difficult applications easier. But the application and development of a coil with flux concentrators can involve additional time and costs to properly develop the coil to the application. We at Zion industries use flux intensifiers as dictated by the application and have the ability to design, manufacture and develop the tooling with flux concentrator materials in house. If you have a challenging induction application, we would be glad to review it with you.

Lou Ghinga

Estimator

Zion Industries, Inc.

One way we measure Total Case Depth at Zion Industries

It is important when discussing how we measure total case depth to first state that the only way that we (Zion) heat parts to austenitizing temperatures is through the use of induction coils.

The methodology outlined below is SOP for Zion Industries unless instructed otherwise by our customers or a part specific specification.

1. We take the induction hardened part and section it in a manner to expose the area that we need to measure the total case depth in.
2. The next step is for the part to be sandblasted in the area that we need to measure the case depth in.
3. Using a 10X eye loupe we then measure the total case depth by going in from the surface at 90° and measuring how deep the “shinny” portion of the part is. Note that the induction hardened depth will remain “shinny” while the soft area of the part will turn a matt grey.

It is our experience that the portion of the case that is at or above HRC 40 (approximate) will remain shinny when the sectioned part is sandblasted.

Why do we use this approach?

In induction hardening steel parts, heating the parts to the correct depth is only ½ of the job. The other half of the job is to ensure that the properly heated parts are quenched correctly. It is common to have induction hardened parts that, depending on alloy, required case depth, and part geometry, display a significant difference between the “heat effected zone” and the hardened zone.

Note that many specifications define a total case depth as “total heat effected” which is what you would typically see, using a macro approach, if you prepare a sectioned part for total case depth measurement using an acid wash. However, once again that only qualifies how deep you heated the part, not neither necessarily how deep you hardened it nor how effective you’re quenching systems are.

We at Zion, through many years of experience, are confident that in using the method of sandblasting to qualify total case depth we have a methodology that is an accurate and cost effective approach to measuring the effectiveness of our induction hardening process.

Should you have any concerns or questions please do not hesitate to contact us.

Ken Feuerstein
Quality Manager
Zion Industries, Inc.

Causes of Cracks during Heat Treat

The heat treating process can be an intensely stressful process for the material involved. The material must first be heated to the point where austenitization can occur, and then cooled rapidly enough to have the transformation into martensite take place, but avoid the possibility cracking. It can be a delicate process at times.

Cracking during heat treat can be caused by several factors. One of the factors that may initiate a crack may be the heating of the material itself. As the material is heated it undergoes a volumetric change both as a result of transformation products being produced and thermal expansion. At times “cracks” that become evident during this phase are really material imperfections, seams and inclusions from the manufacturing process.

 

(100x photo of crack)

Cracks can occur from uneven quenching. While this can be somewhat controlled during the quenching cycle, it is also a major function of part geometry and should be considered during the design stage of the component. Holes, sharp edges, grooves, slots and corners can all be potential crack initiation zones. At a sharp edge or edge of a hole for example, the heating and cooling rates can be substantially higher than the surrounding areas. This puts tremendous strain on the material in these regions during the heating and quenching cycles. While those features may be necessary in the component, it is important to exercise good engineering practices and properly chamfer or radius those areas to prevent sharp corners and edges. When this is not practical, certain materials may be placed in holes and other critical areas to help act as a heat sink and dampen the shock during the quenching operation, this can be costly and the efficiency of the heat treat operation will suffer.

Additionally material selection and process can contribute to the possibility of cracking. High carbon and alloy materials with high hardenability often exhibit a higher tendency to initiate and propagate cracks. Also, as is the case often with Induction heat treating of multiple zones, care must be taken to temper the material before subsequent heat treating, especially if the zones are close together or part geometry or specific requirements mandate it.

We at Zion Industries look forward to working with you on specific parts that may be a problem currently or that you may have had a problem with cracking in the past. Our team would be happy to evaluate the project and help offer a solution. 

Lou Ghinga

Estimator

Zion Industries, Inc.

What is it that we really do anyway ?

You might find yourself asking that question as you look at our website or even after you talk to one of us here at Zion on the phone. We do a lot of things that are centered around induction heat treating. Remember, induction heat treating is a heat treating process where the treated area is typically a specific area of the part, not the entire part itself. Although it could sometimes be the entire area of a part – depending on certain circumstances. The induction heating services that we provide are numerous. 

Let me give you a better picture of what we do. Induction heat treating for hardening specific areas of a part. Maybe like a bearing wear area on a shaft for example. Induction annealing for softening specific areas of a part. Induction brazing or soldering allows us to join together brass or copper pieces by binding them with a silver solder material. We also furnace temper or induction temper parts – this is to remove the brittleness that can occur after heat treating. Usually we work with parts that are less than 120 lbs. and easily handled by hand. 

Our capabilities include being able to work with you on every level from engineering support and prototype development / testing up to large volume production runs with programs in the millions of pieces at any of our locations. By the way, we’re in Grand Ledge, Michigan; Valley City, Ohio and Hildebran, North Carolina. 

In addition to the above, we also can straighten shafts, magnetic particle inspect parts by the use of ultra violet light and even freight forward your products to their next destination – wherever that may be. We offer these services even if you do not have a need for induction heat treating help. 

We are also industry leaders in powdered metals applications that require induction heat treating. Which, by the way, if you’ve never had the experience in working with powdered metals – is a science all by itself. 

Heck, sometimes we even are known for our corny jokes or riddles like this one: “What occurs only once in a minute, twice in a moment but never in a 1,000 years ?” Any takers ? If you can figure this out – I’ll send you a free Anti- Stress Kit. Send your answer to my email address at JBode@ZScan.com 

Our pricing is competitive. Just send us your prints with specifications and target pricing, and we’ll be happy to show you ! Our intent is to exceed your expectations by improving your balance of price, delivery and quality while meeting the needs important to your company through an open partnership where we work together with you. 

Do you have a “problem job” that is giving you headaches ? We’d love to look at it with you. Our depth of induction expertise is un-matched in our industry. It doesn’t matter if it’s involving powdered metals, difficult geometries or finding a better source (and price) for a current production part. We can make a difference that will make you smile ! 

John Bode

Sales

Zion Industries, Inc.

Possible causes of soft parts during induction heat treating

The process of induction hardening is based on the same principles as any other heat treating operation designed to harden parts. The process is dependant on several factors to be successful, bringing the material to the proper temperature, cooling the material rapidly to allow the transformation of martensite to occur, and finally the general chemistry and ability of the material to harden properly. When one or more of these critical factors are not present, the material may end up with soft spots or remain soft entirely.

The factors that we as heat treaters have the most control over are the heating and quenching of the parts.

It is important to bring the materials to the proper temperatures in order for the austenitic phase to occur. In some cases, based on the material, it may be necessary to hold the temperature for a fixed amount of time to allow all the material to fully transform and avoid undesirable by-products that that can later reduce the materials hardness.

It is just as important to quench a material properly to produce the desired hardness. Improper quenching can occur if a part is quenched too slowly by using the wrong quenchant for a certain material, or not using enough quenchant to remove the heat quickly enough. Also, most water based quenchants use additives such as a polymer to slow down the cooling to prevent cracks; the addition of too much of this substance (polymer) reduces the ability to remove the heat quickly enough and can cause soft parts. Care must also be taken to cool the part sufficiently to prevent residual heat from tempering the part.

One of the most important factors to allow proper hardness to be achieved is one that we have very little control over, the basic chemistry and properties of the steel. It is important to understand that modern steels, while very tightly controlled in their composition, still do have a tolerance for how much carbon and various other alloying agents that promote hardenabilty are present.

It is important to understand and design around these tolerances.  Doing so could help to prevent a situation where a heat of steel can be on the low side of the carbon and alloy range, and would not be able to achieve the hardness if it was designed around the high side of the range.

Also during manufacturing or subsequent operation, steel can loose carbon on the surface, also known as decarburization. This will sometimes result in localized soft spots or a hardened layer below the softer decarb area.

These are just a few of the common things that will cause your parts to be on the low side of your hardness tolerances.

 

Lou Ghinga

Estimator

Zion Industries, Inc.

Choosing the Right Induction Machine for the Job

When determining the proper Induction Machine for your job, several things to consider including the case depth and surface area of the part to be hardened.

            First let’s talk about induction machines in general.  Each induction machine is characterized by its output power (kW) and its output frequency (kHz).  When choosing your equipment, these are the most important numbers you will need to know.  At Zion we have induction machines ranging in power from 5 – 300 kW and frequencies from 3 – 450 kHz.  Not every machine can operate at every power level and every frequency.  Typically the frequencies are fixed and the power outputs are stated as maximums.  A typical machine rating would be 100kw and 10kHz, where the power level is a maximum and the frequency is fixed.

            Knowing what your case depth requirements are will help you choose the correct machine frequency (kHz).  The following table can be used as a guideline to determine the correct frequency for your required case depth.

Frequency (kHz)	Required Case Depth (inches)
1	.250 – .370
3	.130 – .250
10	.060 – .130
450	.015 – .060

            Determining your power (kW) requirements takes slightly more math.  First you must determine the surface area (in^2) of the part to be hardened.  For a simple shaft with a diameter (D) of 1” and a hardened length (L) of 2”, the surface area is D x π x L or 6.28”.  Once you have determined your surface area, you simply multiply this by a power density factor of 10 kW/in^2.  For our example, this gives you a value of 62.8 kW required to effectively heat up this shaft.

            So in a nutshell you can see that there is much to determining the right induction machine for the job.  Each induction machine can be different and can provide different results for your induction hardening requirements.  We would be happy to talk with you about any of your induction equipment questions.

 

Bob Puls Jr.

President

Zion Industries, Inc.

Total vs. Effective Case Depth

One of the benefits of induction hardening is the ability to selectively apply a surface hardness or case hardness to steel materials. The case hardness will allow the piece to have superior wear and strength characteristics at the surface, but allow the interior of the piece to remain flexible. 

Case hardness is defined as the outer surface that has been made harder than the interior, or core. The term case depth refers to the depth of the case, or hardened layer of a piece of material. Case depth is typically measured as “total” or “effective”. The two terms are sometimes misunderstood, but are different and it is important to understand those differences.

The term total case depth refers to the depth of hardness where the hardened layer reaches the same hardness and properties as the base or core material. Total case depth is typically measured by sectioning the work piece and polishing and etching with an acid solution to reveal the depth of the hardened layer. The measurements can then be taken visually and measured using a calibrated eyepiece or scale to qualify the total depth.

The term effective case depth refers to the depth where a hardness measurement drops below a specified point. The hardness will then continue to decline until the “total” case depth is reached. The hardness at the effective depth is specified based on the characteristics required and the hardenabiltiy of the material. For example, high carbon steel that may have a minimum surface hardness of 60 HRc may call for an effective case depth of 0.120” at 50 HRc. The method of determining effective case depth involves sectioning the piece and polishing the surface. Measurements of the hardness are then taken at regular depth intervals until the hardness drops to the specified range. This distance from the surface is then measured to determine the effective depth.

 At Zion Industries we work with our customers to make sure that we understand their requirements, and when necessary can help clarify the requirements that may be on a third party print. It is important to understand that the measurement method called for on the print was established at the engineering stage, and the design intent must be followed as the method of measurement is determined.

Lou Ghinga

Estimator

Zion Industries, Inc.

Success Story: Back Up Supplier

If you’ve been reading our other recent blogs, hopefully by now you’re getting a better understanding of what Zion Industries is about and how diverse our capabilities are.

We have enjoyed numerous successes with many of our partners in a wide variety of challenges. There are a lot of things that make us very different from what you may be use to in working with some of our competitors out there, but I’ll save that for another article.

We are diversified in working with partners from numerous industries including automotive, aerospace, military, lawn and garden, off road vehicles, powdered metals, mining and a lot more. If you drive a Ford, GM, Chrysler, Toyota, Lexus, Honda, Audi, BMW, VW or Harley Davidson – some of the parts that we work on are found on those vehicles and a lot of other brands too.

Some of our partners do their own induction heat treating in – house. But what happens if they experience a critical breakdown or significant quality problem that takes time to fix ? How happy does that make their customers ? Have you ever had the pleasure of being the one that gets to explain to your customer why you have to hold up production of their products because of a problem that you have ? That’s always fun. However, things happen and sometimes problems arise that take time to fix.

Another good problem that some of our partners experience from time to time is that they can’t keep up with the demand for their products – and that’s a good problem to have I would say. One of our partners has just that kind of a problem sometimes. And that’s where we’ve been able to lend a helping hand.

While the economy has been having fits and flutters affecting us all in one way or another, some businesses have been experiencing steady or even surging production such as this particular company that we partner with. When they are faced with production overloads, we are called in to help them get caught up. Overflow work is sent to us and we process their parts quickly and efficiently to their required heat treating specifications to help them keep up with their demand as it fluctuates. When business is normal for them, they do all the parts themselves.

By working together in this way, we are providing a back up resource for their needs when they need us.  When we’re not needed, we are in ready standby for them at all times. They have never had a back-up partner before working with us in any aspect of their operations but we have proven to them that our reliability, availability and consistency of quality can actually enhance their operations and add value to their demanding customers.

I guess you could say that we’re really their insurance partner. They know we can be relied on for help at a moment’s notice. Have you ever considered back up help ? What would you do if your induction heat treater had a problem that was affecting you ? Wouldn’t it be nice to have a back up plan ?  

John Bode

Sales

Zion Industries, Inc.

Ever want to be a STAR?

Zion Industries values their employees and wants to show appreciation for good works.  We have a program called STARZ … each of our three plants participates in this employee driven system.  Management appreciation is typically slow in coming and sometimes misses the most worthy.

The STARZ program accepts nominations from our workers’ peers.  The criteria are revolved around the core values which Zion Industries hold dear.  Those core values are: Devoted to Honesty, Passionate for the Customer, Committed to Quality, and Dedicated to Family.  Each team member can nominate another for a single act or continuous efforts related to those core values.  The system rewards the winner of the month’s STARZ award for each plant.

Here in North Carolina we have modified this approach and called it “Employee of the Month”.  This modification adds a reward to the normal half of a day off with pay. North Carolina added designating a special parking place, closest to the door and when selected we arrange for a catered lunch to be provided at award time for that special employee.

We strive to show appreciation, as the core value of Dedicated to Family keeps us looking out for each other.  The customer benefits by the continuous improvements that are a fall out of this recognition program.

Gary Wolf

Plant Manager,

North Carolina Plant