Thanks to all who visited us at the WAFIOS’ Spring & Grinding Days event, March 21-22, 2024. We were proud to show off our brand new Economy Oven prototype, the PS-106E-BASIC. Our PS-106E BASIC was designed with cost conscious customers in mind who still want the quality and reliability of a Pyromaitre Oven.

The PS-106E BASIC is a “no frills” low cost oven with a small, narrow footprint, with a 10” wide belt and a 72” long chamber, ideal for small springs. The PS-106E BASIC is CQI-9 ready, will require very low maintenance, and will offer a significantly lower price than Pyromaitre traditional models- we estimate nearly 40% less at this stage of our development.

The PS-106E BASIC is in its final stages of development and is expected to be available this summer!

Other PS-106E BASIC Features:

• Lower Position: the direct shaft driven gearbox mounted on the oven’s side allows the oven to sit lower to the ground, ideal for receiving parts.
• New Programming: allows for a great belt speed variability. Times can be as fast as 1 minutes and theoretically unlimited while keeping the gearmotor cool.  
• Reliability: +/-20F uniformity for a ~40% lower price.

If you’re like me, you might be wondering why special management philosophy is needed to achieve such a common-sense goal. The answer might just be that manufacturing has not changed, but the market it serves has. Craft production is the popular term used to describe the origins of manufacturing, Skilled craftsmen fit parts or components at assembly. Everything produced was essentially one of a kind. In the early 1900’s Henry Ford is credited with the development of mass production; this was essentially the development of common gauging standards used to eliminate fitting by skilled craftsmen.

Evolution of Lean Manufacturing

What change occurred that made mass production a term of historical reference? We, the market, changed. As the old saying goes, variety is the spice of life, and that is exactly what competition in our free-market society has delivered. Our craving for variety has had a significantly negative impact on the market share of mass producers. As was the case with mass production, the automotive sector is the breeding ground of Lean Manufacturing  

The development of Lean Manufacturing is credited to Taiichi Ohno of Toyota. Therefore lean manufacturing is synonymous with the Toyota Production System (TPS). Its development is simply an evolution that occurred in a specific environment. Ironically, the U.S. government played a role in defining that environment. Toyota had a workforce it could not reduce, a market that demanded variety, fixed floor space and limited finances. To be successful in this environment, Toyota had to identify a new model of manufacturing. How fortunate that today’s manufacturing environment is nearly identical to that of post-WWII Japan 

Buzzword Bingo 

The terms associated with lean manufacturing remind me of IBM’s Buzzword Bingo commercial, only broadcast in Japan.

• Muda – elimination of waste or nonvalue-added processes 
• Muri – overburden or unreasonableness, standardized work 
• Poka-yoke – mistake proofing 
• Mura – smoothness or flow of work, just-in-time (JIT) 
• Kanban – Visual indication, pull system 
• Kaizen – continuous improvement, the “5 Whys” 

These buzzwords represent the six primary areas of focus or the measure to improve one manufacturing process.

Six Sigma is often associated with lean manufacturing, but it is an independent statistical process measurement and management tool implemented to reduce or eliminate process variation.

The Soak -Time Myth

Is soak time a necessary process required to produce the desired metallurgical properties- full transformation to tempered martensite? Is soak time merely a poka yoke devised to compensate for varying furnace designs or the myriad of loading/ processing arrangements? Is soak time muda, and can it be eliminated? 

Necessary

Tempering, like many manufacturing processes, has its fair share of rules of thumb. One such handy rule is one hour per inch of cross section. This nice linear relationship is easy to remember, but this is clearly not a rule based in science. If it were, how would you explain induction tempering? 

In 1945, Hollomon and Jaffe published their works to describe the time-temperature relationship of tempering. Their Hollomon-Jaffe[1] tempering parameter depicts the correlation of change in hardness of martensite in steel as a function of temperature and time. The rate of carbide growth or coalescence from martensite, which produces the decrease in hardness during the tempering process, is affected by both time and temperature.

Pyromaitre has integrated the work of Hollomon-Jaffe and Larson-Miller into our proprietary Pyrograph™ heat-transfer simulation software (Figure 2). The program is based on Heisler unsteady heat transfer in cylindrical body formulas, and it gives a graphical representation of the temperature gain at the surface and at the core of a cylinder as a function of time and temperature in the furnace. For carbon and low-alloyed steels, the application will calculate the as-tempered hardness for your simulated recipe. It has proved to be a valuable process-development tool for our customers. 

Poka-Yoke

A tempering oven is a heat-transfer machine, yet, in current practice, ovens are standardized around a heat- or temperature-uniformity procedure. There is no true standard procedure for heat transfer measurement. Soaking at temperature is merely the mistake-proofing method, or poka-yoke, for making heat transfer uniform. 

A conventional batch oven is probably the best example to illustrate why soak time is a poka-yoke. The parts on the outside edges of the load come up to temperature significantly faster than those in the center of the load (Fig. 3). This delta T during the heat-up can be several hundreds of degrees, and there is typically no indication when the parts in the center of the load have reached set point. 

Oven design, type, age and manufacturer, as well as loading density and method, are all factors impacting heat transfer. Wasteful excess time is merely the equalizer. 

Muda

It becomes quite clear that soak time is a non-value-added process, or muda. Eliminating this wasteful process and maximizing productivity and quality requires a bit more effort than simply touching the up arrow on your temperature controller. Precision is mandatory – not only precision of temperature uniformity but precision in repeatability of heat transfer rates. Furnace design is a key factor in the performance of the tempering process further down the Larson-Miller curve. 

Lean and Green

What’s the next big movement in manufacturing? In the author’s humble opinion, it’s Lean and Green. Lean will expand beyond the manufacturing process to encompass complete business structures and processes. We envision a shift away from global trade of products to global trade of intellectual properties. We will begin to see more manufacturers shift to local manufacturing and/or assembly in each of the markets they serve. We might even see them advertise or tout the Green impacts of domestic manufacturing and their responsibility to their customer’s communities. You have been following Toyota, haven’t you?  

Continuous Rapid Tempering of an Induction hardened Crank shaft

The case file describes the introduction of a Pyromaitre Continuous Conveyor Oven to temper Induction hardened Forged Steel Crank shafts rapidly in less than an hour (cycle time -In to Out).  This replaces the existing Batch Process using Pit Retort Type and Box Ovens. The process time -Tempering /Stress Relieving in a batch Oven is usually 3-4 Hours from Load to Un load. The introduction of Continuous Conveyor Pyromaitre Ovens allowed the process to be straight line integrated with a Robotic “Pick and Place” system via an Overhead gantry. The cam shaft transport between the Induction harden, Temper and Grind Line were synchronized and automated. The savings by replacing the Batch Furnaces with the continuous Pyromaitre Stress Relieving Oven was not only in space, and Time but also reduction in in Process and Energy Cost . 

Reported benefits by an Indian Forging Company manufacturing Automotive and Industrial Crank shafts are described below with specific examples of Energy and Cost savings. 

Conventional Tempering Process: (In Vertical Retort Batch Furnace)

• 240-300 minutes cycle time at 210-350 °C including heat up, soaking at temperature (120 minutes) and cooling before unload
• 10-20 crankshafts of 65-170kg each part in process (~1300-1700 kg batch load)
• Output approximately 350 kg/hr.
• Batch Process
• Number of Vertical Retort Furnaces in Underground Pits used with necessity for overhead loading and unloading manual systems.

Pyro Tempering Process: (In continuous conveyor Pyro ovens)

• 45-60 minutes cycle time In to Out including cooling to room temperature.
• 8 crankshafts/hr. with 650kg/hr. output in a PYRO-P-4412 Oven @ 210-350 °C
• 8 crankshafts/hr. with 1360kg/hr. output in PYRO-P-4422E/P6011E and P6411E @ 210-350 °C
• Continuous Process allowing an integration with Robotic pick and place overhead gantry transfer of crankshaft from Induction Machine to Pyro Tempering Oven to final grind machine in an Inline Lean manufacturing layout
• Less parts in process
• Savings in Space

Energy and cost reduction on tempering of induction hardened cam shafts in a Pyro continuous electrically heated stress relieving furnaces.

The Company used the following methodology to measure the impact of Energy and Cost reduction by introducing a PYRO Continuous rapid tempering Furnace to replace the batch Pit type retort and Box furnaces.

1. Measurement of specific Energy consumption.
2. Identity heat Loss areas
3. Study of hot air convection system.
4. Implementation of corrective measurers
5. Monitor heat consumption after installation of the Pyro Ovens.

Benefits derived were:

• Power saving of 6 Kw per Cam shaft Tempered
• Surrounding temperature reduced and normalized
• Monthly Power Saving (2013) is 25,200 kWh @ Rs. 200,000
•  Annual Power savings (2013) is 302,400 kWh @Rs 2,449,000
• Specific energy consumption reduced from 13.5kWh/crankshaft to 7.5kWh/crankshaft
• Heat losses reduced by 5,160 kCal/crankshaft
• Energy consumption reduced by 44.4%
• Improved Air circulation by variable blower directions
• Installed vestibules at Intel and outlets of Oven to reduce heat losses
• Installed heat barrier plates to restrict heat emissions to outside areas (Shop floor environment impact).

Four models of Seven numbers (7) Pyro Conveyor Continuous tempering were supplied for different size crank shafts in two (2) Plants and three (3) Divisions to the Indian Forged Crank shaft manufacturer.

Rapid heating is the process by which a material can be heated to precise temperatures in a short period of time, and it has many uses. This article will summarize how PYRO Rapid Heat Transfer transfers heat to metal parts using an ultrahigh rate air convection movement that blows across those surfaces.

How Is Heat Transferred?

The three different ways that heat moves through matter:

1. Conduction – when particles touch each other directly
2. Radiation – waves moving off an object transfer their warming effect on nearby objects
3. Convection – where molecules move from areas of higher temperature towards ones with lower temperatures over time.

Normal Standards And Practices

Ovens are designed to transfer heat, but they don’t do this very well in certain circumstances due to their calibration limitations. For instance, two different ovens will often pass inspections for uniformity and temperature accuracy. However, these machines behave quite differently when heating different loads despite having similar settings. Conventional oven processes use lower temperatures for a longer time, while extremely fast induction processes are common after hardening with an Induction process at a higher cost and little or no flexibility. Pyro technology gives the same advantages as induction but with much more flexibility.

How Does the Pyro Rapid Heat Transfer Work Differently?

A high-precision oven requires not only uniform temperature but also a very even heat transfer. Rapid heating is achieved using turbines(Fans). However, this isn’t enough for the desired effect: it takes many fans placed in special positions to achieve the desired result. The PYRO Oven takes a different approach to how heat is transferred than others with specially designed fans. It combines convection and radiation as a secondary source of heat.

The turbines and chambers are designed with aspects that maximize air velocity at varying points along its path so as not only does it transfer more energy, but it does it in a uniform manner across all sections of the model’s bodywork.

Download Study Case

One of the challenges we face when analyzing steel parts such as springs is their complex geometrical configurations. It is therefore difficult, dare I say impossible in the case of springs, to directly assess the latter and measure their hardness. In the best of worlds, a section of the spring is cut and shaped into a cube which is then easier to manipulate, with no risk of moving during the hardness test. However, cutting quenched steel means generating heat which may affect the data due to migrating carbon atoms inside the steel matrix. Taking into account the cooling time, we obtain what is closer to air quenching, which assuredly affects the hardness measurements.
In order to maintain the same properties as those of the original heat-treated part, the quenched steel part must be cut without overheating it. The ideal maximum temp to reach is 200°C (400°F), which doesn’t give much wiggle room to find an easy and effective cutting technique. In practice, immediately after cutting, the piece should be easy to manage with bare hands, at a maximum temp of around 50°C (120°F). Tolerance to heat may of course vary from one person to another.

Paying attention to the heat of a cut part is therefore a good place to start to ultimately obtain accurate hardness data. Most metallurgy laboratories have a diamond or carbon blade saw with permanent water cooling to ensure a low, uniform cutting temperature. When using a grindstone (a common practice), cutting must be performed slowly, with the part ideally plunged into fluid (such as water) during the process. Remember: the more you heat the part during cutting, the more it will lose its original hardness properties. This cannot be emphasized enough if we want to make sure that we have the right heat treatment recipe to ensure maximum control of the quality of our parts.

The most commonly used quenching practice involves oil, which is not as dramatic as quenching in water, especially when the steel is strongly carbon-based. As for air quenching a steel part, the desired effects are moderate, rendering the part a bit more flexible but less resistant to erosion.

On the other hand, quenching by plunging or pulverizing oil on the metal heated to more than 900°C (1650°F) is never performed without adding another heat treatment, because the part becomes a bit too fragile for normal usage. The carbon must therefore be redistributed, because it can remain stuck in the grain boundaries, these small pieces that make up the solid structure of our steel and whose size is determined by the heating and cooling temps. To avoid this issue, the part is heated to between 200 and 700°C (400 and 1300°F) without triggering atomic alterations. When the part is air-cooled, the carbon atoms have just enough energy and time to transport into the grains, resulting in a part with greater flexibility and less chance of breakage under sudden shock. This also means a more linear stretch, which is so important for springs.

Choosing the right tempering process guarantees optimal performance and a longer service life. Unfortunately, this particular treatment is only reserved for steels. That said, while it could be very useful for other metals, their atomic structure would react differently. Each metal has its own recipe to change its properties.

You’ll notice that this blog is not reserved for confirmed metallurgists, although some may have difficulty explaining this physical process in layman’s terms. Since the dawn of time, man has hardened steel without really understanding the subtleties of this atomic-level transformation. Only in the 19th Century did scientists come to understand this phenomenon which was long associated with such things as magic and spiritism. It all depends on the atomic transformation of steel.

Now when we say steel, we mean iron with a pinch of carbon. Because pure iron cannot be quench hardened, 0.2 to 2% carbon must be added to its mass; if we add more, it becomes cast-iron, which is another type of metal. Therefore, construction steel, which contains 0.18% carbon (also known as mild steel), shows very little reaction to tempering and is actually the only steel that can be quenched in water without it becoming brittle like pane glass. As for the other nuances, it depends on the amount of carbon involved.

Carbon atoms, as we know, are infinitely minute; so much so (compared to large iron atoms and the other elements) that they can not only insert themselves between the latter without altering the atomic structure of the part but can also move around inside the structure, regardless of the heat fluctuations at play. Another important fact is that iron can alter the layout of its atomic structure during its solid state, which is remarkable for a metal.

For steel, this atomic-level transformation occurs at around 730°C (1350°F). It is easy to detect because above this temperature, both iron and steel lose their magnetism. During the cooling process, tiny carbon atoms become trapped and are unable to return to their original configuration, as steel was in its initial state. During rapid cooling, such as in ice water for example, carbon atoms stay where they are, and because they are unable to move as fast, this creates distortions in the atomic structure of the matrix, which results in microscopic cracks. When oil is used to cool the part, however, the change in temperature is less dramatic, and because it is less intense, the carbon atoms partially reposition themselves in the right place, with a few atoms blocking and deforming the atomic structure in ambient temperature, which is enough to significantly increase the mechanical properties of the steel without weakening it against the slightest shock. Finally, if the cooling time is long enough, the carbon atoms revert to their initial position and the steel to its original state. Now some specialists might find this explanation too simple, but ultimately, the tempering phenomenon is just that.

Stress relieving removes a large part of the produced internal tension and significantly prolongs the part’s service life, with no major complications. While this treatment is easy to do, particularly if we use an oven specifically designed for this type of treatment (as are those built by Pyromaître Inc.), it may be harder to verify its efficacy and to prove that the maximum amount of residual stress has indeed been removed. One scientific method, X-ray diffraction[i], can confirm and validate the anticipated outcomes by bombarding a sample of treated steel with X-rays and analyzing the intensity of these rays according to their projection into space. The result of the heat treatment is then evidenced by a curve produced by the synthesis of the diffraction analysis.

The equipment required to perform this type of test is relatively costly, and if adequate tools are not available, there may be delays in getting results, as few industries possess mechanical characterization labs similar to those found at university research facilities. Luckily, manufacturers have developed a simpler, more practical method to ensure optimal stress relief outcomes. These industries perform physical testing to determine the effects of expansion on their springs post-treatment. However, each type of spring must undergo individual testing to measure expansion post-treatment… which basically means that each case is different.

I’m looking at the relevant literature to see whether anyone in our field has introduced any new testing standards that (a) could be easily applied to the majority of spring models (length, width, and diameter) and (b) could confirm the success of a treatment. The greatest challenge in finding a general rule pertaining to expansion is that springs don’t expand in only one direction, which considerably increases the number of prediction errors regarding the deformations created by the treatment.

I have not given up just yet! I will continue looking into this. I hope that eventually I can write an interesting article on this issue. I will let you know before year’s end. If any of you happen to have expertise in this area or have read on the subject, feel free to share your thoughts here.

[i] Scientific American. X-Ray Crystallography: 100 Years at the Intersection of Physics, Chemistry, and Biology.
https://blogs.scientificamerican.com/scicurious-brain/scicurious-guest-writer-x-ray-crystallography-100-years-at-the-intersection-of-physics-chemistry-and-biology/

For an industrial oven manufacturer, the toughest challenge is obviously making sure that the heat is evenly distributed. It would be wrong to think that this is better achieved by batch ovens than by conveyor belt ovens. The laws of physics being infallible, many technical aspects must be considered for each heat treatment, regardless of the oven used. Remember, the goal is to bring each part – and not the inside of the oven, as many believe – to the desired temperature and as fast as possible to enable its center to reach the same temperature as that of its surface. Rapid execution and uniformity are the prime directives of oven builders and manufacturers who must use a lot of ingenuity in designing the technical functionalities of each oven so as to address these challenges.

‘’ Since 1981, Pyromaitre has created innovatively designed industrial ovens that drastically reduce cooking time; the heat transfer in these ovens is so efficient that customers can increase their output in an oven that is up to 70% smaller.’’ AN OVERVIEW OF CLEANTECH IN QUÉBEC, 2016

A good oven is characterized by computerized burners (or heating elements) and innovative strategies to install the right fans to evenly distribute the heat to the various zones of the oven. The space inside the oven is also another important factor to consider. With advances in stringent industry standards, such as AMS 27591 which allows for a maximum variation of 6°C for average-temp treatments, before purchasing an oven, make sure that load testing has been conducted, supported by a certified temperature curve profile. No-load testing (no simulations of the total number of parts normally processed in the oven) is not really representative; the oven must be loaded to simulate actual processing conditions.

1 : web reference = https://www.an-answer.com/TT/HeatTreatSpec-AMS2759_3D.pdf

Here are a few suggestions to try and change their way of thinking, because before deciding on who will manufacture your next heat treatment ovens, you first have to be sure of some things BEFORE the oven is up and running so as not to run into recurring problems down the line.

First of all, a quality industrial oven has several temperature adjustment and maintenance controls in form of deflectors for the different heating zones as well as computer-controlled heat sensors to optimize the heating treatment temperature to ±10ºC. In this regard, Pyromaître’s specs are more accurate than are those of CQI-91 standards (±5ºC or ± 10ºF). This ensures that the parts we treat correspond exactly to our clients’ specs.

Certified documents guarantee that your investment matches your technical requirements. These documents must be provided to and accepted by the buyer and their specific standards.

Make sure that the manufacturer in question is available for any post-sale adjustments, as parameters such as gas quality, average ambient temperature (which can vary from one area to another on the planet), and even the altitude where the oven is used may have a direct impact on the quality of the combustion or the heat transfer by electrical components.

A high-quality oven means avoiding a ton of problems – and saving you time and money.

1 CQI-9 AIAG (Automotive Industry Action Group). Special Process: Heat Treatment System Assessment (3rd ed.). 2011.

What’s important about this scientist is that he was a true research pioneer in the area of X-ray diffraction for crystal analysis, an interest partly fed by his fascination with this new technology. Over time, data collection, computation, and statistical analysis using modern computers have considerably altered heat treatment practices since Dr. Bain first compiled his findings on the effects of cementite (a carbon concentrate) during tempering. The advanced X-ray diffraction technologies demonstrated in recent literature lead me to believe that these earlier metallurgical standards must be revised, not only to boost the performance of tempering and stress relief processes but to make them more cost-effective.

1Paxton, H. W. & Austin J. B. Historical account of the contributions of E. C. Bain. Metallurgical Transactions. 1973.

The parameters used in heat treatments to reduce the hardness and increase the durability of tempered steels are traditionally determined by equations like the Holloman-Jaffe parameter, directly inspired by the Larson-Miller relation. These equations measure the effect of the different metallurgical transformation stages, such as tempering and stress relieving. However, these older formulas pertain to isothermal (Constant Temperature) treatments that are practically non-existent in industrial-level facilities because of the heating temp offset which precedes the minimum maintenance time at the ideal temp to obtain the desired physical, mechanical, and metallurgical specifications.

Although these equations are still widely used in the heat treatment industry, a certain number of procedural challenges have been identified related to temperature optimization and time estimates for tempering or relief treatments; today, they have attained the limits of metallurgical predictability and are generally considered too high. That said, recent studies report using sound scientific data to optimize these equations to make them more reliable in predicting post-treatment outcomes and to update changeover times and oven heat parameters.

In an article by Lauralice Canale1, different methods are presented to address the problems related to these basic equations, including the findings of Gingras2, Guo3, Inoue4, and Wan5. Undoubtedly, the Larson-Miller and Holloman-Jaffe parameters, the gold standard in the realm of heat treatments, must be optimized for industrial applications.

1 Canale, L. et al. A historical overview of steel tempering parameters. International Journal of Microstructure and Materials Propreties. 2008.

5 Wan, N. et al. Mathematical model for tempering time effect on quenched steel based on Holloman parameter. J. Mater Sci. Technol. 2005.

If you want to learn more about average-temp heat treatments (200 to 1000°F), follow my blogs. After several decades developing this cutting-edge technology, Pyromaître now masters this process. With its extensive line of ovens, we can now ensure a more rapid and more accurate final production phase for your treated parts by substantially reducing our oven times from 30 to only 10 minutes, with the same exceptional results. Many manufacturers trust us to do the job right and are sold on the technical superiority of our facilities. Stay tuned to learn more!

Allow me to introduce the fundamental principles supporting our innovative approach, namely, the Larson-Miller parameter and the more recent Holloman-Jaffe parameter. To fully appreciate the demonstration of these principles, go to the Reports – Stress relieving section of our website, where you will find a few articles, such as the 2013 article High-speed tempering of gears: A comparative study, which provides a good synthesis of our work. For a more practical perspective, the articles Test Report Axles Shaft 1 and 2, also on our website, accurately describe how we are able to lower our treatment times to satisfy customer demands in terms of thermal treatment results. You will find all this and more in my upcoming blogs.