Originally shared April 10, 2023

Continuing from where we left off in the previous article, TAT Technologies’ President, Harb Nayar, had developed the basic idea to replace generated Endo with “Dial-An-Atmosphere” N2-Based atmospheres for sintering. But going from the basic idea to actual adoption in the PM industry would take a lot of proving to convince individuals running sintering operations that nitrogen-based atmosphere could meet not just ALL normal requirements of sintering such as strength, hardness, carbon, and dimensional controls but also HIGHER degrees of reproducibility, flexibility and safety to sinter a variety of compositions and sizes in the same furnace.

Though the energy crisis had proved the vulnerability of reliance on Endo gas, it was a standard that most of the PM industry had used for decades. One plant manager told Harb that moving away from Endo was like adopting a new blood type in the human body! He wasn’t telling Harb it was an impossibility, but it was just so hard to imagine without proof. The method of beginning the CONVERSION PROCESS became a steep challenge for Harb, but he accepted the risk of not knowing what it would take and where it might end up.

The conversion process passed through various “GATES” before just a couple of PM plants decided to partially adopt the N2-based atmosphere. These gates are briefly described below:

Gate 1: Sponsor - For any big new venture you often need a sponsor willing to invest, and many new ideas never get off the ground due to a lack of funding. Luckily, this first gate was relatively easy to pass through because Harb’s employer, Airco Gases (later BOC Gases), accepted the basic idea in just one meeting with senior management. They happened to already be in search of some application that could use the N2 gas which was being vented out from their air separation plants to meet the increasing demand of O2.

To meet Harb’s challenge, Airco committed to invest in a real sintering furnace and all necessary testing equipment to be installed at Airco’s Central Research Lab in Murray Hill, NJ. Appropriate manpower was also budgeted.

Gate 2: Initial Lab Testing - Using simple “green” TRS bars of common steel compositions like Fe-C and Fe-Cu-C, Harb and his team easily reproduced sintered parts using a blended mixture of N2, H2, CO and small amounts of CO2, CH4 and H20 to give an overall chemistry that was almost exactly the same as Endo gas - and the outcome was great.

However, two issues soon emerged. CO is both toxic and expensive, which led to the question: Do we have to have CO? This led to testing without CO in the blended gas. With some minor adjustments, it was quickly realized that one can do without CO, and a new differentiation emerged: Endo is a Carbon “Reactive” gas whereas blended N2-base gas is Carbon “Neutral” gas. This was a very critical discovery and gave the team a lot of encouragement.

The second issue was that the blended atmosphere now being called Dial-An-Atmosphere was several times more expensive than Endo gas. H2 was the most expensive ingredient. This led to many experiments which establish that 40% H2 was not needed for most of the compositions being used in 1970s. They found that depending upon the steel part composition, they could use H2 in the 5-15% range and achieve properties equivalent to Endo gas. That also encouraged Harb to keep moving forward.

Gate 3: Trials at PM Plants with Real Parts - Harb and his team asked cooperating PM plants to submit REAL parts to sinter at Airco’s lab so the plants could compare them with parts sintered under Endo in their own production. During this time at Airco’s Lab, a new issue emerged: As we put more samples through the lab furnace, we observed some soot on the parts when sintered under Dial-An Atmosphere. It was soon realized that N2-based was too pure and dry for the delubing portion of the sintering cycle. We needed an oxidant in the N2. This is when the “N2 Bubbler” concept was developed. In this method, the water was heated electrically and N2 was bubbled through the water. The exiting N2’s dew point was controlled by the temperature of the water column inside the keg.

Gate 4: Sharing Lab Data - Harb’s team had done enough lab work and were ready to share their findings with the PM industry. It was done in two ways:

  1. A presentation to the APMI West Penn Chapter’s meeting at Aiello’s Cafe in Ridgway, PA in 1975 or 1976. This presentation well received and gave the impression that PM plants would be receptive.

  2. Harb released the paper Nitrogen-Based Sintering Atmosphere, published in Modern Developments in Powder Metallurgy; Proceedings of the 1976 International Powder Metallurgy Conference (Chicago), MPIF, Princeton, NJ.

Gate 5: Field Testing - Soon after the presentation at the APMI West Penn Chapter’s meeting, two local companies agreed to Airco’s request to do field testing at their parts making plants. These were Pennsylvania Pressed Metals, Emporium PA, owned by Ken Gerg and Brockway Pressed Metals, Brockway PA, headed by Jim Reitz. Airco brought its portable N2 and H2 tanks and other needed equipment and a team of 4-5 engineers and technicians to carry out several weeklong trials in the field. With only a few minor issues, the trials were successful.

Within the next couple of years, more and more PM parts makers got interested in converting from Endo to N2-based. During this ongoing conversion process, one more very useful development took place which helped to both reduce cost and provide much better control in the sintering process: Harb developed the idea for ATMOSPHERE ZONING combined with double curtain boxes at the end of the cooling section of the furnace. This idea will be covered in detail as a separate item in one of the near future information sharing letters from TAT.

It was not until N2-based started becoming the STANDARD industry atmosphere and began to gradually replace Endo - not just in Pennsylvania, but other parts of the US and around the world. Dial-an-Atmosphere was replaced by a new term: Controlled Atmosphere Sintering, with varying gas chemistries along the length of the furnace. Newer delubing technologies and other improvements and promotions were initiated by other industrial gas and furnace companies to support this new sintering atmosphere standard, and other industrial gas companies began their own developments and promotions.

Some key advantages of N2-Based over Endo gradually became clear:

  1. The chemistry of atmosphere is more consistent over time, and it can be easily changed.

  2. The ability to have atmosphere zoning in a manner like temperature zoning.

  3. Better carbon controlled at parts’ surfaces.

  4. The ability to sinter ferrous, non-ferrous, and stainless-steel parts in the same furnace.

  5. No generator related maintenance – only simple flow meters are needed.

  6. No flame on the exit end of the furnace so parts do not get re-heated and discolored.

  7. Safety is improved by removing CO and greatly reducing H2.

  8. Better Carbon footprint. No natural gas is needed for the sintering atmosphere.

It sounds straightforward now, but it was a tremendous challenge. It required constant persistence, a lot of hard work from the researchers to the technicians, and no small amount of persuasiveness. It also needed a long-term commitment from an investor, which in this case was Airco/BOC. That’s why Harb wanted to tell this story – the current press-sinter PM industry is starving for innovation that will carry it into this new century as a vibrant, thriving, and modern industry. It needs to compete with wrought steel products not just on saving at the machining step but DIRECTLY on mechanical properties. Many of PM’s troubles can be traced to a perception that Press-Sinter has matured – so it is time to change that perception!

But as this story shows, innovation requires acceptance of risk, hard work, and even the understanding that some roads may lead nowhere. Harb and Airco understood that back in the 1970s, but they persisted, and now Nitrogen-based sintering atmosphere is a standard fixture at almost every PM company in the world. Drive around a PM heavy area like Elk County, PA and you will see many Nitrogen and Hydrogen tanks. Their innovation pushed the industry forward and yielded incredible profits at the same time. For the sake of the industry’s growth and for your own bottom lines, don’t be afraid to take some risks! Let’s all help push PM to be a truly modern manufacturing industry that is continuously on the innovative and improvement road.

For a more detailed look at Harb’s Nitrogen-based atmosphere innovation, please check out the paper mentioned earlier titled Nitrogen-Based Sintering Atmosphere, published in Modern Developments in Powder Metallurgy. (1977.0016) We can provide it to you if you email This email address is being protected from spambots. You need JavaScript enabled to view it. or This email address is being protected from spambots. You need JavaScript enabled to view it..