Heat Treating NASA Telescope Parts

Metlab heat treats and processes many parts and components for the United States military, government projects, and NASA. Recently, several telescope and mirror parts made of pure aluminum, copper, and titanium were treated for the new High-Resolution Mid-Infrared Spectrometer (HIRMES), that NASA is developing to expand the boundaries of astronomy research.

HIRMES-1

Cutaway illustration of HIRMES instrument.

A heavily modified Boeing 747SP that carries a 2.5m-diameter infrared telescope flies above ~95% of the Earth’s atmospheric water vapor, allowing astronomers to gain access to wavelengths that are not possible to observe from the ground, even with the most powerful ground-based telescopes.

Nasa jet
Modified Boeing 747SP equipped with an infrared HIRMES telescope

HIRMES’ prime investigation is a detailed study of the processes leading to the formation of planetary systems over a spectral range rich in ionic, atomic, and molecular lines. The HIRMES science program will determine the structure and evolution of protoplanetary disks and will increase our ability to model these systems as they evolve from homogeneous disks to fledgling planetary systems.

At the beginning of their lives, stars significantly interact with their environments, and the HIRMES program will advance our understanding of the ways these interactions regulate star formation.

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Industrial Heating Magazine Feature: Metlab Specializing in the Heat Treatment of Large Parts

Recently Industrial Heating Magazine featured Metlab as part of a company profile as a member of the Metal Treating Institute:

Metlab isn’t your typical commercial heat treater. Founded in 1928 as a manufacturer of aluminum spars for biplanes, the company is credited with the patent for the first drop-bottom gantry furnace.

But today, the Wyndmoor, Pa.-based company is known for its huge pit furnaces and its ability to heat treat parts weighing anywhere from a few ounces to 50,000 pounds. In fact, Metlab has more than 30 furnaces on-site – including pit furnaces as big as 15 feet x 12 feet deep, which are believed to be the largest in North America.

Metlab Steel Rods

Load of modified H-11 steel rods, 2 feet in diameter x 16 feet long, being prepared for air quenching.

The company also has vertical pit furnaces measuring 4 feet in outside diameter x 16 feet deep with the ability to extend to 18 feet deep for heat treating long, slender parts used in oil drilling, mill pinion shafts, bar stock and tubing. A pit nitriding furnace and a car-bottom tempering furnace (6 feet x 9 feet x 16 feet) complement the large-parts department, and the company has several integral-quench batch furnaces and support tempering equipment for heat treating small parts.

Metlab acquired the John V. Potero Company in 2001, allowing it to process small parts and provide a wide range of heat-treatment services. These include case hardening, nitriding, protective atmosphere annealing, hardening, quenching, tempering, stress relieving, solution annealing and age hardening. What’s more, the recent investment in vacuum furnaces has further expanded the company’s offerings into bright hardening of tool steels and stainless steel.

Deep-case carburizing and hardening, as well as nitriding of large and small gears and shafts, are core competencies of Metlab. The ability to heat treat these parts to precise and accurate case depths and hardness while maintaining geometric integrity makes the company unique in the field of commercial heat treatment. What really sets the company apart from its competition, however, is its ability to process parts in large, atmosphere-controlled equipment specifically designed for processing gears, pinion shafts, bearing races and other large industrial components.

Fabricated gear wieghing 40,000 pounds being removed from Metlab's largest pit furnace.

Fabricated gear weighing 40,000 pounds being removed from Metlab’s largest pit furnace.

This longtime MTI member offers more than thermal processes. With three full-time metallurgists on staff and an in-house metallurgical laboratory, Metlab has the ability to analyze microstructure and case depth to ensure all parts are processed accurately and on time. The company also offers black oxide finishing, failure analysis and metallurgical consulting.

As for recent developments, a recirculating water system funded in part by a grant from the Department of energy coupled with rebuilds of the two large pit furnaces has made Metlab more competitive from a cost-savings and water-recycling standpoint.

As for the future, Metlab intends on acquiring new equipment and adding new processes to complement its core offerings. Recent projects involving the heat treatment of nose cone and rocket exhaust gas nozzles as well as long, slender down-hole tooling indicate the need for more capacity to process large parts. In addition, capacity to nitride gears, axles, shafts, and large industrial valves calls for equipment upgrades.

Posted in Annealing, Black Oxide, carburizing, Flame Hardening, Heat Treaint Small Parts, Heat Treating, Nitriding, Vacuum Heat Treating | Leave a comment

Heat Treating Off-Road Racing Gears For University Projects

Metlab is active in providing heat treat services and consultation to colleges and universities that feature automotive engineering. The Rowan University Society of Automotive Engineering (SAE) group reached out to Metlab for consultation on their latest project, a Baja endurance racing vehicle.

The SAE is a hands-on engineering club focused on challenging students to learn how to design, build, and race vehicles. The students were looking for a source to manufacture gears and pinions. Metlab provided a manufacturing source as well as heat treating consulting and the carburizing and hardening services at no cost.

“We discussed the heat treating process at length with the students so they could gain insight into the processes and expand their manufacturing and engineering experience.” comments Mark Podob, President of Metlab. “The heat-treating process is critical to the durability of these key components in racing, especially for off-road, where the conditions are extreme. We are always open to helping students learn and be a part of the manufacturing process for their projects.”

Gear and Pinion
Example of a gear and pinion for off-road vehicles

Off Road Racer

Engineering in action! Student driver in the Canadian competition.

SAE BAJA collegiate challenge is all about durability and endurance. Students are tasked to build an off-road vehicle powered by a 10 HP Briggs & Stratton engine that can make it through a 4-hour endurance race. The car must perform through rocks, mud, sand and an assortment of challenging obstacles. The vehicle design was the first series Rowan participated in and marked the start of Rowan Motorsports in 2002.

Team

The Rowan Society of Automotive Engineers with team cars.

“We would like to thank Metlab again for the sponsorship! With your help, we were able to finish our new car and compete with it in a competition in Canada. The blue car is our brand-new car. The red and tan cars are from previous years. Our next competition is in April in Tennessee.”
Elizabeth Henning
President of Rowan SAE

Metlab has assisted students at Georgia Tech, Temple, Drexel, University of Pennsylvania, and the U.S. Naval Academy on their SAE Automotive Engineered Car programs, providing them with no-charge heat treatment services and engineering consultation. In partnership with several gear manufacturers who utilize Metlab for their heat treating requirements, the students have been able to procure gear sets for their vehicles economically.

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Furnace Upgrades, Water Recirculating Cooling System Installation With Small Business Advantage Grant

As part of its continuing maintenance improvement program, Metlab recently completed a rebuild and upgrade of its two large heat-treating furnaces. These furnaces designated P-1 and P-2 are believed to be the largest atmosphere-controlled pit furnaces in North America. With work zones measuring 12′ in diameter by 8′ tall and 15′ in diameter by 10′ tall, the equipment is used to neutral harden, carburize and harden, nitride, anneal, and stress relieve large components or multiple quantities of parts. With a capacity of up to 50,000 pounds per heat treat cycle, typical components processed include large gears and bearing races, rocket exhaust nozzles, forgings, castings, large weldments and other industrial components.

Metlab Quench

A load of windmill bearing races rasing from Metlab’s furnace designated P-1 before quenching in an 18,000-gallon oil tank. Each of the three races measures about 6 feet in diameter by 12 inches tall, weighing more than 2,000 pounds after carburizing.

Capital expenditure of more than $200,000 included new nickel base alloy retorts, cast ceramic floors, insulation, and upgrades to the furnace structure. The furnaces utilize different atmospheres to process parts including endothermic gas for neutral hardening and carburizing, ammonia for nitriding, or nitrogen and argon for scale-free processing. The furnaces rely on sand seals to contain the different gases. The sand seals for both furnaces were also redesigned and replaced. In addition, finned copper tube coils for cooling the sand seals were changed with closed welded stainless-steel chambers for better efficiency.

The rebuild to each furnace took about a month. While the nickel base alloy and stainless steel for the retort and sand seals were purchased as fabrications, Metlab maintenance personnel took over 350 hours to weld the different components together. A temperature uniformity survey (TUS) after completion demonstrated that the furnaces meet the strict requirements of AMS 2750E.

Metlab welder
Metlab maintenance personnel welding the cooling chamber for the sand seal on the furnace.

As part of the upgrades, Metlab utilized funds received from a Small Business Advantage Grant from the PA Department of Environmental Protection.

PA DEP

This grant was used to incorporate a closed loop recirculating water system to cool the sand seals and fans of each furnace. The cooling water requirements of the furnaces are more than 20,000 gallons per week. The savings in water, not to mention the environmental benefits of recirculating water, are substantial and were recognized by the DEP as a significant benefit, resulting in the grant. Equally important is the elimination of the need to discharge heated water into the sanitary sewer system.

Metlab furnace

P-2, Metlab’s largest atmosphere-controlled furnace, showing the new nickel base alloy retort and sand seal installed. Also shown in the foreground is plumbing for the new water cooled sand seal.

Metlab employee

Rocket exhaust nozzle forging is hardness inspected by a Metlab inspector, after normalizing, hardening and double tempering in Metlab’s largest furnace, P-2.

The Small Business Advantage Grant provided a 50% matching grant for funds spent on the equipment to Metlab. The cost of the recirculation system, purchased from Dry Coolers, Oxford, MI, including piping modifications and installation was about $35,000.
Metlab began the planning and purchasing of the furnace upgrades and cooling equipment in late 2016. Acquisition of funding, as well as material and components, allowed the project completion in early 2018.

 

 

 

 

Posted in Annealing, carburizing, Double Tempering, Heat Treating, Nitriding, Stress Relieving | Leave a comment

Airplane Bulkhead Component Heat Treating

Metlab comes across many unique and interesting heat treating projects each year. Some have a history lesson to accompany the project. Recently, a newly fabricated structural bulkhead for a Ryan ST-A historic aircraft (circa.1934), was treated in the Metlab facility. The customer, Classic Metalcraft, was referred to Metlab by another heat treater that did not have the equipment to properly process the large part.

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Ryan ST-A (Aerobatic) training aircraft circa. 1934

Ryan Aircraft was the manufacturer of the famous Spirit of St. Louis airplane. The Ryan ST’s were a series of two-seat, low-wing monoplane aircraft. They were used as sport aircraft, as well as trainers by flying schools and the military of several countries. The “ST” series (for “Sport Trainer”) was the first design from the company, introduced in 1933. This aircraft was followed by the “ST-A” (A for Aerobatic) which was developed with a more powerful engine.

“We manufacture aircraft parts for displays and museums,” states David Paqua from Classic Metalcraft. “We recently expanded our practice to accept complete restoration work for antique aircraft. Enter the Ryan STA. We decided to produce an exact replica of the Ryan. We obtained copies of the Ryan factory drawings and proceed to fabricate components for the fuselage, landing gear and wings. The most difficult part that needed to be fabricated was the #2 bulkhead. Not only is it tough to replicate without heavy pressing equipment, but it requires heat treating by a knowledgeable firm to prevent distortion. This is where Metlab came into the picture.”

The bulkhead component is a structural piece fabricated with 4130 steel. This segment was located just forward of the instrument cluster. The #2 bulkhead component carries all the stress of the flying wires, landing gear as well as the wing attachments. It was vital indeed to properly fabricate and heat treat this assembly while maintaining a flat section.

Fuselage
The fuselage jig is allowing accurate positioning of the bulkheads and upper and lower stringers. The bulkheads will be covered by a 2024 alloy aluminum skin of .032 thickness.

Paqua explains, “The skin of the aircraft is affixed to the bulkhead. It is critical for the part to have the proper minimum mechanical properties to support the skin as well as remain in shape through the heat-treating process to maintain the aerodynamic characteristics of the aircraft.”

Metlab developed a special fixture to maintain the flatness of the component during processing. Additionally, Metlab consulted with the customer and advised them to tack weld additional bracing inside the component to keep the integrity of the shape and help with the flatness of the entire component during the heat-treating process.

Bulkhead collage
Bulkhead component prior to heat treating.

The physical dimension of the bulkhead is 26” wide X 39” tall and about 2” in section size. The part is quenched and tempered to 180,000 PSI UTS, minimum, about HRC 40 – 44. The part was processed in one of Metlab’s 4′ diameter by 16′ work zone pit furnaces and then clamped on a flat plate for tempering to maintain flatness. Post heat treatment inspection consisted of verification of the hardness and flatness.

Watch The Video:

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Heat Treating Parts For An Off-Road Race Car

Metlab is an active supporter of many university educational programs featuring race car construction. This year Metlab provided expertise and heat-treating services for Georgia Tech Off-Road, a student led team under the Mechanical Engineering Department of the Georgia Institute of Technology. The team built an off-road race car for the Baja SAE International Competition in Gorman, CA that was held in April of 2017. Students from the university designed and built an off-road car which was then judged on design, dynamics, suspension, maneuverability, and other criteria.

IMG_2085

Georgia Tech Student-built; Off-road race car “in action” at the SAE Competition

Georgia Tech Student-built; Off-road race car “in action” at the SAE Competition

Victor Law is the GT (Georgia Tech) Off-Road Team Leader and spearheaded the project. “In 2014, we didn’t go the competition; the team was just too small. However, in 2015 we recruited more members and we could enter the competition in 2016. That was also the first time we went through entire design process. Before, we were using legacy designs from the past. From this 2016 race, we found that the spindles, axles, and shafts held up great. On the other hand, our gears proved to be under-designed. An analysis was needed to consider the forces coming from the inboard braking loads. This forced us to use an older set of gears for the race.”

Part of the racing design / build program involves donations and supplies from various companies. Law explains “Materials and funding come from sponsors like General Motors (GM), John Deere, and others, and from the University. We will purchase materials and some sponsors like Metlab will provide “in kind” parts or services to offset costs as well as help with manufacturing consultation. I reached out to Metlab in October of 2016 to help with a front axle from a previous year car. The axle had failed due to lack of heat treating.

Metlab’s President, Mark Podob explains “We helped the team by reviewing and consulting with them on the advantages of heat treating several key components. The heat treating increases the yield strength of the material. As an example, the front and rear axles were fabricated from 4340 steel. While the existing components held up well, for replacement parts, the heat-treating process that we did more than doubled the yield strength. Without our heat treating, there is the risk of the front wheels seizing and fracturing.”

We jointly determined that the front axles, rear axles, output and input shafts and gears had to be heat treated. The parts were processed in several batches and turnaround time was about two weeks. The axles and shafts were all made from 4340 alloy steel and critical areas were induction hardened to HRC 50 – 52. This provided those parts with high strength and wear resistance. Wheel spindles were made from the same alloy and through hardened to HRC 38 – 42 for strength. A set of gears were also heat treated to HRC 50 – 52, ensuring that they would stand up to the rigorous operating conditions of off-road racing.

The car was built with the heat-treated parts and made ready for the competition. The GT Off-Road team was one of 92 teams in the competition. Here are the competition results:

  • Overall – #42
  • Acceleration – #34
  • Hill Climb – #38
  • Maneuverability – #44
  • Suspension – #21
  • Endurance – #51
The GT Off-Road Racing Team with their 2017 race car

The GT Off-Road Racing Team with their 2017 race car

Law exclaims, “Overall we were very excited about the results and we gained a lot of experience. We had several new members and finalized a new off-road car design. We saw some problems and will be fixing them for next year. Our target is to be in a Top 20 position for 2018. We are grateful for all of Metlab’s help, especially as a resource for heat treating gears, and look forward to working with them again.”

Metlab has assisted students at Georgia Tech, Temple, Drexel, University of Pennsylvania, and the U.S. Naval Academy on their SAE Automotive Engineered Car programs, providing them with no-charge heat treatment services and engineering consultation. In partnership with several gear manufacturers who utilize Metlab for their heat treating requirements, the students have been able to procure gear sets for their vehicles economically.

Posted in Heat Treaint Small Parts, Heat Treating, Heat Treating Drive Train Spindle, Heat Treating Race Car Parts, Induction Hardening | Leave a comment

Metlab Applies Black Oxide To A Suit of Armor

Metlab recently black oxide finished a suit of armor for an artisan. The armor was manufactured by M & M Metals of Jeffersonville, PA. The complete suit of armor consists of about 125 hand-formed metal plates, and will cover and protect the wearer from head to toe.

Robert (Mac) McPherson, owner of the business and manufacturer of the armor has been handcrafting suits of armor since the late 1970’s, and is considered among the best in the world.

The armor is based on a late 15th-century statue of St. Florian (patron saint of firefighters) in a German church. While the form and detail of the armor in the statue were retained, the proportions had to be altered to fit the customer, who is a tall man with a “mature figure”. Mac spent many hours forming 1050 medium carbon steel sheet into the various components that comprise the suit. Each plate was shaped using only hand tools, and was then hardened and tempered. Afterwards, each individual component was ground and polished. Blackening this suit of armor represented the culmination of many months of work.

Black oxide imparts a deep, black, lustrous appearance to the parts being coated and replicates the surface finish of the part.

Black oxide imparts a deep, black, lustrous appearance
to the parts being coated and replicates the surface finish of the part.

The modern black oxide coating that Metlab applied to the armor is very durable and attractive. Black oxide finishing is offered in addition to the current array of heat treating services. Black oxide is classified as a conversion coating. The black oxide processing of the armor consisted of taking individual pieces and placing them in large work baskets and running the baskets through the black oxide line. About eight individual cycles were required for the parts. The process, characterized as a “hot black oxide process” is carried out at 265°F to 285°F. After blackening, the parts were coated with a dry-to-the-touch oil and then hand wiped to remove excess oil, providing the pieces with a lustrous, glossy finish.

It may seem strange that there is any market for medieval armor, but the demand is greater today than it has been for centuries. Worldwide, there are tens of thousands of medieval reenactors in numerous different organizations. While many dress in their armor for “living history” events (imagine Civil War reenactors, but set them a few centuries earlier) most of them fight in some sort of tournaments. Some organizations compete with wooden weapons and others use blunted and edgeless steel ones. Most of these tournaments, melees, and “wars” are fought on foot, but some are done from horseback. There is currently a large and growing jousting scene.

Jousts range from the choreographed spectacles with breakaway lances that one finds at Renaissance Faires and medieval-themed dinner theaters to competitive jousts using solid lances with steel heads. There is also a niche for the modern armorer who makes high quality armor for collectors.

St Florian statue in Germany on which the armor is modeled

St Florian statue in Germany
on which the armor is modeled

This is the second suit of armor that Metlab has blackened for M & M. The first suit was done over 10 years ago, and that armor was based on English effigies (tomb sculptures) and artwork of the mid-15th century. In addition to what is shown in the picture, the armor included another helmet, two additional visors, and a steel plated saddle. The owner not only cut an impressive figure, but has jousted very successfully in the armor.

Effigy of Sir John Cressy, from which most of the details of his armor came from. Photography by Cameron Newham.

Effigy of Sir John Cressy, from which most of the details of his armor came from. Photography by Cameron Newham.

Historically, most armors were polished bright, and left “white”, but many were blackened, russeted, or blued. Sometimes these colors were built up by slow rusting, like antique firearms. This produces a brown or black color depending on whether the steel is steamed. Other times, the armor was made a shade of blue or purple by controlled heating. This is like the color one sees on antique watch hands. Another common method of creating a black finish was to bake on a coat of oil, like seasoning a frying pan. These methods can produce an attractive color and some degree of rust prevention.

In addition to suits of armor, Metlab uses its black oxide process in a variety of industrial applications in widespread industries. Some examples include:

• Retail: Store displays and fixtures.
• Automotive: Cans for oil filters, numerous under the hood fasteners
• Electrical: Wire strippers and cutters
• Home / Garden: Tree toppers – jaws and clipping tools
• Gearing: Small gears for tiny timers and electrical switches
• Firearms: Gun components, shotgun shell magazines

Metlab has complete heat treating capabilities along with extensive experience to provide consulting for complex and unique projects and applications.

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Metlab’s Quality Assurance System

Metlab has a reputation for providing quality heat treating and surface finishing services. To ensure quality in every order processed, the company is focused on a complete quality management system. The quality system is run by Rachel Piccari, whose main function is to work with customers and the Metlab production facility for complete quality assurance.

Rachel Piccari - Quality Control

Rachel Piccari – Quality Control

“I work with Metlab’s customers to make sure what they are asking for is feasible and technically sound.” states Piccari. “I review each customer purchase order to check that all of the information that is provided on their order is clear, so we start each project correctly.” Over the past four years since her start with the company, the quality system has been updated and continuously improved to keep Metlab at the forefront of meeting specifications in various heat treating processes. Metlab’s processing and paperwork is ISO-9001 compliant, and as such is subject to continual review.

Piccari explains, “I invest quite a bit of time translating the customer instructions to our actual in-house processes. There are over a dozen terms in use for nitriding alone. And often customers send parts for heat treating and designate the steel by a trade name rather than the AISI or UNS steel designation. Ironing out the commercial request into a technical document can sometimes be a challenge, but this up-front order clarity makes the parts being processed flow through the shop floor efficiently. In addition, quality is measured at various points along the process as the parts are treated. If there is a question regarding treating a part, the customer will be notified to explore solutions for resolving that issue. I will review all the paperwork and results and make sure it fits with what customer has required. Additionally, I’ll write the certifications to go along with the job to finalize the project.”

Depending on the type of heat treatment specified by the customer, Metlab will issue a certification documenting the process and metallurgical results.  This can include surface hardness, or in the case of carburized and/or nitrided parts, surface and core hardness and case depth. For more complex requirements, certifications may include chemical analyses, and mechanical property evaluation such as tensile tests, Charpy impact strength, stress rupture, fatigue and metallurgical analysis. Metlab has even done salt spray testing on nitrocarburized parts to ensure that they meet the corrosion resistance requirements.

Rachel started with Metlab as a lab technician, checking part hardness, performing microhardness traverses on case hardened parts, and doing routine metallographic analysis. She has moved into the Quality Control position and is currently enrolled in an Engineering degree program in Philadelphia, as well as the Metal Treating Institute (MTI) 2017 YES Management Training Program. This program focuses on improving the leadership and people skills of individuals from the heat treating community.

In addition, Piccari has been training a new person to take over the lab, allowing her to focus entirely on Metlab’s Quality Assurance program. The experience in the lab gave her hands-on training to be able to identify quality issues and trace them back to the source to continuously improve the company’s processes. As an example, Rachel headed up a project to investigate the optimum stop-off paint and techniques for masking carburized and nitrided components, leading to more reliable procedures for heat treating these parts.

Metlab heat treats parts in accordance with all military and industry specifications. Jim Conybear, the director of operations for Metlab, oversees the overall quality function for the company. Jim has been a member of the AMEC Committee (Aerospace Materials Engineering Committee) which is under the auspices of the SAE, for over 40 years. Along with engineers from the commercial heat treating community as well as representatives from aerospace companies including Boeing, Bell Helicopter, Lockheed Martin, Northrup Grumman and others, AMEC defines and maintains the specifications that are the standards for heat treating parts. Their stated objective is “to coordinate and utilize the knowledge, experience, and skill of engineers and technologists to develop and maintain material and process specifications that conform to sound, established engineering and material practices within the aerospace industry.” Jim is heading up the AMEC subcommittee that is revising AMS 2759, the specification which establishes the general requirements for the heat treating processes for steel parts. He has also been involved in defining the requirements for nitriding as well as quenching.

Metlab, through its focus on personnel and participation in continuous quality improvement, maintains its position as a leader in the supply of thermal heat treating processes to over 3,000 companies in a variety of industries.

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Nitriding and Carburizing

Nitriding and carburizing are the two most common heat treatment practices for surface hardening functional components. The main difference is that in nitriding, nitrogen atoms are made to diffuse into the surface of the parts being processed, whereas in carburizing, carbon is used. There are advantages and disadvantages to both processes.

Nitriding

Nitriding is a surface hardening treatment, where nitrogen is added to the surface of steel parts either using a gaseous process where dissociated ammonia as the source or an ion or plasma process where nitrogen ions diffuse into the surface of components. Gas nitriding develops a very hard case in a part at relatively low temperature, without the need for quenching. The process has the advantage of being able to penetrate blind holes, and also allows for the masking of parts to keep areas which may need further machining soft. Also parts of different sizes and shapes may be nitrided in the same cycle, allowing for versatility of the process. Ion nitriding, on the other hand, is a more restrictive process. For uniform case depths in a load, parts must be of similar size and geometry. Also, masking is difficult, and penetration of blind or through holes is not possible.

gear1 gear2

Large gear after nitriding treatment in Metlab’s facility (l) and close-up of gear teeth. Gear teeth will subsequently be ground to remove approximately 0.002″ stock and provide surface finish required for the application.

Nitriding is carried out at temperatures below the transformation temperature of alloy steels, so that with proper manufacturing techniques, there is little or no distortion. In general, parts to be nitrided are heat treated to the proper strength level, and final machined. The parts are then exposed to active nitrogen at a carefully controlled temperature, typically in the range of 925°F to 985°F. This temperature is usually below the final tempering temperature of the steel so that nitriding does not affect the base metal mechanical properties. As a result, a very high strength product with extremely good wear resistance can be produced, with little or no dimensional change.

The components to be nitrided are often stress relieved prior to final machining so that the only size changes observed are growth of about 0.0005″. In some cases, nitrided components are surface ground after nitriding to remove the most outermost brittle layer (eta phase) produced by the process, or to bring parts into a tight tolerance.

Parts can be masked avoid hardening some areas, such as gear hubs and bores, keyways, threaded holes or bearing surfaces, which are easily machined after nitriding. Typical applications for nitriding include gears, cranks and camshafts, cam followers, valve parts, plastic injection molding screws and dies, die casting tools, forging dies, extrusion dies, injectors, and firearm components.

Materials that can be nitrided include low carbon steels, which will develop file hardness, alloy steels such as 4130, 4140, 4340 and Nitralloy 135M which are the most common nitriding steels and special application steels including, mold steels (P-20), air hardening tool steels (A-2 and D-2), hot work and shock steels (H-13 and S-7), high speed steels (M-2, M-4 and M-42), and stainless steels (304, 316, and 17-4 PH).

A prime application for nitriding is plastic injection mold components, including screws, tips and barrels. The hardness of the nitrided layer is especially useful in reducing wear from plastic molding, particularly when abrasive plastics like glass filled polymers are extruded.

feed-nozzles feed-screw

An array of plastic injection molding feed screws and nozzles.

Carburizing

Carburizing is a heat treat process that produces a surface which is resistant to wear, while maintaining toughness and strength of the core. This treatment is applied to low carbon steel parts after machining as well as high alloy steel (4320, 8620, 9310, 17CrNoMo6-7) bearings, gears and other components.  Parts that require increased wear resistance and fatigue strength are excellent candidates for carburizing.

Similar to nitriding, carburizing increases strength and wear resistance by diffusing carbon into the surface of the steel. This created a hard case while maintaining a substantially less hardness in the core.

Most carburizing is done by heating components in either a pit furnace or sealed atmosphere furnace and introducing carburizing gases at temperature. Gas carburizing allows for accurate control of both the process temperature and carburizing atmosphere (referred to as carbon potential). Carburizing is a time/temperature process; the carburizing atmosphere is introduced into the furnace for the required time to ensure the correct case depth is achieved. Carburizing is carried out at temperatures above the transformation of steel, so that quenching and tempering to develop the hardness in the case and core is required. After carburizing, the work is either slow cooled for later hardening, quenching and tempering or quenched directly into oil and then tempered. Since there are microstructure changes associated with the hardening process, some size change or distortion can be expected. This can be an issue for closely toleranced parts.

Common practice allows for leaving parts oversize and finish machining or grinding after hardening.  For close tolerance work, like bearings and gears, fixture or press quenching maybe used to minimize the amount of post-heat treat finishing required. Depending on the material, deep freezing and a second temper to reduce retained austenite may be required.

Among the most common carburizing applications is gears and pinion shafts. Carburizing economically imparts a hard surface improving wear as well as increases the fatigue strength. An advantage of carburizing is the ability to impart deep cases, up to 0.300″ which is especially useful for very large gears, such as those used for steel rolling mill applications.  Large bearing races, which are subject to compressive stresses, are also a prime application for carburizing. Bearings which are carburized, similar to gears and pinions have a tough core with a hard, wear resistant outer surface. This allows the parts to withstand heavy shock loads without premature damage or cracking which can sometimes be a problem for through hardened parts.

large-gear

Gear rim measuring ∅ 81″ O.D. x ∅ 66″ I.D. x 28″ Tall, weighing approximately 13,000 pounds made from 17CrNiMo6 Steel, carburized to 0.185″ case depth and quenched using sizing plates on the inside diameter to minimize out of roundness. T.I.R. and taper both measured less than 0.030″.

rolling-mill-gears

Gear rolling mill transmission with an assortment of carburized and hardened gears and pinions.

metlab-heat-treating-sequence

Sequence showing large steel mill pinion being removed from the carburizing furnace and transferred to the quench tank to be hardened and subsequently tempered. Pinion weight is about 24,000 pounds.

Which Process to Specify?

In general, the application dictates whether nitriding or carburizing should be the process of choice. For lightly loaded, precision components where distortion can be a major consideration, nitriding is the appropriate choice. A functional case depth up to 0.030 – 0.035″ can be economically achieved. Depending on the material, a surface hardness in excess of HRC 65 is not out of reach. Applications such as guides, rails, extrusion screws and precision gears are ideal candidates for nitriding.  For more heavily loaded parts like large gears and bearings, carburizing may be a better choice. Deeper case depths, a requirement of coarse toothed heavily loaded gears and bearings can readily be economically achieved.

Depending on the application, nitriding may be a less expensive heat treatment process. Although this can be balanced by the cost of the base metal used to manufacture the part.

Quality

The quality standards to determine case depth and hardness are the same, i.e., test coupons are run with the work and cut, mounted, polished and etched. A microhardness traverse is taken and surface, core hardness and case depth are measured.

Processing Times:

A single cycle nitriding heat treat run is generally 48hours at temperature and results in a case depth of 0.015 – 0.020″. Carburizing times for the same case depth are shorter. There are fundamental differences between the two processes.

Nitriding is most commonly carried out on prehardened alloy steels like 4140, 4340 or Nitralloy 135M. The most common applications are gearing. The temperature of the process is in the range of 925°F – 975°F which is below the tempering temperature of the steels being processed. Hence there is little or no distortion, only about 0.0005″ growth due to the nitrogen diffusion into the part. So no post heat treatment machining is needed. Carburizing on the other hand, is a high temperature process, and allowance for additional grind stock due to rehardening is necessary. And post carburizing machining is almost always a requirement.

How Metlab Can Help

In addition to an extensive range of thermal processing services, including vacuum heat treating, the Metlab facility includes capabilities for both nitriding and carburizing. Furnaces up to 15′ in diameter and 12′ deep or 4′ in diameter by 16′ deep are available for large or long and slender parts. A nitriding service is available for parts up to 22′ long. All processing equipment is calibrated and heat treating is carried out under stringent control, with equipment in compliance with government MIL specifications. This ensures reliable, predictable and repeatable heat treating results. With an on-site metallurgical laboratory parts are evaluated and certified to MIL or customer specifications for hardness and case depth. With metallurgists on staff applications and requirements can be discussed and reviewed with appropriate processes recommended.

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Heat Treating Race Car Parts With Quick Turnaround For Race Event

Metlab has worked with a number of NASCAR and Indy Racing Car Teams and also companies that restore antique cars, sports and muscle cars and has a history of heat treating race car parts that must endure severe conditions. Big B Manufacturing is a specialty machine shop located in Klingerstown, PA which specializes in design and engineering as well as machining of small and large components. They also make and race off road cars. Big B brought a project to Metlab that required the heat treating of four (4) link arms.  The arms are fabricated from 4130 steel and TIG welded with 4130 filler. The suspension parts are for Big B Manufacturing’s racing team.

Metlab Heat Treating Race Car Parts
Control arms and other racing car suspension parts

Josh Blyler, Vice President of Big B comments, “Big B has been racing for 20 years. We started in go-carts, then micro sprints. About 10 years ago we started racing off-road 4-wheel drive trucks and we have been having fun doing this ever since. Additionally Big B makes parts for a few different racing companies. We make parts that get used in micro sprint racing, monster trucks, and Ultra4 off-road trucks.”  Blyer adds, “For this particular project we needed these parts completed in a very short time-frame to be able to attend an upcoming race event.”

4x4 Racing

The 4×4’s take a beating in the “King Of Hammers” competition
(Click to watch the video of the 4×4’s in action)

For the project, Blyler consulted with Mark Podob of Metlab to provide some background for the project. “I was looking for suggestions on how hard to make the control arms. All of the top tier teams heat treat their links but nobody really knows how hard. I did some testing on other teams’ links and they all seem to be in the low 30 HRC range. What I wanted was to get the most tensile strength out of the suspension parts, but not to let them get too brittle so they would fail prematurely. I was open to suggestions. I was told that because the parts were welded, they had to be normalized first to eliminate the heat affected zone from welding, but again I was looking for Metlab’s heat treating expertise.”
After analyzing the project, Podob provided some guidance for the heat treating process, “Looking at the data for hardness vs. % elongation and R.A., both mechanical properties which are a measure of ductility or toughness, there is not much degradation in these properties if we take the material to the HRC 36 – 40 range. This would give Big B about  ~ 160 to 195 KSI tensile strength with plenty of toughness to avoid failure from impact or fatigue.”

Additionally, Blyler had concerns that the parts would not remain flat, and decided that they should start with one set, assess the parts, and then process the balance.  Byler added, “To minimize any distortion from heat treating, I bolted in temporary spacers in all the tab slots. This helped them keep their shape during the normalizing and hardening process. Each end of the link has threaded holes that I wanted to keep intact as best as possible. These threads are where the Heim joint threads into and they needed to stay in good shape with minimal distortion.”  (Note: A Heim joint is also known as a rod end bearing, specifically developed for steering on race trucks as they are heavier duty than ordinary automobile or truck rod ends.)

From this point the parts were sent to Metlab’s facility and went right into processing.  Metlab normalized the parts by heating them under a protective atmosphere to 1650°F. They were held at temperature for one hour per inch of thickness. After a sufficient soak time at temperature, parts were slow cooled. Parts were then reheated to 1550°F, also soaked for one hour per inch of thickness under a protective atmosphere, and then oil quenched. All of the high temperature excursions were done with the parts under a protective atmosphere to prevent decarburizing or oxidation. Then the parts were tempered at a temperature appropriately selected to provide the hardness and tensile properties desired. Parts were checked for hardness to ensure that proper results were obtained.

Blyler concludes, “Metlab was able to turn the parts around within two days after heat treatment! This is just one example of why we have been working with Metlab for over 18 years. Metlab provides all of our heat treating, nitriding, and thermal stress relieving needs.”

Picture1

Big B‘s 4×4 frame with finished link arms and components

Picture2

 

Big B’s 4×4 “Twisted Mistress” takes home several trophies.

Blyler exclaims, “We finished this car up late last Friday night and raced it Saturday morning. I was not sure how things were going to shake out since I had zero seat time and was also concerned on what issues we may be fighting with on a fresh car. Ultimately the car was flawless and we took the win over 115 other competitors. We had a six minute lead over the second place finisher and I could not be more pleased.”

About Big B Mfg.
Located near Harrisburg, Pennsylvania, BIG B MFG will provide over 50 years of experience with manufacturing, design and engineering and full production capability that will ensure your company can realize lower material and assembly costs while ensuring high quality in an ever changing market place.

Big B Mfg Logo

 

 

Posted in carburizing, Heat Treaint Small Parts, Heat Treating, Heat Treating Race Car Parts | Tagged | Leave a comment