Heat Treat Tips: Atmospheres, Gas Chambers, and Thermocouples
One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks shared by some of the industry’s foremost experts.
For Heat Treat Today’s latest round of 101 Heat Treat Tips, click here for the digital edition of the 2019 Heat Treat Today fall issue (also featuring the popular 40 Under 40).
Today’s tips come to us from Nel Hydrogen covering atmospheric solutions and Wisconsin Oven Corporation with a tip on gas chamber issues. Additionally, Pelican Wire provides 4 quick tips on Thermocouples.
Heat Treat Today welcomes you to submit your own heat treat tip for Heat Treat Today's 2020 Fall issue to benefit your industry colleagues. You can submit your tip(s) to karen@heattreattoday.com or editor@heattreattoday.com.
Heat Treat Tip #11
Compliance Issues? Try On-Site Gas Generation
On-site gas generation may help resolve compliance issues. Growth and success in thermal processing may have resulted in you expanding your inventory of reducing atmosphere gases. If you are storing hydrogen or ammonia for Dissociated Ammonia (DA), both of which are classed by the EPA as Highly Hazardous Materials, expanding gas inventory can create compliance issues. It is now possible to create reducing gas atmospheres on a make-it-as-you-use-it basis, minimizing site inventory of hazardous materials and facilitating growth while ensuring HazMat compliance. Modern hydrogen generators can serve small and large flow rates, can load follow, and can make unlimited hydrogen volumes with virtually zero stored HazMat inventory. Hydrogen is the key reducing constituent in both blended hydrogen-nitrogen and DA atmospheres—hydrogen generation (and optionally, nitrogen generation) can be used to provide exactly the atmosphere required but with zero hazardous material storage and at a predictable, economical cost. (Nel Hydrogen)
Heat Treat Tip #12
Oven Chamber Failing the Test? Try This!
When having difficulties passing a temperature uniformity test, check the pressure of the heating chamber. This can be done with a pressure gauge that reads inches of water pressure. The best uniformity is achieved when the pressure is neutral or slightly positive (0” to +.25” wc). If the pressure is negative (even slightly), it can draw a stream of outside cold air into the chamber, causing cold spots. For the best results and ease of analysis, permanently mount a gauge to read the pressure. Any issues with pressure can be easily recognized and corrected. (Wisconsin Oven Corporation)
Heat Treat Tip #70
Type N Thermocouple (Nicrosil / Nisil)
Type N Thermocouple (Nicrosil/Nisil): The Type N shares the same accuracy and temperature limits as the Type K. Type N is slightly more expensive and has better repeatability between 572°F to 932°F (300°C to 500°C) compared to Type K. (Pelican Wire)
Heat Treat Tip #71
Know Your Thermocouple Wire Insulations
Know your thermocouple wire insulations. When is Teflon® not Teflon®? Teflon® is a brand name for PTFE or Polytetrafluoroethylene owned by Chemours, a spin-off from Dupont. FEP is Fluorinated Ethylene Propylene. PFA is Perfluoroalkoxy Polymer. All three are part of the Fluoropolymer family but have different properties. Of the three compounds, PTFE has the highest heat resistance, PFA second highest and FEP third. The higher the heat resistance the more expensive the insulation. Keep that in mind when specifying the insulation and only pay for what you need. (Pelican Wire)
Heat Treat Tip #72
Resistance Temperature Detectors (RTDs)
Resistance Temperature Detectors (RTDs) are replacing thermocouples in applications below 1112°F (600°C) due to higher accuracy and repeatability. Typical constructions are multiconductor cables with nickel-plated copper conductors. (Pelican Wire)
Heat Treat Tip #74
When to Use Type K Thermocouples
Type K thermocouples should only be used with the appropriate Type K thermocouple wire. Type K measures a very wide temperature range, making it popular in many industries including heat treating. An added benefit with Type K is that it can be used with grounded probes, ungrounded probes, and exposed or uncoated wire probes which are attached to the probe wall, measure without penetration, and have a quick response time respectively. (Pelican Wire)
Heat Treat Tip #100
The Right Furnace Atmospheres Will Pay Dividends
Save money on your furnace atmospheres by employing the driest and leanest furnace atmosphere blends possible. Furnace atmospheres are a compromise between keeping it simple and supplying exactly the atmosphere to meet the unique requirements of each material processed. Organizations have different priorities when it comes to atmospheres—heat treat specialists may want to be able to run as many different materials as possible using a limited array of atmosphere types, while captive heat treating operations often want exactly the atmosphere approach to maximize the benefits for their specific processes/products.
The dewpoint (water content) of the atmosphere in the furnace is a key factor in its performance. At high temperatures, water in the atmosphere can break down, releasing oxygen that can cause oxidation. You must maintain a high degree of reducing potential to achieve the surface finish and processing results desired. If the furnace atmosphere gas is wet, you’ll need a gas blend richer with hydrogen than you would if your atmosphere blend had a lower dewpoint (less water vapor content). Since hydrogen costs 10 times more than nitrogen, it is more economical to run a leaner atmosphere than a richer atmosphere. By running the driest atmosphere blend possible, you may find that you can lean down your atmosphere (consistent with the metallurgical needs of your product/process) by reducing the proportion of hydrogen and increasing the nitrogen. In doing so, you may recognize meaningful savings.
Check your furnace atmosphere raw materials and process and obtain the driest atmosphere possible. Control your atmosphere dewpoint by adding humidity as needed to the driest starting blend possible rather than accepting a wet atmosphere and trying to process your parts. You’ll achieve the best compromise of excellent results at the lowest cost. (Nel Hydrogen)
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