VACUUM FURNACES TECHNICAL CONTENT

Heat Treat 2019 is coming, and one of the great benefits of gathering with 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. The inaugural list of 101 Heat Treat Tips was published in the FNA 2018 Special Print Edition. This special edition is available in a digital format here.

Today's Technical Tuesday features 10 Tips -- all from the Vacuum Furnaces category and all supplied by the same equipment manufacturer.

Heat Treat Tip #24

Dirt In, Dirt Out!

Parts going into the furnace should be as clean as possible. Avoid placing parts in the furnace that contain foreign object debris (FOD). FOD on work surfaces going into the furnace will contaminate the furnace and the parts themselves. Dirty work in, dirty work out. FOD comes in many forms. Most common: oil, grease, sand in castings or grit blasting operations, and metal chips that generally originate from the manufacturing process before the parts are heat treated. It could also be FOD from the shipping process such as wood or plastic containers used to ship the parts.

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Heat Treat Tip #26

When a Helium Leak Detector Doesn't Help

If an air leak cannot be found with a helium mass spectrometer, take apart the gas backfill or partial pressure solenoid valves to ensure they are clean. A small piece of debris can cause a valve to leak a process gas into the furnace that will not be found with a leak detector. Debris is often found in the valve seats when piping to the valve was disturbed in some way such as new piping or repair that stirs up contaminants in the line.

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Heat Treat Tip #46

O2 Analyzer Helps Ensure Gas Purity

In addition to monitoring dewpoint at the farthest location from the gas source in your heat treat facility, an oxygen analyzer is also recommended as an additional tool for monitoring gas purity. Generally, the analyzers used to measure dew point drift low over time. One may think they have a very low dew point gas, however, it could be the dew point analyzer is beginning to fail. Quarterly checks of the dew point analyzer's accuracy should be taken; some OEMs recommend replacing the sensors annually. Oxygen analyzers provide a more stable reading over a period of time and build redundancy in confirming gas purity when coupled with the dew point analyzer.

Heat Treat Tip #48

Seal Threaded Connections

Ensure threaded connections have adequate sealing protection on them to prevent air leaks through the threads where applicable. Wipe off excess sealant once the connection is made.

1. SWAK from Swagelok is excellent
2. Apply to the male threads only, not on any other surface as it could contaminate the system the component is being installed on.
3. Excess SWAK can be removed with a solvent such as acetone
4. Finger tight first, then tighten with a wrench
5. After the sealant is dry (recommend 24hrs by manufacturer) do not loosen as this could break the seal once cured.

Heat Treat Tip #61

Start With the Obvious

When a problem arises with the furnace, always start the troubleshooting process with the last item that was worked on. Start with the obvious; don't look for a needle in the haystack. For example, if the furnace will not pump into high vacuum and maintenance was just performed on the furnace with the pneumatic pressure valves being shut to perform that maintenance operation, the pneumatic valve to the main poppet valve on the diffusion pump may not have been re-opened, causing the diffusion pump main poppet valve to not open.

Heat Treat Tip #74

Make Sure Your Gas Meets Spec

Ensure each delivery of process gas is accompanied by a certification identifying purity, oxygen content, and dew point. For example, nitrogen should be 99.998% pure, 10 ppm oxygen max, and a dewpoint no higher than -89°F. With contaminated gas or gas that does not meet the criteria above, parts processed in the furnace and subjected to the partial pressure of the gas or quenched with the gas may also become contaminated, typically in form of oxidation and/or decarburization. Generally varying purity is not a concern, however, the specific purity of the gas required needs to be conveyed to the gas supplier and a certification supporting the gas type you ordered was delivered. An accompanying certification by the gas supplier goes a long way in audits and other disputes.

Heat Treat Tip #76

Specification Checklist for Vacuum Furnace Purchase

If you're planning on purchasing a new vacuum furnace, create a technical specification for the manufacturer(s) that clearly outlines the performance, functions, and accessories required on the furnace. The specifications should be reviewed by multiple departments including but not limited to engineering, quality, production, and management.

1. List of department sign-offs required (engineering, production, maintenance, quality)
2. Applicable documents required (i.e., AMS2750E, AMS2769)
3. List of parameters to be recorded (temperature, pressure, flow rate, etc.)
4. List of required alarms
5. Physical location of furnace and associated components such as control system and surge tank
6. Units of measurement (°F or °C, torr or Pascals, minutes or hours)
7. How many process gases and what type
8. Cooling rate requirements (This will help decide what quench pressure design furnace is required, for example, 2 bar or 10 bar.)
9. How many work thermocouples are required
10. What pre-testing verification is required for final acceptance. For example, thermal uniformity survey temperature points and tolerances, vacuum pump downtime and levels, leak up requirements, quench tests, process validation tests.

Heat Treat Tip #84

Clean the Door—Every Time!

Wipe down the front door O-ring and both flanges every time before the door is closed to ensure there is no debris on the O-ring or flange. Over time, the debris will damage the O-ring and pit the flange causing sealing issues.

Heat Treat Tip #91

Include Maintenance Team in New Vacuum Purchase Process

Include the maintenance manager in any furnace purchase decision. The manager and team are the ones tasked with troubleshooting, repair, and preventative maintenance. The maintenance manager will make sure the furnace has clear access for maintenance and replacement of major components including vacuum pumps, cooling motor, hot zone, and heat exchanger. The longer it takes to repair the furnace, the more downtime and lost revenue because the furnace is not running.

Heat Treat Tip #94

Inspect Replacement O-Rings

When replacing an O-ring, be sure the new O-ring is clean and undamaged (free of cuts, nicks, tears, or gouges) and that the splice joint is solid and true. Use a conservative amount of vacuum grease on the O-ring to ensure a tight sealing furnace. Not too much grease is needed. Rule of thumb: a light gloss or sheen, but no build-up.

All of today's tips were submitted by Solar Manufacturing.

If you have a heat treat-related tip that would benefit your industry colleagues, you can submit your tip(s) to doug@heattreattoday.com or editor@heattreattoday.com