Vac Aero International Inc

Diagnosing Discolored Work in Vacuum Heat Treating

/ FEATURED NEWS, MANUFACTURING HEAT TREAT, VACUUM FURNACES TECHNICAL CONTENT

Source: VAC AERO International, Inc.

Part discoloration after vacuum heat treating? What can heat treaters do to prevent this? In this best of the web, Q&A-style article, witness the heat treating industry gather around to exchange ideas and find a solution to the problem. Part position, backfill gas level, contaminated quench gas, or an air leak could all be to blame in this Technical Tuesday.

Dan Herring weighs in on the issue as well. To read The Heat Treat Doctor's® diagnosis, click the link below. Learn how the color and position of the discoloration give clues as to the source of the problem.

An excerpt:

"So, what else could be happening? Let The Doctor add a few thoughts to the discussion. First, the fact that the discoloration (staining) is brown in coloration suggests that the oxide is forming on the part surface during cooling when the temperature is in the range of (approximate) 245ºC – 270ºC (475ºF – 520ºF). This is supported by the fact that the oxidation does not occur “during natural cooling” (which we assume to mean cooling under vacuum). Second, the fact that the discoloration is more evident at the bottom of the load suggests the phenomenon is (gas exposure) time dependent, that is, the longer the parts take to cool through the critical range, the greater the chance for discoloration."

Read more: Discolored Work in a Vacuum Furnace – The Heat Treat Community Answers the Clarion Call

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High-Temp Differential-Expansion Problem and How to Solve It

/ BRAZING, BRAZING TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT, MANUFACTURING HEAT TREAT NEWS

 

 

Source: Vac Aero International Inc.

 

 

 

 

If you’ve ever tried to braze together materials that have widely different Coefficients of Thermal Expansion (COE’s), you know that the material with the higher expansion rate will grow faster than the other when heated and contract faster when cooled down. You also know that once the two different materials have been brazed together and cooling begins, the shrinkage-rate differences between those two materials can produce significant shear stresses at the brazed interface between them and be so strong that the thin brazed joint may be torn apart at either interface. Other similar weaknesses and damage can result as well.

In this HTT Best of the Web Technical Tuesday feature, Dan Kay of Kay and Associates, a vacuum and atmosphere brazing consultant, explains the details of this problem and the solution.

Dan Kay
Brazing Engineer
Kay and Associates

An excerpt: “Today’s brazing technology is based on a strong foundation of the brazing experiences of many people around the world over a period of many decades (even centuries). I’ve now been very active in the brazing world for almost 50 years and, like my predecessors in the world of brazing, I’ve learned a lot about this fascinating joining process (and I’m still learning). In the article, I’d like to share with you one of my brazing experiences from many years back, one that involved high-temperature differential-expansion between an 18″ (45 cm) diameter tool steel die and a thin carbide plate (round disc) that needed to be brazed to the die’s front surface for wear-protection.”

In this article, Dan, who is also a HTT consultant, helps readers understand the high-temp differential-expansion problem, explore what steps can be taken to prevent it, and ties it all together so that readers can clearly understand what to do.

Read the entire article from Vac Aero International,  An Old High-Temp Differential-Expansion Problem

Image source: Vac Aero International Inc.

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