The rebuild included a new 330 stainless steel muffle, new silicon carbide heating elements, new cooling sections, and new furnace controls to meet CQI-9 requirements. The CQI-9 controls package includes data acquisition, preventative maintenance alerts, remote connectivity, furnace parameter trending, and temperature deviation alarms.
The partner chosen for this rebuild, Gasbarre Thermal Processing Systems, designs, manufactures, and services a full line of industrial thermal processing equipment, offering batch and continuous thermal processing equipment for both atmosphere and vacuum applications as well as a full line of alloy fabrications, replacement parts and auxiliary equipment.
During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat TreatToday’s101 Heat TreatTips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.
Today we continue an intermittent series of posts drawn from the 101 tips. The tips for this post can be found in the FNA edition under Hardness Testing, CQI-9 Compliance, and Hardening/Tempering.
Heat TreatTip #22
Properly preparing a hardness sample can save time and money.
Inspection Mistakes That Cost
Rockwell hardness testing requires adherence to strict procedures for accurate results. Try this exercise to prove the importance of proper test procedures.
A certified Rc 54.3 +/- 1 test block was tested three times and the average of the readings was Rc 54 utilizing a flat anvil. Water was put on the anvil under the test block and the next three readings averaged Rc 52.1.
Why is it so important that samples are clean, dry, and properly prepared?
If your process test samples are actually one point above the high spec limit but you are reading two points lower, you will ship hard parts that your customer can reject.
If your process test samples are one point above the low spec limit but you are reading two points lower, you may reprocess parts that are actually within specification.
It is imperative that your personnel are trained in proper sample preparation and hardness testing procedures to maximize your quality results and minimize reprocessing.
Whether you need to meet rigid CQI-9 standards or not, what are the top 3, nay 4 best practices that nearly every in-house heat treat department ought to follow to make sure their pyrometer stuff is together?
Daily furnace atmosphere checks. Use an alternative method to verify your controls and sensors are operating properly and that there are no issue with your furnace or furnace gases.
Daily endothermic generator checks. Using an alternate method to verify your control parameter (dew point typically) or the gas composition is accurate will alleviate furnace control issues caused by bad endothermic gas.
Verify/validate your heat treat process every 2 hours OR make sure process deviations are automatically alarmed. this is a solid practice to ensure your controls and processes are running properly. This practice can help ensure that parts are being heat treated to the proper specification intended.
Conduct periodic system accuracy tests (SATs) per pre-defined timelines in CQI-9. Good pyrometry practices are an essential part of heat treatment. Because of the importance of temperature in heat treatment, ensure timeliness of all pyrometry practices addressing thermocouple usages, system accuracy tests, calibrations, and temperature uniformity surveys.
Control of Back Tempering With Induction Heat Treating
Induction heat treating is a selective hardening process. When hardening an induction path close to an area that had previously hardened, the heat from the hardening the second path tempers back the area that was previously hardened. This is a particularly common issue when tooth by tooth hardening of small gear teeth. Back tempering will reduce the hardness on the adjacent area and this effect may range from a few to over 10 HRC points.
Factors to Minimize Back Tempering
Process Issue
Questions to ask
Correct & repeatable placement of quenches
Can quench position be verified and set up repeatedly in the same position?
Verification of quench flow
Is the quench flowing freely through the quench system? Are the quench holes blocked? Are the flowmeters reading accurately?
Integrity of the quench
Was the percentage polymer measured? Is the quench quality okay? Is the quench contaminated?
Inductor design
Is the inductor designed to minimize heat on the tip? Is the quench effectively cooling the part?
Retained heat
Is a skip tooth hardening pattern being used to minimize residual heat in the induction hardening zone? Is the scan speed appropriate?
