How to Estimate Tooling Temperature at Oven Exit

Why estimate when you can measure?

An infrared surface thermometer uses a laser to pinpoint an item/spot. These are not too expensive and are fairly reliable. Be certain to select one that reads within your expected temp ranges.

Thanks for the input, but the tooling does not exist so it's hard to measure. I am working on proposing an upgrade to an existing process including estimated costs. I am assuming the tooling will not reach the same temperature as the parts being heat treated because of the material and mass differences.

Hello JRiversW.

Your work; does it soak long enough to come all the way to the temp of the oven?

Hi Doorman.

No. There is a 700-800°F difference. Parts spend about 3 minutes at 1520°F, then another 9 minutes slowly cooling before I have to touch them again. FYI - The upgrade is adding automation.

If the tooling is positioning the work and is in contact then it will need to be reasonably close to the heat treat temperature. As it will act as heat sink and draw heat away from the parts being heat treated. The area in contact will be poorly heat treated if the positioning tooling does not get as hot. Also the positioning tool the larger it is the bigger heat sink it becomes the longer it will take to heat the part. The more wasted energy doing so.

Thanks ozzb.

Right. I need to minimize contact area and tool mass. Currently the work is in direct contact with the steel mesh oven conveyor belt though, so I think the affects of properly designed tooling on the process will be negligible.

My thought in starting this discussion was if I assume the tooling will be at the same 600-800°F as the work, and it turns out not to be, I will add unnecessary cost to the equipment moving the tooling back to the entry side. Costs have to be balanced against benefits.

This tooling just holding the part in position or being clamped in to it? The temperature you mentioned a tempering process? How is the part being taken out of the tooling? If its being left to cool in the tooling. Then a conveyor may do.

The tooling is just keeping orientation so automation can unload the parts immediately instead of waiting for cooling as required for manual unloading. I expect a very light contact pressure = to part wieght. The process is annealing, after 9 minutes of cooling parts are still at 600-800°F.

Parts being hand loaded?

No. Parts are coming from an automated process.

Then I would try to keep the tooling as hot as possible. The more heat they retain the less energy used to heat them back up. Plan on them being the 800°.

GA, ozzb. I would like to do that but...

I did not mention the previous process is nearly cryogenic so the tooling may need to be cooled to avoid thermal shocks to the small parts. I have 20 feet of transport distance to do that.

I have been a trying not to give out too much info, due to confidentiality concerns.

This discussion is leading me to think I should include some additional time for process development in my proposal.

Might be better to preheat the parts to reduce thermal shocks. All so of your tool fixturing. Ceramics can be cast in any shape for easy replacement. Will not conduct heat to the part as metal will or away.

Good Morning ChazL,

Thanks, I think I can get the answer I need with that.

Considering the temperatures you mention, except if your tool is poished, most of the thermal power exchange will come from radiation from the walls of the oven, and power transmission is governed by the (simplified) following equation:

P = ε * 5.68 10^-08 (Toven^4-Ttool^4)

This gives P in Watts, with Toven and Ttool in KELVINS (very important)

ε is the emissivity of the part and the oven, as a first rough value, you vcan probably consider equal to 0.8

Then you estimate the mass and thermal capacity of you material and solve a first order differential equation; provided the part is not to thick (let's say les than one inch)

little bit boring but efficient