Shim Stock for Carbon Potential 2

[swall]

Anyone have the procedure or a link to the procedure for using shim stock to evaluate carbon potential in an atmosphere furnace?

 

[redpicker]

I don't know about "the procedure", but a procedure I have used is

Using 0.08% Carbon 0.010" thick shim stock.

clean and weigh 0.010" shim stock (or whatever thickness you are using). Weigh to nearest .0001 g (0.1 mg)
This is Initial Weight (IW)

place in furnace for 20 minutes

cool in vestibule under atmosphere to below 1000F

clean and re-weigh shim
This is Final Weight (FW)

The percent increase in weight is

(FW-IW)/FW * 100

But, the initial shim had 0.08% C so,

% C = ((FW-IW)/FW * 100) +.08


Note, generally, the carbon content of the shim stock is unknown, but relatively low, 0.06-0.08. We always used 0.08.

Note 2, we would typically use a 1" by 2" shim (approximate dimensions). IIRC, they nomially weighted about 2.5 grams.

Note 3, care has to be taken on cooling from temperature to prevent oxidation. We had shim vestibules built into furnace.

Note 4, the soak time doesn't really depend on thickness, but is just the amount of time it takes to come to equalibrium. We did trials and found 15 and 20 minute shims to be equal, so we settled on 20 minutes. ymmv.

 

[swall]

Thanks, redpicker. Just what I was looking for.

 

[jsokal]

Hi,
Just to add, it is important that the shims be clean. Degrease them well and keep them wrapped in clean paper tissue and handle them onlt with clean white gloves to prevent contamination.

 

[unclesyd]

Read the last sentence in this article.

http://www.industrialheating.com/CDA/Archives/1de5f1c1b4cb7010VgnVCM100000f932a8c0____

Other approaches to Carbon Potential

http://www.furnacecontrol.com/ShimTest.htm

http://www.process-electronic.com/english/Products_Accessories.htm

 

[swall]

Thanks, unclesyd. Those last two devices are very interesting. I'll read the IH article as soon as my secret decoder ring comes in the email.

 

[swall]

Well, I registered and was able to open the link, which referenced the Sept 2004 issue of IH. I found the heading in the archives, but couldn't access it. I'll try it later or just call them for a hard copy.

 

[unclesyd]

You might want to contact these people for a copy of the article if you can't move through Industrial Heating. It is very quick and inexpensive, about $15.00.

http://www.lindahall.org/

IH is a very good magazine if you are involved in any type of heating. It use to be free for anyone in the trades.

 

[swall]

Finally got it off the website. Don't know why it worked today and didn't the previous two days. Good article.