Temperature of Shrinking Disc

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What are some techniques that might be used to determine the temperature of damaged metal that is being repaired using a shrinking disc mounted on a grinder?I have tried a infrared thermometer and I was supprised that it did not give accurate temperature reads.  All the readings during the heating process were low.  Perhaps some type of crayon heat sensitive marker or paint exists and would work.  The temperature range for the shrinking disc process to operate properly is between 230 degrees F(steam), 1400 degrees F (blue), and 2,000 degrees F (red).Please share any thoughts.    ThanksRSOHC
Reply:Are you talking about using a shrinking disc on sheet metal?  Is this a Sunchaser Disc or a home made one?  Fluted vs a smooth stainless steel disc.  What is the RPMs of your grinder?  Can you post pictures of what you are shrinking and your grinder disc setup?CharlieLast edited by 59halfstep; 08-01-2009 at 07:04 AM.Reason: addedCharlie
Reply:I am using a shrinking disc on new 20 gauge cold rolled steel from a fabrication shop.  The test is to remove bumps made with a hammer.  Then it will be "high stretch area" on a front fender on a 67 Pontiac which is also 20 gauge.  The disc has flutes is from Sunchaser and the grinder is a 6000 rpm Makita from Sunchaser.  I have also ordered a smooth 9-inch stainless steel disc from Wray Schelin.  The grinder setup is with a rubber backing, a 9-inch phenolic backing, and then the 9-inch stainless steel disc all from Sunchaser.  I thought that I would be able to track the temperature of the sheet metal with an infrared thermometer but that didn't work.  Next I am considering some "Tempilstiks" that I found in a Stoody Industrial and Welding Supply Catalog.  Base on my current understanding, "good" shrinking occurs between 230 degrees where stream is generated with a spray bottle of water and 1400 degrees where blue heat occurs.  Red heat at 2200 degrees is too high and a crater results.  So I am looking for a way of knowing where I am at in the range of 230 degree and 1400 degrees.  I will try to figure out how to post some pictures.
Reply:Ok I see what you are thinking here.  You will get a shrink from using the disc long before you start to turn the metal blue.  Just take an area and work the disc over it to get it warm to hot.  Then you can just remove your disc and you can use a water spritz, a wet rag, or even let it air cool with an air hose or just let it cool.  You will get a shrink as it cools.  Use your hand and feel between applications.  If you have a problem getting the right feel, put a cotton rag between your hand and the panel.  It is a process ,just work slowly at it.  You can use a little dish soap in the spritzer water for a lube.  Especially on Aluminum to keep it from galling on the disc.I have never used a Sunchaser.  I do have one or Wray's and it works slick.  The flutes on the edge of the sunchaser can cut deep on your skin so be very alert with it. Don't be concerned with the actual temp.   Go down to your local body shop and have them give you a junk door or fender.  (A cold six pack and walking in the back door with it should get you a used panel.)  Take the panel home grind off the paint and work an area with your hammer and dolly to stretch an area and then try to work it down with the disc.   You may like to log on the Metalmeet and do a search there.  Good luck   Post some pictures. CharlieCharlie
Reply:If you can on the back side of the sheet tape some electrical tape on the area you are working. Then hit the tape with the thermometer. Most IR units have a fixed emissivity that works well on black anodized aluminum and electrical tape, as well as similar surfaced and colored objects. On reflective metal not so well. I doubt it's very hot at all though. If you are getting results what difference does it make?
Reply:If it's really worth the trouble, you can tape a thermocouple to the back side of the steel sheet and, using an appropriate meter (some, like an old Amprobe FS-3, have temperature scales for such use when using the right type of t-couple), get a direct reading while you are working.Being thin, the temperature at any given area will be changing quickly as you make and break contact . If you mapped the temperature, you'd end up with something like a contour map showing elevation, but it being true only for that instance.If you did go with Tempilsticks, you could mark the back side with parallel lines using a few different temperatures, and watch with a mirror as you worked.
Reply:In the case of hammer bumps is the theory to heat and shrink the bump only or do you heat the whole area in hopes of pulling the bump out?
Reply:You will work the disc  ( Stainless Steel) over the panel and the high areas that are the stretched metal will get the hottest from the friction of the disc action.  You work the disc over the general area to shrink.  That is how the shrink takes place.  It is an amazing process.  CharlieCharlie
Reply:Originally Posted by 59halfstepYou will work the disc  ( Stainless Steel) over the panel and the high areas that are the stretched metal will get the hottest from the friction of the disc action.  You work the disc over the general area to shrink.  That is how the shrink takes place.  It is an amazing process.  Charlie
Reply:Hi,I'm new here, but have been experimenting with shrinking discs for a number of years now.  Been a welder for over 30 years.  The best way to determine if you have reached the correct temperature for shrinking using a shrinking disc is by quenching the metal.  If you see steam, you are shrinking. You do not want to see a color change.Different surfaces require different amounts of time to get a shrink.  If you are shrinking an area that is a smooth bulge, each application of the disc must be longer in order to shrink than if it were a surface with small high spots here and there.My youtube channel shows how to use a shrinking disc for metal shaping or dent repair:http://www.youtube.com/profile?user=...nn&view=videosThe are pretty easy to make for yourself as well:http://allshops.org/cgi-bin/communit...=9980121727059If these links are inappropriate for this forum, please delete.JohnLast edited by John Kelly; 08-03-2009 at 11:37 AM.