Cosmo Posted September 16, 2013 Share Posted September 16, 2013 My mother is an optometrist and had an old unit for tempering photochromic lenses around. I know that to temper lenses it needs to get to 400 degrees Celsius , so it may be able to heat treat blades. The unit appears to have some kind of thermocouple, and thermostat as it automatically turns on and off to maintain some preset temperature. However, the unit has no controls save for a single switch. Is there any way I can modify it to make it useful for heat treating blades? Also, where in Canada can I procure some more salt, as the unit is running a little low. The unit in question is a Mini-20 manufactured by Kirk Optical. Quote Link to comment Share on other sites More sharing options...
Steve Sells Posted September 16, 2013 Share Posted September 16, 2013 most blades need tempering at around 350F to 500F range which is about about half the temp that your unit currently operates at, What is the volume?, as the hot blade will raise the temps a bit if martempering, if you are not, then volume it is not as much of an issue. There is also the question of getting proper salts for your temp range, and adjusting the controllers operating temps, because not all your blades or blade steels will need the same tempering temp. And remember not all salts are liquid at the same temps. Find out what adjustments you can make to the glass tempering unit, and go from there. you may find building a unit form the start may be less costly than converting this one. I dont know without more information. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted September 16, 2013 Share Posted September 16, 2013 You do realize you will need a much hotter system to harden the blades before the low temp tempering occurs, right? Usually salt baths are used on the hotter side as that is where the even temperature and lack of oxidation really helps out. Quote Link to comment Share on other sites More sharing options...
Rich Hale Posted September 16, 2013 Share Posted September 16, 2013 DAng,,,now I have to find one of those and then forge some eyeglasses..... Quote Link to comment Share on other sites More sharing options...
Cosmo Posted September 18, 2013 Author Share Posted September 18, 2013 You do realize you will need a much hotter system to harden the blades before the low temp tempering occurs, right? Usually salt baths are used on the hotter side as that is where the even temperature and lack of oxidation really helps out. Yes, I do. I was thinking about pulling it apart an seeing if there is some way of adjusting the thermostat. I was just curious as to whether anyone had done something somewhat similar. Quote Link to comment Share on other sites More sharing options...
JNewman Posted September 18, 2013 Share Posted September 18, 2013 An Ontario source for salts is Park Thermal in Georgetown. They sell the salt in minimum 50lb bags. I have actually been thinking of either buying or making a low temperature salt bath. I can harden out of the forge easily but tempering is harder especially the ends of longer bars. I have done some austempering with preheated oil. But the oil really smokes up the shop and using hot oil has some flammability issues. Right now I am subbing out the heat treating but my last bill was around $500. Quote Link to comment Share on other sites More sharing options...
Ric Furrer Posted September 24, 2013 Share Posted September 24, 2013 John, A low temp is not a big deal. Assuming no liability here: I have two.. one is vertical which has some precautions for heating and not getting pressure build up from the bottom before the top is liquid...think cannon. the other is a horizontal which is little more than a steel "U" with ends welded on. I heat it with a 3/4" black pipe and an 1/8" hole every 1"...like small candle flame. Feed in gas via a venture cone and light. My horizontal expands when heated and the sides buckle a faction...this allows the liquid salt on the bottom to come up and around the solid salt so no pressure builds. With a vertical it is possible and likely to have the bottom go liquid and when the top finally starts to melt it will be pushed up and out of the tube with force. I have seen some tube bottoms bulging on vertical pots....not good. Some have several burners for the vertical and heat the top first and then the middle and finally the base. Some use a tapered rod which they pull before bottom firing the tube. Use what you think is best, but be aware that salts are not a no fuss solution and can be dangerous. Black iron (low carbon steel) is fine for low temp pots, but stainless is better. You MUST have a plan in place to deal with the eventual pinhole leak and all the hot liquid salt pouring out. If you run them long enough it will occur. Failure usually occurs at the weld joint, but can be anywhere. Ric Quote Link to comment Share on other sites More sharing options...
JNewman Posted September 24, 2013 Share Posted September 24, 2013 Chances are until I either put an addition on my shop or buy my neighbours shop to move my pattern shop into I am going to delay setting up a salt pot. Partly due to the fact I want to leave lots of room around a large volume of molten salt. Even with subbing out the HT I make good money on the bars but it would be nice to keep it all in house. Quote Link to comment Share on other sites More sharing options...
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