Tasked with some some large work out of plastic. First series of parts were Delrin (well some copolymer acetal that our materials guy ordered) They were about 40x20x1 after finished, and had bolt holes in the bottom, so I was able to keep the warping to a minimal,machined on a fixture plate to keep flat and the parts would be bolted flat. These parts were also oil annealed in shop before being machined.
The next series of parts have no bottom mounting holes, and are 20x8x1.5. They get a decent amount of work done to them, and have some deep slots. Originally they ordered Derlin, but after some research I was able to persuade them to purchase Ertalyte. From my findings, it doesnt warp. Now I have never had to cut the stuff, and would prefer not to have to post anneal the parts due to their complexity.
Does anyone have experience when Ertalyte, and could give me some concrete info on how well it holds it shape. One post I found mentioned taking a 1" thick 12x12 piece, removing .75 off one side, and the material would remain flat. How flat is what Im looking for.
Ertalyte is rather expensive, a compression molded Acetal (Pomalux) hardly warps at all and is much cheaper. Ertalyte machines similar to Acetal, it has much better wear properties. Ive only cut a sample piece of round on a lathe though, so dont know much about warping with flat stock. I would of asked for a sample piece from your supplier first before you put all the eggs in the basket. You can call Alro plastics to get definitive information on it, they have great application engineers.
We ordered two blocks from our local supplier. Quadrant who actually makes it is right down the road. We have to use the material for it properties. Most of the machines we build are food processing machines
You most likely will have to stress relieve before roughing & again before finishing
Most of these materials are stress relieved before you get them, but you will have to check to see from the manufacture to see if they have stress relieved after cutting out your pieces, if they have then you can got straight to roughing, then stress relieve again before finishing
Our experience with Derlin has been to pre anneal even though the manufacturer says the stock has gone through their process. Never have we post annealed before finishing operations. With our annealing we do remove alot of the stress, and some of our machining does put stress back in. Even with Derlin, not post annealed I was able to keep a large part within .015 flatness before being bolted down to the machine. I hoping to find Ertalyte to be a blessing compared to Derlins behavior. I was assuming the post annealing operations were for people holding tight holes tolerances, and dimensions tolerances of tenths.
Ertalyte (PET) Flatness?
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