PS thermoforming problem (material on the edges)

[milicav]

Hi All.
I was wondering is someone could help me regarding the problem during PS thermoforming. We are using 0.95mm sheet made out of 50% virgin PS and 50% film from thermoforming process.
We are producing PS containers, but we have a huge problem with edges. There are fine leftovers of material on the edges and those leftovers look like fine hair.
We tried to heat the cutting knives but we ended up with knives melting film even on low temperatures.
Also, stainless steel plate is used as machine bed.
Could anyone help?
Thank you!

[One of Many]

Are these fine hairs from trimming the container from Styrofoam PS sheet?

My guess is, the formed parts may not have cooled enough to trim. Try trimming a cold part and see if the edge is still stringing out. The cutting edges of the steel rule knife trimming die can absorb heat when cutting with short cycle times. The knife edge should never touch the stainless bed. Some form of stop limits should leave .025-.05mm gap so the knives do not hit against metal. Spraying the knives with silicon dry lubricant periodically can help to avoid the PS sticking to the knife edges. If the PS and knife were cold when cutting, I cannot imagine it sticking or producing fine hairs on the edges.

Have you tried using a fan to cool the formed parts and the trim knives as they come off the forming die before they are trimmed?

If you have cooling water on this former, the stainless steel bed could be water chilled which would chill the edges of the PS as it cuts. Sometimes more space/time between the forming section and trimming section gives the parts time to cool.

DC

[milicav]

ok, so what we tried is following

We heated bottom of the table to 120C and now have less "hairs".
The cutting operation is not on same step as the forming, so it does have some time to cool down until next operation.
So, heating down - good
heating knives - very very bad

I had some project of PS being cool down way low to become fragile, but there's no method available that can be cost effective for test purposes

[One of Many]

ok, so what we tried is following

We heated bottom of the table to 120C and now have less "hairs".
The cutting operation is not on same step as the forming, so it does have some time to cool down until next operation.
So, heating down - good
heating knives - very very bad

I had some project of PS being cool down way low to become fragile, but there's no method available that can be cost effective for test purposes

It sounds like you have found your solution or you are nearing it. As you have found, there is a difference in to warm, to cold and cooled just right. That narrow temp range can make the difference in styrene since it has such a short cooling cycle and narrow temperature working envelope. Finding the happy medium between where it wll cut without being brittle and minimizing hairs is the goal. Regulating the temp of everything in contact can be just as important. Including an open door or cooler breeze on one side of the machine or the other.

Thermal forming is a process of learning to read the subtle characteristics of any material, form a theory of the cause and makes some changes until you learn what effects the conditon at hand to an acceptible result. Add that lesson to your bag of tricks and use it the next time you see it in the material.



DC

[milicav]

now we will try to heat the lower cutting table more, up to 200C to see what happens...

Any other suggestions would help.

Thanks

[panic]

It's been a while from the last post here, but if you add to the recipe about 30% STYROLUX you'll have a major improvement