Posts: 1
From:Mount Victory. Ohio, USA
Registered: Mar 2003

posted March 18, 2003 01:37 PM               

---

I would like to know what the difference between thermoplastic and thermoset molding machines for injection molding is

Thank You

IP: Logged

Posts: 123
From:McHenry, IL USA
Registered: Nov 2002

posted March 19, 2003 07:07 AM               

---

From my recolection, a TS machine has a shorter screw, and uses a highly heated mold to allow the chemical "set' of the matrix used. Once it's "set", added heat won't distort the part.

TP machines uses a longer screw, and a cooler mold which also "temporarily "sets" the molten polymer matrix to the intended shape. Higher heat (near the softening point of a TP) will cause distortions, warpage, etc.

IP: Logged

Posts: 1
From:Brisbane, QLD, Australia
Registered: Apr 2003

posted April 09, 2003 01:30 AM            

---

The thermoset screw has a very small compression ratio compared to TP screws, will generally have a cooling/heating channel gundrilled along it's axis, and has a very 'open' smearhead design to allow easy flow of the melt through the smearhead.
Barrels are maintained at about 80 degrees C (could vary for different TS materials) and we found that a jacket around the barrel that recirculated heated oil gave the best result. I think die temperatures were in the region of 175 Deg C. One multi cavity mould we had used a hotrunner styled system that was maintained at 80 deg c via recirculated oil. It is important that barrels are replaced before any appreciable wear occurs. If the barrel wear is too great in the metering section then the screw will be difficult (sometimes impossible) to extract from the barrel. This is because the material taht has set in the worn metering section has a larger diameter that the less worn end of the barrel...so the screw is effectively wedged in the barrel bore.
Thermoset polyester doughs and similar materials can be used by making a 'stuffer box' which is basically a large bore ram and cylinder that forces the dough into the feed throat when the screw is charging.
Hope this helps.
Rod.

IP: Logged

All times are ET (US)