Compression Molding of Thermoset Rubber / Plastic 1

[NEngineer]

We have heated debate in our group. One section of group is claming that PSI for reading is required and important on compression molding machine while other group claiming that tonnage force for reading is important and required on compression molding machine. Please give your suggestion and advices with support of some examples.................

 

[patprimmer]

I don't really understand your question. I suspect something is lost in a translation to English.

As I think you mean pressure reading on the hydraulic oil circuit or tonnage clamp of the machine, I will answer on that assumption. I am presuming this is thermoset via compression moulding, not injection moulding.

Either can be used, but only in conjunction with other information.

You really need the pressure that is applied to the plastic.

This can be measured by calculating the force applied to the plastic by taking the cross sectional area of the clamping ram times hydraulic line pressure to give the clamp.

Once you have the force, you calculate the projected area of the moulding, and divide the fouce by the projected area for effective pressure on the moulding while it is curing.

The required pressure will vary with temperature, required cycle time, part geometry and resin grade.



Regards

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[NEngineer]

To patprimmer,

Let me clarify more on this. Say for example you have two different tonnage machines one is 75 Ton and other is 500 ton.

Now you have made one part on 75 tonnage machine with force showing on gage 70 ton while pressure is 2000 PSI. Now if you want to use that mold on 500 tonnage machine, what will you set on gage? e.g. 70 tonnage of force or 2000 PSI. If you set 70 tonnages, your pressure is not 2000 PSI and if you set 2000 PSI then your force is not 70 ton on 500 tonnage machine.

 

[patprimmer]

If it moulds good at 75 tonne, set 75 tonne.

It is important to use the necessary force, but it is a waste to use excess and at over 6 times the previous satisfactory force, it may even damage the mould or make ejection of the parts impossible.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.