direct gate maintenance

[lnm123]

Do direct valve gates require more maintenance than submarine edge gates? We tranistioned about 2 yrs ago to valve gates on a small but detailed tight tolerance PolyCarb part that requires significant packing to reduce sink. Since intorducing the valve gate, I've seen a lot more problems with stringing that required gate repairs. Should this be expected?

 

[MikeHalloran]

Did someone get a commission for talking you into this 'transition'?



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I agree with Mike's sentiments.

It is not sensitive to drool and it is sensitive to shear.

Valves increase cost, increase complexity and increase shear, to increase control of a variable that is never a problem.



Regards

eng-tips, by professional engineers for professional engineers
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[ToolEng1]

This issue is seen if hot runner temp is too high or as you say if the tip/valve is damaged. Depending on the type of PC melt temp should be around 290ºc. Generally if the process is set correctly, even if the valve gate shut off is damaged you should not get stringing. I suggest you contact your hot runner supplier and ask for a hardened valve pin and seat. Then review your process settings. Something else to check: make sure cooling circuits around the nozzle face & cylinder area are working sufficiently.

Submarine gates are pretty good and rarely need maintenance unless you use a glass filled material where a lot of wear happens. The only down side to this type of gate when moulding PC is the risk of gate bloom or cold slug flow lines, but depending on the part this can normally be processed out.

 

[patprimmer]

If a sub gate results in jetting, a "cow horn" gate might work. you need to aim the flow into a dead end corner as the material extruding from the gate when moulding PC will be fairly solid or rubbery, and will be inclined to deflect off a wall and retain its rod like form and then further set so that the rod ends up looking like a partly squashed PC worm on the surface of the moulding.

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.