uncured silicon rubber moulding

[akash ananthaswamy]

Hi, We manufacture silicon polymer insulators using transfer injection moulding machine. I am having difficulty in recognizing a problem. During moulding, once in a while I have streaks of uncured rubber of size of runner (3mm) occurs. I tried increasing mould temperature and time. it results in over curing of rubber and loss of elongation and strength. generally the rubber breakdown as soon as it is removed from the mould. I am unable to understand the reason why uncure happens. I though it was airlock due to insufficient vents in mould. so i tried bumping. but still the problem persists. Rubber mixing is not an issue because i have mixed it sufficiently. any tips or suggestion would be very helpfull.

 

[3DDave]

Are the streaks in the same location?
If this is a multicavity mold is it in all cavities, some of the cavities, varies which cavities have the problem, or just one?
Is it possible there is something trapped in the mixer that prevents material entering a certain area of the mixer to avoid being mixed?
Is once-in-a-while related to startup, to some regular interval, multiple failures in a row sometime during the day with all production before or after being perfect?
Does every part get closely inspected in the same area to see if the properly cured parts are uniform in that area or not uniform?
Are there cold sprue and runner temperature sensors?
Are there heaters and are the heaters given individual thermal sensors?
Can you measure the power applied to each of the heaters to see if there is any variation from some typical version?