Strange flaw on records

[Milkmustache]

Hi everyone,

We're a pressing plant in south of China, these days some strange flaws always appear on the center of records after pressing, and always on the B side(the upper side). it appear irregularly, and always appear on the ending groove, where between the groove and label.

I‘d like to know if it's because the cooling effect is not good? 'cause we're in south of China, the summer is wet and hot, and we have to bake the labels longer than winter now. Sometimes when I decrease the pressing time, it'll be better, but sometimes those flaws still there.

Does anyone know about this? Thanks a lot for your help!

Thanks
Frenkie

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Below 3 problems only appear once, I'm not sure if it's same problem. Thanks

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[Rad]

Cooling water temp? Looks like you have steam going in before separation (leaky steam valve? bad timing?), something funky going on with the moulds not cooling properly on one side or the pvc compound foaming. does it do the same with coloured compounds? that would mean it is not the pvc. If it happens only with black compound, you should try to dry it first.
Hot and humid... Spain during a heatwave... :-/

[Milkmustache]

Cooling water temp? Looks like you have steam going in before separation (leaky steam valve? bad timing?), something funky going on with the moulds not cooling properly on one side or the pvc compound foaming. does it do the same with coloured compounds? that would mean it is not the pvc. If it happens only with black compound, you should try to dry it first.
Hot and humid... Spain during a heatwave... :-/

Hi Rad, thanks for those advises! I found out that the cake is too hot, about 167 degree, so cause the stamper burned also... yes, the summer here is very hot and humid too, the fan on the extruder is too small to cool down, so I've to decrease the temp of extruder.

I've tried to decrese the temp of extruder heating zone to 119/115 degrees now, the cake is around 150 degrees, no more this flaws, but still the stamper will be like burned. If I only heat up the extruder and don't use it for a while, the cake is also too hot and strange flaws appear. I think it's because the fan on extruder is too small and temp is so high now.

BTW, the compound is from a france supplier, it's the first time we use it. We always buy from Germany before. This new compound is harder than Germany's, I can't even leave a fingerprint on cake.

Thanks
Frenkie

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[llary]

Something is messed up with your moulds, cycle or cooling water.

What is the temperature and pressure of your cooling water? Do you have a chiller or just cooling tower?

What is your steam pressure?

What cycle times are you running for heating, dwell and cooling?

[Rad]

Wow....
Unless you are running steam at 40 bar, wich I hope you don't... that is the ugliest skid mark from burned PVC I've seen. Right now we are battling our own extruder heating up a little... Spanish summer from hell... If it is the same french supplier we had some 8 years or so ago, the temperature profile should be 120, 120, 120 and let it melt by viscous shear force... It needs lots of cooling. The other problem may be the first zone is too hot and the rest too cool. But definitely something going on with your extruder and compound. Maybe it's time to pull the screw and barrel and clean everything.

[montalbano]

Record is not properly cooled down, just add some seconds to the cooling cycle.
Also I'd check that the hoses are properly connected to the inlet and outlet of the mould, as the heat exchange should start from the center and move towards the edge, which instead looks properly cooled (well shaped) in the picture.