- #1
DCarr10760
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Hi folks,
This is my first post. It is a problem in a manufacturing process and I am hoping to find some information and a solution.
I manufacture high voltage pinhole detection systems use in the manufacture of plastic products. At the moment we have a system in place testing thermoformed LDPE vessels. They are simailar to baby bottle liners in size.
After the parts are thermoformed they are advanced to a test station where they are placed in an electrode fixture (a family mold arrangement, sometimes referred to as a probe and cavity fixture) the probe (Male) is charged to -9kVDC and the cavity (Female) is grounded. The test time is approximately 1 second. Our detection circuitry trips when a 600 uA current passes through a circuit in series with the HV generator.
The problem is that we are imparting a static charge to the surface of the parts under test. The customer has measured voltages as high as -4000 volts. They have tried to neutralize the charge with ionizing bars and a surface voltmeter checks at zero volts. However the next day the parts are again charged sometimes to 1000 volts or more.
Samples have remain charged for several months now.
Untested samples (not HV leak tested) often have a surface charge of up to -1000 vDC or more and after ionizing treatment maintain a voltage of only up to -400 vDC. This level is satisfactory. Higher voltages are not.
At the time of the test, the product is between 150F and 200F.
I am wondering is it possible we are forming an electret?
If so is there a critical temperature the products should be brought down to before bombarding them with voltage to avoid a permanent charge?
Where can I learn more about electret formation?
Many thanks to all!
David C
This is my first post. It is a problem in a manufacturing process and I am hoping to find some information and a solution.
I manufacture high voltage pinhole detection systems use in the manufacture of plastic products. At the moment we have a system in place testing thermoformed LDPE vessels. They are simailar to baby bottle liners in size.
After the parts are thermoformed they are advanced to a test station where they are placed in an electrode fixture (a family mold arrangement, sometimes referred to as a probe and cavity fixture) the probe (Male) is charged to -9kVDC and the cavity (Female) is grounded. The test time is approximately 1 second. Our detection circuitry trips when a 600 uA current passes through a circuit in series with the HV generator.
The problem is that we are imparting a static charge to the surface of the parts under test. The customer has measured voltages as high as -4000 volts. They have tried to neutralize the charge with ionizing bars and a surface voltmeter checks at zero volts. However the next day the parts are again charged sometimes to 1000 volts or more.
Samples have remain charged for several months now.
Untested samples (not HV leak tested) often have a surface charge of up to -1000 vDC or more and after ionizing treatment maintain a voltage of only up to -400 vDC. This level is satisfactory. Higher voltages are not.
At the time of the test, the product is between 150F and 200F.
I am wondering is it possible we are forming an electret?
If so is there a critical temperature the products should be brought down to before bombarding them with voltage to avoid a permanent charge?
Where can I learn more about electret formation?
Many thanks to all!
David C