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Kenplas Forum ==> Blow Molding (Machine) ==> Pet Preform Heating Versus Bottle Blowing
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glass transition temperature (Tg) was found to linearly decrease about 6C from zero to 45 percent initial crystallinity.

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11/22/2007 9:49:46 PM By TomTom
In ten years a white preform geting kicked off before the sidel starts running means its too hot,(beverage cold fill), but in the new hotfill process I've been doing for the last 3yrs it means your going to make a good hot-fill bottle as long as your molds are around 138c and the preform around 130. The preform turning white is coalesence (not sure of the spelling) if your preform is to cold, bottles could then be blowing out. Or your preform is just to cold at the tip around the gate area. I would check on your start-up % also. If your talking about sidels.
jwkinney

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6/22/2005 10:44:14 PM By Jeffrey
About you first question, most likely answer is low IV, usually because a poor drying. Low IV means more reactive terminals at PET macromolecules. Both situations may derive from this single cause. Solution, if there is any good enough would be blow moulding under lower temperatures of preform. Usually you should try to keep this temperatures 20 degrees higher than TG (Temperature Glass Transition)of resin you are using. Manufacturer of your resin can easily suply this information about their product.
Anyway, most of cases, this temperatures should be within 90 to 110 degrees Celsius.
If this thing is happening despite temperature, which is inside this range I provided, call your preform manufacturer, bacause you have a sever problem on resin.

Your second question can't be answered easily, mainly because there is a huge amount of right answers. To guide you, I would say that Low pressure could be around 4 to 12 BAR and High Pressure around 28 to 40 BAR. Reasons that justify this wide range are variations of IV, temperature of preform, amount of moisture in your preforms, grade of aging and so on... Even environment temperature may change this conditions, especially under quick transitions. 10 degrees Celsius are enough to cause a sensible alterations on Blow Moulding recipes.

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6/22/2005 10:43:42 PM By Mauro
1)Can anybody let me know what are the most probable
causes of preforms suddenly getting white while
coming out of the oven and/or Bottlls suddenly getting burst or bottle bottom getting stuck while the bottle comes out of the mould.

2)what is the required Low pressure and High Pressure to blow a preform of 21.8 gm

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6/22/2005 10:42:35 PM By Khawar Nadeem
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