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Extruder screen pack is right plastic squeeze a shaping influence
From;    Author:Stand originally

In extruder in cramming a course, melt stock is defeated to give a pattern through screen pack. Screen pack makes stock gets filtering, can improve the mixture result of stock. But, screen pack also can make process produces wave motion, bring about back pressure and melt stock temperature to rise, still can decrease sometimes.

The screen pack of extruder is secured to be in poriferous or on groovy baffle, can make be formed between extruder and mould so sealed. The pressure that clean screen pack place generates is lesser, the likelihood has 50 ~ 100lb/in2(1lb=0.4536Kg only, 1in=25.4mm) . As the addition of pressure, the foreign matter amount in the colophony that holds back on screen pack becomes much, thereby block screen pack.

Screen pack can affect the temperature of melt stock

Should change when the screen pack of block, pressure can drop suddenly, the temperature of melt stock also may drop, the measure that creates a product thereby produces change. To hold the same size of the product, can adjust the screw rotate speed of extruder, also can adjust the linear rate of extruder. When pushing a circular product, these change won't cause serious problem possibly, but squeezing piece compressed or when the product with irregular appearance, the change of melt stock temperature may affect the over all dimension of the product. For instance, in a compressed mould, colder melt stock may make sheet center slants thin, and make periphery slants thick. This kind of circumstance can pass pair of moulds automatic or the hand is moved adjust get corrective.

At the back of screen pack transformer, deploy to be able to make sure melt stock enters the gear pump of the mould steadily, can prevent the happening of afore-mentioned problems. But, the adjustment that the temperature change that melt stock produces after screen pack changes still needs to pass pair of moulds will solve. In the meantime, because gear pump is damaged easily by hard impurity, accordingly, gear pump also needs to get the protection of careful screen pack.

The account that some horniness PVC processes business not to wish to use screen pack is, screen pack can make temperature of PVC melt stock produces degradation elevatory and easily, need the stock with finer thermal stability so, raised the cost of material thereby. If use transformer of PVC appropriative screen pack, also can raise cost. Or of business of treatment of most horniness PVC is so evasive use screen pack, or is used what do not take transformer is thick filter device, filter only the impurity of bigger grain.

How to choose screen pack

Steel wire is the material of metallic screen pack with the most commonly used extruder. Although stainless steel is costlier, but can use at certain PVC product line or other circumstance to rust with avoiding to appear. Nickel alloy screen pack is applied at avoiding by fluorine polymer or the circumstance that PVDC place corrodes.
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