阀门试压设备Die drool, or plateout, can cause a host of problems for extrusion processors. Here is how to stop the problem before it starts. 口模流涎或者叫模垢，可能对挤出加工者引起很多问题。本文就是解决这些问题的方法。 彩相纸
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Fig 1. A long-land die controls thermoplastic swell to a normal range, drawing down into a sizer.
图1 长通道口模将热塑性塑料的出口膨胀控制在标准范围内，然后牵引进入定径套
Fig 2. Here, thermoplastic swell is excessive and impinges on the outer die lip, causing die drool, shown close up (inset).热塑性塑料出口膨胀严重，对外模唇有不良影响，引起口模流涎，如近镜头所示。采摘网
东方人体One extrusion processor was emphatic （强调的）to me about it: “If you extrude olefinic or thermoplastic elastomeric compounds,” he told me, “you will experience the die drool problem.”
一个挤出加工者对我强调说：“如果你挤出聚烯烃或者热塑性弹性体共混物，你可能会遇到口模流涎问题。”
He’s right. It doesn’t matter if you are extruding sheet, film, pipe, tubes, or profiles—you can come face-to-face with drooling dies in any of these processes.
他是对的。但是，不要紧。如果你挤出片材、膜、管、软管或者型材---你可得在任何这些工艺中面对口模流涎问题。
Die drool shows up as a buildup on the die lips. This buildup can either be the same color
as the material being extruded, or in some cases appears yellow or red. Often this buildup will create unacceptable machine-direction lines in the extrudate. And after a period of time this buildup will ultimately break-off and attach itself to the extrudate, resulting in additional aesthetic flaws.
口模流涎显著表现为模唇堆料（堆积）。这种堆积物可能与挤出材料的颜一样，在某些情况下也可能是黄或红的。这些堆积物常常沿着流动方向在挤出物上划出不可接受的纹道。过了一段时间后，这些堆积物会最终破碎并附着到挤出物上，最终引起额外的美学缺陷。
Die drool is also commonly referred to as plateout. To find the root cause of the problem, you’ll need to analyze the “big three” areas to identify what’s to blame（归咎于）:
口模流涎常常也叫做积垢。为了到问题的根本原因，你需要分析三大板块，以确定要归咎于什么原因：
•Material: Each thermoplastic is unique, with compounded alloys being the most problem
atic. Compounded thermoplastics (those that have additives combined with the base resin) have the highest probability of additives exuding, also known as migration. For example, in rigid PVC compounds, there are internal and external lubricants, typically low-melting waxes, which can migrate out of the material matrix. Along with these constituents, plasticizers are added to make PVC flexible; these are also prone to migration when critical shear rates are achieved.
材料：每种热塑性塑料都是独特的，共混合金是最蛋疼的品种。共混热塑性塑料（挤出树脂＋助剂）具有助剂析出的最大可能性，助剂析出也称为迁移。例如，在硬PVC共混物中，添加有内外润滑剂，一般是低熔点蜡，它们会迁移到基体材料的表面。在这些组分中，还有增塑剂也添加到PVC中以增加PVC柔性。当达到临界剪切速率时，这些助剂都有析出倾向。
Reactor grades of olefinic polymers such as polypropylene and high-, medium-, or low-density polyethylene are less problematic; however, they still can be the bane （灾星，祸害）of the processor. Many olefinic thermoplastics are a combination of different molecul
ar-weight grades to achieve certain physical characteristics. The resin supplier can blend high-molecular-weight resin with a low molecular weight to increase the modulus (stiffness), and at high shear rates there can be migration, leading to die buildup. However, on polyolefins and non-compounded thermoplastics, the root cause of die buildup typically is not material-related, so further investigation will likely be necessary:
反应器牌号的聚烯烃，如聚丙烯和高、中、低密度聚乙烯较少有问题。但是，它们仍然可能成为加工者的灾星。许多聚烯烃热塑性塑料是不同分子量牌号的并用，以求达到某种特性。树脂供应商可能用低分子量树脂掺混高分子量树脂，以提高模量（刚性）。在高剪切速率下，低分子量树脂可能迁移，导致口模积垢。但是，对于聚烯烃和非共混热塑性塑料，口模积垢的根本原因一般不是与材料相关的，所以进一步的研究是必要的。
•Machine: The next area to analyze is the extruder. It is important to know the physical condition of your extruder, especially the barrel and screw. Excessive screw wear or even moderate barrel wear can cause problems. Barrel and screw wear are problematic because a single-screw extruder is not a positive pumping device, and any wear reduces
output, requiring a higher screw speed to maintain the desired rate. Higher screw speeds, in turn, lead to additional frictional heat imparted to the thermoplastic, causing a melt separation and die drool/buildup.
机器：接着要分析的一个版块是挤出机。最重要的是要知道你的挤出的实际条件，特别是机筒和螺杆。过分的螺杆磨损甚至是中等的机筒磨损都能引起问题。机筒和螺杆之所以引起问题，是因为单螺杆挤出机不是一个正向泵送设备，任何磨损都减少产量，从而要求更高的螺杆转速以维持所要求的产率。反过来，较高的螺杆转速又导致额外对热塑性塑料有害的摩擦热，最终引起熔体分离和口模流涎/积垢。
张紧轮
•Tooling: Tooling design plays an important role in the die-drool problem. The two key design criteria（指标） are drawdown（牵引）and land length（通道长度，指螺杆末端到口模外表面的长度）. But before even thinking about die design you should inspect the condition of the die lip. Die lips should be sharp and “dressed” (deburred) to a 0.25-mm (0.010-in.) edge. If the edge has a larger radius, say 0.75 mm (0.030 in.), material can build up inside the radius and create an area that will lead to continued die drool. The aesthetic flaw will exhibit itself in the form of “smear marks” on the extrudate.
On the matter of design, drawdown and land length are inseparable parameters. They are a main root cause for die drool, but probably the least understood. To best understand their inter-relationship, let’s review them in detail:
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