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注塑成型:了解注塑成型中的压力损失


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One of the more prominent trends in processing is the need for higher 塑料 pressures to mold parts. There are lots of reasons to go this way: longer flow paths, more complex geometries to achieve greater functionality, thinner walls to save weight, higher cavitation, stiffer polymers, and filled compounds. While these trends do cut costs, they also keep narrowing the molder’的处理窗口。关于机器和加工策略,成型者可以采取什么措施来应对这一趋势?

了解填充和包装零件的压力要求是开发合理的加工窗口以及提高质量和利润的关键。处理器’s first step is to understand how machines develop 塑料 pressure, and make sure to buy the right press for the parts to be molded. Electric machines provide all pressures in “plastic” psi—there is no hydraulic pressure. Hybrids and full-hydraulic machines may report actual 塑料 pressure on the monitoring screen, or they may report hydraulic pressures.

如果您的印刷机报告液压压力,则必须确定该螺杆尺寸的增压比,以便将液压压力转换为“plastic”压力。 (有关计算,请参阅sciencemolding.com/articles/Intensification_ratio.pdf。)要在机器之间复制处理条件,必须复制“plastic”压力,而不是液压。您可以使用经过认证的传感器来校准液压机,以获取准确的液压读数,但是我还没有找到一种方法来确保对电机上的机器压力传感器进行校准。任何一台机器都能告诉您准确的压力很重要:如果一台机器告诉您注射压力为21,500 psi,则需要知道它的确是21,500 psi。

 

哪里压力都消失了?

In Scientific Molding procedure, parts are filled 90% to 99% in the first injection stage: That is, we make a short shot. If the part is short we know the 塑料 pressure at the 恩 d of flow is zero. We also know the pressure in the nozzle from the reported or calculated 塑料 pressure. Nearly all machines report the pressure at transfer, or at the 恩 d of first-stage injection. This transfer pressure is not always peak pressure during injection.

让’s为例:我们正在制作一个小型的1英寸。² insulator from PC with some thin walls in a 4-cavity mold. The machine reports a hydraulic pressure at transfer of 2040 psi (hydraulic), and the part is 96% full and short. To find the 塑料 pressure in the nozzle, you need to multiply 2040 psi ×机器的增强比,在这种情况下为14.7:1。因此,喷嘴中的压力为29988 psi。如果我们有一个短镜头,“pressure loss”填充零件至96%的压力为整个29,988 psi。

Where did all this pressure go? Is there anything we can do to reduce the 压力损失? The process window will open up and quality will be higher if lower pressures are required.

流路是已知的:塑料流经喷嘴,浇口,流道,浇口,最后填充零件。多少“plastic” pressure did each of these components eat up? To find out the 压力损失 for each component of the flow path, we need to make a few short shots and maybe dig out a part or two. (Every mold will make a short shot in its life, so when you are building it make sure it has the ability to push out a short.)

调整截止或转移位置,以使小块超出门。然后再次调整传送位置,仅使出料口和流道成为可能。最后进行一次大扫除。如果我们记录了这些镜头在传输时的压力,那么我们现在已经有了所需的数据(请参见图表),并且可以通过设置带有条形图或图表的电子表格(上面)来使其看起来更漂亮。

所以所有的压力都去了哪里—全部29,988 psi?数据表明,通过喷嘴的流量约为2400 psi。浇口和浇口消耗了12,036 psi;闸门约3000 psi;零件的压力约为12,000 psi。您可以’在没有客户的情况下对零件不做任何事情’的许可,并且登机门完全在正常范围内;但是浇口和浇口已经可以进行改动了。

但是不要’t simply open up the runner: The 压力损失 will be less, but a larger runner also provides less shear, which will actually increase the viscosity of the polymer and wastes resin. You need a mold flow analysis to find the best compromise.

 

关于作者

约翰·博泽利 是密歇根州米德兰(Midland)的注射成型解决方案(Scientific Moulding)的创始人,该公司为包括LIMS和其他专业领域在内的注射成型商提供培训和咨询服务。电子邮件[email protected]或访问sciencemolding.com。

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