注射知识 | 6分钟读

注塑成型:了解进料喉温度之间的联系& Bridging

节省时间并 通过适当控制进料口温度来赚钱。在某些情况下—but 不 all—it can help you solve a 桥接 problem.
#最佳做法

分享

Facebook分享图标 LinkedIn分享图标 Twitter分享图标 通过电子邮件共享图标 打印图标

As one of the most important temperature zones in an injection molding process, the feed throat deserves more of your attention. Why? About 80% of the processes I work on have issues 与 feed-throat temperature control and 桥接. A bridged feed throat causes significant downtime as well as being a frequent flash point for processors’ tempers.

这表明类型1的桥是由进料喉咙过热引起的。

图。1  这表明类型1的桥是由进料喉咙过热引起的。注意大部分未融化的颗粒有些松散地粘在一起。

优化机器性能’的进料区将提供更稳定和一致的过程。此外,您将获得更多的正常运行时间和更好的零件一致性,从而使您在车间的工作变得更加轻松。您可能可以减少螺丝旋转 时间稍长一些,但真正节省时间和金钱的是 变异 in screw rotate time from shot to shot. Less 变异 in screw rotate times provides more consistent 塑料ation times and, most importantly, better melt uniformity shot to shot. Stabilization of screw recovery also provides better part consistency and there is a chance of a slight cycle time improvement.

首先让’涵盖了进料口的功能:

 •  It provides a clear, free-flowing path for 塑料 granules, powders, and liquids (i.e. liquid color) into the feed section of the screw.

 •  它可以防止颗粒等粘附或结块。这就是所谓的“bridging”饲料的喉咙。避免 桥接节省了清理喉咙的时间,更重要的是, prevents a potentially dangerous safety issue. A bridged feed throat allows pressure to build up so high it can blow the 塑料 and even the hopper to the ceiling. You would be surprised how many plants have pock marks in the ceiling due to 塑料 being blown out the feed throat. Think about this the next time you look into a hopper.

 • 它为聚合物加热时的挥发物,空气和废气提供了通风口。这些气体包括颗粒之间的空气,残留水分,润滑剂和在聚合物处或附近易挥发的其他添加剂’s melt temperature.

 •  It provides for venting of volatiles 与out providing a condensation area for these gases. Improper venting and subsequent condensation can cause screw slippage, feeding issues, bubbles, splay and other cosmetic defects in your parts. This actually requires the feed-throat temperature to be higher than commonly used.

优化机器性能’的进料区将提供更稳定和一致的过程。

接下来让’s define 桥接. Seems simple 恩 ough—it’s anything that blocks the free flow of granules in and volatiles out of the feed section of the screw. However, there are actually two types 桥接. It is critically important to recognize each, as they have different causes and therefore different remedies.

 •  类型1(最不常见): 进料口的堵塞是由单个颗粒粘在一起引起的(见图1)。在桥接材料的样本中,您可以看到 个人 颗粒,几乎没有完全融化。它们很容易分解。进料喉咙太热和/或螺杆进料段中聚合物的废气足够热,足以充分加热颗粒以至于 聚在一起。 (同样的情况通常在温度设置过高的干燥料斗中发生。)您可能会打断桥。—plastic rods work nicely—with 这个过程几乎没有中断。如果您遇到1型堵塞,则降低进料喉的温度应避免这种桥接, 但不是 2型桥。

由止回阀,螺钉或枪管磨损造成的进料喉管的2型桥。

FIG 2 由止回阀,螺钉或枪管磨损造成的进料喉管的2型桥。 Note the solid clump of mostly melted 塑料.

 •  类型2(最常见 and most dangerous): The blockage in the feed throat is cause by a clump of 塑料 that’几乎完全融化了 (Fig. 2). A 几个 partially melted granules may be included, but the bulk of the bridge is a solid clump of 塑料. This is 进料口温度过高引起的。有许多可能的原因,包括:

     一种。单向阀磨损或不当类型;

     b. Worn screw;

     c. Worn barrel;

   d。结合以上。

我们行业中的许多人没有区别 between Type 1 and Type 2 桥接. The common reaction to 2型桥将降低进料口的温度。降低进料口温度将 解决2型桥,实际上会使情况变得更糟。您必须找到磨损的组件并进行维修或更换。这里的问题是没有人愿意关闭机器,更不用说将其拆开以找到罪魁祸首了。每个人都希望压力机运转起来。

要了解进料口中这种塑料实心球的形成,我们需要回顾螺杆设计的几个方面以及它如何熔化塑料。假设你有一个“general-purpose”L / D为20:1的螺钉,您将获得10个进给,五个过渡和五个计量部分的螺钉。通过观察(非常谨慎的反吹)进料口可以看到10次进料中的大部分。检查这些螺纹中是否有熔化的塑料。只需清除螺钉,然后慢慢将螺钉吸回,然后检查您能看到的螺纹。

这些是深层飞行,意在钻出颗粒s 前进并将其运送到过渡区进行融化。螺丝的进给部分是 designed to melt 塑料 and should 不 have melt or solid masses of 塑料 in any of the flights. If there is 塑料 (molten or solid) in the feed section of the screw, it is proof the problem is 进料区的温度,它是温度的四个标志之一 a Type 2 bridge.

如果螺杆的进料口或进料部分包含熔化或凝固的塑料,则您知道比热进料口更大的问题。问题是止回阀泄漏或磨损的螺杆/机筒使塑料回流很大,以至于注射时熔融的塑料被完全推回到进料口。这在重复注射期间发生。熔融的塑料被推回到进料区,然后随着螺杆的旋转将一些熔融的塑料推入进料口,在此处冷却并凝固,通常随着螺杆的旋转变圆成球形。进料口被桥接,但原因是 进料口温度。

If the feed throat or feed section of the screw has melted or solidified 塑料 you know you have bigger problem than a hot feed throat.

Remember, that these deep feed flights are filled 与 both 塑料 granules and air during processing. 其实很多空气 在两者之间 the granules. This air gets warm, expands and needs to be vented through the hopper. Melted 塑料 in the feed zone or feed throat prevents this. Pressure builds up and blows a wad of 塑料, and sometimes even the whole hopper, to the ceiling. You do 不 want to be looking down the feed throat when this happens. As a safety measure, never look into the hopper or feed throat until you are sure it is safe to do so and 总是戴安全眼镜,或者更好的是戴护目镜. 检查您工厂的天花板上是否有过去的2型桥产生的痘痕。

Bottom line: The feed throat is a critical zone to control for melting 塑料 properly and producing acceptable cycles and parts. If you have 桥接 issues, check out the type and potential causes. There are machine-performance and safety concerns, so take the time to 恩 sure that the feed throat, screw, check valve, and barrel are working properly. And do 不 forget to clean out the feed-throat cooling lines. They are often plugged.


关于作者:  John Bozzelli is the founder of 注塑成型解决方案/科学成型 在密歇根州米德兰(Midland),向注塑成型商提供培训和咨询服务,其中包括 LIMS和其他专业。联系 [email protected]

相关内容