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提高品质&先进的螺杆设计提高生产率

大多数模塑商仍在使用避风港的螺杆设计’30年以来变化不大。但是他们不’t need to.  
#scientificmolding #processingtips #螺丝

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在11月, Tech Days网络研讨会系列, Plastics 技术 主持了一个会议“Establishing &保持稳健的成型过程,” in which I participated. During this webinar there was a short discussion on new injection molding machines, which spurred a conversation about screw design 和melt uniformity, one of my pet topics within the molding industry.

FIG 1 Melt model of a 一般用途 injection 拧。

 

FIG 1 Melt model of a 一般用途 injection 拧。

这次网络研讨会上的一个引人注目的评论是著名的注塑成型创新者Mike Durina 他经营自己的公司 MD塑料。迈克指出,大多数模塑商仍在依靠“general-purpose”螺丝设计可以追溯到30年前。通过这段时间对计算机进行的所有技术改进, 没有 has been done to improve 熔体均匀度. We still use “general-purpose”(GP)螺丝,著名的螺丝设计师Bob Dray明智地称其为 “no-purpose”螺丝。那是他们做的 均匀地熔化塑料。用均匀熔化的塑料进行加工似乎是当务之急,但几乎没有引起人们的注意。这需要改变。

Why is 熔体均匀度 important? Well, 您 would be hard-pressed to name a single common molding/part problem that melt non-uniformity does 不 cause or exacerbate. To name a few:

 1.  Weak weld lines;

 2. 零件故障/性能问题;

 3.  Warping;

 4. 灌装不均匀;

 5. 大理石花纹(彩色漩涡/斑点);

 6. 树脂降解,出现黑点;

 7.  Long color-change times;

 8.  Short shots;

 9. 经常清洗螺丝;

 10.  Longer cycles.

FIG 2 Degraded polymer at junction of flight 和root diameter of a 一般用途 screw 表示 死角。

 

FIG 2 Degraded polymer at junction of flight 和root diameter of a 一般用途 screw indicates dead space.

那么,如何获得熔体均匀性呢?从图1所示的GP螺杆的熔融模型开始。如图所示,所有粒料通常都不会熔融,并且所产生的固相床破裂会导致混合和降解不佳(以及导致上述问题)。 。同样,在螺纹与齿根直径相配合的区域中,塑料通常会停滞并降解。图2显示了通常的聚合物降解,通常在拉动螺钉进行清洁或维修时会看到这种降解。虽然我没有实际统计数据,但我的经验是,今天运行的所有计算机中至少有50%至80%会出现此问题。即使只有25%,也仍然是我们模塑行业的主要问题。业界为什么要忍受这一点?做 必须忍受这个?

FIG 3 在此防护螺钉中,请注意即使清除后,绿色聚合物仍处于防护条中。这表明 dead space.

 

FIG 3 在此防护螺钉中,请注意即使清除后,绿色聚合物仍处于防护条中。这表明 死角。 (照片:乔·卡斯卡拉诺)

事实是 the industry does 不 have to use GP screws. There are solutions, but be careful who 您 talk to. When anyone begins to ask machine suppliers 和most screw manufactures about these problems, the knee-jerk response is, “Try our barrier screw.” 谨慎进行。图3显示了典型的屏障型螺钉 it was purged. Note the green polymer is still in the barrier flights. Since this is 后 purging, 您 can understand that this material stays there during production 和will degrade with time. You will get even more degradation 和black specks. So, if barrier screws are 不 the answer, what is?

FIG 4 Melt-uniformity 拧。

 

FIG 4 Melt-uniformity 拧。

Back in the late 1980s I was fortunate 恩 ough to have worked on a company-sponsored research program to solve problems of mixing color concentrates into natural resins. After spending one-and-a-half years 和over $200,000 on around 10 different barrier screw designs that did 工作中,我们开发了熔体均匀性螺钉(图4)。它不是障碍螺丝。这个“melt uniformity” screw passed rigorous instrumental requirements for color distribution 和uniformity. Further we trialed it in seven different production machines making complex parts for six months. The results were impressive (see accompanying table).

The data speaks for itself. Replace 您r 一般用途 screws with melt-uniformity screws. You will save time, make 您r life easier on the shop floor, 和make significantly more money.

Not convinced? Mike Sepe, a 不ed materials expert 和fellow Plastics 技术 专栏作家,实际上是在为模塑商工作时购买了其中一种螺钉。他写了一篇关于自己在 2012年4月专栏 看看Sepe对此有何评论:“当我们放入新螺杆时,熔体温度降低了60ºF和背压从300 psi降低到75 psi液压。颜色掺入和未融化的问题消失了;缩短了周期时间;并且停止定期清洁螺钉。螺丝在七个月内就收回了成本,并开始了一次运转革命,最终整个工厂看到通用螺丝被混合螺丝取代。的数量‘material problems’ and ‘processing problems’ 只是消失了是一个启示。”

唯一的主要问题:今天, I cannot find a shop to make this design properly. Believe it or 不, I took a print to a screw shop in Michigan 和their response was, “不,我们不会做到…一个高中生可以做一个更好的设计。”认真地说,如果有人知道有一家做螺丝的小商店,请告诉我。我需要更换已有的东西。

关于作者:  John Bozzelli 是...的创始人 注塑成型解决方案/科学成型 in Midland, Mich., a provider of training 和consulting services to injection molders, including LIMS, 和other specialties. Contact [email protected]

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