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挤出机黑点防治方法  发帖心情 Post By:2010/3/25 15:45:00 [只看该作者]


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Stop Black Specks!<!-- InstanceEndEditable -->
<!-- InstanceBeginEditable name="Synopsis" --><!-- InstanceEndEditable -->
<!-- InstanceBeginEditable name="Author" -->

By Frank Van Haste

 

 

[此贴子已经被作者于2010-3-25 15:47:10编辑过]


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  发帖心情 Post By:2010/3/25 15:48:00 [只看该作者]

Black specks in film or sheet–especially in light-colored or clear plastics–lead to scrap, unscheduled shutdowns, and dissatisfied customers. Specks can also cause holes in film or sheet when it’s later oriented or thermoformed.

There are two possible sources for black specks. Either you bought them with your raw material, or you manufactured them in your extrusion system by one of several mechanisms.

 

薄膜或者片材上的黑点,特别是浅色或透明塑料,会导致废料、不必要的停机以及客户不满。当用于取向加工或热成型时,黑点还在薄膜上会片材引起孔洞。

出现黑点有两个可能的源头。要么你从原材料上引进了黑点,要么你从挤出系统通过几种机制中的某种机制制造了黑点。

 

If specks appear in your product, first examine statistically representative samples of the raw material closely to be sure it isn’t the source. Raw material can also contain formulation defects known as “unmelts,” which char instead of melting, becoming a dark speck surrounded by a gel. Contaminants in raw material are uncommon these days, but not unheard of.

 

假如黑点出现在你的产品中,首先要检查具有统计代表性的原材料样品,以确保其不是源头。原材料也可能含称为不熔物的组成缺陷,它不熔融而是碳化了,成了一种被凝胶包裹的黑点。这年头,原材料污染比较少见,但也不是闻所未闻。

 

Specks or unmelts are more likely in off-spec or post-industrial recycled material. If you find contaminants in your raw material, confer with your supplier about remedies and increase your QC testing of incoming material.

 

黑点或不熔物更可能出现在副牌料或后工业回收材料中。如果你在原材料中发现污染物,那就与你的供应商商量补救办法,并增加你的后续材料的质量控制测试。

 

[此贴子已经被作者于2010-3-25 16:08:14编辑过]

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  发帖心情 Post By:2010/3/25 15:49:00 [只看该作者]

Complex downstream=
Complex downstream plumbing–such a long flow adapters, melt pumps, and screen packs–tends to create hang-up points where heat-sensitive resins can degrade and form black specks. (Photo: Davis-Standard)

If your raw material tests clean, then you’re making specks somewhere in your process. Small amounts of polymer are being overheated, exposed either to high temperatures for a short time or to moderately high temperatures for longer periods.

 

如果你的原材料是干净的,那么你就是在加工中制造了黑点。少量的聚合物被过分加热,要么是短时间暴露于高温,要么是长时间暴露于中等高温。

 

When an area of very high temperature occurs in the barrel, downstream plumbing, or die, it’s typically caused by a problem in the control system–a bad thermocouple, runaway heater band, or a relay stuck in the wrong position. Any material passing through the affected zone is potentially vulnerable to degradation.

 

当机筒或口模出现某个高温区域时,通常是由控制系统造成的问题--坏的热电偶、失控的加热带、在错误位置卡住的继电器。流过受影响区域的任何材料都可能易于降解。

 

Small amounts of resin can hang up and be exposed to normal process temperatures for abnormally long periods in a worn or pitted screw, barrel, or die, or in cracks in chrome plating. This material de­grades over time, breaks loose with thermal cycling and the drag of polymer flow, and can make lots of black specks.

 

 

在磨损的螺杆、机筒或者口模,或者镀铬层的裂缝中,少量树脂会形成挂壁并在极其长的时间内暴露于通常的加工温度。这种材料会随着时间降解,随着热循环和聚合物料流的拖曳而破碎,由此造成很多黑点。

 

If you suspect an equipment problem, work with your maintenance department to identify and correct it. If you can eliminate control failures and worn equipment as causing the contamination, look next at system configuration, material characteristics, and process conditions.

 

如果你怀疑设备有问题,那就与设备维修部门一起确认和纠正它。如果你能消除引起污染的控制缺陷和破损设备,接着你要看看系统配置、材料特征和工艺条件。

[此贴子已经被作者于2010-3-25 16:34:00编辑过]

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  发帖心情 Post By:2010/3/25 15:49:00 [只看该作者]

Downstream plumbing下游管道
The screw and barrel rarely cause degradation, though vents or complex mixing or barrier sections may do so. Degradation usually arises downstream from the extruder–for example, in plumbing that forces abrupt changes in the polymer flow path or in components such as breaker plates, screen packs, static mixers, and melt pumps. These can have potential hang-up areas, like a too-abrupt taper into an adapter fitting.

 

螺杆和机筒罕有引起降解的,尽管排气口或复杂的混合段或复杂的屏障段的确会引起降解。降解通常会出现在挤出机的下游--例如,在聚合物流动路径突然变化的管道或在多孔板、过滤网、静态混合器和熔体泵之类的部件上。这些部件具有潜在的壁挂区域,如同一个过分尖锐的锥形物放进一个接头中那样。

 

Large or complex dies for film or sheet can also be the culprits if they contain low-flow areas where polymer can overheat. Your experience from past teardowns and inspections is the best indicator of whether degradation is developing in areas of slowed or stagnated flow. In blown film dies, it could be the point where each port is fed or where a splitter feeds a spiral. In cast film and sheet dies, trouble could arise where the shoulder starts to spread out or in the relaxation chamber at the land just before the die lips. Once identified, these areas should be given particular attention in future cleanings. They may require local use of higher temperatures plus chemical purging compounds.

 

对于薄膜和片材来说,大或复杂的口模也可能是造成黑点的罪魁祸首,因为他们可能含有低流动区域,聚合物在这里被过分加热。机器拆卸和观察的经验最好地表明了降解是否在慢流区或滞留区形成。在吹膜口模中,也会是出料口被填满料的地方或where a splitter feeds a spiral(不会翻译)。在流延膜和片材口模上,麻烦可能会出现在模肩开始展开的地方,或在模唇前的松弛通道中。一旦确认,在以后的清洗中,这些地方应该特别留意。这些地方要使用局部高温加上化学清洗物。

[此贴子已经被作者于2010-3-25 17:17:47编辑过]

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  发帖心情 Post By:2010/3/25 15:50:00 [只看该作者]

Heat sensitivity热敏性
Heat tolerance of the polymer is also part of the picture. Heat-sensitive materials like PVC, ABS, and EVOH, or engineering resins like acetals, PC, nylon, or polyesters are more likely to degrade than heat-tolerant polyolefins. An extrusion system that processes LDPE with no problem might degrade heat-sensitive EVA in a matter of minutes. Make certain that residence times are not excessive and melt temperatures are below critical levels.

 

聚合物的耐热性也是与黑点有关的一部分。PVC、ABS和EVOH之类的热敏性材料或者POM、PC、尼龙或聚酯类的工程树脂比耐热性的聚烯烃更容易降解。加工LDPE没有问题的挤出系统可能会使热敏性的EVA在一分钟内降解。要确保停留时间不太长,并且熔体温度要在临界水平以下。

 

Specks caused=
Specks caused by contamination or degraded plastic can create holes when film or sheet is oriented or thermoformed.
(Photo: ISRA Surface Vision)

Also, consider throughput rate and shear sensitivity. Obviously, running too hot can lead to degradation. But on occasion, running too cold can, too. Forcing a cool material to flow can generate excessive shear energy and localized degradation in the screw’s flow channel.

 

此外,还要考虑产率和剪切敏感性。显然,机器运转过热会导致降解。但是,偶尔机器过冷运转也会导致降解。强迫一种冷的材料流动会产生极大地剪切能,并在螺杆的流道中产生降解。

 

Finally, consider the shutdown schedule and procedures. Stoppages and shutdowns for adjustments, die changes, or maintenance often extend residence time and cause material degradation. In a system operated five days a week, small amounts of residual material in the extrusion system acquire substantial heat history as the machine slowly cools and starts up again. So it’s common for a system on five-day operation to begin producing black specks only a few weeks after a complete teardown and cleaning.

 

最后,还要考虑停机计划和程序。调式、更换口模或者维修造成的停机常常延长了停留时间,并引起降解。在一个每周开五天的设备中,随着机器慢慢地冷却和再次启动,挤出系统中少量的残留物质会获得足够的热历史。所以,在一个设备完全拆卸和清洗后的几个星期中,一个每周开五天的设备通常会产生黑点。

[此贴子已经被作者于2010-3-29 10:31:34编辑过]

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  发帖心情 Post By:2010/3/25 15:50:00 [只看该作者]

When all else fails当你黔驴技穷时
In the real world, hardware design or operating conditions that are overstressing your material may not be immediately fixable. You may know that your material is susceptible to degradation, but changing resin isn’t an option without customer approval. Or you realize that weekend shutdowns are killing you, but you can’t justify going to 24/7 operation. In such predicaments, purging compounds can play an important role in managing contamination.

 

在现实情况中,硬件设计或操作条件对材料有过多的要求,不可能立即维修。你也许知道,你的材料易于降解,但是没有客户的同意,更换树脂不是一个选项。或许你意识到周末停机很折磨人,但是你不能把开机时间排得满满的。在这样的困境下,清洗化合物在污染物管理上会助你一臂之力。

 

When problems result from hardware configuration or condition–die geometry, known hang-up areas, or even slightly worn screws–periodic use of a purging compound as preventive maintenance will attack degradation at an early stage and minimize troubles during startup. But remember, purging won’t eliminate the root cause of the degradation, so if your system is spewing out black specks at an intolerable rate, that’s not the best time to try a purging compound.

 

当问题来源于硬件配置或者条件-口模结构、已知的壁挂区域,即使对轻微磨损的螺杆周期性使用清洗化合物作为一种防护措施,将会在初期阶段抵制降解,减少在启动时的麻烦。但是,要记住,清洗并不会根除降解。所以,如果你的系统产生黑点的速度可以容忍,那就不是你使用清洗化合物的最好时机。

 

If weekend shutdowns are the cause of contamination, use a high-performance purging compound to remove heat-sensitive materials from the system Friday night–not after the fact on Monday–to avoid startup problems and unscheduled teardowns for cleaning.

Finally, use the right kind of purging compound for your situation. In general, mechanical purging compounds are best for color and material transitions in relatively small and simple systems. Chemical purging compounds are best for large or complex systems or for addressing pesky contamination issues like black specks.

 

如果周末停机是导致污染的根源,那么你要使用高性能清洗化合物清除星期五晚上残留在系统中的热敏性物质,而不是在星期一等出了问题后来解决问题,从而避免启动问题和无计划的拆卸清洗。最后,根据你的情况,选用正确的清洗化合物。一般地,机械清洗化合物最适宜于在小而简单的设备中的颜料和材料换料。化学清洗化合物则最适宜于大而复杂的系统或者适宜于解决像黑点之类的令人讨厌的污染问题。

[此贴子已经被作者于2010-3-29 12:13:38编辑过]

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  发帖心情 Post By:2010/3/25 20:54:00 [只看该作者]

看到一篇帖子说机械清洗化合物是矿物粉填充PE,而化学清洗化合物则是能在受热和压力条件下产生气体的材料,能够达到机器死角,改变残余物分子结构,最佳使用温度在249~288度。

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  发帖心情 Post By:2010/3/26 7:23:00 [只看该作者]

以下是引用hnix在2010-3-25 20:54:02的发言:
看到一篇帖子说机械清洗化合物是矿物粉填充PE,而化学清洗化合物则是能在受热和压力条件下产生气体的材料,能够达到机器死角,改变残余物分子结构,最佳使用温度在249~288度。

孟工的解释很好啊,学习了。


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  发帖心情 Post By:2010/3/26 12:13:00 [只看该作者]

  多麻烦啊。国内的国情谁会那么无聊用化学清洗?注塑机的用填充母粒混洗衣粉,双螺杆直接就是hnix的高填充填充高温摩擦冲洗。便宜啊。至于工人受不受得了,那另一说。

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  发帖心情 Post By:2010/3/26 12:46:00 [只看该作者]

以下是引用jason在2010-3-26 12:13:09的发言:
  多麻烦啊。国内的国情谁会那么无聊用化学清洗?注塑机的用填充母粒混洗衣粉,双螺杆直接就是hnix的高填充填充高温摩擦冲洗。便宜啊。至于工人受不受得了,那另一说。

杨老板的经验很好啊,值得学习。


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