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如何解决常见的七个切粒问题?  发帖心情 Post By:2012-09-26 14:30:00 [只看该作者]


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Solve Seven Common Pelletizing Problems

解决常见的七个切粒问题

 

John BellScheer Reduction Engineering GmbH

上海北京顺德(翻译和评述)

 

一、       评述

 

这篇文章很棒!

看到这篇文章,我想起了七个小矮人,人小但是有分量。小小的切粒机,大家都摆弄过,一个简单的机械。对于切粒机,玩不好,你就会手忙脚乱;玩不好你的产品就没有卖相;玩不好,你的造粒粒子在注塑机里下不了料。小小切粒机也有名堂呢。



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  发帖心情 Post By:2012-09-26 14:34:00 [只看该作者]

 

一、       翻译

 

Here's a quick how-to on keeping your pelletizing line churning out quality product. 本文给出了使切粒生产线生产合格产品的速效绝招。

 

 


图片点击可在新窗口打开查看此主题相关图片如下:切粒机的七个问题.bmp
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Plastic pellets are typically aspirin-shaped and produced on a die-face cutter, or right-angle cylinders manufactured on a strand line. Either way, they are the preferred material choice for injection molders, profile extruders, and compounders that reintroduce reclaimed scrap into virgin processes.

 

塑料切粒具有典型的阿司匹林药片形状,要么是在模面切刀上生产的或者拉条在直角滚刀上制造的。对于注塑成型商、型材挤出商和将回料引入到新料加工体系中的共混商,无论是哪种方法,都是最好的材料选择。

 

Dozens of pelletizing technologies are available today targeting a host of processes, such as high-output polymerization/finishing lines, dedicated high-output and small-batch custom compounding, concentrate and micro-pellet production, and reclaim.

 

目前,有十几种切粒技术应用于一堆加工工艺。如,高产率的聚合终端生产线、精致的高产率小批次客户定制共混线、中间体和微切粒生产线以及回收料生产线。

 

Of these technologies, two stand out for satisfying the broadest range of processor needs: strand pelletizers, which also include automatic strand-management designs; and die-face cutters, which encompass both underwater and water-ring designs. Each technology offers a unique set of features and benefits suited to particular process needs. Each process also has its own set of challenges and problems that require a certain level of expertise and understanding … and sometimes special attention.

 

在这些技术中,有两种技术引人注目,它们满足最宽范围的加工者需要:拉条切粒机,其中也包括自动拉条管理设计机构;模面切粒装置,它既包括水下切粒也包括水环切粒装置。上述两种技术都有一套独特的特点和满足特殊加工需求的优点。上述每种工艺都有其挑战和问题,从而要求一定水平的经验和理解,有时还需要一些特别的注意。


[此贴子已经被作者于2012-9-26 14:36:09编辑过]

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  发帖心情 Post By:2012-09-26 14:38:00 [只看该作者]

 

UNDERSTAND YOUR PELLETIZING OPTIONS
 
理解你的切粒选用方案(零)


Conventional strand pelletizers are among the oldest types of pelletizers and are generally considered to be the simplest. They are used on a broad range of polymers typified by high melt strength and resistance to breakage. Resin manufacturers and compounders can process the widest range of materials on these systems—everything  from unfilled olefinics to engineering resins filled up to 90% by weight. The pellets are cylindrically shaped with right-angle edges and have a good degree of uniformity.


传统的拉条切粒机是一类最古老的切粒机类型,一般认为是最简单的。它们适用于宽范围的聚合物,这些聚合物具有高的熔体强度、耐拉断的特征。树脂制造商和共混商可以在这些造粒系统上加工最宽范围的材料—从未填充的聚烯烃到重量百分比达90%的填充工程塑料之类的任何东西。这些粒子是圆柱形的,边缘呈直角,具有较高程度的粒形均一性。


Along with their broad utility, these types of pelletizers represent the largest installed base. In these systems, molten polymer is extruded through a series of die holes and formed into strands that drop into a water bath to be quenched and then pass through an air knife and into the pelletizer. Bath residence time is determined by the cooling characteristics of the polymer.


伴随这些广泛应用的是,这些类型的切粒机要求最大的安装基座。在这些系统中,熔融的聚合物从一系列模孔中挤出成料条,料条垂落进入水槽退火,然后通过一个气刀进入切粒机。水槽退火时间是由聚合物的冷却特征确定的。


Machine designs have been refined over the years to significantly reduce maintenance and labor for cleanout. Tool-less entry; cutter disassembly in less than 2 min; long-wearing bed knives with four usable edges; eccentric knife adjustments; and wear-resistant, low-deflection rotors are but a few of the features offered on newer models.


多少年来,机器设计都在优化,结果极大地较少了维修和清扫的劳动量。减少工具进入切粒机的机会;切刀拆卸时间不超过2分钟;长期耐用的四刃定刀;同心刀具调整;耐磨且变形的马达,这些不过是新式切粒机的一些特征。


Meanwhile, underwater pelletizer technology has evolved significantly over the past 30 years and has become a significant choice in reactor discharge, polymer finishing, compounding, and most notably, recycling. From an operational viewpoint, startup of these systems is arguably the most complex of all pelletizers. However, once up and running, performance is generally unattended unless the line is stopped or production is disrupted. In either case, as well as for startup, sophisticated PLC-based control systems are available to automate the process and provide alarms.


同时,在过去三十年中,水下切粒机技术得到了极大发展,成为反应器卸料、聚合物终端、共混,特别是塑料回收的主流选择。从操作的观点看,这些系统的启动是所有切粒机中最复杂的,这一点是有所诟病的。但是,一旦启动和运行,一般而言,其运行可以无人值守,除非生产线停机或者生产中断。无论哪种情况,如同启动一样,复杂的PLC基控制系统可以用于自动控制工艺并提供报警。

Upon startup, pressurized process water is pumped into a pellet chamber that is joined to the die plate. A cutter-shaft assembly transiting the chamber spins a knife hub over the die face. Polymer strands extruding through the holes are cut into uniform-length pellets by the passing blades. The pellets are instantly jacketed and cooled and then conveyed into an overhead transfer pipe for added cooling time. The pelletizer operates as a closed-loop system free of air. Upon exiting the transfer pipe, the slurry empties into a centrifugal dryer, where the separated water flows into a circulating tank. Pellets are conveyed through the dryer by lifter vanes and are discharged to a collection bin.


在启动时,加压的加工水(料条冷却水)被泵入与模板连接的切粒室。穿过切粒室的的切刀-刀轴结构在模面上旋转着刀轴。从模孔中出来的聚合物料条挤出物被扫过的刀叶切成均一的粒子。粒子立即被水包住和被冷却,然后输送到上端的输送管道,以便给予进一步的冷却。切粒机作为一个没有空气的闭环系统运转。当流出输送管道时,水粒浆液被清空到一个离心干燥机中,在这里被分离的水流进循环箱。粒子接着被旋风送料机提送到干燥器,最后在一个集料仓中卸料。


One underwater system utilizes a patented die technology to make the system insensitive to melt-flow interruptions and startup issues encountered with other manufacturers. Whether during startup or processing, the die technology eliminates the need for a water bypass found on other machines, and greatly simplifies the operator’s interaction with the equipment.


有一个水下切粒系统利用了一种专利口模技术,使得切粒系统不再敏感于别的制造商遇到的熔体流动的波动问题和启动问题。无论是启动还是运行期间,这种口模技术不必象别的机器那样安装旁通水管,从而极大地简化了操作者与设备的互相作用。


Both strand and underwater pelletizing presents some unique challenges to resin manufacturers, compounders, and reclaim operations, including the following set of commonly encountered considerations.
 

拉条切粒和水下切粒都给树脂制造商、共混商和回料业务提出了一些独特的挑战,包括下述常常遇到的一些考虑。


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  发帖心情 Post By:2012-09-26 14:39:00 [只看该作者]

 

DEALING WITH FINES

处理细料(一)

 

Fines are seemingly endemic to many crystalline materials such as general-purpose polystyrene. They are an issue for processors because they can alter the bulk density of materials, degrade or burn in the barrel of an extruder, and present a nuisance in conveying. The primary objective for resin producers is to produce consistent pellet geometries to a target length and diameter with no contamination from fines or foreign material.


对于许多结晶,如通用聚苯乙烯,细粉似乎是一种特有的危害。它们对加工者成为问题,因为它们改变了材料的堆密度,在挤出机机筒中会降解或者烧焦,在输运过程中也让人讨厌。树脂生产商的主要目标是生产持续的粒形,具有既定的长度和直径,没有来自微细物或外来材料的污染。


Fines can be reduced by controlling a few machine adjustments and one very important process parameter. The temperature of the strand line should be as close to the Vicat softening point of the material as possible when entering the cutter. This ensures that the strand is being cut as hot as possible to avoid fracture.


通过控制一些机器调节和一种很重要的工艺参数,细粉可以减轻。当进入切刀时,料条的温度应尽可能接近材料的维卡软化点。这样确保了料条尽可能受到热切,从而避免破碎。


Selecting the correct rotor with a suitable cutting angle for the particular polymer is of vital importance in minimizing fines during processing. Use Stellite or tool-steel rotors for unfilled polymers wherever possible. Maintain a keen edge on rotor and bed knives to avoid shattering the polymer. The post-cut apparatus, whether pressurized or vacuum, should avoid entrained air.


对于特定的聚合物,选择特定的切粒角度的动刀,对于在加工中减小细粉特别重要。对于未填充聚合物,尽量使用司太立合金钢(Stellite)或者工具钢动刀。使动刀和定刀刀口保持锋利,以防弄碎聚合物。对于切粒之后的后续设备,无论加压还是真空设备,都要避免裹入空气。


For underwater lines, be sure to maintain sufficient knife pressure against the die face during the process. Regulate the residence time of the post-cut pellet to ensure the pellets are warm when entering the dryer.

对于水下切粒线,要确保在加工中维持足够的顶住模面的刀压。调节切粒后的停留时间,以确保粒子进入干燥机时是热的。 (廖注:冷粒子过于硬脆,在干燥过程中的运动易造成摩擦破碎,产生细粉。)

 

 

SOLVING TAILS
 
解决拖尾问题(二)

 

A tail is a little protrusion on the edge of a pellet and resembles the shape of a hockey stick on the cut edge. It looks like a smear or tear at the bottom of the cut where the cutting apparatus has failed to make a crisp, clean cut. A correctly cut pellet from a strand pelletizer should be a right-angle cylinder. A correctly cut pellet from an underwater pelletizer should be nearly a perfect sphere.


 

所谓拖尾,就是粒子边缘有些鼓出,切割边缘就像曲棍球杆的形状。它看起来象一个位于切口底部的污染物或者撕扯物,在此处,切割装置没能进行干脆利落的切割。拉条切粒的正确的切割粒子应该是一个直角圆柱体,水下切粒机的正确切粒应该近于一个完美的球形。


 

Tails produce fines in materials that normally are not susceptible to them. Assuming all process parameters check out, tails can be generally diagnosed as a cutting problem. For strand lines, swap the rotor to provide a fresh, keen cutting edge and change the bed knife to provide a fresh cutting edge. Another adjustment is re-gapping the machine to the value in the manufacturer’s manual. In underwater lines, inspect the die plate, because tails are often caused by nicks and grooves. Be sure to check each blade to ensure there are no nicks.
 

通常不容易出现细粉的材料也会因为拖尾而产生细粉。假定所有的加工参数都检查过了,拖尾一般可能被诊断为切割问题。对于拉条切粒生产线,更换动刀以提供崭新的锋利的切刃,更换定刀以提供崭新的切刃。另一个调整是按照制造商手册规定的数值重新确定机器间距。在水下切粒线中,检查模板,因为刻痕和沟槽常常引起拖尾。要检查每个刀刃,确保没有刻痕。


[此贴子已经被作者于2012-9-26 14:49:08编辑过]

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  发帖心情 Post By:2012-09-26 14:41:00 [只看该作者]

 

IMPROVING STRAND CONTROL
 
改进料条控制(三)

 

Jack straws are the same as “longs” and can range from longer than nominal pellet length to several inches. Jack straws (also known as angle cuts) are an indicator of poor strand control at the point where the strands are presented to the cutting rotor. A jack straw results from a strand being presented to the rotor in an attitude that is not perpendicular. Therefore, the ends will be angled when cut.


Jack straws(细长条)就像长条库腿,其长度可以在比常规粒子长度长到几个英寸长范围内变动。细长条(也称为斜角切割粒子)表明料条喂入动刀时的料条姿态控制不好。细长条起源于料条以不垂直的姿态喂入动刀。


The distance between the feed rolls (the nip point) and the rotor (the cut point) is called the push distance, because there isn’t anything controlling the strand in that span. A pelletizer is not unlike a wood planer. If the feed rolls are misaligned or in poor condition, the plastic strands will not be presented to the cutting apparatus perpendicular to the cutting plane. The problem is exacerbated because the strands will start crossing over on top of each other, causing a further deterioration in cutting quality.


在喂入辊(咬入点)和动刀(切割点)之间的距离叫压进距离,因为在这个跨度上没有任何东西控制料条。切粒机不同于木板刨床(廖注:木板是刚性的,料条是柔性的,木板比料条更容易正确推进)。如果喂入辊安装不正,或者工况差,那么塑料料条就不会以垂直于切割面的姿态喂入到切割装置。由于料条开始彼此交叉,引起切割质量的进一步恶化,问题变得更加严重。


Crossing strands will force the feed rolls apart and the tension on the strands will be lost. As a result, the strands will momentarily drop, causing them to turn sideways. Ideal cutting occurs when the feed rolls are in good condition, the strands being extruded are the same diameter, and other process variables mentioned below are within normal limits.


交叉料条将迫使两个喂入辊彼此分开,料条失去张力。结果,料条将暂时垂落,引起料条偏向喂入辊的两边。要出现理想的切粒,须得喂入辊处于好的工况,挤出的料条具有一样的直径,下面将要提到的加工变量位于常规限度内。


Among the warning signals is an upper feed roll in poor condition with grooves, checks, or discoloration (hardened from age or heat). Other common problems include a worn lower feed roll, which causes loss of traction; an improper strand tempering process causing strands to snake wildly; and a worn stranding plate, which produces strands of various diameters. Manufacturers should also be aware of an extremely worn rotor and/or bed knife that actually resists the strand as it’s being pushed to the cut point. Also to be avoided is a cutter which runs at an excessive RPM for the diameter of the strand, causing it to wag.


出现上述问题的预警信号是,上喂入辊处于糟糕的工况,存在沟槽、裂纹或者变色(老化或热导致的硬化)。其它的常见问题包括下喂入辊磨损,那将引起牵引力的损失。不正确的料条淬火(廖注:比如水槽中的水冷)工艺将导致料条象蛇一样剧烈弯曲。磨损的挤条模板将产生各种直径不同的料条。制造商还要警惕极端磨损的动刀和/或顶住料条的定刀,因为是定刀把料条推到切割点的。还要避免的是防止切刀在超高转速下运转;相对于料条直径,这种超高转速会引起料条摇摆(廖注:料条直径的粗细与切刀的动量传递具有关联,往往会形成共振,造成料条抖动和摇摆)。


In underwater systems, longs are in most cases produced by an imbalance of feed rate versus cutter speed. Increase the cutter speed to match the feed rate or decrease the feed rate to match the maximum cutter speed. Make sure that there are enough knives on the cutter head to ensure correct pellet geometry and check if any holes are slow moving or blocked from polymer flow.
 

在水下切粒系统中,细长条产生的最多情况是是喂入速度对切刀速度的不匹配。需要增加切刀速度来匹配喂入速度,或者减小喂入速度来匹配最大的切刀速度。要确保在切割刀头上有足够的刀片,以确保正确的粒子几何形状,并检查是否有任何模孔发生聚合物料流的慢动或阻塞。

[此贴子已经被作者于2012-9-26 14:49:50编辑过]

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  发帖心情 Post By:2012-09-26 14:43:00 [只看该作者]

 

STRAND MIGRATION
 
料条漂移(四)

 

Strand migration is a condition whereby strands tend to bunch on one side of the feed table, resulting in diminished pellet quality, longs, and processing disturbances. If the pelletizer cutting plane is not parallel to the stranding plate of the die, the strands will tend to crowd right or left. Other causes of strand migration include inconsistent gap of the lower feed roll to the doctor blade, and inconsistent diameter of the lower feed roll.

料条漂移就是料条在喂入平台上存在向一边集束的倾向的状态,它导致料粒质量变差、存在细长条和加工紊乱。如果切粒机切割平面没有平行于挤出机挤条模板,那么料条将倾向于拥挤到右边或左边。料条漂移的其它原因包括下喂入辊与刮刀的间隙不恒定、下喂入辊的直径不一致。

 

AVOID SHRINK VOIDS
 
避免收缩空穴(五)

 

Shrink voids and hollow pellets are evidence of improper strand tempering. A shrink void can be as slight as a dimple on the end of a pellet or can be so severe that the pellet has a hollow core, much like a swizzle stick. The condition occurs when a strand has a core temperature near a molten state and contracts rapidly once cut.


收缩空穴和空洞粒子表明料条淬冷不恰当。收缩空穴可能轻微到粒子端面上的一个小坑,也可能严重到成为一个空心粒子,就象调酒棒那样。这种状况出现的时机是,料条的芯部温度接近熔融状态,且料条被切粒后马上收缩。


Strands that are properly tempered have a consistent cross-sectional temperature gradient and have no response or reaction to a cooling medium (water or air) when cut. Shrink voids occur when process water is either too warm or too cold for the particular polymer, thus freezing the outer surface of the strand, creating a hard shell, and trapping heat in the core. In addition, there is insufficient soak time in the air or water to allow the core heat of the strand to migrate to the strand surface for good cross-sectional cooling.


没有正确淬冷的料条,其界面的温度梯度保持恒定,切割时对冷却介质(空气或水)没有响应或反应。收缩空穴出现的时机是加工水(或翻译为工艺水)对于特定的聚合物要么太热要么太凉的时候,这样就把料条的外表层冷冻住了,产生了一个硬壳,把热量窝留在料条芯部。此外,料条在空气或水中没有足够的浸泡时间,从而不能允许料条芯部的热量转移到料条表面,从而也就没有好的截面冷却。


Underwater pellets can also suffer this condition due to entrained volatiles in the melt. An important precaution is to check the vacuum port on the extruder.
 

在水下切粒的粒子,由于困住了熔体中的挥发物,也会碰到这种情况。一个重要的注意是检查挤出机上的真空口。
[此贴子已经被作者于2012-9-26 14:50:36编辑过]

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  发帖心情 Post By:2012-09-26 14:53:00 [只看该作者]

 

PROCESS ADJUSTMENT FOR DOUBLES/ZIPPERS

工艺调整防止连粒(六)

 

 

Doubles or zippers are a series of pellets that are attached to each other, in some cases by a thin film of polymer, either end to end or tangentially. Several process-control issues can individually or collectively cause the problem.


连粒是一系列粒子彼此相连的情形,在某些情况下,粒子之间通过薄膜端面对端面或者以切向的方式连接一起。几个工艺问题可以独自或者一起导致这个问题。


The process water may be too hot. Lower the temperature to adequately quench the surface of the pellet. Another cause may be low water flow, which can contribute to pellets moving slowly out of the cutting chamber, resulting in agglomeration. If the die holes are too close together for the product, die swell may be creating contact between the pellets during the extrusion process. Replace the die with fewer holes at a larger spacing.

 加工水可能太热。降低水温以给予粒子表面足够的淬冷。另一个原因可能是太低的水流速度,它将导致粒子慢慢移出切粒室,从而导致粒子团聚。如果口模的孔眼挨得太近,在加工过程中出口膨胀将会产生粒子触碰。用大间距孔数少的口模替换有问题的口模。

 

A CRACKED KNIFE CAN BE COSTLY
 
破刀可能更费钱(七)

 

A bed knife is a solid piece of carbide in which Invar, a stainless-steel alloy, is brazed in place, making it possible to allow threads through which the carbide bed knife is mounted to a holder. A cracked bed knife typically occurs following rotation of the edge. Steps can be taken to avoid this by carefully following the recommendations in the manufacturer’s machine manual. It is often not understood that the Invar alloy plug containing the threads is held in place by silver solder and has a shear limit easily overcome by using too much torque when mounting. A bed knife cracked during rotation or installation can easily become dislodged and fly about in the pelletizer, destroying the cutting edges of the rotor and resulting in a very costly repair.
 

定刀是一个坚硬的碳化钢片,因瓦合金(一种不锈钢合金)铜焊到碳钢片的一定位置,这样碳钢定刀就可以通过螺纹安装到支架上。一般地,定刀的刀锋发生转动后就会出现破刀现象。可能要采取措施避免这种问题,方法是遵照制造商设备手册上推荐的办法去做。

 

(全文完)


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  发帖心情 Post By:2012-09-26 20:35:00 [只看该作者]

excellent!

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  发帖心情 Post By:2012-09-27 14:51:00 [只看该作者]

学习了,受教了

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  发帖心情 Post By:2012-09-27 16:33:00 [只看该作者]

学习,在今后的生产过程中多注意


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