Purging is widely used as an easy way to clean out materials from the extruderand die and to avoid a time-consuming stripdown cleaning There are many typesof materials used for purging, both commercial purge products and "homeengineered" purges. These materials generally fall into two categories:chemical purges and mechanical abrasive purges. Many combine both chemical andabrasive actions.Chemical purges work by attacking the plastic residue like asolvent. Many of them also incorporate a foaming action and require a 5-min"soak" in tbe barrel to allow the chemical action to work.
Mechanicalabrasive purges work by scouring and scrubbing material off the metal surfaces,using friction and shear. Processors do a lot of trial-and-errorexperimentation to find the right purge material and technique. No"magic" purge material will work best for all materials. Commercialpurge products are generally more expensive than "home engineered"purges. But if you can use less material with the commercial purge, or get tbejob done quicker, the total cost may actually be less.
Processorshave run all sorts of materials through extruders, in the quest for a cheap andeffective purge material. For instance,in the U.S. Midwest many operators use cattle-feedcorn, because it's readily available and does a fairly good job of scouring outthe machine. Here are two effective homemade purges:
Mix #/; S0% HDPE (or another htgh-viscosity resin) +50%diatomaceous earth (DE): DE is finely milled fossil shells of tiny seaorganisms. It is readily available in garden supply stores. DE looks like afine powder, but the particles have very sharp, angular edges, which produce ascouring action. Processors who run sheet and film use this purge, as it cansometimes get rid of die lines, saving a lengthy die teardown.
*Mix #2; HDPE or other viscous resin with kitchen cleanser andwater: Mix a slurry of water and three or four cans of Comet or Ajax kitchen cleanser in abucket. Feed HDPE at a normal purging rate and temperature, and slowly pour theslurry into the main feed port. The water in the slurry will flash to steam,which gives a very good cleaning effect combined with the abrasive in thekitchen cleanser. (Safety note: Warn any operators nearby that steam maydischarge from extruder openings. Do not look into the die or vents unlesswearing a full polycarbonate face sbield andlong-sleeved shirt.) Probably themost important thing is to purge often. The object is to prevent old materialsfrom being "baked on" the metal surfaces.Once this happens, purgingwill generally not be able to remove thematerial, and a manual stripdown cleaningwill be the only remedy. One mistake many processors make is to run the purgeonly at a fixed screw rpm. It's much more effective to vary the speed, changingfrom low to medium to high rpm, running for perhaps30 sec at each speed. Thisinduces different shear rates against the metal surfaces, helping to dislodgeold material from the walls.
清机是把用于把挤出机和口模内材料清除出来的简易而广泛的方法，它避免了耗时的拆机清洗。有很多材料可用于清机。既有商用的清机产品，也有自个儿特制的清机产品。这些材料常分成两类：化学清洗剂和机械摩擦清洗剂。许多清洗剂同时具有化学和摩擦功能。化学清洗剂象一种溶剂一样进攻塑料残渣。许多化学清洗剂还加入一种发泡功能，需要在机筒内“浸泡”5分钟，从而发挥化学作用。
机械摩擦清洗的原理是从金属表面摩擦和冲刷掉残留材料，使用的是摩擦和剪切的方式。加工者做了很多试错试验来找到合适的清洗材料和方法。没有什么“神奇”的材料对所有材料都管用的材料。商用清洗材料一般比自己制造的清洗材料贵。但是，假如你使用较少的商用清洗剂材料能更快把活干好，那么实际成本可能更小。
加工者需要廉价而有效地清洗材料。比如，在美国中西部许多操作者使用喂牛的玉米，因为它容易得到，对机器有好的清洁作用。下面介绍两种自己制造的有效地清洗剂：
---1#混合物：50%HDPE＋50%硅藻土
---2#混合物：HDPE＋水＋去污粉。将HDPE以通常速度在熔融温度下加入螺杆。将去污粉用水在桶里搅拌成浆液，从主喂料口慢慢加入浆液。这些浆液因为发泡而冲击、摩擦、清洗螺杆。
