To Discuss Extruder Lifespan in Wood-plastic Composite Making

Jul 19,2016

Some PE wood-plastic Composites corporations, which are making floor/stand column/wall board/ keel /flower box board/chair building decoration materials email and ask us if there are any cost-effective solutions to be chosen for the short lifespan problem of their segment barrel and screw element of twin-screw extruder. 

Before to answer these questions, let us check the formula of typical PE wood-plastic composites material first, shown as right (PVC wood-plastic composites has a different working condition, will be discussed in another article).

formula of typical PE wood-plastic composites material

In the formula of typical PE wood-plastic composites, the wood powder proportion even is 60% and up, which means most of material is wood powder now. Or you are looking for a better wood- plastic product sense of reality, to increase the proportion of ultra fine diameter wood powder particle, and to increase the proportion of the herbaceous plant fiber etc., then it’s no wonder that both frictional wear which is on the barrel inner wall and shear abrasion which is on the screw elements surface are quite sharp. If more recycle PE to be used , clearly it’s worse to have some sediment impurities in it. 

To decrease the equipment investment, a lot of companies chose two pieces of “C” form bimetallic liner as a segment barrel core parts when they purchased a twin screw extruder normally, the protective alloy layer is Ω101. but these two bimetallic liners inside the barrel two holes are not welded, there are two gaps exist between two liners top and bottom. the gaps will be expanded with the alloy layer’s abrasion as well as the alloy layer edge fatigue over time. The expanded two gaps provide spaces for wood-plastic material, and then more and more material gathering inside two gaps because of the back pressure , result in the liner edge cracking under a strong extruding, and lead to the decline of production and even can’t extrude product anymore. 

A set of disassembled two “C” form bimetallic liner was shown to us by one of our customers (See right), and it’s clearly that the alloy layer isn’t wear-off, just cracked on the sharp corner of the “C” shape, we should say it is an unusual failure. That is the reason why the high-end market in Europe and in America, no any wood-plastic products manufacturing enterprises use this kind of two “C” form bimetallic liners as the wear resistance way to protect the segment barrel. If simply put this liner structure inconsequence and lead to the non normal failure, blame the alloy layer of anti wear performance is obviously unreasonable. It may mislead us can't find the right reason, can't take a correct countermeasures.

bimetallic liner

Apparently, the structure is the key to solve the problem, that’s why we should use an integral oval liner, due to this kind of liner has no gap, no the spaces for wood powder and recycled PE remain. The cost-effective oval liners recommended are high-chromium iron Ω101A, which is equivalent to the 043 material of German W&P company, and the super hard high-vanadium iron Ω102A oval liner which is with higher wear-resistance feature and equivalent to the 99.3 material of German W&P company. Certainly if our latest researched and developed SiC composite ceramic oval liner can be used, there's no one to worry about the service life whatever under a severe wear and corrosion working conditions, such as the PVC wood-plastic composites to be run. 

Chief Engineer Office / Shanghai Omega Machinery Co., Ltd.

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