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How to prolong the service life of twin-screw extruder barrel and screw segment element Jun 27, 2022

How to prolong the service life of twin-screw extruder barrel and screw segment element

Influence of high strength wear on the service life of barrel and thread components:

There are roughly three kinds of wear: ordinary wear, material corrosion wear and high strength wear in production processing:

Common wear: when plastic base materials, auxiliary materials and additives are mixed into the barrels, there must be have friction, friction causes wear of the barrels and screw elements.  In particular, fillers such as calcium carbonate and fiberglass added granules making tend to have much more friction on metal than molten plastic.

Corrosion and wear  

Auxiliary materials and addictive agents may be corrosive, directly corrode the inner wall of the barrels, resulting in reduced barrels’ life.

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High strength wear (strong wear zone)

 

There are usually four strong heavy wear areas in an extruder: feeding area, adding glass fiber reinforce or filler area, intermediate area, and die head( shafts ends) area.

 

Mechanical wear is severe in feeding area.   At this time, the auxiliary material is not fused (not melt) yet, and it is basically in a solid state.  The inner wall of the barrels are directly rubbed against the solid material, which makes the inner wall wear badly, which is the first strong wear zone

 

side feeder for glass fiber adding barrel is the another strong friction area, the glass fiber is filament, in the fiber inlet will be tied to the point of the "8" shape hole, here the barrel will face a problem: the glass-fibers will wrap the top sharp corner of the barrels' "8" shape holes and sometimes it will make the top sharp corner  a very deep groove;  In addition, the glass fiber is cut and sheared by the high speed, resulting in more torn fibers. The torn fibers contain sharp ends, which greatly increase the wear force and wear the inner wall of the barrels.

 

In the middle area, the top of the twin screw is under pressure, and the middle area of the screw is in a bending state in high-speed operation, and the deflection (bending) is the largest, the sweeping chamber is very severe, and the wear of the cylinder is obvious.

 

shafts end area(extrusion terminal), the top area of the screw(shafts with segments) in the cantilever state, under the influence of gravity, to sag.   After the material processing, the top of the screw(shafts) will be lifted, and the outer diameter of the screw elements will friction with the inner wall of the barrels, this will cased the resulting in wear and tear.

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Others:

 

·        Operating conditions (temperature, pressure influence)

 

Extruder working environment is very harsh, the melting temperature of plastic is generally higher, such as: polycarbonate(PC) melting temperature reaches about 240 degrees Celsius, nylon(PA) reaches about 280 degrees Celsius, PPS reaches about 290 degrees Celsius.   At high temperatures, the physical properties of the metal decrease, resulting in reduced barrels and segments' life.

 

·        Water, air, oxygen and other components in the cylinder

 

When the barrels are mixed with oxygen, water vapor, the wearing and tearing capacity of the barrels will be increased.

 

Working temperature, pressure, moisture and air in the barrels are difficult to change.  At present, the barrels' body can only be made of more wear-resistant and corrosion-resistant materials to extend the life of the extruder barrels' body and screw segments components.

 

There are carbon steel, stainless steel, alloy steel, metal powder steel on the market.  Compared with other steel, metal powder steel is a kind of steel produced under harsh and picky conditions by powder metallurgy technology, which makes metal powder metallurgy raw materials into powder and then according to a fixed ratio.

 

Compared with ordinary cast and forged steel, powder steel has small segregation of nickel, chromium and molybdenum elements, fine grain size, fine sulfide inclusions and uniform distribution, so it improves mechanical properties and is more wear-resistant and corrosion-resistant.   barrels and screw segments made of powder steel can prolong their service life.

 

The most widely used material is nickel - base alloy for barrel, screw segment, die head, extrusion mold and Etc.;

If you have any question, please call me by cell phone: +86 139 516 66922/ Mr. Chen, you also can friend me by WhatsApp or Wechat:

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from: Lianshuwan-Menbing/ Translate by Chen Hong

 

 

 

 

 

 

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