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Screw and barrel combination of these two parts the quality of work, the plastics materials, products quality and production efficiency, have a significant impact. Their work quality and accuracy of two parts manufacturing and assembly space related. When the 20 were badly worn extruder output decline, they should be arranged on the screw, barrel maintenance.
1, screw and barrel because of damage
1, screw in the machine barrel rotation, the friction between the two materials and to make screw and barrel of the working surface of the gradual wear and tear: Screw diameter gradually reduced, the inner barrel diameter gradually increasing. In this way, screw and barrel with the diameter of the gap, with both the gradual wear and tear a little bit of increase. However, since the cylinder head and manifold in front of the resistance has not changed, increasing the material being extruded move forward leakage flow, that is, material from the diameter gap at the direction of flow of the feed increased. The result extruder production dropped. This phenomenon has also caused material in the machine barrel residence time, resulting in material decomposition. If it is polyethylene, the decomposition of the hydrogen chloride gas strengthened the screw and barrel corrosion.
2, the material in any of calcium carbonate and glass fiber filler, can speed up the screw and barrel wear.
3, since there is no plasticizing material evenly, or foreign matter mixed metal compound, so that a sudden increase in screw rotation torque, this torque exceeds the ultimate strength of the screw, so that screw is broken. This is a non-accident damage.
2, screw repair
1, the screw is broken, according to the actual cylinder diameter to consider, according to the normal gap and barrel give the diameter of the new screw manufacturing deviations.
2, wear screw thread diameter of the reduced surface treated, thermal spraying wear-resistant alloy, and then by grinding to size. This method generally have a professional spray-processing repair, the cost is still relatively low.
3, in the screw thread part of the wear surfacing wear-resistant alloy. According to the extent of wear and tear screw welding 1 ~ 2mm thick, and then grinding to the size of screw. This wear-resistant alloy by C, Cr, Vi, Co, W, and B-material composition, increase screw resistance to wear and corrosion resistance capabilities. Professional surfacing works on the high cost of such processing, in addition to special requirements of the screw, it seldom used.
4, repair screw can also be used method of hard chromium plated, chrome is also the wear and corrosion-resistant metal, but the hard chromium layer of relatively easily.
3, machine cylinder repair
The inner barrel surface hardness higher than the screw, and its damage much later than the screw. The scrap is the diameter of barrel diameter, which increases wear and tear because of the time. Its restoration as follows:
1, due to increase in the diameter of barrel wear and tear, if there is a certain degree of nitriding layer can take the machine barrel bore directly Boring, grinding to a new diameter size, and then click here to diameter of the preparation of a new screw.
2, cylinder diameter re-trimmed by machining cast alloy, the thickness of 1 ~ 2mm between, and then finishing to size.
3, under normal circumstances barrel wear faster homogenization segment can be paragraph (take 5 ~ 7D long) through the bore hole finishing, adding a nitriding steel bushings, inner hole diameter of the light of screw diameter, leaving In normal with the clearance, preparation for processing.
To stress here that the screw and the barrel of these two important parts, one is the slender thread rod, a relatively small diameter and long holes, and their mechanical processing and heat treatment processes are more complex, assuring accuracy are more difficult. Therefore, these two parts to repair worn or replaced with new parts, we must do a comprehensive analysis of the economic point of view. If the cost of repairs and low cost more than the new ones screw on the decision to repair, which may not necessarily be the right choice, the cost of repairs and updating the cost comparison, only one aspect. Also depends on the cost of repairs after the use of screws and repair time and cost of upgrading and updating the use of time, the ratio of screw. Program before using the ratio of the small economy is the right choice.
4, screw and barrel manufacturing materials
Manufacture of screw and barrel, the current domestic commonly used materials for 45,40 Cr and 38CrMoAlA, their performance in Table 3-1.

 

Import extruder screw and barrel manufacturing materials, commonly used alloy steel has 34CrAINi7 and CrMoV9. The yield strength of this material are about 900MPa. The nitriding treatment, hardness 1000HV above, both have good anti-corrosive wear.

 

If the surface of screw and barrel bushing spraying or casting methods, the material may refer Table 3-2 and Table 3-3.
5, squeezing the work of the system of product quality issues
(1) The screw and barrel assembly gap is too large
1, there are transverse wrinkles;
2, cross-sectional geometry and size of errors large;
3, surface-focus
4, production fell
(2) Barrel heating temperature instability
1, surface roughness, there is Watermark;
2, section size instability, geometry errors large;
3, product strength is not good, easy to embrittlement;
4, the surface mass and
(3) The screw speed of instability
1, variation in section size;
2, there are horizontal wrinkles;
3, speed too fast, the surface rough, easy to brittle fracture, there are lumps.