Extruder Screw BarrelCause Of Damage And Repair Method
Screw and barrel of the combination of these two parts of the quality of work, the material of the plastic, the quality of products and production efficiency, have an important impact. Their working quality is related to the manufacturing accuracy of two parts, the assembly gap. When the two parts of the serious wear and tear, the output of the extruder, it should be arranged on the screw, barrel repair or replacement.
First, the cause of damage to the screw and barrel
1, the screw rotation in the barrel, the material and the friction between the two, so that the screw and the barrel of the working surface gradually wear: screw diameter gradually reduced, the barrel of the hole diameter gradually increased. In this way, the screw and the barrel with the diameter of the gap, with the gradual wear and tear of the two slightly increased. However, since the resistance of the head and the manifold in front of the barrel does not change, this increases the leakage flow when the extruded material is advanced, i.e., the flow of material from the diameter gap to the feed direction. As a result, the extruder production is reduced. This phenomenon also makes the material in the barrel to increase the residence time, resulting in material decomposition. If it is polyethylene, the decomposition of hydrogen chloride gas to strengthen the corrosion of the screw and barrel.
2, if the material such as calcium carbonate and glass fiber filler, can speed up the screw and barrel wear.
3, because the material is not plasticized evenly, or a metal foreign body mixed with the material, so that the screw rotation torque force suddenly increased, this torque exceeds the screw strength limit, the screw twist. This is an unconventional accident damage.
4, screw and barrel installation level, straightness, the gap is not adjusted in place, fastening screws are not reinforced. In the boot when the screw barrel friction, speed up the screw barrel damage.
5, before the start of the warm-up time, the screw barrel in the accumulation of raw materials have not been fully softened, the boot torque is too large, or there is a large piece of softening materials, resulting in screw barrel sprain or collapse. And damage to the gearbox.
Domestic high-quality extruder will generally install the overload protection of the main motor of the extruder, to a certain extent, can protect the screw barrel, greatly reducing the screw sprain, breaking the situation occurred. But if the force at the screw structure is weak or time suddenly, the screw is still possible to damage the situation.
Second, the screw repair
1, broken screw, to carefully check the barrel is a serious injury, if the barrel can continue to use, according to the actual diameter of the barrel to consider, according to the normal clearance with the barrel to give the new screw diameter deviation manufacture.
2, the wear screw diameter reduced thread surface after treatment, thermal spray wear-resistant alloy, generally thickened in 2-3mm, and then by grinding to the size. This method is generally a professional screw barrel manufacturers spray processing repair.
3, wear part of the screw in the wear part of the wear-resistant alloy. According to the degree of screw wear surfacing 1 ~ 2mm thick, and then grinding the screw to the size. This wear-resistant alloy consists of C, Cr, Vi, Co, W and B and other materials, increasing the anti-wear and corrosion resistance of the screw. Professional welding plant on the high cost of this processing, in addition to the special requirements of the screw, generally rarely used.
4, repair the screw can also be used on the surface hard chrome plating method, chromium is also wear and corrosion-resistant metal, but the hard chrome layer is easier to fall off.
Third, the barrel repair
The inner surface of the barrel is harder than the screw, and its damage is much worse than the screw. Repair of the barrel: the inner surface of the barrel hardness is higher than the screw, it is more damage than the screw late In addition, I believe that the barrel is because the cylinder is cylindrical, the friction area is large, screw rib edge force is small, as well as raw materials in the screw groove as a result of the design of the thrust surface is upward movement So that the damage to the barrel than the screw too late The scrapping of the barrel is that the diameter of the inner diameter increases due to time wear. It is repaired as follows:
1, due to wear and increase the diameter of the barrel, if there is a certain nitriding layer, the barrel can be directly bore hole, grinding to a new diameter size, and then press the diameter of the new screw.
2, the barrel diameter by machining the re-cast alloy, the thickness of 1 ~ 2mm, and then finishing to the size. This method is costly.
3, under normal circumstances the homogenization of the barrel wear faster, this section (take 5 ~ 7D long) by boring finishing, matched with a nitriding alloy steel bushing, the hole diameter with reference to the screw diameter, stay Normal with the gap, the processing preparation. Efficient rod tube feeding section wear is also faster. Use should always be checked.
It is important to note here that the two important parts of the screw and the barrel are slender rods, one that is smaller and longer in diameter, and that their machining and heat treatment processes are more complex and that the accuracy is guaranteed The Maintenance of the screw barrel must be sent to the manufacturers to deal with the whole, otherwise there may be a new screw and the old barrel does not match the problem.
So, after the wear of these two parts is to repair or replace the new pieces, we must fully analyze. If the cost of repair is lower than that of the new screw, it is not necessarily the right choice. The comparison between the repair cost and the update cost is only one aspect. Also see the repair costs and repair the use of screw time and update costs and update the screw to use the ratio of time. The use of small ratio of the program was economic, is the right choice.
4, screw and barrel manufacturing materials
Manufacturing screw and barrel, the current domestic commonly used materials are 38CrMoAlA, 45 (generally used for alloy barrel) and 40Cr.
In summary, the screw barrel as the core components of extrusion machinery, its design, processing, installation and maintenance require professional and technical personnel focus on participation.