Since the advent of twin-screw extruder, it has been widely used in the field of plastic modification, and is the core equipment in the field of modification. Each modification factory takes good care of twin-screw extruder, but in daily work, it is inevitable to encounter the loss and repair of equipment. So in order to avoid or reduce the loss, how to repair after the failure, the next let me introduce you some small knowledge about the maintenance and repair of the extruder.
I. Maintenance of twin-screw extruder
In order to ensure the safe and stable production of the twin-screw extruder and extend its service life, it is necessary to strengthen the maintenance work of the twin-screw extruder, the basic contents are as follows:
Maintenance when equipment operation
Materials are not allowed to contain impurity, and hard materials such as metal and sand are strictly prohibited from entering the hopper and barrel; When opening the cover of the exhaust chamber, it should also prevent foreign objects from falling into the barrel; The extruder should keep enough holding time after heating up, and turn on the machine after the disk movement should be light before driving; The screw is only allowed to start at a low speed, the idling time should not exceed 2 min, and the feeder should be fed in a hungry way before gradually increasing the speed.
Extruder daily maintenance
The oil and lubricating oil should be replaced once every 4000h after operation. If the main motor is a DC motor, the motor carbon brush should be checked once a month, and the record should be made, and the carbon brush should be replaced if necessary. The electric control cabinet should be purged once a month, check the wear of the screw and barrel every quarter, and make a record; Check the gear, bearing and oil seal of the gearbox once a year; When the machine is shut down for a long time, it should be treated with anti-rust and anti-fouling.
II.Repair of twin-screw extruder
Screw and barrel damage causes
1.
The screw rotates in the barrel, and the friction between the material and the two causes the working surface of the screw and the barrel to gradually wear out: the diameter of the screw gradually shrinks, and the diameter of the inner hole of the barrel gradually increases. In this way, the diameter gap between the screw and the barrel increases a little with the gradual wear of the two. However, since the resistance of the head and the distribution plate in front of the barrel does not change, this increases the leakage flow when the extruded material advances, that is, the flow of the material increases from the diameter gap to the feed direction. As a result, the output of extruder decreases. This phenomenon also increases the residence time of the material in the barrel, resulting in material decomposition. In the case of polyethylene, the hydrogen chloride gas generated by decomposition strengthens the corrosion of the screw and the barrel.
2.
Materials 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 there are metal foreign bodies mixed into the material, the rotation torque force of the screw suddenly increases, and the torque exceeds the strength limit of the screw, making the screw twisted. This is an unconventional accident damage.
The repair of the screw
1.
The twisted screw should be considered according to the actual inner diameter of the barrel and manufactured according to the deviation of the outer diameter of the new screw from the normal clearance with the barrel.
2.
The surface of the thread with a reduced diameter of the wear screw is treated, thermally sprayed with a wear-resistant alloy, and then ground to size. This method is generally processed and repaired by professional spray factories, and the cost is relatively low.
3.
Surfacing wear-resistant alloy on the threaded part of the wear screw. Surfacing welding 1~2mm thick according to the degree of screw wear, and then grinding the screw to size. This wear-resistant alloy is composed of C, Cr, Vi, Co, W and B materials, which increase the wear resistance and corrosion resistance of the screw. Professional surfacing plant for this kind of processing cost is very high, in addition to the special requirements of the screw, generally rarely used.
4.
The repair screw can also be coated with hard chromium on the surface, chromium is also a wear-resistant and corrosion-resistant metal, but the hard chromium layer is easier to fall off.
Repair of the barrel
The inner surface hardness of the barrel is higher than that of the screw, and its damage comes later than that of the screw. The scrap of the barrel is the increase of the inner diameter due to time wear. Its repair methods are as follows:
1.
If the barrel increases in diameter due to wear, if there is a certain nitrided layer, the hole in the barrel can be directly boring, grinding to a new diameter size, and then prepare a new screw according to this diameter.
2.
The inner diameter of the barrel is machined and re-cast, the thickness is between 1~2mm, and then finished to size.
3.
Under normal circumstances, the homogenization section of the barrel wears quickly, this section (take 5~7D length) can be boring and trimmed, and then equipped with a nitrided alloy steel bushing, the diameter of the inner hole is referred to the diameter of the screw, and left in the normal matching gap for processing and preparation.
Here to give you a tip, the two important parts of the screw and the barrel, one is a slender threaded rod, one is a relatively small diameter and long hole, their mechanical processing and heat treatment process are more complex, the accuracy of the guarantee is more difficult. Therefore, whether to repair or replace the new parts after wear of these two parts must be comprehensively analyzed from an economic point of view.
If the repair cost is lower than the cost of replacing the new screw, it is decided to repair, this is not necessarily the right choice, and the comparison between the repair cost and the renewal cost is only one aspect. In addition, it also depends on the ratio of the repair cost and the time of using the screw after repair to the renewal cost and the use time of updating the screw. It is the right choice to adopt the scheme with small ratio only economically.