The increase in the unit capacity of machinery, the intensification of processes, and the increasing volume of processing of filled materials has lead to significant wear of the corresponding parts of the equipment.The authors have therefore undertaken to establish the rules and the character of the damage of the working organs of polymer-processing equipment using extrudersas an example, and to suggest the design and technological measures for a prolonged life of the equipment in the processing of filled plastics.In order to gain actual data on the distribution of wear along the working organs, to establish the zones of maximum damage, and to determine the kind of wear in the different zones, the authors have investigated the extruders in several plants of the branch (Table I). The investigations included checking of the diameters of the worm turns and depressions in every working zone; the width of the turns at the crest and at the base was measured with a micrometer, and the internal diameter of the bushings with dial inside calipers.The precision of the measurements was • mm. All measurements were taken after careful removal of plastic traces from the parts. A chart of the measurements was prepared for every part.The analysis of the results (Table 2) showed that the intensity of wear of the working organs of different types of equipment differs significantly from each other and that it depends on the design characteristics (geometry) of the worms, the method of surface hardening, the kind of material processed, the way of introducing the filler, etc. Subjected to increased wear are complex and expensive parts and units, the restoration and replacement of which requires long interruptions of the production and therefore leads to significant expenditures.The wear of the worms is not uniform, neither along the length nor over their profile. In the case of single-worm extruders the minimum wear is observed in the loading zone, the maximum wear in the compression zone. An intermediate wear occurs in the dosing zone. Thus, if we take the wear of the worm in the compression zone as 100%, the wear in the loading zone is 10-15% and 80-120% in the dosing zone for unfilled polymers, and 23-71% for polymers containing secondary raw materials and fillers.Across the profile of the worm maximumwear was detected on the crests and the pushing faces of the worm loops, and also on the fillet (chamfer) at the transition from the recession to the pushing faces (see Fig. Id). The degree of wear of the recession is lower by a factor of 6-10 than that of the loop crests.The lowest wear is observed on the loop faces opposite to the pushing faces (tailing faces).In the average the wear of the extruder cylinder is lower by 60% than that of the worm [i]. However, it represents a more complicated, laborious, and consequently a more costly part; it is usually considered as a part of the equipment with a long life which can be replaced only in the case of an overhaul.As a result of this the production costs caused by excessive wear of the ...
When a polymer material moves in an extruder screw channel, an important role in creating conditions for mixing and heating the material is played by the friction between the material processed, the screw, and the cylinder. The friction is accompanied by a deleterious phenomenon, wear of the working members of the equipment.The wear of the working members of the equipment when plastics are processed depends on. the quality of its construction, the form of the material being processed, and the salient features of the technological proeessing. The principal causes of the wear can thus be divided into technological (depending on the processing conditions, the form of the material processed, and the operating conditions of the equipment) and design causes (associated with the distinctive features of the construction, the material, and the manufacturing process of the parts) [1].The objective technological causes of the equipment wear are: a faster processing rate, higher outputs of new polymer materials that cause more wear, and larger bulk, thermal, and chemical loads on the working members. According to the data of [2], a faster processing rate (as a result of higher temperatures and pressures) shortens the equipment lifetime three to four times.The "filler factor," on which the abrasability of the processed composition depends, is the leading factor that determines the rate of wear. Most fillers are based on compounds with a Mohs' hardness of 1 to 7. Thus, asbestos, kaolin, limestone, silica flour, glass fiber, refractory compounds (carbides, borides, nitrides, oxides), metal powders, etc. are used as fillers [3]. The rate of wear increases abruptly when compositions with a filler are processed [1].
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