â‘¡Maintenance knowledge of mechanical parts
Mechanical faults can generally be divided into two types: accidental faults and natural faults. Accidental faults are mostly caused by improper maintenance or adjustment, violation of operating rules, etc., and should be avoided as much as possible. Although natural failure is difficult to avoid, it can extend the effective working time of the machine by improving the level of use and maintenance.
There are three main failure modes of mechanical parts: fracture, deformation and surface failure. The following introduces the wear, deformation, cleaning methods and disassembly of printing machinery parts.
a) Wear of printing machinery parts
During the working process of a machine, if the size, shape and surface quality of the surface of a relatively moving part change, it is called wear.
The main causes of parts wear are friction and molecular gravity. Wear can be divided into abrasive wear, mechanical friction wear and adhesive wear. The reasons that affect the wear of mechanical parts are generally: speed, pressure, lubrication, temperature, material, processing and coordination.
b) Deformation of printing machinery parts
In the maintenance process, wear is one of the main factors of mechanical damage, but the slight deformation of parts is easy to be ignored. Often, after the repaired worn parts are assembled, the technical performance of the machine does not meet the requirements. This is related to metal deformation. In actual production, the deformation of the basic part should be paid special attention, because if the basic part is deformed, it will affect the mutual relationship of all parts assembled on this basic part and the mechanical performance of the mechanism. Therefore, in the repair process of parts, we must check both the wear of the mating surface and the mutual position accuracy of the parts (especially the basic parts)? For the mechanical deformation of the first overhaul, we must pay attention to its internal stress. Is there any deformation after 12 to 20 months? For hot-worked parts, corresponding measures should be taken to remove internal stress.
â‘¢ Disassembly and assembly of printing machinery
Mechanical repair personnel have to face the problems of disassembly and assembly when repairing printing machinery, especially assembly, which will directly affect the performance of the machinery. The assembly quality is not high, which will cause serious wear and tear of the machinery.
a) Mechanical disassembly
Because there are many types of printing machinery and the shapes of parts are different, it is difficult to describe them one by one. Here are the general disassembly principles.
First, before disassembling, you must understand the structure, function, and principle of the machine, and first consult the relevant technical information and instructions. From the practical point of view, determine the dismantled parts, the parts that can not be dismantled should not be disassembled as much as possible, but for the parts that are not disassembled, they must go through overall inspection to ensure quality.
Secondly, in the process of disassembly, the order of surface and inside should be used to disassemble, first remove the external accessories, tubing, etc., and then disassemble in the order of the assembly first and then the parts. List the numbers and avoid untidy stacking. It is also important to use tools reasonably during disassembly. Tools must be compatible with the parts being disassembled. If you want to remove the threaded connector, you need to use a suitable wrench, and you need to use special tools to remove the static fittings.
In addition, the disassembly should create conditions for assembly, and the non-interchangeable parts should be marked or placed in pairs to facilitate reset during assembly. This can ensure assembly accuracy and reduce unnecessary wear.
b) Mechanical assembly
During assembly, the matching accuracy and dimensional accuracy must be guaranteed. In order to ensure the matching accuracy, the matching method, repair method and adjustment method can be used during assembly. The dimensional accuracy mainly refers to the degree of error of the assembly size of each part in the assembly, that is to say, in the assembly, it is necessary to pay attention to eliminate the cumulative error to avoid adverse effects on the machine due to the increase of the cumulative error.
Sealing in assembly is also very important. In printing machines, sealing is mainly used for air pumps, gear boxes and other parts. Air leakage and oil leakage will occur when the seal fails. Therefore, the sealing material used in the repair should be appropriate, the assembly should be reasonable, the liquid sealant should be used for static sealing, and the dry adhesion type, dry peelable type, and non-dry sticky type should be adopted according to the different nature of use. And semi-dry viscoelastic types and other varieties.
The preparatory work before assembly must not be overlooked. Its contents include inspection before assembly, cleaning during assembly and assembly of components. The last is the trial operation after assembly, which has two functions. One is to check the quality of the assembly; the other is to adjust the machinery.
c) Cleaning of mechanical parts
The cleaning of mechanical parts is an indispensable part of machine repair. The cleaning content is mainly to remove oil and rust.
There are three methods for degreasing and cleaning: alkaline solution degreasing, organic solvent degreasing, and metal cleaning and degreasing. The alkaline solution mentioned here is mainly the alkaline solution with emulsifier added, which has a good effect on cleaning mineral oil. The so-called organic solvent generally refers to gasoline, kerosene, etc. It can dissolve various fats and oils without damaging parts. In addition to gasoline and kerosene, alcohol, acetone, and ether can be used for small parts and adhesive parts with high accuracy. And other organic solvents. The metal cleaning agent is a new type of synthetic detergent. It has a variety of functions such as wetting, penetration, emulsification, and dispersion due to the reduction of interfacial tension of the base surface active substance, which makes it have a strong decontamination ability. The use of this cleaning agent is non-toxic, non-corrosive, non-flammable, non-explosive, non-polluting, and has a certain rust prevention ability, and the cost is also low, and it has been widely used.
Derusting and cleaning methods mainly include mechanical methods and chemical methods. Mechanical derusting is generally carried out with wire brushes, scrapers, emery cloth, etc., and sometimes electric grinding wheels and wire wheels can also be used. Mechanical descaling is easy to leave scratches on the working surface, and it is only suitable for derusting the surface of unimportant parts. Chemical rust removal generally uses hydrochloric acid, sulfuric acid and phosphoric acid to remove alkaline metal oxides. The method is simple and the rust removal effect is good. When using this method to remove rust, it is necessary to grasp the concentration ratio of the solvent.
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