Wear is a very common phenomenon in machining process, which may be caused by many factors, such as workpiece material, environment, processing method, etc. Mechanical wear will have adverse effects on the processing quality, precision and efficiency of products. Therefore, for those who are engaged in machining industry, it is very important to do a good job in the prevention of mechanical wear.
Common types and characteristics of mechanical wear
The common wear types in machining mainly include running in wear, hard grain wear, surface fatigue wear, thermal wear, phase change wear and hydrodynamic wear.
Running in wear is the wear of machinery under normal load, speed and lubrication conditions. This kind of wear generally develops slowly and has little impact on processing quality in a short term.
Hard grain wear refers to the damage of parts caused by mechanical cutting or grinding due to the abrasive particles falling from the parts themselves or the hard particles entering the machine tool from the outside, mixed into the processing area, which has a serious impact on the processing quality.
Surface fatigue wear refers to the damage of parts caused by tiny cracks or shift pits under the action of alternating loads. This kind of wear is usually closely related to such factors as pressure, load characteristics, machine material, size, etc.
Hot wear refers to the phenomenon that the heat generated in the friction process acts on the parts, causing them to temper, soften, burn and wrinkle. This kind of wear usually occurs in high-speed and high-pressure sliding friction, and the wear is destructive, accompanied by the nature of accident wear.
Corrosive wear is a chemical action, that is, chemical corrosion causes wear. When the part surface contacts with acid, alkali, salt liquid or harmful gas, it will be subject to chemical erosion, or the part surface will combine with oxygen to generate hard and brittle metal oxides that are easy to fall off, which will wear the part.
Phase change wear refers to the wear of parts caused by the long-term operation of parts under high temperature, the metal structure grains on the surface of parts become larger when heated, and the grain boundaries are oxidized around, resulting in small gaps, which make the parts fragile and reduce wear resistance.
Hydrodynamic wear is the wear of the part surface caused by the impact of liquid or particles mixed in liquid on the part surface at a fast velocity.
Causes of Parts Wear and Preventive Measures
Some wear belongs to the category of normal wear, such as mutual friction between parts, wear caused by hard particles, fatigue wear of parts under long-term alternating load, corrosion of parts by chemical substances, and changes in metallographic structure or matching properties of parts surface under high temperature conditions.
For the mutual friction between parts, ensure that the parts are clean and lubricated enough. For wear caused by hard particles, it is necessary to prevent parts from being exposed and ensure that parts are clean and covered. For the fatigue wear of parts caused by long-term alternating load, eliminate the clearance and select appropriate lubricating grease, which can reduce the additional vibration of the system and improve the machining accuracy of parts. For the corrosion of chemicals on parts, harmful chemicals must be removed and the corrosion resistance of parts must be improved. For changes in the metallographic structure or matching properties of the part surface under high temperature conditions, efforts should be made to improve the working conditions, or the parts should be made of high temperature resistant and wear-resistant materials.
Abnormal wear includes wear caused by failure of repair or manufacturing quality to meet design requirements, wear caused by violation of operating procedures, and wear caused by improper transportation, loading and unloading, and storage. To prevent this kind of wear, we should strictly check the product quality, be familiar with the mechanical properties, operate carefully, master enough lifting knowledge, and be careful in operation to avoid improper operation.
If the machine has been overhauled, its service life may be shortened, which may be caused by deformation of basic parts, damage to the balance of parts, failure to perform running in and low hardness of parts.
The deformation of basic parts will change the relative position of each part, thus accelerating the wear of parts and shortening the life of parts. Reasonable installation and adjustment can be adopted to prevent deformation. Part balance destruction refers to the unbalance of high-speed rotating parts, which accelerates part damage and shortens part life under the action of centrifugal force. Strict action balance test measures shall be taken to prevent. Running in of replaced parts without matching surface will increase wear, so it is necessary to run in the accessories. The repaired parts were improperly selected, the surface hardness could not be reached, or the heat treatment was unqualified. Materials shall be selected as required, and reasonable heat treatment shall be carried out.