Wear is the main form of component failure. The parts that fail due to friction and wear in general machines account for 70% to 80% of all scrapped parts. Wear is inevitable, but we can reduce or slow down wear based on our understanding of the wear results.
Wear is a phenomenon of mutual loss between the contact surfaces of moving friction pairs, and is the main and common form of component failure. The metal lubrication medium metal interaction between the friction pairs of agricultural machinery movement is extremely complex, and the forms and effects of action between each part make the wear process and reasons of the friction surface very complex. However, it is generally believed that the wear and tear of friction surfaces are mainly related to mechanical factors (elastic and plastic deformation, vibration); Molecular physical factors (diffusion, heating, adsorption, contact melting); Chemical factors (chemical adsorption, electrochemistry, decomposition and formation of polymer chains in lubricating oil), etc. Therefore, wear is the sum of mechanical, physical, and chemical phenomena. Wear and tear will seriously affect the lifespan and reliability of machines, leading to a decrease in mechanical efficiency and an increase in energy consumption. The parts that fail due to friction and wear in general machines account for 70% to 80% of all scrapped parts. There are multiple explanations for the process and causes of wear, and different explanations also explain the process and mechanism of wear to a certain extent. Although the observed phenomena and conclusions are limited by experimental conditions and cannot be used to explain and summarize all wear phenomena, we can analyze and propose technical measures to reduce or slow down wear based on our understanding of wear results.
1. Analysis of Main Wear Forms of Agricultural Machinery Parts
The wear of agricultural machinery parts mainly includes abrasive wear, adhesive wear, and corrosion wear. The following will analyze their characteristics and principles.
1.1 Abrasive wear
The hard abrasive particles that enter between the surfaces of friction pair parts have a "cutting" effect on the surface of the parts during relative motion, causing surface wear of the parts, which is called abrasive wear. Abrasives may enter from the outside world (such as dust and impurities in oil), or they may already exist on the friction surface (such as sand in castings or impurities in plated parts), or they may be products of the wear process (such as the peeling of metal oxide films). The rate of abrasive wear is directly proportional to the motion speed of the friction pair; The higher the hardness of the abrasive, the greater the wear; When the abrasive size is similar to the clearance between the mating pairs, the wear amount Z is greater. Abrasive wear is prone to occur between parts with high motion speed, high load, and easily mixed impurities on the friction surface, such as between the crankshaft main journal and the main bearing, between the connecting rod journal and the bearing, between the piston, piston ring and cylinder wall, and between the valve guide and valve stem. After a certain period of use, most of these parts have obvious traces of abrasive wear on their surfaces.
1.2 Adhesive wear
When the friction surface of a part is subjected to excessive mechanical and thermal loads, it embeds with each other and produces plastic deformation, causing local high temperatures and being in a molten state. Relative sliding causes the surface material of the part to transfer or break, and this phenomenon is called adhesive wear. The degree of adhesive wear is related to the strength of the adhesive point. If the strength of the adhesive point is lower than the surface strength of the friction pair, tearing or material transfer occurs at the adhesive point, and the material transfer between the two friction surfaces is extremely slight. The friction surface is also relatively smooth, with only slight scratches, which is usually referred to as external adhesion. If the strength of the adhesive point is higher than that of the material on one side of the two friction surfaces, tearing or material transfer will occur on the weaker friction surface material, causing local rough tearing damage on the weak material surface, which is usually referred to as internal adhesion. In most cases, adhesive wear on the friction surface results in both internal and external adhesion, with some adhesive points separating from the outside and others from the inside. On rough friction surfaces with high contact load, poor lubrication conditions, insufficient cooling strength, and high relative sliding strength, it is easy to experience adhesive wear. Moreover, the higher the surface load and temperature of the parts, the more severe the adhesive wear phenomenon. Once adhesive wear occurs, it develops rapidly and can cause serious damage to parts in a short period of time, as well as leading to major accidents in diesel engines. The mating surfaces of the cylinder, piston, and piston rings of a diesel engine, as well as the mating surfaces of the journal and bearings, are high-risk areas for adhesive wear. Improper use, incorrect maintenance and adjustment, and inadequate material and surface quality of parts can easily lead to adhesive wear.
1.3 Corrosion and wear
The surface of a part, due to the action of corrosive gases or liquids, undergoes electrochemical reactions to form a chemical reaction film. Under mechanical loads, surface friction causes the chemical reaction film to detach from the base metal, forming a new reaction film that is then destroyed. This recurring phenomenon is called corrosion wear. Corrosion and wear are generally divided into two categories: oxidation corrosion and special medium corrosion. Oxidative corrosion wear is commonly present in the friction of diesel engine parts, and its damage feature is that the friction surface of the metal exhibits uniform and fine wear marks along the sliding direction. The wear rate of oxidative wear is Z small among various types of wear. The performance of the oxide film on the friction surface plays an important role in the wear of parts. The oxide film formed on the surface of the parts can reduce the friction coefficient and wear rate of the parts, improve their resistance to abrasive wear, and also help prevent adhesive wear. Diesel engines should reduce the frequency of high load operation and the working time at full speed and full load during operation to avoid damage to the oxide film and extend the service life of the diesel engine. Special medium wear is caused by the corrosion of friction pair parts with acid, alkali, salt and other media, which destroys the oxide film under load and friction. This oxidation wear has a higher wear rate and greater wear amount. The cylinder wall of a diesel engine is an area where special media corrosion and wear often occur. The elements such as lead and chromium in the bearing alloy are easily corroded by acidic substances in lubricating oil, forming black spots on the surface of the bearing anti-wear alloy, gradually expanding into sponge like soft tissue and causing small pieces to fall off.
2. Measures to reduce wear and tear
(1) Newly purchased or overhauled large agricultural machinery must undergo strict running in operation before it can be put into operation to avoid scratches and burns caused by local overload and overheating, resulting in abnormal wear and tear.
(2) Carry out maintenance work as required, keep the oil, water, gas and other systems clean, and reduce abrasive wear caused by the intrusion of abrasive particles.
(3) Ensure that the lubrication system is working properly, select the correct lubricating oil, replace the lubricating oil in a timely manner, ensure that the oil circuit is unobstructed and the oil pressure is normal, and prevent dry friction from occurring.
(4) Keep the engine temperature within the normal range. If the engine temperature is too low and the cylinder does not receive good lubrication, the wear of the cylinder wall will increase, and the water vapor in the cylinder is prone to condense into water droplets, dissolving acidic gas molecules in the exhaust gas and generating acidic substances, causing corrosion and wear on the cylinder wall. If the temperature is too high, it will reduce the strength of the cylinder, and at the same time, the lubricating oil film will be damaged due to high temperature, causing increased wear on the cylinder wall.
(5) Proper operation and use of machinery can effectively reduce wear and tear by avoiding prolonged operation under excessively cold or hot conditions, maintaining the normal technical condition of the machine.
2023 December 5th Week VAFEM Product Recommendation:
Agricultural machinery requires better seals for contaminated conditions, provisions for misalignment, and economical mountings for shafts and housings. VAFEM offers bearings for disc harrows, planters, mowers, rakes, all types of balers, tillage, seeding and forage harvester equipment, combines, cotton pickers/stripers, and other agricultural equipment like silo unloaders and grain elevators.
We also offer a complete line of insert ball bearings, shaft mounted with either tapered adapters or locking collar or set screws. Our proven seal designs include low torque shields to heavy-duty triple lip seals. Disc harrow bearings are also available with either round, square, or hexagonal bores. All bearings are available with or without re-lubrication holes.
https://www.vafem.com/products/Agricultural-Bearings/775.html
2023-12-28