Abstract: Wear is the main form of component failure. 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.

Keywords: agricultural machinery; spare parts; Wear characteristics

0 Introduction

Wear is a phenomenon of mutual loss between the contact surfaces of motion friction pairs, and is the main and common form of component failure. The metal lubricant metal interaction between the friction pairs of agricultural machinery is extremely complex in terms of the form and effect of the interaction between each part, making the wear process and causes of the friction surface very complicated. But it is generally believed that the wear and tear of friction surfaces is 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 the machine, reducing mechanical efficiency and increasing energy consumption. 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 within a certain range. 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 the wear results.

1 Analysis of the main wear forms of agricultural machinery parts

The wear of agricultural machinery parts mainly includes abrasive wear, adhesive wear, and corrosive wear. The characteristics and principles of these are analyzed below.

1.1 Abrasive wear

The hard abrasive particles that enter between the surfaces of the friction pair parts produce a "cutting" effect on the surface of the parts during relative motion, causing wear on the surface of the parts, which is called abrasive wear. Abrasives may enter from the outside (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 peeling off 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 size of the abrasive is similar to the clearance of the mating pair, the wear amount Z is large.

Abrasive wear is prone to occur between parts with high motion speed, high load, and easily mixed impurities on friction surfaces, such as between the crankshaft main journal and main bearing, between the connecting rod journal and 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 component is subjected to excessive mechanical and thermal loads, it becomes embedded and undergoes plastic deformation, causing local high temperatures and melting. Relative sliding causes the material on the surface of the component 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 called external adhesion. If the strength of the adhesive point is higher than the material strength of one of the two friction surfaces, tearing or material transfer will occur on the weaker friction surface material, causing local rough tearing damage to the weak material surface, which is usually referred to as internal adhesion. In most cases, the internal adhesion and external adhesion of adhesive wear on the friction surface occur simultaneously, that is, some adhesive points separate from the outside and some adhesive points separate from the inside.

On rough friction surfaces with high contact loads, poor lubrication conditions, insufficient cooling strength, and high relative sliding strength, adhesive wear is prone to occur, and the greater 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, leading to major accidents in diesel engines. The mating surfaces between the cylinder, piston, and piston ring of a diesel engine, as well as the mating surfaces between the journal and bearings, are high-risk areas for adhesive wear. Improper use, incorrect maintenance and adjustment, and parts materials and surface quality that do not meet the requirements can easily lead to adhesive wear.

1.3 Corrosion and Wear

The surface of a component, due to the action of corrosive gases or liquids, generates a chemical reaction film through electrochemical reactions. 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 cyclic phenomenon is called corrosion wear. Corrosion and wear are generally divided into two types: oxidation corrosion and special medium corrosion.

Oxidative corrosion wear is commonly present in the friction pairs of diesel engine components, characterized by uniform and fine wear marks on the metal friction surface along the sliding direction. The wear rate of oxidative wear is Z small among various types of wear. The performance of oxide film on the friction surface plays an important role in the wear of parts. The oxide film formed on the surface of the component can reduce the friction coefficient and wear rate of the component, improve its resistance to abrasive wear, and also help prevent adhesive wear. Diesel engines should reduce the operating frequency of high loads and decrease the working time of 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 under the action of 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 wear-resistant 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 before being 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 works properly, select the correct lubricating oil, replace the lubricating oil in a timely manner, ensure smooth oil flow and normal oil pressure, and prevent dry friction from occurring.

(4) Keep the engine temperature within the normal range. If the engine temperature is too low, the cylinder will not receive good lubrication, and the wear of the cylinder wall will increase. In addition, the water vapor inside 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 of 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, which will aggravate the wear of 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, and maintaining the normal technical condition of the machine.

2025 March 3rd Week FK Product Recommendation:

Flange Cartridge Units:

They are units of rigid cast iron housings with piloted flange cartridge and wider inner ring bearing inserts.

Standard painting in green (other colors are available for choices).

Standard duty (FC200) and medium duty (FCX) are available for this series.

End caps by pressed steel are capable of protecting against external polution and dusts.

The self-aligning ability of the ball bearings can compensate for slight static mis-alignemnt of the shaft. The bearing inserts are locked onto the shaft by means of set screws, eccentric locking collars, adapter sleeves and concentric locking collars etc.

Lubricants filled inside the spherical ball bearing inserts can be standard grease, low/hight temperature grease and food grade grease.

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