Currently, there are still many counterfeit and inferior agricultural machinery parts on the market, especially some key parts, which seriously affect the use of agricultural machinery. At best, they affect the reliability of the machinery; at worst, they can cause accidents, affecting the safety of the machinery and personnel, and resulting in significant economic losses for users. In response to the product quality problems in the agricultural machinery parts market, based on years of market supervision and inspection experience, the author provides several simple and intuitive methods for identifying counterfeit and inferior agricultural machinery parts for farmers' reference.
1. Comparison Method
The comparison method relies on human touch and vision (and may also use a magnifying glass or comparison microscope) to compare the surface of the part being tested with a standard sample with known surface roughness values to determine the surface roughness of the part. The comparison method is simple, quick, and has a certain degree of accuracy, facilitating on-site inspection of the surface roughness of agricultural machinery parts. Generally speaking, for parts with a surface roughness Ra > 2.5 μm, direct visual inspection and comparison with a sample block are possible. If visual inspection alone is insufficient, one can use their palm, fingernail, or pin to run over the part or sample block and judge by feel. For example, the surface roughness Ra of the cast iron cylinder head top of a diesel engine is 3.2 μm, and the surface roughness Ra of the working surface of the shift fork head of a small four-wheel drive is 6.3 μm. For parts with a surface roughness Ra of 0.25–0.32 μm, a 5–10x magnifying glass is used for observation and comparison. For example, the surface roughness Ra of the bolt fit of the Dongfanghong-75 drive wheel is 1.6 μm, and the surface roughness Ra of the crankshaft main journal is 0.63 μm. For parts with a surface roughness Ra < 0.32 μm, a comparison microscope (magnification 25-50x) is used for comparison. For example, the surface roughness Ra of the sealing end face of the Dongfanghong-75 sealing ring is 0.2 μm, and the surface roughness Ra of the outer circle of the piston pin of the 195 diesel engine is 0.16 μm.
To ensure and improve the accuracy of the comparison method, the selected standard sample should ideally have the same processing method and texture, and the same geometric shape and material as the surface being measured.
2. Visual Inspection Method
During processing, handling, and storage, agricultural machinery parts often develop burrs, indentations, damage, or cracks due to vibration, impact, and collisions, affecting their use. The following are a few examples illustrating the basic requirements for parts:
(1) Damage to the mating surface of the cylinder head and engine block will cause poor sealing, cylinder leakage, and cylinder head gasket failure; burrs on the working surfaces of the cylinder liner and piston will cause cylinder scoring.
(2) The surface of shaft parts should be smooth, free of oxide scale, spots, dents, and burrs. The working surface should be free of scratches, black spots, knife marks, dents, dents, and rust.
(3) Castings should be free of obvious casting defects such as cracks, looseness, dents, and porosity.
(4) Wooden parts: mainly check if the material can be substituted, and whether there are cracks or deformations.
(5) Rubber parts: check for aging, as aged rubber products will lose their elasticity and crack.
(6) Quality inspection of V-belts: Good quality V-belts are soft to the touch, have good elasticity, and are relatively uniform in size without obvious unevenness in thickness; conversely, poor quality V-belts generally have two layers of cloth covering the surface; good quality V-belts have a dense and thick texture, while poor quality ones are less dense. Good quality rubber has a glossy black color and good elasticity; poor quality rubber has a dull gray color, poor elasticity, and excessive recycled rubber content. Good quality reinforcing layer has orderly arranged cords, generally in two or three rows; poor quality reinforcing layer cords are arranged haphazardly. The quality of the yarn itself directly affects the quality of the V-belt. Good yarn is generally a blend of cotton and nylon, without joints. When the yarn is peeled from the rubber, it is covered with rubber, indicating strong adhesion between the yarn and rubber. Poor-quality yarn is usually made of nylon, with more joints. When peeled from the rubber, there is no rubber adhering to the yarn. After a period of use, the yarn and rubber easily separate, causing the V-belt to lose its elasticity.
3. Weighing Method
This method is generally used to assess the quality of castings, such as track rollers, drive wheels, idler wheels, and track shoes, among other agricultural machinery parts. The weight of castings is specified in the machine's specifications; for example, the weight of track shoes is 8.58–9.86 kg. The castings themselves generally meet the standard requirements; only a few manufacturers, due to cost-cutting measures, produce castings with quality significantly different from the standard requirements.
4. Testing Methods
(1) Hardness Determination
For agricultural machinery parts requiring high hardness, such as gears, bearings, valve rocker arm shafts, and piston pins, a simple method can be used for inspection: Use a medium-tooth flat file (about 70-80% new) to slowly and forcefully file the surface of the part. If the file slips without producing iron filings, the hardness is very high, above HRC50; if the file slips slightly with a small amount of iron filings, the hardness is relatively high, between HRC40 and 50; if the file is obstructed and produces a lot of iron filings, the hardness is not high, below HRC40. Alternatively, a broken piece of a hacksaw blade can be used to scratch the part. Slipping without leaving a mark indicates high hardness; leaving a shallow mark indicates relatively high hardness; leaving a clear mark indicates low hardness.
(2) Material Determination
Cast steel parts produce a crisp sound when struck, and the machined areas are bright white. Touching them leaves no carbon black residue on the fingers. Ductile iron also produces a crisp sound when struck, but the machined areas are dark gray, and touching them leaves carbon black residue on the fingers. Gray cast iron produces a dull sound when struck, and the machined areas are dark gray in color. Touching it leaves black residue on the fingers. High-manganese steel parts are sometimes replaced with carbon steel; this can be determined by using a magnet. A weaker magnet indicates high-manganese steel, while a stronger magnet indicates carbon steel. High-manganese steel parts can also be replaced with silicon-manganese steel; this can be determined by the color of the rust. High-manganese steel rusts black, while silicon-manganese steel rusts red.
(3) Crack Inspection
Cracks in crankshafts and flywheels can lead to broken shafts, cylinder damage, and flywheel breakage during assembly. To check for cracks, suspend the part and tap it lightly with an iron rod. A clear, crisp sound indicates a good result, while a dull, hoarse sound may indicate a crack.
(4) Geometric Dimension Inspection
Some parts, such as shafts, thin-plate parts, and rubber parts, are prone to deformation due to improper manufacturing, transportation, or storage. To inspect shafts, place them flat on a glass counter and rotate them. Observe the light leakage at the point where the part contacts the glass. Light leakage indicates a bent shaft. When inspecting the clutch driven plate steel sheets or friction plates, lift them up and observe them in front of your eyes, or place them on a flat glass surface and use a height gauge to measure the height of the four edges to determine if they are bent.
Through years of market supervision and inspection of agricultural machinery parts and anti-counterfeiting activities, it has been found that over 90% of agricultural machinery parts dealers cannot identify substandard agricultural machinery parts. The quality problems of substandard agricultural machinery parts mainly include unqualified materials, inadequate or absent heat treatment, low machining precision, and non-compliance with dimensional, geometric, and surface roughness standards. Some of these quality problems are difficult to identify using the above methods, making it easy to pass off inferior products as genuine ones. Therefore, internal quality checks, especially on materials, heat treatment quality, dimensional tolerances, and geometric tolerances, are also necessary.
