Maintenance precautions for square hole agricultural machinery bearings

Square hole agricultural machinery bearings are key components used in agricultural machinery (such as tractors, harvesters, rotary tillers, etc.) to transmit power and support rotating parts. Their square hole structure (usually square or rectangular) cooperates with the transmission shaft and needs to withstand high loads, frequent starts and stops, and harsh environments (such as mud, water, and high temperatures). To ensure the service life of bearings and the reliability of agricultural machinery, the following matters should be paid special attention to during maintenance:

1. Daily inspection and cleaning

Appearance inspection

Wear of square holes:

Regularly check whether there are scratches, deformations or excessive wear on the inner wall of square holes (the standard diameter deviation is usually H7~H9). If the fit clearance between square holes and shafts exceeds 0.3mm, bearings should be replaced or shaft holes should be repaired in a timely manner (such as reprocessing after welding);

Check if there are cracks at the edge of the square hole due to impact. If the crack length exceeds 5mm, the bearing needs to be replaced.

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Sealing status:

Confirm whether the dust cover and rubber sealing ring are intact, without damage or detachment, to prevent mud and sand from entering the interior of the bearing;

; If the seal is aging (such as rubber hardening or cracking), it is necessary to replace it with a seal of the same model (priority should be given to choosing oil resistant and high temperature resistant materials).

Cleaning and maintenance

Removing foreign objects:

After operation, use high-pressure air (pressure ≤ 0.6MPa) to blow away mud, straw, and other debris from the bearing surface and square hole to avoid hard particles getting stuck in the mating surface;

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It is forbidden to use water or steam to directly rinse the bearings (which may cause grease emulsification failure). If cleaning is necessary, diesel or specialized cleaning agents can be used to wipe and air dry.

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Rust prevention treatment:

When parked for a long time, apply a thin layer of rust prevention oil (such as mineral oil type rust prevention oil) on the surface of the bearing and wrap it with plastic film to prevent rusting.

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2. Lubrication Management

Lubricating grease selection

Type matching:

Select lubricating grease according to the working environment temperature:

Low temperature environment (<-20 ℃): Select lithium based low-temperature lubricating grease (drip point ≥ 180 ℃, low low-temperature torque);

;

High temperature environment (>50 ℃): Choose composite lithium based or polyurea based grease (drip point ≥ 250 ℃, resistant to high temperature oxidation);

Dusty environment: Use extreme pressure grease containing molybdenum disulfide (MoS ₂) to enhance wear resistance.

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Performance requirements:

The cone penetration of lubricating grease (25 ℃) should meet the bearing load requirements:

For light loads (such as small rotary tillers): choose 310-340 (0.1mm) soft grease;

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Heavy loads (such as large tractors): Use 265-295 (0.1mm) of stearic acid.

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Filling specifications

Filling amount:

The filling amount of lubricating grease in the bearing chamber is 1/3~1/2 space. Too much will cause an increase in stirring heat, and too little will result in insufficient lubrication;

; The mating surface between the square hole and the shaft needs to be coated with a thin layer of lubricating grease (with a thickness of about 0.1-0.2mm) to reduce wear.

Replacement cycle:

Replace lubricating grease after continuous operation for 200-300 hours or quarterly operation;

; If the lubricating grease turns black, clumps, or contains metal powder, it should be replaced immediately and the bearings checked for damage.

III. Key points for installation and disassembly

Installation specifications

Shaft and hole fit:

Before installation, clean the surface of the shaft and square hole, remove burrs and oil stains, and ensure a smooth fit surface;

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Use a press or specialized tool to slowly press in the bearing, and do not directly strike with a hammer (which may cause deformation of the square hole or cracking of the bearing inner ring);

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The interference fit should meet the design requirements (usually 0.01~0.03mm), and insufficient interference fit can cause looseness during operation.

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Alignment adjustment:

After installation, check the coaxiality (deviation ≤ 0.1mm) of the bearing and transmission parts to avoid additional load due to eccentricity; Adjust the bearing clearance (such as through washers or nuts) to ensure there is no jamming or abnormal vibration during operation.

Disassembly precautions

Tool selection:

Use a puller or hydraulic disassembler to disassemble the bearing, and do not forcefully pry it out with a pry bar (which may damage the square hole or shaft);

; If the bearing and shaft rust, they can be soaked in penetrating oil (such as WD-40) for 24 hours before disassembly.

Damage inspection:

After disassembly, check whether there are any strains or indentations on the shaft and square hole. If the damage depth is greater than 0.05mm, it needs to be repaired or replaced;

; Record the reasons for bearing disassembly (such as wear and tear, fracture) to provide reference for subsequent maintenance.