The working environment of agricultural machinery self-aligning roller bearings is poor - with high dust, strong vibration, and frequent impact loads. The installation quality directly determines whether it can withstand the harsh working conditions on the ground. The installation methods are mainly divided into two categories: cold installation and hot installation. Conical bore bearings also have special installation methods such as tightening sleeves and hydraulic nuts. Below, explain every detail from five dimensions: pre installation preparation, cold installation method, hot installation method, special installation method for tapered hole bearings, and post installation inspection.
1. Preparation before installation - do not do this step, the environment must be clean and dry afterwards.
. There is a lot of dust on the agricultural machinery maintenance site, but the bearing installation area must be kept dust-free. Lay a clean layer of plastic cloth or cardboard on the ground, and all parts and tools should be placed on it, not directly on the muddy ground. Self aligning roller bearings are most afraid of sand particles entering the raceway. One grain of sand is like a groove, and the raceway can be worn out in a few days.
Check each part one by one. After opening the bearing box, do not rush to install it. Rotate the inner ring by hand to feel whether it is flexible, whether there is any jamming or abnormal noise. Check for scratches, peeling, rust on the raceway surface, and deformation of the cage. Simultaneously inspect the journal and bearing seat holes - the journal surface must be free of scratches, rust, and burrs, and the bearing seat holes must be free of casting burrs and sand residue.
Cleaning and oiling of mating surfaces.
. Wipe the shaft neck and bearing seat holes with a clean dust-free cloth dipped in anhydrous ethanol, wipe dry, and then apply a thin layer of light oil (oil or grease can be used) on the mating surface to reduce installation friction and prevent dry wear and tear. Be careful not to apply too much oil, as a thick oil film can reduce the actual interference and cause the bearing to loosen after operation.Confirm clearance and fit. After the installation of self-aligning roller bearings, a certain radial clearance needs to be retained to compensate for thermal expansion and shaft deflection during operation. Before installation, check the table according to the bearing model to confirm the recommended residual clearance value (usually check the clearance range corresponding to the bearing inner diameter). This is the goal of subsequent installation adjustments.
Tool preparation. Copper rod or copper sleeve (used for tapping and pressing), press machine or hydraulic press (used in large quantities), induction heater or oil bath heating tank (used for hot installation), torque wrench (used for locking nuts), inner diameter dial gauge (used for measuring clearance), plug gauge (used for inspecting end face adhesion), and heat-insulating gloves (used for hot installation parts).
2. Cold fitting method - used for small sizes and light interference fit
Applicable scenarios: bearings with small sizes (generally below 80mm inner diameter), small interference fit, and commonly used for temporary replacement on agricultural machinery maintenance sites.
.Heart rod pressure method. Insert the bearing onto the dedicated installation tube (core rod), with the outer diameter of the core rod slightly smaller than the inner diameter of the bearing. Use a press to evenly press the bearing onto the shaft. When pressing in, equal pressure must be applied to the entire circumference of the end face of the ring, and it is absolutely not allowed to only press one side, otherwise the bearing will tilt and the raceway will be subjected to force on one side, resulting in permanent deformation.
Copper rod tapping method (the most commonly used on-site manual method). Place the copper rod tightly against the inner ring end face of the bearing, and use a hammer to strike alternately and evenly along the circumference of the copper rod. Slowly install the bearing onto the shaft. The function of a copper rod is to evenly distribute the hammering force across the entire end face, avoiding direct damage to the raceway caused by hitting the bearing. When striking, it should be symmetrical, lightly tapped, and slowly installed, and excessive force should not be applied. If the inner ring of the bearing is large, a copper rod can be used to evenly apply force around the end face of the inner ring, and it is important to avoid hitting only one side.
Sleeve installation method. Similar to the principle of copper rod method, a sleeve made of soft metal (copper or low carbon steel) is directly pressed onto the bearing end face and struck with a hammer. Sleeve method is more labor-saving and uniform than copper rod method, especially suitable for slightly larger bearings. The inner diameter of the sleeve should be slightly smaller than the outer diameter of the bearing, and the end face of the sleeve must be completely in contact with the end face of the bearing.
The iron rule of cold fitting: Do not apply force to the wrong circle.
. When the shaft is tightly matched with the inner ring, only force can be applied to the end face of the inner ring; When the outer ring is tightly matched with the seat hole, only force can be applied to the outer ring end face. Never transmit pressure through rolling elements and retainers, otherwise the raceway and retainers will be crushed.III. Hot fitting method - must be used for large-sized and heavy interference fit
Applicable scenarios: when the bearing size is large (inner diameter of 80mm or more), the interference fit is large, cold fitting cannot be pressed in, or the fitting surface is damaged by pressing.
. This is the most commonly used installation method for large self-aligning roller bearings in agricultural machinery, such as the 222 and 223 series.The heating temperature is strictly controlled at 80-100 ℃, with a maximum not exceeding 120 ℃. Excessive temperature can cause annealing of bearing rings and rolling elements, resulting in a decrease in hardness and wear resistance, and a sharp reduction in lifespan. The heating temperature of bearings with seals and dust covers should not exceed 80 ℃, as the temperature resistance of seals is much lower than that of metals.
There are four heating methods, choose according to the site conditions:
Oil bath heating method (most recommended): completely immerse the bearing in the heating oil tank, maintain the oil temperature at 80-100 ℃ for more than 30 minutes (extend the large bearing appropriately), until the inside and outside of the bearing are isothermal.
. The oil bath is heated most evenly and will not overheat locally.Induction heating method: Use an induction heater to quickly heat the inner ring of the bearing. The heating time is short (about half of the oil bath time), but attention must be paid to avoiding local temperatures exceeding 100 ℃. The bearing needs to be continuously rotated to ensure uniform heating.
.Electric heating plate heating method: Place the bearing flat on a 100 ℃ electric heating plate, flip it several times to make the heating uniform. It is simple and practical, and can be used for both large and small bearings.
.Electric furnace heating method: Place it in a closed automatic temperature control electric furnace for uniform heating and accurate temperature control, suitable for heating multiple bearings in one batch.
.It is strictly prohibited to directly heat with an open flame.
. It is not possible to directly bake the bearings with a blowtorch or gas welding flame, as the local temperature is extremely difficult to control and the raceway can be annealed in just a few seconds.Key points for hot installation operation. Wear insulated gloves and quickly place the heated bearing onto the shaft, pushing it all the way to the bottom to ensure that the inner ring end face is in close contact with the shaft shoulder. After cooling and shrinking on the shaft, the bearing will tightly hold the shaft neck, which is the core principle of hot installation. Do not rotate the bearing during the cooling process to prevent scratches on the raceway.
After cooling, the locking nut must be tightened. After the bearing shrinks, if there is a locking nut or locking washer, it must be tightened immediately after the bearing is completely cooled to prevent axial clearance caused by the contraction of the bearing in the width direction. After tightening, use a feeler gauge to check if there is a tight fit between the inner ring end face and the shaft shoulder, and there should be no gap.
4. Special installation method for tapered hole self-aligning roller bearings - the most commonly used in agricultural machinery
A large number of tapered holes (inner taper 1:12) are used in agricultural machinery self-aligning roller bearings, which can be directly installed on tapered shafts or fitted on cylindrical shafts through tightening sleeves or backing sleeves.
. The core of cone hole installation is to control the interference by adjusting the clearance, and the clearance must be used to determine whether the installation is in place.Method 1: Install the tightening sleeve+lock nut
Applicable scenario: Install tapered hole bearings on cylindrical shafts, which are the most common in agricultural machinery.
.Installation steps:
Step 1, wear clean gloves, place the locking sleeve on the platform, and remove the locking nut.
.Step 2, clean the surface of the shaft. If a shaft with a shoulder requires a spacer ring, install it first.
.Step three, insert a screwdriver into the notch of the tightening sleeve, and place the tightening sleeve on the shaft, inserting it into the shoulder of the spacer ring, with the threaded side facing the shaft end.
. When installing on a shaft without a shoulder, pay attention to fitting the tightening sleeve in the installation position of the bearing.Step four, install the bearing on the tightening sleeve.
. When there is a spacer at the shoulder of the shaft, press the inner ring end face of the bearing against the spacer. Install the locking nut onto the tightening sleeve.Step 5, use a special wrench to tighten the locking nut to the end face of the bearing inner ring, and stop when the torque of the wrench increases significantly.
. Be careful not to overtighten, otherwise the clearance will be compressed and the bearing will overheat and lock up.Step six, measure the radial clearance. This is the most crucial step. Measure the radial clearance after installation with an inner diameter dial gauge, and compare it with the initial clearance before installation. The reduction in clearance is a reflection of the interference fit. According to the bearing inner diameter check table, confirm whether the residual clearance has reached the recommended installation clearance target value. If the clearance is too small (interference fit is too large), loosen the locking nut and fine tune the axial position before tightening again; If the clearance is too large (insufficient interference), continue to tighten the locking nut and measure repeatedly until the clearance meets the standard.
Step seven, after the clearance is qualified, use a locking washer or locking card to stop the locking nut.
. Lock washer stop: Remove the lock nut, align the inner claw of the lock washer with the shaft keyway, and then install the lock nut. After tightening, pull one outer claw of the lock washer into the outer diameter cut of the lock nut. Locking card locking: Align the outer diameter cut of the nut with the shaft keyway, insert the locking card and fix it with washers and screws.Step 8, after installation, apply lubricating oil to the bearings and cover them with plastic film to prevent dust.
.Method 2: Installation of hydraulic nut (recommended for large bearings)
Applicable scenario: Large self-aligning roller bearings, when manually tightening the locking nut is insufficient or precise control of clearance is required.
.The installation steps are similar to the tightening sleeve method, but the difference is that hydraulic nuts are used instead of manual tightening:
Install the hydraulic nut on the tightening sleeve and use a special wrench to tighten it against the inner ring end face of the bearing. At this time, the piston is in the unloading position.
. Connect the oil pipe of the oil pressure pump to the oil pressure nut, slowly press the control rod of the oil pressure pump to increase pressure, and the oil pressure gauge will move until the bearing clearance begins to change. Record the pressure value on the gauge and the radial clearance at this time. Based on the inner diameter of the bearing, find the recommended residual clearance as the target value, continue to apply pressure, and repeatedly measure the clearance until the target value is reached. Then remove the oil pipe, remove the oil pressure nut, replace the locking nut and stop it.The advantage of the hydraulic nut method is that it can precisely control the clearance, avoiding excessive manual tightening that may cause the clearance to be too small.
.Method 3: Disassemble the bushing installation (for tapered hole bearings with disassembly bushings)
Applicable scenario: In situations where frequent disassembly and assembly are required, disassembling the bushing can prevent damage to the shaft neck during disassembly.
.Installation steps:
Place the removal liner and locking nut sleeve on the platform, clean the shaft surface, and install the spacer ring on the shaft with the shoulder.
. Place the small inner diameter end of the bearing against the shaft shoulder or spacer ring, and loosen the bearing onto the shaft. Insert the small outer diameter end of the removal liner into the inner diameter of the bearing and match it with the bearing. When inserting, align the two to avoid end face interference and collision. Install the locking nut on the shaft so that the end face of the locking nut is pressed against the end face of the removal liner. Slowly tighten the locking nut and press the release liner into the inner diameter surface of the bearing until the torque of the wrench increases and stops. Record the initial clearance, continue tightening and repeatedly measuring according to the target clearance. After reaching the standard, remove the locking nut, replace the locking washer or locking clamp.Method 4: Oil injection installation method (hydraulic nut+oil injection, recommended for extra large bearings)
Applicable scenarios: Extra large self-aligning roller bearings, where the bearing taper hole is tightly matched with the tightening sleeve, and high-pressure oil is used to expand the inner ring of the bearing and reduce the torque of the locking nut.
.Installation steps: Place the bearing on the shaft, screw the hydraulic nut onto the shaft so that the piston faces the bearing.
. Tighten the nut by hand until it just touches. Pump lubricating oil (with a viscosity of approximately 300mm ²/s at 20 ℃) into the hydraulic nut until the pushing distance of the bearing reaches 2-2.4mm. During the pushing process, measure the clearance repeatedly until the target value is reached. Remove the oil pipe, remove the hydraulic nut, and replace the locking nut to stop it.