How to determine the heating installation temperature for self-aligning roller bearings?

When determining the heating installation temperature for self-aligning roller bearings, it is necessary to comprehensively consider various factors such as the bearing material, the fit interference amount, and the installation environment. The following are the specific methods and precautions for determination: 
### 1. Core Influencing Factors Analysis
#### 1. **Bearing Material and Heat Treatment Characteristics**
- **Common Materials**: Radial roller bearings typically use high-carbon chromium bearing steel (such as GCr15), and their tempering temperature is generally between 150℃ - 180℃. The heating temperature should be lower than the tempering temperature (usually ≤ 120℃) to avoid a decrease in material hardness and loss of dimensional accuracy due to excessively high temperatures.
- **Special Materials**: If the bearing uses special materials such as ceramics or stainless steel, the temperature range recommended by the manufacturer should be followed (for example, the heating temperature for ceramic bearings can be appropriately increased, but generally not exceeding 150℃). 
#### 2. **Matching Interference and Installation Requirements**
- **Low interference (light interference fit)**: The heating temperature can be controlled within 80℃ - 90℃. At this point, the expansion of the bearing inner hole is sufficient to meet the installation requirements (for example, for a bearing with an inner diameter of 100mm, the inner hole expands by approximately 0.08 - 0.10mm at 80℃).
- **High interference (heavy interference fit)**: The temperature can be increased to 90℃ - 100℃, but the expansion must not exceed the tolerance requirements for the fit (for example, for a bearing with an inner diameter of 200mm, the inner hole expands by approximately 0.20 - 0.25mm at 100℃).
- **Formula for calculation**:
Inner hole expansion (ΔD) = D × α × ΔT
Where: D is the inner diameter of the bearing (mm), α is the linear expansion coefficient of the material (approximately 11 × 10⁻⁶/℃), ΔT is the temperature rise (℃).
**Example**: For a bearing with an inner diameter of 100mm, heated from 20℃ to 100℃, ΔT = 80℃, ΔD = 100 × 11 × 10⁻⁶ × 80 ≈ 0.088mm. 
#### 3. **Installation Environment and Matching Components**
- **Environmental Temperature**: If the installation site has a low temperature (such as during outdoor operations in winter), it is necessary to appropriately increase the heating temperature (by 5°C - 10°C) to prevent insufficient expansion of the bearing before installation due to rapid heat dissipation.
- **Shaft Material**: When the shaft is made of steel, the normal temperature is sufficient; if the shaft is made of cast iron (with a lower linear expansion coefficient), the temperature may need to be increased to 90°C - 110°C to ensure the clearance between the bearing and the shaft.

### 2. **Specific Steps for Determining Temperature**
#### 1. **Refer to the Technical Manual of the Bearing Manufacturer**
- Most brands (such as SKF, FAG, NSK) will clearly recommend the heating temperature range (usually 80°C - 120°C) in their manuals. For example:
- SKF radial roller bearings recommend a heating temperature of ≤ 120°C;
- Domestic bearings usually recommend 80°C - 100°C.
- If the manual does not specify, contact the supplier to obtain the temperature parameters for the specific model. 
#### 2. **Calculate the temperature rise based on the fit interference amount**
- **Step 1**: Determine the required minimum expansion amount (ΔD_min), which must meet the installation gap requirements for interference fit (generally 1.5-2 times the interference amount).
For example: The interference amount is 0.05mm, ΔD_min = 0.075 - 0.10mm.
- **Step 2**: Reverse calculate the temperature rise ΔT using the expansion formula: ΔT = ΔD_min / (D × α).
Example: D = 100mm, ΔD_min = 0.10mm, ΔT = 0.10 / (100 × 11 × 10⁻⁶) ≈ 91℃. That is, heating to 20℃ + 91℃ = 111℃, but it needs to be controlled within a range of ≤ 120℃. 
3. **Take into account the temperature error of the heating equipment**
- The temperature control accuracy of the induction heater is relatively high (±5℃), and it can be set according to the calculated temperature;
- The oil bath heating has poor temperature uniformity, so the set temperature needs to be increased by 5℃ - 10℃ (for example, if the target temperature is 100℃, the actual set temperature should be 105℃), and the temperature in the middle of the oil tank should be monitored in real time using a thermometer. 
#### 4. **Simulation Testing and Verification**
- For the first-time installed bearing model, you can first select the same specification of used bearings for heating tests:
- Heat them to the preset temperature and then measure whether the change in the inner hole size conforms to the calculated value;
- Try to install them. If there is any jamming or looseness, adjust the temperature and repeat the test (each adjustment range of 5℃ - 10℃).

### **III. Prohibitions and Safety Limits for Temperature Control**
- **Absolute prohibition of exceeding 120℃**: Exceeding this temperature may cause the following issues for the bearings:
- The hardness of the rollers and raceways to decrease (for example, GCr15 steel may lose 2-3 HRC hardness when heated above 120℃);
- Deformation or aging of the cage (especially for plastic or brass materials).
- **Avoiding excessively low temperatures**: If the temperature is insufficient (e.g., <80℃), the insufficient expansion of the inner hole may result in excessive installation resistance, potentially scratching the shaft neck or causing damage to the bearing.
- **Real-time temperature monitoring**: Use thermocouples or infrared thermometers to directly measure the temperature of the inner ring of the bearing (not the temperature displayed by the equipment), for example:
- During induction heating, the temperature of the inner ring of the bearing should reach the set value and remain for 1-2 minutes;
- During oil bath heating, the bearing must be fully immersed and the oil temperature should be stable for 10-15 minutes (ensuring consistent temperatures for both the inner and outer rings). 
### **Summary**
The core logic for determining the heating temperature is as follows: set the upper limit at the "material safety temperature" and the lower limit at the "expansion amount required for the fit clearance". Adjust dynamically based on the equipment characteristics and installation environment. In practice, it is recommended to first refer to the manufacturer's data and conduct dual verification through theoretical calculations and on-site tests to ensure that the temperature is controlled within the safe range of 80°C - 120°C, while avoiding bearing failure or installation problems caused by temperature deviations.