In the process of assembly of mechanical transmission system, the assembly mode of bearing directly affects the service life, reliability and operation performance of equipment. For the interference fit structure between bearing and shaft and bearing and seat hole, reasonable selection of hot or cold assembly technology combined with size expansion theory has become an important technical means in the field of mechanical assembly.

This paper will systematically sort out the technical principles, application conditions, process flow and matters needing attention of bearing hot installation and cold installation, so as to help assembly personnel to complete high-quality bearing installation work scientifically and standardly.

1.Overview of the principle of hot and cold bearing installation

For the interference fit structure, with the help of the principle of thermal expansion and cold contraction, it can effectively reduce the external force impact in the assembly process and avoid bearing damage:

✅ Hot fitting (inner ring expansion assembly)

By heating the inner ring of the bearing, it expands more than the actual size of the shaft and is easily assembled to the shaft.

Suitable for the structure of the inner ring and shaft fit as interference, and the outer ring and seat hole fit as clearance.

✅ Cold assembly (outer ring contraction assembly)

By cooling the outer ring of the bearing, its contraction is smaller than the seat hole size, which facilitates smooth assembly.

Suitable for the structure of the outer ring and seat hole fit as interference, inner ring and shaft fit as clearance.

Through scientific control of heating or cooling, avoid violent impact and damage, to achieve efficient and reliable assembly effect.

2.Application and process specifications of hot fitting technology

Common hot loading heating methods

Calculation of dimensional expansion during hot installation

According to the thermal expansion formula:

among ：

ΔD: Diameter expansion (mm)

D0: original inner diameter of bearing (mm)

α: Material linear expansion coefficient (steel is about 11×10⁻⁶/℃)

ΔT: heating temperature difference (℃)

For example, the inner diameter of a bearing is 100mm and the heating is 80℃. The theoretical expansion is about:

Enough to overcome the conventional fit and achieve smooth assembly.

⚠ Precautions during hot installation

The heating temperature should be controlled to not exceed 120℃. The excess part should be based on the bearing manufacturer's standard to avoid affecting the material structure and hardness.

Uniform heating to avoid local overheating or excessive temperature difference, prevent bearing deformation.

Clean the surface before assembly and remove oil and impurities.

After the heating is completed, assemble as soon as possible to prevent the temperature drop from weakening the expansion effect.

3 Application and process specifications of cold installation technology

Common cold installation cooling methods

 Calculation of size shrinkage during cold installation

Similarly, based on the reverse calculation of thermal expansion:

pay attention to ：

Δ T is negative, indicating a decrease in temperature.

The normal temperature of liquid nitrogen is-196℃, and the cooling range is large, which is suitable for high interference structures.

for instance ：

The outer diameter of a bearing is 200mm, the cooling is 150℃, and the theoretical shrinkage is:

Easy to overcome the conventional overplus, safe and reliable.

⚠ Precautions during cold installation

Use special insulation container to ensure the safety of liquid nitrogen operation.

During the cooling process, the bearing should be completely immersed and cooled evenly.

Wear protective equipment to avoid frostbite caused by contact with liquid nitrogen on the skin.

During the bearing return temperature after assembly, the environment should be kept dry to prevent condensation water vapor from causing corrosion.

4Scope of application and restrictions of hot and cold installation

restrictive condition ：

Before hot mounting and cold mounting, the mating structure design must be strictly confirmed to prevent assembly damage caused by misjudgment.

For large size or high precision bearings, standardization methods such as induction heating and liquid nitrogen cooling are preferred.

The temperature and time of heating and cooling must be strictly controlled to avoid affecting the material performance and assembly accuracy.

5Common problems and technical suggestions❗ Common misconceptions

The heating temperature is too high, resulting in bearing tempering and hardness reduction;

After cold installation, the temperature is not controlled and the bearing warms up, and the residual internal stress affects the operation of the bearing;

Non-dedicated tool auxiliary assembly leads to uneven deformation of the bearing raceway;

The assembly surface is not clean, which affects the actual interference effect.