The process flow of bearing freezing assembly box mainly includes four steps: preliminary preparation, freezing treatment, heating treatment, removal and inspection. The following is a detailed introduction:
preliminary preparation
Cleaning work: Clean the bearings, bearing seat holes, and related components, remove oil stains, rust, burrs, and other impurities, ensure the cleanliness of the assembly surface, and avoid impurities affecting assembly accuracy and bearing performance.
Dimensional inspection: Measure the inner and outer diameters of the bearing and the size of the bearing seat hole, check whether the fit tolerance meets the requirements, confirm the roundness and surface roughness of the shaft, and provide accurate dimensional basis for subsequent assembly.
Preparation of tools and materials: Prepare liquid nitrogen, freezer, temperature sensor, heater (for heating stage to prevent frosting or freezing), temperature control instrument, mechanical arm or automation equipment (for placing and removing bearings), insulation material (such as cotton wool to reduce liquid nitrogen volatilization), etc. Meanwhile, depending on the size and shape of the bearings, specialized tools such as cooling buckets, cover plates, nozzles, and sleeves may need to be made.
Freezing treatment
Bearing placement: Place the cleaned bearings on the brackets or trays inside the freezing chamber, ensuring that the bearings are placed smoothly and in the appropriate position, avoiding direct contact with liquid nitrogen to ensure uniform cooling. If using auxiliary tools such as cooling buckets, the bearings should be correctly placed in the cooling buckets according to the design requirements and covered with cover plates.
Liquid nitrogen injection: precise introduction of liquid nitrogen into the processing chamber through a liquid nitrogen injection system. Liquid nitrogen can enter the cryogenic tank through spray, gas flow or direct injection. For example, in spray cooling, liquid nitrogen is injected into the cavity through the nozzle, forming cooling mist around the bearing, and rapidly reducing the bearing temperature; Gas flow cooling refers to the formation of a cold gas flow after the evaporation of liquid nitrogen, which covers the surface of the bearing and has a relatively uniform cooling effect; Direct injection refers to the direct injection of liquid nitrogen into the freezing chamber, which rapidly lowers the temperature of the bearing through the evaporation and heat absorption of liquid nitrogen.
Temperature control: The freezer is equipped with a high-precision temperature control system, consisting of temperature sensors, heaters, and temperature control instruments. The temperature sensor monitors the internal temperature of the chamber in real time. The heater is used to prevent frosting or freezing of the freezing equipment when the temperature is too low, maintaining uniform temperature. The temperature control instrument adjusts the temperature inside the freezer in real time based on the feedback of the temperature sensor, ensuring the stability of the temperature of the bearing during the freezing process and achieving the expected cooling temperature of the bearing (usually between -150 ℃ and -196 ℃).
Cooling time control: Based on the material and size of the bearing, the cooling time is precisely controlled to ensure that the bearing maintains a certain period of time (usually several hours) in a low-temperature environment, in order to achieve the ideal cooling effect, so that the physical properties of the bearing material change, such as residual stress and internal stress are released, and the crystal structure is improved, thereby improving the hardness, wear resistance, and fatigue resistance of the bearing.
Heating treatment
Slow heating: After the freezing treatment is completed, the bearing needs to be gradually heated to room temperature. The heating process needs to be carried out slowly, generally at a rate of 10-20 ℃ per hour, to prevent thermal stress and crack formation. It can be heated naturally or assisted by a heater, but the heating rate must be strictly controlled.
Temperature monitoring: During the heating process, continue to use temperature sensors to monitor the temperature changes of the bearings, ensuring a smooth and uniform heating process and avoiding damage to the bearings caused by drastic temperature changes.
Extraction and Inspection
Bearing removal: After the bearing is heated to room temperature, it can be removed by a robotic arm or manually. During the extraction process, attention should be paid to gentle operation to avoid collision or damage to the bearings.
Performance inspection: Conduct necessary checks and tests on the removed bearings, such as visual inspection, to check for defects such as cracks and deformations in the bearings; Dimensional inspection to confirm whether the size of the bearing has changed due to freezing treatment; Performance testing, such as hardness testing, wear resistance testing, etc., to confirm whether its performance has achieved the expected effect.