What should be paid attention to in the processing of precision rubber and plastic components and their extended products for household appliances?

The processing of precision rubber-plastic components of household appliances and their extended products should focus on the four core requirements of dimensional accuracy, material performance stability, environmental protection and safety, and batch consistency, and combine the functional requirements of different parts of household appliances (sealing, shock absorption, insulation and appearance) to control key links. The specific precautions are as follows:

Selection and pretreatment of raw materials

Accurately match the working conditions of household appliances: choose rubber and plastic materials according to the use of components, such as PVC modified material+magnetic strip for refrigerator door seal, which should give consideration to cold resistance (not brittle at -30℃) and elasticity; Nitrile-butadiene rubber (NBR) is used for the damping pad of washing machine, which is resistant to water and detergent corrosion; Food-grade silicone rubber for sealing ring of rice cooker conforms to FDA and GB 4806 standards, and has no peculiar smell and no harmful substances.

Drying treatment of raw materials: plastic particles (such as ABS and PP) should be dried before processing (temperature 80~120℃, time 2~4 hours), and the water content should be controlled below 0.05% to avoid bubbles and shrinkage marks in injection molded parts; Rubber raw materials need to be mixed and vulcanized in advance to ensure uniform hardness (Shore hardness deviation ≤ 2).

Environmental compliance control: Prohibit additives containing heavy metals such as lead and cadmium, and give priority to materials with low VOC (volatile organic compounds) to meet the requirement that the odor grade of interior decoration of household appliances is ≤3, especially suitable for products used in confined spaces such as air conditioners and refrigerators.

Die design and machining accuracy control

Product requirements for die accuracy adaptation: the die cavity tolerance of precision components of household appliances (such as air conditioner valve sealing ring and microwave oven door control switch rubber sleeve) should be ≤±0.01mm, and H13 die steel should be used and quenched (hardness ≥HRC52) to ensure the wear resistance and durability of the die; The mold should be designed with a reasonable exhaust slot (depth of 0.01~0.03mm) to avoid scorch marks and material shortage during the molding of rubber and plastic parts.

Demoulding and shrinkage compensation: according to the shrinkage of rubber and plastic materials (such as silicone rubber shrinkage of 2%~4%, ABS shrinkage of 0.4%~0.8%), adjust the mold size and reserve shrinkage allowance; Design demoulding inclination (1 ~ 3) to prevent deformation of thin-walled parts (such as wire harness sheath with thickness less than ＜0.5mm) during demoulding.

Positioning design of insert mold: For components with metal inserts (such as oil seal of motor shaft of household appliances and rubber sleeve of switch contacts), precise positioning pins should be set in the mold to ensure that the coaxial deviation between the insert and rubber layer is ≤±0.05mm, so as to avoid assembly sticking caused by the offset of the insert.

Control of key parameters of molding process

Injection molding/molding process parameters are stable.

Injection molding parts: control the barrel temperature (such as PP material 180~220℃, PC material 260~300℃), injection pressure (50~120MPa) and holding time to prevent dimensional deviation; Thin-walled precision parts need to increase injection speed and reduce cooling deformation.

Molded parts: Rubber seals are molded at constant temperature (temperature 150~180℃, pressure 10~20MPa), and the vulcanization time is accurately controlled (error ≤±10s), so as to avoid insufficient elasticity due to insufficient sulfur or brittleness increase due to excessive sulfur.

Size uniformity of extrusion process: For extruded parts such as household appliance sealing strips and water pipes, the extrusion speed should be controlled to be synchronized with the traction speed (deviation ≤ 2%), and the temperature of the cooling water tank should be controlled by sections to ensure that the cross-sectional dimension tolerance is ≤±0.1mm, and the surface is smooth and free of wavy lines.

Precision control of secondary processing: when the components need to be cut and punched, CNC equipment is used for processing, such as the tolerance of the shaft hole of the air guide blade of the air conditioner is ±0.03mm to ensure the precise fit with the motor shaft; Special glue (such as special adhesive for silicone rubber) should be selected for bonding process, and the bonding surface should be clean and free of oil stain, so as to ensure the bonding strength ≥ 5N/cm.

Quality inspection and whole process control

Dimensional accuracy detection: use image measuring instrument and CMM to detect key dimensions, such as the tolerance of magnetic attraction distance of refrigerator door seal is ±0.05mm, and the tolerance of lip thickness of washing machine bearing seal ring is ±0.02mm；; Form and position tolerances (roundness and parallelism) shall meet the requirements of drawings.

Performance test to match the life of household appliances: special tests are conducted according to the usage scenarios of household appliances, such as the high and low temperature cycle test of seals (-40℃~120℃, 1000 cycles), the fatigue test of shock absorbers (no deformation after 100,000 compression rebounds), and the cooking test of food contact parts (no deformation and no odor at 121℃ for 30min minutes).

Batch consistency control: adopt automatic production line (manipulator loading and unloading, online detection) to reduce manual intervention; Take 5% samples from each batch for full inspection, and record key parameters (such as hardness, size and tensile strength) to ensure that the deviation between batches is ≤ 3%.

Protection requirements for packaging and storage

Anti-deformation packaging: Thin-walled parts and special-shaped parts (such as silicone air guide strips at the air outlet of air conditioners) need to be packaged in customized blister boxes to avoid extrusion deformation; Seals should be packaged independently to prevent the surface from being contaminated with oil or dust.

Storage environment control: rubber and plastic parts should be stored in a cool and dry warehouse (temperature 15~25℃, humidity 40%~60%), away from heat sources and ultraviolet rays, and be sampled regularly during the warranty period to prevent the materials from aging.