During mould vulcanization of the rubber products, the rubber material will flow out along the parting surface of the mould, forming the overflow rubber edge, the amount and thickness of the rubber edge depend on the mould structure, precision, plate parallelism of the plate vulcanization machine and the amount of residual rubber. Now the rubber edge on the products made by the mould without edge is particularly thin, which can be moved away very easily. But this kind of mould is expensive and easy to damage, so most of the rubber products need to be trimmed after vulcanization.
1. Hand trimming
Hand trimming is an old method, which includes punching the edge by hand, trimming edges with scissors, scraping, etc. The quality and speed vary from person to person, requiring the geometric dimensions of the finished products must meet the drawings, and no scratches or deformations are allowed. Before trimming, the trimming position and technical requirements should be clear, the correct methods and tools should be mastered.
2. Mechanical trimming
Mechanical trimming refers using a variety of special machines and the corresponding process to trim rubber edges. Now it is a more advanced trimming method.
(1) Mechanical die-trimming by using the pressure machinery, trimming die, trimming knife to remove the rubber edge. This method is suitable for the model products such as bottle stopper, leather cup, etc, which can be put on the baseplate of the trimming knife. For products with higher rubber content and less hardness, it’s better to use impact trimming method to reduce uneven edge and side depression due to the great elasticity. And for products with lower rubber containing rate and higher hardness, the method of die-trimming can be adopted. In addition, mechanical trimming can be divided into cold trimming and hot trimming, cold trimming means to trim at room temperature, the quality is better when trimming pressure is higher. Heat refers to trim at high temperature, but should prevent to contact with the product for a long time to affect the quality of the product.
(2) Mechanical cutting trimming suits for bigger size products by using special tools. Generally, different products use different trimming knives. For example, the tire surface air holes and exhaust line parts after vulcanization have different lengths of rubber edges, they must be trimmed by using knives with groove in the tire rotation conditions.
(3) Mechanical grinding trimming are common used for rubber products with inner holes and outer circles. The grinding tool is the grinding wheel with a certain thickness of particles. The precision of this edge grinding is very low with rough grinding surface and there may rubber scraps to affect the effects.
(4) Low-temperature shot blasting trimming are used for the precision products with high quality requirements, such as o- ring, small packing leather, etc. Using liquid nitrogen or dry ice to cool the products to the temperature below the brittleness, and then spray metal or plastic pellets at high speed to break and fall off the edges.
(5) The low temperature brush trimming is used to remove the rubber edge of the frozen rubber products with the help of two nylon brushes rotating around the horizontal axis.
(6) Low temperature drum trimming is the earliest way of frozen trimming. By using the impact force generated by the rotation of the drum and the friction between the products, the rubber edge of the products that have been frozen below the brittle temperature will break and fall off. The shape of the drum is generally octagonal, so as to increase the impact force of the products in the drum. The speed of the drum should be moderate, and the efficiency can be improved by adding abrasives. For example, the trimming process of rubber plug of electrolytic capacitor is to use low temperature drum for trimming.
(7) Low temperature vibration trimming is also known as vibration freezing trimming. The products vibrate spirally in the ring seal box. Due to strong impact between products and between products and abrasives, the frozen brittle rubber edge falls. Low temperature vibration trimming is better than low temperature drum trimming, which has lower damage rate and higher production efficiency.
(8) Low temperature swinging and shaking trimming is applicable to small or micro products, or micro rubber products with metal framework, together with abrasives to trim the rubber edges in the product holes, corners and grooves .