There are many kinds of molded rubber products with different shapes and some complex structures. Air bubbles, lack of glue, clear scars, dents and other appearance quality defects will be generated during the molding and vulcanization process. The following is a strategic analysis of the causes of pocket gas in molded rubber products, and the corresponding solutions are introduced.
Ⅰ. Reasons for the air in the molded rubber products
1. Mold structure:
The model parting lines of complex products are too few, and the gas is not easy to escape. The mold has no glue groove or the glue groove size is too small. There is no vent hole or the vent hole is not located properly. All of the above reasons can produce nest gas or bubbles.
2. Compound formula:
In formula design, the chemical reaction between the compounding agents produces bubbles due to ill-consideration. At a certain vulcanization temperature, the gas decomposed by the rubber compound itself may overflow with low volatile matter. In addition, there is moisture inside and on the surface of the compound, which will also vaporize during vulcanization and cause pockets.
3. Molding process:
(1) Consider factors such as the specific gravity and volume of the rubber compound. The quality of the semi-finished product is not appropriately greater than the quality of the finished product;
(2) The shape and placement of the semi-finished product in the cavity are improper;
(3) The pressurization speed is too fast during the vulcanization operation, and the gas cannot be discharged in time.
Ⅱ. Methods to prevent the air in molded rubber products
1. Reasonably design the mold structure, and design the necessary parting lines, glue running grooves and exhaust holes. For complex molded rubber products with high qualification rate requirements, it is best to use a mold with injection flow glue holes.
2. In formula design, the characteristics of raw materials should be comprehensively considered, and raw materials with high moisture content should not be used or used sparingly. If such materials must be used, appropriate pretreatment must be done. Formulate a suitable rubber mixing process to ensure that more water can be removed from the rubber after mixing.
3. Do a good job in the maintenance of the vulcanization equipment and molds, keep the equipment running normally, the molds are clean, the rubber running grooves and the air holes are unobstructed.
4. Formulate a reasonable semi-finished product forming process, and pay attention to the influence of the shape of the material on the quality of the product. Make different shapes and sizes of semi-finished products for different products. In addition, a little calcium carbonate or talc powder is applied to the surface of the semi-finished product, which is also beneficial to improve the appearance quality of the product.
5. The boosting speed of the vulcanizing machine should be appropriate, not too fast, and pay attention to multiple pressure reduction and exhaust.
6. Reasonable use of vulcanization temperature.