During the vulcanization process of rubber O-rings produced by molding, the rubber material quickly fills the entire mold cavity as the filled material requires a certain amount of interference. The excess rubber material flows along the parting line, resulting in varying thickness of the rubber edges in the inner and outer diameters.Since rubber O-rings require strict quality and appearance control due to their sealing function, even small rubber edges can potentially affect the overall sealing performance. Therefore, after vulcanization, the finished products need to undergo edge trimming to remove these excess rubber edges. This process is called edge trimming. However, generally speaking, the smaller the size and the more complex the configuration, the higher the difficulty and the more time and labor-consuming it becomes.
There are two methods for trimming molded rubber O-rings, namely manual trimming and mechanical trimming.Manual trimming is the traditional method, where excess rubber edges are gradually trimmed off along the outer edge of the product using hand tools. It requires a high level of skill to minimize product scrap rate. Manual trimming has low investment costs but low efficiency and quality, making it suitable for small batch production.There are two methods of mechanical trimming: grinding with a grinding wheel or sandpaper, and low-temperature cryogenic trimming.Currently, there are five forms of cryogenic trimming: vibration cryogenic trimming, swing or jiggle cryogenic trimming, rotary drum cryogenic trimming, brush grinding cryogenic trimming, and shot blasting cryogenic trimming.
Rubber undergoes a transition from a high elastic state to a glassy state under certain low temperature conditions, causing it to become harder and more brittle. The rate of hardening and embrittlement depends on the thickness of the rubber product. When an O-ring is placed in a cryogenic trimming machine, the thin edges of the product become hardened and brittle due to freezing, while the product itself retains a certain level of elasticity. As the drum rotates, the products collide with each other and with abrasives, resulting in impact and abrasion that breaks and removes the excess rubber edges, achieving the trimming purpose. The product will regain its original properties at room temperature.
Cryogenic trimming at low temperatures is efficient and cost-effective. However, the effectiveness of inner edge trimming is relatively poor.
Another method is grinding with a grinding wheel or sandpaper.
The vulcanized O-ring is mounted on a sandbar or nylon bar with a matching inner diameter size, driven by a motor for rotation. The outer surface is processed using sandpaper or a grinding wheel to remove the excess rubber edges through friction. This method is relatively simple and convenient, with higher efficiency than manual trimming, especially suitable for small-sized products and large batch production. The disadvantage is that this type of trimming relies on grinding with a wheel, resulting in lower accuracy and rougher surface finish.
Every company needs to choose a suitable edge trimming method based on its own circumstances and product dimensions. It is important to be flexible in selecting the method in order to enhance the product and reduce waste, ultimately improving efficiency.
Post time: Oct-18-2023