Rubber grommets are rubber rings placed around an opening in a surface. Grommets are usually intended to protect either the opening from tearing or breaking, or they are intended to protect whatever objects that pass through the opening. Rubber grommets typically serve the latter function, as they often protect wires or cords that pass though openings in metal surfaces that would otherwise be too jagged or sharp.
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The plastic or rubber insulation around electrical cables is particularly vulnerable to abrasion or to breaking after repeated flexing at its point of entry, which is why rubber grommets are necessary. Some varieties of less durable wiring are themselves vulnerable to damage if exposed to thin, hard surfaces because of the risk of crimping. Rubber grommets that serve a protective function for wiring are usually broad and round which prevents thin wiring from becoming crimped at an angle. In industrial settings, punched sheet metal through which wires pass is usually fitted with rubber grommets because of the demanding conditions present in such conditions. Many warehouses and factories are equipped with movable or retractable power sources. After repeated tugging and movement, power cables may become disconnected or damaged in other ways. Certain rubber grommets are specially fitted to snugly hold wires at the point of contact to avoid accidental damage to the connection points.
Rubber grommets are usually made of extruded rubber, which is made by forcing raw rubber materials (rubber stock) through machinery that heats and pressurizes it. Once the stock achieves a semi-liquid state, it travels into a die, which is a tool designed to mold raw materials into a specific shape. When the product emerges from the die, it is cooled and treated, and in some cases subjected to additional processing to increase its strength and durability. Rubber extruders can produce grommets of any size, shape, or composition, though different kinds of grommets cannot be produced by the same die; a factory that specializes in grommets, for example, would need several separate extrusion lines to produce multiple grommet types. Extruded grommets can be made from natural or synthetic materials. Silicone grommets, which can withstand sustained higher temperatures compared to completely organic rubber materials, can be used in automotive or other mechanical applications where heat exposure is likely. Other extruded rubber grommets can be infused with different kinds of chemicals to give them a range of desirable qualities. Heat resistance, ultra-violet ray resistance and increased durability may be necessary qualities for rubber grommets in some applications, especially when exposure to extreme weather conditions is expected.