What Is a POM Rod?
POM rod is a round bar made of POM (polyacetal). It is used as a raw material for mechanical shaft element parts that require abrasion resistance, such as cams and gears, as well as reliability parts that require chemical resistance and fuel resistance. It is often used in applications where metals were originally used, helping to reduce the weight of parts.
POM resin was first marketed worldwide by DuPont in 1959 under the trade name Derlin. It is a crystalline thermoplastic and an engineering plastic with many advantages including moldability, mechanical strength, abrasion resistance, impact resistance, fatigue resistance, creep resistance, insulation properties, and chemical resistance.
POM resin is melted and blended in an extruder and molded in a round mold to form round rods.
Uses of POM Rods
POM rods are used as pre-processing raw materials for manufacturing sliding parts and parts with complex shapes. POM resin has high mechanical strength, self-lubricating properties, and good moldability.
As mechanical parts, POM resins are used in bearings, valves, and gear parts, due to their wear resistance and self-lubricating properties. It is also used in automotive parts because its sliding properties can be further improved by blending with lubricants.
Spacers installed between boards are widely used as electrical components due to their excellent electrical insulation properties and are manufactured by drilling and tapping POM rods.
Although POM rods are inferior to polytetrafluoroethylene (PTFE), another engineering plastic, in terms of chemical resistance, they are less expensive per weight than PTFE. Therefore, POM rods are used as components for stirring chemicals in beakers and test tube stands.
Principle of POM Rods
The higher the crystallinity of a plastic, the lower its coefficient of friction. POM resin has a particularly high crystallinity characteristic among engineering plastics. Therefore, it has a very low coefficient of friction and self-lubricating properties. The coefficient of friction varies depending on the material with which it comes in contact, but POM resin has a particularly low coefficient of friction with metals, making it an ideal material for sliding parts such as cams, gears, and bearings.
These parts are produced by cutting POM rods using a lathe or milling machine or by gear cutting using a hobbing machine. Because of their good formability, they can be processed by tabletop machines or by hand. In many cases, the general public purchases POM rods through online shopping or home centers for DIY processing.
On the other hand, one of its disadvantages is that it is opaque. Although POM resin is a highly durable material, acrylic, vinyl chloride, and polycarbonate resins are used when transparency is required, such as for peepholes.
Other disadvantages include flammability due to the presence of oxygen in the molecular structure, low weather resistance, poor adhesiveness, inability to bond using adhesives (welding is possible), and inability to withstand strong acids. Therefore, care should be taken when selecting materials for use in explosion-proof designated areas, outdoors, or in environments where strong solvents or cleaning agents are used.
Types of POM Rods
POM rods are classified into several types according to resin composition and blending.
1. Homopolymer
Homopolymer, in which only formaldehyde units are polymerized, is a typical example. Although dimensional stability is somewhat difficult to achieve, homopolymers are highly crystalline and have excellent mechanical strength, abrasion resistance, and heat resistance.
2. Copolymer
Copolymers are synthesized by polymerizing trioxane and comonomers. Compared to homopolymer, dimensional stability and moldability are improved.
POM resins blended with rubber or glass fiber and molded into POM rods are also available. These are used in applications where higher impact strength and rigidity than usual are required.