Round Rod in POM C 1000 mm red

A round rod in POM C is copolymer acetal in cylindrical blank form, meant for turning, milling and drilling of individual parts. The acetal combination of low friction, wear resistance and dimensional stability is the reason it is one of the most used engineering plastics in automatic lathes and in the machine shop.

POM C has a density of 1.41 g/cm³, a heavy and compact material for a plastic. The long-term temperature is 105 degrees, the lowest service temperature minus 40 degrees. The fire rating is HB according to UL 94. Water absorption is low, around 0.8 percent at saturation, which is a decisive property for dimension-critical parts. Where nylon (PA) grows a few tenths in a damp environment, POM stays at the same dimensions, and that is often the reason POM is chosen over PA in premises where humidity varies between winter and summer.

Mechanically POM C is stiff, tough and has low creep under load. The creep behavior matters for bushings and spacers that sit under constant axial or radial load through long duty cycles. Wear resistance against steel is good, and the coefficient of friction is low in the dry state without lubrication. The material has good spring properties, which makes it useful for snap-fit parts and clip-mounted components.

The round rod format is used where the part is turned, milled or drilled out of a cylindrical blank: bushings and plain bearings in conveyors, guide sleeves in press tools, spacers in assembly fixtures, shaft sleeves and coupling pieces, threaded connections for powder handling, gears with a small module, locating pins and slide elements in automated lines. In smaller sizes POM C also turns up in water meters, dosing pumps and valve parts where dimensional stability and chemical resistance to clean liquids matter more than resistance to strong chemicals.

POM stands up to clean water, alcohols, oils and most aliphatic solvents. Strong acid and strongly oxidizing media should be avoided. The material is not UV resistant in natural color, so outdoor use over longer periods calls for a black pigmented grade or another material.

Machining is forgiving and productive. Turning gives a bright surface straight away without polishing, so long runs are often made without any secondary operation. Drilling and threading are clean and predictable. The chip is dry and runs out of the lathe without winding itself around the tool. Standard tools in HSS or carbide work fine, and speeds can be kept high without the material melting or going gummy. It is exactly this combination of fast machining and good surface finish that makes POM popular in automatic lathes.

POM C cannot be bonded the way styrene plastics or acrylic can. Mechanical fasteners, threading, threaded brass inserts or ultrasonic welding are the usual methods. Where needed, the surface can be activated with flame or plasma treatment before bonding with a special primer.

The rod normally comes in natural color, from beige to a light yellowish white, and the shade can vary between batches because the material is pigmented with a light base protection. The difference is cosmetic and does not affect mechanics or dimensional stability. Black POM C is available for outdoor use or where the part has to have a dark surface.

In the choice between POM C and POM H the rule of thumb is this: POM C is tougher and takes both machining and shock loading better, POM H is harder and has a higher degree of crystallinity but is more prone to center porosity in thick rods, which shows up in deep drilling or internal turning. For most turned parts POM C is the safer choice.

Do you need help choosing the right diameter or comparing POM C against other acetal grades? Get in touch.

In red and 1000 mm long, the rod gives the same material for turning with a color that stands out in the machine.