Choosing a Plastic for Industrial Components: A Selection Guide

Start from requirements, not from a material name

Before comparing polymers, write down what the part actually has to survive: maximum and minimum service temperature, mechanical loads and whether they are sustained or intermittent, chemical or fluid exposure, UV or outdoor exposure, electrical requirements, any flammability rating, and whether dimensional stability matters more than strength.

Most poor material decisions come from specifying a grade before these are established, then discovering a mismatch at qualification.

The polymers commonly used for industrial mouldings

PA6 and PA66 (nylon)

Strong, tough and abrasion resistant, with good temperature performance; the usual choice for mechanical parts, housings carrying load, and components subject to wear. PA66 has a higher melting point and better stiffness at temperature than PA6; PA6 is slightly tougher and easier to process.

The critical caveat: both are strongly hygroscopic. They absorb moisture from the atmosphere, which changes dimensions and mechanical properties in service. They must also be dried thoroughly before moulding, or the result is splay marks and degraded properties. Any design using nylon must allow for moisture-related dimensional movement.

Glass-filled grades greatly increase stiffness and strength but shrink differently along and across the flow direction, which raises warpage risk and accelerates tool wear.

POM (acetal)

Excellent dimensional stability, low friction, good fatigue resistance and much lower moisture absorption than nylon. The standard choice for gears, bearings, sliding parts and precision components where dimensions must stay put.

It has a narrow processing window and degrades if held too hot for too long, producing an unmistakable odour and surface defects. Shrinkage is high, so shrinkage compensation in the tool needs to be right. Bonding and painting are difficult because of its low surface energy.

ABS

Good impact strength, easy to mould, good surface finish, readily painted and plated, and inexpensive. Widely used for enclosures, covers and housings where appearance matters and loads are moderate.

Limited temperature resistance, poor UV stability unless stabilised, and moderate chemical resistance. Not a structural material, and not a good outdoor material without protection.

PC (polycarbonate)

Very high impact strength, good temperature resistance, and optical clarity; the usual choice for transparent mouldings, lenses, sight glasses and protective covers.

Notch sensitive, so sharp internal corners must be avoided. Susceptible to stress cracking in contact with certain chemicals. Requires thorough drying and high melt temperatures, and moulded-in stress is a real concern for optical parts.

PC/ABS blends trade some of the impact and temperature performance for easier processing and lower cost.

PBT

Good dimensional stability, good electrical properties and good chemical resistance, with much lower moisture absorption than nylon. Common in electrical components, connector bodies and parts requiring stable dimensions in humid conditions.

Notch sensitive, and requires drying before processing. Often specified in glass-filled form for electrical housings.

PP (polypropylene)

Low cost, low density, excellent chemical resistance and good fatigue life, notably in living hinges, where it is effectively without peer. Used for containers, closures, chemical-resistant parts and high-volume components where cost dominates.

Low stiffness, poor performance near and below freezing unless modified, poor UV resistance unstabilised, and high shrinkage which must be accounted for in the tool.

Comparison at a glance

These are the grades we routinely process. Specific grade selection within each family still matters considerably: two PA66 grades from different suppliers can behave differently enough to require separate process settings.

Practical points that are easy to miss

Filled grades change more than stiffness

Adding glass fibre increases stiffness and strength and reduces shrinkage along the flow direction, but not across it. That anisotropy is a leading cause of warpage in filled parts. Filled materials are also abrasive and wear gates, cores and slides faster, which affects maintenance planning.

Colour is not cosmetic only

Pigments and masterbatch can affect shrinkage, crystallisation behaviour and impact properties. A part qualified in natural material may behave measurably differently in black or in a specific colour match.

Regrind has to be controlled

Reprocessing degrades polymer chains and reduces mechanical properties. If regrind is permitted, the allowed percentage should be specified and controlled, not left to judgement on the shop floor.

Material behaviour also drives most surface defects; see common moulding defects and their causes for how drying and melt temperature show up in the finished part.