The reasons
Why plastic replaces metal
Most switches come down to one or two of these. Which ones matter depends on what the part does.
-
Runs with little or no grease
Nylon, acetal, UHMW and PTFE-filled grades have low friction of their own, and oil- or MoS₂-filled nylons carry lubricant in the material. With no grease, there’s nothing to wash out, collect grit or reach the product.
-
Doesn’t rust
Plastic doesn’t rust or pit in water, steam or washdown, and needs no plating or paint to protect it.
-
Resists many chemicals
PTFE, PVDF and PEEK hold up to acids, caustics and solvents that attack stainless steel and many alloys. Resistance varies by plastic, so the chemical and the temperature decide the grade.
-
Much lighter
Most of these plastics weigh one-fifth to one-eighth as much as steel. Change parts are easier to lift, and moving parts put less load on drives and bearings.
-
Quieter
Plastic gears, sprockets and rollers damp vibration instead of ringing, so they run with less noise than metal on metal.
-
Gentler on what it meets
A plastic part wears before the steel chain, wire rope or shaft it runs against, so the cheaper, easier part is the one that gets replaced.
-
Product slides off
UHMW’s slick surface lets grain, powder and wet material slide instead of building up on hopper and chute walls.
-
Doesn’t conduct electricity
Plastics insulate, so they’re used for spacers, standoffs and mounts that keep circuits apart or isolate a part from the frame.
The usual replacements
Plastics that replace metal
Six plastics cover most metal replacements. Each has a different strength, and a different thing to watch.
| Plastic | Best at | Watch for | Max service, °F | Expansion* |
|---|---|---|---|---|
| Nylon | Strength, toughness and bearing wear. Oil- and MoS₂-filled grades for running dry. | Takes up moisture and grows slightly in wet or humid service. | 210 | 4.5 |
| Acetal | Holding close tolerances, low friction and low moisture uptake. | Not for strong acids. | 185–195 | 6.1–6.8 |
| UHMW | The lowest friction, with high abrasion and impact resistance. | Soft and flexible, and expands the most. | 180 | 11.1 |
| PET | Holding its size in wet service, with good wear. | Less tough than nylon under impact. | 230 | 3.9 |
| PTFE | Chemicals, heat and very low friction. | Soft, and creeps under sustained load. | 500 | 8.9 |
| PEEK | Heat, chemicals and strength together. The closest to metal. | The highest cost of the six. | 480 | 2.6 |
*Coefficient of linear thermal expansion, in/in/°F × 10⁻⁵. For comparison: steel about 0.65, bronze about 1.0, aluminum about 1.3. Typical published values. Grades vary.
On the drawing
What usually changes
Plastic doesn’t behave quite like metal, so a few things are often set differently. They’re settled on the drawing by you or the equipment maker, and we machine to it.
| Steel | ~0.005" | |
|---|---|---|
| Aluminum | ~0.009" | |
| Nylon | ~0.032" | |
| Acetal | ~0.043" | |
| UHMW | ~0.078" |
Calculated from typical expansion values. Grades vary.
-
Size moves with temperature
Plastic expands several times more than metal. Clearances and tolerances are often set for the temperature the part runs at, not the temperature it’s measured at.
-
Some plastics take up moisture
Nylon grows slightly in humid or wet service. Acetal, PET and UHMW barely change.
-
Sharp inside corners get a radius
Plastic can crack at a sharp inside corner under load, so a small radius is common.
-
Threads cut or inserts fitted
Threads can be cut straight into the plastic, or threaded inserts fitted for a stronger, reusable thread. We fit them before the part ships.
Getting a quote
From metal part to plastic part
No mold needed. We machine from solid stock, from one part to production runs.
-
The drawing
With the plastic called out, or ask us and we’ll suggest suitable plastics for the part.
Send a drawing -
The metal part
Send the part or photos. We measure it and machine it in the plastic you choose.
Reverse engineering -
One prototype first
Try one plastic part on the machine, then order the production run.
Quote a prototype
Upload drawings or photos of the metal part on the quote form.
Buyer questions
Metal-to-plastic FAQs
Something else? Call (630) 904-2525.
It depends on the load, the heat and what the part does. Many bushings, sprockets, guides and change parts run well in plastic, and some parts are better left in metal. That decision stays with you or the equipment maker. We suggest suitable plastics and machine the part.
Many can. Nylon, acetal, UHMW and PTFE-filled grades have low friction on their own, and oil- or MoS₂-filled nylons carry lubricant in the material.
It depends on the load, speed, heat and what it runs against. In many wear parts, the plastic is chosen so that it, rather than the costlier mating part, is the one that wears. We keep your drawing, so a replacement is a simple reorder.
Yes. If any clearances or tolerances need to change for plastic, they come from you or the drawing, and we machine to them.
No. We machine from solid stock, so a single part, a prototype or a production run needs no tooling.
Yes. We machine aluminum, brass and bronze as well as plastics.
Standard quote
Ready to quote the plastic version?
A drawing or the metal part is enough to start. Experienced help from your first quote to the finished part.