10 Examples Where Plastic Replaced Metal

The Challenge

After being in the metals fabrication industry for over a quarter-century, I have come across countless applications where different metals are utilized to maximize their strengths—and when they are not.

I was speaking with an old “steel” friend who wondered why I made the switch from metals to plastics. The statement “plastic is never going to replace good American steel” was made.

While this is true for many applications, metal’s little brother plastic has many benefits that aluminum, bronze, carbon, alloy, and stainless steel can’t match. Even some of the super steels.

I was issued a challenge to come up with 10 instances where plastic replaces metals. It has been accepted! And so, to my metal friends: strap yourself in.

1. Plastics in History: The Fishing Lure

If you have seen It’s a Wonderful Life, you know George missed the boat on plastic windshields for aircrafts. Curbell didn’t. Born in 1942, we have been supplying plastics to many industries. During that time period metals were in high demand for the war effort and companies experienced shortages of aluminum and steel. One such company was a manufacturer of a surface lurer which shared its name with a popular dance* of the era. The metal lip was replaced with plastic and it did not swim as well, so the body changed from wood to plastic, and it worked beautifully. It is still one of the best bass lurers today.

2. Now You See It, Now You Don’t: Guarding

A manufacturer purchased two new high-speed laser cutting machines. The units came with an expanded metal guard to keep the operators from coming in contact with moving parts while still allowing the user to see the work piece. Unfortunately, at the end of the shift the users had tired red eyes from the exposure of the laser arc. It was decided the metal guard would be replaced by a tinted polycarbonate that has shielding properties against the wavelength of light produced. No eye drops needed.

3. Turn, Turn, Turn: Industrial Positioner

Think of your microwave turntable beefed up a bit. These are commonly used with hardened metal balls in a machined track for rotational purposes, or just sandwiched metal-on-metal. The problem is the grease does not stay where it needs to be; it gets contaminated with abrasive particles, and without the proper lubrication, the track surfaces wear over time. When a self-lubricating plastic—like oil-filled nylon—or a slippery plastic—like UHMW—is used, the mating surfaces are great slide partners. These plastic alternatives reduce the need for maintenance and prolong the life of the fixture.

4. Look Out Below: Sheaves

High above the ground a wire rope is used on a crane boom to lift and place items mechanically. This hardened steel rope begins to fray when it starts to grind away at the hardened steel rope sheave. It won’t be long until both will need to be replaced on account of wear and safety concerns. A moly-filled** nylon sheave replacement will extend the life of the rope and has the strength to perform under the weight of the objects being moved. Some applications see 4-times the life of the rope.

5. Now That Is Harsh: Chemical Valves

Businesses that utilize chemicals for manufacturing know that even stainless steel has the potential for chemical attack. Sometimes, they must use very expensive alloy steels to withstand the environment. Machining this material is difficult and the costs associated elevate.

Atop of the thermoplastic triangle, PEEK stands as an excellent alternative. It’s very machinable, stable enough to achieve tight tolerances, and unaffected by the chemicals and temperatures. PEEK brings value to those who switch, such as cost-savings as a long-term solution. Read our PEEK vs Ultem® article for a great head-to-head comparison.

6. Don’t Fall In: Hopper Liner

Humidity, rain, and snow can all have effects on medias like grain, sand, soils, cement, and even food mixes. Many times, the material cakes or tends to adhere to any imperfection on the metal hopper walls. These blockages need to be manually removed by turning off the machine, or even worse, while running. Not a fun job if there is rotary grinding happening below. UHMW to the rescue! The ice-like surface lets the media slide unimpeded. Better production and improved safety.

7. Now That is a Tasty Burger: Mold Plate

In food processing facilities, wash downs are extremely important to food safety. Within a patty making machine, ground beef, chicken, turkey, pork, and non-meat alternatives are formed into the food of summer. These portion sizes are controlled to a fraction of a gram. When stainless-steel mold plate thicknesses increase so does their weight, resulting in a part that is unmanageable by a single operator, which results in longer shut downs and more manpower. PET is used to decrease the weight, maintain the tolerances necessary, and stand up to the cleaning process. More burgers per hour!

8. Bang, Boom, Bam: Dump Truck Liners

There are several dynamics when loading items like rocks. They are heavy and cause quite an impact during loading. During unloading they are severely abrasive while sliding along the dump body. The metal solutions to this have been numerous. Abrasion Resistant Plates with 500 BHN are so hard the media does minimal scraping damage. Unfortunately, it is so brittle it shatters like glass. Steel manufacturers lowered the BHN to 321. This product worked great against impact while holding up to the scraping well. In fact, the government liked it so much they decided to use it for armored vehicles. Sorry, none for you.

Special welding procedures, overlays, and other players came from overseas with new technologies and good products. It didn’t help workers with hearing loss from the repeated exposure.

Urethane is a great material for the impact of these materials. Mechanically fastened to the bodies, it resisted dents and abrasions while deadening the sound. The back end of the bodies was lined with a special grade of UHMW. Sliding abrasion and accumulation of dirt is no longer a concern.

9. Is That Metal in My Soup: Recalls

Throughout the food processing, conveying and packaging industry, product contamination is a major concern. Foreign substances getting past detection equipment is sparking the industry for better systems and materials. Stainless steel is a go-to construction material for good reasons: integrity, corrosion resistance, and chemical resistance. But there are areas like wear strips or pads on conveyors that use plastics for their slipperiness.

The problem early on was detection. Manufacturers turned to the color blue which was good for visual detection, but when in a casing or box it was not. Improvements were made and metal detectable grades were added. Now, X-ray detectable plastics are available in some grades, UHMW, Acetal, PBT, PEEK and PPSU are now being used for impellers, scrapper blades, mixers, timing screws, fillers, cappers, pistons, nozzles, and just about anywhere chemical resistance, wear, and durability are needed.

10. My Tractor: Bushing

I like to think I am mechanically inclined, at least a little. When the wheel on my big green cutting machine got wobbly, I figured I could fix it. Sure enough, the bronze bushing had seen the last of its days. It was a sacrificial part so I ordered a new one from the manufacturer. A few days later the package arrived and to my surprise, it is now plastic! (This happened with the propeller on my remote-control speed boat as well.)

What large OEMs know is plastic is a less expensive option than bronze, and that wear, chemical resistance, and lubricity do not take a back seat. I can attest to the performance having replaced the bushing.

*Mic Drop*

There you have it: ten examples of where #metaltoplastic has occurred. I want to also thank a few of our valued manufacturer partners for their resources: Ensinger, Rochling, and Plaskolite. Now it’s off for my free round of refreshments. Thanks Steel Guy!

*If you know the name of the lurer from above, I might even throw in a special discount for you!
**Molybdenum disulphide-filled (MOS2) nylon