Plastic plain bearings with minimal play?

Do injection-molded guide elements meet the requirements of mechanical engineering?

Plastic plain bearings have now become established in mechanical engineering and automation technology as an alternative to bushings made of bearing metals. While brass bushings require lubrication, the so-called“Igus® bushings”can generally be operated in a dry-running mode.
(Igus® is a registered trademark of IGUS GmbH, Cologne)

Injection molding processes are used to manufacture these relatively low-cost components. However, this presumably entails some disadvantages:

1. Given the wide variety of materials, compromises must obviously be made during tool design. Thus, despite differences in processing temperatures and the resulting shrinkage rates of the compounds, minimal clearance must be ensured during use. This often results in larger gaps, which can lead to a rather loose fit within the assembly. Consequently, high-precision guides are often not feasible.
   
2. Since they are tool-dependent, injection-molded bushings are subject to standardization. As a result, custom dimensions cannot be produced on short notice. Multifunctional sealing and guiding elements tend to be difficult to produce.
   
3. Prototype parts or small production runs of bushings, with or without a flange, are often machined from round semi-finished stock. The blend (i.e., the plastic mixture with its fillers) is designed to have flow properties suitable for thin-walled component geometries. Solid material therefore generally has a different microstructure because the wall thicknesses actually intended for such parts are significantly exceeded in a thick blank. As a result, filler accumulation, stresses, and voids can occur, preventing the part from meeting production standards.

» Ultimately, these limitations push the developer to their limits:

• Custom-Made Plain Bearings
• High-precision sliding elements with minimal clearance
• Small-batch production and prototypes of plastic bushings
• Multifunctional plasticguide and sealing elements

The solution is quite simple…

There is now a wide variety of plastic compounds available in the form of extruded solid rods. These compounds are both high-performance and cost-effective. With knowledge of the application and the performance data of these compounds, it is possible to manufacture collar bushings, guide rings, sliding elements, and many other dry-running components. Manufacturers of these high-performance thermoplastics strive to obtain as many certifications as possible for their materials, such as FDA, USP Class VI, KTW, and EHEC. Stress in the blank can be relieved through upstream tempering processes. Furthermore, due to the high strength of the thermoplastics, virtually no compromises need to be made regarding tolerances and, consequently, clearances. This makes these materials suitable for many challengingapplications in the food and beverage industries and in medical technology.

Below are a few examples of what creative solutions might look like:

Ultimately, any geometry that can be produced through machining is structurally feasible.

What do you think? Do you like them?

Stefan Bock