Plastic bearings tested and proven on Cromax shafting
Bearings must be able to withstand a high amount of wear, particularly in heavy-duty, industrial applications in the construction or agricultural industries. For these types of applications, many designers are surprised to learn that plastic bearings can be an ideal alternative for metal bearings for a number of reasons.
Plastic bearings made of special, self-lubricating plastics have many advantages, including:
- No maintenance
- No external lubrication
- High mechanical strength
- Vibration dampening
- Insensitivity to dust and dirt
- Compensation for misalignment
Plastic bearings are also self-lubricating. This eliminates dirt and dust buildup, which can cause metal bearings to seize, leading to unforeseen downtime and extra expenses. In addition, when compared to bearings made of conventional materials, plastic bearings are often less expensive. For example, igus®’ iglide® Q2 bearings made of high-performance, self-lubricating plastic, can withstand a static load of up to 17,400 psi (120 MPa), and are especially suitable for heavy-duty slewing applications such as those found in hydraulic connections.
Shaft material put to the test
Different shafting materials are recommended for different types of plain bearings and each shaft/bearing combination will have different wear results. In some cases, wear on the shaft is more common than on the bearing itself.
The best combinations for iglide plastic bearings depend heavily on the bearing’s polymer material blend. For this reason, igus continually performs wear tests on its plastic bearings using a wide range of different shafting materials. Recently, a series of tests confirmed iglide Q2 plastic bearings have an extremely low wear rate when used in combination with hard chrome-plated shafts.
Especially good results were achieved when iglide Q2 was used in combination with hard chrome-plated Cromax shafts from steel manufacturer, Ovako. The tests were carried out with 4,350 psi (30 MPa). The bearings tested had a diameter of 20 mm and a length of 20 mm. This resulted in a force of 2,700 lbs. (12,000 N), which corresponds to 1.2 tons or the weight of a small car. The slewing angle was 60 degrees and 30 movements per minute were achieved in the test.
Lubricated brass bearings were also tested, to serve as a reference. During the testing, the metallic bearing “flowed,” i.e. became wider at the contact area to the shaft. However, this reaction did not take place in the test using iglide Q2 bearings. In fact, there was no measurable wear at all on the shafts paired with iglide Q2. Also, there was no significant difference in wear whether a hardened chrome-plated base material (Cromax 482IH) or a non-hardened chrome-plated base material (Cromax 280X) was used. This flexibility enables more efficient and low-cost bearing/bolt connections.
Dry-running, not lubricated
Another costly necessity in heavy-duty applications is lubrication. Metal bearings require regular greasing and maintenance, which results in increased costs and the need to for extra manpower. However, using self-lubricating plastic bearings eliminates the need for external lubrication. Since they are inherently lubricated, plastic bearings run completely dry, which greatly reduces costs. Plus, Cromax is corrosion-resistant thanks its hard-chrome outer layer.
Technology close-up: iglide Q2
Due to the demand, igus’ standard range of the iglide Q2 plastic bearings, which was introduced in 2011, has expanded. iglide Q2 plain and flange bearings are now available for all standard shaft diameters up to 75 mm. igus also offers inch sizes up to 2 inches. iglide Q2 is ideal for industrial applications thanks to its high mechanical strength – the bearing can withstand static loads up to 17,400 psi (120 MPa) – and is particularly suitable for heavy-duty slewing applications such as those which can be found in all hydraulic connections.
iglide Q2 is:
- Lubrication- and maintenance-free
- Wear-resistant and sturdy under high loads
- Resistant to dirt and dust
- Has an extremely reasonable price-to-performance ratio
iglide Q2 can be used in a variety of applications such as agricultural engineering, commercial vehicles, construction machinery, jig construction or in the general mechanical engineering arena.
During the test using a lubricated brass bushing, the shafts show heavy signs of wear. The test had to be abandoned when the brass bearing seized at 150,000 cycles. (Source: igus Inc.)
There was little to no wear during the test with iglide Q2 plastic plain bearings when used in partnership with the Cromax shafts from Ovalo. The shafts still revealed little to no wear even after 200,000 cycles. (Source: igus Inc.)
The graph compares the wear from iglide Q2 plastic plain bearings and brass bushings. There was little to no wear with the plastic busing in comparison with the brass bushing.