Put to the test: Are engineered plastic bearings resistant to Skydrol LD-4?

What is Skydrol?

Used in aviation products for more than 40 years, Skydrol LD-4 is a hydraulic fluid manufactured by Eastman Chemical Company. Skydrol is made of a fire-resistant phosphate ester along with several additives to inhibit corrosion and prevent erosion damage to servo valves. It includes a purple or blue dye to easily distinguish it from other fluids. Skydrol is not compatible with many plastics which can soften, and eventually deteriorate, with exposure. Therefore, aircraft manufacturers must be careful when selecting materials and components. To prove the resistance of four selected iglide® materials against Skydrol LD-4, we carried out some tests.

Test set up

Test specimens made of iglide® W360, iglide® H, iglide® X, and iglide® J respectively were stored in Skydrol LD-4 (EASTMAN). They were placed in 100% concentrated medium for 1,000 hours at room temperature. A hole was drilled in each of the test specimens so that they could be suspended in the separating layer between the medium and the air. Experience shows that the medium is most aggressive there. The specimens were removed then analyzed in the igus® laboratory. As analysis criteria, the mass and the Shore D hardness of the test specimens (see Table 2), as well as the color, gloss, and surface changes before and after the exposure were determined and evaluated according to the criteria from Table 1.

Table 1: Evaluation Criteria


The results in Table 2 demonstrate that the four tested materials remained within the limits of a resilient material in all categories. Additionally, no change in the surface could be detected in the drilled test specimens.

Table 2: Test Results


Based on the results of the measurements and the optical examinations, the resistance of the examined iglide® materials to the used media is evaluated as follows: iglide® W360 resistant to Skydrol LD4 (EASTMAN) (100%; Resistant; 1,000 h): iglide® H resistant to Skydrol LD4 (EASTMAN) (100%; Resistant; 1,000 h): iglide® X resistant to Skydrol LD4 (EASTMAN) (100%; Resistant; 1,000 h): iglide® J resistant to Skydrol LD4 (EASTMAN) (100%; Resistant; 1,000 h): The drilled test specimens show no visual evidence of chemical attack. Interested in learning more about engineered plastic components? Contact igus® here or call us at (800) 521-2747.