Non contact wear measurement on pneumatic seals
Abstract An experimental methodology aimed at the evaluation of wear in pneumatic seals is presented. New equipment was designed and manufactured in order to measure the radial thickness of worn material on the sealing edge both axially and circumferentially, by means of a laser sensor, as well as to avoid the necessity of disassembling the seals. The methodology is intended as an instrument for a quick comparison of seal prototypes and is proposed as an alternative to those methods that globally quantify the wear of samples by measuring their loss of weight or volume. Results obtained on a NBR commercial lip seal are presented.
Accelerated Life Test for Reliability Evaluation of Pneumatic Cylinders
Pneumatic cylinders are intended to be designed for high reliability and long lifetimes. Evaluating such designs through conventional life tests is difficult as the affordable test time is too short to generate a meaningful amount of failure data. In this paper, we design and implement an accelerated life test (ALT) for evaluating the reliability of pneumatic cylinders. From a detailed analysis of failed samples from field operation, the major failure mechanisms that affect the reliability of pneumatic cylinders are identified, e.g., wear and tear of sealing rings. For these failure mechanisms, temperature and frequency are found out to be the significant stresses of the pneumatic cylinders. A two-factor-four-level full-factor design of ALT is, then, performed to set up an ALT plan for the pneumatic cylinders. A total number of 95 samples are tested according to the ALT plan, and a mixed Arrhenius-inverse-power-law model is used to fit the test data and predict the reliability under normal operation conditions. In addition, a normal stress test of eight samples is performed to validate the reliability predicted by the ALT. The results show that using the proposed ALT, the reliability of the pneumatic cylinder can be predicted with satisfactory accuracy. It is also shown that the designed ALT plan requires only 38.77% of the testing effort of other conventional life tests.
An equation for the abrasive wear of elastomeric O-ring materials
Abstract An empirical equation was obtained via dimensional analysis, which relates the abrasive wear volume to the friction force, specimen load, sliding distance and specimen breaking strength for O-ring materials. Wear experiments on O-rings molded from four nitrile compounds and one polyurethane material were conducted on a special pin-disc-type testing machine. Specimens cut from a size 330 O-ring were held against a roughened rotating steel wear cylinder with a load which varied from 5 to 15 lbf. Both the specimen and the wear cylinder were immersed in an abrasive mud of the type used for oil well drilling. The sliding velocity was held constant at 11 in s−1. The wear resistance of the polyurethane was two times better than the best nitrile compound.