Abstract
In this paper the behavior of an O-ring made of NBR rubber was investigated under extreme conditions. The effect of the extreme initial compression, operating pressure and extreme temperature conditions were examined. The rubber material was tested in simple tension, pure shear and equibiaxial tension modes complemented with a Dynamic Mechanical Thermal Analysis (DMTA) to capture the viscoelastic behavior of the material. For the investigation, a large-strain viscoelastic material model was developed by the authors, to take into account the large deformations caused by extreme conditions. Insufficient space during installation causes extreme initial compression consequently leading the material to crack on the contacting outer surfaces. It was found that the excessive strain and friction induced shear stress contributes primarily to this phenomenon. Extreme operating pressure causes the seal to penetrate into the gap between the shaft and the housing. This behavior damages the material and cracks appear on the seal. High strain areas were found in the proximity of the gap in the material. The analysis of the extreme operating temperature showed that during cooling the O-ring can completely loose its ability to seal at -70°C. There are three contributing factors: the speed of cooling, the temperature and the coefficient of thermal expansion.
Highlights
O-rings are one of the most widely used seals today
The rubber material was tested in simple tension, pure shear and equibiaxial tension modes complemented with a Dynamic Mechanical Thermal Analysis (DMTA) to capture the viscoelastic behavior of the material
It can clearly be seen that the O-ring fills the groove completely, and right after assembly high strain areas occur in the middle of the O-ring, on the side of the O-ring, (a) where it is in contact with the housing and the shaft and where the material penetrates between the gap of the housing and the shaft
Summary
Váradi energy-, and healthcare industry as well as in household appliances Their operating principle follows: when compressing an elastomer material into a smaller space, it changes its’ shape. During this procedure the material urges to restore its’ original shape and as a result, force acts on the contacting surfaces, contact pressure is developing. After operating pressure is applied, as the rubber material is nearly incompressible, it transfers the operating pressure to the surrounding surfaces, increasing the initial contact pressure. This self-sealing effect makes O-rings to be an effective, economical yet simple type of seal
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