The supercooling installation method is principally possible for polymer and metal bearings, but in the case of metal plain bearings only applicable for bearings with a bronze or nickel-copper matrix. With other metal alloys, the supercooling process could lead to undesirable structural changes.
Sliding bearings with a bronze or nickel-copper matrix, owing a thermal expansion coefficient of a » 18…20 x 10-6 1/K (bronze) and a » 13…16 x 10-6 1/K (nickel-copper), offer sufficient contraction for the supercooled parts to be inserted in the prepared bores without needing to apply any force. When working with polymer bearings (deva.tex®) it has to be considered, whether it has glass fiber backing layer or pure polymer fiber reinforcement. Deva.tex® with glass fiber backing layer has a coefficient of thermal expansion of
a » 13 x 10-6 1/K) while pure polymer reinforced materials have a » 60…100 x 10-6 1/K.
The process can be applied with operating temperatures of up to 120 °C. In such cases no additional securing of the bearing is necessary. If the a value of the bearing exceeds that of the housing, higher operating temperatures are also permissible.
In steel construction or hydraulic steelworks, where higher stress forces may occur and the support parts have inadequate wall thickness, the alternating deformation might cause the plain bearing to loosen, even despite good coverage. In such cases additional securing in line with DN 2.32 is recommended. This additional securing also needs to be provided when diagonally introduced forces could lead to shearing stress for the
The media most frequently used for supercooling are dry ice (CO2) and liquid nitrogen (N2). Both substances need to be treated as hazardous materials. Corresponding personal protection equipment is mandatory when handling dry ice or liquid nitrogen. The applicable accident prevention regulations need to be complied with.
Suitable as an insulating tank would be a wooden box, for example, which is completely lined with approx. 30 mm thick styrofoam. A lid prevents rises in temperature and ensures that the bearings are cooled down faster.
The entire bearing needs to be covered by the refrigerant. Depending on the size, the application period amounts to approx. 30 to 60 minutes for liquid nitrogen and approx. two hours if dry ice is used. The dry ice needs to be crushed quite finely (approximately to walnut size).
the larger the bearing diameter, the more beneficial the supercooling influence will be
the thicker the bearing wall, the less beneficial the supercooling influence will be
s = n * ∝1 * ∆T * D