The Casting of Cutlass Bearings
Common Defects
A). Damage due to dry running.
B). Loss of clearances due to damage from abrasive particles.
C). Damage caused by shaft misalignment or vibration.
Preparation
All work should be carried out in strict accordance with the relevant ThistleBond Technical Data Sheet. Product selection and application should be based on the nature of the damage and the amount of time available for the repair to be carried out.
Surface Preparation
A suitable mould must be manufactured, this can be done by using one of the two techniques outlined below:
a). Produce a centralising jig for the existing outer sleeve of the bearing and machine a suitable metal insert to the configuration of the internal dimensions of the bearing. This should then be centralised within the outer sleeve to produce a mould.
b). Alternatively, UPS 205 FG Fluid Grade Ceramic (TR205) and UPS 235 BG Urethane Ceramic Fluid (TR235) can be used to cast an inner mould. This can be done by coating the internal surface of a new bearing/ bush with two coats of UPS TAC 872 Release Agenet. Once allowed to dry, the bearing can be centralised in a jig and one of the UPS 205 FG Fluid Grade Ceramic (TR205) can be poured in a thin stream to fill the centre cavity. When the material has cured the original bearing may be removed leaving the cured core adhered and centralised in the jig.
Produce a new outer sleeve from suitable materials or alternatively, remove all existing rubber from the existing sleeve and prepare the internal surfaces by grit blasting to Swedish Standard SA 21/2 ensuring a minimum profile of 75 microns, using an angular abrasive. Clean the component thoroughly with ThistleBond Universal Cleaners and treat the surface of the former with a minimum of two coats of ThistleBond Release Agent and allow to dry.
Priming System
Apply the UPS 075 Elastomeric Primer supplied with the UPS 300 FG '60' Durometer Fluid Grade Elastomer or UPS 315 FG '80' Durometer Fluid Grade Elastomer product in a thin film using a stiff bristled brush to the entire prepared area. All surfaces to which the material is to bond to must be treated.
Application Technique
Mix the selected ThistleBond product in accordance with the Technical Data Sheet. Using a short Bristled Brush, wet out the internal surfaces of the former and the internal diameter of the outer sleeve. Position the former and outer sleeve into the mould and centralise. Immediately pour the remainder of the pre mixed material in a thin stream in order to prevent excessive air entrapment. Continue to pour until the material fills the mould to the desired level and allow to cure in accordance with the data sheet, after which, the bearing can be removed and any excess material removed using a sharp knife.
