Cast White Metal Bearings

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GBH Enterprises, Ltd.

Engineering Design Guide: GBHE-EDG-MAC-5710

Cast White Metal Bearings Information contained in this publication or as otherwise supplied to Users is believed to be accurate and correct at time of going to press, and is given in good faith, but it is for the User to satisfy itself of the suitability of the information for its own particular purpose. GBHE gives no warranty as to the fitness of this information for any particular purpose and any implied warranty or condition (statutory or otherwise) is excluded except to the extent that exclusion is prevented by law. GBHE accepts no liability resulting from reliance on this information. Freedom under Patent, Copyright and Designs cannot be assumed.



Engineering Design Guide: Cast White Metal Bearings CONTENTS SECTION 1 SCOPE 1 2 BACKING MATERIAL 2 3 SURFACE 3 4 THICKNESS 4 5 CLEANING PROCEDURE 5 6 TINNING 6 7 WHITE METAL 7 8 BOND SOUNDNESS 8 9 WITNESSED INSPECTION 9 10 MACHINING 10 11 FINAL INSPECTION OF BOND FOR SEAL RINGS 11



APPENDIX A - METHOD OF CALCULATING REFLECTANCE RATIO DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE



1 SCOPE This Engineering Design Guide applies to white metal cast onto steel backings. It does not apply to thin shell wrapped bearings. It is intended to guide the ordering of emergency repairs and spares for bearings and seals. 2 BACKING MATERIAL Steel backings should be in LOW CARBON STEEL to BS 970, 040.A20, in t he normalized condition. 3 SURFACE The surface to be white metalized should be fine-turned or ground to a finish of 6.3 µ m Ra. No surface damage is permissible. 4 THICKNESS The nominal white metal thickness should have been specified by the makers, but if no data is available then use the following: ( a) floating rings 0.5 mm

fixed rings 1 mm (b) half shells:

< 150 mm dia. 1 mm 150 - 300 mm dia. 2 mm > 300 mm dia. 3 mm



5 CLEANING PROCEDURE The steel backings should be cleaned by the following procedure: (a) A high pressure paraffin jet. (b) Degreasing. (c) Alkaline electrolytic bath cleaning. (d) Cold water washing. (e) Etching in strong (50% per volume) hydrochloric acid. Parts not to be

bonded should be painted with a 15% solution of sodium silicate in distemper.

6 TINNING After cleaning, the steel should be immediately dipped in zinc ammonia chloride flux (surfaces not to be bonded should be protected by painting with a 15% sodium silicate solution). The shell should then be coated by dipping into a bath of hot tin (330°C). A second dipping in tin at 250°C should be done just prior to casting the white metal. 7 WHITE METAL

Use WM TO BS 3332/2 or BS 3332/8

Wherever possible casting should be carried out by centrifugal arrangement.

Bore to be machined clean.



8 BOND SOUNDNESS First, the bore should be machined to obtain a clean surface. An ultrasonic test should be carried out both from white metal side and from steel side with a 10 mm dual probe to establish the quality of the bond. Note: A reflection will be seen from the interface. For a perfect bond this reflection is about 30% of the refraction obtained from metal/air (see Appendix A) For poor bonds it becomes greater. The metal interface of the reflection should be calculated with the formula given in Appendix A. If the reflection ratio is 30% larger than the calculated value the bond is suspect and the bearing should be rejected. The bond on seal rings to be 100% on bearings, 90% minimum. 9 WITNESSED INSPECTION The Inspector should stamp each item after ultrasonic acceptance. 10 MACHINING Final machine and check dimensions. 11 FINAL INSPECTION OF BOND FOR SEAL RINGS Carry out a second ultrasonic test - this should show 100% bond for acceptance.



DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE This Engineering Design Guide makes reference to the following documents: BRITISH STANDARDS BS 970 Specification for Wrought Steels for Mechanical and Allied

Engineering Purposes (referred to in Clause 2). BS 3332 White Metal Bearing Alloy Ingots (referred to in Clause 7 and

Date post:	02-Nov-2014
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