Cast White Metal Bearings

GBH Enterprises, Ltd.

Engineering Design Guide:
GBHE-EDG-MAC-5710

Cast White Metal Bearings

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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)

0.5

mm

fixed rings
(b)

floating rings

1

mm

1
2
3

mm
mm
mm

half shells:
< 150 mm dia.
150 - 300 mm dia.
> 300 mm dia.


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


Cast White Metal Bearings

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