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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter from Ferodo Limited discussing the properties and performance of different brake disc materials.

Identifier  ExFiles\Box 141\3\  scan0104
Date  13th September 1932
  
x719.
All Communications to be addressed to the Company.

FERODO LIMITED

FERODO
RECD. TRADE MARK
BRAKE & CLUTCH LININGS

CODES: WESTERN UNION FIVE LETTER EDITION, BENTLEY'S COMPLETE & 2ND PHRASE, MARCONI INTERNATIONAL, LIEBER'S CODE, LIEBERS LATEST CODE, A.B.C. 5TH & 6TH EDITIONS.

TELEPHONE: 19 CHAPEL-EN-LE-FRITH (4 LINES)
TELEGRAMS: FRICTION, PHONE, CHAPEL-EN-LE-FRITH.

CHAPEL-EN-LE-FRITH,
VIA STOCKPORT, ENGLAND.

September 13th 1932

YOUR REF. HS{Lord Ernest Hives - Chair}/RM.{William Robotham - Chief Engineer}22/KT.
OUR REF. FJF/WAC.

Depots:
LONDON
222, TOTTENHAM COURT RD W. 1.
ABERDEEN
26, GUILD STREET.
BELFAST
8, 10 & 12, MONTGOMERY ST
BIRMINGHAM
202, CORPORATION ST
BRIGHTON
84, QUEEN'S ROAD.
BRISTOL
19, PARK STREET.
CARDIFF
39, CHARLES ST
DUBLIN
120, UPPER ABBEY ST
GLASGOW
70, WATERLOO ST
LEEDS
25, HUNSLET RD
LIVERPOOL
1-3, BERRY STREET.
MANCHESTER
32, CATHEDRAL ST
NEWCASTLE-ON-TYNE
WORSWICK CHAMBERS,
10, WORSWICK ST
OFF PILGRIM ST

Messrs. Rolls Royce Limited,
DERBY.

For the attention of Mr. W.A.Robotham.

Dear Sirs,

In further reference to our letter of the 10th instant and referring first to the last paragraph of your letter of the 8th instant, may we explain that we find the original Discs, Part No. G.78524 supplied in Ferodo Bonded Asbestos RAD.13/047, were finished with a black surface dressing - but we have discontinued this practice for some time and the Discs recently supplied to you were left in their natural colour, but in every other respect they are exactly similar to the original Discs. We do not think you will find any difference between the performance of the coloured and plain discs as, in our experience the colour dressing, which was merely superficial, in no way affected the co-efficient of friction or any other essential feature of the Discs.

We note that you would like to try a few Discs in our VDM/20 quality material. You referred to BLM/20 but the symbol VDM/20, which no doubt you wished to indicate by your reference 'BLM/20', refers only to brake liners; the symbol for discs in practically the same material is VDM/20.

The characteristics of VDM/20 material, which is a moulded product, are substantially different to those of RAD.13 - for instance the coefficient of friction range is considerably lower. When running RAD.13 gives a c.o.f. of .41 at 100°F rising to .44 at 400° F and falling again to 0.4 at 550°F.{Mr Friese} This material can be used satisfactorily when lubricated with oil or grease. VDM/20, on the other hand, has a "running" c.o.f. of 0.31 at 100° F, rising steadily to 0.36 at 550°F and, unlike RAD.13, is not satisfactory in the presence of oil or grease - hence for best results it should be used perfectly dry. The values of the c.o.f. for both materials are given against 0.4/0.6 carbon steel.

It is, of course, difficult for us to decide which is the better material for your servo-motor facing and we suggest that a trial only will demonstrate any advantage which one may have over the other, for which purpose we are sending you six Discs to Part No. G.100583.

Speaking generally, we are of the opinion

[Handwritten note in left margin:] see over

[Circular stamp at bottom:] 14 SEP 1932 R.R. LTD. D.E.D.
  
  


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