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 use and properties of Litharge (Lead Oxide) in friction and clutch linings.
| Identifier | ExFiles\Box 141\1\ scan0118 | |
| Date | 9th April 1936 | |
| FERODO LIMITED All Communications to be addressed to the Company. TELEPHONE: 19 CHAPEL-EN-LE-FRITH (4 LINES) TELEGRAMS: FRICTION, PHONE, CHAPEL-EN-LE-FRITH. FERODO REGD. TRADE MARK. BRAKE & CLUTCH LININGS CHAPEL-EN-LE-FRITH, STOCKPORT, ENGLAND. CODES: WESTERN UNION FIVE LETTER EDITION, BENTLEYS COMPLETE & 2ND PHRASE, MARCONI INTERNATIONAL, LIEBER'S CODE, LIEBER'S LATEST CODE, A.B.C. 5TH & 6TH EDITIONS. Depots:- LONDON 222, TOTTENHAM COURT RD W. 1. ABERDEEN 26, GUILD STREET. BELFAST 8, 10 & 12, MONTGOMERY ST BIRMINGHAM 188, CORPORATION ST BRIGHTON 84, QUEEN'S ROAD. BRISTOL 118, VICTORIA STREET. CARDIFF 39, CHARLES ST DUBLIN 120, UPPER ABBEY ST GLASGOW 70, WATERLOO ST LEEDS UNSLET RD LIVERPOOL 1-3, BERRY STREET. MANCHESTER 32, CATHEDRAL ST NEWCASTLE-ON-TYNE WORSWICK CHAMBERS. 10, WORSWICK ST OFF PILGRIM ST 9th. April 1936 YOUR REF. OUR REF. JNL/KM Dr. F.{Mr Friese} Llewellyn Smith, Messrs. Rolls Royce Ltd., DERBY. Dear Dr. Smith, I thank you for your letter of April 8th. enquiring for information on the merits or disadvantages of Litharge in materials of the type Hycoe and our "No.6". Litharge, or Yellow Lead Oxide, is an old-fashioned rubber compound material, and its use dates from the time when, along with Lime and Magnesia, it was the best known agent for accelerating the vulcanization of rubber mixings. It is very heavy being, in fact, 93% metallic Lead, and this imparts a high specific gravity to mixings in which it is employed. In friction linings it has advantages for some purposes in that under heat of rubbing the Lead Oxide becomes changed to metallic Lead as there is nearly always a reducing atmosphere during friction heat, particularly when the lining is rubber-bonded. Changing thus to metallic Lead it melts at around 327°C and is apt thereby to induce a fade. In clutches, which in our viewpoint are not intended to slip, at any rate to produce temperatures of this order, we consider this property a definite fault, and although many of our brake linings embody Lead ( a Ferodo world-wide patent incidentally) we do not apply the principle to clutch linings. Further arguments against its use are:- 1. In a clutch application it applies additional unnecessary weight. 2. We do not care to use accelerators in friction linings generally because, while acceleration means a saving in time and temperature, it is one of our principles that brake linings should be cured at high temperatures. You will see that this is incompatible with the objects to be gained by using accelerators. (In brake linings we use metallic Lead which is not an accelerator.) 3. The accelerating effect of Litharge does not rest when the product is finished vulcanized. In vulcanizing the Litharge remains as a mixture of Lead and Lead Sulphide, which has a very definite ageing and deteriorating effect, the product becoming harder and more brittle the longer it remains in stock. | ||