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).
The processes for oil blacking and heat blacking metal components.
| Identifier | ExFiles\Box 38\6\ Scan179 | |
| Date | 16th April 1919 | |
| R.R. 220 A (100 T) (S.P. 575, 16-4-19) 6. 2354. OIL BLACKING The work to be treated, which should be bright and free from scale or rust but may be oily, is incorporated with a mixture of tempering oil and sawdust as follows:- Weight of work.........1 cwt. 1 qr. " " sawdust.......5 lbs. " " oil.............5 lbs. The sawdust is preferable pinewood but other kinds work satisfactorily. The tempering oil is obtained from Messrs. Gilman & Son, Birmingham. The mixture is placed in a rotating "kettle" which is bottle shaped receptacle with a narrow mouth capable of being rotated round its own axis and tilted from a nearly vertical position through horizontal into a position in which the contents can be discharged. The inside dimensions are about 3½ ft. long x 2 ft. diameter. These are heated by gas jets and are kept rotating during the colouring process. The temperature of the kettle is about 350°C; the usual time required is 20 to 30 minutes, and when the work attains the desired colour the riddles are emptied into riddles resting in large metal trays by tilting the kettles whilst they are still revolving. The riddles separate the sawdust from the work and the latter is then thrown out to cool, then washed with a mixture of equal parts of turpentine substitute and common oil. The excess oil is drained off in a centrifugal separator and the work is then ready for packing. The above treatment can be used for hardened articles, in which case the cooling process tempers the work. It can also be used for colouring soft work. HEAT BLACKING The articles to be heat-blacked may be of steel or cast iron, and, if oily, should be washed with paraffin oil and drained. This operation is necessary to remove any dust and small pieces which remain on the surface after machining operations. Such particles adhere firmly after the heat treatment and as, for instance, in the case of screw threads, may necessitate the employment of a sizing operation which would remove the coating. The washed articles are then placed in, or conveyed through, a furnace heated up to a temperature of 650°C, to 700°C in a strongly oxydising flame. The time taken to heat up to this temperature is about 10 minutes, after which they are quenched in, or conveyed through, oil for 35 seconds. The oil used should be either cottonseed or whale, preferably the former, and the temperature of the oil in the quenching tank should not be allowed to exceed 100°C. This ensures proper cooling and no risk of firing. On emersion from the oil, the articles are dipped momentarily into paraffin oil to remove surface quenching oil, and then well rubbed in fine, clean sawdust, and blown with air. It is important that the flame should be as oxydising as possible without causing the surface of the metal to blister or flake. The air is supplied from a rotary compressor giving a pressure of about 20 lbs. per sq.in. This air is supplied to both | ||