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).
Page detailing die molding techniques, including pin extraction, curing, and construction for materials like Bakelite.
| Identifier | ExFiles\Box 39\3\ Scan096 | |
| Date | 24th May 1921 guessed | |
| -3- Holes are molded by hard steel pins inserted in the die. The material closes and grips these, and generally they have to be left in the molded piece and extracted afterwards. On large production these pins, where they are in the line of pressure, are extracted by a small ram in the press, and a stripper plate, and this method is recommended by the General Bakelite Co. as reducing scrap, but is not used by the average jobbing molder because of the great cost of the press and of the dies. Big dies are steam-jacketed by holes bored in the body of the die. After the "curing" operation, which in big pieces like aeroplane propellers takes several hours, cold water is turned into the steam passages and the mold is cooled with the dies still closed to eliminate distortion. On quantity production work even quite small dies are jacketed and heated and cooled in this way. But in small production work on small and medium pieces like distributor parts, the dies are solid and are heated by conduction from the steam heated platens of the press. They are transferred to a cold press, to cool off under pressure, after the "curing" operation is over. The dies are then opened and steel pins extracted from the holes, and the die is refilled for the next job. The whole secret of success apparently lies in the construction and design of the dies, if one excepts the questions of time in the dies, which is important and can only be arrived at by experiment, and the grade of material used. The tendency is always to get quicker production by not giving the material time to cure thoroughly. In big pieces the inner parts will then still be in powder form, which can be ascertained by breaking samples. The details of die construction include such matters as holding of inserts, withdrawing of pins, guiding of the two halves, etc. and are a trade secret with each molding concern. It is noticeable, however, that though all sorts of intricate parts, which formerly were made as die castings, are now being molded in Bakelite, the typical Bakelite molding for quantity production (of which the modern distributor head of any American ignition is a type) has all holes, inserts, etc. in the line of pressure. This doubtless makes a much cheaper die and reduces manufacturing cost, as the inserts are not displaced by the molding pressure. | ||