The forging procedure, including flash and contracting allowances.
| Identifier | ExFiles\Box 109\3\ scan0004 | |
| Date | 21th November 1939 guessed | |
| - 2 - Forging Procedure. We will now consider the forging procedure, analysing the constructions of the dies and the reasons for their various features as they arise. The piece of material, or blank, from which a forging is made is called the "use", and in the case of small levers is mostly made direct from the bar with the axis of the lever co-axial with the length of the bar from which it is made. The larger levers are made from bar which has been hand worked down to more nearly resemble the rough shape of the forging, and, or, depending on the importance of the piece, it may be further roughed out in a "use" die and finishing dies combined in one pair of dies. This method is adopted in the case of Conn. Rod and Crankshaft forgings and similar highly stressed parts, as being less violent in regard to the rate of distribution of metal in the dies and resulting in a more uniform and suitable grain flow. The ideal "use" would of course be one which filled the die without any surplus. As this is a practical impossibility a certain amount of metal must be forced out between the faces of the dies. Flash Allowance. This surplus metal is known as the "flash", and extends around the whole of the forging and is formed in a recess out in each face of the die to suit various weights of forgings. When the dies meet after a succession of 6 or 8 blows, the "flash" metal has a thickness of .025 to .030 for small levers, .040 to .050 for levers 5" to 6" long, and in approximately this proportion to .125 for a Conn. Rod forging. The "flash" is removed in stripping or "flashing" dies with the small forging cold, and hot in the case of the larger forgings. Contracting Allowance. This is an important feature and is necessary to ensure that the correct sizes are obtained when the forging has cooled from forging temperature to cold. | ||
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).