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 calculations for helical compression springs and formulas for square wire springs.
| Identifier | ExFiles\Box 158\4\ scan0041 | |
| Date | 12th June 1936 guessed | |
| -4- Rate per inch of spring deflection: 5 / 1.14 = 4.4 lbs. per inch. For most helical compression springs where the wire diameter is not over one-fifth the mean spring diameter these formulas are satisfactory. On steel springs of over ½" diameter wire, which would be in the hot wound class, a modulus of 10,500,000 lbs. will be found more satisfactory than the 11,500,000 lbs. which is used for springs made of under ½" material. If instead of steel monel metal is used: G=9,200,000 and for phosphur bronze - G=6,250,000 will be found quite satisfactory. It will be noticed that in no calculation does material hardness enter. A dead soft spring will have the same rate as a glass hard one and will function the same up to the elastic limit of the material. This means that a spring from steel with a high elastic limit will undergo a greater deflection before its elastic limit is reached and hence hold a greater load as its rate per unit deflection in the same. Formulae for Square wire. Square wire is frequently used for spring and using the same characters as before we find: S = 9 P D / 4 d³ F = P 5.58 D N / G d⁴ Any springs coiled to a small mean diameter, the square wire on coiling becomes keystone shape, the inner side of the wire becoming broader than the outer. The cross section of the wire then looks like a truncate pyramid. Manifestly, calculations of the solid height of the spring from wire size direct would fail. If we let: O D = outside diameter of spring. P D = pitch. i.e. O.D. minus wire size. d = original wire size d = width of wire inside after coiling. | ||