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).
Specification guide for ordering torsion springs, including calculation formulas and diagrams of various types.
| Identifier | ExFiles\Box 158\4\ scan0050 | |
| Date | 12th June 1936 guessed | |
| Torsion Springs Specifications when ordering Material Beyond this specification it is necessary to submit a drawing with full description or a sample. Torsion springs are entirely special. The springs used in torsional action, i.e., one which puts the helix under a twisting action, are an entirely different problem than compression springs. The former puts the material in bending and the latter in torsion. Due to the variety of load points and tests, the best method of calculation is as if the load were concentrated at the spring center. The load then becomes inch pounds of torque. Stress calculations again revert to S = M V / I Here M = inch lbs. torque V = d/2 I = πd⁴/64 for circular wire Wherein d = wire diameter Substitute and simplify we obtain: S = 10.2 M / d³ The entire wire section is also subject to a direct tensile load set up by the tangential pull on the wire at right angles to the cantilever loading. This stress equals 8 M / πD d² which is derived from load area considerations. The total stress is the summation of these two stresses. Safe commercial formulas as published by Stewart, S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} Journal, August, 1925, give: (1) Inch pounds for safe load = 20,000 d³ (2) Inch pounds per turn = E d⁴ / 11.5 N D (3) Total turns for safe deflection = N D / 130 d Wherein: d = wire diameter D = mean diameter of spring N = Number of coils E = Modulus—30,000,000 for steel In considering torsion springs the variations in loads due to wire and diameters not being exact must be considered. In case a bar is used in the center of the spring the bar must not be large enough for any wrapping or binding. Such action will either bend or break the spring. A torsion spring must always operate so that the coils tend to wind up—i.e., increase in number, and consequently cause a reduction in spring diameter. When ordering Torsion Springs we require a sample, sketch or blue print or a description of the conditions under which the spring must operate. These drawings show only a few of the various styles of Torsion springs which we make. HINGE ENDS SHORT HOOK ENDS STRAIGHT TORSION STRAIGHT OFFSET SPECIAL ENDS DOUBLE TORSION | ||