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).
Directions for studying materials, detailing test procedures for crushing load, ageing, density, water absorption, and tool wear.
| Identifier | ExFiles\Box 24\2\ Scan214 | |
| Date | 21th February 1922 guessed | |
| 572 DIRECTIONS FOR THE STUDY OF — An initial load of about 100 kilogrammes per sq. cm shall be applied and the initial length of the specimen read under this load, in order to eliminate the compression due to bedding on the ends. The load ultimately registered shall include this initial load. A series of loads shall then be applied to the specimen and the yield for each load shall be determined after one minute and ten minutes respectively. The yield shall be measured by the change of distance between the two compressing surfaces by means of two direct-reading gauges, one on each side of the specimen, the mean of the two being taken, or, alternatively, the two gauges may be combined so as to give a single mean reading. A magnification of not less than 100 should be used. For the 15 mm specimen, the minimum load that gives a yield of 0.5 mm, when computed from the following formula, shall be deemed to be the crushing load :— Yield = y + (0.25 y / y') where y and y' are the yields in millimetres at ten minutes and one minute respectively. When the dimensions of the specimen are less than 15 mm the permissible yield shall be reduced in proportion. 10. Ageing. To test the ability of a material to retain its mechanical characteristics after exposure to high temperature, specimens of the form and dimensions shown in Fig. 9 shall be maintained for a prolonged period at the grade temperature of the material. To ascertain the effect of the heat treatment, specimens shall be tested at intervals by being allowed to cool to a temperature between 15° C. and 20° C., and then tested for cross-breaking strength as described in Clause 8 (a), and the results obtained compared with those obtained before the heat treatment. MISCELLANEOUS. 11. Density. When density (mass per unit volume) is an important factor for ascertaining the suitability of a material, it shall be determined at 20° C. and shall be expressed in grammes per cubic cm. Note.—The density (mass per unit volume) of a solid heavier than, and unaffected by, water can be accurately determined by the following method :— The weight (M1) of a stoppered weighing bottle filled at 20° C. with freshly boiled distilled water is first determined. An accurately weighed sample of the material, of weight M2, is then introduced into the partially emptied bottle, and any air bubbles removed by placing the unstoppered bottle in a vessel, which is then exhausted with an air-pump. The bottle is then filled at 20° C. with air-free distilled water, re-stoppered, and weighed (M3). The weight of the water displaced by the solid is given by the following expression :— Weight of water displaced = M1 + M2 — M3, and, assuming D as the density of water at 20° C. (i.e. 0.998), the density of the material * is given by the following formula :— Density of material = (M2 / (M1 + M2 - M3)) × D 12. Water Absorption. A specimen 5 cm square and 5 mm thick shall be dried in a desiccator at a temperature from 15° C. to 20° C. until it ceases to lose weight, and then weighed with the usual precautions. It shall then be immersed in water at room temperature for 24 hours. The specimen shall be taken from the water and, after removing the surface moisture by wiping, shall be weighed again. The weight shall be taken to the nearest milligramme in each case. The percentage absorption of water shall be computed on the original weight of the specimen. TOOLING CHARACTERISTICS. The tooling characteristics of the materials shall be determined by the tests specified in Clauses 13 and 14. 13. Tool Wear. Tool wear shall be determined by making four equal cuts having a total length of 1 600 ft. (helical). The tool wear shall be measured at the end of each cut of 400 ft. (helical). For the purpose of grading the material, the tool wear shall be ascertained by measuring the length of the face of the tool on the axis where the maximum wear has taken place (see Fig. 14), and shall be expressed in mils.† FIG. 14.—Method of Measurement of Tool Wear. A = Length of face of new tool. B = Length of face of worn tool. A minus B = Tool wear. (a) Specimen. When practicable a specimen 14 inches long, 2 inches external diameter and 1 inch internal diameter shall be... * It is unnecessary to take account of the density of air in this calculation. † The following are suitable methods of measuring the tool wear :— (i) The use of a reading microscope, the tool being viewed in the direction of maximum wear and measurement being made of the depth of the worn surface at right angles to the top face of the tool. (ii) The use of a micrometer direct, or measuring from a suitable fixed stop on the holder, thus avoiding removing the tool. | ||