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 the study and testing of hard composite dielectrics and insulating materials, including electrical tests and temperature grading.
| Identifier | ExFiles\Box 24\2\ Scan208 | |
| Date | 21th February 1922 guessed | |
| 566 DIRECTIONS FOR THE STUDY OF The adoption of the methods of test given here is strongly commended to manufacturers and to users of these materials, so that a uniform practice in tests of this nature may be established. It is anticipated that if tests such as these are generally applied in Works Laboratories and elsewhere for the purpose of studying composite insulating materials, considerable improvements in quality will result. The Director of the E.R.A. will value comments and criticism from those who have occasion to use any of the tests given in this Specification. INTRODUCTION. Hard Composite Dielectrics (Insulating Materials), for which the tests given in this Specification are applicable, comprise the following :— Vulcanized* rubber, Vulcanized materials other than rubber, Unvulcanized materials, whether moulded to final shape, or in forms such as sheet, rod, or tube from which parts may be machined. This Specification defines methods of testing such materials with a view to ascertaining their electrical and mechanical characteristics, and suitability for different classes of service. For the purpose of the complete Specification the following characteristics, which are not dealt with in this Specification, will be subject to further research :— Surface breakdown, Dielectric losses, Burning (inflammability), Flash-point, Fire resistance, Action of solvents. Limits to the values to be obtained in the tests are not set in this Specification for purchasing for particular purposes. Such limits may be derived later when more test-results are available, obtained by the methods herein defined. All the tests are suitable for investigating the characteristics of a particular grade of material, but the simpler tests are also suitable for checking individual consignments. SPECIFICATION. 1. Temperature Grading. Hard composite dielectrics are graded according to the temperatures they will withstand. If a material purports to have a given temperature grade it shall fulfil the requirements of Clauses 3, 5, 7, 8, and 10 of this Specification with respect to that temperature. This Specification gives limits for the plastic yield test only (see Clause 7). This test has been found suitable for ascertaining the approximate grade temperature of most materials, but it should be understood that the grading as found by the plastic yield test has no value unless, at the temperature so determined, the results of the resistivity, electric strength, and other * The term "Vulcanized" denotes that a chemical combination between sulphur and rubber, or other organic material, has been effected. tests specified to be carried out at that temperature also are satisfactory. ELECTRICAL TESTS. 2. Conditions of Test. Tests are provided for machined and for moulded specimens under the conditions given below. These conditions do not apply in every case, but in order to demonstrate the general characteristics of a given material, tests shall be carried out under the conditions scheduled at the end of each clause to which they apply. Except in the case of specimens to be immersed in oil [see (h) below], each specimen shall be given a preliminary treatment, being wiped carefully with petroleum spirit, specific gravity not exceeding 0·68 at 15° C. (a) New condition, at a temperature from 15° C. to 20° C. (b) New condition after remaining in a desiccator for 24 hours. The specimen to be tested whilst in the desiccator at a temperature from 15° C. to 20° C. (c) New condition after remaining in a controlled atmosphere, relative humidity 80 per cent, for 24 hours. The specimen to be tested whilst in the controlled atmosphere at a temperature from 15° C. to 20° C. (d) New condition after heating in an oven for one hour at grade temperature, preparatory to testing in the oven at grade temperature. (e) After immersion in distilled water for one week at a temperature from 15° C. to 20° C., and afterwards removing surface moisture by wiping, preparatory to testing at a temperature from 15° C. to 20° C., within 10 minutes of removal from the reagent. (f) After immersion in an approximately 10 per cent solution of salt in water for one week at a temperature from 15° C. to 20° C., followed by swilling with distilled water, and then removing surface moisture by wiping. The test to be made at a temperature from 15° C. to 20° C. within 10 minutes of removal from the reagent. (g) After immersion in sulphuric acid solution (specific gravity 1·25 at 15° C.) for one week at a temperature from 15° C. to 20° C., followed by swilling with distilled water, and then removing surface moisture by wiping. The test to be made at a temperature from 15° C. to 20° C. within 10 minutes of removal from the reagent. (h) After immersion in mineral transformer oil (specific gravity approximately 0·86 at 15° C.) for one week at grade temperature (but never higher than 100° C.) preparatory to testing in the oil at grade temperature (but never higher than 100° C.). (i) After immersion in any other reagent which may be required to meet special conditions. | ||