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 outlining testing procedures for untreated electrical insulating papers.
| Identifier | ExFiles\Box 24\2\ Scan244 | |
| Date | 30th January 1923 guessed | |
| ELECTRICAL INSULATING PAPERS (UNTREATED). from every roll, or on separate sheets from each ream:— (a) The paper shall be saturated with a dilute solution of hydrochloric acid, specific gravity approximately 1·1, and then immersed in a potassium ferrocyanide solution to precipitate the iron present. Each iron particle will produce a blue spot on the paper. The number of deeply stained particles per square foot of paper shall be stated. (b) A 1 per cent. solution of silver nitrate shall be applied to the surface of the paper. Each metallic particle will produce a black spot on the paper. The number of black spots per square foot of the paper shall be stated. (c) The sample of paper shall be dipped into a 1 per cent solution (by volume) of acetic acid, and then allowed to air-dry for 1 hour while lying flat on a cloth. When dry, the sample shall be dipped again in a solution containing 0·1 cub. cm acetic acid and 0·1 gramme of potassium ferricyanide in 100 cub. cm distilled water. Each metallic iron particle will produce a blue spot on the paper, and each copper, brass or gun-metal particle a red spot. The number of blue and red spots, respectively, per square foot of the paper shall be stated. Note.—The potassium ferricyanide solution should be tested before use with some precipitated ferric hydroxide dissolved in strong nitric acid, and diluted with water. The potassium ferricyanide solution should give no blue precipitate or coloration. 10. FLASH TEST FOR CONDUCTING PARTICLES. It is not necessary to condition the paper prior to carrying out this test, provided the paper has been stored so as to attain the condition of ordinary room humidity. The paper shall be drawn at a speed of 2 feet per minute between a metallic plate and a system of overlapping rollers, arranged as shown in Fig. 4. The rollers shall be of brass, 3 inches long and 7/8 inch diameter. The edges of the rollers shall be rounded to a radius of 1/32 inch. Each roller shall exert a pressure of approximately 10 oz. on the paper under test. The paper shall be subjected to an alternating potential difference of 50 volts (R.M.S.) per mil thickness of the paper. The frequency of the potential difference shall be 50 ~ per second. A resistance shall be inserted in the testing circuit to limit the current so that the electrodes are not damaged when a puncture occurs. An electric lamp or other suitable indicator shall be used to demonstrate failure of the insulation. On a failure occurring the defective spot shall be marked and the paper then drawn back and passed through a second time. The ability of the part originally defective to pass test on second application shall be noted. Not less than 5 square feet of paper shall be tested. The number of punctures per square foot shall be stated. 665 11. CRINKLING UNDER TENSION. Note.—It is sometimes necessary to investigate the tendency of paper to crinkle, especially after " varnish treatment " when wound under tension between rollers. The crinkling is associated with the elongation and the porosity of the paper. Further information is required before a satisfactory clause can be drafted. 12. MICROSCOPICAL EXAMINATION. A microscopical examination of the paper shall be carried out for the purpose of identifying the fibrous materials from which it had been made. The approximate percentage of the constituent fibres shall be stated. The following method of preparing the samples for microscopical examination and the means of identification of the fibres are recommended by the U.S. Bureau of Standards *:— " Ten specimens, each about the size of a sixpence shall be cut from separate sheets, when the paper is submitted in sheets, or from different positions in the length of the roll, when the paper is submitted in a roll. The 10 specimens shall be torn into small pieces and placed in a 50 cc beaker to which approximately 20 cc of a 0·5 per cent solution of caustic soda is added. The beaker is placed on a hot plate or stove and brought to a boil, but the boiling is not continued for more than a minute or two. The liquor is drained off and the pieces of paper are washed several times with tap water, care being taken that none is lost. They are then washed with approximately 20 cc of 0·5 per cent solution of hydrochloric acid, and then washed twice more with tap water. A portion of the small pieces is rolled between the fingers into a pill about the size of a small pea and transferred to a test tube, which is half filled with water. The test tube is shaken until the paper is disintegrated into fibres. By means of a glass tube of about 5 mm internal diameter a representative amount of the fibres is transferred to a glass slide and the water removed by placing several thicknesses of hard filter paper on either side of the slide. After the excess water has been thus removed, a strip of filter paper is placed on the fibres to absorb any traces, leaving the fibres dry, but not so dry that there will be difficulty in separating them. Two or three drops of the zinc-chloride-iodine stain described below are placed on the fibres, which are teased out with steel needles until the fibres are reasonably uniformly distributed and free from knots of fibres. " Composition and Preparation of Zinc-Chloride-Iodine Stain.† 25 cc saturated zinc chloride solution at 70° F.{Mr Friese} (21·1° C.). 5·25 gm potassium iodide. 0·25 gm iodine. 12·5 gm distilled water. * Circular No. 107, "The Testing of Paper." † This formula is tentative. Its value is subject to a number of factors that are now being studied by the Paper Section, Bureau of Standards, U.S.A. | ||