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).
Journal page detailing various testing procedures for oils and an article on international salesmanship.
| Identifier | ExFiles\Box 32\4\ Scan277 | |
| Date | 5th October 1928 | |
| 554 THE ELECTRICAL REVIEW. OCTOBER 5, 1928. Tests for Organic Acids.—Acidity in oils is generally due to partial decomposition of the oil, accompanied by the liberation of fatty acids, which act as corrosive agents. Properly refined mineral oils are entirely free from acidity, but nearly all vegetable and animal oils possess it in a varying degree. To test, about 10 gm. of oil are slightly heated with about 50 c.c. of pure, acid-free, 95-per cent. alcohol, and the liquid is agitated. When cool a few drops of phenol-phthalein is added, and the solution titrated with a centi-normal solution of potassium-hydroxide until the red colour appears. The number of milligrams of potassium-hydroxide required per gram of oil gives the acid number, which should not exceed 0.2 milligrams. Saponification Test.—This gives the number of milligrams of potassium-hydroxide required to completely saponify the combined and free fatty acids. The reagents required are an approximately half-normal solution of hydrochloric acid, the exact value of which has been determined by titrating with potassium hydroxide, and an alcoholic solution of potassium-hydroxide containing 40 gm. of pure potassium-hydroxide in 1 litre of pure alcohol. One to two gm. of oil are placed in a flask fitted with a condenser neck, together with 25 c.c. of alcoholic potassium-hydroxide. The contents are boiled on a water bath until saponification is complete (generally about 15 min.). A few drops of phenol-phthalein indicator are then added, and the excess alkali titrated with the hydrochloric-acid solution. The standard of the potassium-hydroxide solution may vary somewhat, and in order to check this, it is necessary to heat another 25 c.c. of potassium-hydroxide for the same length of time as in the previous instance, and titrate it with the acid solution. The difference between the number of c.c. of acid solution used in the two tests is then expressed in milligrams of potassium-hydroxide, and calculated per gm. of oil gives the saponification number. Viscosity.—This is a comparative test embodying the measurement by the rate of flow of the oil through a given orifice. It is really an indication of thickness, as opposed to fluidity, of the oil. Temperature is a very important consideration. Viscosity is usually measured by some form of commercial testing apparatus such as Redwood’s Viscosimeter. Viscosity is not of great importance with transformer oils, since the internal heating will soon render the oil thin enough for efficient circulation. With switchgear the conditions are entirely different, and the thickness of the oil may seriously affect its arc-quenching abilities. For a like reason the freezing point is an important consideration for switchgear likely to be exposed to low temperatures. Tests for Resins.—Incompletely refined oils easily resinify. Resin may be detected if a sample of oil is shaken with a quantity of boiling water and held at 100 deg. C. for some time. Its presence is indicated by the precipitation of fine white granules at the point of separation of the oil and water. Flash Point.—This is the temperature at which the oil gives off inflammable vapours, and is important on account of fire risks. It is usual to check the flash point with some form of recognised closed testing apparatus, e.g., the Pensky-Martens flash tester. The following would doubtless not be notable for accuracy, but it has been suggested as a substitute, should a commercial testing apparatus not be available. It should succeed in detecting an oil with a dangerously low flash point. A sample of oil is placed in a porcelain crucible which is heated on a sand bath. The crucible is covered with a piece of tinplate in which are two small holes, one for a thermometer and the other as a “touch” hole. At, say, every 10 deg. C. above 130 deg. C. a lighted match is inserted in the “touch” hole; when the first faint explosion of mixed oil-vapour and air occurs, the flash point is indicated. Sludging.—The formation of sludge is not of as great importance with switchgear as with transformers, since with the former the oil must be periodically cleaned. With transformers, however, the matter is different; as long as moisture is kept out of the oil, the life of transformer oil is indefinite. So-called non-sludging oils are more expensive than those with a greater sludge tendency, since they must be better refined. It has been found that the deposit of sludge is chiefly composed of oxidisation products, the copper apparently acting as a catalytic agent and accelerating the deposit. In order to reduce the possibilities of oxidisation, oil tanks should be air-tight, and apart from electrical considerations, corona, and the consequent formation of ozone should be rigorously avoided, since ozone is a very powerful oxidising agent. The following non-sludging test has been approved by B.E.S.A. Specification 148—1927; Pure dry air is passed through 100 c.c. of oil at the rate of 0.07 cu. ft. per hour (about 3 bubbles per sec.), the oil being heated at 150 deg. C. in a 200-c.c. flask. The flask should also contain a piece of polished copper of 5 sq. in. surface area, and the heating should continue for 45 hours. The deposit may be weighed after filtering and washing with petroleum spirit, and should not exceed 0.1 per cent. for Class A and 0.8 per cent. for Class B of the original weight of oil (100 c.c.). Filtering.—Dust and other suspended foreign matter may usually be removed by filtering through some finely woven linen. It will be seen that some of the foregoing are standard oil tests, applicable to all types of oil (lubricating, &c.). Most of them are fairly simple, and could be undertaken by most test departments. It is possible that some of the more complicated tests (sludging, saponification, and so on) would have to be taken for granted, although reagents could be purchased ready prepared, and thus save some trouble. If the simpler tests were carried out systematically and periodically, it would then be possible to state something definite regarding one vulnerable point, when trouble occurs. Salesmanship Abroad. WHEN the same old advice has been given in the same old way during a period of many years, the same old listener hardens his heart and, with a superior air, passes on his way. But some of the old things have to be constantly reiterated because they are true and have been ignored, though they are matters of first importance. For more than twenty years we have advocated here that British foreign traders should make a closer and more specialised study of overseas markets—their language, temperament, art, literature, and all that goes up to make what we call “customs and conditions.” Editorially, and from the pens or mouths of expert observers in various markets, the counsel come, and we have done our best to trumpet it forth, hoping to influence the minds of men engaged in planning a trading policy for electrical export firms. But personnel changes are always taking place, and new firms or companies are continually coming into a developing industry; so, after all, it may be necessary and quite justifiable to repeat the same old truths again and again, even after the lapse of years. The British electrical export trade has made such great progress that it would be absurd to suggest that such advice has not been acted upon. It has happened that special efforts or campaigns made in a particular market, or several markets, have been permitted to run their course, produce their volume of business, and die out instead of being persistently continued. New men have come along and other measures have been recommended or taken, but the world has undergone such marked changes that there is ever need for these and other new men who will adopt new ways adapted to changing market conditions and requirements. To all such men connected with the electrical | ||