For DRIVERS, MECHANICS & FOREMEN. .
Page 21
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A PRIZE OF TEN -SHILLINGS is awarded each week to the sender of the best letter which we publish on this page ; all others are paid for at the rate of a penny a line, with an allowance for photographs. All notes are edited before being published. Mention your employer's name, in confidence, as evidence of good faith. Address, D., M. and P., " The Commercial Motor," 7-15, Rosebery Avenue, London, E.C. 1.
Lamps Alight.
On Saturday, the 10th August, light your lamps at 9.2 in London, 10.0 in Edinburgh, 9.20 in Newcastle, 9.20 in Liverpool, 9.12 in Birmingham, 9.12 in Bristol, and 10.5 in Dublin.
Home-made Electric Arc Heating Apparatus.
The sender of the following communication has been awarded the 10s. prize this week.
[1885] "H.M." (West Bromwich) writes The growing demand for a higher quality in heat-treated steels, and for a constant improvement of the physical properties of the metal is making the electric furnace a commercial necessity, both in the manufacture of the metal and in its hardening and tempering.
"The enclosed sketch [which we have had redrawn. —ED.] shows a home-made apparatus for electric arc heating. The are has been successfully used for heat ing steel and obtaining hardening temperatures; and it is specially applicable for localizingthe hardening in a, certain part of the piece, the point of a cutting tool being a notable example. The two barrels are filled with salt water, and take the place of a more expensive transformer and rheostat.
"The following is a description of the apparatus: D is a, wooden table upon which is placed a rubber mat, and a cast-iron plate (C) is placed upon the mat as shown ; B is the carbon holder, and is a, very simple thing to make ; H is an insulated handle with a shield to protect the hand from the heat of the arc ; V is voltmeter ; A ammeter; CB, circuit breaker and G the dynamo ; F, shunt field with rheostat ; fc cast-steel terminal plates ; E E, steel castings ; T is the lathe tool to be hardened ; S, switch. The wofking of the apparatus is as follows e---By raising or lowering the steel terminal plates (K K1) in the barrels the current value can be regulated so that the tool (T) is heated to the desired temperature.
"A welding heat can also be obtained with this apparatus, which makes it very useful in a wellequipped garage where numerous repairs are reqaired. It is essential that all parts cf the body be protected from burns, as the heat and actinic rays from the are will burn any exposed part in the same way that a, burning glass does on a. hot day. Therefore, gauntlets, face shield and coloured eye-glasses must be worn.
"The steel is only heated at a spot directly under the carbon, and to heat the desired surface it is neces• sary to keep the carbon moving in a circle. It should not be brought too near the cutting edge of the tool, and the are should be started at a very low voltage,
which is steadily increased to the desired point by adjusting the shunt rheostat of the dynamo. The carbon must also be kept a short distance away from the steel, for if it touches it is very likely to be fused at that point. The correct hardening temperature must be judged by the eye, which, however, can be gauged after a little experience.
"The rapidity with which a piece of steel can be heated to a hardening or welding temperature is the greatest recommendation of the apparatus just described, as it takes only two or three minutes to heat quite a large surface on a fairly thick piece of steel, and when used for welding pieces together, the ends or faces being clean from slag or scale, readily unite.
"Hoping the above will be both useful and interest-'ing to many readers requiring some such apparatus as the above." • [We do not see any real need for the rubber mat, as the voltage dealt with is of so low a value that the insulation of the table should be ample for the purpose. An improvement, we should think, would consist of a handy means of elevating and depressing , the terminal plates.—En.]
Simple Oil Tests forthe Workshop.
[1886] " TN." (Gillingham) writes It is rather important that drivers of steam and petrol wagons and also garage foremen should know a few simple tests for oils and greases. Many a valuable chassis has been spoiled by the use of unsuitable lubricants, and too many responsible men are quite content to use any oil which happens to be at hand at the moment. Many of the rule of thumb tests so frequently advocated are useless. "The first simple test is for ascertaining the presence of acid. A polished copper plate should be immersed in the lubricant for a, few moments. If there is no acid present, no change will be noticeable on the surface of the plate. A trace of acid, however, will dim the surface.
"To determine whether amineral oil is pure, a small quantity of lIsS0a (sulphuric acid) should be ,added to a small quantity of the oil. Discoloration will follow if the oil contains any fatty material. The temperature should rise about 35 degrees F. on the addition of the acid if the oil be of good quality. "A test for the solidification of lubricating oil is to smear two polished iron plates with a thin layer of the oil. These should then be placed one on the other with the treated surfaces in contact. After -a few days, if the plates do not slide as freely as whea the oil was first applied, it may be taken that the oil is one that tends to solidify.
"Should it be desired to test mixed oils containing both mineral and fatty constituents, a small quantity of the lubricant should be mixed with a strong solution of caustic potash. The whole should then be shaken, and a fairly solid body will be formed varying in thickness or density with the quantity of fatty matter present in the oil, Of course, this does not give any indication of the relative proportions of the mineral and fatty matters present. With a pure mineral oil there will be, at most, a slight cloudiness, --but saponification will be marked if either animal or vegetable fats are present."