Зображення сторінки
PDF
ePub
[blocks in formation]

The medium of 5,000 feet is usually employed in ordinary work. but in specific cases it is sometimes desirable to run them at a lower or higher rate according to requirements. We recommend a number of revolutions equivalent to a surface speed of 5,500 feet. This does not indicate that they cannot be run at a higher or lower speed, but that it is a good average speed to produce good results. To allow an ample margin of safety it is recommended that wheels should not be run at a surface speed exceeding 6,000 feet. Every shop should have a speed indicator in order that the speed of its grinding machinery may be known.

Grading of Landis Grinding Wheels.

NUMBERS

The grains are numbered according to the number of meshes per lineal inch of the sieve through which they have passed. For example, No. 30 is a grain that will pass through a sieve having thirty meshes to the inch, but will not pass through a sieve having thirty-six meshes. The fineness, or number, of the emery or corundum used in making a wheel determines the "number” of the wheel.

The grains (and similarly the wheels) are numbered as follows: 10, 12, 16, 20, 24, 30, 36, 46, 54, 60, 70, 80, 90, 100, 120, 150. In this list the lower numbers indicate the coarser grains, the higher numbers, the finer ones.

When ordering wheels, be sure to specify diameter, shape, thickness, size of center holes, the grade and grain or description of material to be ground and speed proposed to run the wheels. If possible, give shape number.

For grinding hardened steel and cast-iron, wheels made by what is known as the silicate process give very good results, but the vitrified wheel in our experience is the better for general use.

A soft wheel is less apt to change the temperature of the work or become glazed.

A wheel is most efficient when just soft enough not to glaze and hard enough not to wear away rapidly.

Use a fine grained wheel for finish, a coarse wheel to remove stock. For general grinding a 24 combination grain wheel gives excellent results.

A good practice is to have several grades of wheels on hand best adapted for your different classes of work.

Always keep a spare wheel or two on hand for emergencies.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

CHAPTER XII

USEFUL INFORMATION FOR AUTO REPAIRMEN.

Anti-Freezing Cooling Solutions–Substances Usually Combined with Water

Advantages of Different Solutions—Electrolytic Action Not Desirable The Best Mixture-Extinguishing Fires in Volatile Liquids—First Aid to the Injured—Schaefer Method of Artificial Respiration—The Repair Shop Medicine Chest-Remedy for Burns, Cuts and Abrasions—Wounds and Painful Injuries—Home-made Aseptic Gauze.

Anti-Freezing Cooling Mediums.-To lower the freezing point of water it is possible to add various substances and the proportions added determine the point at which the solution will congeal. Among the materials commonly used may be mentioned common salt, alcohol, glycerine and calcium chloride. The alkaline solutions produce a distinct electrical action wherever two dissimilar metals are used together in the cooling system, such as the brass tubing of a radiator and the solder used at the joints; the cast iron water jacket and the aluminum or brass plates used to close the core print holes; the aluminum pump casing and steel or bronze impeller, and at many other points which will vary with the design of the car and the materials of the components. The alcohol solutions evaporate very quickly, the glycerine solution affects the rubber hose, and the salt solutions leave an incrustation as the water evaporates. It is reasonable to expect electrolytic action when metals of different potential are used together in any alkaline solution, which are electrolytes of high value. Taking it all in all, the selection of the best solution involves a consideration of many facts and various requirements must be considered in the selection of that most suitable. Considering the qualities of such a compound it will be seen that no one will combine all the desirable features, so in selecting the solutions the following should be kept in mind: To begin with, and it is a highly important consideration, the solution used should have no corrosive action, nor should its use prove deleterious on the metals or rubber used in the circulating system. It must be easily dissolved in or combined with water, must be reasonably cheap and not subject to rapid waste by evaporation, and should not be of such character that it will deposit sediment or foreign matter in the jackets, pipes or radiator water spaces. Its boiling point should be as high, if not higher than, that of water, and it should not congeal at temperatures ordinarily met with where it is used.

Substances Usually combined with Water.-Alcohol is prepared by destructive distillation of various vegetable substances which contain starch or sugar, such as potatoes, beets and numerous grains and fruits. Any starchy material will serve for the production of alcohol and the real question is one of cost, which varies with the locality in which the manufacture is carried on. It mixes readily with water, and does not congeal at any known temperature, though its boiling point is about 175 degrees Fahrenheit, and above this point evaporation is rapid. It is a very volatile liquid and will evaporate at very moderate temperatures. The alcohol generally used is denatured by the addition of a substance which renders it unfit for drinking purposes and because of the recent removal of the government tax it may be obtained for about 60 cents a gallon.

Glycerine is obtained as a by-product in the saponification of fats in soap and candle making, and is an oily substance which will vary in color from reddish brown when crude to a colorless liquid when pure. Crude glycerine sometimes contains free acids in small quantities though it may be purified and the color removed when it is to be used for certain purposes. This substance has a much higher boiling point than water, ebullition taking place at a temperature of 554 degrees Fahrenheit. Glycerine when pure is a sweet, colorless liquid and is mixable with water and alcohol in any proportion. It is most largely used in the manufacture of nitroglycerine, though utilized to some extent in pharmacy, soapmaking, filling instruments which require a liquid seal and which are exposed to low temperatures, and sweetening wine. It can be obtained in single gallon lots at a cost about $1.50.

Calcium chloride is a by-product of the Weldon process of obtaining chlorine which is to be incorporated into bleaching powder, from manganese ore and hydrochloric acid. It is a salt and is produced in the form of crystals, the crude material being yellowish white in color, though after purification it is clear white. It may be obtained directly from marble or chalk by dissolving these materials in hydrochloric acid. It is comparatively cheap and may be obtained in 10 pound sheet iron drums at nine cents per pound. Chemically pure its cost will vary from 30 to 60 cents per pound. It is very soluble in water, and while it is in solution it will lower the freezing point. It may contain free acid in the crude form, though this may be neutralized by the addition of a little slaked lime. Water will be evaporated rapidly at temperatures in excess of 185 degrees and salt will remain in the form of crystals. While calcium chloride solutions have been very popular they are not so well thought of at the present time because of a certain electrical action which is set up when the water circulation system is composed of dissimilar metals, as is commonly the case in motor car construction and corrosion at the points of juncture is unavoidable. As hydrochloric acid is used when this salt is obtained, there may be some free acid in combination with the cruder grades, and corrosive action will be noted. The corrosive action of chemically pure salt is very slight, though electrical action will be noted if dissimilar metals are employed, regardless of the purity of the salt in the solution.

Advantages of Different Solutions. The substances previously discussed all have advantages, some as relates to first cost. others to freedom from trouble. Alcohol is without doubt the best material to use from the viewpoint of action on metal or rubber, as it does not form deposits of foreign matter, will not freeze at known temperatures, and has no electrical effect. It is extremely volatile, however, and because of its low boiling point will eraporate at temperatures much less than that of the boiling point of water, and the solution in the water circulation system of the modern motor car often heated to this point, especially when the

« НазадПродовжити »