Part 14 (1/2)

_Arc Welding Machines_--A consideration of the function and purpose of the various types of arc welding machines shows that the only reason for the use of any machine is either for conversion of the current fro to direct, or, if the current is already direct, then the saving in the application of this current in the arc

It is practically out of the question to apply an alternating current arc to welding for the reason that in any arc practically all the heat is liberated at the positive electrode, whichcurrent, half the heat is liberated at each electrode as the current changes its direction of flow or alternates Another disadvantage of the alternating arc is that it is difficult of control and application

In all arc welding by the use of the carbon arc, the positive electrode iswith metallic electrodes this may be either the piece to be welded of the rod that is used as a filler

The voltage across the arc is a variable quantity, depending on the length of the flaases liberated in the arc With a carbon electrode the voltage will vary from zero to forty-five volts With the e will vary from zero to thirty volts It is, therefore, necessary for the welding machine to be able to furnish to the arc the requisite a varied, and furnish it at all ti apparatus is a resistance in series with the arc This is entirely satisfactory in every way except in cost of current By the use of resistance in series with the arc and using 220 volts as the supply, frohty to ninety per cent of the current is lost in heat at the resistance Another disadvantage is the fact that e their resistance as their te the a on the temperature of the resistance

There have been various ood many machines have been put on the market for this purpose All of them save some power over what a plain resistance would use Practically all arc welding enerator sets, the e and current, this enerator delivering approximately seventy-five volts direct current Then by the use of a resistance, this seventy-five volt supply is applied to the arc Since the voltage across the arc will vary from zero to fifty volts, this machine will save from zero up to seventy per cent of the power that the machine delivers The rest of the power, of course, has to be dissipated in the resistance used in series with the arc

A enerator set which can be purchased fro piece of fence ound around a piece of asbestos, gives results equally as good and at a very small part of the first cost

It is possible to construct a machine which will eliminate all losses in the resistance; in other words, eliminate all resistance in series with the arc A machine of this kind will save its cost within a very short ti it in figures, the results are as follows for average conditions

Current at 2c per kilowatt hour, metallic electrode arc of 150 ae across the e across the carbon arc 35 Supply current 220 volts, direct In the case of thethis arc is sixty-six cents per hour With the carbon electrode, 220 per hour If a enerator set with a seventy volt constant potential machine is used for a welder, the cost will be as follows:

Metallic electrode 252c Carbon electrode 84c per hour With a e at the arc and eliminate all the resistance in series with the arc, the cost will be as follows: Metallic electrode 72c per hour; carbon electrode 42c per hour This is with the understanding that the arc is held constant and continuously at its full value This, however, is practically impossible and the actual load factor is approxi a welder as it is usually operated, this result will be reduced to one-half of that stated in all cases

CHAPTER VII

HAND FORGING AND WELDING

S heated iron, steel or other e_--Theof a shallow pan for holding the fire, in the center of which is an opening froh which air is forced to ure 48--Tuyere Construction on a Forge]

Air is forced through this hole, called a ”tuyere” (Figure 48) by means of a hand bellows, a rotary fan operated with crank or lever, or with a fan driven from an electric motor The harder the air is driven into the fire above the tuyere the en is furnished and the hotter the fire becoh which the ashes that drop from the fire may be cleaned out

_The Fire_--The fire isa sasoline, over the tuyere, lighting the waste, then starting the fan or blower slowly Gradually cover the waste, while it is burning brightly, with a layer of soft coal The coal will catch fire and burn after the waste has been consumed A piece of waste half the size of a person's hand is a coal” A lu coal breaks easily, shows clean and even on all sides and should not break into layers The coal is broken into fine pieces and wet before being used on the fire

The fire should be kept deep enough so that there is always three or four inches of fire below the piece of h fire above the work so that no part of theheated comes in contact with the air The fire should be kept as s these rules as to depth

To es To es in a compact mass and loosen the fire in the center Add fresh coal only around the edges of the fire It will turn to coke and can then be raked onto the fire Blow only enough air into the fire to keep it burning brightly, not so h the top of the coal pack To prevent the fire fro out between jobs, stick a piece of soft wood into it and cover with fresh wet coal

_Tools_--The _ha about a pound and a half

The _sledge_ is a heavy ha a handle 30 to 36 inches long

The _anvil_ is a heavy piece of wrought iron (Figure 49), faced with steel and having four legs It has a pointed horn on one end, an overhanging tail on the other end and a flat top In the tail there is a square hole called the ”hardie” hole and a round one called the ”spud”

hole