Sheet Brass

Sheet brass can be welded to brass or to sheet Steel after sufficient experimenting to determine the proper heat and pressure.

Sheet Aluminum

Sheet aluminum of some grades can be spot-welded but the surface will be rough and pitted where the die points touch it.

Sheet Copper

Sheet copper is hard to weld because of its low resistance, but it can be done by an experienced operator using sufficient current.

Table XI. Power And Time For Butt Welding

Limits As To Thickness Of Metal

There is a limit to the thickness of sheets which can be spot-welded and to the sectional area of pieces which can be butt-welded because of the heating of the dies or clamps by the large amounts of current required for heavy work. If enough cooling water is passed through the dies to prevent overheating, it will also carry off some of the heat from the work and a point is soon reached where the area of contact of the dies becomes so great as to be a disadvantage. Theoretically, it is possible to weld any size section with a comparatively small current by leaving it on long enough, but in practice we must take radiation into account, for a point is soon reached where radiation equals the heating effect of the current and, at this point, the temperature remains constant.

Power Required

The power required for butt and spot welding is easily determined from the cross section and material of the piece, because considerable experimental data is available. As previously stated, the power required for this kind of welding varies inversely as the time consumed in making the weld. This means that the longer you can take to do the work, the less current you will require; and the quicker you wish to accomplish the work, the more current you must use. The total amount of energy in kilowatt hours will be the same in either case, but a larger transformer must be used for rapid work.

Fig. 111. Coffee Pol with Spot-Welded Spout.

Table XII. Butt Welder Data

As the rate charged for current varies in different places, we have figured the current at one cent per Kw. hour to give a basis for calculating the cost. Multiply the prices given above by the rate per Kw. hour charged by your local electrio light company, and that will give your cost for current for 1000 welds.

Tables XI, XII, and XIII will give a good idea of the power and time required for various thicknesses of metal with butt welding and spot welding, and it will be well to compare the effect of time on the current used.

Table XII is different from Table XI for similar sizes of section because of the difference in the time taken per weld.

Table XII is based only on the use of iron rods, the diameters being given in Column 1. Table XIII is based upon steel, but in the form of sheets. The costs of making the welds as given in Tables XII and XIII are very interesting and should be carefully noted.

Cost Of Butt And Spot Welding

The cost of welding by both butt and spot methods can easily be figured from tables XII and XIII by determining the cost of current for the operating conditions under consideration and adding the required amount for labor and overhead charges in the shops. The latter item is very important and will have a noticeable influence on the cost of welding in most shops. The labor for handling the material to and from the welding machine is just as important as that of the operator himself, and the cost of such labor, together with the interest and depreciation on the purchase price of the welding machine and the cost of installing, are part of the overhead expense. Articles of special shapes will require different amounts of current and experiment alone will show the current required; this factor, with the labor and overhead expenses, will give the cost. It will be self-evident that the better provision one makes for handling the work, the lower will be the cost per unit produced.

Table XIII. Spot Welder Data

Based on using fairly clean stock, this table will give an idea of the time and current required in welding different gages of sheet steel.

As the rate charged for current varies in different places, the current has been figured at one cent per kw. hour to give a basis for calculating the cost. Multiply the prices given above by the rate per kw. hour charged by the local electric light company, and that will give the cost for current for 1000 welds in any given locality.

Strength Of The Weld

The strength of the weld should equal from 75 per cent of the original material on heavy stock up to 95 per cent of it on light stock, when finished to the same diameter or thickness as the piece; this can be made 100 per cent or greater, if a reinforcement can be left on in the form of an upset. The strength of a weld is slightly increased by working after welding, unless there is too much carbon or silicon in the iron. The metal is not damaged by welding with either the butt- or spot-welding systems, if properly done, because the heat can be controlled so exactly. The oxide which may be present at the joint is usually forced out into the upset and ground off; so a burned weld is a rare thing with this system. In the early days of the Thomson system, there were complaints of weak spongy burnt welds, when made by butt welding, but this was largely due to inexperience and the tendency to heat the metal too much. If an excess of heat is applied, either by using too high a current or leaving it on too long, the metal may be weakened within the heating radius and break about an inch from the joint.