Weeks' Electric Rotating Furnace as Applied to the Brass Foundry Industry

By F. J. RYAN, Philadelphia

Philadelphia in 1908 saw the birth of the rocking electric furnace idea applied to the problem of brass, zinc and nonferrous alloys. To Charles A. Weeks, a Philadelphian, must go much of the credit for both the conception and the solution. of the problem because of his untiring efforts in the face of unusual obstacles.

To see how clearly Mr. Weeks seemed to have sensed a solution of the electric brass furnace problem, we have only to inspect the equipment shown in Fig. 1 which might readily be mistaken for a photograph of a modern installation, whereas it was taken nearly 10 years ago at the works of the General Electric Co. where Mr. Weeks carried out many tests in cooperation with the designing engineers of the same organization. Some of the zinc ingots produced can be seen on the plat form at the side of the furnace. Comparison of the original furnace with the present design as shown in Fig. 2 shows only a general refinement and solution of operating, and mechanical problems without radical changes in the basic thought.

Two Vital Problems

Brass melting presents two vital problems: Segregation and volatilization of zinc.

Segregation results from the different fusion or melting temperatures of the different alloys. In other words if you have three alloys, each with a different melting or mixing point, you will find that at the time when the material with the lowest melting point has become liquid, the other two are still sluggish and will not combine unless some method of stirring is

resorted to. On this account in a still bath hand stirring or rabbling must be resorted to, or else sufficient heat to bring all the constituents to the combining temperature must be applied. In such cases, however, the zinc has reached a point where it becomes volatile and a large part passes off as gas.

A solution for this condition in an electric furnace is automatic stirring whereby the surface exposed to the arc is

continually changed. The revolving furnace is designed to accomplish this result.

It has always been recognized that a great advantage would be gained if the heat could be applied at both the top and bottom of the charge. Mr. Weeks seems to have secured this result in his first experimental furnace. He secured both the

result mentioned and obtained a mechanical means of stirring the bath.

How Bottom Heat is Secured

The application of bottom heat is obtained through the absorption value of the refractory lining; that is, the lining section exposed directly to the electric arc absorbs a large amount of heat and when this in turn becomes the hearth as the furnace rotates, it gives out the absorbed heat to the charge from the bottom. With the steady alternation of the hearth against the charge there is a continual application of heat. While this alternation is going on, the charge is stirred by the movement of the furnace body. Further, by the alternation of the exposed refractories, the wear from burning or fusing from the high heat of the arc is reduced to a minimum.

Briefly, without going into technical results which cover a wide field and would take a large amount of space, it can be seen from practical observation that through the simple discovery of Mr. Weeks, important problems in the field of brass foundry melting have been solved, at least until such a time. as our ever changing mechanical and chemical applications bring to us some new discovery.

In the following paragraphs will be reviewed briefly the principal details in connection with the construction and method of operating this equipment.

Furnace Lining

All available refractory materials applicable to this type of furnace equipment have been experimented with and while fair success resulted from the use of 9-inch clay blocks with a 6-inch layer of electrically fused magnesite mixed with china clay and boric acid, it was finally decided to recommend for the present a special silica lining.

The blocks.composing this lining are reduced to a minimum with a proper allowance for shrinkage. Actually, the circular section is composed of six interlocking blocks capped at each end with a solid capping piece. Between the shell and the lining is placed 2 inches of insulating material in a loose form

which allows for the expansion of the main lining and reduces radiation to a minimum.

By constructing the lining in this manner, quick replacement is made possible and a large percentage of the checking wear eliminated as would be the case in a lining composed of small brick.

From the reports received from a large manufacturing concern in this country, the writer has every hope that

within a short space of time it will also be possible to supply a lining of magnesite blocks made under a special process in the same form as the present lining. Experiments so far carried out show promising results. The furnace of course, can be lined with any other materials chosen by the operator.

Electrodes

Graphite electrodes are recommended on account of their current carrying capacity and lightness which allows for ease of handling and cuts down loss in breakage. The furnace however, can be adapted to the use of carbon electrodes where desired.

One of the chief radical changes from the original furnace design is the method of taking power into the furnace. In previous designs it has been necessary to have objectionable overhead swinging cables to allow for the movement of the furnace drum. Such construction causes loss in voltage on account of excessive length of cable and necessitates a very much greater amount of room for installation than is necessary under the design submitted, whereby the current is taken in through a shoe at the bottom of the furnace out of the way of the operator. This also allows for the placing of the transformers close to the furnace.

In this type of construction it also is not necessary to disconnect the cables when the furnace body is removed from the rollers for relining.

Mechanical Operation

Briefly the furnace, as will be noted from Fig. 2, is a circular steel drum located on four rollers with double gearing at each end of the drum connected with a driving shaft at the rear. The shaft is connected to a gear reduction to allow for two complete revolutions per minute. By a special method of automatic switches the drum can be rotated to any percentage of its circumference at the will of the operator, a special control making it possible to set operation at any given point.

Water connections are made through permanent entrance from below to a sliding water jacket which allows for a larger flow or cooling capacity at a low pressure, and also eliminates flexible and overhead piping.

The electrodes, it will be noted, are driven by a wheel stationed at the axis of the furnace, making no movement on the part of the operator necessary except a gripping of the wheel, and allowing the motion of the furnace body to take care of the necessary movement.

Both the electrode clamp and the electrode socket at the entrance of the furnace are water cooled at both sides of the furnace.

On account of the method of lining and the genera! simple construction of the furnace it is possible to put in a