US2029176A - Drawing furnace - Google Patents

Description

Jan. 28, 1936. LE ROY A. LINDBERG DRAWING FURNACE Filed Jan. 14, 1935 2 Sheets-Sheet 1 Jy/emara2? Jan. 28, 1936. LE ROY A. LINDBERG 2,029,175

DRAWING FURNACE Filed Jan. 14, 1935 2 Sheets-Sheet 2 J mr,

Patented Jan. 28, 1936 DRAWING FURNACE Le Roy A. Hndberg, Evanston, 111., assignor to Lindberg Engineering Company, Chicago, 111., a

corporation of Illinois Application January 14, 1935, Serial No. 1,753

2 Claims.

My present invention relates to a drawing or tempering furnace. The special improvements herein disclosed are such as to supply the charge under treatment with highly heated air which is maintained at substantially uniform temperature at every point in the furnace. This is accomplished in part by heating the furnace through convection only. The present improvements are directed also to the arrangement and location of the several operating units, each with respect to the others, so as to promote accessibility, safety, and eiflciency in service. With a furnace so constructed and operated, distinctly superior results are attainable.

These and other objects 01' my invention may be realized from a construction as shown in the accompanying drawings wherein Figure 1 is a central vertical section through the furnace in its entirety;

Fig. 2 is a horizontal section therethrough on line 2-2 of Fig. l; and

Fig. 3 is an enlarged detail in section on line 3-3 of Fi 1.

So far as concerns my present invention, the furnace may be of any of the usual types-muffie, well, etc. By way of example, a well type of furnace is illustrated. As shown, it utilizes in its construction certain walls which define a well W open at the top but adapted to be closed by a lid L which may be moved to and from position with the aid of an elevating hook 5 and a swinging bracket 8. When in the closed position indicated in Fig. 1, the well is substantially sealed against the outside atmosphere. The well constitutes the chamber in which the charge is heat-treated.

To one side of the well and separated therefrom by a wall I!) is a heating chamber E. This chamber extends vertically adjacent the well to one side thereof for substantially its entire length. The wall I ll terminates short of the chamber bottom so as to leave a communicating opening of ample size. A duct l5 extends from this opening inwardly and upwardly within the heating chamber to connect with a housing 18 wherein may be mounted a tan ll 0! the blower type. The discharge opening 28 of the housing lies adjacent a partition 2| extending horizontally across the heating chamber above the blower. The fan shaft, as shown, is journaled in bearings 22 carried exteriorly upon removable panels 23 forming part of spaced walls 24 between which the heating chamber is located. By removing these panels the entire unit may be taken out into a pit alongside of the well, whenever required. Connection with a power source may be conveniently established by a belt running from a pulley 29 on the fan shaft.

Mounted within the heating chamber preferably by suspension, ls a heating unit U which desirably comprises interconnected resistance coils adapted to be heated through connection with a source of electrical energy. This heating unit, as shown, comprises a head 25 below which the coils are supported and above which is a cap plate 26 of enlarged size or diameter adapted to rest upon a shelf 21. Electrical connections disposed on the upper side of the cap plate may be protected by a cage 28, as shown. It will be observed that the heating unit is very accessible and may easily be removed, whether hot or cold, to be replaced by another similar unit, the entire operation requiring perhaps not more than two minutes time.

At a point in the upper region of the heating chamber, preferably just above the heating unit therein, is a distributing passageway 30 extending circumferentially around the well. Numerous ports 3| establish communication between this passageway and the interior of the well. The arrangement is such that the heated air1 is supplied directly to a charge within the we i.

The charge to be treated may be placed in a pot P of a size and shape to fit within the well. Desirably the walls of the pot and its bottom are foraminous to promote the direct circulation of heated air therethrough. When introduced into the well the pot may be rested upon a series of blocks 35 by which the bottom of the pot is supported in an elevated position above the opening to the duct l5. Accordingly, there is maintained throughout the well and heating chamber an uninterrupted passageway through which air may be circulated and recirculated in response to operation of the blower. The direction of circulation preferably, but not necessarily, is laterally from the heating unit, thence downwardly through the charge chamber, and then upwardly through the heating chamber. As will be explained later, the circulation may possibly be reversed and still produce satisfactory results.

In practice, the air of maximum temperature is that which freshly leaves the heating unit. Passing into the annular distributing chamber, it then enters the well at the top to be immediately drawn downwardly through the charge in the pot. On its way to the bottom of the well the air is cooled somewhat as the result of interchange of heat units. The air which then is relatively cool and dense enters the blower, and is again advanced to the heating unit to be reheated and recirculated as before. The conduction of heat to the charge is direct and is accomplished by convection. The walls surrounding the charge impart little or no heat through radiation.

Two important features of this invention are (1) the speed of air circulation and (2) the remote location of the heating unit. The blower type of fan which is recommended may be operated at a speed of say 3600 R. P. M. to circulate air at a high rate of speed. With air circulation of such rapidity, there is substantially no temperature change during travel through the circuit, once the air is heated to a working temperature. It may accordingly be feasible to circulate the air in either direction although, in theory at least, it is preferable that the air should proceed downwardly through the charge chamber. The blower type of fan is suggested as it works better against a back pressure and exerts a positive propelling force which results in greater circulating capacity.

There is a distinct advantage in having the heating unit located remotely with respect to the charge chamber. The chamber for each may be constructed with special reference to the temperatures it must s and, and insulation between these chambers will serve as mutual protection. Higher temperatures may, with safety to the charge, be employed in such an arrangement. The dangers of overheating, excessive temperature fluctuations, etc., in the charge chamber are greatly reduced by having the heating unit remotely located. And the heating unit itself is better protected against damage resulting from mishandling of the charge as it is moved into or out of the furnace.

As already suggested, the present improvements may be embodied in various types of furnaces, and the foregoing description of a well type is by way of example only. The entire construction might be above ground as well as below. Of importance is (l) the employment of a heating unit which is removed from the charge; (2) the removability of the heating unit independent of everything else; (3) the independent removability of the blower; and (4) the circulation of air at a temperature and speed which will insure controlled direct and uniform heating of the charge.

I claim:

1. In a drawing furnace having a charge chamber open at the top together with a removable cover therefor. the combination of walls defining a separate heating chamber extending vertically adjacent the charge chamber and in free communication therewith adjacent its bottom, means providing a horizontal distributing passage circumferentially of the charge chamber in its upper region and in communication with the upper region of the heating chamber, a heating unit mounted within the heating chamber, and means below the heating unit for drawing air from the bottom region of the charge chamber, sending the air upwardly past the heating unit to be thereby raised in temperature, and then circulating the heated air through the distributing passage for downward discharge into the charge chamber.

2. In a drawing furnace, the combination of walls defining a charge chamber and, insulated therefrom, a, heating chamber in adjacent relation with spaced communicating passages therebetween, means within the heating chamber for positively circulating air directly through both chambers. a heating unit within the heating chamber for heating the air so circulated, a mounting for the circulating means such that the latter may be removed through one wall of the heating chamber without disturbing the circulating means, and a mounting for the heating unit permi'ting the latter to be removed directly from the heating chamber without disturbance of the circulating means.

LE ROY A. LINDBERG.

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