US2801275A - Electric furnace - Google Patents

Description

July 30, 1957 H. JERU 2,80l,275

ELECTRIC FURNACE Filed Jan. 9, 1956 2 Sheets-Sheet 1 ***az y U 63 Gb 3 az 2 ///4 33 V 1 I J I /i 6` /NVENTOE &ay/wu d 0.

July 30, 1957 H. JERU mcmc FURNACE Filed Jan. '9, 1956 2 Sheets-Sheet 2 H'ENRI JE e u b SM; ;1. aw

United States Patent O My invention has for its object an electric fumace of the resistance type adapted for the execution of metallurgical treatments, for the production of glass, for the baking of foodstufi or again as a kiln or drier.

' My improved fumace is characterized by the fact that the" inner metal walls lining the'furnace chamber form heatingelements which are interconnected at one end or `atboth ends, said walls bounding and supporting the insulating filling.

According tothis arrangement, the heating elements t thus forming the walls of the furnace chamber extend throughout the length of the latter. They are connected with the supply of electric energy and are interconnected so as to form the desred electric circuit. These connections may be designedso as to form a star or delta groupmg.

In particular, one of the heating elements may form the vault and/or the walls of the fumace while the other heating element forms the hearth, the two elements being interconnected at one end of the furnace. The heating walls serve also as carriers for the outer insulating filling constituted for instace by a mass of sand which is furthermore held in position by a suitably reinforced outer cas This fumace is of a simple, speedy and economical execution and its efliciency is very high. The magnetic fields produced by the two heating elements which are very near each other compensate each other mutually so that when the fumace is fed with altcrnating current, its consumpton of reactive energy is low, its cos being high.

I have illustrated by way of example in accompanying drawings a preferred embodiment of the electrc fumace according to my invention. In said drawings:

Fig. 1 is a diagrammatic showing of the furnace. v

Fig. 2 is a longitudinal sectional view of said furnace.

Fig. 3 is a transverse sectional view thereof on a larger scale.

Fig. 4 is a view of a detail of the front end of the furnace.

Fig. 5 is a modified wiring diagram.

Fig. 6 is a view similar to that of Fig. 5 illustrating a modification.

The fumace includes chiefly two heating elements 1 and 2 extending throughout the length of the furnace. The element 2 forms for instance the walls and the vault of the fumace while the element 1 forms the hearth. The elements 1 and 2 are interconnected at 3 at one end of the fumace so that the whole system 1--2-3 is in the shape of a hairpin with elongated arms. The arms of this hairpin are connected through leads 4 and 5 with the terminals of a transformer 6 the secondary of which is designated by the reference 6a and the primary by the reference 6b.

The hearth 1 s constituted for instance as illustrated in Fig. 3 by a fiat strip of mild steel extending throughout the length of the fumace and the lateral edges of which are raised so as to form a guideway for the parts to be heated.

Said hearth 1 is laid on a base 7 of refractory bricks and the terminal edges of the conductive wall 2 forming the vault of the fumace also rest on said support to either side of the hearth.

This arrangement 1-2-7 is embedded inside a sand filling 8, which filling is held in position over a foundation mass 9 of concrete by sidewalls 10 made of concrete or of metal sheet, said sidewalls being held in position in their turn by shaped iron members 11 forming reinforeements and interconnected through upper stays as shown at 12.

The end of the fumace on the side facing the transformer 6 is closed by a plug of molten cement. The other end of the fumace is closed by a sash door 13.'

At the latter end, the connection 3 between the two heating elements 1 and 2 is provided by welding the hearth 1 and the vault 2 at the points 14 and 15 to a metal plate 16 (Fig. 4) forming the front of the furnace.

In front of the door 13 is formed a pit 17 inside which may be positioned a table 18 which forms an intermediate carrier surface between the fumace and the loading and unloading surface 19.

When introducing into the kiln the shaped members to be treated, it is possible to use one or more carriages each constituted by a frame 20 running over small wheels 21. The members to be treated 22 are laid on said carriages with the interposition of asbestos plates 23 adapted to insulate electrically said members 22 from the carrier frame 20. Said members 22 may be secured to the carriage by a clamping member 24 with the interposition of an insulating plate 25.

Pyrometric rods 26 extend through the sand filling 8 inside protecting tubes 27 welded to the wall 2 forming the vault and opening into the furnace.

The upper wall 2 and the hearth 1 of the fumace may be in one or more sections having the same or dilferent cross-sectional shapes. It is also possible to short-circuit successive sections of the furnace through the agency of copper blades 28 which are urged towards or away from the wall 2 through the agency of screws 29 controlled by hand-wheels 30. It is possible thereby to provide for a modification and adjustment of the temperature at different points of the length of the furnace.

The fumace according to my invention may be fed with one-phase or with three-phase current. In this latter case, it is possible through suitable connections to execute any desred delta or star groupng.

Instead of the one-phase connection illustrated in Fig. l, it is possible to resort to the three-phase grouping of Fig. 5, in which case the different phases of the transformer secondary 6a are connected with separate points of the heating elements such as 31, 32 and 33.

The furnace constituted as described is of a simple and economical structure and is applicable to all fields for instance those of metallurgy, glass-making, biscuit baking or else as kilns.

The walls 2 and the hearth 1 may be made of ordinary mild steel When the temperature to be reached s 700 C. or thereabouts and they may be made in fact of any other electrically conductive metal or alloy such as cast iron for instance. For higher temperatures up to 1050 C., it is preferable to resort to refractory metal sleets.

The fumace according to my invention may be designed as a tunnel kiln inside which the articles to be treated are shifted in a continuous manner. The heating elements 1 and 2 may be designed so as to form only the sidewalls which latter are interconnected at one end of the furnace while the hearth and the walls are constituted by refractory slabs. It is also possible to design the heating elc- Patented July 30, 1957 ments in a manner such that each of them forms a sidewall and one half of the vault or' else each' element may include any desired fraction of the vault, of the side walls i and/orofthe hearth. .i i i i the furnace, means for interconnecting said two sheets at least at one 'of their ends, a supply of three-phase current,

of the furnace, a second metal sheet for'ming the hearth of the furnace, means for interconnecting said two sheets at least at oneof their ends and means for connecting said two sheets with `a supply'of'electric energy and an insulating filling carried by and extending over the first sheet.

2. An electric furnace coniprising a refrctoryfoundation, a lower metal plate testing on said foundation and forming the hearth of the furnace, a further, uppei` metal plate forming thesidewallsv and the vau1t:of:the furnace chamber and resting over the refracto'y foundation to either side of the first`p1ate, an`e1ectrica1ly conductive connection between the two metal plates, a supply of electric current connected with said plates and' an insulating filling carried by and resting on-the second plate,

3. An electric resistance furnace comprising a metal sheet forming at least part of the .yault and .the sdewalls of the furnace, a secondmetal. sheet forming the hearth of the furnace, means for interconnecting said two sheets ;lt least at one of their ends, a suppiy of three-phase current, a star connection through which electric energy is fed from said supply to said sheets and an insulating filling carried by and extending over the first sheet.

4. An electric resistance furnace comprising a metal sheet forming at least part ofthe Vault and the sidewalls of the furnace, a second metal sheet forming the hearth of a delta connection through which electric energy is fed from said supply to said sheets and an insulating filling carried by and extending over the first sheet.

5. An electric fu'nace comprising a refractory foundation,' a lower metal plate'resting on said foundation and forming the 'hearth of the furnace, a further upper metal plate forming the sidewalls and the vault of the furnace chamber and resting over the refractory foundaton to either side of the first plate, an electrically conductive connection between the two metal plates, a supply of electric current connected with said plates, a mass of sand carried by and resting on the second plate, an outer casing enclosing at least partly said mass of sand to hold same in position and reinforcing members holding said casing in position over the mass of sand.

6. An electric furnace comprising arefractory found&- tion, a lower metal plate resting on said foundationtand forming the hearth of the furnace, a further upper metal plate forming the sidewalls and the vault of the furnace chamber. and `'esting over the refractory foundation to either side of the first plate, an electrically conductive connection between the two metal plates, a supply of electric current connected with said plates, a'plur'ality of 'No references cited.

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