US 3822873 A
A furnace for melting or heating metals comprising a furnace compartment enclosed by a refractory lining and a crucible for the melt arranged in the furnace compartment. Contacts are provided at the lower region of the furnace compartment, these contacts being arranged in the current circuit of a monitoring device and such contacts are electrically connected with one another by metal which may possibly flow out of the crucible into the furnace compartment. A baffle or guide plate, preferably a sheet-metal deflector or guide, engages beneath the contacts and extends at least over the region of the furnace compartment spanned by the crucible. The baffle plate is exposed to the thermal radiation emanating from heating elements.
Description (OCR text may contain errors)
United States Patent 1191 Pletscher FURNACE FOR MELTING OR HEATING METALS I Inventor: Oskar Pletscher, Marthalen, Switzerland Assignee: Gebruder Pletscher, Marthalen,
Switzerland Filed: July 12, 1973 Appl. No: 378,414
Foreign Application Priority Data July 17, 1972 Austria 6142/72 References Cited- UNITED STATES PATENTS 1,889,604 11/1932 Jones "ls/1x 2,525,882 10/1950 Ferguson ..266/33'R 11 3,822,873 1451 July 9, 1974 Primary ExaminerGerald A. Dost Attorney, Agent, or Firm-Toren, McGeady and Stanger  ABSTRACT A furnace for melting or heating metals comprising a furnace compartment enclosed by a refractory lining and a crucible for the melt arranged in the furnace compartment. Contacts are provided at the lower region of the furnace compartment, these contacts being arranged in the current circuit of a monitoring device and such contacts are electrically connected with one another by metal which may possibly flow out of the crucible into'the furnace compartment. A baffle or guide plate, preferably a sheet-metal deflector or guide, engages beneath the contacts and extends at least over the region of the furnace compartment spanned by the crucible. The baffle plate is exposed to the thermal radiation emanating from heating elements.
8 Claims, 1 Drawing Figure PATENTEU Jul 9% t l FURNACE FOR MELTING DR HEATING WTALS BACKGROUND OF THE INVENTION The present invention relates to a new and improved construction of furnace for melting or heating metals and is of the type comprising a furnace compartment or chamber enclosed by a refractory lining as well as a crucible for the melt arranged within the furnace compartment.
In furnaces of this type, which hereinafter will be conveniently referred to as heating furnaces, especially if electrical heating elements are embedded in the refractory lining, the metal possibly flowing out of the crucible and into the furnace compartment tends to oftentimes lead to serious interruption in the operation of the furnace and damage. This is not only apparently the case where the melt completely runs out of the crucible which has burst, but also then so even if the melt tends to trickle in droplet-form through fissures or cracks in the wall of the crucible. This is so firstly because even slight amounts of metal which have leaked out of the crucible must be removedfrom the furnace compartment, and particularly because the leakage metal can directly contact the heating elements or owing to sputtering or spraying of the metal upon contact with fixed parts of the furnace can come into contact with the heating elements and at such location cause mechanical, chemical and electrical damage, requiring the exchange of the heating elements. Apart from these factors there is also an eminent interest in detecting metal leaks early enough, in other words incipient metal break-out from the crucible, since in this way it is possible to obtain significant information concerning the general condition of the crucible, especially the impending danger of progressive failure thereof.
In practice one was previously satisfied with periodically examining, on the basis of experience, the crucible and based upon such examination result carrying out a further, although already timewise limited use thereof. It should be apparent, however, that with such technique it is essentially only possible to avoid with a degree of certainty bursting of the crucible. On the other hand, there cannot be prevented the occurrence of damage predicated upon melt material which has leaked. For the purpose of overcoming these cumbersome, in fact with the previously discussed conditions even unsuitable control techniques, a known construction of furnace proposes the provision of contacts at the lower region of the furnace compartment, these contacts being located at the current circuit of a monitoring device. These contacts are intended to be electrically connected with one another by any metal which possibly flows out of the crucible and arrives at the region of the furnace compartment. However, for the continuous monitoring of the crucible wall there is provided a complicated and expensive sheathing of the crucible with surface electrodes.
SUMMARY OF THE INVENTION Another and more specific object of the present invention aimsat attaining the sameeffect and the same I gage beneath the contacts, this guide plate extending at least over the region of the furnace compartment which is spanned or covered by the crucible and such guide plate is subjected to the thermal radiation of heating elements.
The guide plate or sheet metal guide possesses a temperature which prevents the solidification of droplets of leaked metal which impinge thereat and thus retains the metal in a fluent state, so that it can flow along the guide plate towards the contacts. The guide plate there- I fore so-to-speak increases the operable zone of the contacts, which owing to such surface-adhering action no longer need possess a surface-like extent or elongation. In particular, by virtue of this construction the electrical problems are more easily controlled. The guide plate can be designed to possess a substantially pot-like configuration, and therefore possesses surface portions which to a considerable degree are subjected to the thermal radiation directed towards the crucible. With such construction the guide plate simultaneously serves as a screen against metal spray. This function is then realized to a more pronounced extent if the guide plate forms the lower closure of a jacket surrounding the crucible, especially since such jacket is not only capable of entraining the metal spray but furthermore also can catch the entire quantity of melt which may run out.
Advantageously the upper edge of the jacket together with that of the crucible forms a gap which is at least approximately completely sealed. In this way there is prevented an exchange of the air located in the space enclosed between the jacket and the crucible. Consequently, the longevity of the crucible, but at the same time also the thermal transfer or conductivity through the wall of the crucible, is improved. This is so because the carbon at the crucible wall in conjunction with only a limited quantity of oxygen forms CO and thus cannot burn-out. Consequently, there is not formed any brittle, breakable layer of increasing thickness, the formation of which not only causes weakening of the mechanical strength but also impairment of the thermal conductivity of the crucible wall. The space enclosed between the jacket and crucible can incipiently contain a protective gas atmosphere.
BRIEF DESCRIPTION OFTHE DRAWING DETAILED DESCRIPTION OF THE PREFERRED I EMBODIMENTS Describing now the drawing, in the single FIGURE there is depicted in sectional view a substantially cylindrical heating furnace F constituting an exemplary emcorporates a furnace compartment or chamber 1 which 'is enclosed by a multi-layer lining 2 formed of refractory material. At the innermost layer 3 of such refractory lining 2 heating elements, for instance heating spirals or coils which have been schematically depicted by reference character 20, are embedded in grooves 22 or the like which open in the direction of the furnace compartment l. The floor or bottom 4 of the furnace compartment l is also formed of a suitable refractory material, and at the center of the floor 4 there opens a discharge channel 5 for the leaked metal, also sometimes conveniently referred to herein as leakage metal. Above the mouth 5' of the discharge or outlet channel 5 there is located a pedestal or socket 6 upon which rests a crucible 7 or equivalent structure.
Between the floor 7a of the crucible 7 and the pedestal or'socket 6 there is located a guide or baffle plate 17, for instance a sheet metal deflector or guide, which forms the lower closure of a cylindrical jacket or shell 8 which surrounds the crucible 7. The annular or ringshaped gap 9 enclosed by the upper edge 8' of the jacket 8 and the upper edge 7' of the crucible 7 is sealed by a ring seal 10 formed of a suitable material. Electrical contacts 11 and 12 are mounted at the guide plate or sheet metal guide 17'which may be inclined in the direction of such contacts 11 and 12. Further, the contacts 11 and 12 are operatively connected by the schematically depicted conductors 13 leading via a channel or throughpassage opening 14 out of the furnace compartment 1, with a switch arrangement 15 of a suitable and thus merely schematically illustrated warning device and/or shutdown device of a monitoring mechanism, generally indicated by reference character 24.
Since the jacket 8, which especially by means of its lower portion together with the guide plate 17 forms a substantially pot-shaped unit, is directly subjected to the thermal radiation emanating from the heating elements 20, any possible present leakage metal which has arrived-through a fissure or crack at the wall of the crucible 7 at the intermediate compartment 16 enclosed between this jacket 8 and the crucible 7, remains in a molten state and therefore is flowable or fluent. With appropriate construction of the guide plate 17 even a small available quantity of leakage metal will be delivered to the contacts 11 and 12, so that the same will be electrically connected with one another and the monitoring mechanism will respond and trigger an optical or acoustical signal and activate the shutdown device. The
heated guide plate 17 thus imparts a remote-control action to the contacts 11 and 12. This also is the case even if the guide plate 17 does not possess any or any especially pronounced gradient or slope in the direction of the contacts 11 and 12, since the leakage metal will tend to spread out in any event over the surface of the guide plate 17 and will soon reach the region of the contacts 11 and 12. Constructing the guide plate 17 to possess a certain gradient hence constitutes only a slight modification. In the same sense it would be possible to enlarge the electrical contact surface, for instance by arranging a number of contact pairs or by using contacts in the form of concentric rings, grids and the like.
With the illustrated constructional embodiment metal spray to the extent that such is even formedcannot reach the heating elements 20. For this purpose alone of course the jacket 8 need not be extended up to the upper edge 7"of the crucible 7. Such construction has accordingly the advantage that upon bursting of the crucible owing to unforeseen circumstances the melt can be caught. if the gap 9 between the upper edge of the jacket 8 and the crucible 7 is maintained narrow or even sealed, so as to render more difficult an exchange of the air enclosed in the compartment 16 or in fact to completely suppress the same, then, after the enclosed oxygen together with the carbon of the crucible (to the extent that such is formed of this material) has combined to form CO there is formed so-to-speak a protective gas atmosphere, in which there is suppressed progressive burning-out of the crucible wall. As already mentioned there thus does not exist the brittle and easily crumbling layer consisting only of a binder,
which otherwise forms at graphite crucibles a poor heat-conducting outer skin and reduces the mechanical strength of the crucible wall. The longevity of the crucible and its operational reliability are thus considerably increased and the consumption of energy reduced. It should be understood that it is also possible to use a particular protective gas. These measures employed in conjunction with a furnace used for heating a metallic melt have further significance since the leakage metal arriving at the compartment 16 cannot oxidize and its electrical conductivity accordingly is not reduced, for instance by the formation of an oxide skin.
Instead of contacts having a surface-like remote control action brought about by a guide plate it would of course be possible to also use surface-like contacts. For instance, there could be mounted at the floor 4 of the furnace compartment 1 about the socket or pedestal 6 and in recesses also within such socket, for instance at the region of the mouth 5 of the discharge channel 5, electrodes or contacts in the form of concentric rings, rods, grids or grate-like constructed electrodes. Thus, for instance, it would be possible to mount two more or less small meshed grids in superimposed relationship, if desired at a spacing above the floor, in which the metal droplets would be caught, whereby an electrical connection between these grids would be established. At
.the same time such grid-like contacts would prevent the spraying or sputtering of the liquid metal. As already explained, depending upon the particular cir cumstances a combination of such electrodes with a guide plate could be provided.
Finally, it is mentioned that the guide plate, especially however the jacket forming therewith a potshaped unit, could have a blackened outer surface in order to improve the heat transfer to the crucible.
While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,
What is claimed is:
l. A furnace for melting or heating metals, comprising a furnace compartment, a refractory lining enclosing the furnace compartment, a crucible for the melt arranged in the furnace compartment, contact means arranged at the lower region of the furnace compartment and disposed in the current circuit of a monitoring device. said contact means being electrically connected with one another by metal which possibly escapes out of the crucible into the furnace compartment, a guide plate engaging with the contact means,
said guide plate extending at least over the region of the 5. The furnace as defined in claim 3, wherein the upper edge of the jacket and theupper edge of the crucible form a gap, and means for at least substantially 7 completely sealing said gap.
6. The furnace as defined in claim 5, wherein the region between the jacket and the crucible defines an intermediate compartment containing a protective gas.
7. The furnace as defined in claim 1, wherein said guide plate is sloped in the direction of the contact means.
8. The furnace as defined in claim 1, wherein said heating element means are arranged at the region of the refractory lining.