GB1594008A - Electric resistance heated furnace - Google Patents

Description

(54) ELECTRIC RESISTANCE HEATED FURNACE (71) We, KOHASZATI GYAREPITO VALLALAT, a body corporate organised under the laws of Hungary, of 1138 Budapest, Révész u.9, Hungary, do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to an electric resistance heated furnace provided with a fibrous, fireproof, heat insulating lining, the furnace being intended, for instance, for heat treatment.

Such industrial furnace constructions provided with a fibrous, fireproof, heat insulating lining, which are suitable for heat treatment, are known. Such constructions are described for instance on pages 74 to 81 of the May copy, 1974 . . of the USA periodical: "Industrial Heating", National Publishing Co., 1400 Union Trust Building, Pittsburgh, PA 15219 in the article of F. H. Fidler under the title of "Energy conserving ceramic fiber linings for heat treating furnaces", and furthermore on pages 74 to 82 of the April 1975 copy of: "Industrial Heating" in the article of Johns-Manville Co., under the title of "Guide to lining furnaces with ceramic fiber".

The common characteristics of these furnaces is that most of the linings made of fireproof, fibrous, heat insulating material, are for gas or oil furnaces and not for industrial furnaces with electric resistance heating.

Further common characteristics of these gas and oil furnace constructions is that there is no heat source (ensuring the heating of the furnace) on the surface of the lining made of fibrous, heat insulating material, the burners being placed in a wall specially developed for this purpose, from a traditional, generally chamot type fireproof material, which is substantially more solid than the fibrous, heat insulating, fireproof materials.

These furnace constructions are unsuitable for fastening the electric heaters onto the loose, fibrous, fireproof, heat insulating lining, and are unsuitable to prevent such local overheating of the fibrous, heat insulating lining, caused by the electric heating resistors, as a result of which, the surface of the fibrous, heat insulating lining melts, the lining thereby losing its heat insulating effect, and becoming unsuitable to perform its technological task.

The quoted deficiencies of the described furnace constructions do not permit utilization of the advantages in terms of energy, construction and operation given by the fibrous, fireproof, heat insulating materials, in case of electric resistance heating.

The object of the invention is to provide a furnace in which, in addition to using electric resistance heating, the furnace lining is made of fibrous, fireproof, heat insulating material, and the advantages in terms of energy, construction and operation advantages given by the fibrous, fireproof heat insulating lining, are optimally utilizable.

According to the invention there is provided an electric resistance heated furnace to be used, for instance, for heat treatment, the furnace comprising an outer casing, an inner heat insulating working lining of fibrous, fireproof material, at a side of which remote from said casing is disposed a plurality of vertical columns, each vertical column being formed by a plurality of ceramic bricks resting one upon another, and every pair of vertical columns dividing the surface of the working lining into a vertical heating channel, a plurality of heat resistant steel rods secured at one of their ends to said casing, the rods passing through the working lining and respective grooves of said ceramic bricks to secure the working lining to said casing, and said brick columns incorporating projections which support horizontally arranged heating resistances.

The electric resistance heaters supported by the ceramic bricks ensure the heating of the furnace. The bricks participate as structural units in fastening the fibrous heat insulating lining to the furnace outer casing and furthermore these ceramic bricks, formed into vertical columns, divide the surface of the lining into channels, in which the air, constituting the atmosphere of the furnace, or other gaseous medium flows in order to prevent the local overheating of the lining, caused by the heating resistors. In a further advantageous construction, the medium heated by the heating resistors is circulated by one or more fans in communication with the heating channels formed on the surface of the lining and this medium heats up the furnace lining, mainly by convective heat transfer.

Compared to furnaces provided with linings made of traditional fireproof material, the heat storage, the specific electric consumption, and the weight of the steel structure of the furnace are several times lower, the cycle of heat treatment is shorter, and output of the furnace is higher.

The construction of the furnace provides a solution, which can prevent the local overheating of the fibrous, fireproof, heat insulating lining, caused by the electric resistance heaters.

The invention will now be described, by way of example, with ;reference to the accompanying drawings in which: Figure 1 is a horizontal cross-sectional view on the line A-A of Figure 2 of a corner of a furnace constructed in accordance with the present invention; Figure 2 is a cross-sectional view on the line B-B of Figure 1; Figure 3 is a cross-sectional view, towards one end of the furnace, of part of the furnace of Figures 1 and 2; Figure 4 is a vertical cross sectional view of the part of the furnace shown in Figure 5; and Figure 5 is an enlarged horizontal crosssectional view of part of the furnace shown in Figure 1.

Figures 1 to 3 show the bogie-hearth construction of the furnace for heat treatment according to the invention. A bogiehearth 2 with a refractory lined loading surface is provided to carry the charge to be heated, the bogie-hearth also constituting the bottom of the furnace. There is a door 3, at the end of the furnace. The side wall of the furnace is formed by a fibrous, fireproof, heat insulating working lining 4. The lining is fastened to a furnace outer casing 8 by means of a plurality of vertical columns, each column being formed of ceramic bricks 5 continuously resting on each other in a vertical direction and also by means of heat-resistant steel rods 7, fixed at one of their ends to an inner surface of the casing 8 and passing through the lining 4 and grooves 6 defined between adjacent bricks. Ceramic bars 10.

are placed in projections 9 formed on the bricks 5, with heating resistors 11 being wound on the ceramic bars.

The heating resistors 11 are carried in an insulated condition to an independent, known electric connection, through a ceramic sleeve 12 (Figure 4) fitted into the fibrous, fireproof heat insulating lining 4.

The vertical brick columns divide the inner surface of the fibrous lining 4 into vertical heating channels 13. The heating channels 13 are, in the embodiment illustrated, closed towards a chamber 15 of the furnace by a heat resistant steel plate 14, arranged perpendicularly to the ceramic brick columns.

One or more circulating fans 17 driven by an electric motor 16 is or are provided for the purpose of circulating the furnace atmosphere 19 through the heating channels 13, and bottom channels 18 formed on the surface of the bogie-hearth 2.

Operation of the furnace according to the invention is as follows.

The charge to be heat treated is loaded onto the bogie-hearth 2, and the furnace is closed by means of the door 3. The or each circulating fan or fans 17 driven by electric motor 16, is or are started and the heating resistors 11 are heated up by switching on the electric current. The furnace atmosphere circulated by the or each fan 17 in the heating channels 13 receives the heat energy generated by the heating resistors 11, and flows through the bottom channels 18 into the furnace chamber 15, then transmitting the received heat energy to the charge 1, mainly with convective heat transfer, the atmosphere flowing again through the fan or fans 17 into the heating channels 13, for the purpose of repeated heating.

It is apparent that the furnace construction is suitable for its lining to be made of fibrous, fireproof, heat insulating material with the application of electric resistance heating. Consequently in comparison with the electric resistance heating furnaces, made of traditional, fireproof, e.g. chamot, lining, the following advantages in terms of energy, construction and operation given by the fibrous, fireproof, heat insulating lining are optimally utilizable.

Heat conductivity of the fibrous, fireproof, heat insulating lining is about 1/10th, and its volume weight is about 1/15th of a lining made of chamot for the same purpose. Consequently heat storage of the electric resistance heating furnace lining, made of fibrous, fireproof, heat insulating material is about 30-40 times less, as a result of the several times less thickness and weight of the fireproof lining.

Further favourable consequences of this advantage in respect of construction and operation, are the following.

In intermittent running industrial furnaces, the heating is substantially quicker as a result of the reduced heat storage, compared with that of the traditional one, thereby for instance, the heat treatment cycle becomes shorter, productivity of the furnace increases, while the specific electric power consumption decreases at the same time. The extremely light lining can be used with a steel structure with many times lower weight, making the furnace cheaper and quickly constructible. Installation time of the fibrous, fireproof lining, delivered generally in rolled-up, quilt-like condition, is a fraction of the installation time of the traditional refractory brick.

The flexible light fibrous, fireproof, heat insulating lining material can be delivered to the location of furnace operation, already mounted into the furnace steel structure without the risk of damage. Because of the prefabricaton possibility the furnace construction is substantially faster, requiring less preparatory work at the same time.

A further significant advantage is that the bricks are suitable for fulfilling the following tasks. The fibrous, fireproof, heat insulating lining is fixed to the furnace casing and the heating wires are held in such a manner, that damaged heating wire sections can be easily removed from the projections 9 formed on the bricks, and are similarly easily replaceable with new heating wires. Furthermore, the brick columns divide the inner surface of the lining into heating channels which when closed by the plate 14 serve to prevent the local overheating or melting, i.e. the fast wear of the lining, by circulating the furnace atmosphere in these channels.These characteristics and arrangements of the bricks ensure at the same time the fast, efficient, and uniform, mainly conductive transfer in the whole of the furnace chamber of the heat energy to be transferred to the heat-treatable products, thereby improving the quality of heat treated products, simultaneously ensuring a high heat treating capacity.

WHAT WE CLAIM IS: 1. An electric resistance heated furnace to be used, for instance, for heat treatment, the furnace comprising an outer casing, an inner heat insulating working lining of fibrous, fireproof material, at a side of which remote from said casing is disposed a plurality of vertical columns, each vertical column being formed by a plurality of ceramic bricks resting one upon another, and every pair of vertical columns dividing the surface of the working lining into a vertical heating channel, a plurality of heat resistant steel rods secured at one of their ends to said casing, the rods passing through the working lining and respective grooves of said ceramic bricks to secure the working lining to said casing, and said brick columns incorporating projections which support horizontally arranged heating resistances.

2. A furnace as claimed in claim 1 wherein the heating channels are open towards the interior of the furnace.

3. A furnace as claimed in claim 1, wherein said heating channels are closed by a heat resistant steel sheet fixed to said brick columns, the heating resistances are disposed horizontally in said closed channels between said brick columns, and the channels, at one of their ends are in communication with one or more fans, whilst at the other of their ends, they are in communication with channels formed in a hearth of the furnace.

4. A furnace as claimed in claim 3, wherein said heating resistances are arranged in vertically staggered planes.

5. An electric resistance heated furnace substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. less, as a result of the several times less thickness and weight of the fireproof lining. Further favourable consequences of this advantage in respect of construction and operation, are the following. In intermittent running industrial furnaces, the heating is substantially quicker as a result of the reduced heat storage, compared with that of the traditional one, thereby for instance, the heat treatment cycle becomes shorter, productivity of the furnace increases, while the specific electric power consumption decreases at the same time. The extremely light lining can be used with a steel structure with many times lower weight, making the furnace cheaper and quickly constructible. Installation time of the fibrous, fireproof lining, delivered generally in rolled-up, quilt-like condition, is a fraction of the installation time of the traditional refractory brick. The flexible light fibrous, fireproof, heat insulating lining material can be delivered to the location of furnace operation, already mounted into the furnace steel structure without the risk of damage. Because of the prefabricaton possibility the furnace construction is substantially faster, requiring less preparatory work at the same time. A further significant advantage is that the bricks are suitable for fulfilling the following tasks. The fibrous, fireproof, heat insulating lining is fixed to the furnace casing and the heating wires are held in such a manner, that damaged heating wire sections can be easily removed from the projections 9 formed on the bricks, and are similarly easily replaceable with new heating wires. Furthermore, the brick columns divide the inner surface of the lining into heating channels which when closed by the plate 14 serve to prevent the local overheating or melting, i.e. the fast wear of the lining, by circulating the furnace atmosphere in these channels.These characteristics and arrangements of the bricks ensure at the same time the fast, efficient, and uniform, mainly conductive transfer in the whole of the furnace chamber of the heat energy to be transferred to the heat-treatable products, thereby improving the quality of heat treated products, simultaneously ensuring a high heat treating capacity. WHAT WE CLAIM IS:

1. An electric resistance heated furnace to be used, for instance, for heat treatment, the furnace comprising an outer casing, an inner heat insulating working lining of fibrous, fireproof material, at a side of which remote from said casing is disposed a plurality of vertical columns, each vertical column being formed by a plurality of ceramic bricks resting one upon another, and every pair of vertical columns dividing the surface of the working lining into a vertical heating channel, a plurality of heat resistant steel rods secured at one of their ends to said casing, the rods passing through the working lining and respective grooves of said ceramic bricks to secure the working lining to said casing, and said brick columns incorporating projections which support horizontally arranged heating resistances.

2. A furnace as claimed in claim 1 wherein the heating channels are open towards the interior of the furnace.

3. A furnace as claimed in claim 1, wherein said heating channels are closed by a heat resistant steel sheet fixed to said brick columns, the heating resistances are disposed horizontally in said closed channels between said brick columns, and the channels, at one of their ends are in communication with one or more fans, whilst at the other of their ends, they are in communication with channels formed in a hearth of the furnace.

4. A furnace as claimed in claim 3, wherein said heating resistances are arranged in vertically staggered planes.

5. An electric resistance heated furnace substantially as hereinbefore described with reference to and as shown in the accompanying drawings.