An electric heating furnace

Abstract

The present invention relates to an electric heating furnace, which comprises electrodes, electrode holders, furnace shell flange seats, and heating elements; the electrode holders are connecting pipes with flange plates provided at one end, and the electrode holders are fixedly connected to the furnace shell flange seats through the flange plates; one end of a protection tube is hermetically sleeved in the flange seat, the other end of the protection tube extends towards the furnace chamber, one side of the electrode is hermetically connected to the electrode holder, the other side of the electrode extends into the protection tube of the furnace shell flange seat and is connected to one end of the heating element, and the other end of the heating element extends towards the furnace chamber; air inlet holes are formed in the outer peripheral surface of the electrode holder, an inflation joint is arranged on the air inlet holes, and the inflation joint is connected to a protective gas transmission pipeline; a copper row is fixedly connected to the outer end part of the above-mentioned electrode. With the structure of the present invention, the protective gas enters from the joint and then enters the furnace chamber along the corundum tube, bringing back the heat conducted to the electrode part in the furnace chamber to the furnace chamber again, thereby playing a triple role of cooling the electrode, protecting the molybdenum wire, and saving energy.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy production, and relates to an electric heating furnace, in particular to a heating electric furnace with a protective gas, and more particularly to a hydrogen-passing molybdenum wire electric heating furnace. Background Art

[0002] In the powder metallurgy production process, electric heating furnaces are used in both the reduction and carbonization processes. Currently, the electric heating furnaces in the domestic same industry often adopt Figure 1 the electrode structure as shown. At both ends of the electrode 1, a pair of pressure blocks 14 are serially arranged. The two pairs of pressure blocks respectively press the copper bus 12 and the molybdenum wire 10 to achieve conductive connection. After the nuts at both ends of the electrode are tightened, the bakelite pad 15 insulates and fixes the electrode on the metal furnace shell 7, and the asbestos pad 16 plays an insulating and sealing role. The molybdenum wire passes through the gap of the heat preservation layer 9 into the furnace chamber. Generally, hydrogen is filled into the electric furnace for such purposes as the process gas, and molybdenum wire is used as the heating element. The molybdenum wire and the external power supply of the furnace are conductively connected through the electrode. The electrode generally adopts a metal material with good electrical conductivity. The electrode is fixed on the metal shell of the furnace. On the one hand, the electrode and the furnace shell will be sealed to prevent the leakage of hydrogen in the furnace. On the other hand, an insulating material is also used for transitional connection between the electrode and the metal shell of the furnace to prevent short circuit of the power supply.

[0003] The heating furnaces described in the prior art and its patent documents usually use a masonry body composed of refractory bricks for heat preservation and insulation. Since a hydrated binder is used when laying the refractory bricks, the newly built furnace generally contains more moisture, which requires baking the furnace before the furnace is officially used. During baking, the moisture in the furnace is heated and evaporated by the slow heating of the molybdenum wire through electricity. Before baking, hydrogen is introduced into the furnace chamber to replace the air in the furnace. The heat preservation material in the furnace is generally a porous material, and it is difficult to completely replace the air in the furnace. The heating element is generally woven by multiple strands of molybdenum wire. When the overheated molybdenum wire contacts water vapor or the remaining air, it will be oxidized and burned out. When energized, some of the woven molybdenum wire has poor heat dissipation, and the local temperature may exceed 800 °C. When the temperature of the molybdenum wire rises to 520 °C and contacts air, it will start to be slowly oxidized to form Mo2O3; when the temperature rises above 600 °C, the molybdenum wire is quickly oxidized to MoO3. When the molybdenum wire is heated to 700 - 800 °C and contacts water vapor, MoO2 will be generated. When it is further heated, MoO2 will be continuously oxidized to MoO3. This oxidation causes the molybdenum wire to exfoliate and burn out from the outside to the inside, reducing the conductive cross-sectional area. Since hydrogen is introduced into the furnace chamber during baking, the molybdenum heating element in the furnace chamber will not be burned out under the protection of the reducing atmosphere generated by hydrogen. However, the molybdenum wire lead-out section passing through the heat preservation layer to the electrode lacks sufficient hydrogen protection. During baking, the overheated molybdenum wire in this part contacts the water vapor and air precipitated in the heat preservation layer and will be oxidized and burned out. The severely burned molybdenum wire has a reduced conductive cross-sectional area, resulting in an excessive surface heat load, which will shorten the service life of the molybdenum wire. It increases the production cost and reduces the production efficiency.

[0004] To solve the problem of molybdenum wire burnout, the usual solution is to replace the burned-out heating element. Chinese Patent CN206440125U discloses an easily maintainable molybdenum wire furnace. Paragraph

[0029] of the patent specification states that " Figure 1 As shown in FIGS. 2 to 3, a movable brick is provided in the furnace chamber, a cover plate is provided outside the furnace chamber, one end of the electrode is fixed on the bottom molybdenum wire, and the other end passes through the cover plate and is movably connected to the cover plate. The end of the electrode passing through the cover plate is provided with an external thread, and the insulating sleeve is pressed on the electrode by the thread and fixes the electrode on the cover plate, while the cover plate is fixed on the molybdenum wire furnace." However, since furnace shutdown for maintenance is required, it still affects production efficiency and increases costs.

[0005] In addition, for the heating furnaces in the prior art, not only is the molybdenum wire lead-out section prone to oxidation and burnout during the baking process and production process, shortening the service life of the molybdenum wire lead-out section, but also since the temperature in the furnace chamber of the above-mentioned heating furnace can reach over 1600 °C at the highest, and the thermal conductivity of molybdenum is relatively high, the molybdenum wire lead-out section generates heat by itself and also needs to conduct the heat in the furnace chamber to the electrode 1, causing the temperature rise on the electrode surface to often reach over 200 °C. This electrode structure has no measures to control the electrode temperature rise. The high-temperature electrode will damage the nearby sealing asbestos gasket, causing hydrogen leakage in the furnace, and will gradually carbonize the nearby bakelite gasket, resulting in insulation failure and discharging to the metal furnace shell, causing an electrode short-circuit fault. Summary of the Invention

[0006] The object of the present invention is to design a new type of electric heating furnace, which enhances the protection of the heating element, reduces or avoids the problem that the molybdenum wire lead-out section is prone to oxidation and burnout, and reduces electrode short-circuit faults.

[0007] To solve the above technical problems, the electric heating furnace of the present invention includes an electrode, an electrode seat, a furnace shell flange seat, and a heating element; the electrode seat is a connecting pipe with a flange at one end, and the electrode seat is fixedly connected to the furnace shell flange seat through the flange; one end of the protection tube is hermetically sleeved in the flange seat, the other end of the protection tube extends towards the furnace chamber, one side of the electrode is hermetically connected to the electrode seat, the other side of the electrode extends into the protection tube of the furnace shell flange seat and is connected to one end of the heating element, and the other end of the heating element extends towards the furnace chamber; an air inlet hole is opened on the outer peripheral surface of the electrode seat, an inflation joint is arranged on the air inlet hole, and the inflation joint is connected to a protective gas delivery pipeline; a copper row is fixedly connected to the outer end of the above-mentioned electrode.

[0008] For further improvement, the sealing and fixing component between the above-mentioned electrode and the electrode holder includes a first locking nut. Near the locking nut, a stepped shaft is provided. The inner wall of the electrode holder is provided with a positioning protrusion offset relative to the stepped shaft. The bakelite sleeve sleeved on the electrode is clamped on the positioning protrusion and the stepped shaft, playing a role in positioning the electrode. The locking nut on one side of the electrode is a bakelite nut, including an internal thread and an external thread. The internal thread of the locking nut is threadedly connected to one end of the electrode, and the external thread is threadedly connected to the electrode holder. An asbestos rope is filled between the locking nut and the bakelite sleeve. Tighten the nut to fix the electrode to the electrode holder and compress the asbestos rope filled between the nut and the bakelite sleeve, which can prevent the hydrogen in the furnace from leaking from the electrode part.

[0009] For further improvement, the sealing and sleeving component between the above-mentioned protective tube and the flange seat includes a second nut. The nut is provided with an internal thread and an external thread. The internal thread of the nut is threadedly connected to the protective tube, and the external thread is threadedly connected to the flange seat. An asbestos rope is filled between the second nut and the inner wall of the end of the flange seat. During assembly, the asbestos rope between the second nut and the inner wall of the flange seat is compressed to achieve the packing seal connection between the protective tube and the flange seat.

[0010] For further improvement, a sealing gasket is provided between the above-mentioned flange seat and the electrode seat, and is fastened and sealed by bolts.

[0011] For further improvement, the outer end of the electrode clamps and fixes the copper bar to the electrode through two copper nuts.

[0012] For further improvement, a heat insulation layer is provided between the above-mentioned furnace shell and the furnace chamber, and the other end of the protective tube extends through the heat insulation layer into the furnace chamber.

[0013] For further improvement, an exhaust and pressure relief device communicating with the furnace shell is provided in the above-mentioned furnace chamber.

[0014] For further improvement, the above-mentioned protective tube is preferably a corundum tube; the above-mentioned heating element is preferably a molybdenum wire, and the heating element is tied and connected to the other side of the electrode;

[0015] For further improvement, the above-mentioned electrode is any one of molybdenum electrode, graphite electrode, tungsten electrode or copper electrode.

[0016] For further improvement, the above-mentioned furnace shell is welded and fixed to the flange seat.

[0017] Adopting the structure of the present invention, a cavity opening in the furnace chamber is formed between the electrode holder and the corundum tube sleeved on the flange seat. There is an inflation joint in the air inlet hole of the electrode holder. After the protective gas such as hydrogen enters from this joint, it enters the furnace chamber along the corundum tube, bringing back the heat conducted to the electrode part in the furnace chamber to the furnace chamber, playing a triple role of cooling the electrode, protecting the molybdenum wire and saving energy.

[0018] The present invention realizes that the electrode is cooled by gas during the working process, and its beneficial effects include:

[0019] 1. When the protective gas is the same as the process gas required in the electric furnace, the flow rate of the protective gas introduced into the furnace can be included in the process gas flow rate. The protective gas can bring most of the heat originally dissipated and lost from the electrode part back to the furnace chamber, which has a certain energy-saving effect. The more electrodes the electric furnace has, the more obvious the energy-saving effect in this regard.

[0020] 2. The present invention enables the heating element such as molybdenum wire to be always protected by gas during the furnace baking and normal operation, and the molybdenum wire hardly burns out. Compared with the electrodes with ordinary structures, the service life of the molybdenum wire of the electrodes adopting the structure of the present invention is extended by more than 4 times, avoiding the frequent replacement of expensive molybdenum wire and reducing the furnace repair cost.

[0021] 3. The present invention enables the maximum temperature rise of the electrode part not to exceed 60 °C, eliminating the danger of the high-temperature hydrogen in the furnace leaking and exploding due to the seal at the electrode part being damaged by high temperature. Standard seals made of elastic materials such as fluororubber and silicone rubber can be used at this part, making the seal safer and more reliable.

[0022] 4. The present invention enables the maximum temperature rise of the electrode part not to exceed 60 °C, eliminating the fault of the power supply short circuit caused by the carbonization of the insulating parts at the electrode part and improving the reliability of the electric furnace operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic structural diagram of a heating element of an electric heating furnace in the prior art.

[0024] Figure 2 is a schematic structural diagram of an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the invention to the following embodiments.

[0026] Embodiment 1:

[0027] As Figure 2The electric heating furnace shown has a flange seat 6 welded to the furnace shell 7, and a heat insulation layer 9 is provided between the furnace shell and the furnace chamber. Its heating elements include electrodes 1, electrode seats 4, and heating element molybdenum wires 10. The electrode seat is a connecting pipe with a flange plate at one end. A gasket is provided between the flange seat and the flange plate of the electrode seat, and they are tightly sealed and connected by bolts. A corundum tube 11 is hermetically sleeved inside the flange seat. The other end of the corundum tube extends through the heat insulation layer towards the furnace chamber. One side of the electrode is hermetically fixed to the electrode seat, and the other side of the electrode extends into the corundum tube of the furnace shell flange seat and is tied and connected to one end of the molybdenum wire. The other end of the molybdenum wire extends towards the furnace chamber. An air inlet hole 13 is opened on the outer peripheral surface of the electrode seat, and an inflation joint is provided on the air inlet hole. The inflation joint is connected to the protective gas delivery pipeline. Two copper nuts 2 are threadedly connected to the outer end of the electrode, and a copper bus bar 12 is clamped and fixed between the nuts, realizing the electrical connection from the external power supply to the molybdenum wire inside the furnace.

[0028] The hermetically fixed connection component between the above-mentioned electrode and the electrode seat includes a first locking nut 3. Near the locking nut, a stepped shaft is provided. The inner wall of the electrode seat is provided with a positioning protrusion misaligned with the stepped shaft. A bakelite sleeve 5 sleeved on the electrode is clamped on the positioning protrusion and the stepped shaft. The locking nut at one end of the electrode is a bakelite nut, including an internal thread and an external thread. The internal thread of the locking nut is threadedly connected to one end of the electrode, and the external thread is threadedly connected to the electrode seat. An asbestos rope is filled between the locking nut and the bakelite sleeve.

[0029] The hermetically sleeved connection component between the above-mentioned corundum tube and the flange seat includes a second nut 8. The second nut has an internal thread and an external thread. The internal thread of the nut is threadedly connected to the corundum tube, and the external thread is threadedly connected to the flange seat. An asbestos rope is filled between the second nut and the end of the flange seat.

[0030] The electric heating furnace adopting the above structure of the present invention has a simple structure, reliable sealing, and is easy to implement. The protective gas enters the electrode seat through the joint and then enters the furnace chamber along the corundum tube, bringing the heat conducted to the electrode part in the furnace chamber back to the furnace chamber, and enabling the molybdenum wire to always have gas protection during operation, with a long service life. It reduces the temperature of the electrode, can reduce the heat loss at the electrode part, and plays a triple role of cooling the electrode, protecting the molybdenum wire, and saving energy.

[0031] In addition, since a cooling and protective gas is continuously filled into the electric furnace from the electrode during operation, the above-mentioned furnace chamber is provided with a connection communicating with the furnace shell. When the pressure in the furnace chamber is too high, the gas is discharged through the exhaust and pressure relief device to ensure the safe use of the heating furnace.

[0032] It should be particularly noted that:

[0033] 1. The filled cooling and protective gas includes but is not limited to hydrogen, and can also be inert gases such as argon and nitrogen.

[0034] 2. The present invention is applicable not only to the electrode structure with molybdenum as the conductive element, but also to the electrode structure with materials such as graphite, tungsten, and copper that have poor oxidation resistance as the conductive element.

[0035] The embodiments of the above specific manner are only used to explain the present invention and are not used to limit the present invention. Without departing from the gist of the present invention set forth in the claims, changes and alterations can be made to the specific embodiments. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electric heating furnace, characterized in that: It includes an electrode, an electrode holder, a furnace shell flange seat, and a heating element; the electrode holder is a connecting pipe with a flange at one end, and the electrode holder is fixedly connected to the furnace shell flange seat through the flange; one end of the protective tube is hermetically sleeved in the flange seat, the other end of the protective tube extends towards the furnace chamber, one side of the electrode is hermetically fixedly connected to the electrode holder, the other side of the electrode extends into the protective tube of the furnace shell flange seat and is connected to one end of the heating element, and the other end of the heating element extends towards the furnace chamber; air inlet holes are formed on the outer peripheral surface of the electrode holder, an inflation joint is arranged on the air inlet holes, and the inflation joint is connected to a protective gas delivery pipeline; a copper row is fixedly connected to the outer end of the above-mentioned electrode; The sealing and fixing component between the electrode and the electrode holder includes a first locking nut. Near the locking nut, a stepped shaft is provided, and positioning protrusions are arranged on the inner wall of the electrode holder in a staggered manner relative to the stepped shaft. The bakelite sleeve sleeved on the electrode is clamped on the positioning protrusions and the stepped shaft; the locking nut at one end of the electrode is a bakelite nut, which includes an internal thread and an external thread. The internal thread of the locking nut is threadedly connected to one end of the electrode, and the external thread is threadedly connected to the electrode holder; an asbestos rope is filled between the locking nut and the bakelite sleeve; The sealing and sleeving component between the protective tube and the flange seat includes a second nut. The nut has an internal thread and an external thread. The internal thread of the nut is threadedly connected to the protective tube, and the external thread is threadedly connected to the flange seat; an asbestos rope is filled between the second nut and the end of the flange seat; The outer end of the electrode clamps and fixedly connects the copper row to the electrode through two copper nuts; A sealing gasket is arranged between the flange seat and the electrode holder and is fastened and sealed by bolts; A heat insulation layer is arranged between the furnace shell and the furnace chamber, and the other end of the protective tube passes through the heat insulation layer and extends towards the furnace chamber.

2. The electric heating furnace according to claim 1, wherein, An exhaust and pressure relief device communicating with the furnace shell is arranged in the furnace chamber.

3. The electric heating furnace according to claim 1, characterized in that, The furnace shell is welded and fixedly connected to the flange seat.

4. The electric heating furnace according to claim 1, characterized in that, The electrode is any one of a molybdenum electrode, a graphite electrode, a tungsten electrode, or a copper electrode.

5. The electric heating furnace according to claim 1, characterized in that, The heating element is a molybdenum wire, and the heating element is tied and connected to the other side of the electrode; the protective tube is a corundum tube.

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