A method for building a medium frequency induction furnace

Abstract

The present invention provides a method for building a medium frequency induction furnace, including the steps of preparing a furnace lining material, preparing a furnace lining membrane, knotting a furnace bottom, knotting a furnace wall, baking the furnace and sintering. Compared with the prior art, the present invention is characterized in that: the acidic furnace lining material is easy to obtain and the furnace lining component is pure; the furnace building process is easy to operate, no special tools are required, and the furnace lining has high compactness after completion; the furnace baking time is short; during use, the furnace lining has no hidden danger of perforation, is not prone to cracks, and is easy to maintain in later use; and has a long service life.

Description

Technical Field

[0001] The invention belongs to the technical field of medium frequency induction furnaces, and in particular relates to a method for building a medium frequency induction furnace. Background Art

[0002] Medium frequency induction furnace is a commonly used casting and smelting equipment. It has the characteristics of high melting efficiency, good power saving effect, low temperature around the furnace, less smoke and dust, good working environment, uniform metal composition, fast melting temperature rise, easy furnace temperature control, high production efficiency, etc. It is widely used in cast iron, cast steel and other processes.

[0003] In the prior art, the wet furnace building method is generally used for medium frequency induction furnaces. This method causes the fluidity of the furnace lining sand to deteriorate after adding boric acid, resulting in uneven compactness of the furnace lining sand during casting, which is easy to cause the furnace to be disconnected when taking the mold, resulting in the furnace made by the wet furnace building method. The service life is short, and the number of furnaces used is between 10-100. At the same time, because the furnace lining is prone to capillary cracks on the inner wall of the furnace during repeated heating and cooling, and further develops into cracks, it requires more maintenance in the later stage. Summary of the invention

[0004] The object of the present invention is to provide a method for building a medium frequency induction furnace which can improve furnace building working conditions, shorten furnace building period and extend furnace life.

[0005] To achieve the above object, the present invention provides a method for building a medium frequency induction furnace, comprising the following specific steps:

[0006] 1) Preparation of furnace lining material: adding high-purity microcrystalline quartz sand to a high-temperature sintering agent and a mineralizer, mixing, and stirring evenly to obtain the furnace lining material;

[0007] 2) Preparation of furnace lining membrane: Use steel plate to make furnace lining membrane according to the size of the furnace;

[0008] 3) Knotting the furnace bottom: laying a heat-insulating protective layer on the inner wall of the induction coil, laying asbestos cloth or asbestos board on the furnace bottom refractory bricks laid with the heat-insulating protective layer, and laying the refractory material prepared in step 1) on the asbestos board, scraping it flat, and then tamping it with a hammer to obtain the furnace bottom;

[0009] 4) Knotting the furnace wall: placing the furnace lining membrane in the furnace bottom, positioning it with a wooden membrane at the furnace mouth and tightening it in time, and then adding the refractory material obtained in step 1) into the inner cavity of the knotting layer in batches along the outer wall of the furnace lining membrane, and using a ramming fork to move the inner cavity circumference point to ram and prepare the furnace wall;

[0010] 5) Baking the furnace: bake the furnace bottom, furnace wall and furnace mouth, the baking temperature is set to 1550-1640℃, and the baking time is set to 10-15h;

[0011] 6) Sintering: The furnace is baked to cause crystal transformation in the furnace bottom, furnace wall and furnace mouth, so that the furnace bottom, furnace wall and furnace mouth form a sintering layer - semi-sintering layer - hardened layer - loose layer from the inside to the outside, completing the furnace construction.

[0012] Preferably, the thickness of the steel plate in step 2) is set to 2-3 mm.

[0013] Preferably, the thermal insulation protective layer in step 3) is configured by laying 1-2 layers of 2mm thick asbestos cloth, and the specific laying method of the thermal insulation protective layer is: laying the asbestos cloth along the inner circle of the induction coil into a cylindrical structure with an interface overlap width of not less than 80mm.

[0014] Preferably, the thickness of the refractory material laid on the asbestos board in step 3) is set to 70-80 mm.

[0015] Preferably, the specific method for placing the furnace lining membrane in step 4) is as follows: when the furnace lining membrane is placed in the furnace bottom, three positioning feeler gauges are placed between the inner wall of the induction coil and the furnace lining membrane to ensure that the relative error between the center of the furnace lining membrane and the center of the induction coil is set between 0-3mm.

[0016] Preferably, the order of tamping in step 4) is: first tamping the area close to the inner wall of the induction coil and the outer wall of the fetal membrane, and then tamping the central area.

[0017] Preferably, in step 5), the furnace bottom, furnace wall and furnace mouth are naturally dried for 2 hours before being baked.

[0018] Preferably, the specific steps of baking the furnace bottom, furnace wall and furnace mouth in step 5) are as follows: bake the furnace at a low power of 20% of the normal power for 2-3 hours, and after the contact side of the furnace wall and the outer wall of the furnace lining membrane forms a certain strength, bake the furnace at normal power for 2 hours or more to complete the baking.

[0019] The application of the technical solution of the present invention has the following beneficial effects:

[0020] (1) The refractory material used for preparing the furnace lining in the present invention has small quartz grains (grain size 6μm-260μm) and does not use H3BO3 used in traditional processes. Through the action of mineralizers, the α-phosphotarzite conversion rate is high after the first furnace is sintered, thereby achieving a short furnace baking time and having excellent volume stability, thermal stability and high high-temperature strength.

[0021] (2) In the present invention, the furnace lining membrane is made of steel plates, so that the furnace lining membrane does not need to be taken out during the first smelting and can be directly used as furnace charge.

[0022] (3) In the present invention, a heat insulating protective layer is provided at the bottom of the furnace to effectively ensure the heat preservation effect of the medium frequency induction furnace.

[0023] (4) In the present invention, the dry furnace construction method is adopted. Since the refractory material of the furnace lining has good fluidity, the dead corners are easy to be tightened. At the same time, since no other debris is mixed into the furnace lining sand, the furnace lining composition is single and pure, and the sintering effect is good.

[0024] (5) After a complete furnace baking, the medium frequency induction furnace of the present invention forms four layers from the inside to the outside: sintered layer - semi-sintered layer - hardened layer - loose layer. After the first furnace baking, the thickness of the sintered layer is about 10 mm. After 5-10 times of normal smelting, the sintered layer gradually becomes thicker and can eventually reach 30-40% of the thickness of the entire furnace lining, so that the medium frequency induction furnace has the characteristics of high strength and dense structure.

[0025] (6) After a complete furnace baking, the present invention forms a loose layer between the furnace wall and the hardened layer, which makes it have the characteristics of insulation and heat insulation. In addition, since the sand particles are easy to loosen, they can effectively offset the displacement of the furnace lining due to volume expansion or contraction when it is heated or cooled, thereby achieving the purpose of extending the service life of the medium frequency induction furnace.

[0026] (7) The furnace lining material of the present invention does not require the addition of additives such as boric acid and silica sol, and has good fluidity. During the furnace building process, it only needs to be pounded with a tamping fork, and the corners or joints can be filled and compacted without any loose parts. In addition, the moisture content in the refractory furnace lining material is low, and the moisture is easy to discharge. The moisture in the furnace lining can be basically eliminated by drying the furnace once, and the furnace lining is kept dry during the smelting process, so that the service life is greatly extended, and more than 200 furnaces can be smelted in one furnace building.

[0027] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 It is a structural schematic diagram of the furnace lining in the present invention;

[0030] Figure 2 It is a schematic diagram of the baking furnace curve in the present invention.

[0031] in:

[0032] 1: sintered layer, 2: semi-sintered layer, 3: hardened layer, 4: dispersed layer. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0034] In order to make the above-mentioned purposes, features and advantages of the present invention more clear and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. It should be noted that the drawings of the present invention are all simplified and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the implementation of the present invention; the "number" mentioned in the present invention is not limited to the specific number in the examples in the accompanying drawings; the directions or positional relationships indicated by "front", "middle", "back", "left", "right", "up", "down", "top", "bottom", "middle", etc. mentioned in the present invention are based on the directions or positional relationships shown in the drawings of the present invention, and do not indicate or imply that the devices or components referred to must have a specific direction, nor can they be understood as limitations on the present invention.

[0035] See also Figure 1 and Figure 2 As shown, a method for building a medium frequency induction furnace provided by the present invention specifically comprises the above steps:

[0036] 1. Preparation of furnace lining materials: The furnace lining materials are first made of acidic refractory materials, high-purity microcrystalline quartz sand and powder, mixed with high-temperature sintering agent and mineralizer. The chemical composition is shown in Table 1:

[0037] Table 1: Chemical composition statistics of furnace lining materials (excluding sintering agent)

[0038] name <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O]]> <![CDATA[Na2O+K2]]> <![CDATA[H2O]]> Proportion(%) ≥97.5 ≤0.72 ≤0.41 ≤0.1 ≤0.5

[0039] Table 2: Statistics of physical properties of furnace lining materials

[0040] granularity Material density Recommended operating temperature (℃) Maximum operating temperature (℃) ≤4mm 2.1g / cm3 1500-1550 1600 ≤4mm 2.1g / cm3 1530-1580 1620 ≤4mm 2.1g / cm3 1560-1600 1650

[0041] As shown in Table 2, the furnace lining material has small quartz grains (grain size 6μm-260μm), does not use H3BO3 used in traditional processes, and due to the effect of mineralizer, the α-phosphotarzite conversion rate is high after sintering in the first furnace, so the furnace baking time is short, and it has excellent volume stability, thermal stability and high high temperature strength.

[0042] 2. Prepare furnace lining membrane: It is made of 2-3mm steel plate according to the size of the furnace.

[0043] 3. Knotting the furnace bottom: first, place 1-2 layers of 2mm thick asbestos cloth close to the inner wall of the induction coil, and fold the lower edge of the asbestos cloth toward the inner wall of the induction coil. Then, place 2-3 layers of 6-10mm thick asbestos cloth or asbestos board on the refractory bricks at the bottom of the furnace, and ensure that the overlap width of the asbestos board interface is not less than 80mm. Place a 70-80mm layer of furnace lining material on the bottom of the furnace, scrape it flat, and then use a hand hammer (pneumatic pounder) to tamp and flatten it to obtain the furnace bottom.

[0044] 4. Knotting the furnace wall: After the furnace bottom is knotted, place the furnace lining membrane to knot the furnace wall; when the furnace lining membrane is calibrated, it can be positioned with a wooden mold at the furnace mouth, and tightened in time and pressed with a pressure iron; when the furnace lining membrane is placed and positioned, use a tamping fork to tamp the furnace wall.

[0045] Preferably, when placing the furnace lining membrane, the center of the furnace lining membrane should be aligned with the center of the induction coil, and the error is not allowed to exceed 3mm.

[0046] Preferably, the specific method of ramming the furnace wall is as follows: the knotting sand material should be added to the inner cavity of the knotting layer in batches along the outer wall of the furnace lining membrane, and the thickness of each batch of material is about 20 to 50 mm. During the knotting process, in order to ensure the knotting tightness of the furnace lining, the impact point of the ramming fork should be moved along the circumference of the inner cavity for ramming;

[0047] Preferably, the tamping sequence is to first tamping the area close to the inner wall of the induction coil and the outer wall of the fetal membrane, and then tamping the central area.

[0048] 5. Oven: Oven includes four stages: natural drying, low power oven, high power oven and heat preservation (see Figure 2 The specific implementation steps are as follows:

[0049] A. After building the furnace, wait for natural drying for 2 hours;

[0050] B. Bake the oven at 20% of normal power for 2 to 3 hours;

[0051] C. Bake the oven at normal power for more than 2 hours to complete the baking.

[0052] 6: Sintering: After a complete furnace baking, the furnace bottom, furnace wall and furnace mouth form 4 layers from the inside to the outside: sintered layer 1, semi-sintered layer 2, hardened layer 3 and loose layer 4 (see Figure 1 After the first furnace baking, the thickness of the sintered layer is controlled at 10 mm. After 5-10 normal smeltings, the sintered layer gradually becomes thicker and can eventually reach 30-40% of the thickness of the entire furnace lining.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for building a medium frequency induction furnace, the method specifically comprising the following steps: 1) Preparation of furnace lining material: adding high-purity microcrystalline quartz sand to a high-temperature sintering agent and a mineralizer, mixing, and stirring evenly to obtain the furnace lining material; 2) Preparation of furnace lining membrane: Use steel plate to make furnace lining membrane according to the size of the furnace; 3) Knotting the furnace bottom: laying a heat-insulating protective layer on the inner wall of the induction coil, laying asbestos cloth or asbestos board on the furnace bottom refractory bricks laid with the heat-insulating protective layer, and laying the refractory material prepared in step 1) on the asbestos board, scraping it flat, and then tamping it with a hammer to obtain the furnace bottom; 4) Knotting the furnace wall: placing the furnace lining membrane in the furnace bottom, positioning it with a wooden membrane at the furnace mouth and tightening it in time, and then adding the refractory material obtained in step 1) into the inner cavity of the knotting layer in batches along the outer wall of the furnace lining membrane, and using a ramming fork to move the inner cavity circumference point to ram and prepare the furnace wall; 5) Baking the furnace: bake the furnace bottom, furnace wall and furnace mouth, the baking temperature is set to 1550-1640℃, and the baking time is set to 10-15h; 6) Sintering: The furnace is baked to cause crystal transformation in the furnace bottom, furnace wall and furnace mouth, so that the furnace bottom, furnace wall and furnace mouth form a sintering layer - semi-sintering layer - hardened layer - loose layer from the inside to the outside, completing the furnace construction.

2. The method for building a medium frequency induction furnace according to claim 1, characterized in that: The thickness of the steel plate in step 2) is set to 2-3 mm.

3. The method for building a medium frequency induction furnace according to claim 1, characterized in that: The heat insulation protection layer in step 3) is set to a 1-2 layer asbestos cloth structure, and the thickness of the asbestos cloth is set to 2mm.

4. The method for building a medium frequency induction furnace according to claim 3, characterized in that: The specific laying method of the heat insulation protection layer is: laying the asbestos cloth along the inner circle of the induction coil into a cylindrical structure with an interface overlap width of not less than 80 mm.

5. The method for building a medium frequency induction furnace according to claim 4, characterized in that: The thickness of the asbestos board in step 3) is set to 6-10 mm.

6. The method for building a medium frequency induction furnace according to claim 5, characterized in that: The thickness of the refractory material laid on the asbestos board in step 3) is set to 70-80 mm.

7. The method for building a medium frequency induction furnace according to claim 1, characterized in that: The specific method for placing the furnace lining membrane in step 4) is as follows: when the furnace lining membrane is placed in the furnace bottom, three positioning feeler gauges are placed between the inner wall of the induction coil and the furnace lining membrane to ensure that the relative error between the center of the furnace lining membrane and the center of the induction coil is set between 0-3mm.

8. The method for building a medium frequency induction furnace according to claim 7, characterized in that: The order of tamping in step 4) is: first tamping the area close to the inner wall of the induction coil and the outer wall of the fetal membrane, and then tamping the central area.

9. The method for building a medium frequency induction furnace according to claim 1, characterized in that: In the step 5), the furnace bottom, furnace wall and furnace mouth are first dried naturally for 2 hours before being baked.

10. The method for building a medium frequency induction furnace according to claim 9, characterized in that: The specific steps of baking the furnace bottom, furnace wall and furnace mouth in step 5) are as follows: bake the furnace at a low power of 20% of the normal power for 2-3 hours, and after the contact side of the furnace wall and the outer wall of the furnace lining membrane forms a certain strength, bake the furnace at normal power for 2 hours or more to complete the baking.

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