Production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine

Abstract

The invention discloses a production process of electrical grade magnesium oxide powder for single-end heating tubes of a hot bending machine, belonging to the technical field of magnesium oxide production. The production process includes the following steps: Mineral electrofused magnesium oxide is successively crushed, pulverized, sieved, and spheroidized to obtain magnesium oxide pellets. The magnesium oxide pellets are calcined at 1180-1200 °C for 2 h to obtain magnesium oxide powder. The magnesium oxide powder, magnesium aluminate spinel, and high-hydrogen-content silicone oil are mixed evenly to obtain a mixture. The mixture is subjected to magnetic separation and screening treatment to obtain the electrical grade magnesium oxide powder. Through detection, the electrical grade magnesium oxide powder prepared by the invention has extremely low impurities and magnetic susceptibility substances, and excellent electrical properties at the same time. Applying the electrical grade magnesium oxide powder prepared by the invention to the production of single-end heating tubes of a hot bending machine can significantly improve the service life of the single-end heating tubes of the hot bending machine.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium oxide production, and particularly relates to a production process of electrical grade magnesium oxide powder for single-end heating tubes of heat bending machines. Background Art

[0002] The single-end heating tube of a heat bending machine is a device for processing plastic sheets such as acrylic, plexiglass, PC, PVC, and SBS. The single-end heating tube of a heat bending machine accurately positions the angle, adopts an advanced infrared heating and water circulation cooling system, and automatically forms instantaneously. It has the advantages of accurate angle, fast speed, high efficiency, no deformation, no paste board, and no bubbling of the processed workpieces. The single-end heating tube of a heat bending machine is specifically applied to aspects such as the observation window of a space shuttle and the curved screen of a mobile phone screen.

[0003] The single-end heating tube of a heat bending machine consists of a stainless steel cylindrical shell, a nickel-chromium alloy heating wire, and electrical grade magnesium oxide powder and other structures. Its core lies in the electrical grade magnesium oxide powder. The functions of the electrical grade magnesium oxide powder in the single-end heating tube include insulation and heat transfer. Among them, insulation is used to prevent the nickel-chromium alloy heating wire from contacting the stainless steel cylindrical shell; heat transfer is used to transfer the heat generated by the nickel-chromium alloy heating wire to the stainless steel cylindrical shell, and then used for the heat bending processing technology of plastic sheets.

[0004] Currently, the key to restricting the heating power and service life of the single-end heating tube of a heat bending machine lies in the quality of the electrical grade magnesium oxide powder. The electrical grade magnesium oxide powder is mainly processed from magnesite. The properties of the electrical grade magnesium oxide powder such as pressure resistance, insulation, density, and trace element content are the key to determining the quality of the product. Among them, trace elements (such as iron, carbon, sulfur, phosphorus, etc.) will reduce the pressure resistance performance of the electrical grade magnesium oxide powder and cause problems such as blackening of the magnesium powder. In order to improve the quality of the electrical grade magnesium oxide powder and thus improve the service life of the single-end heating tube of a heat bending machine, it is necessary to improve the production process of the electrical grade magnesium oxide powder. Summary of the Invention

[0005] The purpose of the present invention is to provide a production process of electrical grade magnesium oxide powder for single-end heating tubes of heat bending machines to improve the quality of the electrical grade magnesium oxide powder.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A production process of electrical grade magnesium oxide powder for single-end heating tube of a hot bending machine includes the following steps: Crushing mineral electrofused magnesia to ≤5 mm to obtain coarse powder of mineral electrofused magnesia, further pulverizing the coarse powder of mineral electrofused magnesia, controlling the D50 particle size after processing to be 0.25 mm to obtain homogenized coarse magnesia powder, screening the homogenized coarse magnesia powder to obtain gradient coarse magnesia powder, spheroidizing the gradient coarse magnesia powder to obtain magnesia pellets, calcining the magnesia pellets at 1180 - 1200 °C for 2 h and then cooling to room temperature to obtain magnesia powder, mixing the magnesia powder, magnesium aluminate spinel, and high hydrogen content silicone oil evenly to obtain a mixture, and subjecting the mixture to magnetic separation and screening treatment to obtain the electrical grade magnesium oxide powder.

[0008] Further, the proportion of coarse powder above 500 mesh in the gradient coarse magnesia powder is ≤1.0%.

[0009] Further, the particle sphericity of the magnesia pellets is 0.80 - 0.85.

[0010] Further, the mass components of the magnesium aluminate spinel are 78% Al2O3 and 22% MgO.

[0011] Further, the viscosity of the high hydrogen content silicone oil at 20 °C is 20 mPa.s, and the hydrogen content is 1.0% - 1.8%.

[0012] Further, the mass ratio of the magnesia powder, magnesium aluminate spinel, and high hydrogen content silicone oil is 1000:2:0.2.

[0013] Further, the mineral electrofused magnesia is produced by the following steps:

[0014] Artificially crushing natural magnesite, screening through 80 - 100 mesh to obtain natural magnesite powder, calcining the natural magnesite powder at 2750 - 2850 °C for 10 - 12 h, and after calcination, naturally cooling for 168 - 240 h to obtain mineral electrofused magnesia.

[0015] Further, in the mineral electrofused magnesia, the magnesia content is ≥97.5%, the calcium oxide content is ≤0.5%, the iron(III) oxide content is ≤0.3%, the silicon dioxide content is ≤1.0%, the aluminum oxide content is ≤0.5%, the carbon content is ≤0.3‰, the sulfur content is ≤0.3‰, and the phosphorus content is ≤0.3‰.

[0016] The beneficial effects of the present invention:

[0017] The present invention provides a production process for electrical grade magnesium oxide powder used in single-ended heating tubes of a hot bending machine. The electrical grade magnesium oxide powder prepared by the production process of the present invention has the following characteristics: (1) low carbon, low sulfur, and low phosphorus (average mass component content): carbon content ≤ 0.03‰, sulfur content ≤ 0.015‰, phosphorus content ≤ 0.05‰; (2) content of magnetic susceptibility substances (average mass component content) ≤ 0.02‰; (3) flow rate ≤ 32 s / 100 g; (4) tapped density reaches 2.35 g / cm 3 -2.50 g / cm 3 ; (5) insulation resistance (1000 V high voltage) ≥ 10000 MΩ, insulation withstand voltage (0.5 mA.5 s) ≥ 3000 V. After testing, the electrical grade magnesium oxide powder prepared by the present invention has extremely low impurities and magnetic susceptibility substances, and at the same time has excellent electrical properties. Applying the electrical grade magnesium oxide powder prepared by the present invention to the production of single-ended heating tubes of a hot bending machine can significantly improve the service life of the single-ended heating tubes of the hot bending machine. Detailed implementation manners

[0018] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0019] The present invention provides a production process for electrical grade magnesium oxide powder used in single-ended heating tubes of a hot bending machine:

[0020] First, the natural magnesite in the processing raw materials of the present invention is mined from the Huazi Yu ore in Haicheng.

[0021] Then, the first step in producing electrical grade magnesium oxide powder for single-ended heating tubes of a hot bending machine is to produce mineral fused magnesia, including the following steps:

[0022] Manually crush the natural magnesite, pass it through a 80-100 mesh sieve to obtain natural magnesite powder, place the natural magnesite powder under the condition of 2750-2850 °C and calcine it for 10-12 h. After calcination, naturally cool it for 168-240 h (7-10 d) to obtain mineral fused magnesia.

[0023] Among them, the main component of natural magnesite is magnesium carbonate, and it also includes impurities such as silicon oxide, calcium oxide, iron oxide, aluminum oxide, and sulfur. Under the high temperature condition of 2750-2850 °C, magnesium carbonate decomposes into magnesium oxide and carbon dioxide, and the carbon dioxide escapes, and the overall content of magnesium oxide increases. In this process, sulfur escapes in the form of gases such as sulfur dioxide and sulfur trioxide, and finally mineral fused magnesia is obtained.

[0024] Finally, the production of the magnesium oxide powder for the single-end heating tube of the hot bending machine includes the following steps:

[0025] (1) Crush the mineral fused magnesia with a jaw crusher to ≤5 mm to obtain the coarse powder of mineral fused magnesia;

[0026] (2) Place the coarse powder of mineral fused magnesia in a ceramic grinder for processing, and control the D50 particle size (median particle size) after processing to be 0.25 mm to obtain the homogenized coarse powder of magnesia;

[0027] (3) Place the homogenized coarse powder of magnesia in a classifier for screening, and control the proportion of coarse powder above 500 mesh to be ≤1.0% to obtain the gradient coarse powder of magnesia;

[0028] (4) Place the gradient coarse powder of magnesia in a shaper for spheroidization treatment, and after treatment, obtain magnesia pellets, and control the particle sphericity of the magnesia pellets to be 0.80 - 0.85;

[0029] (5) Place the magnesia pellets in a high-temperature rotary kiln and calcine them at 1180 - 1200 °C for 2 h. After calcination, cool them to room temperature to obtain the magnesia powder;

[0030] (6) Place the magnesia powder, magnesium aluminate spinel (mass fraction of Al2O3 is 78%, and that of MgO is 22%), and high-hydrogen-content silicone oil (viscosity 20 mPa·s (20 °C), hydrogen content 1.0% - 1.8%) in a high-frequency mixer according to the mass ratio of 1000:2:0.2 and mix them evenly to obtain a mixture;

[0031] (7) Place the mixture in a magnetic separator with 12000 Gauss for magnetic separation treatment and in a three-dimensional vibrating screen for screening treatment, and then obtain the magnesium oxide powder for electrical engineering.

[0032] The specific implementation methods are as follows:

[0033] Example 1

[0034] Production of mineral fused magnesia:

[0035] Manually crush the natural magnesite, sieve it through an 80-mesh sieve to obtain the natural magnesite powder. Place the natural magnesite powder in a calciner at 2750 °C for 10 h. After calcination, cool it naturally for 168 h to obtain the mineral fused magnesia. After testing, the average mass fraction content of the mineral fused magnesia produced in this example is shown in Table 1 below:

[0036] Table 1 Average mass fraction content of mineral fused magnesia in Example 1

[0037] Component MgO <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> C N S Trace impurities Content 97.51％ 0.99％ 0.48％ 0.28％ 0.48％ 0.28‰ 0.28‰ 0.30‰ Balance

[0038] Example 2

[0039] Production of mineral fused magnesia:

[0040] Manually crush natural magnesite, screen it through a 90-mesh sieve to obtain natural magnesite powder. Place the natural magnesite powder in a calcination furnace at 2800 °C for 12 h. After calcination, cool it naturally for 240 h to obtain mineral fused magnesia. After testing, the average mass component content of the mineral fused magnesia produced in this example is shown in Table 2 below:

[0041] Table 2 Average mass component content of mineral fused magnesia in Example 2

[0042] Component MgO <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> C N S Trace impurities Content 97.60％ 0.95％ 0.48％ 0.26％ 0.45％ 0.25‰ 0.25‰ 0.28‰ Balance

[0043] Example 3

[0044] Production of mineral fused magnesia:

[0045] Manually crush natural magnesite, screen it through a 100-mesh sieve to obtain natural magnesite powder. Place the natural magnesite powder in a calcination furnace at 2850 °C for 12 h. After calcination, cool it naturally for 240 h to obtain mineral fused magnesia. After testing, the average mass component content of the mineral fused magnesia produced in this example is shown in Table 3 below:

[0046] Table 3 Average mass component content of mineral fused magnesia in Example 3

[0047] Component MgO <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> C N S Trace impurities Content 97.69％ 0.92％ 0.46％ 0.26％ 0.44％ 0.25‰ 0.25‰ 0.28‰ Balance

[0048] Example 4

[0049] Production of magnesia powder for single-ended heating tube of hot bending machine:

[0050] The mineral electrofused magnesia produced in Example 1 was crushed to ≤5 mm with a jaw crusher to obtain coarse mineral electrofused magnesia powder. The coarse mineral electrofused magnesia powder was then processed in a ceramic pulverizer, and the D50 particle size (median particle size) after processing was controlled to be 0.25 mm to obtain homogenized coarse magnesia powder. The homogenized coarse magnesia powder was then sieved in a classifier, and the proportion of coarse powder above 500 mesh was controlled to be ≤1.0% to obtain gradient coarse magnesia powder. The gradient coarse magnesia powder was placed in a shaping machine for spheroidization treatment, and magnesia pellets were obtained after treatment. The sphericity of the magnesia pellets was controlled to be 0.80. Then, the magnesia pellets were placed in a high-temperature rotary kiln and calcined at 1180 °C for 2 h. After calcination, they were cooled to room temperature to obtain magnesia powder. The magnesia powder, magnesium aluminate spinel (mass composition: 78% Al2O3, 22% MgO), and high hydrogen content silicone oil (viscosity 20 mPa·s (20 °C), hydrogen content 1.0% - 1.8%) were mixed evenly in a high-frequency mixer according to a mass ratio of 1000:2:0.2 to obtain a mixture. The mixture was successively subjected to magnetic separation treatment in a magnetic separator with a magnetic field of 12000 Gauss and screening treatment in a three-dimensional vibrating sieve to obtain the said electrical grade magnesia powder.

[0051] After testing, the components and electrical properties of the produced electrical grade magnesia powder are as follows:

[0052] 1. Low carbon, low sulfur, and low phosphorus (average mass component content): its carbon content ≤0.03‰, sulfur content ≤0.015‰, and phosphorus content ≤0.05‰;

[0053] 2. Content of magnetic substances (average mass component content) ≤0.02‰;

[0054] 3. Flow rate ≤32 s / 100 g;

[0055] 4. Tap density reaches 2.35 g / cm 3 ;

[0056] 5. Insulation resistance (1000 V high voltage) ≥10000 MΩ, insulation withstand voltage (0.5 mA·5 s) ≥3000 V.

[0057] Among them, the detection standards for flow rate, tap density, insulation resistance, and insulation withstand voltage refer to the Mechanical Industry Standard of the People's Republic of China "Electrical Grade Magnesia" JB / T 8508-1996.

[0058] Example 5

[0059] Production of electrical grade magnesia powder for single-end heating tubes of hot bending machines:

[0060] The mineral electrofused magnesia produced in Example 2 was crushed by a jaw crusher to ≤5 mm to obtain coarse powder of mineral electrofused magnesia. The coarse powder of mineral electrofused magnesia was then placed in a ceramic crusher for processing, and the D50 particle size (median particle size) after processing was controlled to be 0.25 mm to obtain homogenized coarse magnesia powder. The homogenized coarse magnesia powder was then placed in a classifier for screening, and the proportion of coarse powder above 500 mesh was controlled to be ≤1.0% to obtain gradient coarse magnesia powder. The gradient coarse magnesia powder was placed in a shaper for spheroidization treatment, and after treatment, magnesia pellets were obtained. The particle sphericity of the magnesia pellets was controlled to be 0.84. Then, the magnesia pellets were placed in a high-temperature rotary kiln and calcined at 1190 °C for 2 h. After calcination, they were cooled to room temperature to obtain magnesia powder. The magnesia powder, magnesium aluminate spinel (mass composition: 78% Al2O3, 22% MgO), and high-hydrogen-content silicone oil (viscosity 20 mPa·s (20 °C), hydrogen content 1.0% - 1.8%) were mixed evenly in a high-frequency mixer according to a mass ratio of 1000:2:0.2 to obtain a mixture. The mixture was successively subjected to magnetic separation treatment in a magnetic separator with a magnetic field strength of 12000 Gauss and screening treatment in a three-dimensional vibrating screen to obtain the said electrical-grade magnesia powder.

[0061] After testing, the components and electrical properties of the produced electrical-grade magnesia powder are as follows:

[0062] 1. Low carbon, low sulfur, and low phosphorus (average mass component content): its carbon content ≤0.02‰, sulfur content ≤0.015‰, and phosphorus content ≤0.04‰;

[0063] 2. Content of magnetically sensitive substances (average mass component content) ≤0.02‰;

[0064] 3. Flow rate ≤30 s / 100 g;

[0065] 4. Tap density reaches 2.40 g / cm 3 ;

[0066] 5. Insulation resistance (1000 V high voltage) ≥10000 MΩ, insulation withstand voltage (0.5 mA·5 s) ≥3000 V.

[0067] Among them, the detection standards for flow rate, tap density, insulation resistance, and insulation withstand voltage refer to the Mechanical Industry Standard of the People's Republic of China "Electrical-Grade Magnesia" JB / T 8508-1996.

[0068] Example 6

[0069] Production of electrical-grade magnesia powder for single-end heating tubes of hot bending machines:

[0070] The mineral electrofused magnesia produced in Example 3 was crushed to ≤5 mm with a jaw crusher to obtain coarse mineral electrofused magnesia powder. The coarse mineral electrofused magnesia powder was then processed in a ceramic grinder, and the D50 particle size (median particle size) after processing was controlled to be 0.25 mm to obtain homogenized coarse magnesia powder. The homogenized coarse magnesia powder was then sieved in a classifier, and the proportion of coarse powder above 500 mesh was controlled to be ≤1.0% to obtain gradient coarse magnesia powder. The gradient coarse magnesia powder was placed in a shaper for spheroidization treatment, and magnesia pellets were obtained after treatment. The sphericity of the magnesia pellets was controlled to be 0.85. Then, the magnesia pellets were placed in a high-temperature rotary kiln and calcined at 1200 °C for 2 h. After calcination, they were cooled to room temperature to obtain magnesia powder. The magnesia powder, magnesium aluminate spinel (Al2O3 with a mass fraction of 78% and MgO with a mass fraction of 22%), and high-hydrogen-content silicone oil (viscosity 20 mPa·s (20 °C), hydrogen content 1.0% - 1.8%) were mixed evenly in a high-frequency mixer at a mass ratio of 1000:2:0.2 to obtain a mixture. The mixture was successively subjected to magnetic separation treatment in a magnetic separator with a magnetic field strength of 12000 Gauss and screening treatment in a three-dimensional vibrating sieve to obtain the said electrical-grade magnesia powder.

[0071] After testing, the components and electrical properties of the produced electrical-grade magnesia powder are as follows:

[0072] 1. Low carbon, low sulfur, and low phosphorus (average mass fraction content): its carbon content ≤0.02‰, sulfur content ≤0.010‰, and phosphorus content ≤0.04‰;

[0073] 2. Content of magnetically sensitive substances (average mass fraction content) ≤0.02‰;

[0074] 3. Flow rate ≤28 s / 100 g;

[0075] 4. Tap density reaches 2.50 g / cm 3 ;

[0076] 5. Insulation resistance (1000 V high voltage) ≥10000 MΩ, insulation withstand voltage (0.5 mA·5 s) ≥3000 V.

[0077] Among them, the detection standards for flow rate, tap density, insulation resistance, and insulation withstand voltage refer to the Mechanical Industry Standard of the People's Republic of China "Electrical-Grade Magnesia" JB / T 8508-1996.

[0078] It should be noted that in this article, terms such as "including, containing" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such a process, method, article, or device.

[0079] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine, characterized in that: The following steps are involved: The mineral fused magnesia is crushed to ≤5mm to obtain the mineral fused magnesia coarse powder, and the mineral fused magnesia coarse powder is further crushed to control the D 50 The particle size is 0.25 mm, and a homogenized coarse powder of magnesium oxide is obtained. The homogenized coarse powder of magnesium oxide is sieved to obtain a gradient coarse powder of magnesium oxide, and the gradient coarse powder of magnesium oxide is spheroidized to obtain magnesium oxide pellets. The magnesium oxide pellets are calcined at 1180-1200° C. for 2 hours, and then cooled to room temperature to obtain magnesium oxide powder. The magnesium oxide powder, magnesium aluminum spinel, and high hydrogen silicone oil are uniformly mixed to obtain a mixture, and the mixture is successively placed in a 12000 Gauss magnetic separator for magnetic separation and a three-dimensional vibration screening machine for screening to obtain the electrical grade magnesium oxide powder; The sphericity of the magnesium oxide granules is 0.80-0.85; The mass usage ratio of the magnesium oxide powder, magnesium aluminum spinel and high hydrogen content silicone oil is 1000:2:0.

2.

2. The production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine according to claim 1, characterized in that: The magnesium oxide gradient coarse powder has a proportion of coarse powder above 500 meshes ≤ 1.0%.

3. The production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine according to claim 1, characterized in that: The mass composition of the magnesium-aluminum spinel is 78% Al2O3 and 22% MgO.

4. The production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine according to claim 1, characterized in that: The high hydrogen silicone oil has a viscosity of 20 mPa.s at 20° C. and a hydrogen content of 1.0%-1.8%.

5. The production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine according to claim 1, characterized in that: The mineral fused magnesium oxide is produced by the following steps: The natural magnesite is artificially crushed and passed through an 80-100 mesh sieve to obtain natural magnesite powder, and the natural magnesite powder is calcined at 2750-2850°C for 10-12 hours. After the calcination is completed, it is naturally cooled for 168-240 hours to obtain mineral fused magnesium oxide.

6. The production process of electrical grade magnesium oxide powder for single-end heating tube of hot bending machine according to claim 5, characterized in that: The mineral fused magnesium oxide has a magnesium oxide content of ≥97.5%, a calcium oxide content of ≤0.5%, a ferric oxide content of ≤0.3%, a silicon dioxide content of ≤1.0%, an aluminum oxide content of ≤0.5%, a carbon content of ≤0.3‰, a sulfur content of ≤0.3‰, and a phosphorus content of ≤0.3‰.