Ultra-coarse tungsten carbide and preparation method thereof

Abstract

The invention discloses ultra-coarse tungsten carbide and a preparation method thereof, and the preparation method comprises the following steps: providing ultra-coarse tungsten oxide particles with the water content of 3-5 wt%, the average particle size of the ultra-coarse tungsten oxide particles being 28-45 [mu] m; loading the ultra-coarse tungsten oxide particles into a boat, placing the boat in a closed reduction furnace, introducing hydrogen, and carrying out a reduction reaction to obtain ultra-coarse tungsten particles; wherein the temperature of the reduction reaction ranges from 950 DEG C to 1100 DEG C, the boat loading amount ranges from 2.8 Kg / boat to 3.5 Kg / boat, the circulation time ranges from 45 min / boat to 60 min / boat, the hydrogen flow ranges from 8 m < 3 > / h to 15 m < 3 > / h, and the hydrogen dew point ranges from-65 DEG C to-75 DEG C; the ultra-coarse tungsten particles and carbon are mixed, and a carbon mixed material is obtained; performing high-temperature carbonization on the carbon-containing mixture to obtain tungsten carbide particles; the tungsten carbide particles are crushed and sieved, the ultra-coarse tungsten carbide is obtained, and the average particle size of the ultra-coarse tungsten carbide ranges from 30 micrometers to 60 micrometers. According to the method, the ultra-coarse tungsten particles with high purity and more uniform particle size distribution can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of cemented carbide manufacturing, and more specifically, to an ultra-coarse tungsten carbide and a preparation method thereof. Background Art

[0002] Tungsten carbide is an important raw material for preparing tungsten-containing cemented carbide. The properties of the prepared cemented carbide depend largely on the properties of the tungsten carbide raw material.

[0003] High-quality ultra-coarse tungsten carbide is a high-quality raw material for preparing mining cemented carbide due to its large grain size, complete crystal structure, small micro deformation, few structural defects, high microhardness and other advantages. Coarse-grained tungsten carbide can meet the requirements of high impact toughness and excellent fatigue resistance of mining tools. The prepared cemented carbide can be widely used in the continuous mining of soft rocks under extreme working conditions and the continuous operation of modern roads and bridges. It can also be used for stamping dies, cold heading dies, rollers, etc. that require high toughness, thermal fatigue resistance and thermal shock resistance.

[0004] At present, there are mainly the following processes for producing ultra-coarse tungsten carbide powder at home and abroad: 1. Ultra-coarse tungsten carbide powder is prepared by high-temperature reduction and high-temperature carburization process. The ultra-coarse tungsten carbide powder prepared by this process has fuller grain development and good wear resistance, but it has defects such as high energy consumption and large equipment loss. 2. Alkali metal doped tungsten oxide is used as raw material to prepare ultra-coarse tungsten carbide powder. The ultra-coarse carbon tungsten powder prepared by this process has coarser particle size, but it has defects such as many false particles and poor wear resistance. The third is to use wet hydrogen high-temperature reduction and high-temperature carburization to prepare ultra-coarse tungsten carbide powder. This process has better primary particle development and good wear resistance for preparing tungsten carbide powder, but it has defects such as high equipment requirements and unstable wet hydrogen atmosphere control. In the traditional alkali metal doping process, due to the uneven doping of alkali metals during doping, the alkali metal distribution is uneven, resulting in abnormally coarse particles; and the tungsten powders are easy to sinter and grow during the high-temperature carburization process, resulting in incomplete carburization, and exist in the form of W2C (brittle phase), which ultimately reduces the wear resistance of tungsten carbide powder. Therefore, the process of preparing ultra-coarse tungsten carbide powder by doping process needs to be improved. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art, provide an ultra-coarse tungsten carbide and a preparation method thereof, and obtain ultra-coarse tungsten particles with high purity and more uniform particle size distribution.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for preparing ultra-coarse tungsten carbide comprises the following steps:

[0008] Providing ultra-coarse tungsten oxide particles with a water content of 3wt% to 5wt%, wherein the average particle size of the ultra-coarse tungsten oxide particles is 28μm to 45μm;

[0009] The ultra-coarse tungsten oxide particles are loaded into a boat and placed in a closed reduction furnace, and hydrogen is introduced to perform a reduction reaction to obtain ultra-coarse tungsten particles; wherein the temperature of the reduction reaction is 950°C to 1100°C, the loading amount is 2.8Kg / boat to 3.5Kg / boat, the cycle time is 45min / boat to 60min / boat, and the hydrogen flow rate is 8m 3 / h~15m 3 / h, hydrogen dew point is -65℃~-75℃;

[0010] Mixing the ultra-coarse tungsten particles and carbon to obtain a carbon-blended mixture;

[0011] Carburizing the carbon mixture at high temperature to obtain tungsten carbide particles;

[0012] The tungsten carbide particles are crushed and sieved to obtain the ultra-coarse tungsten carbide, and the average particle size of the ultra-coarse tungsten carbide is 30 μm to 60 μm.

[0013] The invention also discloses an ultra-coarse tungsten carbide which is prepared by the preparation method.

[0014] Implementing the embodiments of the present invention will have the following beneficial effects:

[0015] In the embodiment of the present invention, tungsten oxide particles with a certain water content are used as raw materials. Water will gradually evaporate into water vapor during the high-temperature reduction reaction, thereby increasing the pressure in the furnace and promoting hydrogen to enter the interior of the tungsten oxide particles to undergo a reduction reaction, thereby making the reduction reaction more complete. At the same time, the high pressure in the furnace will also promote the reaction of water vapor with tungsten oxide to form volatile hydrates. These hydrates are reduced on the surface of the reduced tungsten powder and low-valent tungsten oxide, causing the tungsten particles to grow, thereby obtaining ultra-coarse tungsten particles and ultra-coarse tungsten carbide.

[0016] The present invention introduces water into the reduction furnace through the tungsten oxide raw material. On the one hand, the water can be evenly distributed in the raw material to evenly drive the tungsten particles to grow. On the other hand, it will increase the pressure in the furnace and the dew point of hydrogen in the furnace, thereby avoiding the increase of the pressure load of the pipeline by inputting high dew point hydrogen through the pipeline.

[0017] The present invention adopts tungsten oxide raw material with a certain water content, and cooperates with low boat loading, low hydrogen flow rate and long circulation time to prolong the reduction reaction time, make the reduction reaction more complete, reduce the content of false particles, and obtain high-purity ultra-coarse tungsten particles and ultra-coarse tungsten carbide with more uniform particle size.

[0018] The present invention uses water in the tungsten oxide raw material as a particle enlargement agent, and compared with the prior art of adding alkali metal ions, it can avoid introducing alkali metal impurity elements. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The present invention discloses a method for preparing ultra-coarse tungsten carbide, comprising the following steps:

[0021] 1) Provide ultra-coarse tungsten oxide particles with a water content of 3wt% to 5wt%, and the average particle size of the ultra-coarse tungsten oxide particles is 28μm to 45μm.

[0022] In this step, the ultra-coarse tungsten oxide particles can be soaked in water and fished out to obtain a certain water content, so that the water can fully infiltrate the raw material, so that it can fully and evenly contact the tungsten oxide raw material during the hydrogen reduction process. In other embodiments, spraying and stirring can also be used.

[0023] The ultra-coarse tungsten oxide particles include one or both of ultra-coarse blue tungsten particles and ultra-coarse yellow tungsten particles. Ultra-coarse blue tungsten particles are preferred because they are easier to produce ultra-coarse tungsten particles.

[0024] The present invention adopts tungsten oxide particles with a certain water content as raw materials. Water will gradually evaporate into water vapor during the high-temperature reduction reaction, thereby increasing the pressure in the furnace and promoting hydrogen to enter the interior of the tungsten oxide particles to cause a reduction reaction, thereby making the reduction reaction more complete. At the same time, the high pressure in the furnace will also promote the reaction of water vapor with tungsten oxide to form volatile hydrates. These hydrates are reduced on the surface of the reduced tungsten powder and low-valent tungsten oxide, which will cause the tungsten particles to grow, thereby obtaining ultra-coarse tungsten particles and ultra-coarse tungsten carbide.

[0025] The present invention introduces water into the reduction furnace through the tungsten oxide raw material. On the one hand, the water can be evenly distributed in the raw material to evenly drive the tungsten particles to grow. On the other hand, it will increase the pressure in the furnace and the dew point of hydrogen in the furnace, thereby avoiding the increase of the pressure load of the pipeline by inputting high dew point hydrogen through the pipeline.

[0026] The present invention uses water in the tungsten oxide raw material as a particle enlargement agent, and compared with the prior art of adding alkali metal ions, it can avoid introducing alkali metal impurity elements.

[0027] 2) The ultra-coarse tungsten oxide particles are loaded into a boat and placed in a closed reduction furnace, and hydrogen is introduced to perform a reduction reaction to obtain ultra-coarse tungsten particles; wherein the reduction reaction temperature is 950°C to 1100°C, the loading amount is 2.8Kg / boat to 3.5Kg / boat, the cycle time is 45min / boat to 60min / boat, and the hydrogen flow rate is 8m 3 / h~15m 3 / h, the dew point of hydrogen is -65℃~-75℃.

[0028] In the above embodiment, the hydrogen dew point of -65°C to -75°C refers to the dew point of hydrogen in the pipeline, that is, the hydrogen in the pipeline has a certain pressure. The higher the dew point of hydrogen, the greater the pressure, and the easier it is to contact and react with the raw materials.

[0029] Hydrogen flow rate, hydrogen dew point, cycle time and boat loading jointly regulate the time of reduction reaction. Under certain hydrogen dew point conditions, the smaller the hydrogen flow rate, the longer the hydrogen stays in the reduction furnace. The longer the cycle time, the longer the reduction reaction of the raw material. The smaller the boat loading, the more complete the reaction.

[0030] The present invention adopts tungsten oxide raw material with a certain water content, and cooperates with low boat loading, low hydrogen flow rate and long circulation time to prolong the reduction reaction time, make the reduction reaction more complete, reduce the content of false particles, and obtain high-purity ultra-coarse tungsten particles and ultra-coarse tungsten carbide with more uniform particle size.

[0031] The average particle size of the ultra-coarse tungsten carbide particles obtained by the method of the present invention is 30 μm to 60 μm.

[0032] In a specific embodiment, the reduction furnace is a fully automatic 15-tube reduction furnace, which includes three temperature zones, the temperatures of the three temperature zones are all 950-1100°C, the boat loading is 2.8 kg / boat-3.5 kg / boat, the cycle time is 45 min / boat-60 min / boat, and the hydrogen flow rate is 8 m 3 / h~15m 3 / h, the dew point of hydrogen is -65℃~-75℃.

[0033] 3) Mixing the ultra-coarse tungsten particles and carbon to obtain a carbon-blended mixture.

[0034] In a specific embodiment, the materials are mixed using a double cone carbon mixing machine, the mass of carbon added accounts for 6.0% to 6.3% of the total mass of the carbon mixed material, and the mixing time is 5 hours to 7.5 hours.

[0035] 4) Carbide the carbon mixture at high temperature to obtain tungsten carbide particles.

[0036] In a specific embodiment, a fully automated high temperature carbon tube furnace is used for high temperature carbonization. The temperature of high temperature carbonization is 2100°C to 2300°C, the boat loading is 20Kg / boat to 26Kg / boat, the cycle time is 60min / boat to 80min / boat, and the hydrogen flow rate is 0.1m 3 / h~0.3m 3 / h.

[0037] 5) The tungsten carbide particles are crushed and sieved to obtain ultra-coarse tungsten carbide, and the average particle size of the ultra-coarse tungsten carbide is 30 μm to 60 μm.

[0038] In a specific embodiment, the crushing is first performed using a ball mill for pre-crushing, and then a fluidized bed air flow crushing is used. The ball-to-material ratio of the ball mill pre-crushing is 1:1, and the time is 5min to 10min; the crushing medium of the fluidized bed air flow crushing is high-purity and high-pressure N2, and the purity is greater than 99.95%. The classifying wheel speed of the fluidized bed air flow crushing is 500 to 1500 rpm, and the pressure is 0.3 to 0.6Mpa.

[0039] A vibrating screen is used to remove coarse particles, and the screening time is 2.5h / ton.

[0040] The invention also discloses an ultra-coarse tungsten carbide which is prepared by the preparation method.

[0041] The following are specific embodiments.

[0042] Example 1

[0043] The raw material is coarse blue tungsten (average particle size 30 μm) without alkaline earth metal doping and water content 4%. A fully automatic 15-tube reduction furnace is used. The three reduction temperature zones are all 1100°C. The boat loading is 3.2 kg / boat and the cycle time is 50 min / boat. The hydrogen flow rate is 13 m 3 / h, hydrogen dew point -70℃; double cone carbon mixing machine is used to mix carbon, the total amount of carbon is 6.2% of the total mass ratio, and the total carbon mixing time is 6.5h; fully automated high temperature carbon tube furnace is used for carbonization treatment, the carbonization temperature is 2200℃, the boat load is 24kg / boat, the cycle time is 75min / boat, and the hydrogen flow rate is 0.2m 3 / h; fluidized bed air flow crushing equipment is used for crushing, and the crushing medium is high-purity and high-pressure N2 with a purity greater than 99.95%. The speed of the grading wheel of the fluidized bed air flow crushing is adjusted to 1500 rpm and the pressure is 0.6Mpa; a vibrating screen is used to remove coarse particles, and the screening time is 2.5h / ton to obtain ultra-coarse tungsten carbide.

[0044] Example 2

[0045] The raw material is coarse blue tungsten (average particle size 30 μm) without alkaline earth metal doping and 3% water content. A fully automatic 15-tube reduction furnace is used. The three reduction temperature zones are all 1100°C. The boat loading is 3.2 kg / boat and the cycle time is 50 min / boat. The hydrogen flow rate is 13 m 3 / h, hydrogen dew point -70℃; double cone carbon mixing machine is used to mix carbon, the total amount of carbon is 6.2% of the total mass ratio, and the total carbon mixing time is 6.5h; fully automated high temperature carbon tube furnace is used for carbonization treatment, the carbonization temperature is 2200℃, the boat load is 24kg / boat, the cycle time is 75min / boat, and the hydrogen flow rate is 0.2m3 / h; fluidized bed air flow crushing equipment is used for crushing, and the crushing medium is high-purity and high-pressure N2 with a purity greater than 99.95%. The speed of the grading wheel of the fluidized bed air flow crushing is adjusted to 1500 rpm and the pressure is 0.6Mpa; a vibrating screen is used to remove coarse particles, and the screening time is 2.5h / ton to obtain ultra-coarse tungsten carbide.

[0046] Example 3

[0047] The raw material is coarse blue tungsten (average particle size 30 μm) without alkaline earth metal doping and with a water content of 5%. A fully automatic 15-tube reduction furnace is used. The three reduction temperature zones are all 1100°C. The boat loading is 3.2 kg / boat and the cycle time is 50 min / boat. The hydrogen flow rate is 13 m 3 / h, hydrogen dew point -70℃; double cone carbon mixing machine is used to mix carbon, the total amount of carbon is 6.2% of the total mass ratio, and the total carbon mixing time is 6.5h; fully automated high temperature carbon tube furnace is used for carbonization treatment, the carbonization temperature is 2200℃, the boat load is 24kg / boat, the cycle time is 75min / boat, and the hydrogen flow rate is 0.2m 3 / h; fluidized bed air flow crushing equipment is used for crushing, and the crushing medium is high-purity and high-pressure N2 with a purity greater than 99.95%. The speed of the grading wheel of the fluidized bed air flow crushing is adjusted to 1500 rpm and the pressure is 0.6Mpa; a vibrating screen is used to remove coarse particles, and the screening time is 2.5h / ton to obtain ultra-coarse tungsten carbide.

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 1 is that water-free coarse particles of blue tungsten are used as raw materials, and the rest are the same.

[0050] Test Case

[0051] The particle size distribution of the ultra-coarse tungsten carbide obtained in Examples 1 to 3 and Comparative Example 1 was analyzed by a laser particle size analyzer, and D10, D50 and D90 were calculated respectively, and then (D90-D10) / D50 was calculated to determine the particle size distribution width, thereby determining the uniformity of the particle size. The results are shown in Table 1.

[0052] The free carbon content, oxygen content and impurity content in the prepared tungsten carbide were tested to determine the quality of the tungsten carbide product. The results are shown in Table 1.

[0053] Table 1: Indices of tungsten carbide products obtained in Example 1 and Comparative Example 1

[0054] Example 1 Example 2 Example 3 Comparative Example 1 D50 / μm 45 40 50 15 D10 / μm 42 38 48 10 D90 / μm 48 43 53 22 (D90-D10) / D50 0.133 0.125 0.1 0.8 Average particle size / μm 45 40 50 15 Free carbon / wt% 0.04 0.05 0.02 0.06 Oxygen content / wt% 0.08 0.06 0.12 0.04 Impurity content / wt% 0.4 0.35 0.48 0.3

[0055] From Table 1, we can see that: 1) the tungsten carbide particles prepared by the present invention can be significantly larger than those in Comparative Example 1, and the particle size distribution is more uniform; 2) the oxygen content of the tungsten carbide prepared by the present invention is slightly higher than that in Comparative Example 1, which should be caused by the introduction of water, but the present invention can control the impurity content to be low, which is not much different from Comparative Example 1 without adding a particle size increase agent. In summary, the ultra-coarse tungsten carbide particles prepared by the present invention have a more uniform particle size distribution and a low impurity content.

[0056] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing ultra-coarse tungsten carbide, characterized in that: The process includes: Providing ultra-coarse tungsten oxide particles with a water content of 3wt% to 5wt%, wherein the average particle size of the ultra-coarse tungsten oxide particles is 28μm to 45μm; The ultra-coarse tungsten oxide particles are loaded into a boat and placed in a closed reduction furnace, and hydrogen is introduced to perform a reduction reaction to obtain ultra-coarse tungsten particles; wherein the temperature of the reduction reaction is 950°C to 1100°C, the loading amount is 2.8Kg / boat to 3.5Kg / boat, the cycle time is 45min / boat to 60min / boat, and the hydrogen flow rate is 8m 3 / h~15m 3 / h, hydrogen dew point is -65℃~-75℃; Mixing the ultra-coarse tungsten particles and carbon to obtain a carbon-blended mixture; Carburizing the carbon mixture at high temperature to obtain tungsten carbide particles; The tungsten carbide particles are crushed and sieved to obtain the ultra-coarse tungsten carbide, and the average particle size of the ultra-coarse tungsten carbide is 30 μm to 60 μm.

2. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The ultra-coarse tungsten oxide particles include one or both of ultra-coarse blue tungsten particles and ultra-coarse yellow tungsten particles.

3. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The average particle size of the ultra-coarse tungsten particles is 30 μm to 60 μm.

4. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The reduction furnace is a fully automatic 15-tube reduction furnace, which includes three temperature zones, and the temperatures of the three temperature zones are all between 950°C and 1100°C.

5. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The material is mixed using a double cone carbon mixing machine, the added mass of the carbon accounts for 6.0% to 6.3% of the total mass of the carbon mixed material, and the mixing time is 5h to 7.5h.

6. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The temperature of the high temperature carbonization is 1900°C to 2300°C.

7. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The loading amount of the high temperature carbonization boat is 20 kg / boat to 26 kg / boat, the cycle time is 60 min / boat to 80 min / boat, and the hydrogen flow rate is 0.1 m 3 / h~0.3m 3 / h.

8. The method for preparing ultra-coarse tungsten carbide according to claim 1, characterized in that: The crushing is firstly performed by using a ball mill for pre-crushing, and then a fluidized bed type air flow crushing is adopted.

9. The method for preparing ultra-coarse tungsten carbide according to claim 8, characterized in that: The ball-to-material ratio of the ball mill pre-crushing is 1:1, and the time is 5min-10min; the classifying wheel speed of the fluidized bed air flow crushing is 500-1500 rpm, and the pressure is 0.3-0.6Mpa.

10. An ultra-coarse tungsten carbide, characterized in that: The method is prepared according to any one of claims 1 to 9.