A controllable grinding and grading process and system for calcium sulfate whiskers with aspect ratio control

Abstract

This invention provides a grinding and grading process and system for controllable aspect ratio of calcium sulfate whiskers, comprising a feeder, a grinder, a classifier, a dust collector, and an induced draft fan connected in sequence. The grinder includes a grinding chamber, a grinding disc assembly, and a grinding disc drive device. The grinding disc assembly includes a rotating grinding disc, several sets of inclined grinding teeth, and a drive connector. The inclined grinding teeth are inclined relative to the generatrix of the outer wall of the rotating grinding disc. The grinder grinds calcium sulfate fiber gypsum into fibrous calcium sulfate whiskers through the inclined grinding teeth of the rotating grinding disc. The classifier separates the fibrous calcium sulfate whiskers into different grades according to particle size, and collects the calcium sulfate whiskers of the same grade to obtain calcium sulfate whiskers with controllable aspect ratio and uniform distribution. The dust collector collects and treats the dust generated during the sieving process of the classifier. The induced draft fan discharges the purified air. The calcium sulfate whiskers processed by the device and process of this invention have a controllable and uniform aspect ratio, significantly improved strength, are less prone to pulverization, and are less prone to reabsorbing water.

Description

Technical Field

[0001] This invention belongs to the field of calcium sulfate whisker preparation technology, and specifically relates to a milling and grading process and system for controlling the aspect ratio of calcium sulfate whiskers. Background Technology

[0002] Currently, the main method for industrializing the production of calcium sulfate whiskers in China is to use natural gypsum as raw material. A hydrothermal method is first used to prepare hemihydrate fibrous gypsum, which is then processed into hemihydrate calcium sulfate whiskers using equipment such as vertical mills and air mills. After drying, the hemihydrate calcium sulfate whiskers become anhydrous calcium sulfate whiskers. However, whiskers produced by this process suffer from problems such as easy pulverization, high water reabsorption rate, and a wide range of aspect ratios with inconsistent thickness. Furthermore, existing preparation processes typically involve sieving calcium sulfate whiskers by volume, making it difficult to collect whiskers with the same aspect ratio. Summary of the Invention

[0003] Therefore, the present invention aims to provide a milling and grading process and system for controllable aspect ratio of calcium sulfate whiskers, in order to solve at least one of the technical problems in the background art.

[0004] This invention is implemented as follows:

[0005] The first aspect of the present invention provides a grinding and grading system for controllable aspect ratio of calcium sulfate whiskers, comprising a feeder, a grinder and a classifier connected in sequence, wherein the inlet of the grinder is connected to the feeder and the outlet is connected to the classifier, and the feeder includes a gypsum feeder and a grinding aid feeder for conveying fibrous calcium sulfate fiber gypsum and grinding aid to the grinder respectively.

[0006] The grinder includes a grinding chamber, a grinding disc assembly built into the grinding chamber and erected vertically, and a grinding disc drive device for driving the grinding disc assembly to rotate. The grinding disc assembly includes a rotating grinding disc, several sets of oblique grinding teeth evenly distributed on the outer wall of the rotating grinding disc, and a drive connector located on the upper end of the rotating grinding disc and connected to the grinding disc drive device. There is a gap between the outer edge of the rotating grinding disc and the inner wall of the grinding chamber. The rotating grinding disc has a cylindrical structure, and the oblique grinding teeth are inclined relative to the generatrix of the outer wall of the rotating grinding disc. The grinder drives the oblique grinding teeth to grind calcium sulfate fiber gypsum into fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution by rotating the grinding disc.

[0007] The classifier is an air-separated sieve, which is used to separate fibrous calcium sulfate whiskers into different grades according to their weight and size, and collect the calcium sulfate whiskers of the same grade to obtain calcium sulfate whiskers with controllable aspect ratio and uniform distribution.

[0008] Furthermore, the air-classifying screening machine includes an annular air duct, a feed hopper connected to the top of the annular air duct, an air inlet pipe and an air outlet pipe connected to the side wall of the annular air duct, and several sets of discharge hoppers arranged at the bottom of the annular air duct and extending downward.

[0009] The discharge hopper is distributed around the annular air duct, the air inlet pipe is sealed and connected to the external blower, and the feed hopper is located in the area where the air inlet pipe meets the annular air duct, and the air inlet pipe is tangent to the annular air duct.

[0010] The annular air duct is also provided with a baffle to prevent airflow circulation, and the baffle is located in the area between the air inlet pipe and the air outlet pipe.

[0011] Furthermore, it also includes a dust collector, which is connected to the classifier and is used to collect and process the dust generated during the screening process of the classifier; an induced draft fan is installed at the end of the dust collector to discharge the purified air.

[0012] Furthermore, a grinding drying chamber is provided at the end of the mill, which is connected to the grinding chamber. The grinding drying chamber is equipped with a drying system. After the fibrous calcium sulfate whiskers are dried in the grinding drying chamber, they enter the subsequent classifier. The function of the drying system is to dry the free water and crystal water of the calcium sulfate fiber gypsum, which is more conducive to the subsequent classification efficiency and avoids the material from clogging the screen surface due to moisture during screening and classification.

[0013] Furthermore, a cooling jacket is installed on the side wall of the grinding and drying chamber. The cooling jacket is either a water-cooled jacket or an air-cooled jacket, which is used to control the temperature and cool the grinding and drying chamber.

[0014] Furthermore, the inlet of the mill is connected to the feed pipe; the feed pipe is a tee pipe, including a straight section and a side branch section; one end of the straight section is the feed port of calcium sulfate fiber gypsum and is connected to the gypsum feeder, and the other end is the discharge port and is connected to the mill; one end of the side branch section is the feed port of grinding aid and is connected to the grinding aid feeder, and the other end is the discharge port and is connected to the side wall of the straight section.

[0015] Furthermore, a guide component is provided on the upper part of the rotating grinding disc, and the surface of the guide component has an arc-shaped structure; the rack of the oblique grinding teeth has a triangular pyramidal structure.

[0016] Furthermore, a vibrating material shaking system is provided on the outer wall of the grinding chamber. The vibrating material shaking system is located at the end of the grinding chamber. The vibrating material shaking system includes an elastic retaining ring sleeved on the outer wall of the grinding chamber and a vibrating motor connected to the elastic retaining ring, which can prevent the material from sticking or clogging after grinding.

[0017] Furthermore, the gypsum feeder has a built-in agitator to initially break up the calcium sulfate fiber gypsum to prevent it from absorbing water and clumping.

[0018] Furthermore, material control valves and material flow meters are installed at the outlet ends of both the gypsum feeder and the grinding aid feeder.

[0019] The second aspect of this invention provides a milling and grading process for controllable aspect ratio of calcium sulfate whiskers. The process utilizes the aforementioned system for milling and grading calcium sulfate whiskers with controllable aspect ratio, and specifically includes the following steps:

[0020] The fibrous calcium sulfate fiber gypsum is conveyed to the gypsum feeder, where the blocky calcium sulfate fiber gypsum is broken up by the action of the agitator.

[0021] The crushed calcium sulfate fiber gypsum and the grinding aid conveyed by the grinding aid feeder are mixed and fed into the mill.

[0022] Under the action of the rotating grinding disc and the oblique grinding teeth in the grinder, and with the help of the grinding aid, the calcium sulfate fiber gypsum is dispersed and ground, separating the fibers in the calcium sulfate fiber gypsum to form fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution range.

[0023] The calcium sulfate whiskers are then fed into a classifier. Utilizing the weight difference of calcium sulfate whiskers with different aspect ratios, the whiskers are separated into different grades according to their aspect ratios by an air-classifying sieve. The whiskers of the same grade are then collected to obtain calcium sulfate whiskers with controllable aspect ratios and uniform distribution.

[0024] Furthermore, it also includes a dust removal process, where the dust generated in the classifier is collected and treated by a dust collector, and then the purified air is discharged under the action of an induced draft fan.

[0025] Furthermore, the grinding aid is one or more mixtures of silicone powder, silicon dioxide, and nano-activated calcium carbonate.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The system of the present invention disperses and grinds the calcium sulfate fiber gypsum, and after passing it through an air classifier, obtains hemihydrate calcium sulfate whiskers with a uniform and controllable aspect ratio.

[0028] 2. The controllable aspect ratio grinding and grading device for calcium sulfate whiskers of the present invention grinds calcium sulfate fiber gypsum into hemihydrate calcium sulfate whiskers with higher strength, more uniform and controllable aspect ratio, and less pulverization by installing a grinding aid feeder on the grinder and combining it with a specific grinder disc design.

[0029] 3. The grinding mill of the present invention increases its crushing force on calcium sulfate fiber gypsum through the rotating grinding disc structure with external inclined grinding teeth. At the same time, it avoids damaging the fiber structure of calcium sulfate fiber gypsum when grinding it, thus preventing the final product from being pulverized. In addition, the inclined grinding teeth are not vertical. When calcium sulfate fiber gypsum enters the grinding mill, the inclined grinding teeth can drive the material to flow with the rotation during grinding, further preventing it from being ground into powder.

[0030] 4. This invention uses an air-separated sieve, which can separate calcium sulfate whiskers according to weight, and then collect calcium sulfate whiskers of different aspect ratios separately, so as to achieve controllable aspect ratio of the final calcium sulfate whisker product.

[0031] 5. The controllable calcium sulfate whisker aspect ratio grinding and grading device of the present invention collects all the required calcium sulfate whiskers and fine dust through an effective through-flow material flow method, with no dust or odor generated throughout the process. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a milling and grading system for controllable aspect ratio of calcium sulfate whiskers in an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of the gypsum feeder in an embodiment of the present invention.

[0034] Figure 3 This is a cross-sectional view of the mill in an embodiment of the present invention.

[0035] Figure 4 This is a cross-sectional top view of the mill in an embodiment of the present invention.

[0036] Figure 5 This is a three-dimensional structural diagram of the oblique grinding teeth in an embodiment of the present invention.

[0037] Figure 6 This is a top view of the air-separated screening machine in an embodiment of the present invention.

[0038] Figure 7 This is a schematic diagram of the raw material calcium sulfate fiber gypsum in an embodiment of the present invention.

[0039] Figure 8 This is a SEM image of calcium sulfate whiskers obtained after grinding and grading in Example 2 of the present invention.

[0040] Illustration: 1-Gypsum feeder, 101-Agitator, 102-Material flow meter, 103-Material control valve; 2-Grinding mill, 201-Grinding chamber, 202-Guide component, 203-Rotating grinding disc, 204-Inclined grinding teeth, 205-Drive connector; 3-Classifier, 301-Air inlet pipe, 302-Feed hopper, 303-Annular air duct, 304-Discharge hopper, 305-Air outlet pipe, 306-Baffle plate; 4-Dust collector; 5-Exhaust fan; 6-Grinding aid feeder; 7-Feed pipe; 8-Vibration motor; 9-Elastic retaining ring; 10-Cooling jacket; 11-Grinding drying chamber, 12-Blower. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] Example 1

[0043] like Figures 1 to 6 The diagram illustrates a controllable aspect ratio grinding and grading system for calcium sulfate whiskers, comprising a feeder, a grinder 2, and a classifier 3 connected in sequence. The inlet of the grinder 2 is connected to the feeder, and the outlet is connected to the classifier 3. The feeder includes a gypsum feeder 1 and a grinding aid feeder 6. The gypsum feeder 1 conveys fibrous calcium sulfate fiber gypsum into the grinder 2, and the grinding aid feeder 6 conveys grinding aid into the grinder 2.

[0044] A feed pipe 7 with a three-way pipe structure is installed at the inlet of the mill 2. The feed pipe 7 includes a straight pipe section and a side branch pipe section. One end of the straight pipe section is the feed port of calcium sulfate fiber gypsum and is connected to the gypsum feeder 1, and the other end is the discharge port and is connected to the mill 2. One end of the side branch pipe section is the feed port of grinding aid and is connected to the grinding aid feeder 6, and the other end is the discharge port and is connected to the side wall of the straight pipe section.

[0045] like Figure 2 As shown, the gypsum feeder 1 has a built-in agitator 101. Since calcium sulfate fiber gypsum has a certain water absorption and is prone to clumping, an agitator is set in the gypsum feeder 1 that stores calcium sulfate fiber gypsum to initially break up the calcium sulfate fiber gypsum to avoid blockage during transportation and to facilitate subsequent combination with grinding aids. The agitator 101 can be a conventional mechanical agitator, which uses agitation force and shear force to break up the blocky calcium sulfate fiber gypsum and keep it in powder form.

[0046] Both the gypsum feeder 1 and the grinding aid feeder 6 are equipped with a material control valve 103 and a material flow meter 102 at their outlets. The material control valve 103 is used to adjust the size of the outlets of the gypsum feeder 1 and the grinding aid feeder 6, thereby controlling the feeding speed of calcium sulfate fiber gypsum and the grinding aid. The material flow meter 102 is used to monitor the flow rate of the gypsum feeder 1 and the grinding aid feeder 6 in real time, facilitating the monitoring of the feeding flow rate of calcium sulfate fiber gypsum and the grinding aid.

[0047] like Figures 3 to 5 As shown, the mill 2 includes a milling chamber 201, a milling disc assembly built into the milling chamber 201 and erected vertically, and a milling disc drive device. The milling disc drive device (including a rotary motor, etc.) drives the milling disc assembly to rotate. The milling disc assembly includes a rotating milling disc 203, several sets of oblique grinding teeth 204 evenly distributed on the outer wall of the rotating milling disc 203, and a drive connector 205 located at the upper end of the rotating milling disc 203 and connected to the milling disc drive device. The drive connector 205 is used to transmit the rotational force of the milling disc drive device to the rotating milling disc 203. There is a gap between the outer edge of the rotating milling disc 203 and the inner wall of the milling chamber 201. The rotating milling disc 203 has a cylindrical structure. The oblique grinding teeth 204 are inclined relative to the generatrix of the outer wall of the rotating milling disc 203, that is, the rack of the oblique grinding teeth 204 is not parallel to the axis of the oblique grinding teeth 204. The mill 2, through its rotating grinding disc 203 with externally mounted oblique grinding teeth 204, increases its crushing force on calcium sulfate fiber gypsum, while avoiding damage to its fiber structure during grinding, thus preventing the final product from becoming pulverized. After processing by the mill 2, fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution range can be obtained, thereby generating whiskers with different aspect ratios.

[0048] Meanwhile, the inclined grinding teeth 204 are non-vertical. When calcium sulfate fiber gypsum enters the mill 2, the inclined grinding teeth 204 can drive the material to flow with the rotation during grinding, further preventing it from being ground into powder. The rack of the inclined grinding teeth 204 has a triangular pyramidal structure, which is beneficial to improving the efficiency and force of crushing gypsum.

[0049] A guide 202 is provided on the upper part of the rotating grinding disc 203. The surface of the guide 202 is an arc-shaped structure, which facilitates the material to slide into the gap between the inclined grinding teeth 204 and the inner wall of the grinding chamber 201.

[0050] In some preferred embodiments, the mill 2 is equipped with a preliminary screening component (not marked in the figure) to facilitate the discharge of qualified whiskers after milling into subsequent units. The preliminary screening component adopts existing technology, such as a rotating drum installed below the milling chamber 201, the outer wall of which is composed of vertical strips arranged with certain gaps. The milled whiskers fall into the inside of the rotating drum, and with the rotation of the drum and the accompanying suction device, the whiskers pass through the gaps between the vertical strips and are discharged into subsequent units. The preliminary screening component and the suction device adopt conventional settings, and their structure, composition, and connection all adopt existing technology, which will not be described in detail here.

[0051] To facilitate the rapid entry of calcium sulfate fibers after grinding into subsequent units, a vibratory material shaking system is installed on the outer wall of the grinding chamber 201. The vibratory material shaking system is located at the end of the grinding chamber 201 and includes an elastic retaining ring 9 that is sleeved on the outer wall of the grinding chamber 201 and a vibratory motor 8 connected to the elastic retaining ring 9. The vibratory material shaking system can be started intermittently. The vibratory motor 8 generates a vibratory force, which is transmitted to the grinding chamber 201 through the elastic retaining ring 9, thereby driving the material to be discharged from the grinding chamber 201 and avoiding blockage and adhesion.

[0052] In some preferred embodiments, the mill 2 can also be horizontally arranged, with the material conveying driven by an externally installed suction device. It can be a conventional arrangement, and its structure, composition and connection all adopt existing technology, which will not be described in detail here.

[0053] A grinding and drying chamber 11 is also provided at the end of the mill 2, which is connected to the milling chamber 201. The grinding and drying chamber 11 has a built-in drying system. The fibrous calcium sulfate whiskers after grinding are dried in the grinding and drying chamber 11 before entering the subsequent classifier 3. The drying system can use an electric heating device to directly heat the material, or it can introduce hot air into the grinding and drying chamber 11. The material is fully dried by contacting the hot air during grinding and flow to achieve the required removal of moisture. The function of the drying system is to dry the free water and crystal water of calcium sulfate fiber gypsum, which is more conducive to the subsequent classification efficiency and avoids the material clogging the screen surface due to moisture during screening and classification. In addition, exhaust vents can be provided on the side wall of the grinding and drying chamber 11 to facilitate the discharge of water vapor generated during drying. A cooling jacket 10 is provided on the side wall of the grinding and drying chamber 11. The cooling jacket 10 can be a water-cooled jacket or an air-cooled jacket for temperature control and cooling of the grinding and drying chamber 11.

[0054] Because the whiskers obtained after grinding mill 2 have a narrow and uniform diameter distribution and a wide length distribution range, whiskers with different aspect ratios have different weights. Classifier 3 uses an air-separated sieve. The air-separated sieve is blown in by an external blower 12 to form an airflow. Under a certain wind speed, whiskers of different specific gravities in the fibrous calcium sulfate whiskers will fall sequentially into the corresponding discharge hoppers according to their specific gravity, following the direction from the inlet to the outlet, thus achieving the sieving of calcium sulfate whiskers of different weights and, consequently, the grading of calcium sulfate whiskers with different aspect ratios. Figure 1 and Figure 6 As shown, the air-separated screening machine includes an annular air duct 303, a feed hopper 302 connected to the top of the annular air duct 303, an air inlet pipe 301 and an air outlet pipe 305 connected to the side wall of the annular air duct 303, and several sets of downwardly extending discharge hoppers 304 arranged at the bottom of the annular air duct 303, the discharge hoppers 304 being distributed circumferentially along the annular air duct 303; the air inlet pipe 301 is sealed and connected to an external blower 12, and the feed hopper 302 is located near the area where the air inlet pipe 301 connects to the annular air duct 303, with the air inlet pipe 301 tangent to the annular air duct 303. A baffle 306 is also provided on the annular air duct 303 to prevent airflow circulation, the baffle 306 being located in the area between the air inlet pipe 301 and the air outlet pipe 305. The specific working process is as follows: the whiskers processed by the mill 2 or the grinding and drying chamber 11 enter the annular air duct 303 through the feed hopper 302. At the same time, the blower 12 introduces air at a certain speed into the annular air duct 303. Under the action of the airflow, the fibrous calcium sulfate whiskers move along the direction of the annular air duct 303. Under the action of the whiskers' own gravity and the friction with the inner wall of the annular air duct 303, the whiskers fall into the corresponding discharge hoppers 304 in sequence and are discharged. Since the whiskers with different aspect ratios have different weights, the whiskers of different weights move different distances under the same wind force. The heavier whiskers fall first, while the lighter whiskers fall later as the airflow takes longer. Thus, the whiskers of different weights fall into different discharge hoppers 304, and the fibrous calcium sulfate whiskers are divided into different grades according to particle size. Subsequently, the calcium sulfate whiskers of the same grade are collected to obtain calcium sulfate whiskers with controllable aspect ratio and uniform distribution.

[0055] In some preferred embodiments, a dust collector 4 is also included, which is connected to the classifier 3 and is used to collect and process the fine dust generated during the sieving process of the classifier 3. Specifically, the dust collector 4 is connected to the outlet duct 305 of the classifier 3. The dust collector 4 can be any dust removal equipment, such as a small bag filter. A dust suction hood is designed at the outlet duct 305 of the classifier 3 to collect dust at the source. The collected dust is drawn into the dust collector body through the pipe by the fan, and then filtered and accumulated by the filter bags to achieve dust removal. An induced draft fan 5 is installed at the end of the dust collector 4, which discharges the purified air from the dust collector 4.

[0056] Example 2

[0057] A milling and grading process for controllable aspect ratio of calcium sulfate whiskers includes the following steps:

[0058] Will as Figure 7 The fibrous hemihydrate calcium sulfate fiber gypsum shown is conveyed to the gypsum feeder 1, and the blocky calcium sulfate fiber gypsum is broken up under the action of the agitator 101.

[0059] Open the material control valve 103 of the gypsum feeder 1 and the grinding aid feeder 6, mix the dispersed calcium sulfate fiber gypsum and the grinding aid conveyed by the grinding aid feeder 6 in the feed pipe 7 and feed them into the mill 2. The grinding aid is silicone powder, which has the characteristics of high temperature resistance and lubrication. It forms a coating on the surface of the whiskers, plays a role in particle dispersion, enhances stability and strength, and can also reduce the water return rate of the whiskers.

[0060] The mixture of gypsum and grinding aid is conveyed to the grinding chamber 201 and falls into the gap between the outer wall of the rotating grinding disc 203 and the grinding chamber 201. Under the action of the rotating grinding disc 203 and the inclined grinding teeth 204 in the grinder 2, the calcium sulfate fiber gypsum is dispersed and ground with the help of the grinding aid. The fibers in the calcium sulfate fiber gypsum are separated to form calcium sulfate whisker powder without destroying the fiber structure of the whiskers. Then, the powder is dried and cooled in the grinding and drying chamber 11 to form fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution.

[0061] The calcium sulfate whiskers are then fed into classifier 3. Utilizing the weight difference in aspect ratio, whiskers of different weights / aspect ratios are separated and collected using an air-classifying sieve. In this embodiment, the calcium sulfate whiskers are divided into five levels according to aspect ratio: below 20, 20–40, 40–60, 60–80, and above 80. Whiskers of the same level are then collected to obtain calcium sulfate whiskers with controllable and uniform aspect ratio distribution. SEM images of whiskers from the below 20 and 60–80 aspect ratio levels, magnified 400 times, are shown below. Figure 8 As shown in (a) and (b);

[0062] The dust collector 4 draws out the fine dust generated in the classifier 3 through the fan, and then enters the dust collector 4 through the pipeline for collection and sedimentation treatment. Finally, the purified air is discharged under the action of the induced draft fan 5.

[0063] Example 3

[0064] A milling and grading process for controllable aspect ratio of calcium sulfate whiskers includes the following steps:

[0065] The fibrous calcium sulfate fiber gypsum is conveyed to the gypsum feeder 1, and the blocky calcium sulfate fiber gypsum is broken up under the action of the agitator 101.

[0066] Open the material control valve 103 of the gypsum feeder 1 and the grinding aid feeder 6, mix the dispersed calcium sulfate fiber gypsum and the grinding aid conveyed by the grinding aid feeder 6 in the feed pipe 7 and feed them into the mill 2. The grinding aid is silicon dioxide, which can enhance the strength and dispersion of whiskers during the grinding process.

[0067] The mixture of gypsum and grinding aid is conveyed to the grinding chamber 201 and falls into the gap between the outer wall of the rotating grinding disc 203 and the grinding chamber 201. Under the action of the rotating grinding disc 203 and the inclined grinding teeth 204 in the grinder 2, the calcium sulfate fiber gypsum is dispersed and ground with the help of the grinding aid. The fibers in the calcium sulfate fiber gypsum are separated to form calcium sulfate whisker powder without destroying the fiber structure of the whiskers. Then, the powder is dried and cooled in the grinding and drying chamber 11 to form fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution.

[0068] Then, the calcium sulfate whiskers are conveyed to classifier 3. Utilizing the weight difference of calcium sulfate whiskers with different aspect ratios, the whiskers with different weights / aspect ratios are separated and collected by an air-classifying sieve. In this embodiment, the calcium sulfate whiskers are divided into five levels according to their aspect ratio: below 20, 20-40, 40-60, 60-80, and above 80. Then, the calcium sulfate whiskers of the same level are collected to obtain calcium sulfate whiskers with controllable aspect ratio and uniform distribution.

[0069] The dust collector 4 draws out the fine dust generated in the classifier 3 through the fan, and then enters the dust collector 4 through the pipeline for collection and sedimentation treatment. Finally, the purified air is discharged under the action of the induced draft fan 5.

[0070] Example 4

[0071] A milling and grading process for controllable aspect ratio of calcium sulfate whiskers includes the following steps:

[0072] The fibrous calcium sulfate fiber gypsum is conveyed to the gypsum feeder 1, and the blocky calcium sulfate fiber gypsum is broken up under the action of the agitator 101.

[0073] Open the material control valve 103 of the gypsum feeder 1 and the grinding aid feeder 6, mix the dispersed calcium sulfate fiber gypsum and the grinding aid conveyed by the grinding aid feeder 6 in the feed pipe 7 and feed them into the mill 2. The grinding aid is nano-activated calcium carbonate.

[0074] The nano-active modified calcium carbonate grinding aid can be quickly and effectively adsorbed on the defective surface of calcium sulfate fiber gypsum, forming a stable interface, reducing the defect concentration on the whisker surface, and improving the grain size distribution of the whiskers. At the same time, due to the oleophilic and hydrophobic surface of the active nano calcium carbonate, it can effectively improve or regulate the rigidity and toughness of the whiskers, thereby improving their strength.

[0075] The mixture of gypsum and grinding aid is conveyed to the grinding chamber 201 and falls into the gap between the outer wall of the rotating grinding disc 203 and the grinding chamber 201. Under the action of the rotating grinding disc 203 and the inclined grinding teeth 204 in the grinder 2, the calcium sulfate fiber gypsum is dispersed and ground with the help of the grinding aid. The fibers in the calcium sulfate fiber gypsum are separated to form calcium sulfate whisker powder without destroying the fiber structure of the whiskers. Then, the powder is dried and cooled in the grinding and drying chamber 11 to form fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution.

[0076] Then, the calcium sulfate whiskers are conveyed to classifier 3. Utilizing the weight difference of calcium sulfate whiskers with different aspect ratios, the whiskers with different weights / aspect ratios are separated and collected by an air-classifying sieve. In this embodiment, the calcium sulfate whiskers are divided into five levels according to their aspect ratio: below 20, 20-40, 40-60, 60-80, and above 80. Then, the calcium sulfate whiskers of the same level are collected to obtain calcium sulfate whiskers with controllable aspect ratio and uniform distribution.

[0077] The dust collector 4 draws out the fine dust generated in the classifier 3 through the fan, and then enters the dust collector 4 through the pipeline for collection and sedimentation treatment. Finally, the purified air is discharged under the action of the induced draft fan 5.

[0078] Comparative Example 1

[0079] No grinding aids were added; all other process steps were the same as in Example 2.

[0080] Comparative Example 2

[0081] The grinding disc of the mill 2 is set to a conventional structure, and the other process steps are the same as those in Example 2.

[0082] Comparative Example 3

[0083] Remove the classifier 3, and the rest of the process steps are the same as in Example 2.

[0084] Comparative Example 4

[0085] The classifier 3 uses a vibrating screen to classify calcium sulfate whiskers into five levels according to the different mesh sizes: 6000-8000 mesh, 8000-10000 mesh, 10000-12000 mesh, 12000-14000 mesh, and above 14000 mesh. The other process steps are the same as in Example 2.

[0086] The products prepared in Comparative Examples 1 to 3 were compared and analyzed with those in Example 2. The morphology (microscopic images) of the products prepared in the examples and comparative examples were observed using high-resolution transmission electron microscopy according to GB / Z 21738-2008. The Mohs hardness was determined according to GB / T230.2-2002. The water solubility was determined according to HG / T 4365-2012. The length, diameter and aspect ratio were determined according to GB / Z 21738-2008.

[0087] The calcium sulfate whiskers prepared in Example 2 were determined to be uniformly dispersed needle-like fibers with a Mohs strength of 3.8, water solubility (3°C) of 0.95 g / L, diameter distribution of 1–2 μm, length distribution of 18–100 μm, and aspect ratio of 35–150. Based on length, the calcium sulfate whiskers were classified into three grades: 400-600 mesh, 600-800 mesh, and above 800 mesh. The calcium sulfate whiskers prepared in Comparative Example 1 were mainly unevenly distributed needle-like fibers with a Mohs strength of 2.6, water solubility (3°C) of 1.73 g / L, diameter distribution of 1–3 μm, length distribution of 60–500 μm, and aspect ratio of 60–300. The calcium sulfate whiskers prepared in Comparative Example 2 were a mixture of powder and fibers, with a Mohs strength of 1.9 and a water solubility (3℃) of 2.35 g / L. Their diameter ranged from 0.5 to 1 μm, and their length from 10 to 20 μm. The calcium sulfate whiskers prepared in Comparative Example 3 were uniformly dispersed needle-like fibers, with a Mohs strength of 3.8 and a water solubility (3℃) of 0.95 g / L. However, the final product contained whiskers with a wide range of aspect ratios. Although Comparative Example 4 classifies calcium sulfate whiskers into five levels: 6000-8000 mesh, 8000-10000 mesh, 10000-12000 mesh, 12000-14000 mesh, and above 14000 mesh, since the diameter of the whiskers is distributed between 1 and 2 μm, whiskers of different lengths and aspect ratios can still be sieved into the same level. For example, whiskers of different lengths (100 μm and 30 μm respectively) but the same diameter (1.5 μm) can be collected at around 9000 mesh through a sieve. In contrast, the embodiments of the present invention can classify the above-mentioned whiskers of different lengths into two levels: 20-40 and above 80.

[0088] Compared with Comparative Examples 1 to 4, the calcium sulfate whiskers prepared in Example 2 have significantly improved strength, low water reabsorption rate, intact fibers, more uniform particle size distribution, and narrower aspect ratio distribution range. At the same time, the whiskers of different lengths can be collected separately, which is beneficial for subsequent packaging and separate use.

[0089] The product prepared in Comparative Example 1, without the addition of grinding aids, retained the fiber morphology but was unevenly dispersed, with a wider aspect ratio distribution, resulting in an uneven finished product. Furthermore, its water solubility increased and the water return rate improved, while the strength of the calcium sulfate whiskers also decreased.

[0090] The product prepared in Comparative Example 2 had some fibers broken or pulverized under conventional milling, losing the characteristics of whiskers and becoming ordinary calcium sulfate, which in turn reduced its strength and made it prone to water seepage.

[0091] The product prepared in Comparative Example 3 integrates calcium sulfate whiskers of different grades into one, with whiskers of varying thicknesses.

[0092] The product prepared in Comparative Example 4 was a mixture of calcium sulfate whiskers with different aspect ratios.

[0093] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A milling and grading process for controllable aspect ratio of calcium sulfate whiskers, characterized in that, The milling and grading system used in the process includes a feeder, a mill, and a classifier connected in sequence. The inlet of the mill is connected to the feeder, and the outlet is connected to the classifier. The feeder includes a gypsum feeder and a grinding aid feeder, used to convey fibrous calcium sulfate fiber gypsum and grinding aid into the mill, respectively. The grinder includes a grinding chamber, a grinding disc assembly built into the grinding chamber and erected vertically, and a grinding disc drive device for driving the grinding disc assembly to rotate. The grinding disc assembly includes a rotating grinding disc, several sets of oblique grinding teeth evenly distributed on the outer wall of the rotating grinding disc, and a drive connector located at the upper end of the rotating grinding disc and connected to the grinding disc drive device. There is a gap between the outer edge of the rotating grinding disc and the inner wall of the grinding chamber. The rotating grinding disc has a cylindrical structure, and the oblique grinding teeth are inclined relative to the generatrix of the outer wall of the rotating grinding disc. The grinder drives the oblique grinding teeth to grind calcium sulfate fiber gypsum into fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution by rotating the grinding disc. The racks of the oblique grinding teeth are not parallel to the axis of the oblique grinding teeth, the oblique grinding teeth are non-vertical, and the racks of the oblique grinding teeth have a triangular pyramidal structure. The classifier is an air-separated sieve, which is used to separate fibrous calcium sulfate whiskers into different grades according to their weight and size, and collect the calcium sulfate whiskers of the same grade to obtain calcium sulfate whiskers with controllable aspect ratio and uniform distribution. The process specifically includes the following steps: The fibrous calcium sulfate fiber gypsum is conveyed to the gypsum feeder, where the blocky calcium sulfate fiber gypsum is broken up by the action of the agitator. The crushed calcium sulfate fiber gypsum and the grinding aid conveyed by the grinding aid feeder are mixed and fed into the mill; the grinding aid is one or more of silicone powder, silicon dioxide, and nano-activated calcium carbonate. Under the action of the rotating grinding disc and the oblique grinding teeth in the grinder, and with the help of the grinding aid, the calcium sulfate fiber gypsum is dispersed and ground, separating the fibers in the calcium sulfate fiber gypsum to form fibrous calcium sulfate whiskers with a narrow and uniform diameter distribution and a wide length distribution range. The calcium sulfate whiskers are then fed into a classifier. Utilizing the weight difference of calcium sulfate whiskers with different aspect ratios, the whiskers are separated into different grades according to their aspect ratios by an air-classifying sieve. The whiskers of the same grade are then collected to obtain calcium sulfate whiskers with controllable aspect ratios and uniform distribution.

2. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, The air-classifying screening machine includes an annular air duct, a feed hopper connected to the top of the annular air duct, an air inlet pipe and an air outlet pipe connected to the side wall of the annular air duct, and several sets of discharge hoppers arranged at the bottom of the annular air duct and extending downward. The discharge hopper is distributed around the annular air duct, the air inlet pipe is sealed and connected to the external blower, and the feed hopper is located in the area where the air inlet pipe meets the annular air duct, and the air inlet pipe is tangent to the annular air duct. The annular air duct is also provided with a baffle to prevent airflow circulation, and the baffle is located in the area between the air inlet pipe and the air outlet pipe.

3. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, The mill is equipped with a vibratory material shaking system and a grinding and drying chamber; The grinding chamber is provided with a vibrating material shaking system on its outer wall. The vibrating material shaking system is located at the end of the grinding chamber. The vibrating material shaking system includes an elastic retaining ring sleeved on the outer wall of the grinding chamber and a vibrating motor connected to the elastic retaining ring. The mill is equipped with a grinding drying chamber at the end, which is connected to the milling chamber. The grinding drying chamber is equipped with a drying system. The fibrous calcium sulfate whiskers after grinding are dried in the grinding drying chamber and then enter the subsequent classifier. A cooling jacket is provided on the side wall of the grinding drying chamber. The cooling jacket is a water-cooled jacket or an air-cooled jacket.

4. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, The upper part of the rotating grinding disc is provided with a guide component, and the surface of the guide component has an arc-shaped structure.

5. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, The inlet of the mill is connected to the feed pipe; the feed pipe is a tee pipe, including a straight section and a side branch section; one end of the straight section is the feed port of calcium sulfate fiber gypsum and is connected to the gypsum feeder, and the other end is the discharge port and is connected to the mill; one end of the side branch section is the feed port of grinding aid and is connected to the grinding aid feeder, and the other end is the discharge port and is connected to the side wall of the straight section.

6. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, The gypsum feeder has a built-in agitator, and both the gypsum feeder and the grinding aid feeder are equipped with a material control valve and a material flow meter at their outlets.

7. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, It also includes a dust collector, which is connected to the classifier and is used to collect and process the dust generated during the sieving process of the classifier; an induced draft fan is installed at the end of the dust collector to discharge the purified air.

8. The milling and grading process for controllable aspect ratio of calcium sulfate whiskers according to claim 1, characterized in that, It also includes a dust removal process, in which the dust generated in the classifier is collected and treated by a dust collector, and then the purified air is discharged under the action of an induced draft fan.

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