Preparation process of metal filtering membrane

Abstract

The invention provides a preparation process of a metal filtering membrane capable of improving the smoothness of a membrane surface, which comprises the following steps: step 1, sizing a silk screen through a slurry pulling process to obtain a sized silk screen; step 2, scraping and extruding the slurry onto one film surface of a plastic film, naturally depositing powder particles in the slurry onto the plastic film surface, then drying the plastic film deposited with the slurry, and forming a film material layer on the plastic film by the deposited slurry; 3, the plastic film is separated from the film material layer located on one face of the plastic film, the face, making contact with the plastic film, of the film material layer forms a smooth face, and the film material layer is wound; and step 4, bonding the membrane material layer with the sizing silk screen after slurry drawing, enabling the smooth surface in the membrane material layer to face outwards in the combined new membrane material, and finally sintering to obtain the new metal filtering membrane.

Description

Technical Field

[0001] The invention relates to the technical field of membrane materials, and more particularly to a preparation process of a metal filtering membrane. Background Art

[0002] The general high temperature resistant metal filter bag is made of metal fiber or metal powder, which is pressed and sintered to form a porous filter material of metal compound, and then welded to form a filter bag. The metal fiber or metal powder is sintered to form a porous metal membrane (metal filter membrane). The metal filter membrane has the characteristics of high temperature resistance, strong acid and alkali resistance, high mechanical strength, and certain flexibility. It solves the problem of high-precision interception of dust particles in high-temperature industrial flue gas and is an ideal high-temperature flue gas dust removal material. However, in addition to the chemical and physical properties of the material, the service life of the metal filter membrane is mostly due to dust blocking the filter bag surface, resulting in failure to intercept dust particles. Although the dust removal system is designed with a back-blowing function to back-blow the dust adhering to the membrane surface into the dust box and then discharge it, the industrial flue gas contains more chemical components, some of which contain certain colloid components. In the process of dust removal, the dust is continuously filtered. The dust continuously flows to the surface of the membrane under the action of high-speed airflow, and is then intercepted by the membrane on the membrane surface. At this time, the speed of the dust is basically zero. The more the dust accumulates, the more it must be back-blown by high-pressure gas in an instant to let the speedless dust leave the membrane surface. Since this is speedless dust, it has a certain block and a certain weight after accumulation and will sink to the bottom of the dust collector. The dust-free membrane surface that is back-blown out will continue to intercept the dust, so the smoothness of the membrane surface can efficiently blow away the dust under the condition of back-blowing. The higher the smoothness of the membrane surface, the lower the adhesion of the dust on the membrane surface, the better the dust removal effect, and the greater the durability of the dust collector.

[0003] In the preparation of traditional metal filter bags, the surface of the membrane is usually made by wire mesh through slurry drawing process + coating process or spraying process. The slurry drawing process generally includes: preparing a high-viscosity metal powder suspension slurry, conveying the wire mesh into the slurry, pulling it out and scraping the surface flat, and then drying it to form a sizing wire mesh. The coating process can be combined with Figure 1 , Figure 2 As shown, the sizing screen 1' is unwound through the guide roller 21' and then passed between the clamps formed by a slurry transfer roller 22' and a sizing roller 23'. The sizing roller 23' is immersed in the slurry tank 3' on the screen to drive the slurry a' to be transferred to the sizing screen 1'. A slurry scraper 4' is provided above the sizing roller 23'. The slurry scraper 4' scrapes the slurry driven by the sizing roller 23' flat, so that the metal powder a'' is coated on the sizing screen 1', and then it is dried in the oven 5' and then rolled up. Therefore, the surface flatness and smoothness of the metal filter membrane is achieved by transferring the powder to the membrane surface of the screen by the slurry scraper and the sizing roller.

[0004] In the above coating process, the metal powder in the slurry is not completely uniform. The surface layer of the metal powder is scraped out by a scraper and coated in a natural state. The powder on the surface of the screen can no longer be controlled. In addition, before the slurry is dried, the metal powder has a high specific gravity and is fluid in the slurry. After drying, the powder particles on the surface of the membrane are uneven, that is, rough. This process causes the surface flatness and smoothness of the membrane to be low. If you want to improve the smoothness of the membrane surface, you have to roll it again, but the air permeability of the filter membrane after rolling will be greatly reduced, affecting the performance of the membrane surface.

[0005] Therefore, the membrane surface of traditional metal filter bags has the following disadvantages: ① The surface flatness and smoothness of the membrane are relatively low; ② The membrane surface has strong adhesion to dust and is easy to be covered with dust; ③ The attached dust is not easy to fall off during backblowing, which affects the dust removal effect and the life of the membrane.

[0006] In view of this, the inventor has made in-depth considerations on the problem of low surface smoothness of the metal filter bag membrane, and has actively researched, improved and tested the invention to develop and design the present invention. Summary of the invention

[0007] The object of the present invention is to provide a preparation process of a metal filter membrane capable of improving the smoothness of the membrane surface.

[0008] In order to achieve the above object, the solution of the present invention is: A preparation process of a metal filter membrane comprises the following steps: Step 1, sizing the screen through a sizing process to obtain a sizing screen; Step 2, scraping and squeezing the slurry onto one of the film surfaces of the plastic film, the powder particles in the slurry are naturally deposited on the surface of the plastic film, and then the plastic film with the slurry deposited is dried, and the deposited slurry forms a film material layer on the plastic film; Step 3, separating the plastic film from the film material layer on one side thereof, forming a smooth surface on the side of the film material layer in contact with the plastic film, and rolling up the film material layer; Step 4, bonding the membrane material layer to the sizing screen after slurry drawing, and making the smooth surface of the membrane material layer in the combined new membrane material face outwards, and finally completing the new metal filter membrane through sintering treatment.

[0009] Furthermore, in step 1, the slurry drawing process includes coating the surface of the single-layer screen with a wetting agent, conveying it into the slurry, pulling it out and flattening the surface, and then drying it to form a semi-finished film material of the sized screen, and finally rolling it up.

[0010] Furthermore, the slurry includes metal powder particles mixed in a water-soluble resin, the fluidity of the slurry in step 2 is greater than the fluidity of the slurry used in the slurry drawing process in step 1, and the metal powder particles in the slurry in step 2 are finer than the metal powder particles in the slurry used in the slurry drawing process in step 1.

[0011] Furthermore, the kinematic viscosity of the water-soluble resin in the slurry used in the slurry drawing process of step 1 is greater than the kinematic viscosity of the water-soluble resin in the slurry of step 2.

[0012] Furthermore, in step 2, the plastic film enters a slurry tank after being unwound, and a slurry scraper is provided at the other end of the slurry tank, and the slurry scraper scrapes the slurry flat onto the upper surface of the plastic film.

[0013] Furthermore, the bottom surface of the slurry tank forms an inclined surface with a lower front and a higher rear corresponding to the traveling direction of the plastic film, and the slurry scraper is located at the rear end of the slurry tank.

[0014] Furthermore, in step 3, the plastic film with the film material layer deposited on the surface is dried and passed through a guide roller to separate the film material layer, and the separated plastic film and the film material layer are rolled up separately.

[0015] Furthermore, in step 4, the film material layer and the sizing screen after slurry drawing are synthesized by a roller machine, and the smooth surface of the film material layer is in contact with the roller surface.

[0016] After adopting the above method, the present invention uses a scraper to control the amount of powder + a plastic film to transfer the powder and naturally deposit it. The film making process is through a slurry pulling process + a film sheet deposition process + a separation and winding process + a bonding process. In the bonding process, the sheet with high smoothness faces outward, which improves the surface flatness and smoothness of the film and effectively reduces the adhesion of dust to the film surface.

[0017] The metal filter membrane prepared by the present invention has the following advantages: ① the flatness and smoothness of the membrane surface are greatly improved; ② the membrane surface has little adhesion to dust and is not easy to be covered with dust; ③ the attached dust is easy to fall off during backblowing, thereby improving the dust removal effect and extending the life of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the coating structure of the existing sizing screen; Figure 2 for Figure 1 A partial enlarged view of the middle A; Figure 3 It is a structural schematic diagram of the slurry pulling step in the present invention; Figure 4 for Figure 3 A partial enlarged view of point B in the middle; Figure 5 It is a schematic diagram of the structure of the film made by the deposition method in the present invention; Figure 6 for Figure 5 A partial enlarged view of point C in the middle; Figure 7 for Figure 5 A partial enlarged view of point D in the middle; Figure 8 This is an enlarged cross-section of a conventional process membrane; Fig. 9 An enlarged cross-sectional view of a membrane obtained by the process of the present invention; DETAILED DESCRIPTION In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0019] Combination Figures 3 to 7 As shown, the present invention discloses a process for preparing a metal filter membrane, which is characterized by comprising the following steps: Step 1, sizing the screen through a sizing process to obtain a sizing screen; Step 2, scraping and squeezing the slurry onto one of the film surfaces of the plastic film, the powder particles in the slurry are naturally deposited on the surface of the plastic film, and then the plastic film with the slurry deposited is dried, and the deposited slurry forms a film material layer on the plastic film; Step 3, separating the plastic film from the film material layer on one side thereof, forming a smooth surface on the side of the film material layer in contact with the plastic film, and rolling up the film material layer; Step 4, bonding the membrane material layer to the sizing screen after slurry drawing, and making the smooth surface of the membrane material layer in the new combined membrane material face outwards, and finally completing the new metal filter membrane through sintering treatment.

[0020] Specifically, in step 1, the slurry drawing process may include coating the surface of a single-layer screen with a wetting agent, conveying the screen into the slurry, pulling the screen out, and flattening the surface, and then drying the screen to form a semi-finished film material, and finally rolling it up.

[0021] The slurries in step 1 and step 2 both use water-soluble resin as slurry, and add water and metal powder particles. The fluidity of the slurry in step 2 is greater than the fluidity of the slurry used in the slurry drawing process in step 1, and the metal powder particles in the slurry in step 2 are finer than the metal powder particles in the slurry used in the slurry drawing process in step 1. The fluidity of the slurry in the step 2 deposition method is better than that of the slurry in the slurry drawing process, and the metal powder particles in the slurry are finer (about 350 meshes). The obtained membrane material layer is used as the main filter surface, and the use of fine powder can have a better filtration accuracy. The metal powder particles in the slurry in the slurry drawing process in step 1 are coarser (about 200 meshes). The purpose is to use coarse particles to fill the mesh holes and make the air permeability of the inner layer of the membrane material better.

[0022] The kinematic viscosity of the water-soluble resin in the slurry used in the slurry drawing process of step 1 is greater than the kinematic viscosity of the water-soluble resin in the slurry of step 2. The kinematic viscosity of the water-soluble resin in the slurry drawing process of step 1 is about 2000mPa.s; in the deposition process of step 2, the dynamic viscosity of the water-soluble resin is about 1200mPa.s, and the fluidity is better. Since the film material in the slurry drawing process is vertically upward and the slurry is easy to flow downward, the viscosity must be large to control the downward flow of the slurry and ensure the uniformity of the powder. In the deposition process, the film material moves in the horizontal direction, and the thickness of the slurry is relatively small, 0.2-0.3mm, which is not easy to flow.

[0023] like Figure 3 , Figure 4 As shown, after unwinding, the screen 11 is stretched and guided by multiple guide rollers, and then enters a first slurry tank 21. The first slurry tank 21 contains slurry a. The screen 11 is sizing by a roller 31 immersed in the slurry a, and then transmitted upward. A first slurry scraper 41 is provided above the first slurry tank 21 to scrape the slurry on the screen 11 flat, and then enters the first oven 51 for drying. The oven is provided with a heating plate 511. After drying, the sizing screen 12 is obtained to form a semi-finished film material, which is finally rolled up.

[0024] In step 2, a plastic film is unwound and then placed into a slurry tank. A slurry scraper is provided at the other end of the slurry tank to scrape the slurry flat onto the upper surface of the plastic film. Figure 5 , Figure 6 As shown, the plastic film 13 enters a second slurry tank 22 after unwinding. The second slurry tank 22 is filled with slurry b. A second slurry scraper 42 is provided at the other end of the second slurry tank 22. The second slurry scraper 42 can scrape the slurry b flat to the upper surface of the plastic film 13 to form a film material layer 14 on the plastic film 13. In this embodiment, the bottom surface of the second slurry tank 22 forms an inclined surface with a low front and a high rear corresponding to the traveling direction of the plastic film 13, and the second slurry scraper 42 is located at the rear end of the second slurry tank 22. When the plastic film 13 is being conveyed, since the surface of the plastic film is very flat and smooth, the powder particles in the slurry b can be naturally deposited on the film surface of the plastic film 13 before drying, and the deposition density is high and uniform. After drying, all the metal powder particles are on the same plane regardless of size.

[0025] In step 3, the plastic film 13 with the film material layer 14 deposited on the surface is dried and separated from the film material layer by a guide roller, and the separated plastic film and the film material layer are rolled up separately. Figure 5 , Figure 7As shown, the plastic film 13 with the film material layer 14 deposited on the surface enters the second drying oven 52 after passing through the guide roller. After drying, the film material layer 14 can be separated by a guide roller 32. The film material layer 14 can be peeled off independently from the plastic film 13. The separated plastic film 13 and the film material layer 14 are rolled up separately.

[0026] The newly formed film layer 14 by the deposition method is heated to about 130°C in the second oven, and the water in the resin is basically dried to achieve a non-flowing state, with a certain flexibility and tensile strength, like paper, and can be peeled off. The resin powder attached to the plastic film surface is in a fluid state before being baked and solidified, but the viscosity is relatively large. Due to the high specific gravity of metal powder particles, they will naturally sink in the slurry, and the particles below will fall onto a smooth plastic film surface. The position of the particles in the lowest layer is constrained to a plane, so that the powder particles are completely arranged neatly and have a smooth surface. Therefore, the side of the film layer that contacts the plastic film forms a smooth surface, while the upper surface is uneven, so the smoothness is worse.

[0027] Further, in step 4, the film material layer 14 and the sizing screen 12 after slurry drawing can be put into a roller machine and rolled together on sand to obtain a new film material after combination. Among them, the roller surface of the roller machine is smooth, and the processing accuracy can be Ra0.4-0.8. During bonding, the smooth surface of the film material layer 14 faces outward and contacts the roller surface. After rolling, the smoothness is still very high. Since the resin is still soft at this time and has not been completely dried, the new metal filter membrane is finally completed after sintering.

[0028] Combination Figure 8 , Fig. 9 The figure shows the cross-section of the membrane of the conventional process and the enlarged cross-section of the membrane made by the process of the present invention. In the figure, 61 and 61' are screens, 62 and 62' are coated fine powders, 63 and 63' are slurry coarse powders, c is the membrane surface formed by the non-deposition method and c' is the membrane surface formed by the deposition method, d is the dust direction, and e is the high-pressure gas backwash direction. By comparison, it can be seen that the outermost membrane surface of the filter membrane surface formed by the present invention is smoother.

[0029] After adopting the above scheme, the main improvement in the present invention lies in the different surface powder processing process of the membrane. The traditional processing process uses a scraper to control the powder amount + roller transfer method (the membrane surface is rough), while the present invention uses a scraper to control the powder amount + plastic film to transfer the powder and naturally deposit it. The membrane making process is through a slurry pulling process + deposition of membrane material sheets + separation and winding process + bonding process. In the bonding process, the smoothest material sheets are facing outward, which improves the surface flatness and smoothness of the membrane, effectively reduces the adhesion of dust to the membrane surface, and ensures the extension of the membrane's filtration efficiency. The bonding can be done by lightly rolling with a double roller machine to ensure the mechanical properties of the original membrane material and the air permeability of the membrane.

[0030] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A process for preparing a metal filter membrane, characterized in that: The following steps are involved: Step 1, sizing the silk screen through a sizing process to obtain a sizing silk screen; Step 2, scraping and squeezing the slurry onto one of the film surfaces of the plastic film, the powder particles in the slurry are naturally deposited on the surface of the plastic film, and then the plastic film with the slurry deposited is dried, and the deposited slurry forms a film material layer on the plastic film; Step 3, separating the plastic film from the film material layer on one side thereof, forming a smooth surface on the side of the film material layer in contact with the plastic film, and rolling up the film material layer; Step 4, bonding the membrane material layer to the sizing screen after slurry drawing, and making the smooth surface of the membrane material layer in the combined new membrane material face outwards, and finally completing the new metal filter membrane through sintering treatment.

2. A process for preparing a metal filter membrane according to claim 1, characterized in that: In step 1, the slurry drawing process includes coating the surface of a single-layer screen with a wetting agent, conveying it into the slurry, pulling it out and flattening the surface, and then drying it to form a semi-finished film material of the sized screen, and finally rolling it up.

3. A process for preparing a metal filter membrane as claimed in claim 1 or 2, characterized in that: The slurry includes metal powder particles mixed in a water-soluble resin, the fluidity of the slurry in step 2 is greater than the fluidity of the slurry used in the slurry drawing process in step 1, and the metal powder particles in the slurry in step 2 are finer than the metal powder particles in the slurry used in the slurry drawing process in step 1.

4. A process for preparing a metal filter membrane as claimed in claim 1 or 2, characterized in that: The kinematic viscosity of the water-soluble resin in the slurry used in the slurry pulling process in step 1 is greater than the kinematic viscosity of the water-soluble resin in the slurry in step 2.

5. The process for preparing a metal filter membrane according to claim 1, characterized in that: In step 2, the plastic film enters a slurry tank after being unwound. A slurry scraper is provided at the other end of the slurry tank. The slurry scraper scrapes the slurry flat onto the upper surface of the plastic film.

6. A process for preparing a metal filter membrane according to claim 5, characterized in that: The bottom surface of the slurry tank forms an inclined surface with a lower front and a higher rear corresponding to the traveling direction of the plastic film, and the slurry scraper is located at the rear end of the slurry tank.

7. The process for preparing a metal filter membrane according to claim 1, characterized in that: In step 3, the plastic film with the film material layer deposited on the surface is dried and passed through a guide roller to separate the film material layer, and the separated plastic film and the film material layer are rolled up separately.

8. The process for preparing a metal filter membrane according to claim 1, characterized in that: In step 4, the film material layer and the sizing screen after slurry drawing are combined through a roller machine, and the smooth surface of the film material layer contacts the roller surface.

Images