CN113798508A - A binder jet 3D printing powder spreading roller device with cleaning function - Google Patents

Abstract

The invention discloses a binder spraying 3D printing powder spreading roller device with a cleaning function, which comprises a supporting plate, a powder spreading roller, a cleaning roller, brush cloth, a stop lever and a dust collecting groove. The cleaning roller and the powder spreading roller are driven by a belt; the outer surface of the cleaning roller is coated with the brush cloth, and when the cleaning roller is cleaned, the brush on the brush cloth scrapes and sweeps the surface of the powder spreading roller. The stop lever is fixed at the front side of the powder laying working direction, and the dust collecting groove is fixed below the cleaning roller. When the automatic powder spreading device works, the brush on the cleaning roller scrapes and cleans the surface of the powder spreading roller, and meanwhile, the brush is rotated to realize self-cleaning through the stop lever. The dust collecting groove below the cleaning roller collects dust scraped off during cleaning, and the dust is prevented from falling into a powder pile. The invention solves the problem of powder adhesion of the powder paving roller caused by static electricity, van der Waals force or adhesive adhesion and the like during powder paving in printing. The powder spreading roller is automatically cleaned while powder is spread, so that the flatness of the powder spreading layer and the surface precision and quality of a printed product are guaranteed, and the powder spreading roller has the advantages of simple structure, low use and maintenance cost and the like.

Description

Binder sprays 3D and prints powder roller device of spreading with clean function

Technical Field

The invention belongs to the technical field of additive manufacturing and forming, and particularly relates to a binder spraying 3D printing powder spreading roller device with a cleaning function.

Background

Binder jet 3D printing (BJ 3DP) was first proposed in 1990 by the american academy of labor Sachs et al. The basic principle is as follows: firstly, metal powder is flatly and uniformly laid into an extremely thin powder layer, then the binder is sprayed and deposited on the surface of the powder layer through a spray head under the control of a computer according to needs, and thus the printing of a layer of section is completed. Subsequently, the bed is lowered to a certain height, a new layer of powder is formed by spreading a sufficient amount of powder, and the spray head sprays the binder again to the specific area. Repeating the steps, and finally bonding the powder in the specific area in a layer-by-layer powder laying and bonding mode to obtain the blank of the required part. Compared with the traditional additive manufacturing technology, the binder-jet 3D printing has the advantages of low manufacturing cost, wide applicable materials and the like, has development potential in the aspects of rapid and mass production, and has attracted much attention in recent years.

The powder bed type printing and forming powder spreading mode mainly comprises a powder spreading roller type mode and a scraper type mode, wherein the powder spreading roller type powder spreading mode has a pushing effect on a powder bed, so that the powder bed density higher than that of scraper type powder spreading can be obtained, and the powder spreading mode is a powder spreading mode which is mainly adopted in the existing printing equipment.

In the process of 3D printing and powder spreading by spraying the binder, due to factors such as static electricity, van der Waals force and the like, a powder sticking phenomenon is easy to occur on the powder spreading roller, and the powder spreading effect is influenced. Particularly, when the powder is bonded on the powder spreading roller after the binder is doped, the flatness and the compactness of the powder layer are seriously reduced, so that the density of a printing blank is reduced, and the forming effect is deteriorated.

The device disclosed in the Chinese patent application, namely an additive manufacturing powder spreading device with a flexible scraper (application publication number: CN110065233A), comprises a forming workbench, a powder spreading roller horizontal movement transmission device, a powder spreading roller rotation transmission device, a flexible scraper device arranged on a supporting mechanism frame and a powder spreading roller arranged on the supporting mechanism frame, wherein the supporting mechanism frame is fixed on a synchronous belt and moves back and forth along a linear track under the drive of the powder spreading roller horizontal movement transmission device; the flexible scraper is fixed on the flexible scraper fixing piece through the adjustable bolt, and the flexible scraper is adjusted to move upwards along the axial direction of the adjustable bolt through the adjustable bolt so as to adjust the fit degree between the flexible scraper and the surface of the powder spreading roller. The invention can effectively remove the fine powder on the powder spreading roller to a certain extent, but the scraper type cleaning combination force adopted by the invention is not tight enough, and the powder spreading roller is difficult to clean when being polluted by the adhesive. The blade edge of the rubber scraper is easily abraded to cause the local cleaning effect to be poor. The collection device for the scraped powder is not arranged, and the scraped powder with the binder component returns to a powder pile to be paved, so that the powder is agglomerated and bonded, and the bonding forming size and precision of parts are further influenced.

Chinese patent selective laser sintering powder paving roller cleaning mechanism (No. CN209598197U) designs a powder paving roller cleaning mechanism, which comprises a workbench, wherein the bottom surface of an L-shaped plate vertical plate is fixedly installed on one side of the top surface of the workbench, a rectangular groove is formed in the bottom surface of an L-shaped plate horizontal plate, a plurality of uniformly and longitudinally distributed installation grooves are respectively formed in two sides of the inner wall of the rectangular groove, electric push rod fixing rods with limiting functions are respectively and fixedly installed in the installation grooves, rectangular plates are arranged in the rectangular grooves, and two sides of each rectangular plate are respectively and fixedly connected with the inner ends of corresponding electric push rod movable rods. The brush hair will spread the powder on powder roller surface and brush the back, and the powder falls into to the collecting vat through the gap between the roller bearing under the effect of gravity, and the effect that supports can be played to spreading the powder roller to the cooperation of second pivot and roller bearing, guarantees to spread the powder roller and normally move in the collecting vat top, can clean spreading the powder roller when spreading powder device work to guarantee to spread the smoothness nature of powder device work. The device of the invention requires large space and a large number of brushes.

The Chinese patent application, namely 'cleaning device of scraper of powder spreader of printer and printer with the same' (application publication number: CN112208101A), designs a cleaning device for the scraper of the powder spreader, which comprises a moving device and a cleaning device. The moving device is connected with the cleaning device and drives the cleaning device to move along a working path. The cleaning device is contacted with the bottom of the scraper of the powder spreader and moves along the scraper to clean. The device needs a movement device matched with the cleaning head, has a complex structure, increases the manufacturing cost, and is not suitable for cleaning a roller type powder spreading structure.

In conclusion, a powder spreading roller cleaning device comprehensively considering the process characteristics of the BJ3DP and the equipment working conditions thereof is needed.

Disclosure of Invention

The powder roller is used for solving the problem that the powder roller is stuck by static electricity, van der Waals force and the like when powder is spread in printing in the prior art. The invention provides a binder spraying 3D printing powder spreading roller device with a cleaning function, which can clean a powder spreading roller in a powder spreading process and ensure the flatness of a powder spreading layer and the surface precision and quality of a printed product.

In order to realize the purpose of the invention, the binder spraying 3D printing powder spreading roller device with the cleaning function comprises a supporting plate, a powder spreading roller, a cleaning roller, brush cloth, a stop lever and a dust collecting groove,

the powder spreading roller and the cleaning roller are both arranged on the supporting plate and are in transmission through a belt;

the outer surface at the cleaning roller of brush cloth cladding, and when clean, brush on the brush cloth is being spread whitewashed roller surface and is being scraped.

The stop lever is fixed on the supporting plate, can be contacted with a brush on the brush cloth, and has an axis parallel to that of the cleaning roller;

the dust collecting groove is fixed on the supporting plate.

Further, the backup pad includes first fixed plate and the second fixed plate of two relative settings, spread the both ends of powder roller, the both ends of cleaning roller are equallyd divide and are rotated the setting respectively first fixed plate with on the second fixed plate.

Further, the advancing direction of the powder spreading roller is taken as the front side, the cleaning roller is located on the front side of the powder spreading roller, and the stop lever is located on the front side of the cleaning roller.

Preferably, the axis of the cleaning roller is higher than the axis of the powder spreading roller;

preferably, the axis of the baffle rod is lower than the axis of the cleaning roller.

By the arrangement, falling objects possibly existing when the cleaning roller works can be ensured not to disturb the paved powder layer area.

Further, be provided with on the shop powder roller axle and spread the powder roller band pulley, be provided with the cleaning roller band pulley on the cleaning roller axle, spread the powder roller band pulley with through belt transmission between the cleaning roller band pulley.

Further, the radius of the cleaning roller is smaller than that of the powder spreading roller, and a gap is reserved between the cleaning roller and the powder spreading roller.

Preferably, the radius of the cleaning roller is 0.2-0.5 times of that of the powder spreading roller;

preferably, the clearance between the cleaning roller and the powder spreading roller is 5-10 mm.

Further, the dust collecting groove is fixed at the lower side of the cleaning roller.

So set up, the dust collecting tank can collect the powder that splashes in the clean in-process of shop's powder roller or the self-cleaning in-process of cleaning roller, avoids having the dust of binder to fall into powder heap, influence printing quality.

Further, the blocking lever may be a sheet, a column, etc., and the blocking lever is in contact with the brush on the cleaning roller.

Further, the brush cloth coated on the cleaning roller is tightly attached to the cleaning roller, and relative sliding does not occur between the brush cloth and the cleaning roller.

Further, the brush coated on the cleaning roller is made of a wear-resistant and heat-resistant flexible polymer material.

Preferably, the flexible polymer material is any one of nylon (PA), polypropylene (PP), polybutylene terephthalate (PBT), Polyester (PET), and polyvinyl chloride (PVC).

Further, the thickness of the brush cloth coated on the cleaning roller is not less than the gap between the cleaning roller and the powder spreading roller;

preferably, the thickness of the brush cloth coated on the cleaning roller is 5-15 mm.

Compared with the prior art, the invention can realize the following beneficial effects:

the invention discloses a binder spraying 3D printing powder spreading roller device with a cleaning function, which solves the problem that a powder spreading roller is adhered to powder due to static electricity, van der Waals force or binder adhesion and the like during printing and powder spreading. Because the brush is adopted for rolling cleaning, the brush is contacted with the powder spreading roller, the scraping and sweeping are uniform, the cleaning effect is good, and the flexible brush can not scratch the powder spreading roller. In addition, the powder adsorbed on the brush can be swept down by the stop lever when rotating through the stop lever, so that the self-cleaning of the brush can be realized. The dust collecting groove can collect powder splashed in the cleaning process of the powder spreading roller or the self-cleaning process of the cleaning roller, and dust with a binder is prevented from falling into a powder pile to influence the printing quality. The powder roller can be cleaned in the powder spreading process, and the flatness of the powder spreading layer and the surface precision and quality of printed products are guaranteed. Meanwhile, the device has the advantages of simple structure, low use and maintenance cost and the like.

Drawings

Fig. 1 is a front view of an adhesive-jetting 3D-printing powder-spreading roller device with a cleaning function according to an embodiment of the present invention.

Fig. 2 is a left side view of an adhesive-jetting 3D-printing powder-spreading roller device with a cleaning function according to an embodiment of the present invention.

In fig. 1 and 2, afirst fixing plate 1, a cleaning roller fixing bearing 2, a powder spreading roller fixing bearing 3, a dust collecting groove 4, apowder spreading roller 5, a powder spreadingroller belt wheel 6, abelt 7, a cleaningroller belt wheel 8, asecond fixing plate 9, acleaning roller 10, astop lever 11 and abrush cloth 12.

Detailed Description

In order to make the technical solution of the present invention clearer, the present invention will now be further described with reference to the embodiments and the accompanying drawings.

Fig. 1 and 2 are a front view and a left side view of the device of the present invention, respectively. In the figure, thepowder spreading roller 5 is driven by a printing device (not shown in the figure) to rotate and move, thecleaning roller 10 and thepowder spreading roller 5 are fixed on the supporting plate and driven by thepowder spreading roller 5 through a belt to rotate, and the brushingcloth 12 coated with a certain thickness on thecleaning roller 10 rubs against thepowder spreading roller 5 relatively, so that thepowder spreading roller 5 is cleaned. The powder adsorbed on the brush is swept down by the blockingrod 11 when rotating through the blocking rod, so that the self-cleaning of the brush is realized. The dust collecting groove 4 can collect powder splashed in the cleaning process of thepowder spreading roller 5 or the self-cleaning process of the cleaningroller 10, and dust with a binder is prevented from falling into a powder pile to influence the printing quality.

The invention provides a powder spreading roller device with a cleaning function and used for adhesive injection 3D printing, which comprises a supporting plate, apowder spreading roller 5, a cleaningroller 10, abrush cloth 12, astop lever 11 and a dust collecting groove 4.

Spreadpowder roller 5 with cleaningroller 10 all installs in the backup pad, just cleaningroller 10 with spread through belt transmission between thepowder roller 5,brush cloth 12 cladding is in the surface of cleaningroller 10, and when clean, brush on thebrush cloth 12 is inspread 5 surface scrapes of powder roller and sweep. Thestop lever 11 is fixed on the supporting plate, and the axis of thestop lever 11 is parallel to the axis of the cleaningroller 10; the dust collecting groove 4 is fixed on the supporting plate.

Specifically, the supporting plate comprises afirst fixing plate 1 and asecond fixing plate 9 which are oppositely arranged; thepowder spreading roller 5 is arranged on thefirst fixing plate 1 and thesecond fixing plate 9 through a powder spreadingroller fixing bearing 3; the cleaningroller 10 is arranged on thefirst fixing plate 1 and thesecond fixing plate 9 through the cleaningroller fixing bearing 2; two ends of thestop lever 11 are respectively fixedly arranged on thefirst fixing plate 1 and thesecond fixing plate 9; the dust collecting groove 4 is fixedly arranged on thefirst fixing plate 1 and thesecond fixing plate 9.

Specifically, the cleaningroller 10 is positioned on the front side of thepowder spreading roller 5 with the advancing direction of thepowder spreading roller 5 as the front side; thestop lever 11 is positioned at the front side of the cleaningroller 10; the axis of the cleaningroller 10 is higher than that of thepowder spreading roller 5. A cleaningroller 10 is installed at the front side of thepowder spreading roller 5 to prevent the powder swept off during cleaning from disturbing the spread powder layer.

Specifically, the blockingrod 11 may be in the form of a sheet, a column, or the like, the axis of the blockingrod 11 is lower than the axis of the cleaningroller 10, and the blockingrod 11 contacts with the brush on thebrush cloth 12 to ensure that thebrush cloth 12 can sweep over the blockingrod 11 to achieve self-cleaning.

Specifically, a powder spreadingroller belt wheel 6 is arranged on the axis of thepowder spreading roller 5, a cleaningroller belt wheel 8 is arranged on the axis of the cleaningroller 10, and the powder spreadingroller belt wheel 6 and the cleaningroller belt wheel 8 are in transmission through abelt 7; when the powder spreading roller works, the rotation of thepowder spreading roller 5 drives the cleaningroller 10 to rotate. More specifically, the radius of the cleaning roller is 0.2-0.5 times of the radius of the powder spreading roller, and the gap between the cleaning roller and the powder spreading roller is 5-10 mm.

Specifically, the dust collecting groove 4 is located at the lower side of the cleaningroller 10, and the dust collecting groove 4 is used for collecting powder splashed in the cleaning process of the powder spreading roller or the self-cleaning process of the cleaning roller, so that dust with a binder is prevented from falling into a powder pile and affecting the printing quality.

Specifically, thebrush cloth 12 is a wear-resistant and heat-resistant flexible polymer material. More specifically, the brush cloth may be any one of nylon (PA), polypropylene (PP), polybutylene terephthalate (PBT), Polyester (PET), and polyvinyl chloride (PVC).

Specifically, thebrush cloth 12 is coated and fixed on the cleaningroller 10 by means of clamping grooves, bonding and the like, the thickness of thebrush cloth 12 is not less than the gap between the cleaningroller 10 and thepowder spreading roller 5, and more specifically, the thickness of thebrush cloth 12 is 5-15 mm.

When the binder spraying 3D printing powder spreading roller device with the cleaning function is used, thepowder spreading roller 5 rotates and advances to perform powder spreading operation, thepowder spreading roller 5 drives the cleaningroller 10 to rotate through thebelt 7, thebrush cloth 12 coated on the cleaningroller 10 and thepowder spreading roller 5 generate relative friction, the surface of thepowder spreading roller 5 is cleaned under the friction effect, and the smoothness and the compactness of a subsequent powder spreading layer are guaranteed. The powder adsorbed on thebrush cloth 12 is swept down by the blockinglever 11 when rotating through the blocking lever, so that thebrush cloth 12 is self-cleaned. The dust collecting groove 4 is used for collecting powder splashed in the cleaning process of thepowder laying roller 5 or the self-cleaning process of the cleaning roller, and the powder with the binder is prevented from falling into a powder pile to influence the printing quality.

Example 1:

the utility model provides a binder sprays 3D and prints shop's powder roller device with clean function, includes backup pad, dust collecting tank 4, shop'spowder roller 5, cleaningroller 10, claddingbrush cloth 12 andpin 11 on cleaning roller.

The cleaning roller is fixed on the supporting plate through a bearing; the axis of the cleaning roller is higher than that of the powder spreading roller and is positioned at the front side of the working direction of the powder spreading roller so as to ensure that powder swept down by the cleaning roller does not fall into a spread powder layer area when the cleaning roller works; the powder spreading roller drives the cleaning roller to rotate through belt transmission; the radius of the cleaning roller is 0.2 times of that of the powder spreading roller, and the gap between the two rollers is 5 mm; the material of the brush cloth is nylon (PA), the brush cloth is bonded and coated on the cleaning roller, and the thickness of the brush cloth is 8 mm. The lower side of the cleaning roller is provided with a sheet-shaped baffle plate, and two sides of the baffle plate are fixed on the supporting plate. A dust collecting groove is arranged below the cleaning roller and used for collecting powder splashed in the cleaning process of the powder laying roller and the self-cleaning process of the cleaning roller.

Example 2:

the utility model provides a binder sprays 3D and prints and spread powder roller device with clean function, includes the backup pad, spreadspowder roller 5, cleaningroller 10, claddingbrush cloth 12 andpin 11 on cleaning roller.

The cleaning roller is fixed on the supporting plate through a bearing; the axis of the cleaning roller is higher than that of the powder spreading roller and is positioned at the front side of the working direction of the powder spreading roller so as to ensure that powder swept down by the cleaning roller does not fall into a spread powder layer area when the cleaning roller works; the powder spreading roller drives the cleaning roller to rotate through belt transmission; the radius of the cleaning roller is 0.5 times of that of the powder spreading roller, and the gap between the two rollers is 10 mm; the brush cloth material is dacron (PET), is fixed in on the cleaning roller through the draw-in groove, and brush cloth thickness is 15 mm. The front side of the cleaning roller is provided with a columnar stop lever, and two sides of the stop lever are fixed on the supporting plate.

Example 3:

the utility model provides a binder sprays 3D and prints shop's powder roller device with clean function, includes backup pad, dust collecting tank 4, shop'spowder roller 5, cleaningroller 10, claddingbrush cloth 12 andpin 11 on cleaning roller.

The cleaning roller is fixed on the supporting plate through a bearing; the axis of the cleaning roller is higher than that of the powder spreading roller and is positioned at the front side of the working direction of the powder spreading roller so as to ensure that powder swept down by the cleaning roller does not fall into a spread powder layer area when the cleaning roller works; the powder spreading roller drives the cleaning roller to rotate through belt transmission; the radius of the cleaning roller is 0.5 times of that of the powder spreading roller, and the gap between the two rollers is 10 mm; the material of the brush cloth is polypropylene (PP), the brush cloth is adhered and coated on the cleaning roller, and the thickness of the brush cloth is 15 mm. The lower side of the cleaning roller is provided with a columnar stop lever, and two sides of the baffle are fixed on the supporting plate. A dust collecting groove is arranged below the cleaning roller and used for collecting powder splashed in the cleaning process of the powder laying roller and the self-cleaning process of the cleaning roller.

Example 4:

the utility model provides a binder sprays 3D and prints and spread powder roller device with clean function, includes the backup pad, spreadspowder roller 5, cleaningroller 10, claddingbrush cloth 12 andpin 11 on cleaning roller.

The cleaning roller is fixed on the supporting plate through a bearing; the axis of the cleaning roller is higher than that of the powder spreading roller and is positioned at the front side of the working direction of the powder spreading roller so as to ensure that powder swept down by the cleaning roller does not fall into a spread powder layer area when the cleaning roller works; the powder spreading roller drives the cleaning roller to rotate through belt transmission; the radius of the cleaning roller is 0.3 times of that of the powder spreading roller, and the gap between the two rollers is 5 mm; the material of the brush cloth is polyvinyl chloride (PVC) brush, the brush cloth is adhered to and coated on the cleaning roller, and the thickness of the brush cloth is 6 mm. The lower side of the cleaning roller is provided with a sheet-shaped baffle plate, and two sides of the baffle plate are fixed on the supporting plate.

Example 5:

the utility model provides a binder sprays 3D and prints shop's powder roller device with clean function, includes backup pad, dust collecting tank 4, shop'spowder roller 5, cleaningroller 10, claddingbrush cloth 12 andpin 11 on cleaning roller.

The cleaning roller is fixed on the supporting plate through a bearing; the axis of the cleaning roller is higher than that of the powder spreading roller and is positioned at the front side of the working direction of the powder spreading roller so as to ensure that powder swept down by the cleaning roller does not fall into a spread powder layer area when the cleaning roller works; the powder spreading roller drives the cleaning roller to rotate through belt transmission; the radius of the cleaning roller is 0.4 times of that of the powder spreading roller, and the gap between the two rollers is 8 mm; the material of the brush cloth is nylon (PA), the brush cloth is adhered and coated on the cleaning roller, and the thickness of the brush cloth is 11 mm. A columnar stop lever is arranged in front of the cleaning roller, and two sides of the baffle are fixed on the supporting plate. A dust collecting groove is arranged below the cleaning roller and used for collecting powder splashed in the cleaning process of the powder laying roller and the self-cleaning process of the cleaning roller.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A binder spraying 3D printing powder spreading roller device with a cleaning function is characterized by comprising a supporting plate, a powder spreading roller, a cleaning roller, brush cloth, a stop lever and a dust collecting groove;

the powder spreading roller and the cleaning roller are rotatably arranged on the supporting plate;

the brush cloth is coated on the outer surface of the cleaning roller, and when the cleaning roller is used for cleaning, brushes on the brush cloth are used for scraping the surface of the powder spreading roller;

the stop lever is fixed on the supporting plate and can be contacted with the brush on the brush cloth;

the dust collecting groove is fixed on the supporting plate.

2. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the supporting plate comprises a first fixing plate and a second fixing plate which are oppositely arranged;

spread the both ends of powder roller, the both ends of cleaning roller are equallyd divide and are rotated respectively and set up first fixed plate with on the second fixed plate.

3. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the powder spreading roller is arranged on the front side of the powder spreading roller, the cleaning roller is arranged on the front side of the powder spreading roller, and the stop lever is arranged on the front side of the cleaning roller.

4. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: spread and be provided with on the powder roller and spread the powder roller band pulley, be provided with the cleaning roller band pulley on the cleaning roller, spread the powder roller band pulley with through belt transmission between the cleaning roller band pulley.

5. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the radius of the cleaning roller is smaller than that of the powder spreading roller, and a gap is reserved between the cleaning roller and the powder spreading roller.

6. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the stop lever is sheet-shaped or column-shaped.

7. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the dust collecting groove is positioned at the lower side of the cleaning roller.

8. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the coating is in on the cleaning roller the brush cloth closely laminates on the cleaning roller, and does not take place relative slip between the two.

9. The binder-spraying 3D-printing powder-spreading roller device with the cleaning function according to claim 1, characterized in that: the brush cloth coated on the cleaning roller is made of a wear-resistant and heat-resistant flexible polymer material.

10. The binder-jetting 3D-printing powder-spreading roller device with cleaning function according to any one of claims 1 to 9, characterized in that: the thickness of the brush cloth coated on the cleaning roller is not less than the gap between the cleaning roller and the powder spreading roller.

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