Method for improving strength of 3D printing graphite green body

Abstract

A method for improving the strength of a 3D printing graphite green body comprises the following steps that powder is prepared, specifically, graphite powder and a reinforcing agent are mixed and stirred according to the mass ratio of 99-95: 1-5, uniform mixed powder is obtained, and the reinforcing agent is water-soluble powder; printing and forming: carrying out printing and forming on the obtained powder through a binder spraying 3D printing technology to obtain a three-dimensional graphite green body; heating and curing: heating and curing the obtained three-dimensional graphite green body twice, and obtaining a high-strength graphite green body after curing is completed; a water-soluble reinforcing agent is added into graphite powder, after jet printing is conducted through a binding agent, the reinforcing agent makes contact with a solvent in the binding agent, curing is conducted twice, the reinforcing agent is bonded with the graphite powder to form a bridge after being heated and dehydrated, the bonding effect is achieved, and the strength of a green body is further improved.

Description

Technical Field

[0001] The invention relates to the field of additive manufacturing printing materials, and in particular to a method for improving the strength of a graphite green body. Background Art

[0002] Binder jet 3D printing technology is to selectively spray a binder fluid onto a continuous powder layer at room temperature to form a green body. This technology has the advantages of high production efficiency, low cost, wide material adaptability, low molding environment requirements, and no need for support structures, and is suitable for large-scale industrial production. However, compared with traditional molding technology, the density of the green body of parts formed by binder jet molding is relatively low, which affects the strength of the parts, especially graphite. The powder is light, the strength of the green body after printing is poor, and the powder is difficult to clean, which restricts its application in binder jet 3D printing technology. In the prior art, the density of the graphite green body is usually increased by changing the printing parameters, such as the thickness of the powder layer, the saturation of the binder, the printing direction, etc., but the effect is not ideal. Summary of the invention

[0003] Based on this, the present invention aims to solve the above problems by adding a reinforcing agent to the graphite powder to improve the strength of the 3D printed graphite green body, so as to meet the requirements of green body powder cleaning and post-processing, thereby promoting the application of binder jet 3D printing technology.

[0004] A method for improving the strength of 3D printed graphite green body, comprising the following steps:

[0005] Powder preparation: Graphite powder and reinforcing agent are mixed and stirred in a mass ratio of 99-95:1-5 to obtain a uniform mixed powder, wherein: the reinforcing agent is a water-soluble powder;

[0006] Printing and molding: The obtained powder is printed and molded by binder jet 3D printing technology to obtain a three-dimensional graphite green body;

[0007] Heating and curing: the obtained three-dimensional graphite green body is heated and cured twice, and a high-strength graphite green body is obtained after the curing is completed;

[0008] A water-soluble reinforcing agent is added to the graphite powder. After the binder is jet-printed, the reinforcing agent comes into contact with the solvent in the binder and is cured twice. The reinforcing agent is heated and dehydrated and then bonds to the graphite powder to form a bridge, which plays a bonding role and further improves the strength of the green body.

[0009] In one embodiment, the temperature of the second curing is higher than the temperature of the first curing.

[0010] The first curing is pre-curing, which makes the green body have a certain hardness, which is convenient for cleaning powder or taking out parts; the second curing temperature is higher than the first curing temperature, which strengthens the bonding effect of the reinforcing agent and further improves the strength of the green body.

[0011] In one embodiment, in the heating and curing step, after the first curing is completed, the three-dimensional graphite green body is cleaned of powder, and after the powder cleaning is completed, a second curing is performed.

[0012] The powder is cleaned after the first solidification, so that the floating powder on the surface of the three-dimensional graphite green body is reduced, and the heat can more easily enter the interior of the green body during the second solidification, and the permeability and penetration effect are better.

[0013] In one embodiment, in the heating and curing step, the temperature of the first curing is 80-120°C.

[0014] In one embodiment, in the heating and curing step, the temperature of the second curing is 160-240°C.

[0015] In one embodiment, in the heating and curing step, the first curing time is 120 to 1440 minutes; the second curing time is 120 to 720 minutes.

[0016] By fully curing, the moisture in the reinforcing agent is removed, making the bonding effect of the reinforcing agent better.

[0017] In one embodiment, in the heating and curing step, during the first curing, the printed three-dimensional graphite green body and the working box are placed in the curing furnace for curing; during the second curing, only the three-dimensional graphite green body is placed in the curing furnace for curing.

[0018] The hardness of the newly printed three-dimensional graphite green body is poor. Taking out the model directly will damage the surface or shape of the green body, so curing it together with the working box can avoid this problem. After the first curing, the surface of the graphite green body has a certain hardness. At this time, the green body is taken out and the powder is cleaned, and then the graphite green body is heated and cured again to obtain a high-strength graphite green body.

[0019] In one embodiment, the enhancer is an organic compound.

[0020] The reinforcing agent is an organic compound. After the green body mixed with graphite for printing is post-processed by degreasing, graphitization, etc., the reinforcing agent can remain in the graphite product in the form of carbon without introducing other impurities, that is, it will not affect the purity of the graphite product.

[0021] In one embodiment, the enhancer is one or both of polyvinyl pyrrolidone and polyvinyl alcohol.

[0022] In one embodiment, in the printing and molding step, the binder used in the binder jet printing is one of polyvinyl alcohol, polyvinyl pyrrolidone, an inorganic binder, and a phenolic resin.

[0023] In one embodiment, in the powder preparation step, the graphite powder and the reinforcing agent are mixed and stirred at a low speed for 1 to 10 minutes.

[0024] The low-speed stirring can not only mix the graphite powder and the reinforcing agent evenly, but also avoid splashing of the graphite powder.

[0025] The water-soluble reinforcing agent powder is introduced into the graphite powder by stirring, and then the mixed powder is printed to form a green body by binder jet 3D printing technology. The green body is pre-cured by heating or microwaves, and then the green body in the powder bed is taken out and re-cured at a higher temperature. This type of reinforcing agent contacts the solvent in the binder, and after heating and dehydration, it is bonded into a bridge and acts as a binder. Compared with directly increasing the saturation of the binder, this method will not cause ink seepage problems and can ensure the accuracy of the product. In addition, the reinforcing agent is an organic compound, and the printed body is post-processed by degreasing, graphitization, etc. The reinforcing agent remains in the graphite product in the form of carbon and will not introduce other impurities. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present invention, a plurality of embodiments will be given below to describe the present invention in more comprehensive manner. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood. The binder jet 3D printing (3DP or BJ) herein works on the principle that a powder spreader lays a layer of powder, and then the print head sprays the binder at the position where molding is required, and finally forms a three-dimensional printed green body by printing layer by layer. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] In one embodiment, the present application provides a method for improving the strength of 3D printed graphite green bodies, comprising the following steps:

[0028] Powder preparation: Graphite powder and reinforcing agent are mixed and stirred in a mass ratio of 99-95:1-5 to obtain a uniform mixed powder, wherein: the reinforcing agent is a water-soluble powder;

[0029] Printing and molding: The obtained powder is printed and molded by binder jet 3D printing technology to obtain a three-dimensional graphite green body;

[0030] Heating and curing: the obtained three-dimensional graphite green body is heated and cured twice, and a high-strength graphite green body is obtained after the curing is completed;

[0031] The temperature of the second curing is higher than the temperature of the first curing.

[0032] A water-soluble reinforcing agent is added to the graphite powder. After the binder is jetted and printed, the reinforcing agent comes into contact with the solvent in the binder. The printed parts are pre-cured by heating or microwaves, and the green parts in the powder bed or work box are taken out and then re-cured at a higher temperature. After the reinforcing agent is heated and dehydrated, it bonds with the graphite powder to form a bridge, which plays a bonding role, thereby obtaining a high-strength graphite green body.

[0033] The method for improving the strength of 3D printed graphite green compacts is described below in conjunction with specific embodiments to further understand the concept of the method for improving the strength of 3D printed graphite green compacts.

[0034] In one embodiment, a method for improving the strength of a 3D printed graphite green body comprises the following steps:

[0035] Powder preparation: Place graphite powder in a sand mixing tank, then add water-soluble reinforcing agent powder, and stir at a low speed for 1 to 10 minutes to uniformly mix the two powders. The mass ratio of the mixed graphite powder to the reinforcing agent is 99 to 95:1 to 5. The reinforcing agent is an organic compound, preferably polyvinyl pyrrolidone and / or polyvinyl alcohol.

[0036] Printing: The prepared mixed powder is conveyed to the powder spreader of the 3D printer. Through the binder jet 3D printing technology, the powder spreader spreads the powder layer by layer on the work box, and the print head selectively sprays the binder layer by layer until the three-dimensional model is printed and the graphite green body is obtained. During printing, the laying thickness of the powder layer can be between 10-200μm, and the specific laying thickness is reasonably selected according to the powder particle size, equipment capacity, and the size of the printed green body. The binder can be any one of polyvinyl alcohol, polyvinyl pyrrolidone, inorganic binder, and phenolic resin.

[0037] Heating and curing: After printing, move the work box together with the graphite green body to the curing furnace for the first drying and curing. The curing temperature is 80-120°C and the curing time is 120-1440 minutes. After the first curing, move the work box to the powder cleaning table to remove excess powder on the surface and inside of the graphite green body, and then place the cleaned graphite green body back into the curing furnace for the second curing. The second curing temperature is 160-240°C and the curing time is 120-720 minutes. After curing, a high-strength graphite green body can be obtained.

[0038] The present application, a water-soluble reinforcing agent is mixed and added in graphite powder, and a mixed powder is obtained by printing by jetting a binder to obtain a green body, and the water-soluble reinforcing agent contacts the solvent in the binder, and the water-soluble reinforcing agent is dehydrated during curing and heating to play a bonding role, and plays the role of a binder to promote the adhesion of graphite powder. Compared with directly increasing the saturation of the binder, the present application introduces a reinforcing agent in the graphite powder, so that it is heated to play the role of a binder, and the problem of ink seepage is not caused, and the precision of the product is ensured while the green body strength is improved. And the reinforcing agent adopts an organic compound, and the graphite green body is in the post-processing process such as degreasing and sintering, and the organic compound will remain in the graphite product in the form of carbon under the action of a high degree, and the purity of the graphite product will not be affected.

[0039] Note: In order to improve the strength of the printed green body, the existing binder 3D printing technology generally adopts the method of increasing the saturation of the binder. Although increasing the saturation of the binder can improve the strength of the green body, it is easy to cause ink seepage problems, affecting the appearance of the printed green body or the printed product, and further affecting the product accuracy.

[0040] In order to further illustrate the advancement and practical effects of the technical solution of the present application, specific embodiments are now given to facilitate understanding.

[0041] Embodiment 1

[0042] Powder preparation: Graphite powder and reinforcing agent with a mass ratio of 95:5 are selected and placed in a sand mixing tank, and mechanical stirring is used to stir at a low speed for 9 minutes to make the two powders uniformly mixed. In this embodiment, polyvinyl pyrrolidone powder is selected as the reinforcing agent.

[0043] Printing: The prepared mixed powder is transported to the powder spreader of the 3D printer. Through the binder jet 3D printing technology, the powder spreader spreads the powder layer by layer on the work box, and the print head selectively sprays the binder layer by layer until the three-dimensional model is printed and the graphite green body is obtained. During printing, the laying thickness of the powder layer is set to 110μm, and the binder saturation is set to 70%.

[0044] Heating and curing: After printing, the work box and the graphite green body are moved to the curing furnace for the first drying and curing. The curing temperature is 100°C and the curing time is 600 minutes. After the first curing, the work box is moved to the powder cleaning table to remove excess powder on the surface and inside of the graphite green body, and then the cleaned graphite green body is placed in the curing furnace again for the second curing. The second curing temperature is 180°C and the curing time is 360 minutes. After curing, a high-strength graphite green body is obtained, and the green body tensile strength is 1.32MPa.

[0045] Embodiment 2

[0046] A method for improving the strength of 3D printed graphite green body, comprising the following steps:

[0047] Powder preparation: Graphite powder and reinforcing agent with a mass ratio of 96:4 were placed in a sand mixing tank, and mechanical stirring was used to stir at a low speed for 2 minutes to uniformly mix the two powders. In this embodiment, polyvinyl alcohol powder was selected as the reinforcing agent.

[0048] Printing: The prepared mixed powder is transported to the powder spreader of the 3D printer. Through the binder jet 3D printing technology, the powder spreader spreads the powder layer by layer on the work box, and the print head selectively sprays the binder layer by layer until the three-dimensional model is printed and the graphite green body is obtained. During printing, the laying thickness of the powder layer is set to 110μm, and the binder saturation is set to 70%.

[0049] Heating and curing: After printing, the work box and the graphite green body are moved to the curing furnace for the first drying and curing. The curing temperature is 120°C and the curing time is 600 minutes. After the first curing, the work box is moved to the powder cleaning table to remove excess powder on the surface and inside of the graphite green body, and then the cleaned graphite green body is placed in the curing furnace again for the second curing. The second curing temperature is 180°C and the curing time is 360 minutes. After curing, a high-strength graphite green body is obtained, and the green body tensile strength is 1.28MPa.

[0050] Table 1 is a comparison of the strength of graphite green bodies formed by binder jet printing before and after adding a reinforcing agent to graphite powder and after curing. Among them, the comparative example is a green body made of graphite powder with a mass ratio of 100 without adding a reinforcing agent; Example 1 and Example 2 are graphite green bodies made by adding a certain proportion of reinforcing agent to graphite powder. All three schemes use binder jet printing, and the parameters such as the thickness of the printed powder layer and the saturation of the binder are consistent. The curing temperature and curing time of the two curings are also basically the same. It can be seen from the test data detected in the table that after adding a reinforcing agent to the graphite powder, the green body strength after adding the reinforcing agent is much higher than the green body strength without adding the reinforcing agent through the same molding method and curing method.

[0051] Embodiment 3

[0052] A method for improving the strength of 3D printed graphite green body, comprising the following steps:

[0053] Powder preparation: Graphite powder and reinforcing agent with a mass ratio of 99:1 are placed in a sand mixing tank, and mechanical stirring is used to stir at a low speed for 2 minutes to uniformly mix the two powders. In this embodiment, polyvinyl pyrrolidone powder is selected as the reinforcing agent.

[0054] Printing: The prepared mixed powder is transported to the powder spreader of the 3D printer. Through the binder jet 3D printing technology, the powder spreader spreads the powder layer by layer on the work box, and the print head selectively sprays the binder layer by layer until the three-dimensional model is printed and the graphite green body is obtained. During printing, the laying thickness of the powder layer is set to 110μm, and the binder saturation is set to 70%.

[0055] Heating and curing: After printing, the work box and the graphite green body are moved to the curing furnace for the first drying and curing. The curing temperature is 80°C and the curing time is 600 minutes. After the first curing, the work box is moved to the powder cleaning table to remove excess powder on the surface and inside of the graphite green body, and then the cleaned graphite green body is placed in the curing furnace again for the second curing. The second curing temperature is 240°C and the curing time is 180 minutes. After curing, a high-strength graphite green body is obtained, and the green body tensile strength is 0.98MPa.

[0056] Table 1 is a comparison of the strength of graphite green bodies formed by binder jet printing before and after adding a reinforcing agent to graphite powder and after curing. Among them, the comparative example is a green body made of graphite powder with a mass ratio of 100 without adding a reinforcing agent; Example 1, Example 2 and Example 3 are graphite green bodies made by adding a certain proportion of reinforcing agent to graphite powder. Each scheme adopts binder jet printing, and the parameters such as the thickness of the printed powder layer and the saturation of the binder are consistent, and then cured at a certain temperature and time. It can be seen from the experimental test data that after adding a reinforcing agent to the graphite powder, the green body strength after adding the reinforcing agent is much higher than the green body strength without adding the reinforcing agent through the same molding method and curing method.

[0057] Table 1 Graphite green body strength comparison

[0058]

[0059] The experimental results in the above table show that the green body generated by adding a reinforcing agent to graphite powder in the technical solution of the present application has a significantly improved strength after heating and curing compared with that before the reinforcing agent was added. Among them, after the first curing (pre-curing), the strength of the graphite green body with the reinforcing agent added is significantly improved; and the green body strength is further increased by curing at a higher temperature. The green body prepared by the technical solution of the present application is simple to operate and low in cost.

[0060] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for improving the strength of 3D printed graphite green body, characterized in that: The following steps are involved: Powder preparation: Graphite powder and reinforcing agent are mixed and stirred in a mass ratio of 99-95:1-5 to obtain a uniform mixed powder, wherein: the reinforcing agent is a water-soluble powder; Printing and molding: The obtained powder is printed and molded by binder jet 3D printing technology to obtain a three-dimensional graphite green body; Heating and curing: The obtained three-dimensional graphite green body is heated and cured twice, and a high-strength graphite green body is obtained after the curing is completed.

2. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: In the heating and curing step, the second curing temperature is higher than the first curing temperature.

3. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: In the heating and curing step, after the first curing is completed, the three-dimensional graphite green body is cleaned of powder, and after the powder cleaning is completed, a second curing is performed.

4. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: In the heating and curing step, the temperature of the first curing is 80 to 120° C., and the time of the first curing is 120 to 1440 minutes.

5. The method for improving the strength of 3D printed graphite green body according to claim 2, characterized in that: In the heating and curing step, the temperature of the second curing is 160 to 240° C., and the curing time of the second curing is 120 to 720 minutes.

6. The method for improving the strength of 3D printed graphite green body according to any one of claims 1 to 5, characterized in that: In the heating and curing step, during the first curing, the printed three-dimensional graphite green body and the working box are placed in the curing furnace for curing; during the second curing, only the three-dimensional graphite green body is placed in the curing furnace for curing.

7. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: The enhancer is an organic compound.

8. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: The reinforcing agent is polyvinyl pyrrolidone and / or polyvinyl alcohol.

9. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: In the printing and molding step, the binder used in the binder jet printing is one of polyvinyl alcohol, polyvinyl pyrrolidone, inorganic binder, and phenolic resin.

10. The method for improving the strength of 3D printed graphite green body according to claim 1, characterized in that: In the powder preparation step, the graphite powder is mixed with the reinforcing agent and then stirred at a low speed for 1 to 10 minutes.

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