A cold isostatic pressing die for ceramic green body forming

Abstract

The utility model relates to a kind of easily demoulding cold isostatic pressing mould for ceramic blank forming, belong to the technical field of ceramic forming.The mould includes rigid base and soft outer mould, the soft outer mould is covered on the rigid base top, and the mould cavity for filling powder is formed between the two.The rigid base is made of metal, and its spherical outer surface in contact with ceramic blank is distributed with multiple spherical crown micro-protrusions.The structure is broken by discrete point contact The vacuum adsorption and mechanical interlocking between blank and mould, thereby effectively solve the demoulding difficulty and rupture problem caused by blank sticking base under high pressure.

Description

Technical Field

[0001] This utility model belongs to the field of ceramic forming technology, and relates to an easy-to-demold cold isostatic pressing mold for forming ceramic blanks. Background Technology

[0002] In the preparation of advanced ceramic materials, cold isostatic pressing (CIP) technology is widely used because it can produce a uniform density distribution and good isotropy within the green body. This technology involves placing ceramic powder encapsulated in a mold in a high-pressure liquid medium, and using the isotropic pressure of the liquid to press the powder in all directions, thereby obtaining a high-density ceramic green body.

[0003] To obtain complex green body shapes, molds are typically made of hard materials such as metal. However, in actual production, especially after high-pressure (usually above 100 MPa) molding of nanoparticles, severe adhesion occurs between the ceramic green body and the molding mold, making demolding extremely difficult. This is mainly because under extremely high isostatic pressure, the mold wall and ceramic powder particles are compressed and interlocked, resulting in a very large contact area and a near-vacuum, tight fit. Simultaneously, the powder particles undergo plastic deformation and flow under high pressure, filling any microscopic depressions on the mold surface, further increasing the effective contact area and microscopic mechanical interlocking. Existing demolding methods usually rely on manual or simple mechanical force for peeling, which easily leads to cracks, gaps, or overall breakage of the ceramic green body, causing product scrap, severely impacting production efficiency and product qualification rate, and increasing production costs.

[0004] Patent CN220262113U proposes a cold isostatic pressing product casing mold made entirely of rubber. Due to the mold's softness and high elasticity, it is less prone to demolding adhesion problems. However, this type of mold is easily deformed during the cold isostatic pressing process, making it unsuitable for preparing ceramic blanks of specific shapes. Existing hard mold demolding technologies typically use release agents to assist demolding. Patent CN114773039A proposes a spinel spherical isostatic pressing method that uses a lubricant spraying method to assist demolding. However, under high pressure, the release lubricant may be squeezed out or penetrate into the blank, resulting in poor demolding effect and potentially introducing impurities into the spherical blank. Furthermore, the initial particle size of spinel ceramic powder is usually in the submicron scale, with generally poor adhesion; this method may struggle to solve the demolding problem of powders in the tens of nanometer scale.

[0005] Therefore, how to fundamentally solve the problem of adhesion between ceramic blanks and hard molds under high pressure while ensuring the shape accuracy of the blanks has become a technical bottleneck that urgently needs to be overcome in this field. Utility Model Content

[0006] The purpose of this invention is to provide an easy-to-demold cold isostatic pressing mold for ceramic green body forming. It aims to ensure the shape accuracy of the green body while fundamentally overcoming the problem of adhesion between the green body and the metal mold under high pressure, thereby achieving complete and damage-free demolding of the green body. The solution of this invention is as follows: A cold isostatic pressing mold for easy demolding of ceramic blanks includes a rigid base and a flexible outer mold. In use, the flexible outer mold is placed over the rigid base, and a mold cavity for filling the blank powder is formed between the two. The rigid base has an integrally formed central protrusion and an outer ring bearing portion. The central protrusion is an upward-protruding hemispherical structure, and its spherical outer surface is distributed with multiple crown-shaped micro-protrusions for contacting the inner surface of the blank. The flexible outer mold has an integrally formed central protrusion and an outer ring support portion. The central protrusion is an upward-protruding double-opening spherical shell structure with an extended neck at the opening edge. The outer ring support portion is sleeved and fixed to the outer ring support portion of the rigid base.

[0007] Furthermore, the rigid base is made of metal.

[0008] Furthermore, the flexible outer mold is made of polyurethane rubber.

[0009] Furthermore, the radius of the spherical micro-protrusion is 2-5mm, and its top protrudes 1-3mm from the spherical outer surface of the central protrusion of the rigid base.

[0010] Furthermore, the spherical micro-protrusions are arranged in a spherical coordinate array on the spherical outer surface of the central protrusion of the base. Specifically, in both the polar angle θ and azimuth angle φ directions, the micro-protrusions are distributed in a grid pattern at fixed angular intervals. Their distribution follows this pattern: along the polar angle θ direction, one micro-protrusion is provided every 5° to 30°; along the azimuth angle φ direction, one micro-protrusion is provided every 10° to 60°.

[0011] Compared with the prior art, the technical effects of this utility model are as follows: This invention designs a spherical crown-shaped micro-protrusion array on the contact surface between the mold and the blank, which disrupts the tight contact between the blank and the mold through discrete point contact. This allows the two to be effectively separated under external force after high-pressure molding, significantly improving the blank's demolding qualification rate.

[0012] Unlike existing techniques that passively apply release agents or rely solely on the elasticity of the mold material, the micro-protrusion structure acts as a localized micro-stress regulator during cold isostatic pressing. It actively releases and redistributes concentrated stress within the green body, promoting uniform flow and alignment of powder particles. This not only aids in demolding but also results in a green body with a more uniform internal density distribution. Simultaneously, the rigid metal base ensures the mold maintains its precise pre-set shape under high pressure, effectively preventing macroscopic deformation of the green body. Meanwhile, the flexible polyurethane rubber outer mold adheres closely to the green body's surface during pressing, ensuring isotropic and uniform shrinkage and preventing residual porosity caused by incomplete shrinkage. This effectively guarantees the subsequent sintering of high-quality ceramic products with stable dimensions and consistent performance.

[0013] Furthermore, this mold structure requires no additional complex equipment or changes to the existing cold isostatic pressing process, exhibiting excellent process compatibility. Moreover, this design concept is not limited by the type of ceramic material, can be quickly extended to molds with different green body shapes, and is suitable for mass production. Attached Figure Description

[0014] Figure 1 Cross-sectional view of the overall structure of a cold isostatic pressing mold for easy demolding of ceramic blanks; Figure 2 A half-sectional schematic diagram of the overall structure of an easy-to-demold cold isostatic pressing mold for ceramic blank forming; Figure 3 This is a schematic diagram of the micro-protrusion surface structure; Figure 4 This is the ceramic blank after cooling in Example 1; Figure 5 This is a ceramic blank after cooling, as shown in Comparative Example 1. in, Figure 3 middle: R1 represents the outer radius of the hemispherical structure of the central protrusion (1a) of the rigid base; R2 represents the radius of the spherical micro-protrusion (1c); H represents the height at which the top of the crown-shaped micro-protrusion (1c) protrudes from the spherical outer surface of the central protrusion (1a) of the rigid base. Detailed Implementation

[0015] The specific embodiments of this utility model will now be described in detail with reference to the accompanying drawings. It should be noted that the basic structure of the molds described in the following embodiments is similar to... Figures 1 to 3 Consistent with what is shown.

[0016] Example 1 This embodiment provides an easy-to-demold cold isostatic pressing mold for forming ceramic green bodies, the structure of which can be referred to as follows. Figure 1(Overall structural cross-sectional view) and Figure 2 (Half-sectional schematic diagram). The rigid base 1 has an integrally formed central protrusion 1a and an outer annular bearing portion 1b. The outer radius of the central protrusion 1a is 50cm, and it is an upwardly protruding hemispherical structure. Figure 3 (Schematic diagram of the micro-protrusion surface structure) As shown, a spherical micro-protrusion 1c is provided on the spherical outer surface of the central protrusion 1a of the rigid base. The radius of the spherical micro-protrusion 1c is 4mm, and its top protrudes 1mm from the spherical outer surface of the central protrusion 1a of the rigid base. The spherical micro-protrusion 1c is arranged in a spherical coordinate array, with one every 10° in the polar angle θ direction and one every 30° in the azimuth angle φ direction.

[0017] The flexible outer mold 2 has an integrally formed central protrusion 2a and an outer annular support portion 2b. The inner radius of the central protrusion 2a is 60cm. The outer annular support portion 2b is fitted and fixed onto the outer annular support portion 1b of the rigid base to form a mold cavity. Powder is poured into the mold cavity through the opening at the top of the flexible outer mold 2, and the mold is vibrated repeatedly to fill the cavity with powder. The entire mold is then vacuum-sealed and subjected to 200MPa cold isostatic pressing. After cold isostatic pressing, the plastic bag is removed, the flexible outer mold 2 is removed, and the ceramic blank is removed from the rigid base 1. The blank is intact and without cracks, and the resulting blank product is as follows. Figure 4 As shown.

[0018] Example 2 The mold structure in this embodiment is the same as that in Embodiment 1 (see reference). Figures 1 to 3 The differences lie in the following parameters: the outer radius of the central protrusion 1a of the rigid base is 40cm. The radius of the spherical micro-protrusion 1c is 2mm, and its top protrudes 1.5mm from the spherical outer surface of the central protrusion 1a. The spherical micro-protrusions 1c are arranged such that one is placed every 5° in the polar angle θ direction and every 10° in the azimuth angle φ direction. The inner radius of the central protrusion 2a of the flexible outer mold is 45cm.

[0019] The flexible outer mold 2b is fitted and fixed onto the rigid base 1b, forming a mold cavity. Powder is poured into the mold cavity through the opening at the top of the flexible outer mold 2, and the mold is vibrated repeatedly to fill the cavity with powder. The entire mold is then vacuum-sealed and subjected to 200MPa cold isostatic pressing. After cold pressing, the sealing bag is removed, the flexible outer mold 2 is removed, and the ceramic blank is removed from the rigid base 1. The blank is intact and without cracks.

[0020] Example 3 The mold structure in this embodiment is the same as that in Embodiment 1 (see reference). Figures 1 to 3The difference lies in the following parameters: the outer radius of the central protrusion 1a of the rigid base is 60cm. The radius of the spherical micro-protrusion 1c is 5mm, and its top protrudes 3mm from the spherical outer surface of the central protrusion 1a. The arrangement of the spherical micro-protrusions 1c is as follows: one is set every 30° in the polar angle θ direction and every 60° in the azimuth angle φ direction. The inner radius of the central protrusion 2a of the flexible outer mold is 60cm.

[0021] The flexible outer mold 2b is fitted and fixed onto the rigid base 1b, forming a mold cavity. Powder is poured into the mold cavity through the opening at the top of the flexible outer mold 2, and the mold is vibrated repeatedly to fill the cavity with powder. The entire mold is then vacuum-sealed and subjected to 200MPa cold isostatic pressing. After cold pressing, the sealing bag is removed, the flexible outer mold 2 is removed, and the ceramic blank is removed from the rigid base 1. The blank is intact and without cracks.

[0022] Comparative Example 1 The difference between this comparative example and Example 1 is that the spherical outer surface of the central protrusion 1a of the rigid base is a smooth surface, without any spherical crown-shaped micro-protrusions (the overall assembly structure of the mold can be referred to...). Figure 1 and Figure 2 However, the central protrusion 1a of the rigid base does not have... Figure 3 (The micro-protrusion features shown). The outer radius of the central protrusion 1a of the rigid base is 50cm, and the inner radius of the central protrusion 2a of the flexible outer mold is 60cm.

[0023] The flexible outer mold's outer annular support portion 2b is fitted and fixed onto the rigid base's outer annular support portion 1b, forming a mold cavity. Powder is poured into the mold cavity through the opening at the top of the flexible outer mold 2, and the mold is repeatedly vibrated to fill the cavity with powder. The entire mold is then vacuum-sealed and subjected to 200MPa cold isostatic pressing. After cold pressing, the sealing bag is removed, the flexible outer mold 2 is removed, and the ceramic blank is removed from the rigid base 1. The edges of the blank adhered severely to the base, causing cracking during demolding, as shown below. Figure 5 As shown.

Claims

1. A cold isostatic pressing mold for easy demolding of ceramic blanks, characterized in that, It includes a rigid base (1) and a flexible outer mold (2). When in use, the flexible outer mold (2) is placed over the rigid base (1), and a mold cavity for filling the blank powder (3) is formed between the two. The rigid base (1) has an integrally formed rigid base central protrusion (1a) and a rigid base peripheral annular bearing portion (1b). The rigid base central protrusion (1a) is an upward protruding hemispherical structure, and its spherical outer surface is distributed with multiple crown-shaped micro-protrusions (1c) for contacting the inner surface of the blank. The flexible outer mold (2) has an integrally formed central protrusion (2a) and an outer ring support portion (2b). The central protrusion (2a) is an upwardly protruding double-opening spherical shell structure with an extended neck (2c) formed at the opening edge. The outer ring support portion (2b) is sleeved and fixed on the outer ring support portion (1b) of the rigid base.

2. A cold isostatic pressing mold for ceramic green forming according to claim 1, wherein The rigid base (1) is made of metal; the flexible outer mold (2) is made of polyurethane rubber.

3. A cold isostatic pressing mold for ceramic green forming according to claim 1, wherein The radius of the spherical micro-protrusion (1c) is 2-5mm, and its top protrudes 1-3mm from the spherical outer surface of the central protrusion (1a) of the rigid base.

4. A cold isostatic pressing mold for ceramic green forming according to claim 1, wherein The spherical micro-protrusions (1c) are arranged in a spherical coordinate array on the spherical outer surface of the central protrusion (1a) of the rigid base. Along the polar angle θ, one spherical micro-protrusion (1c) is set every 5° to 30°; along the azimuth angle φ, one spherical micro-protrusion (1c) is set every 10° to 60°.

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