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Ceramic Sintering Process

XYC Advanced ceramic Manufacture Process


1)Isostatic pressed Process:

Isostatic pressed is to place powder to be pressed in a high-pressure container (cold isostatic press), and use the incompressible properties of the liquid medium and the properties of uniform pressure transmission to uniformly pressurize the sample from all directions. When the liquid medium When the pressure pump is injected into the pressure vessel, according to the principle of fluid mechanics, the pressure is constant and uniformly transmitted to all directions. At this time, the pressure on the powder in the high-pressure container is uniform and consistent in all directions. The method of forming a dense body from barren powder through the above method is called isostatic pressing.


Advantages:  high density, small sintering shrinkage, low mold cost, high production efficiency, and can form slender and large-sized products. has relatively low requirements on the powder, and the powder can be granulated, but the vibration should be ensured when filling the mold.

Disadvantages: The precision of molded products is low, and post processing is required for products that are too complicated.


Classification:

           (1) Cold isostatic pressing  “CIP ISO pressed ” (forming process): press by medium oil or water in room temperature

           (2) Warm isostatic pressing  “WIP ISO pressed ”(forming process): pressurized medium oil, temperature 50-150°C

           (3) Hot isostatic pressing “HIP ISO pressed ”(sintering process):  pressurized medium is inert gas, argon, or nitrogen. The temperature is above 1000°C. Put the alloy powder or ceramic powder into the high-temperature resistant mold, and the high-density product can also be obtained after hot isostatic pressing


CIP Process


CIP Machine

High Presuresschamber

pressurized medium

Cold isostatic pressing (water)

Warm isostatic pressing (oil)

Hot isostatic pressing (gas)


Cold isostatic pressing generally adopts flexible molds, such as rubber barrels or cartons used in the above-mentioned product preparation process. Therefore, the shape of the product after isostatic pressing is irregular, and the accuracy of the product cannot be guaranteed. In addition, isostatic pressing is suitable for products with relatively simple CIP shapes, such as tubular products, rod products, plate products, etc., which belong to cold isostatic pressing. Several common shape products.

The green body after forming needs to leave more margin,

After pre-processing to get the shape of the desired product, it enters the sintering stage。



2)Dry Pressing Process

The advantages of dry pressing are high production efficiency, low labor, low scrap rate, short production cycle, less in post-processing of products, and suitable for mass industrial production;

 the disadvantage is that the shape of the formed product is relatively limited, and the cost of the mold is high. , the internal compactness of the green body is inconsistent, and the uniformity of the structure is relatively poor. Most of the dry-pressed products need to go through cold isostatic pressing again.

Powder requirements: Dry pressing has high requirements for powder, and generally needs to granulate the powder.

(1) The powder needs good fluidity, and evenly distributed particle size can ensure the uniformity of powder filling and promote the consistency of pressure and thickness during molding.

(2) Appropriate water content (0.5%-2%) can ensure compactness during molding.

(3) Reasonable size and evenly distributed particle size (0.05-0.12mm is the best). The particle size is too small, it is difficult to shape, and the pre-processing is brittle. If the particle size is too large, the molding compactness is poor, resulting in defects such as pores.

(4) For some powders that are not suitable for molding, the method used is to spray a certain amount of alcohol to soften the internal binder and increase the molding strength.


Dry Pressing Process


For products with high precision requirements, or large deformation during sintering (such as the above-mentioned plates), it is necessary to leave a certain machining allowance for post-processing

Especially after the sintering of silicon nitride products, there will be a layer of oxide layer on the surface, which is difficult to meet the product requirements, and it is necessary to carry out finishing work. For low precision and uncomplicated shapes, especially for alumina zirconia products, the precision of dry pressing can be controlled within ±0.1mm



3)Injection molding

Injection molding is to mix ceramic powder with an organic binder, and then inject powder into a metal mold at 130-300 degrees through an injection molding machine. After cooling, the binder is solidified and the blank is taken out.





XYC Advanced ceramic sintering process

(1)Pressureless sintering: under the condition of no external pressure, the green body with a certain shape is placed under certain temperature and atmosphere conditions, and undergoes physical and chemical processes to become a compact, stable volume, and a consolidated dense block with certain properties.

The method used for silicon carbide sintering.

(2)Atmospheric pressure sintering: Atmospheric pressure sintering means that materials are sintered under atmospheric pressure without pressurization, which is the most commonly used sintering method at present. It includes normal pressure sintering under air conditions and normal pressure sintering under certain special gas atmosphere conditions

The most commonly used sintering method for oxide ceramics represented by alumina ceramics and zirconia ceramics.

(3)Gas pressure sintering: Gas pressure sintering (GPS) refers to the application of a certain gas pressure, usually N2, in the range of 1 to 10 MPa during the high temperature sintering process of ceramics, so as to inhibit the decomposition and weight loss of ceramic materials at high temperatures, thereby improving the sintering process. Temperature, to a certain extent, promotes the densification of materials and obtains high-density ceramic products.

The most widely used sintering method for silicon nitride.