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Advanced Ceramic Dry Compression Forming Process and Its Advantages and Disadvantages

Press forming. Its characteristic is that the binder content is low, only a few percent (usually 7% to 8%), and can be directly calcined without drying. The shrinkage of the body is small, and automation can be achieved. Dry pressing involves adding a small amount of binder to the powder and granulating according to the above granulation method. Then, the granular powder is placed in the steel mold and pressed on a press. A blank shape. Suitable for pressing products with a height of 0.3-60mm and a diameter of 5-500mm.

Dry pressing process principle Dry pressing

The essence is that under the action of external forces, particles approach each other in the mold, and through internal friction, the particles are firmly connected and maintain a certain shape. This internal friction is applied to the outer adhesive layer of adjacent particles. In any case, when particles come into contact, R will be greater than the scale:, R. Corresponds to the radius or porosity of micropores, as micropore pressure brings particles closer together, also known as “adhesion force”.

1. Spherical contact; 2. Pointed contact

Dry pressed blocks can be considered as three-phase dispersions composed of a liquid phase (adhesive) layer, air, and billet. If the particle size and granulation of the billet are appropriate, the stacking density is relatively high, and the air content can be greatly reduced. As the pressure increases, the billets will change shape, slide against each other, the gaps will be filled, and the contacts will gradually increase and be tightly connected to each other. Due to the closer proximity between particles, the interaction between colloidal molecules and particles is enhanced, resulting in a certain mechanical strength of the green body. If the grading of the raw material particles is appropriate, the binder is used correctly, and the pressure method is reasonable, the dry pressing method can obtain a relatively ideal green density.

Pressurization method and pressure distribution:

In dry compression molding, there are two types of compression methods: simple compression and double-sided compression. Due to different pressurization methods, the friction, transmission, and distribution pressure between the mold and the powder are different, resulting in different densities of the green billet.

Unilateral pressurization:

Only pressurized by the plug. At this point, a pressure gradient is generated due to the frictional resistance between the powder and the mold wall. The lower the pressure, the lower the pressure distribution. D is the diameter. From the figure, it can be seen that the larger the L/D value, the greater the pressure difference inside the billet. The density of the pressed solid is highest at the upper and near mold walls, while the density is lowest at the lower and near mold walls and the center part. Pressure distribution of single sided pressure block: low mode, L/D-0.45; High mode, L/D=1.75.

Double sided compression and single sided compression:

Compared to double-sided compression, it involves simultaneously applying pressure up and down. At this point, there is no change in various frictional resistance, but the effective transmission distance of the pressure gradient is shorter, and the energy loss caused by friction is also reduced. In this case, the density of the billet is relatively more uniform. From Figures 1-2-16, it can be seen that the smaller the product height, i.e. the smaller the L/D, the better the density uniformity. Pressing on both sides results in low density at the center of the billet. Whether it is single sided or double sided pressure, if the mold is coated with lubricant, the pressure gradient will decrease.

Pressurization speed and holding time:

Practice has shown that the pressing speed and holding time have a significant impact on the performance of the blank, which is closely related to the transmission of pressure and the elimination of gas. If the pressure is applied too quickly, the residence time is too short and the gas is not easily discharged. Similarly, when the pressure has not yet reached the required depth and the external force has been removed, it is clearly difficult to obtain satisfactory green billet quality. Of course, if the pressurization speed is too slow and the holding time is too long, the production efficiency will decrease, and it is not necessary. Therefore, the pressing speed and holding time should be adjusted based on the size, thickness, and shape of the billet. Generally, for products with large dimensions and thick walls, with high height and complex shapes, the pressure should be slow, medium to fast, and later slow, and there should be a certain holding time, which is conducive to gas removal and pressure transmission. If the pressure is high enough, the dwell time can be shorter. Otherwise, the pressurization speed is not good, and no gas is discharged, which may cause bubbles, interlayers, cracks, etc. For small-sized slabs, the requirements in this regard are not strict, and the pressing speed can be appropriately increased to improve production efficiency. The stay time can be shorter. Otherwise, the pressurization speed is not good, and no gas is discharged, which may cause bubbles, interlayers, cracks, etc. For small-sized slabs, the requirements in this regard are not strict, and the pressing speed can be appropriately increased to improve production efficiency. The stay time can be shorter. Otherwise, the pressurization speed is not good, and no gas is discharged, which may cause bubbles, interlayers, cracks, etc. For small-sized slabs, the requirements in this regard are not strict, and the pressing speed can be appropriately increased to improve production efficiency.

Advantages and disadvantages of dry compression molding:

Dry pressing forming is a commonly used forming method in the production of special ceramics, due to its simple process, convenient operation, short cycle, high efficiency, and convenience for automated production. In addition, the blank has high density, accurate size, low shrinkage rate, high mechanical strength, and good electrical performance. There are difficulties in producing large billets. One is mold wear, complex processing, and high cost. Secondly, pressure can only be applied up and down, with uneven pressure distribution, density, shrinkage, and cracking. Stratification and other phenomena. With the development of modern forming methods, this drawback has been overcome by isostatic pressing.

KSINO GROUP is a company that specializes in technology research and development, precision manufacturing, and global sales of advanced ceramics and other new materials, as well as providing a complete set of customized application solutions. Our main products include zirconia, toughened zirconia, alumina, silicon nitride, silicon carbide ceramics, etc., which are resistant to ultra-high temperatures, high hardness, acid and alkali corrosion, non magnetic and non-conductive, and have special photochromic effects. Through continuous technological improvement and independent innovation research and development, the company has a wide customer base in precision machinery, photovoltaic energy, new energy, automotive, chemical, medical, semiconductor and other fields.