Pressure filtration molding method for advanced ceramics

1. Process principle of pressure filtration molding

Pressure filtration molding technology is a ceramic molding technology that has developed and received attention in recent decades. Pressure filtration molding is developed through pressurization on the basis of grouting molding. Water is no longer removed through capillary forces, but is driven by pressure. This method of dehydration has a faster rate, thereby improving production efficiency. The main principle is to make the slurry with solid ceramic particles dispersed in the liquid medium under certain conditions enter the model cavity through the slurry pipeline under the action of external pressure. And by filtering out a portion of the liquid medium through a porous filter layer, the ceramic particles are tightly arranged and solidified, forming a ceramic body with a certain shape. The porous mold material can be made of porous stainless steel, porous plastic, and ceramic lamp materials.

2. Process and application of pressure filtration molding

(1) The process of pressure filtration molding

From the perspective of its process principle, pressure filtration molding is very similar to pressure injection molding, and in a broad sense, it can also be seen as pressure injection molding. However, there are still certain differences between the two: firstly, due to the use of a very thin porous filter layer in pressure filtration molding, the requirements for the content of the slurry medium are not as strict as those of pressure grouting. This can adjust the particle parameters and rheological properties of the slurry within a large range, making it easier to form high-performance parts; Secondly, from the perspective of forming pressure, pressure forming can be carried out within a larger pressure range; In addition, pressure filtration molding can achieve an overall uniform body structure by adjusting the model structure and permeability coefficient of complex shaped components in different parts of the molded part, and utilizing mold materials with different curing rates. Therefore, pressure filtration molding is more conducive to forming complex shaped parts.

(2) Application of pressure filtration molding process

Pressure filtration molding combines the characteristics of dry pressing molding and grouting plowing technology. Its ultimate advantage is the absence of macro defects and the ability to achieve high molding density. Therefore, pressure filtration molding is particularly suitable for the formation of ultrafine powders.

3 The main defects of pressure filtration molding

The pressure filtration molding process is mainly affected by the following factors: pressure drop in the green body; The viscosity of the liquid medium; The surface area of the billet; The distribution of pores in the green body; Pressure filtration molding mold. On the one hand, the pressure has an effect on the particles in the Compressibility green layer, making them more closely arranged; On the other hand, pressure can reduce and eliminate the density gradient caused by the geometric shape of the workpiece and the advancing direction of the solidification surface of the blank layer, thereby improving the overall uniformity of the workpiece.

4 Mechanical equipment for pressure filtration molding

According to the traditional concept, the grouting process is the process of dehydrating the slurry into a billet through a gypsum mold. The water migration during this process is determined by the water absorption capacity of the gypsum mold, the slurry performance, and the resistance of the billet layer to water migration. Researchers have given it a new concept of pressure grouting, which transforms the grouting process into a pressure filtration process.

The filter press used in the filter forming process is mainly composed of a filter press part, a filter plate pressing part, a support part, a control part, and an auxiliary part. That is to say, the filter press is generally composed of a frame, a pressing mechanism, a filtering mechanism, and auxiliary parts.

(1) Rack

The frame is the basic component of the filter press, with thrust plates and compression heads at both ends. The two sides are connected by large beams, which support the filter plate, filter frame, and compression plate. To meet hygiene needs, the rack needs to be wrapped in stainless steel.

① Thrust plate

It is connected to the support to seat one end of the filter press on the foundation. The thrust plate of the box type filter press has a feeding hole in the middle, and there are four holes in the four corners. The holes in the upper two corners are for the inlet of washing liquid or compressed gas, and the lower two corners are for the outlet (under flow structure or filtrate outlet).

② Compression plate

Used to compress the filter plate and frame, with rollers on both sides used to support the compression plate rolling on the track of the main beam.

③ Crossbeam

It is a load-bearing component that can be selected from rigid polyvinyl chloride, polypropylene, or stainless steel according to the anti-corrosion requirements of the usage environment

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