Ceramic hot die casting (hot injection molding)is also a grouting method, but it is different from other grouting method. It makes the use of paraffin's heat flow characteristics,the paraffin will be mixed with the raw powder together and formed in the metal mould under the pressure.the raw embryo can maintain the shape after the temperature calm down.It is widely used in special ceramics.

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1. Preparation of paraffin slurry

This process is to join the embryo into the paraffin-based adhesive made of wax for the molding.

Take paraffin (according to the ratio) a certain amount (usually 12.5% ~ 13.5%) after heating and melting into a wax liquid, At the same time drying Banliao(the name we called) in the oven, the moisture content should be not more than 0.2%,This is because when the powder containing water is greater than 1%, the water will hinder the material and paraffin completely infiltration, viscosity increases, so it is difficult to shape.

In addition, when heated, water will form a small bubble dispersed in the slurry, so that the sintered products to form a closed pores, performance will get a deterioration.

when make the wax slurry, we add a small amount of surfactant in the powder (generally 0.4% ~ 0.8%, such as beeswax etc.),it can reduce the content of paraffin wax and improve the forming performance.

There are two specific mixing methods: one is to melt the paraffin heating, and then pour the powder, while heating, stirring side; the other is the powder heated to paraffin solution, while adding the side while stirring. Preparation of wax can be carried out in the rotary kiln,The slurry is then poured into a container, made of wax after solidification in preparation for molding.

the properties of slurry are as follows:

(1) stability

The stability is that when the slurry is heated for a long time without stirring,it is still uniform and non stratification.Usually expressed in terms of stability.

(2) castability

Castability refers to the ability of the slurry full filled into the mold cavity and maintain the desired shape. It is a measure of slurry viscosity and solidification rate of the composite indicators. Generally speaking, if the fineness of the powder is suitable, the powder is dried and the adhesive (paraffin and surface active agent) is suitable, the casting property of the slurry is good.

(3) shrinkage

The rate of shrinkage is that when the wax slurry is cooled and solidified into a solid state by a molten liquid state, there is volume shrinkage. The shrinkage is related to the expansion coefficient of powder and paraffin, the particle size of the powder, the grain shape, the gradation, the ratio of the binder in the wax slurry and the molding temperature. The volume shrinkage of the slurry in the mold cavity is called cold contraction, generally about l%.

2. The working principle of hot die casting machine

At present, the production of the use of hot die casting machine, there are two types, one is manual, one is automatic, but the basic principle of the same. The working principle is that the prepared slurry is placed in a hot die-casting machine barrel and heated to a certain temperature to melt. Under the driving of the compressed air, the slurry in the tube is pressed into the mold cavity through the suction nozzle, The shape and size to maintain a certain time, remove the pressure, the slurry in the mold cavity cooling molding, and then stripping, remove the green body, and some can also be processed, or turning, or drilling and so on.

3. High temperature row of wax

In the process of hot die casting, the embryo must be treated by wax removal before firing. Otherwise, due to the melting of wax at high temperature loss, evaporation, combustion, the embryo will lose the bond and disintegration, can not maintain its shape. Wax removal is to embed the embryo into loose and inert powder which is a protective powder.and it is also called adsorbent (adsor-bent). It is stable at high temperatures, and difficult to bond with the embryo, the general use of calcined industrial A12O3 powder. In the heating process, although the wax will melt, diffusion, but there are adsorbent support the embryo structure. When the temperature continues to rise, the wax is volatile, the combustion is complete, and there is a certain sintering between the powder. At this point, the embryo structure and the adsorbent neither reacts nor sticks together, and the embryo has a certain strength. Usually row wax temperature is about 900 ~ 1100 ℃, depending on the nature of the embryo. If the temperature is too low, there is no definite sintering between the powder, does not have a certain mechanical strength, the loose embryo can not continue the following process; if the temperature is too high, until to the complete sintering, there will be a serious bond and hard to clean the surface of the body. After the wax removal, the surface of the embryo should be cleaned up and then sintered.

4. The advantages and disadvantages of hot die casting

Hot die casting process is suitable for the production of small and medium sized products with complex shape and high precision. The utility model has the advantages of simple equipment, convenient operation, low labor intensity, high production efficiency, small die wear and long service life. But the hot die casting also has shortcomings, such as the process is more complex, large energy consumption (need to be fired several times), a long period of time,but it is not suitable for large and long thin wall products, because it is not easy to fill the mould cavity.