The purpose of using a lubricant is to make the pressure uniform during pressing and to knockout easily after pressing. The lubricant can be mixed in powder or painted on the die wall. There are several different kinds of friction in pressing forming, and they are all affected by lubricant. 

The type of lubricant and the quantity shall be carefully chosen. The presence of lubricant in the powder will affect the flow of the powder and its density, as well as the mixing of powders. Friction in powders is affected by powder type, powder size, powder shape, and ambient medium (such as gas atmosphere) and temperature. The lubricant is burned at the initial stage of sintering. There are two kinds of lubricants: solid lubricant and liquid lubricant.

 

Selection principle:

1) have better lubricity and have certain sticky substance.

2) does not occur chemical reactions with the powder and other harmful effects.

3) does not affect the performance and appearance of sinter.

4) it is easy to be excluded in the process of pre burning or sintering, without causing environmental pollution.

 

1.The lubricant mixed in the powder:

stearic acid and metallic stearates, such as zinc stearate, lithium stearate, calcium stearate, barium stearate, aluminum stearate, liquid paraffin, MoS2 and graphite. The mixture is usually added to the mixture in the form of a fine powder through a biconical mixer. The amount of adding powder is 0.5%-1.0% of the weight of the powder, determined by the shape of the pressing blank and the particle size of the powder: if the powder is fine and the shape of the pressing blank is complex, the amount of the lubricant added is larger.

Most lubricants will reduce the density of the compacts because their density is lower than the density of the mixture. At the same time, lubricant encircle particles that impede the contact of solid particles also results in a reduction in the density of compacts.

 

2.The lubricant painted on the mould

The lubricant painted on the mould can reduce the external friction during pressing. Such lubricants are acetone, benzene, glycerol, oleic acid, and trichloroethane.