What are the key points of profile mold design?

The key points of profile mold design are as follows:

(1)The mold cavity should be streamlined as much as possible,and the cylindrical section of the extruder should gradually change into the product shape section.The first is to avoid dead corners and stagnant materials in the mold,and the second is to make the materials in the mold deform evenly and orderly.

(2)Reasonably design the length of the gap and the straight section to make the flow rate of molten material consistent when exporting the mold.

(3)The determination of die size should consider the deformation,expansion,contraction and other factors when the material is exported.

Determination of the length L of the straight section of the die:in order to adjust the flow rate of molten material in the straight section and make it into the shape of the product,l is proportional to the gap between the die seam,which is determined by factors such as resin type and extrusion speed.Generally,it is expressed in the form of ts/t(TS is the thickness of the product)and l/t.

When extruding profiles with large thickness difference,the straight section of the thick part should be as long as possible,and the thin part should be shorter,so as to achieve the purpose of roughly uniform extrusion pressure distribution.The flow rate of the slit of the die is directly proportional to the cubic power of the slit gap.For example,when the slit of the profile die has both a 2mm thick part and a 4mm thick part,the length of the 4mm thick forming surface is 8 times that of the 2mm part.

Therefore,the uneven discharge can be adjusted by reasonably designing the length of the straight section of the die.

Relationship between die and product shape:one of the most difficult reasons for die design is that the shape of die is different from that of product.To extrude a square as shown in Figure 3-11,the mold must be designed into the shape next to it,otherwise the section of the extruded product is not square.Because the material flow speed in the mold is not uniform,the middle material flow speed is fast,and the material flow near the mold wall is slow.

When determining the die size,in addition to the above deformation factors,we should also consider the expansion of the material outlet die,that is,the size of the melt from the die gap is larger than the die gap.The main reason is that because the melt is compressed in the mold,the pressure behind the outlet mold disappears and expands,and the velocity distribution after the outlet disappears,and the molecules rearrange disorderly and expand.

It must be considered when designing the mold.The expansion is related to the temperature,pressure and other factors of the resin.

Key words:profile mold

Article source:http://www.wx-mould.cn