several PE PVC PIPES Head die moulds in common use - Qingdao Shunlida Plastic Machinery Co., Ltd

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several PE PVC PIPES Head die moulds in common use

Introduction to several Head die moulds in common use

In the current pipes market, PE pipes are using more than PVC pipes. In the production process and current or future projects, it is very necessary to know well of the head die moulds parts of PE pipes. Now two kinds of extrusion head die moulds types which are commonly used are basket type die moulds and spiral mandrel type head die moulds . The two kinds of mouldes are summarized respectively for your reference.

In the pipes extrusion lines , for PE , PVC pipes lines, the head die moulds are very important for them. Their uses are to make the liquid melts from the extruders go through the sections of head dies unifromly .The moulds of pipes are corresponding with the requirements of extrusion products. Which play a decisive role in the working effeciencty and economy of the whole production line .Two basic requirements for head die moulds are :

1.The moulds must suit for the used product material.

2.The moulds must be designed according to the extrusion capacity and the section dimension of pipes strictly.

Ⅰ.Polyolefin die mould

For the polyolefin extrusion, from the development of spider mould to the later spiral type or basket type head die moulds , the purposes are to Eliminate the parting line (joint line)caused by the die head support (holder)as soon as possible. So the material into the haed die is well mixed and the melts are more uniform.

1.the spider die moulds

Shunt (parting)part of die head is scaffolding. The parting line which produces small diamter pipes is cross frame, Die head of large caliber pipe is mostly 6 bar or 8 ribs .The biggest disadvantage is if the pressure parts in front of it are too small , (the joint lines) The confluence line sometimes elimination is not very good. There must be a sufficiently high pressure to make the separation material fusion again. This requires relatively high strength structure, The overall quality of die head is very high . The kind of head die is often used for extrusion PVC.

2.the spider die moulds with the broken plate

The simplest method is a broken plate is placed after the bracket ,the several material flows caused by the bracket are divided into more and smaller material flows , Mechanical stress goes forward from the bracket part, the parting lines are mostly eliminated by the more and smaller material flows. The kind of head die is more used in the production of HDPE , small pipes diameter. Now the kind of head die has been used very little .

3.Spiral mandrel(corerod) head die mould and braket type head die mould

The two kinds of head die mould has involved the elimination of paring lines very well. The core of spiral mandrel head die mould is spiral mandrel. The core of basket type head die mould is tubular with many holes , also be called ""network overlap".The structure and working principle are described separately.

Ⅱ. The structure of spiral mandrel head die moulds

The spiral mandrel head die moulds are also called "spiral fluid head moulds". The melted material into the head die moulds are shunted to the head circumference through the shunt system system firstly----sometimes several star holes or the other shunt system. Then melt into the spiral channel around the outside of the mandrel. The spiral flow depth decreases with near the outflow end,at the same time, The clearance between the mandrel and the die cavity will increase gradually, In the area, there will be overlap between the axial and radial of the mateiral flow . The outflow direction along the die head, The radial flow is reduced, While the axial flow ratio,continued to improve. Eventually all the melts flow along the axial. In this way, fluid flow along the pipe section distributs evenly. This means there is no partial loss of strength. The quality of melt flow around the pipe section is affected by many factors. These factors include physical dimension of head die, e.g. the quantity of flow, the angle of runner twisted,

the helical pitch, the width and thickness of spiral groove, gad width, processed material, especially viscosity, extrusion capacity and material temperature. With the aid of the computer program and the experience of the operator, can optimize the design of the spiral flow. In order to adapt to the specific application scope. In this circumstances, the distribution of wall thickness is very uniform. The kind of die mould can not only eliminate the parting lines very well, these are advantages in these following aspects:

1.Machanical stress and thermal stress are lower , the products have good mechanical strength.

2.strong structure ,so it is suitable for extrusion high viscosity material, at the same time ,head die mould is easy to install and operate.

3.The mandrel is easy to drill, so it is easy to use internal cooling system.

The advantages above make the spiral mandrel die are applied more and more extensively.

The disadvantages of this kind of mandrel die : Because of its relatively complicated structure, This type of die head is sensitive to the change of raw materials. Even small changes in viscosity and rheological properties can cause the change of plastic flow in the spiral body .

The change of pipe diameter has also the similar effect. So the geometry shape of spiral die will be designed well, make the processing range of dieas wide as possible to adapt to different materials and extrusion amount.

Ⅲ. The structure and working principle of the sieve basket type die head

On the sieve basket type die, the material go throgh the braket and the material flow system with multiple-stars holes. Then melt flow through a porous section. The components, seive basket, Here the materil flow is not along the axial direction , but along the radical direction from the inside to the outside. Because the sieve basket has the certain length , in the case of smaller head die diameter ,which provides the large flow area. So in the relatively smaller size head die ,the pressure of the porous section drops. Within the sieve basket area, the melt flow changes the directions twice, then becones the axial. The single strand material flow can mix better, the melt flows are more homogenization.

With the aid of a block element and the adjacent relaxation buffer, Realization of the material flows. Because the area of sieve basket is larger, the pressure of sieve basket type head ie is obviously lower than the other type die mould . The load of the material is relatively small the temperature of the material is relatively low. Which can be easy to increase the output.

The advantage of the kind of head die is better adaptability. Even in the case of higher capacity , it can realize the good uniformilty. The change of pipe diameter and wall thicknesses, PE material model, material viscosity, backpressure can produce the good quality pipes. The biggest disadvantage of the kind of head die mould is not better and more convenient than spiral mandrel type die mould in the following aspects: material fusion, the cleaning of the production processing , disassembling and installing of the moulds .

In short, both of the two kinds of head die moulds have advantages and disadvantages. When you choose the head die mould of PE pipes, according to your production case . The brand of the raw material is not fixed, the capcity is larger, you don't often change the colors of pe pipes and clean , disassemble the head die mould , you had better choose the sieve basket type , You require the uniformity of pipes wall thickness ,the brand of raw material is fixed , you ofen change and dismount the head die mould ,you had better choose the spiral mandrel type .

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