Extrusion Blow molding with Parison Programming

Parison

Tube shaped material from the die of extrusion blow molding machine is called Parison.

History of Parison Programming

Parison programing was invented in 1958 by Denes B. Hunkar. Which helped to make extrusion blow molding a more efficient and productive plastics manufacturing process. The invention of parison programming turned a very simple extrusion blow molding process into a scientific process.

Die

Two types of dies are

1. Convergent Die
2. Divergent Die

Die parts

1. Mandrel
2. Bushing

Mandrel of die

The round shaped metallic block in die around which molten plastic flows is called mandrel of die. Mandrel may be fixed or moveable.

Working of parison programming

Parison programmer is used with hydraulic powered accumulated die head either with convergent or divergent die. In convergent die the diameter of die decreases from molten plastic entering to opening of die and in divergent it increases from machine side to opening of die. For better controlling die head is divided into portions. Each point is called programming point. The complete die head is divided into approximately 200 programmer points.

Total length of parison is dived into programmer points.

Before 1958 parison was of same wall thickness. But if you want to add handle in the blown plastic product that area must have thick section so for this purpose thickness of all the parison has to increase. Which results weight increase and slow process. To overcome this problem blow molder need a solution and parison programmer provide them the solution.

In parison programing either mandrel or bushing is moveable. Thickness of parison can be controlled by the movement of mandrel or bushing. In convergent die, forward movement of mandrel decreases the gap between mandrel and bushing, hence there is decrease in wall thickness of parison, and same is the result when bushing is moving backward. In divergent die case is opposite.

So the wall thickness according to product dimensions is controlled by movement of mandrel. Mandrel moves back and forth to control the thickness during the extrusion of molten plastic in parison form. Gap between mandrel and bushing is controlled by programing points when hydraulic piston reached a specific point the gap either increase or decrease according to parison programmer instruction installed by operator.

Advantages of Parison programmer

Reduced amount of plastic used

Even wall thickness

Equal weight distribution

Equal cooling

Fast production

Better control on parison

High strength at top bottom and handle