In container manufacturing, wall thickness control is an essential point for container quality. For this point the different types of blowing in the case of extrusion blowing the parision control.
Parison control means dynamically controlling the thickness of Parison to obtain a uniform container thickness in an extrusion blow molding machine. Helps maintain the required thickness axially and radially in the product made from Extrusion Blow Molding (BM).
What is parison in parison extrusion?
Now, what is a Parison? It is tubular-shaped molten plastic made on a blow molding machine by extrusion or injection. This viscous melt plastic called Parison is put into two halves of blow molds and molded into mold cavity shape by blowing compressed air.
Why is control required?
When the Parison leaves the head of the extrusion blown machine it will be in the molten state. Due to its own weight, the Parison will elongate resulting in a thinner top compared to the bottom. This will cause uneven thickness of the manufactured item. Also the complex geometries of the product to be molded require varying the parison thickness to obtain a more uniform wall thickness of the product.
How does it work
The space between the nozzle and the head mandrel can be adjusted, so that the internal diameter of the precursor can be modified, and therefore its wall thickness of the final product.
In this system, the mandrel moves with respect to the nozzle, which remains fixed, so that the wall thickness of the precursor varies during each cycle. Modern extrusion machines are prepared to modify the wall thickness of more than 100 different points of the wall for a container.
The advantages:
Uniform article wall thickness and therefore improved quality due to lower thermal stresses during processing.
Balanced distribution of thicknesses and therefore possibility of weight reduction.
Reduction of top and bottom waste and therefore increased production.
Reduction in cooling time due to thickness uniformity and therefore greater production.
CHARACTERISTICS
Closed loop control (multipoint Parison programmer)
The closed-loop electro-hydraulic control system can be installed on the machine to control the parison thickness at various points (30 times or 100 times or more). Since this is a closed loop system the precision is much better than the ordinary system and the resulting container will have the most uniform thickness.
Axial wall thickness control
All systems described above are for thickness control in the Parison axial direction. This is the most common Parison controls.
Radial wall thickness control (PWDS)
In addition to axial wall thickness control, for some specific and complex products, thickness control in the radial direction is required. This is achieved by transforming the uniform annular space through which the parison exits into an elliptical shape.
Time-based and position-based control
Time-based blow molding systems are used in continuous extrusion. that is the parisonel thickness is controlled in a defined interval of time. Here the total time for a parison cycle is divided by the number of points to calculate the time interval.
In accumulator type extrusion blow molding, either time-based or position-based system can be used. In the position-based system, a potentiometer detects the position of the push cylinder (accumulator) stroke and programs the profile points with respect to the position. In the time-based system, the profile points are scheduled with respect to the time taken for the parison push out. To overcome variations in time, the controller automatically updates the time in each cycle and uses it to schedule the next cycle.
Conclusion
Having quality parison control has many advantages such as material savings and better packaging quality, as well as the ability to make complex packaging. We invite you to learn about the high-quality AXH and FKI extrusion machines https://www.akopet.com/copia-de-extrusion-soplo
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