What is Parison Programming?

Parison programming is used in the manufacturing of plastic products to ease the process of blow molding, parison programming is used. Earlier blow molding process was manual in which adjustment of the body and neck and heel was done manually. With the invention of the Parison programmer, this process was automated.

Hunkar, in 1962 developed a system having a processor to control the thickness of the wall and the use of resin. Earlier, there were no established methods of weight distribution along the parts, and unscientific methods were used to control the extruder. To overcome this, Parsion programming was used.

Parison programming is critical and used to maintain the thickness of the wall and develop a complicated design. Most of the machines of extrusion blow molding use Parison Programming. Parison programming is the process of changing the parison thickness as the plastic is extruded. The die head programming can reduce the amount of plastic used and improve the wall thickness distribution and reduce cooling time.

In the die head design, the angle between the bushing and the mandrel is slightly different from the larger gap at the beginning of the land region reduces the pressure loss. The difference in gap thickness between the top and the bottom of the land region allows the programmer to vary the gap by moving either the bushing or the mandrel up and down while the parison is being extruded. Changing this gap during parison extrusion changed the parison thickness and diameter. The operator sets the control system to adjust the gap thickness in those blown container areas that expand the most or thinner in those areas that expand the least.

In the die design, the land region of the die head can be either diverging or converging. In setting up the program controller, the operator must know whether it is the mandrel or the bushing that the programmer adjusts. In addition, the operator must know whether it is a converging or diverging dye. If the mandrel adjusts the gap and it is a converging die raising the mandrel will open the gap. If it is a diverging dye raising the mandrel will close the gap. If the programmer adjusts a movable bushing on a converging die, raising the bushing will close the gap, but if the bushing is controlling a diverging dye raising the bushing will open the gap. This is a bit confusing, but you will quickly understand which adjustment opens and closes the gap for a specific dye head.

The system to make the gap adjustment is a mechanical arm arrangement attached to a hydraulic cylinder. The cylinder piston inside the cylinder is controlled by a servo valve. A linear transducer measures the position of either the movable bushing or the moveable mandrel. This linear transducer feeds that information to a control system that in turn controls a servo valve. When first setting up a parison control program, it is important that the operator set a minimum safety gap. A thickness that will never completely shut off the flow of plastic. A complete stoppage of plastic flow either by a failure of the control system or a setup error would cause a sudden plastic pressure increase in the entire system that could seriously damage the extruder or die head and be dangerous.

A typical programmable die head has these parts a movable bushing or mandrel that adjusts the gap, a position transducer that continuously keeps track of the bushing or mandrel position, the bushing or mandrel is moved up and down by a double-acting hydraulic piston. An electrically controlled hydraulic servo valve adjusts either the oil flow rate or the oil pressure to the hydraulic cylinder. The programmer control panel can be part of the machine control panel or a separate unit.

Understanding the setup and usage of Parison and weight control for intelligent blow moulding can be the difference between just making parts and making a profit by making the best parts possible. The simple principles and usage of Parison and control for intelligent blow molding are used in applications. The weight of the Parison in itself will elongate, resulting in a thinner top portion compared to the bottom portion. The complex design of today’s products requires varying the parison thickness to get more uniform product wall thickness and part weight reduction with better control, and the benefits include reduced cooling time due to uniformity of wall and or part thickness with added productivity to most blow moulding applications. For improved productivity, configure the parison controller. 

Most blow moulding applications can be easily retrofitted on a wide variety of blow moulding machines to provide a consistent wall thickness of blow-molded products. In addition, for improved quality, less material consumption, and reduced scrap, parison control is available for time-based continuous extrusion machines, accumulator machines, and wheel machines.

In time-based or encoder, the steps involved in setting a Parison and control profile are based on weight shot size and die gap. Opening multiple point Parison profiles are displayed graphically on large displays, which allow the profile to be quickly modified and compared to the actual process value. The entered profiles can be stored internally or on removable USB memory sticks, achieving precise, repetitive precision productivity. 

Parison general principles are used to achieve high productivity. For example, the control weight of the parison controls the power cost control, the parison thickness improves the product quality, reduces the cooling time, leads to productivity improvements, and recipes of all Parison parameters reduce setup time.

A good Parison controller is the perfect choice for improved productivity and profit.

Thus Parison programming is the process of changing Parison thickness as the plastic is extruded from the die head. The programming can reduce the amount of plastic used, improve the wall thickness distribution and reduce cooling time.

Following are the advantages of Parison Programming:

  • It reduces the total amount of reduced plastics.
  • It maintains equal and even wall thickness throughout.
  • Weight distribution parison programming is equal.
  • Parison programming maintains equal cooling.
  • Parison programming is used for the fast delivery of products.
  • This programming gives good control on the parison 
  • With the help of Parison programming, the strength of the top, bottom, and handle is high.

Two parameters influence parison blow modeling: swell, which happens because of relaxation of stress, and drawdown of sag because of gravity. The swell and sag of parison depend on die geometry and the conditions under which Parison is operated. Second, the Parison swell depends on the Diameter swell and the Thickness swell. The area swell is the product of Diameter swell and Thickness swell.

The diameter swell B1 and Thickness swell B2 is defined as:

B1 = Dparison / Ddie 

B2 = hparison / hdie 

 Here, Dparison  is parison and Ddie is die diameter. Hparison is parison thickness, and  hdie is die gap opening.

The area swell is defined as follows:

Barea = B1 x B2

Thus blow moulding is the technique using which hollow plastic parts can be formed and joined together. This can be done using three blow moulding techniques. These techniques are- extrusion blow moulding, injection blow moulding, injection stretch blow moulding. These techniques are controlled and operated by Parison Programming.