Parison programming is used in blow molding to automate the process and improve productivity. It involves changing the thickness of the extruded plastic (parison) to control wall thickness and weight distribution. The gap between the bushing and mandrel in the die head is varied during extrusion using a hydraulic system controlled by a programmer. This allows producing parisons with varying thickness to compensate for differences in how areas expand during blowing. Parison programming reduces plastic usage, improves quality and wall thickness uniformity, decreases cooling times, and increases productivity.
2. Introduction
• Parison programming is used in the manufacturing of plastic products
to ease the process of blow molding. 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.
• Parison general principles are used to achieve high productivity. For
example, the control weight of the parison controls the power cost,
the parison thickness improves the product quality, reduces the
cooling time, leads to productivity improvements, and recipes of all
Parison parameters reduce setup time.
3. Introduction
• 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 plastics used and improve the wall thickness distribution
and reduce cooling time.
4. Production of Parison
• 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.
5. Production of Parison
• 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 die.
6. Production of Parison
• If the mandrel adjusts the gap and it is a converging die raising the
mandrel will open the gap.
• If it is a diverging die 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 die raising the bushing will open the gap.
9. Die Head arrangement
• 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.
10. Die Head arrangement
• 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.
11. Parts of Programmable Head Die
• 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, and
• a double-acting hydraulic piston cylinder arrangement that keeps the
bushing or mandrel is moved up and down.
• 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.
12. Parts of Programmable Head Die
• 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.
13. Parts of Programmable Head Die
• 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.
14. Advantages of Parsion 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.
