250 ML Double Station Deflashing Blow moulding Machine

Extrusion Blow Moulding Machine.

Extrusion blow molding machines are used for producing hollow containers from Plastic. Majority of Blow Moulding use HDPE (High Density Polyethylene) resin for producing end products. Poly Propelene PP, Low Density Polyethylene LDPE and engineering plastics such are ABS etc can be blow moulded.

In the abouve video, 100 ml round jar is manufactured from HDPE with auto deflashing. In normal Blow moulding, some runner or flash will be there in the product which should be manually trimmed. In auto deflashing machine, this process is done by machine and reduce the usage of Labour ensuring steady quality and quantity of product.

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Trouble Shooting of Blow Moulding Process

Pitted surface appearance

Possible Reasons:

• Air entrapment inside the mould
• Condensation
• Low Blow Rate
• Low Blow Pressure

Possible Solutions:

• Vent the mould to reduce the air entrapment.
• Check mould finishing, polished mould causes air entrapment. Very coarse mould surface results in rough part surface. Sand blasted mould surfaces are usually desirable.
• Check mould for condensation coolant temperature
• Increase the size of air orifice to allow faster blow rate
• Increase blow pressure.

Vertical groves and lines in the part

Possible Reasons:

• Dirty and / or damaged die

Possible Solutions:

• Clean die surface.
• Scratches in die or core, to be removed
• Check for contamination.
• Set the parison straight to eliminate hold up in die.

Irregular markings on the part

Possible Reasons:

• Water condensate or water leakage in the mould

Possible Solutions:

• Run faster cycle.
• Run warmer mould.
• Stop leakage in the mould.

Rough part surfaces and / or poor gloss.

Possible Reasons:

• Rough parison

Possible Solutions:

• Increase die temperature
• Increase mould temperature
• Increase melt temperature
• Increase extruder speed
• Use low molecular weight resin
• Clean die core

Rippling on parison / melt fracture

Possible Reasons:

• Unsuitable die shape
• Extrusion rate too high

Possible Solutions:

• Increase die land
• Increase die diameter
• Reduce extruder speed

Thin areas or holes on the part surface

Possible Reasons:

• Airflow in head is faster
• Parison is not straight
• Moisture in resin
• Contaminated resin in head or die

Possible Solutions:

• Reduce airflow through head
• Set parison
• Pre heat the resin
• Clean the head and die core

Poor wall thickness distribution – longitudinal

Possible Reasons:

• Parison sagging
• Parison control not working

Possible Solutions:

• Change extrusion rate
• Decrease melt temperature.
• Use low M.F.I. resin.
• Check parison control timings.
• Check parison control pressure.
• Check flow control valve setting.

Poor wall thickness distribution- circumferential

Possible Reasons:

• Non symmetrical parison
• Non symmetrical article

Possible Solutions:

• Set parison straight
• Use larger die
• Optimise article weight
• Use larger die

Excessive dimensional shrinkage of article

Possible Reasons:

• Low blow pressure
• Insufficient cooling
• Melt temperature is too high

Possible Solutions:

• Increase blow pressure
• Decrease mould temperature
• Increase cooling time
• Decrease melt temperature.

Warpage

Possible Reasons:

• Insufficient cooling
• Non uniform cooling

Possible Solutions:

• Reduce mould temperature
• Check for efficiency of water flow in mould channels
• Increase cooling time.
• Check efficiency of mould venting.
• Provide more cooling, especially in pinch of area of the mould.

Parison doughnut formation

Possible Reasons:

• Core temperature is low
• Core gone inside the die

Possible Solutions:

• Allow core to reach temperature equilibrium with rest of the system
• Lower the core slightly (to get the weight of the article, reduce the core diameter)

Thinning or stretching at parting line

Possible Reasons:

• Low blow pressure
• Pinch off is too sharp

Possible Solutions:

• Increase blow pressure
• Check efficiency of airline
• Widen pinch of land
• Reduce head and die temperature

Parison tail sticking to the article

Possible Reasons:

• Parison too long

Possible Solutions:

• Shorten Parison length.
• Increase pinch-of land to compression cool the tail

Black specks in parison

Possible Reasons:

• Degraded resin
• Hold ups in the die head

Possible Solutions:

• Thoroughly clean and purge extruder. Avoid prolonged shutdowns with resin held at high temperature
• Improve streamlining of the melt inside

Contamination

Possible Reasons:

• Poor house-keeping

Possible Solutions:

• Keep production area clean

The Process – EBM

The Extrusion Blow Moulding Process is discussed today. There are two main parts for EBM process – preparing the plastic resin by extrusion and blowing the melt resin inside the container mould.
Extruding:
The granules of the plastic resin is heated and melted into a viscous form. The heating required is supplied by electric band heaters around the extruder barrel. The screw inside extruder barrel is rotated by an electric/hydraulic actuator. This rotation of screw conveys the granules towards the die head of machine and during the travel the granules transformed into a molten viscous paste form. During the conveying the resin is normally compressed to a pre defined ratio thus removing the trapped air.
Forming Parison:
The melt resin is then formed into a Parison or tubular shape by the die head. The die head can be off two types – continuous or intermittent. In continuous type parison is formed continuously from the melt resin conveyed by the screw and barrel during the process. In intermittent type the melt is first accumulated into a accumulator chamber inside die head and during the start of each cycle pushed out to form Parison by applying external force.
Moulding:
The parison thus formed is hanged between the two mould halves and the mould halves closed by fluid/electrical force. Both the half moulds together will form the cavity inside as required and the parison is trapped inside. For complicated shapes of containers, the mould halves itself will have moving parts which will operate during the process.
Blowing & Exhausting Air:
The Parison inside mould will have an externally connected blowpin inside on one end. Compressed air will blow through the orifice of the blowpin to inside of the parison. The compressed air inside parison will press the melt plastic towards the wall of mould cavity. The mould will be cooled by chilled water and as the melt touches the inner wall of mould, will get cooled to a lower temperature. After giving sufficient time for the melt parison to cool to below the glass transmission temp of the resin, the compressed air inside is exhausted out.
Ejecting the blown container:
Once the compressed air inside mould is removed, mould halves are opened to free the blown container. Then the container can be removed from the mould either manually or by a robotic mechanism.
Trimming or deflashing the blown container:
The removed container is then trimmed to remove the excess plastic on the ends of container. This can be done either manually or by an automatic deflashing unit.
Quality Checks:
The deflashed container is then checked for quality like weight, wall thickness distribution, appearance; blow holes, other damages etc. Also periodically, drop test, stack test, leakage test etc are done to ensure the product confirmation.
Cycle time:
The EBM cycle time may be divided into three parts – blowing time, exhaust time and dry cycle time. The blowing time depends on the effectiveness of hest transfer thru the mould by cooling system. A chilled water cooling system for mould and uninterrupted compressed air supply will reduce the blowing time. The heat transfer rate of mould is also important. The exhaust time can be reduced by designing sufficient passage channel for exhaust air (through the blowpin and piping). The dry cycle time depends on the machine automation capability. The lower the dry cycle time of machine, higher the production of Machine.
Power consumption:
Other than the raw material cost, the main component of production cost for blow moulding is the power cost. Modern EBM machines are run by electricity. The enegy requirement may be divided into these sub sections:
Heating – required for heating the raw material to molten Parison.
Extruder Drive – generally an AC induction motor for conveying the material by rotating the extruder screw
Automation Power – generally hydraulic power system for the mould movements, parison pushout if required, wall thickness control etc
Compressed air: For blowing and other related automation process.
Ancillary Equipments like, Material feeder, Granulator etc.

Types of Blow Moulding

There are two types of blow moulding – Extrusion & Injection blow moulding. In Extrusion Blow Moulding, plastic resin is heated up to melt and extruded into a tubular shape called Parison. This Parison is then trapped inside two halves of the required mould and blown by air to the shape of mould. In Injection Blow moulding, first the material is injected to form a preform and then it is blown to the shape. Extrusion Blow moulding is used to produce all types of drums, cans, bottles etc. and injection blow moulding is used to produce bottles.

Continuous Type Blow Moulding:
In continuous blow moulding the Parison – tubular molten raw material – is extruded continuously and the mould moves sidewards after receiving the parison. The blowing will be done in the blowing station and the blown containers ejected. The mould will again move towards the parison and next cycle starts.
Intermittent Type Blow Moulding:
In intermittent blow moulding the molten material is stored in a chamber called accumulator and Parison is ejected intermittently during the start of each cycle. Hence these machines are known as accumulator type blow moulding machines. In Accumulator machines Parison is ejected intermittently at the starting of each cycle. During the blowing time the molten material processed by extruder is stored in the accumulator chamber on the die head.
Injection Blow Moulding:
In normal injection Blow moulding process, the Preform made by injection moulding is directly blown to the required shape of mould. The injection process allows generating better neck formation to the container.
Injection Stretch Blow Moulding:
In normal injection stretch Blow moulding process, the Preform made by injection moulding is first stretched along the axis to orient the structure and then blown to the required shape of mould. This allows creating transparent containers with very low wall thickness and better strength.
Single Stage Injection Blow Moulding:
In single stage moulding, the preform is made and immediately blown to shape in the same machine. The normal injection blow moulding is done by this process. The stretch blow moulding also done in single stage process.
Two Stage Injection Blow Moulding:
In two stage process, first the preform made like any injection mould process. The ready preform then re-heated, stretched and blown to the required shape. Here the preform making and blow moulding are done in two different machines. This process is used normally for stretch blow moulding.