Moulding Techniques

When it comes to pharmaceutical packaging, plastics offer both versatility and durability making them the perfect material. However, mastery of a range of moulding techniques allows us to match the benefits of each technique to the needs of the client. Let’s take a look at some of our commonly used plastic moulding techniques.

What is Injection Stretch Blow Moulding?

Injection Stretch Blow Moulding is a four step process. It entails;

  • Injection- A molten polymer flows from the hot runner block to the injection cavity to produce the desired shape of the preform. A core pin known as a mandrel produces the inner diameter while the injection cavity forms the outer diameter. After a short amount of time the injection moulds and core pins are parted and the preform is held in a neck carrier and rotated by 90º degrees.
  • Stretching and Blowing- Once the preform has been conditioned to the correct temperature, it is then ready to be stretched and blown until it attains the finished shape. The preform is placed within the a blowmould area. The moulds close around the preform and a stretch rod is introduced to stretch the preform lengthways while two levels of air pressure are used to blow the preform circumferentially.
  • Discharge- After being left to cool the moulds open and the preform is removed via a robotic appendage or a drop chutes.

 

 

What is Injection Moulding?

Injection moulding is a highly versatile and repeatable process which makes it perfect for mass production. Injection moulding techniques go all the way back to the 1930s. The process is as follows;

  • Closing- The two halves of the mould close and the cycle timer begins.
  • Injection- Molten plastic is injected into the mould. As the molten plastic enters the mold, the displaced air within escapes through vents in the injection pins and along the parting line between the mould’s constituent halves. This is why runner, gate and vent design are important considerations to insure an evenly filled mould.
  • Cooling- When the mould is full, the part is cooled by allowing water to flow through cooling lines. It is left to cool until it hardens. Cooling times will vary depending on the thickness of the part.
  • Ejection- The mould then opens up and the ejector rod pushes the part out of the mould. It then falls and is collected. Finally the runner (the little line of plastic that flowed into the mould cavity) is removed.

 

 

What is the Extrusion Blow Moulding process?

Extrusion Blow Moulding involves the extrusion of molten plastics over a hollow tube called a parison. It is commonly used for making plastic jars and bottles. The process is as follows;

    • Extrusion- Molten plastic is poured into the parison. The parison is then captured within a cooled metal mould.
    • Blowing- Air is then blown into the parison at varying pressures to achieve the required shape

 

  • Cooling and extraction- The bottle, container or part is left to cool after which it is extracted by opening the mould and ejecting the part.
  • Spin trimming- It is not uncommon for some excess materials to be left behind after the moulding process. This is trimmed off by using a spinning knife which cuts excess away. This is then kept and recycled for further production.

There are two kinds of Extrusion Blow Moulding; continuous and intermittent. In continuous moulding the parison is extruded continuously and the individual parts are cut off by a suitable implement or machine. In the latter technique, molten plastic is poured into the parison intermittently.