How Blow Molding Works (An Overview Of The Process And Function)


Blow molding is a manufacturing process that uses air pressure to form plastic parts into various shapes. The blow molding process begins by melting down the plastic and forming it into a parison or in the case of injection and injection stretch blow molding a preform.

The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass. In the case of extrusion blow moulding the die creates tubes that are then cut into predetermined lengths in a chopping machine. For injection or injection stretch blow moulding, the preform is fed into a reheat furnace for conditioning before being transferred to the mould.

Once at the mould the parison is captured by closing it into cooled metal mold using a clamping system. The preform is then cooled and transferred to the blow moulding machine where it is inflated with air and sealed at the neck. The process can be repeated until the desired shape has been achieved.

Blow molding is a manufacturing technique used to create hollow plastic parts by inflating a heated plastic tube inside a mold until it forms into the desired shape. The technique was invented by Earl Tupper in the 1940s, who patented it as “injection blow-molding.”

There are three main types of blow molding: extrusion blow molding, injection blow molding and injection stretch blow molding.

three main types of blow molding

There are three main types of blow molding:

  • extrusion blow molding,
  • injection blow molding
  • and injection stretch blow molding

These three processes are all used to create bottles and containers with different shapes and sizes. Extrusion blow molding is the most common type of blow molding process used today. It creates bottles with a cylindrical shape that can be made in any size or quantity required by the customer.

Injection blow molded products typically have a tapered shape at one end, but can also be round like a bottle or square like a box (depending on which type of equipment is used).

Injection stretch blown products are characterized by their ability to expand into larger volumes during production than would normally be possible using other methods because they utilize overmolding techniques where two separate materials are joined together as one piece using heat/pressure sealing technology such as infra red welding guns – so there’s no need for adhesive materials!

Extrusion Blow Molding

Extrusion Blow Molding (EBM) is a process for making hollow, low-density objects from a plastic or rubber tube. The process uses an extrusion blow mold, which is similar in concept to an injection mold. EBM is used for producing such things as drinking straws, toilet paper tubes and toothpaste tubes.

The main steps in the process are:

1) Extrusion: A tube of molten plastic is extruded through a die. The die has two parts: one that forms the shape of the tube and another that forms an opening where the air will be forced out when the tube cools. The extruded tube passes through a cooling chamber before going on to step 2.

2) Injection blow molding: Air pressure pushes against one end of the tube while it is still hot enough to deform easily; this causes it to collapse into the shape of the other half of the die.

3) Cutting: A cutting tool slices off excess material from both ends of the cooled and deformed tube, leaving it ready for use by consumers or businesses that make products from PVC tubing (e.g., makers of household appliances).

Injection Blow Molding

Injection blow molding is a method of plastic manufacturing that involves the use of a hollow plastic or metal mold and high-pressure injection to create parts. The process uses heat and pressure to melt the plastic material and push it into the mold cavity. It has several advantages over other methods of injection molding, including better dimensional tolerances, better surface finish and lower production costs.

Injection blow molding can be used in a number of different industries, including automotive and aerospace manufacturing. In addition to being used to manufacture large-scale parts, this process can also be used to build small custom parts that have complex shapes and features.

Injection blow molding is often referred to as “double shot” because it allows manufacturers to produce two different colors or shades on a single piece at the same time. This can be done by adding colorant directly into the molten plastic or injecting it after it’s been molded into its final shape.

Injection Stretch Blow Molding

Injection Stretch Blow Molding (ISBM) is a technology that combines injection molding and stretch blow molding. It offers the advantages of both technologies: low production costs, high quality, high degree of automation and uniformity. The process dates back to the 1950s when it was used for making plastic bags for food packaging. Today, ISBM is used for making a wide range of products including bottles and containers for foods and beverages, cosmetics, pharmaceuticals, detergents and industrial chemicals.

The ISBM process involves two main steps: injection molding and stretch blow molding. Injection molding is performed in an injection press that uses an injection screw to inject molten plastic into a closed mold cavity through an opening called a gate. The molten plastic cools down quickly because of the high pressure exerted by the injection press and solidifies into a shape dictated by the geometry of the mold cavity.

The molded part is then transferred to a second machine called a stretch blow machine where it undergoes stretching in one or more directions while being heated up to its softening temperature. This results in significant dimensional changes which are necessary for achieving certain shapes such as those required by non-return valves on water bottles or tapered necks on cosmetic bottles.

Advantages and Disadvantages of Extrusion Blow Molding

Extrusion blow molding machinery is a key part of the plastics manufacturing process. The machine allows for production of plastic parts by forcing melted material through a die and into a mold cavity. This process allows for creation of hollow, semi-hollow, or solid parts that can be used in a wide variety of industries.


The advantages of extrusion blow molding machinery are numerous, including:

  • Increased productivity and efficiency
  • Reduced costs
  • Higher quality products
  • Greater flexibility in design and production


There are several disadvantages to using blow molding machines, including:

  • The cost of purchasing the equipment and the need for skilled labor
  • The amount of space required by the machinery
  • Potential dangers from overheating and explosions caused by hot plastic


In the end, blow molding is an essential tool for making essential products. The process is used in the manufacturing of everything from food packaging to toys. With this type of molding, it’s possible to create a custom shape that fits your product perfectly while still being cost effective and safe for use with food items like water bottles or baby bottles.

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