Blow Molding

The usage of plastic has become more popular in the world today. It has rapidly started to replace metal and ferrous material as the raw material in most of the industries. Plastic offers many advantages when it is compared with metal. It is easier to manufacture and comes in abundance, which means the supply of plastic will never cease. Besides that, it is lighter in weight, able to take complex shapes, can be made into a big varieties of colour, and is cheaper than metal. The usage of plastic will also contribute to the environment, in a way than mining of raw materials from the core of the earth can be reduced, thus solving many environmental issues nowadays. Plastics are actually chains of polymers held together by a strong but fluid bond. The reason a thin soda bottle is strong enough to withstand the pressure of carbonated liquids is a phenomenon called 'biaxial orientation.' The polymer chains in a plastic bottle form in two directions, creating a very strong webbing effect. The plastic itself can be stretched out without sacrificing strength. To produce such products from plastic, a unique kind of process will have to be implemented on the material. Such process is the blow molding.

Blow molding is also known as blow forming. Blow molding is basically a manufacturing process that is being used to form hollow plastics, such as plastic bottles. The history behind this process can be traced back to the ancient times, particularly is Syria during the first century. The Syrian at that period of time was the pioneers in using air to blow hot material. The method is then revised by the Europeans at the middle ages due to the increasing demand for bottles. A United Stated company, in 1851, further refined the method by introducing plastic to replace glass in the manufacturing process. The most significant improvement in the blow molding industry was marked by the production of a blow molding machine by Ferngren and Kopitke in 1938. The machine was then sold to Hartford Empire Company, putting a stamp in what seems to be the beginning of the commercialization of blow molding process throughout the world. Since then, the process was thoroughly reformed and refined to suit the demanding industry. The introduction of different types of thermoplastics, namely low-density polyethylene (LDPE), high-density polyethylene (HDPE), the polymerization both propylene and butylenes, polypropylene (PP), polyvinyl chloride (PVC), and the debut of biaxial oriented polyethylene terephthalate (PET) have further perfected the method and making it one the most sought after manufacturing there is.

Recently, there are four major types of blow molding process that are widely used in the industry. The first type is the extrusion blow molding. This type is regarded as the simplest type of blow molding. The process in which plastic parts are created is the basic fundamental of every other blow molding processes. The second type is the injection blow molding. This process combines injection molding and blow molding. The next type of process is the stretch blow molding. This process is best used when producing PET bottles which are usually used for water, juice, and other similar products. The stretch blow molding is currently being used for high-volume productions for multi-million worth of products. The fourth major blow molding process is the reheat and blow molding process. This process is a type of stretch blow process. The huge difference will be the stock mold, which is made by an outside vendor. The company which buys these molds will simply have to reheat it so it can be blown afterwards. Therefore, the cost which is bear by the company can be greatly reduced. However, advances in technologies allow more type of blow molding process to be produced. To name a few, the advancement in the process gave birth to a new breed of processes such as Coextrusion Blow Molding of Large Parts, Three-Dimensional Blow Molding, Hard-Soft-Hard and Soft-Hard-Soft Technology, Long-Glass-Fiber-Reinforced Blow Molding, and Blow Molding Foam Technology. Although the process may vary from one to another, it still holds the basic concepts and fundamentals of blow molding.

Blow molding offers many advantages to the industry to date. The main concerns for any engineering or manufacturing company will be cost. These concerns are greatly reduced when it comes to using blow molding process, because the tooling cost of a blow molding process is less than an injection molding. The maintenance costs are also usually lower. Besides that, the piece that is produced using this concept is much lower than any rotational molding process. Apart from that, blow molding process applies the concept of one piece construction. This means that there is no welding or gluing halves part together afterwards. This will save more time and cost in producing any items, apart from minimizing any weaknesses that may come in the joined parts. The seamless construction is very ideal for the productions of liquid filled or airtight containers as it is more durable. Items made from blow molding process also have excellent environmental stress crack resistance. Lastly, quick product revisions are allowed for items made from blow molding processes to increase flexibility.

However, blow molding process does have its disadvantages and limitations. The most obvious limitations that can be observed from the parts made by this process is that it is limited only for hollow and thin walled parts with low degree of asymmetry items. This means that the process is only capable of producing thin walled items that is round in shape such as water bottles. Other symmetrical shapes, such as rectangular or triangle can’t be produced using this method. Furthermore, it has poor control of the wall thickness of the end product. The surface finish of the material is also poor and prone to imperfections if the mold is not carefully inspected. Even though the equipments cost less from other method, it is still considered high due to its nature as a precision tool.