Please Explain The Blow Molding Process

It seems that everyday more and more bottles made by plastic blow molding show up in the marketplace. Even with the huge environmental impact of millions of bottles in the environment, consumers have come to expect and demand the never ending stream of new products packaged in plastic bottles.

These bottles have become increasingly energy efficient and environmentally “green”, and some countries are making great progress. Yet, a great deal needs to be done. It is only a matter of closing landfills and governmental legislation before dramatic change will take place.

Blow Molding Process
Mold Making And Lean Mfg.

The blow molding process is part of the problem and part of the solution. Wise molders can profit from this.

Will biodegradable plastics take over the blow molding process?

No doubt about it, the plastic blow molding of plastic bottles is a growing industry. Now, with the corn based PLA plastic in the marketplace, a new arena has opened up, with new possibilities for profit. In Japan and Europe especially, there is tremendous pressure to use biodegradable plastic in the production of these millions of bottles.

Industry experts cite that blow molding is growing at a rate of over 4% a year, in spite of high resin prices, which are tied to oil prices. Consumer demand is so high that the industry is enjoying a steady growth. As in other plastics fields, such as thermosetting plastics, the push for offshore outsourcing is increasing.

Blow Molding Process
Blow molding machine

How does plastic blow molding work? It is amazing that it works as well as it does and that the bottles can have such thin walls.

Basically, there are 3 stages in the blow molding of bottles: Injection, blowing, and ejection.

A plastic blow molding machine has a heated extruder barrel with a screw inside where the plastic is melted. This molten plastic is fed by the screw mechanism into a manifold which then injects the plastic through tiny nozzles into a hollow, pre-heated mold. This is the preform mold that has the external shape of the bottle.The preform looks a lot like a miniature bottle, complete with the neck and body of the bottle.

Once the preformed part is moved into the cooled blow mold, air is forced into it, almost like a balloon, and this causes the plastic to take the shape of the bottle mold.

Once the part is cooled, the blow mold opens and the finished part is stripped off of it’s mandrel, or core. It is then leak tested, weighed and inspected prior to packaging and shipping. Depending on the specifications, a blow mold may have many cavities, enabling it to produce thousands of bottles a day.

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