Since many factors enter into the design of plastics PET preform moulds, and into the design of products to be pet bottle mould, it is well for product designers, tool designers, and tool makers to have a common understanding of plastics PET preform moulds and PET preform moulding in order to cooperate to the fullest extent in making possible PET preform moulded products of high standards of quality and economy.
Requirements for PET preform mould Designing
To design plastics preform bottle mould, a plastics engineer should have an intimate knowledge of a proper design procedure which is based upon a knowledge of the characteristics of materials; of the technique of PET preform mould building; of the economics of each production schedule; of the tooling cost both to purchaser and to the PET preform mould manufacturers; of PET preform moulding equipment operation; of the special mould steels and alloys; and of the moulding and finishing facilities of his own plant.
The design of plastics PET preform moulds includes, besides the design of the mould proper, the provision for mounting the mould in a press; the provision of means to eject the finished PET bottle mould casting; and a provision for temperature control. There are also finishing tools to be designed, such as drilling jigs, buffing attachments, holding fixtures, cooling fixtures, gages, and other devices for obtaining accurate and economical production.
Two General Types of Plastic moulding in General Use
There are two general types of moulding in general use compression and injection. A compression Mould is one which is open when the material is introduced, and which forms the material by heat and by the pressure of closing. An injection Mould is one which is closed before the material is introduced from an external heating, or plasticizing cylinder. Compression Moulds are usually operated in hydraulic presses; while injection Moulding presses have been developed for either mechanical or hydraulic operation.
The Mould designer does not always have complete information on the product his Mould must produce. Usually a sketch or drawing is supplied, and sometimes a model. The model is useful since a Moulding or finishing feature may appear in three dimensions which would escape notice on a drawing. A model, while desirable, is not absolutely necessary, and most Moulds are built without their use. As the die or the die casting designer, the Mould designer can very frequently find details which may be altered slightly to allow more convenient and economical Moulding. The Mould designer can render a real service by making such suggestions for approval before completing his design.
Single Stage Blow Molding Machine
While PET bottle development was proceeding in the US, a large manufacturer of injection molding machines in Japan, was leading a project to develop a machine to make biaxially oriented PP (polypropylene) containers. They recognized that the prototype machine could be used to produce the new PET bottles and, in December 1975, the One-stage ASB-150 injection stretch blow moulding machine for making the new biaxial oriented PET bottles was unveiled. All one-stage injection stretch blow moulding machines derived from this original Stretch Blow design are referred to as classic one-stage machines, as the concept has long since been extended into other PET developments. The classic one-stage machines design is extremely versatile in that the same basic machine design can be used to make a wide variety of bottles and jars in all shapes and sizes.
Two Stage Blow Molding Machine
In the early developments, performs were made by continuously extruding a PET tube. To make these prefroms, a perform manufacturing machine that took a continuously extruded PET tube, heated and closed one end, and then heated the other and formed a thread finish by blow moulding. This process had a faster output rate, at 12000 preforms per hour, than the early injection moulding routes of 8 and 16 cavity moulds. Being extruded, the performs could be multilayered with barrier materials. The system was overtaken by injection moulded performs as the cavitation increased to 32 and beyond. The quality of the injection moulded (IM) neck, adding for example vent slots, made the IM finish preferable. Moreover, IM technology is available from more than one company, giving customers greater technical and commercial choice. Two-stage technology machines with six blow moulds operating at around 4000 bottles per hour. Subsequent mould and cooling development increased the output to 6000 bottles per hour.