He 480 d Macchina lavorazione materie plastiche

The evolution of plastic processing machinery

Since the Second World War, growing demand for plastic has stimulated the inventiveness of various business owners, leading to the creation of the first industrial technologies for the mass production of plastic containers

The introduction of plastic processing machines marked a pivotal moment for modern industry, revolutionising the manufacturing of numerous products and leading to an ever-changing industrial landscape. Let’s explore, briefly, the origins of plastic processing machines, how they developed, and what lies ahead for them in the future.

The initial technologies serving this industry emerged after World War II, when interest in plastic was at its highest, crossing over various industries and applications. The United States, Germany, and Italy were pioneering countries. One of the reasons why certain particularly innovative companies began to build machines for processing plastics was the irrefutable advantages they offered over glass. Glass, in fact, involved more challenging production processes and the end product is, today as it was then, more fragile and heavier than a plastic container with the same capacity.

One of the first manufacturing techniques honed was injection blow moulding, which allowed manufacturers to produce intricate objects by injecting molten plastic into a mould. The process involves the creation of a preform that is then inserted into a blowing station which creates the final container.

Before that, however, machines for extrusion blow moulding plastic had been invented, which were ideal for producing hollow items. Let’s stop for a moment to examine this particular process, which is common to many plastic processing machines. The process begins with the production of a hollow plastic tube known as a “parison”. This tube is created by melting plastic granules in an extruder, a machine that melts plastic at high temperatures before shaping it. This shaping involves the molten material being pushed and extruded through an extrusion head and a die, into a mould containing a cavity or multiple cavities with the shape of the end product.

During this stage, the plastic is closed inside the mould and made to adhere to the cooled walls of the mould as result of cold air blown through a nozzle at low pressure (6-8 bar) into the mould. The air forces the parison to take the shape of the mould cavity, thereby creating a plastic container in the desired shape. After blowing, the air is released and the plastic container remains inside the mould cavity for a while. Here, the temperature difference between the cold walls of the mould and the hot plastic causes the plastic to cool and solidify.  Once cooled, the blow mould opens and the finished product is taken out.

Last of all, the final category of plastic processing machinery is stretch blow moulding machines for PET preforms (a two-stage system). In this process, the PET preform already exists and in our two-stage blow moulders, the PET preform is loaded into the machine and transferred inside a cavity mould (also known as a blow mould) whose cavity has the desired shape of the end product. A stretching rod is inserted inside the preform and high-pressure compressed air (measuring up to 40 bar) is blown into the preform so that it takes the shape of the mould and therefore the desired shape for the end product. At the same time, the residual heat within the preform helps shape the material and consolidate the shape within the mould. Once the plastic has been left long enough to cool and solidify, the mould is opened and the finished product taken out.

But what developments can we expect to see in plastic processing machines over the course of the 2020s? First of all, customers are increasingly seeking larger machines for greater productivity, and fully electric options. Until recently, in fact, the plastic processing machines were driven by hydraulic power units, using oil,  which made them extremely energy intensive.

Today, however, with  the introduction of full electric technology, these machines are now designed to move powered by electric motors, often equipped with inverters; this had lead to significant efficiency improvements in terms of the energy needed to produce and process plastics. Another trend concerns raw materials, given that the attention focused by the supply chain  – as it transitions towards sustainability  – is shifting to second-life plastic resins. Of course, this feedstock needs to be processed with care and is only usable for certain kinds of products. Nowadays though, many kinds of containers, such as bottles, are actually made of three layers, virgin plastic, recycled plastic, and then virgin plastic again.