When it comes to the plastic bottle manufacturing industry, polyethylene terephthalate is the material that is used most frequently. The process involved in turning the raw material, polyethylene terephthalate (PET), into a commercial plastic bottle involves a number of different steps and industry specific tools.
PET is a type of thermoplastic polymer resin that is commonly used across the industry due to the range of fantastic properties that it possesses, ranging from a high level of chemical resistance to a high rate of impact resistance.
Today, we are going to be discussing some of the most important tools frequently used during the plastic bottle manufacturing process. This process involves turning this raw material into the type of plastic bottle that you would generally see on the shelf of a supermarket. We are going to do this by breaking a traditional process, injection blow moulding (IBM), down into several steps.
The Plastic Bottle Manufacturing Process
Injection blow moulding is an extremely important aspect of the plastic bottle manufacturing process. This process is broken down into four steps. Each step contains specific tools and equipment used to create plastic bottles.
Step One – The Mould Cavity
When polyethylene terephthalate is exposed to a rather strong heat source, it begins to melt down into a liquid form. This molten material then has to go through a manufacturing process known as IBM, or injection blow moulding.
At this stage of the plastic bottle manufacturing process, the molten polyethylene terephthalate is injected directly into a mould cavity. This cavity is shaped like a test tube that you’d likely find in a science classroom. You might also be wondering how the screw top is created, and whether or not it is a difficult process. Luckily, the screw cap is actually moulded onto the top of the test tube shape at this stage. The shape itself is known as a preform parison.
Step Two – Transfer to the Bottle Mould
Once the preform parison has been created, it has to be transferred to a second mould. This mould is different to the first, as it’s shaped like the bottle that is going to be manufactured. The preform parison then has to be clamped down to the second mould. The act of moving the preform parison from one mould to another can be done by hand. However, a lot of companies utilize machinery and equipment that works on a continuous basis. By doing so, they do not have to move the preform parison by hand, as that would be incredibly time consuming and not very cost efficient.
Step Three – Utilizing a Compressor
One of the first things that you should know about blow moulding is that it’s not based on a new, innovative process. It is actually an ancient process that has been used by mankind for around 2 millennia. It was originally used during the process of glass-blowing, something that is still fun to see today.
The type of blow moulding that we see during the IBM process is a little bit different, as it utilizes a modern compressor. These compressors should always be a main priority in any factory setting. This is because all of the different plastic bottle manufacturing processes require an injection of pressurized air. This is something that only a compressor can efficiently produce.
Traditionally, manufacturers would use a type of compressor that is known as a reciprocating compressor. These have the ability to produce a large amount of plant air to create plastic bottles that featured intricate designs.
Nowadays, companies prefer to use low pressure systems that are much more energy efficient, like centrifugal compressors. These compressors are not capable of generating as much power as a traditional compressor, but they do produce a higher rate of air flow. This is incredibly cost efficient, especially when you consider how energy efficient they are.
This plastic bottle manufacturing process step actually involves inserting a thin, steel rod known as a mandrel into the preform parison that was created in the first mould. This mandrel then fills the parison with a large amount of highly pressurized air. The air stretches the polyethylene terephthalate until it is the same shape as the bottle mould that surrounds it.
Step Four – Cooling the Polyethylene Terephthalate
Once the pressurized air has stretched the thermoplastic into the shape of the bottle that is being manufactured, the bottle has to be cooled down quickly. Otherwise, a number of different problems could occur.
This can be done by using tools. It can be done in either a direct or indirect way, depending on the factory setting. For example, a tool could be used to spray pressurized air or carbon dioxide directly onto the bottle. This would be a direct approach.
Other methods involve utilizing a system of pipes that surround the mould, and running cold water through them. This indirect approach could involve utilizing a system of pipes that surround the mould. You could do this by running cold water through them, cooling the PET in the mould down without anything actually touching it. Either way, the bottle has to be cooled down quickly.
After that, you just need to use a tool to trim off any excess polyethylene terephthalate that has leaked during the manufacturing process. If your system utilizes a continuous process, then one bottle will have to be separated from the next.
Other Things to Consider – Quick Drying
One thing that you have to be aware of is the fact that polyethylene terephthalate is known to absorb a large amount of moisture in its natural state. Typically, moisture will make up approximately 0.05% of the raw product that exists before it is melted down. This isn’t good when it comes to the plastic bottle manufacturing industry. Here, a rate no higher than 0.005% is recommended.
That does not mean that it is the end of the world if your raw polyethylene terephthalate does contain a lot of moisture. There are several techniques that you could use to bring the percentage down before you start the plastic bottle manufacturing process.
For example, a lot of companies are known to oven dry their polyethylene terephthalate. This can be done for an absolute maximum of eight hours before it starts to affect the thermoplastic in an adverse way. Another option would be to utilize a hopper dryer. This process is similar to the process involved in oven drying. The difference is that the thermoplastic can be moved into the hopper dryer using an autoloader. This creates an economic advantage in the form of a continuous process.
These tools are essential in the plastic bottle manufacturing process, and without them, we wouldn’t have the PET plastic bottles that we use today.