Hello guys, in this article, I will share some detailed information about the Blow molding process, construction, and advantages.
What is Blow Molding?
Blow Molding is an efficient way to manufacture hollow plastic parts. The method is mostly used to produce bottles and containers. The working process of blow molding is relatively simple compared to injection molding.
It all began when molten plastic material poured through Parison. Parison is a tube-shaped piece of plastic with a hole to pass compressed air through it. Parison is formed when a molten plastic material is pushed through an extruder.
Mainly there are three main types of blow molding methods – 1. Extrusion blow molding, 2. injection blow molding, 3. injection stretch blow molding.
Blow Molding Process –
As mentioned earlier, molten material is formed through parison, which is clamped with the mold, and the air is blown through it. With the help of air pressure, plastic is pushed at the front to match with the mold.
When the parison reached the desired length, the two halves of the mold combine around the parison, locking it at the bottom.
After some time, when the article is cooled and solidified, the mold opens up, and the part is removed.
After discussing the process, let’s discuss different types of blow molding process.
Also Read – Compression Molding Process – A Detailed Guide | Thermosets Composite Compression Molding | Types of Compression Molding | Molds Used for Compression Molding | Advantages | Disadvantages | Applications
Extrusion Blow Molding –
Extrusion blow molding is the most widely used blow molding method. In extrusion blow molding, the molten plastic material is extruded into a parison.
This parison is locked by closing it between the two sides of the cooled mold, and then air is blown into the parison transforming it into the shape of the final product.
Once the article is cooled enough, the mold is opened up, and the component is ejected.
The two variations in extrusion blow molding are namely continuous blow molding and intermittent blow molding.
In continuous extrusion blow molding, the parisons are extruded continuously, and the individual parts are cut separately using a fitting knife.
Talking about intermittent extrusion molding, which mainly falls into two variations, namely straight method, and accumulator method.
The straight method is quite similar to the injection molding method, using a screw to turn and stop to push the material out.
In the accumulator method, the material is gathered until the previous mold is properly cooled and enough material has been collected. A rod pushes the molten material and propels the parison.
Injection blow molding –
The injection blow molding method is mainly used for large-scale manufacturing of hollow glass and plastic products. In this method, the core pin plays a key role as it rotates to a blow molding station to be stretched and cooled.
The injection blow molding method is widely used to manufacture small medical and single-serve bottles.
The primary process cycle of injection blow molding is the screw assembly and extruder cycle, which melts the material.
The molten material is poured into a hot barrel manifold running through different nozzles into a heated cavity and core pin.
An external shape will be created by the cavity mold clamped with a core rod, resulting in the preform’s internal condition. The preform comes with a fully formed jar neck with some material stuck to it.
The mold will open, and the core rod will rotate and clamped into a hollow, cold blow mold. An opening at the rod’s core allows compressed air to be filled in the preform, which expands it to a finished product.
Injection stretch blow molding –
The injection stretch blow molding method is divided into two different, single and double stages.
Talking about the single-stage method, it uses the same machine for preform manufacturing and bottle blowing. The single-stage method is also divided into two processes called 3-station and 4-station.
The 4-stage method is expensive compared to the 3-stage way as it goes like injection, reheat, stretch blow, and ejection.
The latter process eliminates the reheating part and uses latent heat in the preform, resulting in a substantial decrease in heating and tooling costs. The process is quintessential for filling carbonated drinks.
Coming to the two-stage process, it molds the material into ‘preform’ using the injection molding. These preforms are produced using threads on the other end. These preforms are wrapped up and fed after cooling into a heating stretch blow molding machine.
The process uses heated preforms usually above the glass transition temperature. Then, high-pressured air is blown into bottles using metal blow molds.
Advantages of Blow molding process –
- The processing cost of die and tools is meager.
- Ability to manufacture complicated parts and designs.
- Production time is also fast, depending on the product being manufactured.
- It offers the benefits of automation. With automation, the speed of manufacturing can be ramped up significantly.
- The versatility is another key advantage for blow molding. A significant number of customizations possible with products like plastic bottles, containers, jars, etc. That makes blow molding quite lucrative for the pharmaceutical and food industries.
- The external thread can be added without any difficulty.
Disadvantages of Blow Molding process –
- It is heavily dependent on petroleum. As the world’s oil supply is diminishing, the heavy dependence on oil is seen as a drawback for the process.
- It comes with minimal applications.
Final Thoughts –
I tried my best to share my knowledge about the blow molding process in a brief manner. I’d appreciate it if you people will leave your thoughts about the article in the comment box.