What Is a Blow Molding Machine?
A blow molding machine is a manufacturing machine used to create bottles and other hollow plastic products. It uses a process known as extrusion blow molding.
This process begins by feeding melted plastic resin through an extruder into a tube shape, known as a parison. This is then sealed inside the product blow mold and pressurized with compressed air, inflating it into its final form.
Extrusion
The extrusion blow molding process produces the many bottles and containers we use every day to package beverages, foods and cleaning products. It uses the same basic process as other blow molding methods, forcing heated plastic into a mold to create hollow objects and parts. It’s important to note that this is only one type of blow molding, and there are specialized derivations of the process such as reciprocating screw blow molding, multi-layer blow molding, 3D blow molding and suction blow molding that offer added capabilities for specific end markets.
To start the process, the raw plastic (pellets, granules, flakes or powders) is fed into an extruder. The mechanical energy from turning screws and the thermal energy of heaters arranged around a barrel melt and combine the material into a continuous, high-density stream called a parison. The parison is then forced into a die that shapes it into an object. This shape is then inflated with low-pressure air, forming the finished product.
The cooled, solidified product is then ejected from the mold, either automatically by an ejection mechanism or manually by an operator. The excess plastic that forms around the parting line, known as flash, is then trimmed either within the machine or in a secondary trimming operation. This can be accomplished with a mandrel, needle or blow pin, depending on the application.
Clamping
Clamping on a blow molding machine involves capturing the parison and holding it in place. The clamp force must be blow molding machine high enough to hold the preform, withstand the inflating pressure from the parison and cut off any tails and flash. The clamp force should also be low enough not to impose bending moments on the machine frame.
The clamping mechanism comprises a cradle or clamp body 82 which includes a bed plate 84 supported on slide bearings 88 and 92. First and second platens 94 and 96 extend transversely from the bed plate and are adapted to carry mold sections 98 and 102 of the mold 30. Each of the mold sections carries a different molded article such as a bottle with a handle, neck or cap.
Once the mold sections 98 and 102 have reached the correct position, they are clamped closed by hydraulic motors 74 and 76. When the clamping forces are released, the parisons 42 and 43 are severed by knives 45 and 47 respectively.
Another important step is the inflating and cooling of the parison. The temperature of the plastic must be stable to prevent cracking and warping of the plastic as it expands into the shape of the mold. Lastly, blow molding machine factory the ejection of the molded product must be fast and controlled to avoid causing any defects such as sticking or twisting. It is a good idea to watch a video of high-speed parts being ejected to see the details involved.
Blowing
Blow molding machines are used to produce plastic products that have a hollow interior. They use compressed air to inflate the molten plastic into the shape of the mold, much like a balloon. They have a wide variety of uses and are especially useful for producing bottles, such as shampoo bottles and cola bottles. The blowing process involves stretching and blowing, and the amount of material blown depends on the type of polymer and air pressure.
The molded product is then cooled and ejected from the mold. It is a quick and efficient process, making it ideal for mass production of plastic workpieces. The most common raw materials for blow molding are thermoplastics, but engineering plastics such as polyamides and polycarbonates can also be blown molded.
Plastic blow molding has many uses in both the domestic and commercial markets. For example, it is used to make shampoo bottles, plastic sports equipment, and automobile parts. It is also an excellent choice for manufacturing containers and jars for food and beverage packaging.
The process of blowing was developed in the 1930s, and was adapted from glass blowing. This was an ancient technique that was replaced by plastic in the 1940s. It is now one of the most important industrial manufacturing processes in the world, primarily due to the popularity of soft drink bottle production.
Cooling
The cooling process is a crucial step in the blow molding machine. It allows the plastic to cool and harden to a point where it can be ejected from the mold without damaging it or causing it to warp.
This cooling is accomplished by using a system that exchanges cold compressed air between the inside of the product and the outside of the product while it’s being blown. This dual-surface cooling speeds cycles and reduces internal stresses that would otherwise cause the product to tear, warp, or produce specks during the stretch and retraction phase of blow molding.
The two most common types of blow molding are extrusion and injection-blow molding (IBM). With the former, the melted plastic is forced through an extruder to form a hollow tube of plastic called a parison. The parison is then captured by the machine’s clamping unit and blown with air pressure, expanding it against the walls of the mold to give the product its shape.
Wittmann Battenfeld, which acquired Farragtech in late 2019, offers two systems that exchange cold air with the inside of a blown part and the outside of the part while it’s being inflated: The Blow Molding Booster (BMB) and the Blow Air Chiller (BAC). Both equipment types were exhibited at K 2019 in Dusseldorf, Germany. The company promises that both systems can increase production by up to 50% compared to non-cooled parts.
