What Is Blow Molding?
Blow molding is a production process that makes hollow-bodied workpieces. It uses a highly automated manufacturing system that enables a faster production cycle.
Plastic resin pellets are conveyed into the machine using vacuum pumps. These move the pellets into raw material silos or hoppers. The melted plastic is then formed into a parison.
Extrusion
Extrusion is one of the most common processes for producing bottles, containers and drums. The process involves forcing plastic to be shaped into a tube shape by mechanical energy and then allowing it to cool in place. It’s a complicated process that uses multiple factors, including temperature, speed, force and tension to produce consistent results. It produces a wide variety of products, including drainage and irrigation pipe, medical fluid and IV tubing, weather stripping, fencing, deck railings, vinyl siding and automotive components. It can also be used to make drinking straws, the “zip” strip on re-sealable bags and thermoplastic coatings for wire insulation.
The first step in extrusion blow molding is the transport of thermoplastic plastic material from a material hopper to an extruder. This is usually done by vacuum pumps that draw the granulate out of big bags or bulk containers and into the material hopper. Alternatively, compressed air is used to convey the pellets into the hopper. In some systems, the granulate is fed into a distribution plate that divides it equally among four parison heads.
In the next step, the molded plastic is blown in place by air pressure. This makes the parison conform to the shape of the mold as it expands against its walls and solidifies. Once the plastic reaches its final shape, it is cooled and then sent to any finishing operations that may be necessary.
The main advantage of this process is the high level of control it provides. It can be automated and regulated to ensure that the finished product is consistent in both size and quality. To achieve this, the equipment must be carefully assembled and inspected to ensure that it meets production and safety requirements. The hydraulic and lubrication system must be checked and cleaned to prevent malfunction.
Intermittent
In intermittent extrusion blow molding, the plastic melt is not continuously expelled through the machine. Instead, it is collected in an accumulator until Forming Machine enough material has accumulated. This process is best suited for lighter parts that are less expensive to make, as it can reduce the amount of time spent on each part and the production costs.
When the accumulator has accumulated enough melted plastic, it is passed through a rod to form the parison. Then, a hydraulic system quickly pushes the pare out, which can reduce the weight of the molded plastic and allows for systematic control of the wall thickness. There are two types of intermittent extrusion machines: accumulator head and reciprocating screw. The accumulator head method uses an accumulator to collect melted plastic, while the straight intermittent method uses a reciprocating screw to move forward and backward. Both of these methods can be used to manufacture a variety of hollow plastic products, including bottles and containers.
Blow molding is an industrial process that is capable of producing large quantities of hollow plastic objects, such as bottles and containers, for a variety of purposes. It is a simple process that involves Forming Machine factory using heat and air pressure to inflate the plastic to its desired shape, before cooling it and ejecting it from the mold.
There are three main types of blow molding machines: injection stretch, extrusion, and injection-blow hybrid. Injection stretch blow molders combine the injection molding and blow molding processes to create plastic bottles. This type of machinery is used for low-volume production, such as small medical and single-serve bottles.
Extrusion blow molding (EBM) is the most common of all the types of blow molding machines. This process combines injection and blow molding to produce hollow plastic products such as bottles, containers, and other plastic goods. It is the most economical process for making hollow plastic workpieces, and it produces the largest variety of parts. The EBM process is also the simplest and fastest to use. Injection stretch blow moulding (ISBM) is a more complex version of EBM, and it produces more accurate parts than traditional injection-blow molding. It is the most common technique for producing plastic beverage and food containers, as well as automotive ducting and industrial products.
Single-stage
Traditionally production of PET (Polyethylene Terephthalate) bottles requires injection molding of preforms and then subsequent stretching and blowing of those preforms into bottles. This process can be undertaken in two separate machines (the single-stage method) or one integrated machine (the two-stage or integrated single-stage process). Both processes have their own perks and drawbacks, but the decision which to choose will depend on what’s most important to bottle producers and brand owners.
During the early stages of PET bottle development equipment developers took what was called the Integrated Two Stage approach. This involved taking a continuously extruded PET tube and using injection molds with the number of cavities optimized to match the desired output, then blowing these preforms into a bottle shape. This allowed the manufacture of complex shapes, and a range of bottle neck finishes such as vent slots.
A more recent development has seen the introduction of single-stage machines where both injection and blowing are carried out in one machine. This allows the use of dedicated high-performance, multi-layered extruded preforms, allowing for significant reductions in bottle weight as well as higher levels of stiffness and clarity. It is also able to accommodate a wider range of neck diameters than the older 4-station injection, reheat, stretch blow and ejection methods used in the 2-stage process.
These single-stage machines have a more efficient blow station, which reduces cycle times and eliminates the energy costs associated with reheating and conditioning. This type of machine can produce specialty bottles, such as for soft drinks, as well as a range of other applications including oil, cosmetics and detergents.
Single-stage machines are highly cost-effective for the production of specialty products. They can be supplied with injection units from SIPA for the production of dedicated high-performance preforms to achieve optimum characteristics such as thickness, density and neck/cap fit. Combined with a XFORM injection system, they can also be used to produce a wide variety of bottle shapes, sizes and finishes.
