Polyethylene Production with Blow Molding Technology
The machines that heat and plasticize HDPE high density linear polyethylene raw materials, blow them in a suitable mold by blowing method and produce hollow plastic containers are called polyethylene blow molding machines.
In general, the blowing technologies of the machines that have a say in production are as follows:
-Extrusion blow molding (continuous, accumulative and co-extrusion)
-Injection blow molding
-Injection stretching blow molding
Extrusion Blow Molding Machines
Extrusion blow molding technology is one of the most used methods in the blow molding industry. It is a technique similar to the method applied in glass bottle production. It is a molding method that enables the production of various sizes of bottles, drums and similar plastic articles from 2 milliliters to 9000 liters. This method is based on the principle of blowing the parts obtained from the mold in the form of pipes and cut into desired dimensions (also called parison) in a hot mold by blowing air into it until it takes the shape of the surrounding mold without letting it cool. The material in a closed part is forced to flow through a die opening by applying pressure. At this time, a continuous product with a fixed cross section is formed as determined by the material mold cavity. In this way, the hose (parison) is formed from thermoplastic materials. The hose is brought to the vertical flow position by means of the deflection head. The extrusion process is a continuous process, after the hose is cut, another mold is given a hose, or while the hose in the first mold (parison) moves away from the extruder with the mold, the other mold comes in front of the extruder and the hose is taken into it. Then, the hot plastic hose inside the mold is inflated in the mold cavity with the air pressure between 5- 10 bars and the finished product is formed.
The picture below shows the formation of hoses in the extruder.
Parison formation with extrusion Picture
The Advantages of Extrusion Blow Molding Method
-The pressure used in inflation is much lower than the pressure used in injection, another method of shaping the same material. Therefore it is economical. The required extrusion blow molding machine park is cheaper than injection blow molding machines.
-It is possible to produce the screw regions on the produced part and forming the product cover part in a single mold
-Products can be obtained in different geometric shapes and desired sizes
-The neck area and body of the polyethylene water tank always looks good
-There is no burr problem in production and the product always comes out in the same weight.
Picture of extrusion blow molding process
In extrusion blow molding, the piece (parison) is brought to the appropriate position on the mold as shown in the figure. The plastic remaining in the mold is cut from the flowing raw material by a hot knife. Then air is blown into the mold at the appropriate pressure (0.4-1.0 MN / m2). Following swelling, the piece is cooled and removed.
Basic Stages of the Extrusion Blow Molding Process
-Plasticizing and preparing thermoplastic raw material in an extruder
-Routing the molten plastic with a vertical flow
-The molten raw material is turned into a fluid hose called parison and flowed out of the head (The head where Parison flows is also called only the head, extrusion head, blow head and parison head.)
-The clamping of the head flowing parison between a mold with the help of a vise
-Inflating pins or inflating needles (or valves) entering the closed mold
-Inflation of the parison between the cooling walls and the cooled water by means of inflating pins with compressed air and at the end of the inflating process, removing the throat burr
-The mold is opened and the inflated product hangs on the inflation pin
-Deburring of the inflated product from the edge areas
Accumulative head extrusion blow molding is an ideal solution especially for the production of high volume products, polyethylene water tanks. The specially designed head ensures that the raw material transmission is fast and prevents fluctuation marks on the product. The water-cooled inflation pin is hydraulically controlled. Blow group can move up and down. The movement characteristic of the blowing group helps the parison to have a stronger structure and increase its durability during molding and opening the mold. The difference of the machines we use from other extrusion blow molding machines is that, thanks to the changeable head, it enables the formation of a second and third color product as a strip on the hose to be inflated.In this way,we are working with machines with a production capacity of Turkey's largest liters of the product that hygienically and potablely white inner layer, preventing harmful rays (UV) of the sun and moss, dark gray middle layer that prevents odor formation and outer layer that gives blue color and durability.
Polyethylene Products that We Can Obtain with Blow Molding Technology;
- 500 liter horizontal 3-layer polyethylene water tank
- 1000 liter horizontal 3-layer polyethylene water tank
- 1500 liter horizontal 3-layer polyethylene water tank
- 2000 liter horizontal 3-layer polyethylene water tank
- 3000 liter horizontal 3-layer polyethylene water tan