Plastic and Masterbatch Screening
The plastic manufacturing process includes, among other steps, the production of pellets of raw material. A pellet is nothing more than a small portion of some material that has been highly compressed. In the case of the plastic industry, pellets are mainly manufactured from petroleum-based polymers.
On the other hand, different additives or colors can be added to these pellets to obtain particular characteristics of the plastic to be produced. These additives are known as “masterbatch”. The functions of masterbatches can be varied since, in addition to adding color to the plastic, they can provide lubrication, hardness or stabilization against UV light. Masterbatches are also incorporated in the form of pellets.
Plastic manufacturing process
The plastic manufacturing process involves different molding techniques, some of which use the raw material –plastic and masterbatch– in the form of pellets. In these, the pellets are melted to make them moldable.
Pellet molding techniques
The main techniques using plastic and masterbatch in the form of pellets are injection and extrusion molding. In these two high-pressure molding techniques, the pellets are poured into a feed funnel that feeds them into a cylinder containing a worm screw. Subsequently, by different procedures, the plastic is cooled and the specific products are obtained according to each technique.
Disadvantages of pellets
Although pellets are one of the most common forms in which the raw material is used in the plastics industry, they often have some drawbacks. There are different forms of pellets: some are cylindrical and flat; others are rounded, but flat; and others are spherical.
The flat faces of the cylindrical and rounded pellets have a tendency to join together and agglomerate them in pairs or even to form long strands or filaments. These multiple pellet presentations can clog injection and extrusion equipment if they are not separated beforehand. For this purpose, there is screening equipment available to remove unwanted pellets.
Plastic and Masterbatch screening
The plastics industry requires the screening of large quantities of material. For this purpose it uses high-capacity and high-precision equipment. Equipment performing the plastic and masterbatch screening is based mainly on two different operating principles.
Linear pellet screeners
The operation of the linear pellet screeners is carried out by motors that move the material forward in a straight line while it is being screened. These machines can also incorporate a vibration function to facilitate the separation of pieces of different sizes. In some models, a reverse effect of the motors can also be combined in order to describe a parabolic motion.
Tumble gyratory screeners
The operation of the tumble gyratory screeners is based on the separation of particles that takes place on the drum during its rotation. There are tumble gyratory screeners in which the sample moves in a round vibratory form.
On the other hand, there are more advanced models, based on a side-to-side gyratory motion. These screeners have more efficient counterweight systems, without vibration, which guarantee a longer life for the equipment’s motor.
Other plastic screening processes
There are other processes that can be used on plastic pellets, such as dewatering of pellets and screening of pellet powders. Both work on the basis of vibratory screening and classification. To carry out these functions, there are both linear equipment and rotary equipment, depending on the purpose and quantity of product.
The plastic and masterbatch screening industry has made significant advances in recent times with the development of more sophisticated equipment and technologies. There are different options in the market offering quality, reliability and cost-effectiveness in their equipment. Constant research, prompt attention and effective service are also important features when looking for a plastic and masterbatch screening equipment supplier.
