Processing of plastics: technology, equipment

Plastic materials over the past 10-15 years have formed a wide range of directions in which products of their processing can be used. Synthetic material itself is experiencing a period of radical technological changes, as a result of which the market for construction materials is filled with new proposals. It suffices to note the families of composites that displace metals and wood.

In turn, the processing of plastics as a method of obtaining a fundamentally new and, most importantly, more perfect in terms of performance of the material is not so interesting. Maximum with the help of this type of technology can recreate the previous synthetic structure. And yet this line of activity of processing plants is worthwhile for many other reasons, including environmental and financial ones.

Types of plastic waste

Technologists identify 4 categories of plastic waste that can be subjected to secondary processing. First of all, these are single-shot plastics in the form of scrap and directly waste, which can be introduced into masses that are similar in chemical composition. The second category is contaminated single-plastic plastics, for the processing of which, primary purification of technological processes is required. The third group is represented by mixed plastic waste containing foreign impurities.

In essence, the outside particles are the same contaminants, metal or cement elements that require pre-cleaning. Also, the theoretical basis for processing plastics provides for the separation of a group of different-grade plastic materials. In this case, not only plastic and third-party particles of other manufacturing or building materials are mixed, but also different structures of the plastics themselves.

Classification of processing methods

The main classification provides for the allocation of direct molding technology and molding from semi-finished products. As for direct processing, this group includes polymerization methods, contact molding, broaching and wet winding, as well as spraying. Techniques of molding plastic products from semi-finished products are also popular. To this direction of technological development of processing carry molding methods, extrusion, molding from prepregs and premixes. Also, the processing of plastics is physicochemical and mechanical.

Practically all mechanical methods of processing are focused on grinding of the cleared waste with the subsequent obtaining of a homogeneous mass. An important difference of this group of methods is the fact that the product obtained is not distinguished by its physico-chemical properties from the primary raw materials. On the contrary, physicochemical methods are based on technologies of destruction of the structure of the primary material, in the process of which the operational qualities of the obtained substance also change.

Crushing of plastics as a technology of preparation

This is a common operation in the processing industry, which is used not only in working with plastics. Depending on the requirements for the final fraction, the relevant units are connected to work. A universal grinding machine can be called sealers with auger bodies of mechanical action.

In the process of work, the loaded plastic mass is compacted by disk disk-granulators with friction mechanisms. As a rule, two plates are used, one of which preserves a stationary state. Crushing processing of plastic waste largely depends on the characteristics of the material itself.

For hard raw materials, crushers and aggregates equipped with carvers of different shapes are used. Work with polyethylene waste in the form of a film is performed more delicately. For example, on a complex line, which includes nodes for compaction, grinding and granulation. In this case, the knife elements are directly mechanical task of grinding.

Waste separation technologies

In part, this stage is associated with preparatory treatment activities, which have already been discussed above. But the process of separation as such is more extensive and is not limited to cleaning only from dirt. It is also important to carry out the separation after grinding, since small granules are easier to separate from foreign particles. So, the primary separation still provides separation of pieces of plastics from the metal. For this, magnetic and electromagnetic coils are used inside the drum rotating structures into which the target material is loaded.

During the rotation, small elements of colored and black metal lag behind the plastic and are output through special channels. It turns out the initial processing of plastics, which increases the uniformity of their composition. However, with this separation, some of the plastics themselves are lost. As a rule, the share of loss does not exceed 1%. Industrial wastes are used to clean the contaminants. The crushed particles are washed under a stream of water, which is fed under high pressure. Sometimes, to increase the efficiency of the procedure, solvents are added to the water.

Individual processing

The individuality of the processing is due to the fact that only the sorted plastic comes into the working area, ready to be mixed, even with the masses that are suitable for the structure. The processing itself is carried out in different ways, but the main one is considered extruded. A special installation with augers and a loading hopper takes shredded plastic, melts it and feeds it through an extruder to the production line. At the final stage of release, depending on the machine, the operator can change the parameters of the plastic output. The degree of compression of the raw material is also regulated, which also allows choosing the optimal length of the worm in order to ensure sufficient homogenization.

Such processing of plastics is considered to be gentle, in terms of maintaining the operational properties of the material, but this does not mean that it can be repeated endlessly. The fact is that the same plastic substance for this technology can be processed no more than 3-4 times depending on the conditions of use. In the future, the mass is sent to the secondary use line with deeper chemical processing.

Technology of plastic processing without separation

The elimination of the separation and purification phase of plastic waste also determined the specifics of the technology for further processing. Usually for this, melting machines with additional equipment for calendering the material are used. As a result, ready-to-use panels, plates and sheets of plastic are fed to the output. It is a coarse material with a rigid structure, which contains a large coefficient of impurities. Due to the content of third-party particles, the quality of plastic and environmental cleanliness are reduced. On the other hand, the processing of plastics without separation is low cost and in some areas provides the optimal material for technical characteristics.

Casting processing

In order to optimize the processing process, another method of reducing the cost of production was developed. The technology of multicomponent casting is a variant of manufacturing combined products. Its essence lies in the fact that a three-component product is created through several levels of molding. Its basis is a cheap plastic based on the same crude substances, and then follows the level of the average quality of the mass. In turn, the outer layers are a completely cleaned environmentally friendly composition, for the production of which extruder processing of plastics was used.

Manufacture of plastic materials on the basis of multicomponent casting is carried out by the technique providing passage of a waste through several channels. By the way, for internal layers, plastics are not always used. They are often replaced by cheaper material, which includes barium sulfate, talc, ceramics, etc.

Modification of plastic waste

It is not necessary that processing should be oriented towards obtaining the same operational and structural properties as before characterized by the product. This stage opens up wide possibilities for modifying the structure by introducing special additives. For example, secondary processing of plastics with the addition of an ethylene copolymer improves resistance to mechanical stress and elasticity. If such inclusion is introduced into the structure of polyvinyl chloride, then one can count on increasing the resistance to impact.

Equipment for processing

Specialized machines designed to perform processing in full cycle mode, not so much. In Russia, for example, the Reverzer installation is known from the Japanese company Mitsubishi. This is an example of the same extruder machine, equipped with augers and degassing device. Known domestic enterprises and English equipment for processing plastics, the advantages of which demonstrate the installation of EPG. This is a company that offers innovative ways of processing waste through extrusion with blowing.

How to choose the optimal method of processing?

To begin with, tasks that will be faced before the products released should be evaluated. This will initially determine the need for separation, and with the possible use of modifiers. The simplest and cheapest method is the unseparated processing of plastic products, which allows you to obtain quality fences, flooring materials, insulation panels, etc. The technology of processing of refined plastics is usually oriented to the subsequent release of polyethylene packaging.

Conclusion

The industry of processing of synthetic waste is very actual today and is in demand in various spheres of industry. Getting inexpensive and practical raw materials at low cost is the main motive that guides the participants of this market. At the same time, in Russia this sector of industry is not as developed as in Europe. Of the most developed can be identified except that the plant for processing plastics "Plarus", which has been operating since 2009. The technological features of this enterprise include the use of a modern method of processing PET bottles. At the same time, other enterprises are gaining momentum as well, each year increasing volumes of production of processed plastic in various forms.