Extrusion is a method of producing semi-finished products or products from polymeric materials of unlimited length. This process is also used in the food and feed industry. The extruder head extrudes the polymer melt into a forming head with the desired profile. This manufacturing method, along with injection molding of plastics, is currently one of the most popular. Almost all the main types of polymeric materials are subject to extrusion: elastomers, thermoplastics, thermosets, and others. So, the process itself is understandable, so it is worth considering the extruder: what it is, how it works, as well as other points associated with it.
Principle of Operation and Design
Extrusion technology has existed for more than sixty years, and during this time many machine designs have been developed for its implementation. The principle of operation of the device is determined by the essence of the process itself. So, if we consider the extruder, what it is, it becomes clear after determining that this complex physicochemical process proceeds under the influence of mechanical forces under the condition of high-temperature exposure and the presence of moisture. The product is heated during processing due to the fact that mechanical energy is converted into heat released during the struggle against internal friction, as well as plastic deformation of the product or due to external heating.
In the process of extrusion processing, there are several interchangeable parameters, namely: the composition of the raw material, its moisture content and nature. During production, temperature, pressure, as well as the intensity and duration of exposure to the raw materials may vary.
Working methods
Considering the extruder, what is it, we will understand in order. There are three main working methods: cold forming, hot extrusion, and warm processing. Recently, the most common method of hot forming, carried out at high pressure and speed, when there is a significant transition of mechanical energy into heat. To implement the process, you can use a screw extruder, in which the main working body is a screw of a special design that rotates in a cylindrical body. The forming matrix is at the exit.
The extruder scheme suggests that in the design of its working part, the screws and chambers are mounted to accurately perform the tasks. There is a loading chamber where raw materials and mixed additives are introduced, closed chambers in which there are openings for measuring pressure and temperature, as well as the addition of liquid substances and sampling. Augers can be equipped with additional elements, so the product will be moved under additional resistance, and everything will be mixed in the process.
Extruder: what is it and how is it arranged?
The working part of the mechanism, taking into account the stages of the processing process, can be conditionally divided into three zones: the first, which is responsible for the reception of raw materials; the second, responsible for plasticization and compression; the third is the product extrusion zone. The working part of screw extruders can have one of several different designs:
- single screws: cylindrical with constant or variable pitch, conical, helical, conical with a pitch decreasing towards the exit;
- twin screws: rotating in one or different directions;
- twin augers that engage: rotating in one direction and self-cleaning, rotating in different directions and partially cleaned.
Using
The cereal extruder works due to the fact that in the particles of grain located in a closed chamber, when heated, an increase in internal pressure due to evaporation of moisture occurs. Due to the instant depressurization of the chamber, the expansion of the vapor-air mixture occurs, which leads to an increase in the volume of grain particles.
In the feed industry, single-screw mechanisms with a constant pitch and a cylindrical shape of the screw are most often used. The production of extruders of this design uses a set of screws, and between them in a clearly defined sequence there are several retaining washers, and the screws and washers on the stud are fixed with a bolt with a conical head. The casing of the working part is equipped with several longitudinal channels from the inside, which ensure that the product will not twist during movement. At the outlet of the casing there is a conventional flare nut with a hole. Adjusting the gap between the cones of the screw for attaching the screws with the output nut allows you to adjust the temperature of the product. This is how the extruder works. What is it, you already understand, now it remains to deal with other points.
Machinery production
Different models of extruders are characterized by different designs of the elements included in the working part, the number of working chambers, the presence of additional systems with which the technological capabilities of devices are expanded, especially drives, feeders and other parts. The cylinder shape is recognized as the most technologically advanced in terms of manufacturing, which makes its cost price the lowest.
Technology today
So, you can consider how the extruder works. What it is, was described earlier, and now it is worth deciding on some important points. Modern designs of mechanisms implement the technology of dry extrusion. It is so named due to the fact that the whole process is carried out using the heat released during the passage of the product through the working part of the mechanism. It is possible to use steam for extrusion. For this, the device has a chamber for preliminary steam processing of raw materials. Using steam allows you to increase productivity and reduce wear of the main parts and components of the mechanism.
Dry extrusion
The whole process takes no more than 30 seconds. This time is enough for grinding, heat treatment, dehydration, mixing, disinfection, stabilization and volume expansion. You can make an extruder with your own hands, working on this technology. To do this, you will need to purchase all the elements for the future mechanism, which will later be connected in accordance with the device diagram. You will need a screw of a suitable configuration, an electric motor, which will become the basis of the mechanism, the case of the future device, supplying capacity and capacity at the outlet, a chamber in which a vacuum will be created.
Alternative examples
The extrusion process can be used not only in production. There is such a device as a manual welding extruder, which is designed to connect polymer materials, namely films, to each other by heating their edges with simultaneous joining. Most often, such a device is used to connect elements from thermoplastics. These substances are now found everywhere. These are basins, hoses, buckets, barrels, hatches, containers, sewer grilles, elements of the external and internal decoration of the premises. The list can be made quite long. Such an abundance of thermoplastics has led industrial manufacturers to develop highly compact devices that are designed to work with these materials at their places of use. For this, a welding extruder was developed. Its use significantly simplified the work on welding products from synthetic thermoplastics: polyvinyl chloride, polyethylene and polypropylene.