# Control of Physical Processes in an Extrusion Line Polymer Sleeves Production
## 1 Introduction  
The main task of grain producers is to reduce costs and losses to a minimum, as make well as profitable sales [1; 2; 3]. The prices for the services of transport companies, as well as the prices of elevators for the drying, cleaning, and storage of grain significantly increase the cost of the final product (up to 50% of the cost of grain), making it less profitable to sell [4]. Farms are forced to store grain in currents [5] and open areas that are not suitable for long-term storage, thus leading to a loss of quality and, as a consequence, losses. Since the late 1990s, to solve the existing problem, farmers began to use polyethylene sleeves to store dry grain. The birthplace of grain storage technology is Argentina [6]. This technology is also actively used in Canada, Australia, some other countries of the American continent, South Africa, France, Spain, etc. [7; 8; 9]. In the Commonwealth of Independent States (CIS) countries, this technology has been used for several years, since it does not require large investments and can reduce storage costs by at least three times. The efficiency of grain storage depends on several parameters, the most important of which is keeping the microclimate [10; 11] in hermetically sealed bags. This achievement is ensured by the total integrity of the sleeve materials, consisting of high-density, three-layer polyethylene. The white outer layer of the sleeve contains titanium dioxide, which reflects the sun's rays and prevents the temperature inside the sleeve from dropping down [12]. Two black layers on the inside protect the product from the penetration of sunlight. All three layers are inseparable; each of the layers is made of different polymers with different additives and stabilizers. The sleeve material must provide increased strength, absolute tightness, and elasticity [13]. It should be emphasized, once again, that maintaining the microclimate in hermetically sealed bags is responsible for the effectiveness of this technology [14]. Therefore, the basic task of cereal producers is to ensure the general integrity and adequate strength of the materials from which accumulation sleeves are made [15]. From the analysis, it was found that most of the defects in the polypropylene film of the agricultural sleeves for grain arise during their drawing, that is, during the extrusion process [16; 17; 18]. A distinctive feature of these defects is that they cannot be eliminated during the production process (irreparable defects) [18], that is, they have to stop the entire extrusion line and change it [19]. In the extrusion industry, there is an increasing tendency to combine various control devices under the control of one common device that exercises full control and management of all mechanisms of the extrusion line. It should be noted that a plurality of extruder control stages can be implemented in a hierarchical relationship. The most common devices combine temperature control in different areas [20]. Most often, the task of such systems is to maintain the specified melt parameters by controlling the heating of the first two or three zones, which are closest to the zone where the polymer melts. The change in temperature in such zones is carried out automatically by the cascade control system. However, in this way, it is possible to carry out an adjustment at a rather low velocity, since the response of the zones of the working volume to changes in temperature parameters is very slow. Pressure control systems are also often found to rely on a smooth change in screw velocity, in order to maintain a constant pressure of the polymer melt [21]. New types of extruders are often equipped with a microprocessor system that allows simultaneous control and management of the temperature and pressure of the melt, as well as the thickness and width of the extrudate and other extrusion parameters [22]. Some control systems can be combined into general production management.