Increasing the performance and service life of the brushes of the cotton gin under conditions of shock-bending loads

The purpose of this paper is to increase the service life of the brushes in the interaction of the puller brushes and the drum when cleaning cotton from large debris during the cotton removal process. The authors conducted an experimental study to determine the actual value of the number of impacts (touches) of the puller brushes on the surface of the saw drum. The angle of rotation of the serrated drum around its axis during the period of influence of the puller brushes on it was determined. The paper also describes determination of the average number of blows (touches) of the puller brushes on the saw drum.


Introduction
Prediction of the reliability and working life of mechanical systems and creation of the methods of calculating the deterioration of various joints can be done only based on assessing changes in the parameters of the friction unit as a result of deterioration of the working surfaces under specific operating conditions of the machine.Numerous studies show that up to 70-80% of machine failures occur due to deterioration of friction units.In our country, a lot of means is spent annually on the repair of machines and equipment, a huge number of spare parts are produced, a large fleet of machine equipment is used for repairs, and increasingly people are taking part in the field of machine repair and maintenance [1].
Exploitation of equipment in the climatic conditions of the Central Asian republics, characterized by an abundance of light and heat, strong winds and dust storms, low air humidity with high above-zero temperatures, leads to a sharp, (1.5-2 times compared to the temperate climate zone) reduction in the efficiency of machines and mechanisms [2,3].In hot climate zones, machines operate at high temperatures, intense solar radiation, dust storms, low relative air humidity and high dust levels.In dusty air, the size of dust particles varies widely from <0.005 to 0.6 mm or more; dust contains up to 80-95% quartz and oxides of aluminum, calcium, and iron.The service life of machines in such conditions is sharply reduced, the wear rate of parts increases by 2-10 times, and ~80% of them fail due to abrasive wear [4].
High deterioration resistance of quickly wearing parts is the key to ensuring the reliability and working life of machines.One of the ways to increase the deterioration resistance of parts is to select the materials from which they are made.However, using this method, only the deterioration rate can be reduced, but not control the process itself and, what is especially important, the changes in the condition and performance of parts that it causes [5].In addition, the method is not always economically justified due to the scarcity of materials, the complexity of restructuring the technological process, and also because of the need to conduct numerous expensive experiments.

Materials and methods
High deterioration of the bristles of drum brush is a significant drawback in application of removable brush drums in the design of raw cotton cleaners.According to technical specifications, the service life of the brushes is 2500-2600 hours.Consequently, the brushes on the machine are completely replaced twice a year.It is necessary to take measures to increase their durability (Fig. 1).
As we know, the durability of brushes under conditions of shock-bending loads depends on the following main factors: • physical and mechanical properties of the fiber material; • free escape length and bristle diameter; • shape and size of the edge where the bristles bend; • the angle of contact of the bristles with the serrated headset.Among the above factors, the most important is the angle of encounter of the bristles with the serrated set, which is the main indicator for deterioration of the bristles of brush drums, because the angle of encounter of the bristles with the serrated set leads to a change in the friction force between them [6.7].It was experimentally established that when the bristles wear out, the shape and size of the edge at the point where the fibers bend.The serial brush used is a wooden strip with tufts of bristles with a diameter of 0.24 cm; length of free escape of bristles is 25 mm; the edge where the bristles bend is rectangular.
Brush removal of fibrous material from the serrated teeth of technological machines has a number of advantages compared to air removal.This is especially noticeable when using this removal on gins, linters, indirect fiber separators, regenerators, etc. however, due to the undeveloped design of brush drums and the scarcity of bristles, brush removal is used mainly in cotton cleaners for removing large debris.Considering that in recent years brush drums have been developed that do not deform during the construction using non-scarce artificial nylon bristles, the scope of application of brush removal can be significantly expanded [8].
In this regard, the task arose to study some aspects of this type of removal.Information about brush removal in literary sources does not allow optimally solving design problems when creating new machines.There are also misconceptions about the operation of brush drums.Thus, the prevailing opinion is still that the brush drum, in relation to gin-linter machines, works like a fan and the fibrous mass is removed by the air flow developed by the drum.As far as the air flow performs the transport function [9], it is desirable that it be characterized by increased pressures and speeds, which largely depend on the diameter of the removable drum, the frequency of its rotation and especially on the pitch of the brush strips [works of R. Rakhimov, P.N.Tyutin on the removable drums of cotton gin machines [10].
The quality of cotton removal from the serrate drum of a cotton cleaner from coarse litter largely depends on the correct ratio of the speed modes of the serrate drum and the brush puller, the intensity of the impact of the brush pullers on the serrate drum, as well as the stability of the rotation speed of the serrate drum during exposure to it puller brushes.
The purpose of this work is to increase the service life of the brushes in the interaction of the puller brushes and the drum when cleaning cotton from large debris during the cotton removal process; conducting an experimental study to determine the actual value of the number of impacts (touches) of the puller brushes on the surface of the serrate drum; determining the angle of rotation of the serrate drum around its axis during the period of influence of the puller brushes on it; determination of the average number of impacts (touches) of the puller brushes on the serrate drum [11].
There are some theoretical principles that clarify the features of the interaction of the spindle and puller brushes.

Calculation of the touch range of the puller brushes from the serrate drum
According to the conditions of the normal course of the process of removing cotton from a serrate drum in its most approximate state with a bristle puller, the latter should go deeper into the teeth of the serrate drum by 2-2.5 mm (Fig. 1).Consequently, the interaction of the puller with the serrate drum occurs in a small area limited by points Он and Ок ∪  ℎ   =    (rad) (1) Knowing the values ∪  ℎ   we determine: where   is the radius of the serrated drum (Pb);  is the depth of the puller brushes into the teeth of the serrate drum (2-2.5 mm).

Calculation of the angle of rotation of the serrate drum
The radius of the existing serrate drum structure is   = 250 m.Therefore, for a complete revolution of the serrate drum around its axis, its center must pass an arc of length: ∪   = 2  = 2 • 3.14 • 250 = 1570 mm.Theoretically, the angle of rotation of the serrate drum around its axis during interaction with the puller can be determined by comparing the lengths of the arcs ∪  ℎ   и ∪   .

Calculation of the duration of exposure of the puller brushes to the surface of the serrate drum
Knowing revolutions of the grid drum of the existing design Pb = 280 rpm or 6.3 rps, we determine the path through the center of the serrate drum in one second: = ∪  ℎ    ,  = 80 4396 = 0.01

Calculation of the angle of rotation of the puller during interaction with the serrate drum
The rotation angle of the drum puller can be calculated according to the known data using the following formula:  = 2 *   *   / (3) where пс is the number of revolutions of the puller Pc=950 rpm =1.8 rps;  =2•3.14•300•0.01=188°.
If we assume that the number of brush strips on the puller is 12, then within an angle of 188° there are 3-4 strips and, accordingly, the number of impacts will also be within these limits.
The rotation of the serrate drum by an angle   can be determined: ℎ * , (rad/mm) (4) And according to the formula, we determine the arc length of the serrate drum circumference processed by one puller brush.
* =    ` , (5) Obviously, to ensure removal, the peripheral rotation speed of the removal drum  2 must be higher than that of the serrate drum  1 .Removable strips with fiber interact in the saw section.When turning the serrate drum at an angle of 2α, the removable drum will turn no less than 2 2 + .Expressing the time of rotation of the serrate and removable drums at these angles, respectively, through  1 и  Where  1 ,  2 are angular speed of the serrate and removable drums, respectively,  ; ⁄  1 ,  2   angles, rad.
After substituting the values of  1 ,  2 into expression (6), the calculation formula will take the form where K is the assurance factor (K = 1.15-1.25);α is the central angle between two removable strips.
From Fig. 1 it follows that The coordinates of point D are determined from the intersection of circles I and II Due to the presence the serrate board, according to this option, the area of interaction between the removable and serrate drums is halved.The equations in this case will take the form angles  1   2 are determined by formulas ( 3) and ( 4), and the coordinates of point C are according to the same formulas as for point D ( 10) and (11).

Conclusions
Conducted studies have shown that in the immediate removal area, the air flow prevents cotton removal, i.e., the removal operation proceeds mechanically, and the role of the air flow is limited to the transport function.
The results obtained allow objectively evaluating the effectiveness of the interaction of the serrate drum of brush pullers during operation and to optimize the parameters of the cotton removal zone from the serrate drum.
The given formulas allow determining the angular speed of rotation of the removable drum for machines for various purposes.For example, with diameters of 320 and strip 380 mm, the arc spacing 50 mm (α = 15°), i.e., the required speed for the cotton gin.The method we propose can be applied in the practice of designing removable drums for a wide range of machines.

Figure 2 .
Figure 2. The scheme of the interaction of the puller brushes with the serrate drum of the cotton cleaner.