Features of wear of the centrifugal husker blade and dynamics of seed movement



Sunflower and soy seeds are the main oilseed raw materials for the production of vegetable oil and high-protein products.

When processing this raw material, one of the basic operations is peeling. The effectiveness of this process determines the quality and yield of the resulting vegetable oil, cake and meal.

The most effective method of peeling oilseeds is the single-impact method, which is implemented in centrifugal husker. The theory of operation of the centrifugal husker is based on the equations of motion of a particle when it slides with friction on the working surface of the guide blade of a rotating rotary device. In this case, the wear of the working surface of the guide vanes resulting from friction should be uniform in length. However, the operation of the centrifugal husker has shown that periodically alternating wear zones are formed on the working surface of the blade. Experimental research and development of the theory of centrifugal peeling, taking into account this effect, are relevant for the scientific justification of improving the process, equipment and technological regime of processing sunflower seeds and soybeans, ensuring high quality of the husker.

Keywords: method of single blow, centrifugal husker, peeling, movement of the achenes, MRC.

The peeling of oilseeds by a single blow

Hulling of sunflower seeds by the method of single blow, embodied in the centrifugal husker is the best way to branch of a fruit coat with minimal oiling [1]. Development of modern varieties of sunflower seeds is particularly significant, such as hybrid, when fruit coat and kernel are practically grafted. Various designs of centrifugal husker with rectilinear blades cover are known — A1-MCP [2], type MRC-5 [3,4], A1- MRC [5] and centrifugal husker with a curved profile of the rotor blade [6]. In type of centrifugal husker A1-МЦП has rectilinear radial blades, which are made of ceramics.

During production, when mineral or ferromagnetic impurities get on them, the ceramic blades are destroyed. Therefore, for safe operation of the centrifugal husker through cleaning of incoming seeds from various impurities is necessary, it is almost impossible, since inorganic impurities equal to seeds will in any case get into the seed mass.

In the centrifugal husker with backward-curved blades, in working premature separation of the achene occurs under the influence of aerodynamic from the convex surface of the blade, which worsens the effectiveness of peeling.

Centrifugal huskers MRC-5 and A1-MRC have rectilinear-steel and wear-resistant blades, it allows increase their operation term. But in process long-term operation radial blades also subjected to wear. Radial blades of centrifugal husker types MRC-5 and A1-MRC were examined.

In figure 1–3 representing the various zone of wear blade (shows half of gutter): in the lower part, caused by the displacement of the seed flow under the influence of gravity (Fig. 1); passing through the central line (Fig. 2); in the upper part, caused by the displacement of the seed flow under the action of aerodynamic forces (Fig. 3).

There are periodically located hole chafing (wear zones) on the side surface of the blades. The end result of hole chafing is one hundred percent wear of the end part of the blade cover of the centrifugal husker rotor device. It should be noted that the surface of the hole strictly symmetrical relative to the plane of section passing through the central line of the blade cover of the rotor normal to it (Fig. 2). However, such symmetry is not observed on the working surface of other rotor channels (Fig. 1 and 3). The observed displacement of the hole chafing occurs under the action of gravity (Fig. 1). This fact confirms the need to take into account the last term in the solution of the basic differential equation of the relative motion of the achenes along the rotor, containing the acceleration of gravity, which was previously proposed to be excluded in the calculation [7]. The manifestation of this force is possible if the movement of the achenes occurs over the working surface due to inertia and under the action of aerodynamic forces. The longer the flight of the achene between adjacent wells, the stronger this effect is manifested. Wear zone as a result of the leapfrogging motion of the seeds are observed on all surface of the blades cover shown in Fig. 1–3 and Fig. 4, which shows a blade with zones caused by the displacement of the seed flow under the action of gravity (lower part) and under the action of aerodynamic forces (upper part).

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Quite substantial aspect of finishing move of the achenes along the rotor blades, is the presence of holes chafing defined by total wear of the end parts of all rotor blades, regardless of the nature of the symmetry of the holes. The trace of such holes chafing remains only in the outlines of the wear fronts (Fig. 1–4). This effect is posed by a meaningful increase in the final speeds of the achenes flying out of the penult, not quite worn chafing holes (Fig. 2). Figure shows the sequence of the appearance of chafing holes along the trajectory of the achene directed to the sounding board. As a result, the impact force of friction acquires such values that are sufficient to completely wipe out the end hole of chafing first (Fig. 3). Then, by repeated impact chafing mechanism, with the abrupt movement of the achenes, periodically located wear holes are formed.

Figure 4 shows a photo of a radial blade of the centrifugal husker type A1- MRC with a capacity of 200 tons/day for sunflower seeds. The blade is removable plate, the upper and lower edges of which are flanged. The surface along the central line of the blade is somewhat in the direction of rotation of the rotor device. As indicated, on the surface blade cover in its upper and lower parts, 2 large zones of complete wear and formed, consisting of several fused chafing holes, the outlines of which are periodically located along the length of the trajectory of the seed flow. Such wear is also characteristic of the МРЦ-5 blades discussed above. This confirms the abrupt nature of the motion of the achenes in various structures of the centrifugal husker due to the aerodynamic force of the air flow [8]. The lower part of the blade has a longer wear zone along its length, which is obviously due to the downward displacement in the direction of the seed flow under the action of gravity.

It should be noted that in holes wear depicts well the front line the beginning of their wear in the form of hyperbolic curves (Fig. 1–4). Near these fronts, the chafing holes have the greatest depth, the surface of the curvature of which is steeper to the leading fronts, compared with the surfaces of the rear fronts (Fig. 5). Firstly, this means that the greatest concentration of the achenes as they move towards the exit of the channels occurs along the axis of the hyperbola passing through the middle of the working surface. Secondly, this is also explained by the nature of the movement of the achenes, which can be divided into at least the following three stages: pre-midnight movement, intra-midnight movement and post-midnight movement of the achenes. This sequence of movement of the achenes can be repeatedly repeated.

Fig. 5

Consider the movement of the achenes inside the wear hole, the schematic section of which is shown in Fig. 5 where the section is selected inside the hole arbitrarily. The driving force of the process is the centrifugal force of inertia F _И is decomposed into normal _ИН and tangential F _ИТ components to the surface of the well along the direction of movement of the achene. The intra-well movement of the achene ca be defined by two stages: the first stage refers to its movement along the surface along the section curve of the AO, the second stage refers to movement along the segment of curve OB.

In the first phase, normal components partially compensate for the force F _kg = F _k + F _g reducing the total pressure of the achene on the surface of the well (points 1, 2, etc.), which leads to a decrease in the friction force and thereby an increase in the velocity X (in the case of

> 0). It should also be taken into account that with increasing X, the force F and its tangential component also increases, which acquires a maximum value at all points O along the axis O-O' of the cross section of the friction well. At these points, the lifting component of the inertia force decreases to almost zero. Thus, at these points of the cross-section of the wells, there is a qualitative and quantitative change in the processes of movement of the achenes.

In the second phase, F _и fed to the inside, deep into the material of the blade and its normal component to the surfceof the hole coincides in the direction of the force F _kg , leading to increased friction force (according to the case < 0). This leads to an increase in the coefficient of friction and inhibited movement of the achenes along the entire segment of the curve OB. On the surface of the channel at point B, two components of the velocity of the achene arise: the first V _В1 is directed tangentially to the curve at this point, the second velocity — V _В2 is due to the action of the inertia force. As a result, the achene moves with some total initial (outgoing) speed V _ОП =V _В1 +V _В2 in the direction from the work surface, more precisely, the achene moves over the work surface for some time by inertia at a speed of V _{ОП .} The action of aerodynamic forces is superimposed on this movement by inertia. As a result, the flight time of the achene over the working surface is determined by three factors, of which only the first depends on the shape of the curve OB at the point of departure of the achene from the friction hole. This relatively free movement of the achene is stopped by hitting it on an impending work surface moving with angular velocity ω.

The influence of the wear pattern of chafing holes and their periodicity can obviously be explained by various conditions for the formation of the structure of seed flows entering the blade cover of a rotating rotor device. These conditions may be purely design features structuring the flow of the achenes, which is clearly seen from the characteristic wear zones formed at the entrance of the achenes in the lower right part of the blades (Fig. 1–3) of the МРЦ-5 husker. Flow parameters such as the degree of tightness of the achenes in the flow, the degree of preferential orientation of the achenes (the order effect) and other properties are determined by statistical features of the distribution functions of the achenes according to geometric, kinematic and dynamic parameters at the entrance of the achenes to the guide channels. The most characteristic features of the structuring of the flows of the achenes entering the blades cover in the channels of the centrifugal husker rotor are the following:

— differences rotation of achenes in randomly selected cross-section of the flow of achenes due to their varying degrees of tightness;

— different density of achenes in the flow sections due to their varying degrees of tightness at the entrance to the blades cover;

— due to the above properties and taking into account the friction of the achenes on the working surface of the blades, chafing holes are formed, which are created by the slowest moving achenes in this section and having the lowest densities in this section of the flow;

— the possibility of restructuring flow as approaching the speed to the soundboard;

— the flow of the achenes by the flow of air drawn into the channels, contributing to their preferential orientation along the direction of action of the centrifugal force of inertia, as a result of which the orientation of the achenes with the end part in the direction of the deck occurs;

— matching separate pairs oriented achenes in the area of short-term emerging staganant zones;

— the process fascination of the achenes with the air flow and their mutual friction with each other increases as the achenes move away from the axis of rotation of the rotor, it can be neglected when the speed of the achene approaches the speed of the air flow (Haggel effect, the physico-mechanical essence of which is the predominance of aerodynamic force over the friction force);

— with the dense motion of the achenes in the air flow, the lloss of kinetic energy of this flow to chafing against the holes of the channels can be neglected;

— the nature of the structuring of the flow of achenes is a random phenomenon, therefore, the distribution functions of the dynamic parameters of the achenes are normal (Gaussian) functions;

— the magnitude of the relative velocity of the achenes at the outlet of the channel is distributed according to the normal law.

Conclusions .

The review of wear blades cover and dynamic move of achenes show, achenes have the saltatory pattern of move along the surface of the blade cover. As a result, separate section are subjected to wear with the formation of periodically located chafing holes. During long-term operation, the blades are subjected wear, especially their sections, in the area of which the speeds of the departing seeds significantly increase.

Thereby, flow rate calculation of achenes take into account the acceleration of gravity and aerodynamic forces is necessary, which play a decisive role in the complex motion of the achenes in the centrifugal husker channels.

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