RU2600763C2 - Pelletizing screw extruder - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: pelletizing screw extruder relates to processing of high-concentration polydisperse compositions by a feedthrough pressing method, including three-phase, with increased viscosity, limited shear strength, low adhesive ability ones, and can be used in various industries. Pelletizing screw extruder comprises a housing, a screw and a multichannel press-tool, on the inner surface of which facing the material flow and repeating the shape of the screw shank there are extruding channels with converging intake parts of any shape of a rotation body aligned with cylindrical parts, at different angles to the press-tool central axis in the direction of the screw rotation in planes tangential to axial cross-sections of the press-tool in centers of the extruding channels. Angles of the channels inclination increase as they move from the central channel with zero inclination angle. External surface of the press-tool with outlet holes of the channels is made as a convex segment of a sphere, angles of axes inclination of cylindrical parts of the channels differ from axes inclination angles of converging intake parts of the channels and together they increase as the channels move from the central channel with zero inclination angles of both axes.

EFFECT: invention provides higher quality of manufactured products by grain-size distribution, density, mechanical strength and porosity, higher mean efficiency by 2-6 %, as well as reduced by 1-3 % mass and energy losses due to reducing the number of forced shutdowns of the press when loosing stability of the forming process.

1 cl, 10 dwg

Description

The present invention relates to the field of processing by continuous pressing of highly concentrated polydisperse compositions, including three-phase, with high viscosity, limited shear strength, low adhesive ability, and can be used in various industries, for example, in the chemical industry (production of catalysts, sorbents, etc. .d.), food (production of intermediate products, dry concentrates, etc.), agricultural (production of animal feed, granular fertilizers, ma rokapsulirovannyh seeds, etc.), wood, building materials, machinery and others.

Known granulating screw presses for processing highly concentrated polydisperse materials by continuous pressing, close to the claimed in its technical essence and the achieved result: SU 1726256 (class B28B 3/22, publ. 15.04.92) (D1); RU 2198787 (CL B29B 9/06, B28B 3/22, publ. 02.20.2003) (D2).

Each of these presses includes a housing, a screw and a multi-channel press tool. On the inner surface of the press tool surface of the press tool of the above presses (D1, D2), forming channels are made with tapering inlet parts, the intersections of which exclude stagnant “dead” zones between the channels.

The disadvantages of the aforementioned granulating screw presses are the high molding pressure due to the relatively high resistance to mass flow at the inlet to the forming channels at the periphery of the press tool, the decrease in the average productivity of the presses due to their forced shutdowns with loss of stability, a significant dispersion of product quality indicators in terms of particle size distribution, density, mechanical strength and porosity due to a significant difference in the velocities of the expiration of the cords when exiting multichannel o a press tool in the center and on the periphery.

The closest in technical essence and the achieved result to the claimed one is a granulating screw press for processing by the continuous pressing method of highly concentrated polydisperse compositions, including three-phase, with high viscosity, limited shear strength, low adhesive ability, selected as a prototype: application RU 2012128540 (patent RU2510745 (class B29B 9/06, publ. 04/10/2014)) (D3).

The granulating screw press (D3) consists of a housing, a screw and a multi-channel press tool, on the inner surface of which, which follows the shape of the screw shaft, forming channels are made with tapering inlet parts coaxially with cylindrical parts, at different angles to the central axis of the press tool in the direction rotation of the screw in planes tangent to the axial sections of the press tool in the centers of the forming channels, while the angles of inclination of the channels increase as they move away from the central channel from zero angle.

The disadvantages of the known granular screw press (D3): the dispersion of product quality indicators by particle size distribution, density, mechanical strength and porosity, high molding pressure due to the relatively high loss of flow energy at the entrance to the forming channels mainly at the periphery of the press tool, significant mass loss and energy due to forced shutdowns of the press with the loss of stability of the molding process and for this reason the average productivity of the press is lower than the nominal.

These disadvantages are due to the fact that in the prototype (D3) the angles of inclination of the peripheral forming channels are small, since they are limited by the condition that the channels exit to the outer working surface of the press tool having a circle shape. As a result, there are significant energy losses due to a change in the direction of flow in the forming channels and, therefore, a high molding pressure and a small margin of stability for molding dispersed compositions. The loss of stability of the molding, often called the separation of mass from the reefs (cohesive rupture), leads to a forced shutdown not only of the press, but of the entire production line, and this is not only a loss of productivity of the production line, but also direct material and energy losses during equipment cleaning and subsequent start-up technological line.

The technical result, which is achieved by the claimed design of a granulating screw press, is to reduce the dispersion of product quality indicators by particle size distribution, density, mechanical strength and porosity, reduce the molding pressure by reducing the flow energy loss at the inlet of the forming channels mainly on the periphery of the press tool , as well as reducing the loss of mass and energy by reducing the number of forced shutdowns of the press with a loss of stability of the process and molding and an increase for this reason that the average productivity of the press.

The specified technical result is achieved by the manufacture of a granulating screw press, comprising a housing, a screw and a multi-channel press tool, on the inner surface of which is facing the mass flow and repeating the shape of the screw shaft, forming channels are made with tapering inlets of any shape of rotation, the external surface of the press the tool with the outlet holes of the channels is made in the form of a convex segment of the sphere, the angles of inclination of the axes of the cylindrical parts of the channels differ from the angles of inclination of the axes tapering of the entry parts of the channels and together they increase as the channels move away from the central channel with zero tilt angles of both axes.

The granulating screw press (Fig. 1) consists of a housing 1, a screw 2 and a multi-channel press tool 3. The shanks of the screw can be of any shape. The most common are the sphere segment, cone, plane. For forming highly concentrated polydisperse materials with increased viscosity, the screw shank in the form of a sphere segment is most effective.

The intersections of the tapered entry portions of the channels on the inner concave surface of the press tool 3 completely eliminate the “dead” zones between the channels, forming a surface in the form of a set of cells adjacent to each other with sharp concave edges. The gap between the shank of the screw 2 and the press tool 3 is reduced to the minimum acceptable and, taking into account the possible axial oscillation of the screw, is not more than 5 mm.

In FIG. 2a shows a view of a multi-channel press tool 3 from the auger side and characteristic sections of channels with different angles of inclination of the axes of cylindrical and tapering lead-in parts. In FIG. 2b-2d, the diagrams, part of the methodology [1, 2] and the results of calculating the design of the forming channels in the form of tables 1 and 2 are presented on the example of a press tool with 7, 19 and 37 channels with a diameter of 1.5 mm for a granulating press with a screw diameter of 41 mm for forming highly concentrated nitrocellulose solutions.

In FIG. 3 shows a full section AA (FIG. 2 a) of the nineteen-channel press tool 3, FIG. 4, section AA is given in isometry, in FIG. 5 shows photographs of a press tool on a mirror surface, where the outlet openings of the channels on the outer working spherical surface of the press tool are clearly visible.

The external working surface of the press tool, unlike the prototype (D3), has the shape of a convex segment of a sphere (Fig. 1-5). Changing the radius of this segment and shifting the center of the sphere along the axis of the screw allows you to change the convexity of the outer surface and, therefore, the thickness of the press tool and thus adjust the lengths of the forming channels, depending on their location relative to the axis of the screw.

In FIG. 2b shows a channel marking diagram on a marking plane normal to the axis of the screw. Channels are placed in nodes of a triangular (cellular, hexagonal, hexagonal) grid with a uniform pitch. The number of channels along the concentric layers of the hexagonal grid is: 1, 6, 12, 18, ... The number of channels equidistant from the axis of the screw along the layers in the form of concentric circles: 1, 6, 6, 6, 6, 12, 6, ... The total number of channels of the press tool when calculating in any way, it is determined by the sum with a cumulative total of the layers used: 7, 19, 37, ... (Fig. 2b).

The angle of inclination of the cylindrical part of the forming channels increases from 0 ° for the central channel (the 0th layer of channels in the marking diagram of Fig. 26 and in table 1 of Fig. 2 g) to the maximum for the most distant channels on the periphery of the press tool (1st, 3rd or 5th layer of channels in the marking diagram of Fig. 2b and in tables 1, 2 of Fig. 2d, 2e).

The limiting ratios of the angles of inclination of the axes of the inlet and cylindrical parts of the channels on the periphery of the press tool are determined by the condition for these channels to reach the external working spherical surface of the press tool (hereinafter, we call this a condition for the technical feasibility of the design of the press tool) (Fig. 2a, table 1 in Fig. 2d and table 2 in Fig. 2e):

S is the projection onto the marking plane of the vector of the full offset of the channel axis at the exit from the marking point of its center for the outer most remote layer of channels from the axis of the screw (Fig. 2a-2d),

Smax - the maximum offset of the channel exit relative to the marking point of its center is determined by the leg of the right triangle, the hypotenuse of which is equal to the inner radius of the press ring of the press tool on the marking plane, and the other leg is equal to the radius of the circle passing through the marking points of the centers of the outer (maximally remote) layer of the channels or the radius of the axial section of these channels minus the diameter of the channel (Fig. 2A-2D).

The expression S / Smax determines the level of technical feasibility, and the expression 1 - S / Smax shows the margin of technical feasibility of the design of the press tool for a given set of input parameters (arguments) listed below and affecting the design of the press tool.

The main design parameters of the press tool, the values of which only together and the relationship determine its technical feasibility: the number of layers of channels, the shape and thickness of the press tool, the lengths of the inlet tapered parts of the channels, the radius of the outer spherical segment and the location of its center, the ratio of the angles of inclination of the input axes and cylindrical portions of the channels on the periphery of the press tool to the axis of the screw.

Due to the close interconnection of the listed parameters, it is impossible to determine the permissible change intervals of individual parameters. Therefore, the conditions of technical feasibility can be assessed only as a result of repeated calculation of the press tool with variation of the values of one or more of the above parameters (Fig. 2e).

The calculation of several embodiments of a press tool with 19 channels with a diameter of 1.5 mm of a granulating press with a screw diameter of 41 mm for forming highly concentrated nitrocellulose solutions (Fig. 2e) shows that when setting the thickness of the press tool 30 mm and the angles of inclination of the cylindrical parts of the channels: 0 ° for the central channel and 15 ° for the most distant channel on the periphery, the technical feasibility interval for the conical lead parts of the channels is 15-40 °. With a decrease in thickness at the periphery to 20 mm, this interval is 20-49 ° (option 3 of Fig. 2e). With an increase in the central angle of the cone to 70 °, the technical feasibility interval for the conical lead parts of the channels is 15-50 ° (option 8 of Fig. 2e). For the prototype (D3): the angle of inclination of the conical entry part, coaxial with the channel, not more than 21 ° (option 5 of Fig. 2e). For a press tool with 7 and 37 channels, the ratio of the angles of inclination of the cylindrical and tapering portions of the channels varies slightly (options 9-12 of Fig. 2e).

Note: for any combination of the main design parameters of the press tool, it is always possible to choose a ratio of the angles of inclination of the cylindrical and tapering portions of the channels at which the condition of technical feasibility of the design of the press tool is fulfilled.

To minimize the energy loss of the stream during its double rotation in the channel: at the inlet and at the junction of the inlet and cylindrical parts of the channels, the technique [1, 2], partially shown in FIG. 2a-2d for each type of moldable material, press structure and molding mode.

Unlike the prototype (D3), the angles of inclination of the axes of the tapered inlet parts of the channels to the central axis of the press tool can be significantly larger than the angles of inclination of the cylindrical parts of the peripheral forming channels.

In FIG. 1-5, the tapered inlet parts of the channels have the form of mating cylindrical and conical surfaces for peripheral channels or only conical surfaces for internal channels. In the general case, the tapered inlet parts of the channels can have any surface formed by any rotation figure around the axis of the inlet part: straight line, parabola, hyperbola or any combination of the above and other figures.

The proposed device operates as follows. The moldable mass is moved in the press housing 1 (Fig. 1) by the screw 2 from the loading zone to the multi-channel press tool 3. After exiting the channels of the screw 2, the flow of the moldable mass is cut into local flows by sharp concave edges of the intersections of the tapering entry parts, uniformly fills the entry parts of all channels and goes into the cylindrical parts of the forming channels, where the granulate molding process is completed. The greater the angle of inclination of the tapering portions of the peripheral forming channels, the more mass they cut from the screw shank and the less mass enters the forming channels in the central part of the press tool, which makes it possible to align the molding speeds with the channel layers.

An increase in the angle of inclination of the tapering inlet parts of the forming channels on the periphery of the press tool reduces the angle of rotation of the mass flow in the inlet parts of the forming channels on the periphery, in addition, the regulation of the thickness of the press tool, therefore, the lengths of the channels together reduce the flow resistance and, consequently, energy loss molding mainly in the peripheral forming channels. At the same time, alignment of linear, volumetric and mass mass velocities in the forming channels in the center and on the periphery is observed, which allows to improve the quality of the granulate: to obtain a more uniform intermediate product in density, porosity and grain size distribution during the cutting of the cords, which increases consumer properties and improves the presentation granulate.

Thus, for the proposed granulating screw press, in comparison with the prototype (D3), the dispersion of product quality indicators in terms of particle size distribution, density, mechanical strength and porosity is reduced, the molding pressure is reduced due to a decrease in the resistance of the press tool and, consequently, inlet energy loss into the forming channels mainly on the periphery of the press tool, and the loss of mass and energy is also reduced by reducing the number of forced shutdowns of the press with a loss of stability of the molding process and for this reason the average productivity of the press increases.

Information sources

, Deutschland. 2012. 191 c.1. Loginov V.Ya. Single screw molding of three-phase dispersed compositions. Modeling and optimization. // ISBN: 978-3-659-16575-7. LAP LAMBERT Academic Publishing,

, Deutschland. 2012.191 c.

2. Loginov V.Ya., Ravichev L.V., Bespalov A.B. Stability of molding filled dispersed compositions in a single screw press. // Bulletin of SSTU. 2012. No1 (64). Issue 2.P. 398-402.

Claims (1)

A granulating screw press for processing highly concentrated polydisperse compositions, comprising a housing, a screw and a multi-channel press tool, on the inner surface of which is facing the mass flow and repeating the shape of the screw shaft, forming channels are made with tapering inlet parts of any shape of rotation coaxially with cylindrical parts, at different angles to the central axis of the press tool in the direction of rotation of the screw in planes tangent to the axial sections of the press tool in the centers forming channels, while the angles of inclination of the channels increase as they move away from the central channel with a zero angle of inclination, characterized in that the outer surface of the press tool with outlet openings of the channels is made in the form of a convex segment of the sphere, the angles of inclination of the axes of the cylindrical parts of the channels differ from the angles the tilt of the axes of the tapering portions of the channels and together they increase as the channels move away from the central channel with zero tilt angles of both axes.

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