Gravel screening device for concrete production

Abstract

The invention relates to the technical field of screening, in particular to a gravel screening device for concrete production, which comprises a rack, the rack is provided with a supporting surface inclined along the front-back direction, the supporting surface is provided with a screening cylinder, and the screening cylinder comprises a front feeding cylinder and a rear discharging cylinder; the feeding cylinder and the discharging cylinder are both fixedly arranged on the supporting face, a plurality of movable screen cylinders are arranged between the feeding cylinder and the discharging cylinder, and the multiple movable screen cylinders are the same in diameter and are sequentially connected from front to back. An annular screen is rotationally arranged on the peripheral face of each movable screen drum, and meshes of the multiple annular screens are gradually increased from front to back. Each movable screen drum can slide in the direction perpendicular to the supporting face, each movable screen drum is provided with a driving mechanism, the driving mechanisms can drive the annular screens to rotate, the rotating directions of every two adjacent annular screens are opposite, and the screening effect is improved.

Description

Technical Field

[0001] The invention relates to the technical field of screening, in particular to a sand and gravel screening device for concrete production. Background Art

[0002] Sand and gravel are often used as high-quality concrete raw materials due to their good hardness and stable chemical properties and are widely used in the fields of houses, roads, highways, railways, engineering, etc. Before using sand and gravel, it is necessary to screen the sand and gravel through a screening device in order to select sand and gravel of different coarse and fine particles and use the appropriate sand and gravel in construction.

[0003] Most of the existing sand and gravel screening devices are to install the drum screen on the frame at an angle, and use the weight of the material to move, so that the sand and gravel of the required particle size automatically fall into the storage bucket below through the screen, and the rejected waste is discharged from the waste outlet at the tail of the drum screen as the drum screen rotates. However, this screening device makes the sand and gravel stay in the drum screen for a short time, resulting in poor screening effect. Summary of the invention

[0004] Based on this, it is necessary to provide a sand and gravel screening device for concrete production to address the technical problem that the current screening device has poor screening effect.

[0005] The above purpose is achieved through the following technical solutions: A sand and gravel screening device for concrete production comprises a frame, the frame has a supporting surface inclined in the front-to-back direction, a screening drum is arranged on the supporting surface, the screening drum comprises a front feeding drum and a rear discharging drum, the feeding drum and the discharging drum are both fixedly arranged on the supporting surface, a plurality of movable screening drums are arranged between the feeding drum and the discharging drum, the plurality of movable screening drums have the same diameter and are sequentially connected from front to back; an annular screen is rotatably arranged on the outer peripheral surface of each movable screening drum, the mesh openings of the plurality of annular screens gradually increase from front to back; each movable screening drum can slide in a direction perpendicular to the supporting surface, each movable screening drum is provided with a driving mechanism, the driving mechanism can drive the annular screen to rotate, and the rotation directions of two adjacent annular screens are opposite.

[0006] Furthermore, each movable screen drum includes a sleeve, and a front sliding plate and a rear sliding plate are respectively provided at the front and rear ends of the sleeve. A first connecting rod is slidably provided on the front sliding plate, and a second connecting rod is slidably provided on the rear sliding plate. The first connecting rod and the second connecting rod both extend along the axial direction of the movable screen drum. The front end of the first connecting rod is used for sliding connection with the front movable screen drum or feed drum; the rear end of the second connecting rod is used for sliding connection with the rear movable screen drum or discharge drum. The sliding direction of the first connecting rod and the second connecting rod is the same as the sliding direction of the movable screen drum.

[0007] Furthermore, a front swivel and a rear swivel are respectively provided at the front and rear ends of the annular screen, the front side surface of the front swivel is provided with a front annular groove, the rear side surface of the rear swivel is provided with a rear annular groove, the rear end of the first connecting rod is slidably matched with the front annular groove, and the front end of the second connecting rod is slidably matched with the rear annular groove.

[0008] Furthermore, the annular screen is an elastic net, and the first connecting rod and the second connecting rod are staggered in the circumferential direction of the movable screen cylinder, and the first connecting rod and the second connecting rod both correspond to the upper half of the annular screen, and the lengths of the first connecting rod and the second connecting rod are equal; a third connecting rod is fixedly provided on the rear side surface of the front sliding plate, and the third connecting rod is slidably matched with the front annular groove, and a fourth connecting rod is fixedly provided on the front side surface of the rear sliding plate, and the fourth connecting rod is slidably matched with the rear annular groove, and the third connecting rod and the fourth connecting rod both extend along the axial direction of the movable screen cylinder, and the lengths of the third connecting rod and the fourth connecting rod are equal and both correspond to the lower half of the annular screen, and the length of the third connecting rod is greater than that of the first connecting rod, so that the annular screen can extend and retract along its own axial direction during rotation.

[0009] Furthermore, two first connecting rods are provided on each front sliding plate, and two second connecting rods are provided on each rear sliding plate.

[0010] Furthermore, the front sliding plate is provided with a first long hole corresponding to the first connecting rod, a first elliptical slider is fixed on the first connecting rod, and the first elliptical slider slides along the first long hole; the rear sliding plate is provided with a second long hole corresponding to the second connecting rod, a second elliptical slider is fixed on the second connecting rod, and the second elliptical slider slides along the second long hole.

[0011] Furthermore, a first block is slidably provided at the front end of the first connecting rod, and the first block is used to be fixedly set on the movable screen cylinder or feed cylinder in the front, and a second block is slidably provided at the rear end of the second connecting rod, and the second block is used to be fixedly set on the movable screen cylinder or discharge cylinder in the rear, and the first block and the second block have the same structure, and a slide groove is provided inside the first block, and the front end of the first connecting rod slides in cooperation with the slide groove, and the slide groove includes an upper vertical section and a lower inclined section, the upper vertical section is perpendicular to the supporting surface, and the lower inclined section gradually moves away from the annular screen from top to bottom.

[0012] Furthermore, the front and rear ends of the first connecting rod and the second connecting rod are both provided with connecting balls, and the connecting balls are engaged with the slide groove, the front annular groove or the rear annular groove in a blocking manner in the axial direction of the movable screen drum.

[0013] Furthermore, a feed plate is provided on the feed cylinder, and the feed plate is used to guide sand and gravel into the movable screen cylinder.

[0014] Furthermore, a first motor is provided on the front sliding plate, and a second motor is provided on the rear sliding plate. The first motor can drive the front rotating ring to rotate, and the second motor can drive the rear rotating ring to rotate. The first motor and the second motor constitute the driving mechanism.

[0015] The beneficial effects of the present invention are: The sand and gravel screening device for concrete production provided by the present invention can extend the moving stroke of sand and gravel in the screening cylinder by dividing the screening cylinder into a plurality of movable screening cylinders connected front and back, and making the annular screens on adjacent movable screening cylinders rotate in opposite directions. Without extending the length of the screening cylinder, such a setting can save floor space. At the same time, since the mesh openings of the annular screens of each movable screening cylinder are different, the particle sizes of the screened sand and gravel are different. By making each movable screening cylinder slide in a direction perpendicular to the supporting surface, the upper and lower positions of a certain movable screening cylinder can be adjusted, so that the screening time of the sand and gravel inside it can be adjusted, and then the screening effect of sand and gravel with different particle sizes can be adjusted in a targeted manner.

[0016] Secondly, during the rotation of the annular screen, the bottom of the annular screen will gradually stretch when it rotates to the top, and the top of the annular screen will gradually shrink when it rotates to the bottom. Since most of the sand and gravel are located at the bottom of the annular screen under the action of gravity, the sand and gravel stuck in the mesh at the bottom of the annular screen can gradually fall off during the rotation of the annular screen, avoiding the sand and gravel being stuck in the mesh at the bottom of the annular screen, further improving the screening effect.

[0017] Third, the movable screen slides downward in a direction perpendicular to the supporting surface, which can further increase the mesh size of the upper half of the annular screen, making it less likely for sand and gravel on the movable screen to get stuck in the mesh size, thereby further improving the screening effect of the movable screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the three-dimensional structure of a sand and gravel screening device for concrete production provided by one embodiment of the present invention; Figure 2 A top view of a sand and gravel screening device for concrete production provided by one embodiment of the present invention; Figure 3 for Figure 2 Middle AA section view; Figure 4 for Figure 3 A magnified view of the structure at B in the middle; Figure 5 A schematic diagram of the three-dimensional structure of a screening drum in a sand and gravel screening device for concrete production provided by an embodiment of the present invention; Figure 6 A front view of a screening drum in a sand and gravel screening device for concrete production provided by one embodiment of the present invention; Figure 7A top view of a screening drum in a sand and gravel screening device for concrete production provided by one embodiment of the present invention; Figure 8 for Figure 7 A magnified view of the structure at C in the middle; Fig. 9 for Figure 7 Middle DD section view; Fig.10 for Fig. 9 A magnified view of the structure at F in the middle; Fig.11 for Figure 7 Middle EE section view; Fig.12 for Fig.11 Enlarged view of point G in the middle.

[0019] in: 101. frame; 1011. supporting surface; 102. feed barrel; 1021. feed plate; 103. discharge barrel; 104. movable screen barrel; 105. sleeve; 1051. front sliding plate; 1052. rear sliding plate; 106. annular screen; 1061. front swivel; 1062. rear swivel; 107. third connecting rod; 1081. first motor; 1082. second motor; 109. friction wheel; 110. fourth connecting rod; 111. first connecting rod; 112. second connecting rod; 113. connecting ball; 1141. first block; 1142. second block; 1143. slide groove; 117. first long hole; 118. second long hole. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings). In the description of the present invention, it should be understood that the orientation or position relationship indicated by the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. are based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0022] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0023] like Figures 1 to 12 As shown, a sand and gravel screening device for concrete production provided by an embodiment of the present invention includes a frame 101, the frame 101 has a supporting surface 1011 inclined in the front-to-back direction, a screening cylinder is arranged on the supporting surface 1011, the screening cylinder includes a front feed cylinder 102 and a rear discharge cylinder 103, the feed cylinder 102 and the discharge cylinder 103 are both fixedly arranged on the supporting surface 1011, a plurality of movable screen cylinders 104 are arranged between the feed cylinder 102 and the discharge cylinder 103, the diameters of the plurality of movable screen cylinders 104 are the same and they are sequentially connected from front to back; an annular screen 106 is rotatably arranged on the outer circumference of each movable screen cylinder 104, and the meshes of the plurality of annular screens 106 gradually increase from front to back; each movable screen cylinder 104 can slide in a direction perpendicular to the supporting surface 1011, and each movable screen cylinder 104 is provided with a driving mechanism, the driving mechanism can drive the annular screen 106 to rotate, and the rotation directions of two adjacent annular screens 106 are opposite.

[0024] By dividing the screening drum into a plurality of movable screening drums 104 connected front and back, and making the annular screens 106 on adjacent movable screening drums 104 rotate in opposite directions, the moving stroke of the sand and gravel in the screening drum can be extended. Without extending the length of the screening drum, such a setting can save floor space. At the same time, since the mesh openings of the annular screens 106 of each movable screening drum 104 are different, the particle sizes of the screened sand and gravel are different. By making each movable screening drum 104 slide in a direction perpendicular to the supporting surface 1011, the upper and lower positions of a certain movable screening drum 104 can be adjusted to adjust the screening time of the sand and gravel inside it, and then the screening effect of sand and gravel with different particle sizes can be adjusted in a targeted manner. For example, a certain movable screen drum 104 is moved downward in a direction perpendicular to the supporting surface 1011, so that when sand and gravel enter the movable screen drum 104, it needs to move downward a certain distance first, and then move upward a certain distance when flowing out of the movable screen drum 104. Compared with the sand and gravel sliding directly along the inclined surface, the moving distance of the sand and gravel is extended, thereby extending the screening time and improving the screening effect.

[0025] In one embodiment, each movable screen drum 104 includes a sleeve 105, and a front sliding plate 1051 and a rear sliding plate 1052 are respectively provided at the front and rear ends of the sleeve 105, and a first connecting rod 111 is slidably provided on the front sliding plate 1051, and a second connecting rod 112 is slidably provided on the rear sliding plate 1052. The first connecting rod 111 and the second connecting rod 112 both extend along the axial direction of the movable screen drum 104, and the front end of the first connecting rod 111 is used for sliding connection with the front movable screen drum 104 or the feed drum 102; the rear end of the second connecting rod 112 is used for sliding connection with the rear movable screen drum 104 or the discharge drum 103, and the sliding direction of the first connecting rod 111 and the second connecting rod 112 is the same as the sliding direction of the movable screen drum 104.

[0026] In one embodiment, a front swivel ring 1061 and a rear swivel ring 1062 are respectively provided at the front and rear ends of the annular screen 106, the front side surface of the front swivel ring 1061 is provided with a front annular groove, and the rear side surface of the rear swivel ring 1062 is provided with a rear annular groove, the rear end of the first connecting rod 111 is slidably matched with the front annular groove, and the front end of the second connecting rod 112 is slidably matched with the rear annular groove.

[0027] In one embodiment, the annular screen 106 is an elastic net, the first connecting rod 111 and the second connecting rod 112 are staggered in the circumferential direction of the movable screen drum 104, the first connecting rod 111 and the second connecting rod 112 both correspond to the upper half of the annular screen 106, and the lengths of the first connecting rod 111 and the second connecting rod 112 are equal; a third connecting rod 107 is fixedly provided on the rear side surface of the front sliding plate 1051, and the third connecting rod 107 slides in cooperation with the front annular groove, and a fourth connecting rod 110 is fixedly provided on the front side surface of the rear sliding plate 1052, and the fourth connecting rod 110 slides in cooperation with the rear annular groove, the third connecting rod 107 and the fourth connecting rod 110 both extend along the axial direction of the movable screen drum 104, the lengths of the third connecting rod 107 and the fourth connecting rod 110 are equal and both correspond to the lower half of the annular screen 106, and the length of the third connecting rod 107 is greater than the length of the first connecting rod 111, so that the annular screen 106 can be extended and retracted along its own axial direction during rotation.

[0028] During the rotation of the annular screen 106, the bottom of the annular screen 106 gradually stretches when it rotates to the top, and the top of the annular screen 106 gradually shrinks when it rotates to the bottom. Since most of the sand and gravel are located at the bottom of the annular screen 106 under the action of gravity, the sand and gravel stuck in the mesh at the bottom of the annular screen 106 can gradually fall off during the rotation of the annular screen 106, thereby preventing the sand and gravel from being stuck in the mesh at the bottom of the annular screen 106, and further improving the screening effect.

[0029] In one embodiment, two first connecting rods 111 are provided on each front sliding plate 1051, and two second connecting rods 112 are provided on each rear sliding plate 1052. Only one third connecting rod 107 is provided on each front sliding plate 1051 and only one fourth connecting rod 110 is provided on each rear sliding plate 1052. In this way, two first connecting rods 111 and one third connecting rod 107 form a triangular stable structure, and two second connecting rods 112 and one fourth connecting rod 110 form a triangular stable structure, which better supports the front swivel 1061 and the rear swivel 1062, so that the annular screen 106 rotates more smoothly.

[0030] In one embodiment, the front sliding plate 1051 is provided with a first long hole 117 corresponding to the first connecting rod 111, a first elliptical slider is fixed to the first connecting rod 111, and the first elliptical slider slides along the first long hole 117; the rear sliding plate 1052 is provided with a second long hole 118 corresponding to the second connecting rod 112, a second elliptical slider is fixed to the second connecting rod 112, and the second elliptical slider slides along the second long hole 118. This arrangement prevents damage to the first connecting rod 111 and the second connecting rod 112, and prolongs the service life.

[0031] In one embodiment, the front end of the first connecting rod 111 is slidably provided with a first block 1141, and the first block 1141 is used to be fixedly set on the front movable screen drum 104 or the feed drum 102. Specifically, the first block 1141 is fixed on the rear sliding plate 1052 of the front movable screen drum 104 or the rear side panel of the feed drum 102. The rear end of the second connecting rod 112 is slidably provided with a second block 1142, and the second block 1142 is used to be fixedly set on the rear movable screen drum 104 or the discharge drum 103. Specifically, the second block 1142 is fixed on the front sliding plate 1051 of the rear movable screen drum 104 or the front side panel of the discharge drum 103. The first block 1141 has the same structure as the second block 1142. A chute 1143 is provided inside the first block 1141. The front end of the first connecting rod 111 is slidably matched with the chute 1143. The chute 1143 includes an upper vertical section and a lower inclined section. The upper vertical section is perpendicular to the support surface 1011, and the lower inclined section gradually moves away from the annular screen 106 from top to bottom. In this way, when the movable screen drum 104 slides downward, the first connecting rod 111 in front of the movable screen drum 104 and the second connecting rod 112 behind the movable screen drum 104 slide along the lower inclined section of the chute 1143. The rear end of the first connecting rod 111 will stretch the annular screen 106 forward, and the front end of the second connecting rod 112 will stretch the annular screen 106 backward, so that the annular screen 106 is stretched in the axial direction, thereby increasing the mesh above the annular screen 106, further preventing sand and gravel from being stuck in the mesh, and improving the screening effect of the movable screen drum 104.

[0032] In one embodiment, the front and rear ends of the first connecting rod 111 and the second connecting rod 112 are both provided with connecting balls 113, and the connecting balls 113 are engaged with the slide groove 1143, the front annular groove or the rear annular groove in the axial direction of the movable screen drum 104. The surface of the connecting balls 113 is smooth, which can reduce sliding friction.

[0033] In one embodiment, a feed plate 1021 is provided on the feed cylinder 102 , and the feed plate 1021 is used to guide sand and gravel into the movable screen cylinder 104 .

[0034] In one embodiment, the front sliding plate 1051 is provided with a first motor 1081, and the rear sliding plate 1052 is provided with a second motor 1082. The first motor 1081 can drive the front swivel 1061 to rotate, and the second motor 1082 can drive the rear swivel 1062 to rotate. The first motor 1081 and the second motor 1082 constitute the driving mechanism. The output ends of the first motor 1081 and the second motor 1082 are both provided with friction wheels 109. The first motor 1081 and the second motor 1082 act synchronously to keep the rotation speeds of both sides of the annular screen 106 consistent. The support surface 1011 is a rectangular frame structure, and the middle part of the support surface 1011 is hollow, so that when the movable screen drum 104 slides downward in a direction perpendicular to the support surface 1011, an avoidance space can be formed for the first motor 1081 and the second motor 1082 to enter, ensuring the smooth sliding of the movable screen drum 104.

[0035] In combination with the above embodiments, the use principle and working process of the embodiments of the present invention are as follows: In the initial state, the first connecting rod 111 is located in the middle of the first long hole 117, and the second connecting rod 112 is located in the middle of the second long hole 118. The mesh openings of the upper half of the annular screen 106 are larger than those of the lower half.

[0036] First, the position of each movable screen drum 104 is adjusted according to the screening requirements of sand and gravel. When it is necessary to make the screening effect of sand and gravel of a certain particle size better, the corresponding movable screen drum 104 is manually slid downward a certain distance in a direction perpendicular to the support surface 1011, so that the front end of the first connecting rod 111 in front of the movable screen drum 104 will slide from the upper vertical section of the corresponding second block 1142 to the lower inclined section, so that the rear end of the first connecting rod 111 stretches the front end of the annular screen 106; the rear end of the second connecting rod 112 behind the movable screen drum 104 will slide from the upper vertical section of the corresponding second block 1142 to the lower inclined section, so that the front end of the second connecting rod 112 will stretch the rear end of the annular screen 106 backwards, so that the upper half of the annular screen 106 is axially stretched, so that the mesh of the upper half of the annular screen 106 is further enlarged, so that when the annular screen 106 rotates, sand and gravel are not easily stuck in the mesh.

[0037] Then, the driving mechanism at the bottom of each movable screen drum 104 is controlled to operate so that the annular screens 106 on two adjacent movable screen drums 104 rotate in opposite directions. Finally, the sand and gravel are transported to the feed plate 1021, and the sand and gravel enter each movable screen drum 104 from the feed plate 1021 for screening. The sand and gravel with small particle size flows out from the front movable screen drum 104, and the sand and gravel with large particle size flows out from the rear movable screen drum 104. The remaining large particles of ore flow out from the discharge drum 103.

[0038] It should be noted that the vertical movement distance of the movable screen drum 104 is small, so that there will be no gap between two adjacent butted movable screen drums 104 .

[0039] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0040] The above-described embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A sand and gravel screening device for concrete production, characterized in that: The machine comprises a frame, which has a supporting surface inclined in the front-to-back direction, a screening cylinder is arranged on the supporting surface, and the screening cylinder comprises a feeding cylinder in the front and a discharging cylinder in the rear, and the feeding cylinder and the discharging cylinder are both fixedly arranged on the supporting surface, and a plurality of movable screening cylinders are arranged between the feeding cylinder and the discharging cylinder, and the diameters of the plurality of movable screening cylinders are the same and they are sequentially connected from front to back; an annular screen is rotatably arranged on the outer peripheral surface of each movable screening cylinder, and the mesh openings of the plurality of annular screens gradually increase from front to back; each movable screening cylinder can slide in a direction perpendicular to the supporting surface, and each movable screening cylinder is provided with a driving mechanism, and the driving mechanism can drive the annular screen to rotate, and the rotation directions of two adjacent annular screens are opposite.

2. The sand and gravel screening device for concrete production according to claim 1, characterized in that: Each movable screen drum includes a sleeve, and a front sliding plate and a rear sliding plate are respectively provided at the front and rear ends of the sleeve. A first connecting rod is slidably provided on the front sliding plate, and a second connecting rod is slidably provided on the rear sliding plate. The first connecting rod and the second connecting rod both extend along the axial direction of the movable screen drum. The front end of the first connecting rod is used for sliding connection with the movable screen drum or the feed drum in front; the rear end of the second connecting rod is used for sliding connection with the movable screen drum or the discharge drum in the rear, and the sliding direction of the first connecting rod and the second connecting rod is the same as the sliding direction of the movable screen drum.

3. The sand and gravel screening device for concrete production according to claim 2, characterized in that: The front and rear ends of the annular screen are respectively provided with a front swivel and a rear swivel, the front side surface of the front swivel is provided with a front annular groove, the rear side surface of the rear swivel is provided with a rear annular groove, the rear end of the first connecting rod is slidably matched with the front annular groove, and the front end of the second connecting rod is slidably matched with the rear annular groove.

4. The sand and gravel screening device for concrete production according to claim 3, characterized in that: The annular screen is an elastic net, and the first connecting rod and the second connecting rod are staggered in the circumferential direction of the movable screen drum, and the first connecting rod and the second connecting rod both correspond to the upper half of the annular screen, and the lengths of the first connecting rod and the second connecting rod are equal; a third connecting rod is fixedly provided on the rear side surface of the front sliding plate, and the third connecting rod is slidably matched with the front annular groove, and a fourth connecting rod is fixedly provided on the front side surface of the rear sliding plate, and the fourth connecting rod is slidably matched with the rear annular groove, and the third connecting rod and the fourth connecting rod both extend along the axial direction of the movable screen drum, and the lengths of the third connecting rod and the fourth connecting rod are equal and both correspond to the lower half of the annular screen, and the length of the third connecting rod is greater than that of the first connecting rod, so that the annular screen can be extended and retracted along its own axial direction during rotation.

5. The sand and gravel screening device for concrete production according to claim 4, characterized in that: Two first connecting rods are provided on each front sliding plate, and two second connecting rods are provided on each rear sliding plate.

6. The sand and gravel screening device for concrete production according to claim 5, characterized in that: The front sliding plate is provided with a first long hole corresponding to the first connecting rod, and a first elliptical slider is fixed on the first connecting rod, and the first elliptical slider slides along the first long hole; the rear sliding plate is provided with a second long hole corresponding to the second connecting rod, and a second elliptical slider is fixed on the second connecting rod, and the second elliptical slider slides along the second long hole.

7. The sand and gravel screening device for concrete production according to claim 3, characterized in that: A first block is slidably provided at the front end of the first connecting rod, and the first block is used to be fixedly set on the movable screen cylinder or feed cylinder in the front. A second block is slidably provided at the rear end of the second connecting rod, and the second block is used to be fixedly set on the movable screen cylinder or discharge cylinder in the rear. The first block has the same structure as the second block, and a slide groove is provided inside the first block. The front end of the first connecting rod slides in cooperation with the slide groove, and the slide groove includes an upper vertical section and a lower inclined section, the upper vertical section is perpendicular to the supporting surface, and the lower inclined section gradually moves away from the annular screen from top to bottom.

8. The sand and gravel screening device for concrete production according to claim 7, characterized in that: The front and rear ends of the first connecting rod and the second connecting rod are both provided with connecting balls, and the connecting balls are engaged with the slide groove, the front annular groove or the rear annular groove in the axial direction of the movable screen drum.

9. The sand and gravel screening device for concrete production according to claim 1, characterized in that: A feed plate is provided on the feed cylinder, and the feed plate is used to guide sand and gravel into the movable screen cylinder.

10. The sand and gravel screening device for concrete production according to claim 3, characterized in that: The front sliding plate is provided with a first motor, and the rear sliding plate is provided with a second motor. The first motor can drive the front rotating ring to rotate, and the second motor can drive the rear rotating ring to rotate. The first motor and the second motor constitute the driving mechanism.

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