A corn seed breeding screening device
By introducing screening, vibration, telescopic and damping mechanisms into the corn seed screening device, combined with an automatic cleaning system, the problem of insufficient screening in existing devices has been solved, achieving a high-efficiency and low-loss screening effect, and improving sowing uniformity and seedling uniformity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SHANDONG ZHIXINGHE SEED CO LTD
- Filing Date
- 2025-07-17
- Publication Date
- 2026-06-30
AI Technical Summary
Existing corn seed screening devices cannot achieve efficient and low-loss screening, resulting in poor screening effect and failing to guarantee sowing uniformity and seedling uniformity.
A corn seed selection and screening device is adopted, which includes a screening mechanism, a vibration mechanism, a telescopic mechanism and a vibration damping mechanism. The tilt angle of the screen is adjusted by the vibration and telescopic components, and combined with an automatic cleaning system, multiple screenings and impurity separation are achieved, and the vibration amplitude is controlled to reduce seed damage.
It improves screening efficiency, reduces seed loss, ensures uniform sowing and seedling emergence, and reduces equipment maintenance frequency and cost.
Smart Images
Figure CN224423540U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of crop seed screening, and in particular to a corn seed selection and screening device. Background Technology
[0002] Corn seed screening is a core step in modern agriculture to improve yield and ensure quality. It involves quality control throughout the entire industrial chain from breeding to sowing. By screening seeds according to size, it ensures uniformity of sowing by the seeder, avoids wasting seed costs by breaking kernels, improves the uniformity of seedling emergence, and prevents seedlings of different sizes from competing for light and fertilizer.
[0003] In existing technologies, the main screening methods include vibrating screens, drum screens, air classifiers, and planar reciprocating screens. Vibrating screens use a motor to drive the screen mesh to vibrate at high frequency, and use screens with different aperture sizes to screen in layers. Drum screens have sieve holes on the inner wall of the inclined rotating drum. When the seeds rotate with the drum, smaller particles leak out from the holes, and larger particles are discharged from the end. Air classifiers combine wind power with the screen mesh, and use the difference between seed weight and air resistance to separate impurities. Planar reciprocating screens have the screen mesh moving back and forth in a horizontal plane, driven by a crank connecting rod or eccentric shaft. Seeds slide forward on the screen mesh due to inertia. Particles smaller than the sieve holes fall down, and particles larger than the sieve holes move along the screen surface to the end and are discharged.
[0004] Different screening methods have their own disadvantages and limitations. High-frequency vibrating screens have a high seed breakage rate and the screen is prone to clogging. Drum screens have limited grading accuracy. Airflow screens cannot be graded by size, require precise control of air pressure, are complex to adjust, and have high energy consumption. Planar reciprocating screens have slow processing speed and low efficiency, and multi-layer screens are cumbersome to maintain. Existing corn seed screening devices cannot achieve the expected screening effect, and the screening is insufficient, making it impossible to screen corn seeds efficiently and with low loss. Utility Model Content
[0005] To address the problem of insufficient screening during corn seed selection, this invention provides a corn seed selection and screening device.
[0006] This utility model provides a corn seed selection and screening device, which adopts the following technical solution:
[0007] A corn seed selection and screening device includes a screening mechanism, a vibration mechanism, a telescopic mechanism, and a vibration damping mechanism. The screening mechanism includes a mounting frame, a seed screen, and a base plate. The base plate is mounted on the mounting frame, and the seed screen is mounted on the base plate. The vibration mechanism is mounted on the base plate. The telescopic mechanism includes a support frame, a connecting frame, a hinge, and a telescopic assembly. The connecting frame and the telescopic assembly are connected to the base plate via the vibration damping mechanism. The connecting frame rotates on the support frame via the hinge. The telescopic assembly is mounted on the support frame and drives the connecting frame to rotate.
[0008] By adopting the above technical solution, in the corn seed selection and screening process, corn seeds are poured into a seed screen, and the vibration mechanism drives the screening mechanism to vibrate, causing the corn seeds to jump on the seed screen. As they jump, corn seeds or impurities with a diameter smaller than the screen aperture enter the lower structure in sequence, and corn seeds that meet the standards are screened out. During the screening process, the telescopic component drives one side of the connecting frame to move up and down, causing the connecting frame to rotate around the hinge axis, which changes the height of one end of the seed screen and adjusts the tilt angle of the seed screen. As the vibration continues, the corn seeds are repeatedly screened on the seed screen, thereby increasing the number of times the material contacts the seed screen, improving screening efficiency, and making the corn seed selection and screening more thorough.
[0009] Optionally, the telescopic assembly includes a connecting block, a telescopic column, a support sleeve, and a telescopic member. The connecting block is disposed below the vibration damping mechanism, the support sleeve is disposed on the support frame, one end of the telescopic column slides on the support sleeve, and the other end of the telescopic column abuts against the connecting block and can slide in a direction close to or away from the hinge; the telescopic member is disposed on the support sleeve and is connected to the telescopic column.
[0010] By adopting the above technical solution, during the screening process, the telescopic component drives the telescopic column to slide along the support sleeve, and the telescopic column pushes the connecting block to move up and down, so that the connecting frame rotates around the hinge axis. During the rotation, the connecting block slides relative to the telescopic column, overcoming the lateral displacement when the connecting frame rotates.
[0011] Optionally, the side of the connecting block is a right-angled trapezoid, and a rectangular groove is opened on the inclined surface of the connecting block. The inclined surface is installed downwards, and the upper end of the telescopic column is arc-shaped and slides in the groove of the connecting block.
[0012] By adopting the above technical solution, the sliding path when the telescopic column and the connecting block are relatively displaced can be limited, reducing the risk of the connection between the connecting block and the telescopic column falling off. The arc-shaped top of the telescopic column makes the sliding process smoother.
[0013] Optionally, the screening mechanism further includes a baffle plate, which is installed inside the discharge port of the seed screen and slidably connected to the seed screen.
[0014] By adopting the above technical solution, during the corn seed selection and screening process, the corn seeds are screened by vibration within the screen assembly when the baffle is closed. After the corn seeds are screened, the baffle is pushed open to pour out the screened corn seeds that meet the standards.
[0015] Optionally, the screening mechanism further includes an impurity screen, which is installed on top of the seed screen, and the aperture of the impurity screen is larger than that of the seed screen.
[0016] By adopting the above technical solution, larger, lighter impurities are retained in the impurity screen, while the remaining corn seeds are sieved into the seed screen. This separates larger impurities, reduces the amount of impurities falling into the seed screen, and then the corn seeds that meet the standards are screened out through the seed screen.
[0017] Optionally, the seed screen is divided into two layers, with the aperture of the seed screen closer to the bottom plate being smaller than that of the seed screen farther from the bottom plate.
[0018] By adopting the above technical solution, corn seeds that meet the standards can be graded by size during the corn seed selection and screening process, thereby improving the uniformity of corn seed screening and thus enhancing the uniformity of seedling emergence.
[0019] Optionally, the screening mechanism further includes a screen cleaning assembly, which includes a blower installed on the side plate of the impurity screen for cleaning the impurities separated by the impurity screen.
[0020] By adopting the above technical solution, impurities separated by the impurity screen can be cleaned in a timely manner, avoiding clogging of the mesh and reducing the impact on the subsequent selection and screening process of corn seeds.
[0021] Optionally, the cleaning assembly further includes a dredging net and a connecting rod. The dredging net is configured to correspond to the seed sieve, and the connecting rod connects two of the dredging nets. The dredging net has multiple dredging posts, and the dredging posts correspond to the mesh openings of the seed sieve and can slide into the mesh openings.
[0022] By adopting the above technical solution, when the seed screen becomes clogged, the unblocking net moves upward, the unblocking column enters the mesh, and the clogged seed screen is cleared. After the unblocking is completed, the unblocking net moves downward, the unblocking column moves out of the mesh, and leaves enough space for seeds to pass through, reducing the impact on seed screening and minimizing the impact of seed screen clogging on the screening efficiency of corn seeds.
[0023] Optionally, the screen cleaning assembly further includes a comma cam and a drive motor. The drive motor is mounted on the base plate, the comma cam is mounted below the connecting rod and abuts against the connecting rod, and the comma cam is connected to the output shaft of the drive motor.
[0024] By adopting the above technical solution, when the seed screen becomes clogged, the drive motor drives the comma cam to rotate, and the comma cam pushes the connecting rod to move upward, thereby moving the unblocking net upward. The unblocked seed screen is then cleared by the unblocking column. After the unblocking is completed, the connecting rod falls back down, realizing automatic cleaning of the seed screen and extending the equipment maintenance cycle.
[0025] Optionally, the cleaning assembly further includes a screen spring, which is vertically mounted on the side wall of the seed screen, located below the unblocking screen, and connected to the unblocking screen.
[0026] By adopting the above technical solution, after the unblocking column completes the unblocking of the seed screen, the corn seeds that are blocking the mesh will remain in the seed screen. When the connecting rod falls back quickly, the screen spring retracts and drives the unblocking screen to vibrate, which can shake off the residual seeds on the seed screen.
[0027] Optionally, the screening mechanism further includes a buffer pad, which is installed at the lower end of the connecting rod and slidably connected to the comma cam.
[0028] By adopting the above technical solution, after the comma cam rotates to its maximum limit position, the connecting rod stroke undergoes a sudden change and falls back quickly, impacting the comma cam. The buffer pad reduces the damage caused by the impact to the comma cam and extends the service life of the comma cam.
[0029] Optionally, the vibration mechanism further includes a counterweight, which is mounted on the screening mechanism and used to adjust the amplitude of the vibration of the screening mechanism.
[0030] By adopting the above technical solution, the amplitude of vibration of the screening mechanism can be controlled, avoiding the increase in corn seed damage rate due to excessive amplitude, which in turn leads to more broken kernels and waste of seed costs.
[0031] In summary, this utility model has at least one of the following beneficial technical effects:
[0032] By adjusting the tilt direction of the screen and repeatedly sieving the corn seeds, the corn seeds are sieved more thoroughly, improving the sieving effect and reducing corn seed loss.
[0033] Grading and screening corn seeds, strictly controlling the size of the grains, and classifying seeds of different sizes ensures uniform sowing and thus improves the uniformity of seedling emergence.
[0034] Automatic screen cleaning can reduce the impact of screen clogging on the screening process, improve selection and screening efficiency, reduce maintenance frequency, and reduce equipment maintenance costs.
[0035] By controlling the amplitude of vibration, losses caused by damage to corn seeds due to vibration are reduced, the number of broken grains generated during screening is reduced, and corn seed loss is minimized. Attached Figure Description
[0036] Figure 1 This is a schematic diagram of the overall structure of the corn seed selection and screening device in this embodiment of the utility model.
[0037] Figure 2 This is a schematic diagram of the screening mechanism in an embodiment of this utility model.
[0038] Figure 3 This is a schematic diagram of the telescopic mechanism in an embodiment of this utility model.
[0039] Explanation of reference numerals in the attached drawings: 100, screening mechanism; 110, mounting frame; 120, seed screen; 130, base plate; 140, impurity screen; 150, screen cleaning assembly; 151, fan; 152, unblocking screen; 153, connecting rod; 154, comma cam; 155, drive motor; 156, screen spring; 157, unblocking column; 160, buffer pad; 170, baffle; 200, vibration mechanism; 210, vibration motor; 220, counterweight; 300, telescopic mechanism; 310, support frame; 320, connecting frame; 330, hinge; 340, telescopic assembly; 341, connecting block; 342, telescopic column; 343, support sleeve; 344, telescopic component; 345, rectangular groove; 400, vibration damping mechanism; 410, vibration damping spring. Detailed Implementation
[0040] The following combination Figures 1 to 3 The present invention will be described in further detail below.
[0041] This utility model discloses a corn seed selection and screening device.
[0042] Reference Figure 1 A corn seed selection and screening device mainly includes a screening mechanism 100, a vibration mechanism 200, a telescopic mechanism 300, and a damping mechanism 400. The vibration mechanism 200 is installed on the screening mechanism 100, and the screening mechanism 100 is installed on the telescopic mechanism 300 through the damping mechanism 400. When screening seeds, the seeds are poured onto the screening mechanism 100, and the vibration mechanism 200 drives the damping mechanism 400 and the screening mechanism 100 to vibrate, thereby screening the seeds. During the screening process, the telescopic mechanism 300 adjusts the tilt angle of the screening mechanism 100 so that the seeds are screened back and forth.
[0043] Reference Figure 1 and Figure 2The screening mechanism 100 includes a mounting frame 110, a seed screen 120, an impurity screen 140, a base plate 130, a baffle 170, a screen cleaning assembly 150, and two buffer pads 160. The mounting frame 110 consists of four upright columns, which are vertically mounted on the side walls of the four corners of the seed screen 120. The impurity screen 140, the seed screen 120, and the base plate 130 are sequentially fixed to the mounting frame 110 from top to bottom. The impurity screen 140 has a side plate on the left and a discharge port on the right. The impurity screen 140 is a metal woven mesh with square mesh openings that are larger than the openings of the seed screen 120, enabling it to separate larger, lighter impurities. The seed screen 120 consists of two layers. The perforated plates have different aperture sizes. The perforated plate with larger aperture is on the upper layer, which can screen large corn seeds, while the perforated plate with smaller aperture is on the lower layer, which can screen small corn seeds. The discharge port of the seed screen 120 is located on the left side. The bottom plate 130 is installed on the lower layer of the mounting frame 110. The bottom plate 130 is a non-perforated metal plate with the discharge port on the right side. The baffle 170 is a rectangular plate with rectangular openings at both the top and bottom. The height of the baffle 170 in the middle of the two rectangular openings is the same as that of the seed screen 120. It is installed vertically on the left side of the seed screen 120 and is slidably connected to the mounting frame 110. During the selection and screening process, it acts as the left baffle 170 of the seed screen 120.
[0044] The screen cleaning assembly 150 includes two blowers 151, two unblocking screens 152, two connecting rods 153, two comma cams 154, two drive motors 155, and two screen springs 156. Both blowers 151 are mounted on the left side plate of the impurity screen 140. The unblocking screen 152 is a square-mesh metal mesh with a larger aperture than the seed screen 120. Unblocking posts 157 are located at the intersections of the square meshes. The unblocking posts 157 have a circular cross-section and a diameter smaller than the aperture of the seed screen 120. The two unblocking screens 152 are respectively installed below the two layers of seed screens 120, and the positions of the unblocking posts 157 correspond one-to-one with the mesh positions of the upper seed screen 120. Two connecting rods 153 are located at both ends of the unblocking screen 152, and each connecting rod 153 connects to two unblocking screens 152. 153 is installed on the front and rear side plates of the upper seed screen 120, respectively, and is slidably connected to the side plates. The lower end of the connecting rod 153 abuts against the side wall of the comma cam 154. The rotation of the comma cam 154 drives the connecting rod 153 to move up and down. The drive motor 155 is installed below the base plate 130, and its output shaft is connected to the comma cam 154. The motor is used to drive the comma cam 154 to rotate. Two screen springs 156 are installed vertically on the front and rear side walls of the seed screen 120, respectively, located below the unblocking net 152 and connected to the unblocking net 152. They are used to drive the connecting rod 153 to press against the comma cam 154. In the natural state, the screen springs 156 pull the unblocking net 152 away from the seed screen 120, so that the unblocking column 157 is completely separated from the mesh of the seed screen 120, which facilitates the passage of seeds.
[0045] Furthermore, in order to reduce the damage to the comma cam 154 caused by the connecting rod 153, the screen mechanism also includes two buffer pads 160. The two buffer pads 160 are respectively installed at the lower end of the two connecting rods 153 and the contact end with the comma cam 154 to reduce the damage to the comma cam 154 when the connecting rod 153 suddenly drops.
[0046] Furthermore, in order to reduce the transmission of vibration to the lower structure and provide a margin of movement for the vibration of the screening mechanism 100, the vibration damping mechanism 400 can be a rubber damping column, an elastic column, or a vibration damping spring 410. In this embodiment, the vibration damping spring 410 is preferred and four are provided. The upper end of the vibration damping spring 410 is connected to the bottom plate 130 and the lower end is connected to the telescopic mechanism 300.
[0047] refer to Figure 3 The telescopic mechanism 300 includes a connecting frame 320, two hinges 330, a support frame 310, and two telescopic components 340. The support frame 310 includes two columns with inclined tops. The two columns are connected by a crossbeam. The upper part of the connecting frame 320 is fixedly connected to the damping spring 410, and the lower part of the connecting frame 320 is rotatably connected to the top of the support frame 310 via hinges 330. The telescopic components 340 include two connecting blocks 341, two telescopic columns 342, two support sleeves 343, and a telescopic element 344. The side of the connecting block 341 is a right-angled trapezoid, and a rectangular groove 345 is opened on the inclined surface. The inclined surface is installed downwards, and the upper surface is fixedly connected to the lower end of the damping spring 410. The inclined surface is connected to the telescopic element 344. The top of the telescopic column 342 is slidably connected. The telescopic column 342 is a column structure with an arc-shaped top. The cross-sectional width is the same as the width of the rectangular groove 345. When the telescopic column 342 moves up and down, the top of the column slides in the rectangular groove 345. The lower end of the telescopic column 342 is fixedly installed on the telescopic component 344. The telescopic component 344 can be a linear drive structure such as a cylinder, electric push rod, hydraulic cylinder, motor screw, or push rod motor. In this embodiment, the telescopic component 344 is preferably a push rod motor. The two telescopic components 344 extend and retract synchronously. The telescopic column 342 and the push rod motor are both installed in the support sleeve 343. The inner diameter of the support sleeve 343 is the same as the cross-sectional diameter of the telescopic column 342. The telescopic column 342 and the support sleeve 343 are slidably connected.
[0048] The vibration mechanism 200 includes a vibration motor 210 and a counterweight 220. Both the vibration motor 210 and the counterweight 220 are mounted on the base plate 130. The vibration motor 210 is fixedly connected to the base plate 130 and installed in the middle of the base plate 130 to drive the screening mechanism 100 to vibrate. The counterweight 220 is detachably connected to the base plate 130 and is installed on both sides of the vibration motor 210. Different counterweights 220 can be replaced according to different amplitude requirements.
[0049] The implementation principle of the corn seed selection and screening device in this embodiment of the utility model is as follows:
[0050] During the corn seed selection and screening process, the corn seeds to be screened are poured into the device. At this time, the push rod of the telescopic component 344 is pushed out, the telescopic column 342 extends out from the support sleeve 343, the screening mechanism 100 tilts to the left, the baffle 170 blocks the corn seed outlet, the vibration motor 210 is started, and the vibration motor 210 drives the screening mechanism 100 to vibrate. The corn seeds are first spread flat on the impurity screen 140. Through the vibration of the screening mechanism 100, the larger light impurities are separated on the impurity screen 140. Through the airflow generated by the blower 151, the separated light impurities are discharged from the outlet of the impurity screen 140. The remaining corn seeds fall into the seed screen 120. Through the vibration of the screening mechanism 100, the large-particle corn seeds that meet the standards are separated on the upper seed screen 120, and the small-particle corn seeds that meet the standards are separated on the lower seed screen 120. The remaining impurities and broken corn seeds fall into the bottom plate 130.
[0051] After vibration for a certain period of time, the push rod of the telescopic component 344 retracts, causing the telescopic column 342 to retract into the support sleeve 343, causing the screening mechanism 100 to tilt to the right. When the screening mechanism 100 tilts to the right, impurities and broken corn seeds are discharged from the discharge port. After this process is repeated twice, the corn seeds are fully screened. At this time, the screening mechanism 100 tilts to the left, pulling the baffle 170 upward until the lower rectangular opening coincides with the side of the lower seed screen 120. Small corn seeds that meet the standards are discharged from the discharge port of the seed screen 120 through the rectangular opening. The baffle 170 is pushed downward until the upper rectangular opening coincides with the side of the upper seed screen 120. At the designated position, standard large-particle corn seeds are discharged from the outlet of the seed screen 120 through a rectangular opening. After one round of work is completed, the drive motor 155 starts, driving the comma cam 154 to rotate to its maximum limit position. The comma cam 154 pushes the connecting rod 153 to move upward, thereby driving the unblocking net 152 to move upward. The unblocking column 157 is embedded in the mesh of the seed screen 120 to unblock the mesh of the seed screen 120 that was blocked during the breeding process. The comma cam 154 continues to rotate, the connecting rod 153 quickly falls back, and the unblocking net 152 collides with the screen spring 156 to generate vibration, shaking off the remaining corn seeds, thus realizing the automatic maintenance of the device.
[0052] In summary, the device, by adjusting the tilt direction of the screen and repeatedly sieving corn seeds, ensures more thorough sieving, improves the sieving effect, reduces corn seed loss, and classifies corn seeds by size, strictly controlling the particle size and classifying seeds of different sizes to ensure uniform sowing and thus improve seedling uniformity. Automatic screen cleaning reduces the impact of screen clogging on the sieving process, improves selection and sieving efficiency, reduces maintenance frequency, and lowers equipment maintenance costs. Furthermore, by controlling the vibration amplitude, it reduces losses caused by vibration-induced seed breakage, decreasing the number of broken grains generated during sieving and minimizing corn seed loss.
[0053] The above are all preferred embodiments of this utility model, and are not intended to limit the scope of protection of this utility model. Therefore, all equivalent changes made to the structure, shape and principle of this utility model should be included within the scope of protection of this utility model.
Claims
1. A corn seed breeding screening apparatus, characterized by: The system includes a screening mechanism (100), a vibration mechanism (200), a telescopic mechanism (300), and a vibration damping mechanism (400). The screening mechanism (100) includes a mounting frame (110), a seed sieve (120), and a base plate (130). The base plate (130) is mounted on the mounting frame (110), and the seed sieve (120) is mounted on the base plate (130). The vibration mechanism (200) is mounted on the base plate (130). The telescopic mechanism (300) includes a support... The support frame (310), connecting frame (320), hinge (330), and telescopic assembly (340) are provided. The connecting frame (320) and the telescopic assembly (340) are connected to the base plate (130) through the vibration damping mechanism (400). The connecting frame (320) rotates on the support frame (310) through the hinge (330). The telescopic assembly (340) is provided on the support frame (310) and drives the connecting frame (320) to rotate. The screening mechanism (100) further includes an impurity screen (140), which is installed on the upper layer of the seed screen (120), and the aperture of the impurity screen (140) is larger than that of the seed screen (120). The seed sieve (120) is divided into two layers, with the aperture of the seed sieve (120) closer to the bottom plate (130) being smaller than that of the seed sieve (120) further away from the bottom plate (130). The screening mechanism (100) further includes a screen cleaning assembly (150), which includes a blower (151) installed on the side plate of the impurity screen (140) for cleaning the impurities separated by the impurity screen (140). The cleaning assembly (150) further includes a dredging net (152) and a connecting rod (153). The dredging net (152) is set corresponding to the seed sieve (120). The connecting rod (153) connects two of the dredging nets (152). There are multiple dredging posts (157) on the dredging net (152). The dredging posts (157) correspond to the mesh of the seed sieve (120) and can slide into the mesh.
2. The corn seed breeding screening apparatus of claim 1, wherein: The telescopic assembly (340) includes a connecting block (341), a telescopic column (342), a support sleeve (343), and a telescopic member (344). The connecting block (341) is disposed below the vibration damping mechanism (400). The support sleeve (343) is disposed on the support frame (310). One end of the telescopic column (342) slides on the support sleeve (343), and the other end of the telescopic column (342) abuts against the connecting block (341) and can slide in a direction close to or away from the hinge (330). The telescopic member (344) is disposed on the support sleeve (343) and is connected to the telescopic column (342).
3. A corn seed breeding screening apparatus as defined in claim 2, wherein: The side of the connecting block (341) is a right trapezoid, and a rectangular groove (345) is opened on the inclined surface of the connecting block (341). The inclined surface is installed downward. The upper end of the telescopic column (342) is arc-shaped and slides in the groove of the connecting block (341) with the connecting block (341).
4. The corn seed breeding screening apparatus of claim 1, wherein: The screening mechanism (100) also includes a baffle (170), which is installed inside the discharge port of the seed screen (120) and is slidably connected to the seed screen (120).
5. The corn seed breeding screening apparatus of claim 1, wherein: The screen cleaning assembly (150) also includes a comma cam (154) and a drive motor (155). The drive motor (155) is mounted on the base plate (130). The comma cam (154) is mounted below the connecting rod (153) and abuts against the connecting rod (153). The comma cam (154) is connected to the output shaft of the drive motor (155).
6. The corn seed breeding screening apparatus of claim 1, wherein: The cleaning assembly (150) also includes a screen spring (156), which is vertically installed on the side wall of the seed screen (120), located below the unblocking net (152), and connected to the unblocking net (152).