Laser cutting sheet production system
By employing a dual-laser-beam cutting mechanism and a cutting and segmenting mechanism in the laser cutting and manufacturing system, the problem of low manufacturing efficiency has been solved, achieving efficient manufacturing and improved production progress.
Patent Information
- Application Number
- CN202423097061.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-13
- Publication Date
- 2026-02-27
- Estimated Expiration
- 2034-12-13
AI Technical Summary
Existing laser cutting systems have low efficiency, which affects production schedules.
The dual-laser-beam cutting mechanism divides the electrode strip along its width and travel direction to form multiple electrode sheets. Combined with the cutting and dividing mechanism and the moving table, efficient cutting is achieved.
Significantly improve film production efficiency and speed up production progress.
Smart Images
Figure CN223947048U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to the technical field of battery, specifically relates to laser cutting system of making piece. BACKGROUND
[0002] The laminated core is formed by stacking positive sheet - diaphragm - negative sheet in turn for a predetermined number of layers. Laser cutting is widely used in the process of making sheet due to its high efficiency. In the prior art, a single laser head is usually used to cut the sheet material. The laser cuts the sheet material along the width direction of the sheet material to form a single sheet each time, resulting in low efficiency and affecting production progress. SUMMARY
[0003] Therefore, the utility model provides a laser cutting system for making piece to solve the problem of low efficiency and affecting production progress of the existing laser cutting system for making piece.
[0004] The utility model provides a laser cutting system for making piece, it includes: unwinding mechanism, the tab cutting mechanism is set in the downstream of unwinding mechanism, and it is suitable for cutting and forming the tab on the relative both sides of sheet material along the width direction, the cutting and segmentation mechanism is set in the downstream of tab cutting mechanism, the cutting and segmentation mechanism is laser cutting mechanism, the laser cutting mechanism includes two laser lead -out structures, and it is suitable for emitting two laser beams, two laser beams form two scanning paths, two scanning paths are arranged side by side along the width direction of sheet material or are arranged side by side along the direction of sheet material, to divide sheet material along the width direction and the direction of sheet material.
[0005] In an alternative embodiment, two scanning paths are arranged side by side along the width direction of the sheet material, each scanning path includes a first direction path segment, a first width direction path segment, a second direction path segment and a second width direction path segment connected in sequence, the first direction path segment and the second direction path segment are arranged along the direction, and the first width direction path segment and the second width direction path segment are arranged along the width direction; the first direction path segments of the two scanning paths are arranged apart along the width direction, the first width direction path segments of the two scanning paths are connected along the width direction, the second direction path segments of the two scanning paths are arranged apart along the width direction, the second width direction path segments of the two scanning paths are connected along the width direction, and the first direction path segment of one scanning path is connected with the second direction path segment of the other scanning path.
[0006] In an alternative implementation, the two scanning paths are arranged side by side along the running direction of the pole piece strip, each of the scanning paths comprises a third width direction path segment, a third running direction path segment and a fourth width direction path segment connected in sequence, the third width direction path segment and the fourth width direction path segment are arranged along the width direction, and the third running direction path segment is arranged along the running direction; the third width direction path segments of the two scanning paths are arranged apart along the running direction, the third running direction path segments of the two scanning paths are arranged in connection along the running direction, the fourth width direction path segments of the two scanning paths are arranged apart along the running direction, and the third width direction path segment of one of the scanning paths is arranged in connection with the fourth width direction path segment of the other scanning path.
[0007] In an alternative implementation, the laser cutting mechanism further comprises a laser and a beam splitter, the beam splitter is arranged on the laser path of the laser and is adapted to provide laser beams to the two laser lead-out structures.
[0008] In an alternative implementation, the tab cutting mechanism is also the laser cutting mechanism.
[0009] In an alternative implementation, the cutting and separating mechanism is formed with a cutting position below the laser lead-out structure, and the laser cutting system further comprises a moving table, which is arranged below the cutting and separating mechanism and is arranged movable along the running direction of the pole piece strip, the moving table is provided with a suction hole corresponding to the table top of the moving table.
[0010] In an alternative implementation, the laser cutting system further comprises a tail material fixing mechanism, which is arranged above the moving table and close to the cutting position.
[0011] In an alternative implementation, the laser cutting system further comprises a dust removal mechanism, which is arranged integrally with the tail material fixing mechanism.
[0012] In an alternative implementation, the laser cutting system further comprises a residual material collecting mechanism, which is arranged in two, and the two residual material collecting mechanisms are arranged apart along the width direction of the pole piece strip on opposite sides of the tab cutting mechanism, and the residual material collecting mechanism is adapted to collect the cut-off part of the pole piece strip by the tab cutting mechanism.
[0013] In an alternative implementation, the residual material collecting mechanism comprises a conveying structure and a suction structure, the conveying structure and the suction structure are arranged in communication, and the suction structure is adapted to form a negative pressure.
[0014] The technical scheme of the present application has the following advantages:
[0015] After the tab is cut on the pole piece material belt by the tab cutting mechanism, the pole piece material belt is cut to form a pole piece single piece by the cutting and dividing mechanism, and two laser beams can be emitted by the two laser lead-out structures, and the pole piece material belt is divided along the width direction and the belt direction of the pole piece material belt by the two laser beams, so that the wide pole piece material belt can be cut to form a pole piece single piece, and a plurality of pole piece single pieces can be formed in one cutting process, thereby greatly improving the cutting efficiency and improving the production progress. BRIEF DESCRIPTION OF DRAWINGS
[0016] In order to more clearly illustrate the specific embodiments of the present application or the technical scheme in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.
[0017] Figure 1 It is a schematic diagram of the cutting path of the embodiment of the present application.
[0018] Figure 2 It is a schematic diagram of the first embodiment of the scanning path of the embodiment of the present application.
[0019] Figure 3 It is a schematic diagram of the second embodiment of the scanning path of the embodiment of the present application.
[0020] Figure 4 It is a structural schematic diagram of the laser cutting and sheeting system of the embodiment of the present application.
[0021] Figure 5 It is a front view of the laser cutting and sheeting system shown in the figure. Figure 4
[0022] It is a partial structural schematic diagram of the laser cutting and sheeting system shown in the figure. Figure 6 Figure 4
[0023] Figure 7 It is a structural schematic diagram of the laser cutting mechanism of the embodiment of the present application.
[0024] BRIEF DESCRIPTION OF DRAWINGS
[0025] 1, tab cutting mechanism; 2, cutting and dividing mechanism; 3, laser cutting mechanism; 301, laser lead-out structure; 302, laser; 303, beam splitter; 4, scanning path; 401, first tape running direction path segment; 402, first width direction path segment; 403, second tape running direction path segment; 404, second width direction path segment; 405, third width direction path segment; 406, third tape running direction path segment; 407, fourth width direction path segment; 5, moving table; 6, tail material fixing mechanism; 7, dust removal mechanism; 8, residual material collecting mechanism; 801, conveying structure; 802, suction structure; 9, cutting path; 100, tab material tape; 110, tab; 120, tab single piece. DETAILED DESCRIPTION
[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.
[0027] The embodiments of the present application will be described below in connection with Figures 1 to 7 .
[0028] According to the embodiments of the present application, a laser cutting tabbing system is provided, which comprises: a unwinding mechanism; a tab cutting mechanism 1 arranged downstream of the unwinding mechanism and adapted to cut tabs 110 on opposite sides of the tab material tape 100 along the width direction; a cutting and dividing mechanism 2 arranged downstream of the tab cutting mechanism 1, the cutting and dividing mechanism 2 being a laser cutting mechanism 3, the laser cutting mechanism 3 comprising two laser lead-out structures 301 and adapted to emit two laser beams, the two laser beams forming two scanning paths 4 arranged side by side along the width direction of the tab material tape 100 or arranged in parallel along the tape running direction of the tab material tape 100, so as to divide the tab material tape 100 along the width direction and the tape running direction.
[0029] The laser cutting tabbing system of the present embodiment is used to cut tabs 110 on the tab material tape 100 through the tab cutting mechanism 1, and then cut and divide the tab material tape 100 into tab single pieces 120 through the cutting and dividing mechanism 2, and two laser beams can be emitted through the two laser lead-out structures 301, so as to divide the tab material tape 100 along the width direction and the tape running direction of the tab material tape 100. Therefore, the wide tab material tape 100 can be cut and tabbed, and multiple tab single pieces 120 can be formed in one cutting process, greatly improving the tabbing efficiency and production progress.
[0030] As Figure 2 and Figure 3 shown, the following two specific embodiments of the scanning path 4 are introduced respectively.
[0031] In the first embodiment, as Figure 2 shown, two scanning paths 4 are arranged side by side along the width direction of the pole piece tape 100. Specifically, each scanning path 4 includes a first tape running direction path segment 401, a first width direction path segment 402, a second tape running direction path segment 403 and a second width direction path segment 404 connected in sequence, the first tape running direction path segment 401 and the second tape running direction path segment 403 are both arranged extending along the tape running direction, and the first width direction path segment 402 and the second width direction path segment 404 are both arranged extending along the width direction; the first tape running direction path segments 401 of the two scanning paths 4 are arranged spaced apart along the width direction, the first width direction path segments 402 of the two scanning paths 4 are arranged connected along the width direction, the second tape running direction path segments 403 of the two scanning paths 4 are arranged spaced apart along the width direction, the second width direction path segments 404 of the two scanning paths 4 are arranged connected along the width direction, and the first tape running direction path segment 401 of one scanning path 4 is arranged connected with the second tape running direction path segment 403 of the other scanning path 4.
[0032] It is worth noting that, as Figure 2 , in the two scanning paths 4, the first scanning path 4 is A-B-C-D-E(A), and the second scanning path 4 is a-b-c-d-e(a). For the first scanning path 4, the first tape running direction path segment 401 is the AB segment, the first width direction path segment 402 is the BC segment, the second tape running direction path segment 403 is the CD segment, and the second width direction path segment 404 is the DE segment; for the second scanning path 4, the first tape running direction path segment 401 is the ab segment, the first width direction path segment 402 is the bc segment, the second tape running direction path segment 403 is the cd segment, and the second width direction path segment 404 is the de segment. Among them, the ab segment and the CD segment are arranged connected along the tape running direction of the pole piece tape 100, and the pole piece tape 100 is divided along the width direction (that is, the ab segment and the CD segment are located at the middle position of the pole piece tape 100 along the width direction); the BC segment and the bc segment are arranged connected along the width direction of the pole piece tape 100, and the de segment and the DE segment are arranged connected along the width direction of the pole piece tape 100 to divide the pole piece tape 100 along the tape running direction.
[0033] It needs to be further explained that, as Figure 2 , in the scanning path 4, the path segment laser light extraction structure 301 corresponding to the position of the tab 110 does not emit light, that is, does not cut, thereby avoiding cutting the tab 110 by mistake. Specifically, as Figure 2AB segment and CD segment are not cut.
[0034] Therefore, in the first embodiment, as shown in Figure 2 each laser beam forms a plurality of scanning paths 4 along the tape running direction of the pole piece tape 100, and the plurality of scanning paths 4 are continuous paths, that is, the end point of the current scanning path 4 is the starting point of the next scanning path 4. For details, please refer to Figure 2 For a scanning path 4 formed by one laser beam, the end point E of the first scanning path 4 is the starting point A of the second scanning path 4; for a scanning path 4 formed by another laser beam, the end point e of the first scanning path 4 is the starting point a of the second scanning path 4. It is worth noting that only the path segment corresponding to the pole lug 110 needs to control the laser light extraction structure 301 not to emit light.
[0035] In the second embodiment, as shown in Figure 3 two scanning paths 4 are arranged side by side along the tape running direction of the pole piece tape 100. Specifically, each scanning path 4 includes a third width direction path segment 405, a third tape running direction path segment 406 and a fourth width direction path segment 407 connected and arranged in sequence, the third width direction path segment 405 and the fourth width direction path segment 407 are arranged along the width direction, and the third tape running direction path segment 406 is arranged along the tape running direction; the third width direction path segments 405 of the two scanning paths 4 are arranged in a spaced manner along the tape running direction, the third tape running direction path segments 406 of the two scanning paths 4 are arranged in a connected manner along the tape running direction, the fourth width direction path segments 407 of the two scanning paths 4 are arranged in a spaced manner along the tape running direction, and the third width direction path segment 405 of one scanning path 4 and the fourth width direction path segment 407 of the other scanning path 4 are arranged in a connected manner.
[0036] It is worth noting that, as shown in Figure 3 , in the two scanning paths 4, the first scanning path 4 is A-B-C-D, and the second scanning path 4 is a-b-c-d. For the first scanning path 4, the third width direction path segment 405 is the AB segment, the third tape running direction path segment 406 is the BC segment, and the fourth width direction path segment 407 is the CD segment; for the second scanning path 4, the third width direction path segment 405 is the ab segment, the third tape running direction path segment 406 is the bc segment, and the fourth width direction path segment 407 is the cd segment. Among them, the BC segment and the bc segment are arranged in a connected manner along the tape running direction of the pole piece tape 100 and cut the pole piece tape 100 along the width direction (that is, the BC segment and the bc segment are located at the middle position of the pole piece tape 100 along the width direction); the ab segment and the CD segment are arranged in a connected manner along the width direction of the pole piece tape 100 to cut the pole piece tape 100 along the tape running direction.
[0037] It should be further noted that, please refer to Figure 3 The CD section of the present cutting process is connected with the AB section of the next cutting process along the width direction of the pole piece tape 100 to divide the pole piece tape 100 along the running direction.
[0038] Therefore, in the second embodiment, please refer to Figure 3 Along the running direction of the pole piece tape 100, each laser beam forms a plurality of scanning paths 4, and the plurality of scanning paths 4 are discontinuous, that is, after the laser beam scans to form the present scanning path 4, it needs to jump in the width direction and the running direction of the pole piece tape 100, so that the laser beam jumps to the starting point of the next scanning path 4. Specifically, please refer to Figure 3 For one laser beam, after reaching the end point D point of the first scanning path 4, it jumps to the starting point A point of the second scanning path 4 along the width direction and the running direction of the pole piece tape 100; for another laser beam, after reaching the end point d point of the first scanning path 4, it jumps to the starting point a point of the second scanning path 4 along the width direction and the running direction of the pole piece tape 100. It is worth noting that each laser beam will continuously emit light on each scanning path 4 to cut, and there is no light emission during the jumping process of the laser beam along the width direction and the running direction of the pole piece tape 100.
[0039] In summary, the two specific embodiments of the above scanning path 4 can be obtained. In each embodiment, the two scanning paths 4 formed by the two laser beams are completely consistent (that is, the running trend is completely the same), and only the distribution position on the pole piece tape 100 is different. Therefore, two laser beams can be formed by using two laser lead-out structures 301 to cut at the same time.
[0040] In one embodiment, as shown in Figure 7 The laser cutting mechanism 3 also includes a laser 302 and a beam splitter 303, and the beam splitter 303 is arranged on the laser path of the laser 302 and is adapted to provide laser beams to the two laser lead-out structures 301. In this way, the laser cutting mechanism 3 forms a two-head laser mechanism with one output.
[0041] It can be understood that the laser cutting mechanism 3 also includes beam expander mirrors, mirrors and other components, and the laser lead-out structure 301 includes galvanometer mirrors, field lenses and other components, which are used to cooperate with the laser 302, the beam splitter 303 and the like to lead out the laser beams to the pole piece tape 100.
[0042] In one embodiment, as shown in Figure 4 The tab cutting mechanism 1 is also a laser cutting mechanism 3. That is, the tab cutting mechanism 1 is also a two-head laser mechanism with one output, so that the two laser beams respectively form tabs 110 on both sides of the pole piece tape 100 along the width direction.
[0043] Specifically, as shown in Figure 1 The two laser beams emitted by the tab cutting mechanism 1 form two cutting paths 9. In the two cutting paths 9, the first cutting path 9 is A-B-C-D-E, and the second cutting path 9 is a-b-c-d-e. For the first cutting path 9, the AB segment is arranged along the running direction of the tab material strip 100 to form the edge of the tab single piece 120 formed by subsequent processing, and the BC segment, the CD segment, and the DE segment circumscribe the external contour of the tab 110; for the second cutting path 9, the ab segment is arranged along the running direction of the tab material strip 100 to form the edge of the tab single piece 120 formed by subsequent processing, and the bc segment, the cd segment, and the de segment circumscribe the external contour of the tab 110.
[0044] In one embodiment, as shown in Figure 4 and Figure 5 The cutting and dividing mechanism 2 is formed below the laser lead-out structure 301, and the laser cutting tab system further comprises a moving table 5 located below the cutting and dividing mechanism 2 and arranged to be movable along the running direction of the tab material strip 100. The moving table 5 is provided with an adsorption hole corresponding to the surface of the moving table 5.
[0045] It is worth noting that, as shown in Figure 5 In this embodiment, the moving table 5 can move back and forth along the left-right direction. Specifically, first, the moving table 5 is located at the left limit position, and the leading end of the tab material strip 100 to be cut (which has been cut to form a tab 110) is adsorbed and fixed by the moving table 5. Then, the moving table 5 moves to the right and drives the tab material strip 100 to run to the right. During the running of the tab material strip 100, the cutting and dividing mechanism 2 divides the tab material strip 100 to form a plurality of tab single pieces 120. Finally, the moving table 5 moves to the right limit position and stops. After the tab single piece 120 cut on the moving table 5 is taken away, the moving table 5 moves to the left and resets for the next cutting process.
[0046] Of course, in other alternative embodiments, the moving table 5 can also move circularly. It is only required that the moving table 5 can convey the tab material strip 100 forward.
[0047] In one embodiment, as shown in Figure 4As shown, the laser cutting sheeting system further comprises a tail fixing mechanism 6, which is arranged above the moving table 5 and close to the cutting position. In this way, when the moving table 5 moves to the right limit position, the cutting and dividing mechanism 2 completes the last cutting of the pole piece strip 100 on the moving table 5, the tail of the pole piece strip 100 (i.e. the head end of the pole piece strip 100 to be cut in the next cutting process) is adsorbed and fixed above the moving table 5 by the tail fixing mechanism 6, and then the moving table 5 is moved to reset. After the moving table 5 is reset, the pole piece strip 100 is separated from the tail fixing mechanism 6 and is adsorbed and fixed again by the moving table 5.
[0048] In one embodiment, as shown in Figure 4 The laser cutting sheeting system further comprises a dust removal mechanism 7, which is arranged integrally with the tail fixing mechanism 6. The dust removal mechanism 7 is used to remove the dust generated during the cutting process of the cutting and dividing mechanism 2. By arranging the dust removal mechanism 7 and the tail fixing mechanism 6 integrally, the space arrangement of the dust removal mechanism 7 and the tail fixing mechanism 6 is facilitated, and the negative pressure provided to the dust removal mechanism 7 and the tail fixing mechanism 6 is facilitated.
[0049] In one embodiment, as shown in Figure 4 and Figure 6 The laser cutting sheeting system further comprises two residual material collecting mechanisms 8, which are arranged on opposite sides of the tab cutting mechanism 1 along the width direction of the pole piece strip 100, and are adapted to collect the residual material cut by the tab cutting mechanism 1 from the pole piece strip 100.
[0050] Specifically, as shown in Figure 6 The residual material collecting mechanism 8 comprises a conveying structure 801 and a suction structure 802, which are arranged in communication, and the suction structure 802 is adapted to form a negative pressure. That is, the conveying structure 801 conveys the residual material cut by the tab cutting mechanism 1 from the pole piece strip 100 towards the suction structure 802, and the suction structure 802 suctions and collects the residual material under the action of the negative pressure.
[0051] Although the embodiments of the present application are described in conjunction with the drawings, various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and changes fall within the scope defined by the appended claims.
Claims
1. A laser cutting and sheet preparation system, characterized in that, The application relates to a polar plate material belt cutting device. The polar plate material belt cutting device comprises a winding-off mechanism, a polar lug cutting mechanism (1) arranged downstream of the winding-off mechanism and adapted to cut polar lugs (110) on opposite sides of a polar plate material belt (100) along a width direction, and a cutting and dividing mechanism (2) arranged downstream of the polar lug cutting mechanism (1), wherein the cutting and dividing mechanism (2) is a laser cutting mechanism (3) comprising two laser lead-out structures (301) and adapted to emit two laser beams, and the two laser beams form two scanning paths (4) arranged side by side along the width direction of the polar plate material belt (100) or arranged in parallel along the belt running direction of the polar plate material belt (100) to divide the polar plate material belt (100) along the width direction and the belt running direction. The two scanning paths (4) are arranged side by side along the width direction of the polar plate material belt (100), each scanning path (4) comprises a first belt running direction path segment (401), a first width direction path segment (402), a second belt running direction path segment (403) and a second width direction path segment (404) arranged in sequence, the first belt running direction path segment (401) and the second belt running direction path segment (403) are arranged along the belt running direction, and the first width direction path segment (402) and the second width direction path segment (404) are arranged along the width direction. The first belt running direction path segments (401) of the two scanning paths (4) are arranged at intervals along the width direction, the first width direction path segments (402) of the two scanning paths (4) are arranged in connection along the width direction, the second belt running direction path segments (403) of the two scanning paths (4) are arranged at intervals along the width direction, the second width direction path segments (404) of the two scanning paths (4) are arranged in connection along the width direction, and the first belt running direction path segment (401) of one scanning path (4) is arranged in connection with the second belt running direction path segment (403) of the other scanning path (4).
2. The laser dicing system of claim 1, wherein, The two scanning paths (4) are arranged in parallel along the belt running direction of the polar plate material belt (100), each scanning path (4) comprises a third width direction path segment (405), a third belt running direction path segment (406) and a fourth width direction path segment (407) arranged in sequence, the third width direction path segment (405) and the fourth width direction path segment (407) are arranged along the width direction, and the third belt running direction path segment (406) is arranged along the belt running direction. 3. The laser dicing system of claim 1, wherein, The third width direction path segment (405) of the two scanning paths (4) is arranged at intervals along the running direction, the third running direction path segment (406) of the two scanning paths (4) is arranged in connection along the running direction, the fourth width direction path segment (407) of the two scanning paths (4) is arranged at intervals along the running direction, and the third width direction path segment (405) of one of the scanning paths (4) and the fourth width direction path segment (407) of the other scanning path (4) are arranged in connection.
4. The laser dicing system according to any one of claims 1 to 3, wherein, The laser cutting mechanism (3) further comprises a laser (302) and a beam splitter (303), the beam splitter (303) is arranged on the laser path of the laser (302) and is adapted to provide laser beams to the two laser lead-out structures (301).
5. The laser dicing system of claim 4, wherein, The tab cutting mechanism (1) is also the laser cutting mechanism (3).
6. The laser dicing system of any one of claims 1 to 3, wherein, The cutting and dividing mechanism (2) is formed with a cutting position corresponding to the lower side of the laser lead-out structure (301), and the laser cutting sheet system further comprises a moving table (5) arranged below the cutting and dividing mechanism (2) and movable along the running direction of the tab sheet strip (100), the moving table (5) is provided with an adsorption hole corresponding to the table top of the moving table (5).
7. The laser dicing system of claim 6, wherein, The laser cutting sheet system further comprises a tail material fixing mechanism (6) arranged above the moving table (5) and close to the cutting position.
8. The laser dicing system of claim 7, wherein, The laser cutting sheet system further comprises a dust removal mechanism (7) arranged in integration with the tail material fixing mechanism (6).
9. The laser dicing system of any one of claims 1 to 3, wherein, The laser cutting sheet system further comprises a residual material collecting mechanism (8), and two residual material collecting mechanisms (8) are arranged on opposite sides of the tab cutting mechanism (1) along the width direction of the tab sheet strip (100), and the residual material collecting mechanism (8) is adapted to collect the cut part of the tab sheet strip (100) by the tab cutting mechanism (1).
10. The laser dicing system of claim 9, wherein, The residual material collecting mechanism (8) comprises a conveying structure (801) and a suction structure (802), the conveying structure (801) and the suction structure (802) are arranged in communication, and the suction structure (802) is adapted to form a negative pressure.