Fire extinguisher assembling equipment

By using the drive mechanism and cleaning mechanism in the fire extinguisher assembly equipment to remove metal residues and burrs on the cutting surface of the fire extinguisher assembly, the quality problems during the assembly process are solved, and the yield and assembly quality are improved.

CN119260515APending Publication Date: 2025-01-07GUANGDONG JOYAN FIRE FIGHTING TECH CO LTD
View PDF 0 Cites 0 Cited by

Patent Information

Application Number
CN202411588953.4
Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
Filing Date
2024-11-08
Publication Date
2025-01-07

AI Technical Summary

Technical Problem

During the assembly of the fire extinguisher, metal residues and burrs are easily generated on the cutting surfaces of the cylinder, upper and lower seals, which affects the welding quality and sealing properties, resulting in low yield and increased defective products.

Method used

A fire extinguisher assembly equipment is designed, using a driving mechanism to drive the accessory chain and cleaning mechanism, and through rectangular columns, abutment plates, grinding rings and other components, the cutting surfaces of the upper, lower heads and cylinders are cleaned to remove metal residues and Burrs ensure assembly quality.

Benefits of technology

It effectively avoids metal residues and burrs affecting the assembly effect, improves the yield rate of fire extinguishers, reduces the appearance of defective products, and improves the assembly quality.

✦ Generated by Eureka AI based on patent content.

Smart Images

  • Figure CN119260515A_ABST
    Figure CN119260515A_ABST
Patent Text Reader

Abstract

The invention belongs to the technical field of fire extinguisher assembly, and particularly relates to fire extinguisher assembly equipment which comprises a machine body, two accessory chains are in transmission connection with the interior of the machine body through a driving mechanism, abutting plates are fixedly connected between two rectangular columns, the two abutting plates are fixedly connected with limiting columns, and three abutting rods on the same side are jointly and fixedly connected with a U-shaped plate. Mounting grooves are formed in the mounting rings, a plurality of first springs and sliding cylinders are mounted between the mounting grooves and the U-shaped plates, the sliding cylinders are axially and slidably connected between the abutting rods with the middles close to each other, two grinding rings are mounted on each of the two sides of each mounting ring, a fixing plate is fixedly connected to the middle of the machine body, and a limiting strip and a convex plate are fixedly connected to the upper end of the fixing plate; according to the invention, the cutting surface of the fire extinguisher assembly material can be treated when the fire extinguisher assembly material is transported, so that the influence of metal residues and burrs left on the cutting surface on the subsequent stamping and welding effects of an upper sealing head, a cylinder and a lower sealing head is avoided, the finished product rate of fire extinguisher assembly is further improved, and defective products are reduced.
Need to check novelty before this filing date? Find Prior Art

Description

Technical Field

[0001] The invention belongs to the technical field of fire extinguisher assembly, and in particular relates to fire extinguisher assembly equipment. Background Art

[0002] A fire extinguisher is a portable fire-fighting tool. Chemicals are placed in the fire extinguisher to put out fires. Fire extinguishers are one of the most common firefighting equipment and are stored in public places or places where fires may occur. Different types of fire extinguishers are filled with different ingredients and are designed for different fire causes. In the production of fire extinguishers, the pre-prepared cylinder, upper head and lower head need to be assembled together before the raw materials inside the fire extinguisher are filled.

[0003] In the process of assembling a fire extinguisher, the upper head and the lower head are usually pressed or extruded with the cylinder and then welded. This makes it convenient to weld the joints between the upper head and the cylinder, and between the lower head and the cylinder. However, burrs or metal residues are easily generated on the ends of the cylinder, the upper head and the lower head during the preparation process. When the cylinder is subsequently assembled, extruded and welded with the upper head or the lower head, the metal residues enter the weld, thereby contaminating the weld and affecting the welding quality and connection effect, and further affecting the sealing of the fire extinguisher bottle. Therefore, there is room for improvement. Summary of the invention

[0004] The purpose of the present invention is to provide a fire extinguisher assembly device to solve the problems existing in the background technology.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A fire extinguisher assembly device comprises a body, a cylinder, an upper end cap and a lower end cap, wherein two accessory chains are connected to the body through a driving mechanism, and a plurality of cleaning mechanisms are installed between the two accessory chains;

[0007] The cleaning mechanism includes a rectangular column slidably connected to two accessory chains, an abutment plate is fixedly connected between the two rectangular columns, the two abutment plates are fixedly connected to a limiting column, and a placement assembly is symmetrically installed on one side of the two abutment plates close to each other, and the placement assembly includes a mounting ring and two placement pieces, and the two placement pieces include three abutment rods, the three abutment rods are arranged in a semicircular shape, and the three abutment rods on the same side are all fixedly connected to a U-shaped plate together, a mounting groove slidably connected to the two U-shaped plates is opened inside the mounting ring, a plurality of first springs are installed between the mounting groove and the U-shaped plate, and a sliding cylinder axially slidably connected between the abutment rods close to each other in the middle;

[0008] Two grinding rings are installed on both sides of the mounting ring, and the two grinding rings match the inner and outer diameters of the cylinder. A fixing plate is fixedly connected to the middle of the body, and a limiting strip and a convex plate matching the limiting column are fixedly connected to the upper end of the fixing plate.

[0009] The two grinding rings are fixedly connected with a transmission cylinder rotatably connected with the mounting ring, a plurality of meshing teeth are installed on the outer side of the transmission cylinder, and a rack meshing with the meshing teeth is fixedly installed on the upper end of the fixed plate.

[0010] The abutment rods on both sides are equipped with micro suction cups, and the abutment rods are provided with ventilation ducts connected to the U-shaped plates, and the micro suction cups are connected to the ventilation ducts. The middle abutment rod is provided with a one-way air intake valve connected to the ventilation duct, and the U-shaped plate is sealingly and slidingly connected to the mounting groove, and the middle abutment rod is fixedly equipped with a rubber block matching the micro suction cup.

[0011] The sliding cylinder is provided with an arc groove matching the cylinder body on one side facing the center of the mounting ring.

[0012] A conveying mechanism is installed at the input end of the machine body, and the conveying mechanism includes a conveying box connected to the machine body, two transmission shafts are rotatably connected inside the conveying box, three transmission wheels are fixedly installed on the two transmission shafts, and two transmission wheels on the same side are transmission-connected with transmission belts, the conveying box is fixedly connected with isolation columns staggered between the three transmission belts, a blocking assembly is installed inside the conveying box, and the conveying box is equipped with a driving motor transmission-connected to the transmission shaft.

[0013] The blocking assembly comprises a telescopic cylinder installed on the upper end of the conveying box, the telescopic cylinder is drivingly connected with a mounting plate, and a baffle slidably connected with the conveying box and the isolation column is fixedly installed at the lower end of the mounting plate.

[0014] The driving mechanism includes a first gear connected to the transmission shaft, a sprocket meshed with the accessory chain is rotatably connected inside the body, two sprockets close to the conveying box are connected to the second gear, and a transmission gear connected to the body is meshed between the first gear and the second gear.

[0015] The grinding ring comprises a ring plate connected to a mounting ring, a retractable sponge is installed on the inner side of the ring plate, the elastic member is connected to grinding strips slidably connected to the mounting ring, and a plurality of the grinding strips have inclined surfaces at their front ends.

[0016] The present invention can process the cut surfaces of the upper head, the lower head and the cylinder when transporting the fire extinguisher assembly materials, so as to avoid the metal residues and burrs remaining on the cut surfaces affecting the subsequent stamping and welding effects of the upper head, the cylinder and the lower head, thereby improving the finished product rate of the fire extinguisher assembly and reducing the occurrence of defective products. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is further illustrated by means of the non-limiting examples given in the accompanying drawings.

[0018] Figure 1 It is a structural schematic diagram of a fire extinguisher assembly device of the present invention;

[0019] Figure 2 It is a schematic diagram of a first cross-sectional structure of a fire extinguisher assembly device of the present invention;

[0020] Figure 3 It is a second cross-sectional structural schematic diagram of a fire extinguisher assembly device of the present invention;

[0021] Figure 4 It is a third cross-sectional structural schematic diagram of a fire extinguisher assembly device of the present invention;

[0022] Figure 5 for Figure 4 A schematic diagram of the enlarged structure at A in the middle;

[0023] Figure 6 for Figure 4 A schematic diagram of the enlarged structure at B in the middle;

[0024] Figure 7 for Figure 4 Schematic diagram of the enlarged structure at C in the middle;

[0025] Figure 8 It is a fourth cross-sectional structural schematic diagram of a fire extinguisher assembly device of the present invention;

[0026] Fig. 9 for Figure 8 Schematic diagram of the enlarged structure at D in the middle;

[0027] Fig.10 The present invention is a schematic diagram of the installation ring structure of a fire extinguisher assembly device.

[0028] The main component symbols are described as follows:

[0029] Body 1, cylinder 11, upper head 12, lower head 13, accessory chain 14, rectangular column 2, abutment plate 21, limit column 22, mounting ring 23, abutment rod 24, U-shaped plate 25, first spring 26, sliding cylinder 27, grinding ring 28, fixing plate 30, limit strip 31, convex plate 32, transmission cylinder 33, meshing teeth 34, rack 35, micro suction cup 36, ventilation duct 37, one-way air intake valve 38, rubber block 39, conveying box 40, transmission shaft 41, transmission wheel 42, transmission belt 43, isolation column 44, drive motor 45, telescopic cylinder 46, mounting plate 47, baffle 48, first gear 49, sprocket 50, second gear 51, transmission gear 52, ring plate 53, telescopic sponge 54, grinding strip 55. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0031] Example 1: Figure 1-10 As shown, a fire extinguisher assembly device of the present invention comprises a body 1, a cylinder 11, an upper head 12 and a lower head 13. Two accessory chains 14 are connected to the body 1 through a driving mechanism, and a plurality of cleaning mechanisms are installed between the two accessory chains 14.

[0032] The cleaning mechanism includes a rectangular column 2 slidably connected to two accessory chains 14, an abutment plate 21 is fixedly connected between the two rectangular columns 2, the two abutment plates 21 are fixedly connected to the limiting column 22, and a placement component is symmetrically installed on one side of the two abutment plates 21 close to each other. The placement component includes a mounting ring 23 and two placement pieces. The two placement pieces include three abutment rods 24, and the three abutment rods 24 are arranged in a semicircular shape. The three abutment rods 24 on the same side are all fixedly connected to a U-shaped plate 25. A mounting groove slidably connected to the two U-shaped plates 25 is opened inside the mounting ring 23, and a plurality of first springs 26 are installed between the mounting groove and the U-shaped plate 25, and a sliding cylinder 27 axially slidably connected between the abutment rods 24 close to each other in the middle;

[0033] Two grinding rings 28 are installed on both sides of the mounting ring 23. The two grinding rings 28 match the inner and outer diameters of the cylinder 11. A fixing plate 30 is fixedly connected to the middle of the body 1. A limiting strip 31 and a convex plate 32 matching the limiting column 22 are fixedly connected to the upper end of the fixing plate 30.

[0034] When in use, the driving mechanism drives the two accessory chains 14 to move, and then drives a number of cleaning mechanisms to follow the movement of the accessory chains 14, and then the rectangular column 2 places the upper head 12, the cylinder 11 and the lower head 13 of the fire extinguisher from the upper openings of the three abutment rods 24 in sequence between the two mounting rings 23, so that the parallel moving cleaning mechanism drives the upper head 12, the cylinder 11 and the lower head 13 to move forward, and at this time, when the abutment plate 21 moves forward, the limit column 22 will be restricted by the convex plate 32, so that the two abutment plates 21 overcome the resilience of the first spring 26 and engage with each other The upper and lower heads 12 and 13 are moved closer together until the limiting column 22 is located between the limiting strip 31 and the convex plate 32, and the state is maintained. At the same time, in the process of the two abutting plates 21 approaching each other, the upper and lower heads 12 and 13 are driven to approach the grinding ring 28 of the mounting ring 23, so that the cutting surfaces of the upper and lower heads 12 and 13 are brought closer to the abutting grinding ring 28, and the metal residues are polished away. At the same time, after the upper and lower heads 12 and 13 abut against the mounting ring 23, they continue to approach each other, which will make the two mounting rings 23 approach the cylinder 11, so that the two cutting surfaces of the cylinder 11 are respectively aligned with the two The two abutment plates 21 are continuously brought close to each other, and the U-shaped plate 25 compresses the first spring 26 until the abutment plate 21 abuts the upper and lower heads 12 and 13 against the grinding ring 28. Finally, the attachment chain 14 drives the movement to the inclined position of the convex plate 32. When the upper and lower heads 12, 11 and 13 are in contact with each other, the upper and lower heads 12, 11 and 13 are clamped together, and the upper and lower heads 12, 11 and 13 are slid out of the openings of the three abutment rods 24 when the accessory chain 14 drives the three abutment rods 24 to rotate, thereby completing the cleaning before assembly, so as to avoid burrs and metal residues generated by cutting from remaining on the cutting surfaces of the upper and lower heads 12, 13 and the cylinder 11, thereby avoiding affecting the effects of stamping and welding.

[0035] The present invention can process the cut surfaces of the upper head, the lower head and the cylinder when transporting the fire extinguisher assembly materials, so as to avoid the metal residues and burrs remaining on the cut surfaces affecting the subsequent stamping and welding effects of the upper head, the cylinder and the lower head, thereby improving the finished product rate of the fire extinguisher assembly and reducing the occurrence of defective products.

[0036] Embodiment 2: Based on embodiment 1, further improvements are made. The two grinding rings 28 are fixedly connected with a transmission cylinder 33 which is rotatably connected with the mounting ring 23. A plurality of meshing teeth 34 are installed on the outer side of the transmission cylinder 33. A rack 35 meshing with the meshing teeth 34 is fixedly installed on the upper end of the fixed plate 30.

[0037] The rack 35 matches the protruding part of the convex plate 32, so that the rack 35 is aligned with the meshing teeth 34 when the limit column 22 is located between the convex part of the convex plate 32 and the limit bar 31. When the abutment plate 21 drives the upper head 12, the cylinder 11 and the lower head 13 to abut against the grinding ring 28, the transmission cylinder 33 will match the position of the rack 35, so that when the accessory chain 14 drives the cleaning mechanism to move, its meshing teeth 34 will mesh with the rack 35, and then during the movement of the mounting ring 23, the meshing teeth 34 drive the transmission cylinder 33 and the grinding ring 28 to rotate under the restriction of the rack 35, and then the cutting surfaces of the clamped upper head 12, the cylinder 11 and the lower head 13 located inside the grinding ring 28 are rotated and polished until the abutment plate 21 is away from the rack 35 with the cooperation of the convex plate 32 and the first spring 26.

[0038] The abutment rods 24 on both sides are equipped with micro suction cups 36, and the abutment rods 24 are provided with ventilation ducts 37 connected to the U-shaped plate 25, the micro suction cups 36 are connected to the ventilation duct 37, the middle abutment rod 24 is provided with a one-way air intake valve 38 connected to the ventilation duct 37, the U-shaped plate 25 is sealingly and slidingly connected to the mounting groove, and the middle abutment rod 24 is fixedly equipped with a rubber block 39 matching the micro suction cup 36.

[0039] When the upper head 12 enters the inner part of the three abutting rods 24, it abuts against the micro suction cup 36 and the rubber block 39. The same is true for the lower head 13 and the cylinder 11. When the mounting ring 23 abuts against the cylinder 11, the limit column 22 drives the abutting plate 21 to move, so that the two U-shaped plates 25 passing through the inner part of the mounting ring 23 overcome the first spring 26 and approach each other. Since the mounting groove and the U-shaped plate 25 are sealed and slidably connected, when the U-shaped plate 25 is compressed, the air inside the mounting groove will be discharged from the air vent and at the same time, the air will be sucked into the mounting groove through the ventilation pipe 37, so that the micro suction cup 36 abutting against the upper head 12 is adsorbed together with it until the U-shaped plate 25 can no longer move. In this way, after the upper head 12 is fixed by the micro suction cup 36, it can play the role of fixing the upper head 12 when entering the convex part of the convex plate 32. In this way, the cooperation of the meshing teeth 34 and the rack 35 can drive the grinding ring 28 to rotate to grind the cutting surface.

[0040] When the U-shaped plate 25 moves toward the abutment plate 21 under the rebound force of the first spring 26, the air enters the installation groove through the air vents, while the air on the other side of the U-shaped plate 25 can only be discharged to the micro suction cup 36 through the ventilation pipe 37 under the obstruction of the one-way air inlet valve 38, thereby releasing the adsorption of the micro suction cup 36 and the upper head 12. The same applies to the cylinder 11 and the lower head 13.

[0041] An arc groove matching the cylinder body 11 is formed on one side of the sliding cylinder 27 facing the center of the mounting ring 23 .

[0042] The arc groove, the micro suction cup 36 and the rubber block 39 make the cylinder body 11 more stably placed.

[0043] A conveying mechanism is installed at the input end of the body 1, and the conveying mechanism includes a conveying box 40 connected to the body 1. Two transmission shafts 41 are rotatably connected inside the conveying box 40. Three transmission wheels 42 are fixedly installed on the two transmission shafts 41. The two transmission wheels 42 on the same side are both transmission-connected to a transmission belt 43. The conveying box 40 is fixedly connected to isolation columns 44 staggered between the three transmission belts 43. A blocking component is installed inside the conveying box 40. The conveying box 40 is equipped with a driving motor 45 transmission-connected to the transmission shaft 41.

[0044] When the driving motor 45 is working, it drives one of the transmission shafts 41 to rotate, and then drives the three coaxial transmission wheels 42 to rotate. When the three transmission wheels 42 rotate, they will drive the three transmission belts 43 to move, and then cooperate with the two isolation columns 44 to transport the upper head 12, the cylinder 11 and the lower head 13 in sequence and synchronously, and then they are located inside the conveying box 40 under the obstruction of the blocking component. When the blocking component cooperates with the movement of the accessory chain 14 to open the blocking component, the upper head 12, the cylinder 11 and the lower head 13 are driven by the conveyor belt 43 to enter the interior of the machine body 1 and enter the interior of the cleaning mechanism from the open ends of the three abutment rods 24. At the same time, the mounting ring 23 matches the isolation column 44, so the mounting ring 23 and the isolation column 44 jointly guide the upper head 12 after the blocking component is opened until it enters the interior of the three abutment rods 24.

[0045] The blocking assembly includes a telescopic cylinder 46 installed on the upper end of the conveying box 40, the telescopic cylinder 46 is connected to the mounting plate 47 in a transmission manner, and a baffle 48 is fixedly installed at the lower end of the mounting plate 47 and is slidably connected to the conveying box 40 and the isolation column 44. The telescopic cylinder 46 controls the expansion and contraction of the mounting plate 47, and then drives the baffle 48 to slide inside the isolation column 44 through the mounting plate 47, so that the baffle 48 abuts against the upper head 12, so that the conveyor belt 43 can continue to move to continuously convey the subsequent raw materials forward, and then drive the baffle 48 to move upward to release the abutment so that the frontmost material enters the cleaning mechanism.

[0046] The driving mechanism includes a first gear 49 connected to the transmission shaft 41, a sprocket 50 meshing with the accessory chain 14 is rotatably connected inside the machine body 1, two sprockets 50 near the conveying box 40 are connected to the second gear 51, and a transmission gear 52 connected to the machine body 1 is meshed between the first gear 49 and the second gear 51. When the driving motor 45 continuously drives the transmission belt 43 to rotate continuously, the first gear 49 connected to the single shaft 41 will rotate, and then the second gear 51 is driven to rotate through the meshing transmission gear 52, and one of the sprockets 50 meshing with the accessory chain 14 is driven to rotate through the second gear 51, and the other sprocket 50 is driven to rotate through the cooperation of the sprocket 50 and the accessory chain 14, so that the cleaning mechanism of the accessory chain 14 can be driven to work while driving the conveying mechanism to work, saving electrical components.

[0047] The grinding ring 28 includes a ring plate 53 connected to the mounting ring 23, a retractable sponge 54 is installed inside the ring plate 53, and a grinding strip 55 slidably connected to the mounting ring 23 is connected to the elastic member, and a plurality of grinding strips 55 are provided with an inclined surface at the front end. The retractable sponge 54 can be deformed according to the force, and can adapt to the cutting surfaces of different thicknesses. At the same time, the inclined surface can also guide the upper head 12. After entering through the inclined surface, the deformation of the retractable sponge 54 is matched with the grinding strip 55, and the cutting surface is polished during the rotation of the grinding strip 55.

[0048] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the relevant technical field without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A fire extinguisher assembly device, comprising a body, a cylinder, an upper head and a lower head, characterized in that: The inside of the machine body is connected to two accessory chains through a driving mechanism, and a plurality of cleaning mechanisms are installed between the two accessory chains; The cleaning mechanism includes a rectangular column slidably connected to two accessory chains, an abutment plate is fixedly connected between the two rectangular columns, the two abutment plates are fixedly connected to a limiting column, and a placement assembly is symmetrically installed on one side of the two abutment plates close to each other, and the placement assembly includes a mounting ring and two placement pieces, and the two placement pieces include three abutment rods, the three abutment rods are arranged in a semicircular shape, and the three abutment rods on the same side are all fixedly connected to a U-shaped plate together, a mounting groove slidably connected to the two U-shaped plates is opened inside the mounting ring, a plurality of first springs are installed between the mounting groove and the U-shaped plate, and a sliding cylinder axially slidably connected between the abutment rods close to each other in the middle; Two grinding rings are installed on both sides of the mounting ring, and the two grinding rings match the inner and outer diameters of the cylinder. A fixing plate is fixedly connected to the middle of the body, and a limiting strip and a convex plate matching the limiting column are fixedly connected to the upper end of the fixing plate.

2. A fire extinguisher assembly device according to claim 1, characterized in that: The two grinding rings are fixedly connected with a transmission cylinder rotatably connected with the mounting ring, a plurality of meshing teeth are installed on the outer side of the transmission cylinder, and a rack meshing with the meshing teeth is fixedly installed on the upper end of the fixed plate.

3. A fire extinguisher assembly device according to claim 2, characterized in that: The abutment rods on both sides are equipped with micro suction cups, and the abutment rods are provided with ventilation ducts connected to the U-shaped plates, and the micro suction cups are connected to the ventilation ducts. The middle abutment rod is provided with a one-way air intake valve connected to the ventilation duct, and the U-shaped plate is sealingly and slidingly connected to the mounting groove, and the middle abutment rod is fixedly equipped with a rubber block matching the micro suction cup.

4. A fire extinguisher assembly device according to claim 3, characterized in that: The sliding cylinder is provided with an arc groove matching the cylinder body on one side facing the center of the mounting ring.

5. The fire extinguisher assembly equipment according to claim 1, characterized in that: A conveying mechanism is installed at the input end of the machine body, and the conveying mechanism includes a conveying box connected to the machine body, two transmission shafts are rotatably connected inside the conveying box, three transmission wheels are fixedly installed on the two transmission shafts, and two transmission wheels on the same side are transmission-connected with transmission belts, the conveying box is fixedly connected with isolation columns staggered between the three transmission belts, a blocking assembly is installed inside the conveying box, and the conveying box is equipped with a driving motor transmission-connected to the transmission shaft.

6. A fire extinguisher assembly device according to claim 5, characterized in that: The blocking assembly comprises a telescopic cylinder installed on the upper end of the conveying box, the telescopic cylinder is drivingly connected with a mounting plate, and a baffle slidably connected with the conveying box and the isolation column is fixedly installed at the lower end of the mounting plate.

7. The fire extinguisher assembly equipment according to claim 5, characterized in that: The driving mechanism includes a first gear connected to the transmission shaft, a sprocket meshed with the accessory chain is rotatably connected inside the body, two sprockets close to the conveying box are connected to the second gear, and a transmission gear connected to the body is meshed between the first gear and the second gear.

8. The fire extinguisher assembly equipment according to claim 2, characterized in that: The grinding ring comprises a ring plate connected to a mounting ring, a retractable sponge is installed on the inner side of the ring plate, the elastic member is connected to grinding strips slidably connected to the mounting ring, and a plurality of the grinding strips have inclined surfaces at their front ends.