JPH068903A - Method and apparatus for bagging can lid, and bagging tray therefor - Google Patents

Abstract

PURPOSE:To increase the speed of bagging can lids, and to improve efficiency therefor in an operation where a number of can lids are arranged face to face in upright position in a row for bagging by a method wherein the row of can lids is placed on a tray that holds the can lid row from the front and the rear and keeps it in good order, and the can lid row is inserted as it is into the bag. CONSTITUTION:A can lid row 1 in which a specified number of can lids 1a are arranged face to face tightly in upright position is placed on a tray 2 from above and is held upright, being interposed between a front protuberance 8 and a rear protuberance 9. A bag 3, supplied onto a guide rail 5, is held, being attracted by sucking pads 19, provided on the upper and the lower sides, as the pads approach from above and below, and the opening end thereof is extended subsequently when the sucking pads separate from each other. Then, the tray 2 is inserted into the bag 3 while a pair of beak-like members 20a of a bag-holding device 4 are fitted to the opening end of the bag 3. When the tray 2 is pulled back, a push rod is thrust forward, and thereby the can lid row is held inside the bag and after that, the opening end of the bag 3 is folded flat by operation of a temporary folding device 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for packing a row of can lids that are closely attached and aligned in an upright state without sacrificing their postures, and a tray used in the apparatus and method. It is about.

[0002]

2. Description of the Related Art As is well known, in a can manufacturing factory, a can body and a can lid are separately packaged in a predetermined number and shipped to a filling factory. Since it is a relatively thin disk body having a slight convex portion toward, the packaging and shipping of the disk body is generally performed by stacking hundreds or hundreds of them. In the bag filling process prior to shipping the can lids, first, the can lids are stacked in the same direction, and a predetermined number of can lids are separated from the row of the can lids while keeping the aligned state. Generally, one unit is packed in a tubular bag and the opening is closed.

Japanese Patent Publication No. 59-52082 discloses an apparatus for automatically bagging can lids. This device is for packing a predetermined number of can lid cylinders counted by a counting mechanism into a bag. The can lid cylinder is placed on a gutter, and a pair of upper and lower can lids are placed on the same axis as the gutter. An empty bag opened with a suction pad is arranged, and a can lid cylindrical body on a gutter is pushed toward the empty bag by a rod to fill the can lid. Also, in order to expand the bag sufficiently in advance, an air pipe for blowing air into the empty bag is provided.

Further, immediately after the can lid is packed in the bag, the cylindrical bagging body is tilted and sequentially housed in a tilted stock box.

[0005]

Generally, a paper bag is used as a bag for packaging the can lids stacked in a cylindrical shape, and the bag is flatly folded and stocked before use. Even if it is opened with the above suction pad and air is blown into it, it does not expand completely. Therefore, when the can lid cylinder is inserted into the bag, the can lid cylinder pushes and expands the bag and moves forward. Therefore, a resistance force is exerted on the can lid cylinder by sliding contact with the inner surface of the bag. . The resistance varies greatly depending on the amount by which the bag is expanded and the smoothness of the inner surface of the bag, as well as the speed at which the can lid cylinder advances. The resistance acting on the body becomes large, and it is difficult to pack the bag without breaking the aligned state.

In the above-mentioned conventional apparatus, when the can lid cylinder on the gutter is pushed horizontally by the rod and inserted into the bag, the can lid cylinder which is one unit is obtained by simply and closely aligning a large number of can lids. Therefore, it is difficult to maintain the shape of the cylindrical body, and when the can lid moves, the can lid slides against the inner surface of the gutter and the inner surface of the bag to receive resistance, or when the can lids overlap each other, the inside of the bag is repulsed. The can lid on the tip side that moves down falls down and moves to the bottom of the bag as it is, and is pushed by the succeeding can lid there,
It occurs that the fallen can lids are aligned in the opposite direction.

Further, the rear end of the can lid cylindrical body is in contact with the rod until it is inserted into the bag, so that the can lid does not fall down. Only a slight contact with the inner surface of the bag supports the lid, and the can lid on the rear end side easily falls down. Therefore, in the conventional device, it was necessary to tilt the cylindrical bagging body by the moving gutter mechanism of the gutter immediately after inserting the can lid into the bag.

The present invention has been made in view of the above circumstances, and is a device capable of stably and rapidly bagging a large number of aligned can lids in the horizontal direction without disturbing the aligned state. And a method and bagging tray.

[0009]

In order to achieve the above-mentioned object, the apparatus of the present invention has a can lid row in which a large number of can lids are placed upright on a horizontal plane so as to be in close contact and aligned. A bag-filling device for can lids inserted into a bag held open by opening on the same axis as a row, and a tray for holding and placing a predetermined number of can lids in an upright, closely contacted and aligned state,
A push rod is arranged at a front position on the opening end side of the bag so as to be able to move forward and backward with respect to the inside of the bag, and which pushes the can lid row on the tray into the bag when the tray retracts from the inside of the bag. A provisional folding device is provided which is arranged so as to be able to move forward and backward with respect to the bag and which flatly crushes the open end of the bag.

The method of the present invention further comprises a can lid row in which a large number of can lids are placed upright on a horizontal surface so as to be in close contact and aligned.
A method of packing a can lid inserted into a bag held by opening it on the same axis as the can lid row, comprising placing the can lid row on a tray and advancing the tray into the bag. , The can lid row is inserted into the bag together with the tray, and then the tray is retracted from the bag while the push rod is in contact with the rear end of the can lid row inside the bag, and then the push rod is put into the bag. It is characterized in that the bag is retracted from the inside and the open end of the bag is flattened so as to immediately close the rear end of the can lid row.

Further, the tray of the present invention is a bag packing tray for a can lid on which the can lid held in an upright, closely contacted and aligned state is placed, and the receiving surface on which the can lid is placed has a contour of the can lid. A projection that is formed in a concave cross-sectional shape that is substantially the same as a part and that holds the can lid in an upright state at the front end portion and the rear end portion of its receiving surface is approximately equal to the length of a predetermined number of can lids. It is characterized in that the projections at the front end portion are provided at intervals and are elastically displaced.

[0012]

According to the present invention, the can lid row in which a large number of can lids are placed upright on the horizontal surface so as to be in close contact with and aligned with each other is placed on the tray and the tray is kept in the close contact / aligned state. The tray on which the can lid row is placed advances toward the bag held in the opened state and is inserted into the bag, and the can lid row is inserted into the bag accordingly. In that case, the can lid row is placed and held on the tray, and the tray also enters the inside of the bag to push and expand the bag,
Therefore, since the tray receives a part of the resistance force caused by expanding the bag, even if the resistance force is large, that is, the insertion speed into the bag is fast, the alignment of the can lid rows is not disturbed. Absent. When the tray reaches the forward end,
The push rod is inserted into the bag and brought into contact with the rear end portion of the can lid row, and in this state, the tray is moved backward and pulled out from the bag. That is, even if there is an engaging portion for maintaining the posture of the can lid row between the can lid row and the tray, only the can lid row is pressed into the bag and only the tray is pulled out.
Then, the push rod retracts, the open end of the bag is flattened, and the bag packing is completed.

In the tray of the present invention, the receiving surface on which the row of can lids is placed is formed to have a cross-sectional shape almost the same as a part of the outer periphery of the can lid, and the cans are provided at both front and rear ends of the receiving surface. Since the protrusion that supports the lid in the upright state is formed, the can lid row can be stably placed while maintaining its posture. Further, since the projection of the front end portion is configured to be elastically displaced, when the can lid row is advanced relatively along the receiving surface, the projection of the front end portion is pushed by the can lid row to be elastically moved. Therefore, interference with the can lid row when retracting only the tray can be mitigated, and disturbance of the posture of the can lid row can be prevented in advance.

[0014]

EXAMPLES Next, examples of the present invention will be described.
FIG. 1 is a conceptual diagram showing the basic structure of the device according to the present invention, in which a bag holding device 4 for opening and holding a bag 3 and a guide rail 5 for holding a bag 3 in front of a tray 2 on which a can lid row 1 is placed.
In addition, a temporary folding device 6 is arranged.

In the can lid row 1 of interest, a directional disc-shaped can lid 1a that is convex toward the inside of the can is erected so that its surface is perpendicular to the horizontal plane. At the same time, a large number of sheets are stacked in close contact with the same orientation, and the outer shape is almost cylindrical. The tray 2 on which the can lid row 1 is placed is arranged substantially horizontally and is configured to advance toward the bag holding device 4, and the upper surface, that is, the receiving surface 7 thereof, is the lower half of the can lid row 1 or It is formed into a concave arc surface into which about 1/3 of the lower side is fitted. Therefore, the tray 2 is a gutter-shaped elongated member as shown in FIG. 2, and the projections 8 for supporting the can lid 1a in an upright state are provided on the front end and the rear end of the receiving surface 7 thereof.
9 is formed.

Of these protrusions 8 and 9, the protrusion 9 on the rear end side
Is formed by projecting upward so that a step is formed between the receiving surface 7 and the receiving surface 7, while the protrusion 8 on the front end side is formed.
Is formed by attaching a pair of elastic synthetic resin pieces. In addition, the protrusion 8 on the front end side is displaced outward by the elasticity of the tray 2 in addition to the elasticity of itself.
A slit 10 is formed at the tip of the tray 2. Therefore, the projection 9 on the rear end side abuts the can lid 1a at a step between the protruding surface 9 and the receiving surface 7 to support the can lid 1a in an upright state. On the other hand, the protrusion 8 on the front end side holds the can lid 1a between the pair of synthetic resin pieces and holds the can lid 1a in an upright state. The interval between the protrusions 8 and 9 is set to be substantially equal to the length of the can lid row 1 to be placed on the tray 2.

Since the projections 8 and 9 are formed on the tray 2 as described above, the can lid row 1 is preferably placed on the tray 2 from above the tray 2. In that case, it is preferable to temporarily lift up the tray 2 slightly in order to shorten the fall distance of the can lid row 1. A widely known air cylinder can be used as a means for lifting up.

The tray 2 is for inserting the can lid row 1 into the bag 3 with the can lid row 1 placed thereon.
There is provided a drive device for moving the bag forward and backward with respect to the bag 3. That is, the rodless magnet cylinder 11 is arranged in parallel with the tray 2, and the rear end portion of the tray 2 is connected to the movable portion 12 of the rodless magnet cylinder 11. Needless to say, a guide (not shown) is provided to compensate for the linear movement of the tray 2.

A push rod 13 is arranged on the upper side of the tray 2. This push rod 13
When the tray 2 moves backward to the left in FIG.
A rod for pressing down the upper can lid row 1, the rod being parallel to the position retracted from above the tray 2 and on the same axis as the can lid row 1 on the tray 2, and the same as the tray 2. It is designed to move forward and to the rear end. That is, a rodless magnet cylinder 14 for moving the push rod 13 back and forth is arranged on the opposite side of the rodless magnet cylinder 11 with the tray 2 interposed therebetween.
As shown in FIG. 3, a saddle 16 that is inclined downward toward the tray 2 is attached to the movable portion 15. A rodless magnet cylinder 17 having a short stroke is mounted on the saddle 16 so as to operate in the inclination direction of the saddle 16, and a rear end of the push rod 13 is attached to a movable portion 18 of the rodless magnet cylinder 17. The part is cantilevered.

Next, the bag holding device 4 will be described. As described above, the bag holding device 4 is for opening the bag 3 placed on the guide rail 5 and holding it in that state, and is arranged at the end of the guide rail 5 on the tray 2 side. The basic configuration is as shown in FIGS. 4A, 4B and 5.

The bag holding device 4 is a suction pad 1 for opening the bag 3.
9, an opening guide 20 that maintains the bag 3 in an open state, and a stopper 21 that sandwiches the bag 3 between the opening guide 20 and the opening guide 20. The suction pad 19 is a conventionally known one that is pressed against the outer surface of the bag 3 to vacuum-suck the bag 3, and as shown in FIG. One of them is arranged at each side, and they are brought close to and separated from each other by an actuator such as an air cylinder (not shown).

The opening guide 20 is provided with a pair of upper and lower beak members 20a having a semi-arcuate cross section and having a tapered shape, and these beak members 20a are vertically spaced apart from each other and arranged in parallel with each other. Axes 22,22
The brackets 23 extending from the rotary shafts 22 and 22,
It is attached via 23. The opening guide 20 approaches the open end of the bag 3 in a state where the front ends of the pair of beak-shaped members 20a are closed and close to each other, and in this state, the front ends of the beak-shaped members 20a are separated from each other. The bag 3 is inserted into the bag 3 by being opened to hold the bag 3 in an open state.

The mechanism for rotating the beak member 20a as described above will be explained.
Links 22 and 25 extending in the radial direction are attached to the rotary shafts 2 and 22, and the left end portion of the link 24 attached to the upper rotary shaft 22 in FIG.
A right end portion of the link 25 attached to is connected by a connecting rod 26. A rod of an air cylinder 27 is connected to a link 24 attached to the upper rotary shaft 22. Therefore, when the upper rotary shaft 22 is rotated together with the link 24 by the air cylinder 27, the lower rotary shaft 22 is rotated in the opposite direction via the connecting rod 26 and the link 25. As a result, these rotary shafts are rotated. 22, 2
The beak-shaped member 20a attached to the 2 is adapted to open and close.

As shown in FIG. 5, a pair of stoppers 21 for sandwiching the bag 3 between the opening guide 20 and the stoppers 21 are arranged vertically, and when the beak member 20a described above is opened, the outer surface of the tip end portion thereof is opened. Collide with each other and sandwich the open end of the bag 3.

It should be noted that when pulling one bag 3 from the bag 3 (not shown) which is folded and stored in a flat state arranged on the lower side onto the upper guide rail 5, the passage of the bag 3 should not be obstructed. , The guide rail 5 opens left and right, and the suction pad 19
Is in a retracted position, and when the bag 3 is set on the guide rail 5, the suction pad 19 is moved forward and downward to a position where the bag 3 is sandwiched. That is, the suction pad 19 and the opening guide 20 described above, the drive mechanism for opening / closing the opening guide 20, and the pair of upper stoppers 21.
Is attached to the movable table 28. And this movable stand 2
The air cylinder 8 can be moved back and forth with respect to the bag 3 by air cylinders 29 arranged on both left and right sides in a direction parallel to the moving direction. The lower stopper 2
1 is attached to the end of the guide rail 5.

Further, the temporary folding device 6 is for preventing the can lid 1a in the bag 3 from collapsing by crushing the excess portion of the bag 3 on the open end side into a substantially flat shape, as shown in FIG. In addition, by rotating the cylindrical member 31 by the rotary actuator 30 arranged on the side of the guide rail 5, the opening end of the bag 3 is crushed substantially flat by the cylindrical member 31 and temporarily folded. Has been done. In order to prevent the can lid 1a in the bag 3 from falling during this temporary folding, the can lid row 1 in the bag 3 is provided above the guide rails 5.
A can lid retainer 3 that holds the can lid 1a located on the opening end side of the bag 3 between the guide rail 5 and the upright state.
2 is arranged so as to be vertically movable.

The rotary actuator 30 and the cylindrical member 31 rotated by the rotary actuator 30 are moved forward to advance the can lid row 1 in which the bags 3 are packed and the bags 3 are temporarily folded. It is preferable to be configured to move back and forth along 5. With such a configuration, it is possible to simplify the feeding mechanism of the can lid row 1 that has been bag-filled.

As a mechanism for supplying the bag 3 onto the guide rail 5, a mechanism for pulling the bag 3 stocked below the guide rail 5 onto the guide rail 5 by a plurality of suction pads (not shown), Other known mechanisms can be adopted.

Next, the operation of the bag filling device described above will be described. The counted predetermined number of can lids 1a are aligned in an upright and closely contacted state to form a can lid row 1. The can lid row 1 is placed on a tray 2 by being lowered from above. Since the length of the can lid row 1 corresponds to the distance between the projections 8 and 9 on the tray 2, the can lid 1a at the rear end of the can lid row 1 abuts the projection 9 on the rear end side. Are held in an upright state, and the can lid 1a at the front end is sandwiched between the protrusions 8 on the front end side and held in an upright state.

On the other hand, the bag 3 supplied on the guide rail 5
The open end, that is, the end on the side of the bag holding device 4 is movable table 28.
Are moved forward by the air cylinder 29, and the suction pads 19 on the upper and lower sides approach each other, so that the suction pads 19 are sucked.
By separating 9 from each other, the open end of the bag 3 is expanded. In this case, the stroke of the suction pad 19 on the upper side is lengthened so that the center of the opening end of the bag 3 is located at the can lid row 1.
It is almost aligned with the central axis of.

The so-called closed guide 20 in which the tips of the beak members 20a are close to each other
When the mouth of the bag 3 is opened by the suction pad 19,
When the air cylinder 27 operates, it opens.
That is, the beak-shaped members 20a rotate in mutually opposite directions about the axis of the rotary shaft 22, and as a result, the tips of the beak-shaped members 20a are inserted into the inside of the open end of the bag 3 while being separated from each other.

When the beak-shaped member 20a is substantially completely opened, that is, when the shape formed by the inner peripheral surface or the outer peripheral surface thereof becomes substantially cylindrical, each beak-shaped member 20a is formed.
The outer surface of the bag comes into contact with the stopper 21, and as a result, the open end of the bag 3 is sandwiched between the beak-shaped member 20a and the stopper 21, so that the bag 3 is held in the open state and is not moved in the longitudinal direction. Be blocked. At this point, the suction of the bag 3 by the suction pad 19 is released.

When the bag 3 is opened and held as described above, the tray 2 on which the can lid row 1 is placed is advanced toward the bag 3 by the rodless magnet cylinder 11.
It is inserted into the bag 3 through the inside of the opening guide 20. At the forward end of the tray 2, the end of the can lid row 1 reaches near the end of the bag 3, and the entire can lid row 1 is securely inserted into the bag 3. When the tray 2 advances and the can lid row 1 is inserted into the bag 3 in this manner, the tray 2 and the can lid row 1 push and expand the bag 3, so that the resistance of the can lid row 1 due to the forward movement is increased. Power acts. The resistance force increases as the insertion speed increases, but since the bag 3 is also expanded by the tray 2, the resistance force acting on the can lid row 1 is
The tray 2 is smaller than the tray 2, and the can lid row 1 is supported by the projections 8 and 9 on both front and rear sides to maintain the aligned state. Therefore, even when the inserting speed into the bag 3 is considerably increased, The aligned state of the lid row 1 will not be broken, and the can lid 1a will not fall over inside the bag 3 or be inverted.

Then, the saddle 16 is arranged so that the push rods 13 are arranged behind the can lid row 1 on the same axis as the can lid row 1.
The movable portion 15 moved by the upper rodless magnet cylinder 17 and further having the saddle 16 placed thereon moves to the bag 3 side by the rodless magnet cylinder 14. That is, the push rod 13 is moved toward the can lid row 1 in the bag 3 and comes into contact with the rear end portion of the can lid row 1. When the push rod 13 pushes the can lid row 1 toward the inside of the bag 3, the tray 2 is moved backward by the rodless magnet cylinder 11. In that case, since the projecting portion 8 is provided at the front end of the tray 2, the can lid 1a is caught by the projecting portion 8, but the can lid row 1 is prevented from being moved backward by the push rod 13. Since the protrusion 8 is elastically displaceable by inserting the slit 10 at the tip of the tray 2, the protrusion 8 can be easily detached from the can lid row 1, so that the tray 2 disturbs the aligned state of the can lid row 1. Instead, it is pulled out of the bag 3.

Continuing to pull out the tray 2, the can lid holder 3
2 descends to the can end 1 on the rear end side of the can end row 1 in the bag 3.
a is pressed by the can lid presser 32 and held in an upright state, and in this state, the push rod 13 is retracted and pulled out from the bag 3. The push rod 13 retracted to the limit position is moved from above the tray 2 to a sideward retracted position by operating the rodless magnet cylinder 17 on the saddle 16.

After the push rod 13 is retracted,
As the opening guide 20 closes, the movable table 28 moves backward, and the bag holding device 4 moves to a position where it does not interfere with the temporary folding device 6. Then, the rotary actuator 30 rotates, and the cylindrical member 31 crushes the open end of the bag 3 into a flat shape, and temporarily folds the open end of the bag 3. Following this, the can lid retainer 32 rises and the holding of the can lid 1a is released,
A series of bagging work is completed. The can lid row 1 packed in a bag has a cylindrical member 3 in which the open end of the bag 3 is temporarily folded.
By moving 1 along the guide rail 5, it is moved to the folding process of the opening end of the bag 3.

The present invention is not limited to the above-described embodiment, and the detailed structure and means can be replaced with other structures and means as long as the basic operation is the same. The opening guide may be constituted by a plurality of pins or finger members, as long as it holds the opening of the bag in a substantially cylindrical shape. A configuration using a motor may be used.

Further, in the above embodiment, two suction pads on the upper side are provided, but this cuts off a part of the open end of the bag with a predetermined width and length to prevent unnecessary wrinkles during folding. This is to prevent this from happening and to avoid the cutout portion to suck the opening of the bag. Therefore, if such a cutout portion is not provided, only one suction pad on the upper side is required. .

Further, the projection on the tip side of the tray is only required to be able to hold the can lid in an upright state, that is, in a state in which its surface is upright with respect to the horizontal plane. The elastic displacement is not limited to this, and the elastic displacement may be performed by incorporating an elastic member such as a spring in addition to the configuration shown in the above embodiment.

[0040]

As described above, according to the apparatus and method of the present invention, the can lid row is placed on the tray which holds the aligned state on the front and rear sides thereof and is inserted into the bag as it is. Even if there is a large resistance to the can lid row, there is no risk of the can lid row being in an unaligned state, and therefore the can lid row can be inserted at a high speed. it can.

Further, the tray of the present invention is provided with projections for maintaining the aligned state of the can lid row on both front and rear sides, is inserted into the bag with the can lid row being placed, and the projection at the front end portion thereof can be elastically displaced. Therefore, the can lid row can be pulled out while the bag is left in the bag together with the insertion with the constraint described above. Therefore, according to this tray, the can lid row can be inserted into the bag at a high speed, and the work efficiency can be improved. Can be improved.

Furthermore, since the open end portion of the bag is flatly crushed and closed immediately after packing the can lid row, the can lid in the bag does not fall down, and therefore, there is no need to incline after packing.
It can be transferred to the next process of gluing or edge folding as it is horizontal.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of an embodiment of the present invention.

2A and 2B are views showing the tray, in which FIG. 2A is a plan view with a part omitted, FIG. 2B is a view taken along the line BB, and FIG.
It is a C line arrow line view.

FIG. 3 is a schematic perspective view showing a push rod.

4A and 4B are views showing a bag holding device, FIG. 4A is a schematic view showing a state before opening a bag, and FIG. 4B is a schematic view showing a state in which a bag is held open.

FIG. 5 is a diagram showing arrangement positions of suction pads and stoppers.

[Explanation of symbols]

 1 Can lid row 2 Tray 3 Bag 4 Bag holding device 7 Receiving surface 8, 9 Projection 13 Push rod 20 Opening guide

Claims (3)

[Claims] 1. A can lid for inserting a can lid row in which a large number of can lids are placed upright on a horizontal surface so as to be in close contact with and aligned with each other, and the can lid row is inserted into a bag opened on the same axis as the can lid row. In the bag filling device, a tray for holding and placing a predetermined number of can lids in an upright and closely contacted state in an aligned state can be moved forward and backward with respect to the inside of the bag at the front position on the open end side of the bag. A push rod that is arranged and holds the can lid row on the tray in the bag when the tray is retracted from the bag is arranged so as to be able to move forward and backward with respect to the bag, and the open end of the bag is A can lid bagging device, which is provided with a flat folding device for flatly crushing. 2. A can lid row in which a large number of can lid rows are placed upright on a horizontal surface so as to be in close contact with and aligned with each other, and the can lid row is inserted into a bag opened and held on the same axis as the can lid row. In the bag packing method, the can lid row is placed on a tray and the tray is advanced into the bag to insert the can lid row into the bag together with the tray, and then push the push rod to the can lid row in the bag. With the tray in contact with the rear end, retract the tray from the bag and pull it out.
Then, the push rod is retracted from the inside of the bag, and the open end of the bag is flatly crushed so as to immediately close the rear end of the can lid row. 3. A bag packing tray of a can lid for mounting a can lid held in an upright, closely contacted and aligned state, wherein a receiving surface on which the can lid is placed is substantially the same as a part of the contour of the can lid. While being formed in a cross-sectional shape, projections for holding the can lid in an upright state at the front end portion and the rear end portion of the receiving surface thereof are provided at intervals substantially equal to the length of a predetermined number of can lids, A bag tray for a can lid, characterized in that the projection at the front end is elastically displaced.