CN111503371A

CN111503371A - Socket-type anti-slipping mounting construction method for nodular cast iron pipe pulled by pulley combination

Info

Publication number: CN111503371A
Application number: CN202010350369.0A
Authority: CN
Inventors: 韦永坚; 林毅飞; 韦锦培
Original assignee: Guangdong Construction Engineering Co ltd
Current assignee: Guangdong Construction Engineering Co ltd
Priority date: 2020-04-28
Filing date: 2020-04-28
Publication date: 2020-08-07
Anticipated expiration: 2040-04-28
Also published as: CN111503371B

Abstract

The invention relates to a socket joint type anti-slipping installation construction method for a nodular cast iron pipe by pulley combination traction, which comprises the steps of cleaning a bell mouth, installing a pulley block, and adjusting a lifting device of a supporting device, wherein a roller shaft of the supporting device is lifted to support the pipe to be installed, one end, close to the installed pipe, of the pipe to be installed is upwards tilted and aligned with the bell mouth of the installed pipe, then a movable end of a steel wire rope is upwards pulled by mechanical equipment such as a crane and the like, the stress direction of the steel wire rope is changed by a fixed pulley, and the required tension for pulling the steel wire rope is smaller by a movable pulley. The steel wire rope pulls the pipe to be installed to move towards the direction of the installed pipe, and socket fit of the pipe to be installed and the installed pipe is achieved. The friction between the pipe to be installed and the groove is reduced, the effect of quickly installing a large socket pipe is achieved, and the construction period is shortened.

Description

Socket-type anti-slipping mounting construction method for nodular cast iron pipe pulled by pulley combination

Technical Field

The invention relates to the technical field of municipal engineering, in particular to a socket-type anti-slipping mounting construction method for a nodular cast iron pipe pulled by a pulley combination.

Background

At present, the T-shaped nodular cast iron pipe is widely applied to water supply and gas pipelines in cities and towns, adopts a sliding flexible interface, and has the characteristics of simple structure, convenient installation, good sealing property and the like.

The existing connecting T-shaped ductile cast iron pipe is generally installed by adopting a chain block method, namely, after a hook head, a steel rope and a chain block (or an electric hoist) are installed at a joint of a pipeline to be installed, the pipeline to be installed is moved towards the direction of the installed pipeline by manual traction and is in socket fit with the installed pipeline.

The above prior art solutions have the following drawbacks: in actual operation, along with the increase of the caliber of the pipeline, the gravity of the pipeline caused by the increase of the size of the pipeline is increased, so that the friction force between the pipeline to be installed and the groove is increased, the traction force required by installing the pipeline to be installed is increased, the manual traction becomes more time-consuming and labor-consuming, and the improvement space exists.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a socket type anti-slipping mounting construction method for a nodular cast iron pipe drawn by a pulley combination, which has the effects of quickly mounting and connecting socket pipelines and shortens the construction period.

The above object of the present invention is achieved by the following technical solutions:

a socket type anti-slipping mounting construction method for a nodular cast iron pipe pulled by a pulley combination comprises the following steps:

the method comprises the following steps: digging a groove, digging a mounting groove at the bottom of the groove at one side of the pipeline to be mounted, and forming a picking and placing groove at one side of the mounting groove;

step two: hoisting the supporting device into the mounting groove, hoisting the pipe to be mounted into the groove at one end of the mounted pipe, and locating the pipe above the supporting device;

step three: carrying out preparation work such as bell cleaning, rubber ring installation, bell and spigot lubrication and the like;

step four: installing a pulley block, respectively binding two hanging belts between a pipe to be installed and an installed pipe, installing a movable pulley on the hanging belt of the pipe to be installed, installing a fixed pulley on the hanging belt of the installed pipe, wherein the movable pulley and the fixed pulley are both positioned above the axis of the pipeline, then penetrating a steel wire rope, one end of the steel wire rope is fixed with a wheel seat of the fixed pulley, and the other end of the steel wire rope is sequentially wound around the movable pulley and the fixed pulley and then is pulled upwards;

step five: adjusting the supporting device to enable one end of the pipe to be installed, which is close to the installed pipe, to be tilted upwards and face the bell mouth of the installed pipe;

step six: drawing a socket line at one end of the pipe to be installed, which is close to the installed pipe, wherein the distance between the socket line and the socket end is the same as the socket and socket insertion depth;

step seven: pulling a steel wire rope upwards by a crane to pull the steel wire rope to a pipe to be installed and an installed pipe to be inserted into a socket line to be aligned with a bell mouth of the installed pipe;

step eight: adjusting the supporting device to a state of being accommodated in the mounting groove, taking out the adjusting device from the taking and placing groove, and backfilling the mounting groove and the taking and placing groove;

step nine: repeating the steps one to eight until all the pipes to be installed are installed;

the supporting device comprises a base, a plurality of roller shafts with axes at the same horizontal plane are rotatably connected to the upper portion of the base, a lifting device for adjusting the heights of the roller shafts is arranged between the roller shafts and the base, and the rotating axes of the roller shafts are perpendicular to the length direction of the grooves.

Through adopting above-mentioned technical scheme, the tank bottom excavation of slot has the english to place strutting arrangement's mounting groove, still offers the groove of getting that is used for taking out strutting arrangement in one side of mounting groove. Hang strutting arrangement and waiting to install the pipe and put into mounting groove and slot in proper order, strutting arrangement accomodates in the mounting groove this moment, waits to install between pipe and the strutting arrangement contactless. After the cleaning of the bell mouth and the installation of the pulley block are finished, when the lifting device of the supporting device is adjusted, the roller shaft of the supporting device is lifted to support the pipe to be installed, one end, close to the installed pipe, of the pipe to be installed is tilted upwards and aligned with the bell mouth of the installed pipe, then the movable end of the steel wire rope is pulled upwards through mechanical equipment such as a crane and the like, the stress direction of the steel wire rope is changed through the fixed pulley, and the required tension for pulling the steel wire rope is smaller through the movable pulley. The steel wire rope pulls the pipe to be installed to move towards the direction of the installed pipe, and socket fit of the pipe to be installed and the installed pipe is achieved. Wherein the socket line is drawn near the one end of having installed the pipe to the pipe of waiting to install now before the socket joint cooperation to whether the setting through the socket line is convenient for observe the pipe of waiting to install target in place with the pipe socket joint of having installed. After the installation of the to-be-installed pipe is completed, the roller shaft of the supporting device is lowered to be accommodated in the installation groove, the to-be-installed pipe is abutted to the bottom of the groove, then the supporting device is moved to the taking and placing groove from the installation groove to be taken out, the installation groove is backfilled, the taking and placing groove is formed, the groove is backfilled, and the connection of the to-be-installed pipe is completed. Because the friction between the pipe to be installed and the groove is reduced, the effect of quickly installing a large socket pipe is achieved, and the construction period is shortened.

The present invention in a preferred example may be further configured to: elevating gear includes tip respectively with roller articulated first branch and second branch, first branch and second branch are isometric, the other end of first branch and second branch articulates respectively has first slider and second slider, the base is provided with control first slider and second slider are close to or the controlling means who keeps away from each other.

Through adopting above-mentioned technical scheme, the both ends of roller articulate respectively has a first branch and second branch, and first branch and second branch articulate respectively has first slider and second slider to the ascending jack-up of roller when first slider and second slider are close to each other, the roller contracts downwards when first slider and second slider keep away from each other, thereby realizes the lift control to the roller, is convenient for adjust the state of treating the installation pipe.

The present invention in a preferred example may be further configured to: the control device comprises a horizontally arranged screw rod, wherein a forward thread and a reverse thread are arranged on the screw rod, the screw directions of the forward thread and the reverse thread are opposite, the first sliding block and the second sliding block are both provided with threaded holes and are in threaded connection with the screw rod, the first sliding block is in threaded connection with the forward thread on the screw rod, and the second sliding block is in threaded connection with the reverse thread on the screw rod.

Through adopting above-mentioned technical scheme, the screw rod that the level set up rotates with the base to be connected, is provided with the opposite forward screw thread of spiral direction and reverse screw thread on the screw rod, respectively with first slider and second slider threaded connection to when the screw rod rotates, can realize being close to each other or keeping away from of first slider and second slider, and then realize the regulation to roller height.

The present invention in a preferred example may be further configured to: the screw rod is provided with a plurality of groups of forward threads and reverse threads indirectly, and the first sliding block and the second sliding block of each lifting device are in threaded connection with the forward threads and the reverse threads of each group respectively.

Through adopting above-mentioned technical scheme, the multiunit forward screw thread that sets up on the screw rod and reverse screw thread respectively with each elevating gear's first slider and second slider threaded connection to realize that the multiunit roller reciprocates simultaneously, be favorable to the increase and treat the area of contact between the restoration pipe, treat the restoration pipe and support, thereby reduce the area of contact between restoration pipe and the slot, reduce the frictional force between restoration pipe and the slot.

The present invention in a preferred example may be further configured to: and lifting devices and control devices are arranged at two ends of the roll shaft.

Through adopting above-mentioned technical scheme, all be provided with elevating gear and controlling means at the roller both ends and be convenient for support the roller to and the inclination between micro-adjustment roller and the ground is favorable to adjusting the state of waiting to restore the pipe. And two sets of controlling means simultaneous control drive elevating gear jacking roller, also be favorable to the motion of roller more stable.

The present invention in a preferred example may be further configured to: the end part of the screw rod coaxially rotates to form a first bevel gear, the base is rotatably connected with a second bevel gear meshed with the first bevel gear, and one end, far away from the first bevel gear, of the second bevel gear coaxially rotates to form an inserting sleeve.

Through adopting above-mentioned technical scheme, the axis direction through first bevel gear and second bevel gear meshing changes input power, wherein the vertical setting of axis of second bevel gear and grafting cover, and the grafting cover is used for supplying the user to adopt outside instrument to peg graft and drive second bevel gear and rotate, and then realizes that driving screw rotates, realizes the up-and-down motion of roller, and convenient to use person is located the top rotation screw rod of slot, the lift of control roller.

The present invention in a preferred example may be further configured to: the control rod is fixedly provided with a rotating handle at the end part, one end of the control rod, which is far away from the rotating handle, is used for being in plug-in fit with the plug-in sleeve, a hexagonal hole is formed in the top end of the plug-in sleeve, and a hexagonal head in shape fit with the hexagonal hole is convexly arranged at one end of the control rod, which is far away from the rotating handle.

Through adopting above-mentioned technical scheme, the both ends of control lever are installed respectively and are changeed handle and hexagonal head, and the hexagonal hole of grafting complex with hexagonal head is seted up on the top of plug bush to it realizes that the user is located the effect that the screw rod was rotated to the slot top to peg graft the cooperation through control lever and plug bush.

The present invention in a preferred example may be further configured to: the upper end face of the base is in the both sides of roller all are provided with the cushion cap, the stroke of roller up-and-down motion satisfies the messenger the top of roller is less than the up end of cushion cap.

Through adopting above-mentioned technical scheme, the setting of cushion cap is used for temporarily supporting waiting to restore the pipe, and when the earth of slot tank bottom was too soft, can support waiting to restore the pipe through the cushion cap, wherein the top of roller can be accomodate to the position that is less than the cushion cap up end to can be with roller jack-up when waiting to restore the pipe in the needs removal, can place waiting to restore the pipe on the cushion cap when the adjustment.

In conclusion, the invention has the following beneficial effects:

1. the construction method adopts a pulley block combination system construction technology, manual traction is replaced by mechanical longitudinal traction force, the construction efficiency is improved, labor input is reduced, quality control in the socket process is simple by matching with the arrangement of a socket line, and the construction period is shortened;

2. by arranging the supporting device, the roller shaft at the top end of the supporting device is abutted to the pipe to be repaired, so that the position state of the pipe to be repaired towards the installed pipe is convenient to change, the friction force between the pipe to be repaired and the groove is reduced, and the pipe to be repaired and the installed pipe are convenient to plug;

3. through setting up including multiunit forward screw thread and reverse screw thread on the screw rod, and first slider and second slider respectively with forward screw thread and reverse screw thread threaded connection to make first slider and second slider do the motion that is close to each other or keeps away from each other when rotating the screw rod, and then cooperate first branch and second branch, make the roller do upwards or decurrent motion.

Drawings

FIG. 1 is a schematic structural diagram of the present embodiment;

FIG. 2 is a schematic cross-sectional view of the present embodiment;

FIG. 3 is a schematic structural diagram of the supporting device in this embodiment;

FIG. 4 is a schematic view of another angle of the supporting device in this embodiment;

fig. 5 is an enlarged view of a portion a in fig. 4.

Reference numerals: 1. a trench; 11. mounting grooves; 12. a taking and placing groove; 13. a pipe to be installed; 14. an installed tube; 21. a movable pulley; 22. a fixed pulley; 23. a wire rope; 24. a socket line; 3. a support device; 31. a base; 32. a roll shaft; 33. a first support bar; 331. a first slider; 34. a second support bar; 341. a second slider; 35. a screw; 351. a positive thread; 352. reverse threads; 361. a first bevel gear; 362. a second bevel gear; 363. a plug bush; 37. a bearing platform; 4. a control lever; 41. turning a handle; 42. a hexagonal head.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

As shown in fig. 1 to 3, the invention discloses a socket-type anti-slip mounting construction method for a nodular cast iron pipe pulled by a pulley combination, which is characterized in that: the method comprises the following steps:

the method comprises the following steps: digging a groove 1, digging a mounting groove 11 at the bottom of the groove 1 at one side of a pipeline 13 to be mounted, and forming a pick-and-place groove 12 at one side of the mounting groove 11;

step two: hoisting the supporting device 3 into the mounting groove 11, hoisting the pipe 13 to be mounted into the groove 1 at one end of the mounted pipe 14, and locating above the supporting device 3;

step four: installing a pulley block, binding two hanging strips at the middle of a pipe 13 to be installed and an installed pipe 14 respectively, installing a movable pulley 21 on the hanging strip of the pipe 13 to be installed, installing a fixed pulley 22 on the hanging strip of the installed pipe 14, wherein the movable pulley 21 and the fixed pulley 22 are both positioned above the axis of the pipeline, then penetrating a steel wire rope 23, one end of the steel wire rope 23 is fixed with a wheel seat of the fixed pulley 22, and the other end of the steel wire rope is sequentially wound around the movable pulley 21 and the fixed pulley 22 and then is pulled upwards;

step five: adjusting the supporting device 3 to enable one end, close to the installed pipe 14, of the pipe 13 to be installed to tilt upwards and face the bell mouth of the installed pipe 14;

step six: drawing a socket line 24 at one end of the pipe 13 to be installed, which is close to the installed pipe 14, wherein the distance from the socket line 24 to the socket end is the same as the inserting depth of the socket and the socket;

step seven: pulling a steel wire rope 23 upwards by a crane to lead the pipe 13 to be installed and the installed pipe 14 to be inserted and connected to a socket line 24 which is aligned with the bell mouth of the installed pipe 14;

step eight: adjusting the supporting device 3 to be accommodated in the mounting groove 11, taking out the adjusting device from the taking and placing groove 12, and backfilling the mounting groove 11 and the taking and placing groove 12;

step nine: repeating the steps one to eight until all the pipes 13 to be installed are installed; and after all the pipes 13 to be installed are installed, backfilling the groove 1, wherein one pipe 13 to be installed and one groove 1 at one backfilling end can be installed.

As shown in fig. 3 to 4, the supporting device 3 includes a rectangular base 31 and a lifting device located above the base 31, a plurality of roller shafts 32 whose axes are in the same horizontal plane are rotatably connected above the lifting device, and the rotation axes of the roller shafts 32 are perpendicular to the length direction of the groove 1. The upper end face of the base 31 is fixed with bearing platforms 37 in a protruding manner on both sides of the roller shaft 32, and the stroke of the up-and-down movement of the roller shaft 32 is enough to enable the top end of the roller shaft 32 to be lower than the upper end face of the bearing platform 37, so that the roller shaft 32 is accommodated between the two groups of bearing platforms 37.

As shown in fig. 3 to 4, the lifting device includes a first supporting rod 33 and a second supporting rod 34, the ends of which are respectively hinged with the roller shaft 32, the first supporting rod 33 and the second supporting rod 34 are equal in length, and the hinge axis of the first supporting rod 33 and the roller shaft 32, the hinge axis of the second supporting rod 34 and the roller shaft 32 and the rotation axis of the roller shaft 32 are collinear. The other ends of the first supporting rod 33 and the second supporting rod 34 are respectively hinged with a first sliding block 331 and a second sliding block 341, the first sliding block 331 and the second sliding block 341 move on the same horizontal plane, and the base 31 is provided with a control device for controlling the first sliding block 331 and the second sliding block 341 to approach or separate from each other. The control device comprises a horizontally arranged screw rod 35, the screw rod 35 is rotatably connected with the base 31, a forward thread 351 and a reverse thread 352 in opposite screw directions are arranged on the screw rod 35, threaded holes are formed in the first sliding block 331 and the second sliding block 341 and are in threaded connection with the screw rod 35, the first sliding block 331 is in threaded connection with the forward thread 351 on the screw rod 35, and the second sliding block 341 is in threaded connection with the reverse thread 352 on the screw rod 35. So that the first and

second sliders

331 and 341 move toward and away from each other when the screw 35 rotates.

As shown in fig. 4 to 5, both ends of the roll shaft 32 are provided with a lifting device and a control device, and both ends of the roll shaft 32 are lifted and lowered simultaneously. The forward screw thread 351 and the reverse screw thread 352 on the screw 35 are indirectly provided with a plurality of groups, the first slider 331 and the second slider 341 of each lifting device are respectively in threaded connection with the forward screw thread 351 and the reverse screw thread 352 of each group, and the first support rod 33 and the second support rod 34 are respectively in rotational connection with the roller shafts 32 of each group.

As shown in fig. 4 to 5, a first bevel gear 361 is coaxially rotated at an end of the screw 35, a second bevel gear 362 engaged with the first bevel gear 361 is rotatably connected to the base 31, an axis of the second bevel gear 362 is vertically arranged, and an insertion sleeve 363 is coaxially rotated at an end of the second bevel gear 362 away from the first bevel gear 361. Still include that the end fixing has the control lever 4 of changeing the handle 41, the one end that the control lever 4 kept away from changeing the handle 41 is used for with the cooperation of pegging graft cover 363, the hexagonal hole has been seted up on the grafting cover 363 top, the control lever 4 is kept away from the one end protrusion of changeing the handle 41 be provided with hexagonal hole shape complex hexagon head 42 to can be through pegging graft control lever 4 with the grafting cover 363, realize rotating second bevel gear 362 and then drive roller 32 through control lever 4 and do the up-and-down motion.

The setting of roller 32 is used for treating to install pipe 13 and supports to pivoted roller 32 realizes reducing the effect of waiting to install frictional force between pipe 13 and the slot 1, and wherein the height-adjustable of roller 32 is convenient for adjust the state of waiting to install pipe 13.

The screw 35, the first slider 331, the second slider 341, the first support rod 33 and the second support rod 34 are arranged to be connected with the roller shaft 32, and have the effect of simultaneously lifting multiple groups of roller shafts 32, so that the contact surface between the pipe 13 to be installed and the roller shaft 32 can be increased, and the support is more stable. Wherein the threaded connection has a self-locking effect, which is convenient for controlling the lifting of the roll shaft 32.

The second bevel gear 362 and the first bevel gear 361 are engaged in a manner that a user can rotate the screw 35 on the groove 1 through the control rod 4 to realize the control of the lifting of the roller shaft 32.

The embodiments of the present invention are preferred embodiments of the present invention, and the scope of the present invention is not limited by these embodiments, so: all equivalent changes made according to the structure, shape and principle of the invention are covered by the protection scope of the invention.

Claims

1. A socket-type anti-slipping installation construction method for a nodular cast iron pipe pulled by a pulley combination is characterized by comprising the following steps: the method comprises the following steps:

the method comprises the following steps: digging a groove (1), digging a mounting groove (11) at the bottom of the groove (1) at one side of a pipeline to be mounted (13), and further forming a taking and placing groove (12) at one side of the mounting groove (11);

step two: hoisting the supporting device (3) to the installation groove (11), hoisting the pipe (13) to be installed to the groove (1) at one end of the installed pipe (14), and locating above the supporting device (3);

step four: installing a pulley block, binding two hanging straps between a pipe (13) to be installed and an installed pipe (14) respectively, installing a movable pulley (21) on the hanging strap of the pipe (13) to be installed, installing a fixed pulley (22) on the hanging strap of the installed pipe (14), wherein the movable pulley (21) and the fixed pulley (22) are both positioned above the axis of the pipeline, then penetrating a steel wire rope (23), one end of the steel wire rope (23) is fixed with a wheel seat of the fixed pulley (22), and the other end of the steel wire rope is sequentially wound around the movable pulley (21) and the fixed pulley (22) and then is pulled upwards;

step five: adjusting the supporting device (3) to enable one end of the pipe (13) to be installed, which is close to the installed pipe (14), to be tilted upwards and face the bell mouth of the installed pipe (14);

step six: drawing a socket line (24) at one end of the pipe (13) to be installed, which is close to the installed pipe (14), wherein the distance between the socket line (24) and the socket end is the same as the plugging depth of the socket and the socket;

step seven: drawing a steel wire rope (23) upwards by a crane to lead the pipe (13) to be installed and the installed pipe (14) to be inserted into the socket line (24) to be aligned with the bell mouth of the installed pipe (14);

step eight: adjusting the supporting device (3) to be accommodated in the mounting groove (11), taking out the adjusting device from the taking and placing groove (12), and backfilling the mounting groove (11) and the taking and placing groove (12);

step nine: repeating the first step to the eighth step until all the pipes (13) to be installed are installed;

strutting arrangement (3) include base (31), the top of base (31) is rotated and is connected with roller (32) that a plurality of axes are in same horizontal plane, roller (32) with be provided with the regulation between base (31) the elevating gear of roller (32) axis height, the axis of rotation of roller (32) with the length direction of slot (1) is perpendicular.

2. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 1, is characterized in that: elevating gear includes tip respectively with roller (32) articulated first branch (33) and second branch (34), first branch (33) and second branch (34) are isometric, the other end of first branch (33) and second branch (34) articulates respectively has first slider (331) and second slider (341), base (31) are provided with the control first slider (331) and second slider (341) are close to or the controlling means who keeps away from each other.

3. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 2, is characterized in that: the control device comprises a horizontally arranged screw rod (35), wherein a forward thread (351) and a reverse thread (352) with opposite screw directions are arranged on the screw rod (35), the first sliding block (331) and the second sliding block (341) are respectively provided with a threaded hole and are in threaded connection with the screw rod (35), the first sliding block (331) is in threaded connection with the forward thread (351) on the screw rod (35), and the second sliding block (341) is in threaded connection with the reverse thread (352) on the screw rod (35).

4. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 3, is characterized in that: multiple groups of forward threads (351) and reverse threads (352) are indirectly arranged on the screw (35), and a first sliding block (331) and a second sliding block (341) of each lifting device are respectively in threaded connection with the forward threads (351) and the reverse threads (352) of each group.

5. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 4, is characterized in that: both ends of the roll shaft (32) are provided with a lifting device and a control device.

6. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 3, is characterized in that: the end part of the screw rod (35) coaxially rotates to form a first bevel gear (361), the base (31) is rotatably connected with a second bevel gear (362) meshed with the first bevel gear (361), and one end, far away from the first bevel gear (361), of the second bevel gear (362) coaxially rotates to form an insertion sleeve (363).

7. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 6, is characterized in that: the socket is characterized by further comprising a control rod (4) with a rotating handle (41) fixed at the end, one end, far away from the rotating handle (41), of the control rod (4) is used for being in plug-in fit with the plug-in sleeve (363), a hexagonal hole is formed in the top end of the plug-in sleeve (363), and a hexagonal head (42) matched with the hexagonal hole in shape is arranged at one end, far away from the rotating handle (41), of the control rod (4) in a protruding mode.

8. The socket type anti-slipping mounting construction method for the nodular cast iron pipe pulled by the pulley combination as claimed in claim 1, is characterized in that: the up end of base (31) is in the both sides of roller (32) all are provided with cushion cap (37), the stroke of roller (32) up-and-down motion satisfies the messenger the top of roller (32) is less than the up end of cushion cap (37).