EP0418915B1

EP0418915B1 - Cutting apparatus

Info

Publication number: EP0418915B1
Application number: EP90118185A
Authority: EP
Inventors: Katsumi C/O Shoohin Kaihatsu Center Mogi; Hiro C/O Shoohin Kaihatsu Center Ohzeki
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 1989-09-22
Filing date: 1990-09-21
Publication date: 1994-12-28
Anticipated expiration: 2010-09-21
Also published as: EP0418915A2; DE69033884T2; DE69033884D1; DE69015532D1; DE69015532T2; EP0418915A3; EP0623437B1; EP0623437A3; EP0623437A2; KR910005983A

Description

The present invention relates to a cutting apparatus for cutting large objects of different materials, such as stone, wood and other substances according to the preamble of claim 1.
Conventionally, cutting a large stone, for example, is carried out with a cutting blade, a band saw, a wire saw and other cutting methods.
A cutting blade is a device containing a plurality of cutting bits in which chips of abrasive grains, such as fine diamond abrasive grains are firmly embedded. The abrasive layers are bonded to an outer peripheral surface of a disc-like metal base formed by roll processing, by means of metal bond or the like at equal intervals. At present, the maximum cutting blade manufactured has a diameter of 3.5 m and a metal base thickness of 10 mm. For the cutting blade of this dimension or size, the maximum thickness of a material which can be cut is of the order of 1.5 m, and the cutting loss is of the order of 15 mm.
On the other hand, a band saw is a device having a thin strip of metal, which is wide and which is of the order of 1 mm to 6 mm in thickness, is welded to form an endless loop, and the abrasive grains and chips are firmly bonded to one side of the endless thin strip. The endless thin strip is driven by a pair of rotating circular wheels, whose axes are arranged in parallel relation to each other. The wheels are rotated at high speed, thereby cutting stones or the like with the edge of any parallel sections between the rotor bodies.
The wire saw is an endless loop device such that a plurality of cylindrical diamond chips is firmly bonded to a metal wire whose thickness is of the order of a few millimeters to 10 mm. The wire saw is directly wound around the object, and is driven at high speeds with a constant tension applied by a drive apparatus, thereby cutting the object.
However, the above-described traditional cutting methods have the following problems.
First, the cutting blade has the following problem. That is, if the diameter of the cutting blade is increased, the thickness of the metal base must also be increased to provide the blade rigidity. For this reason, the cutting loss increases, and the yield from the object is diminished. Further, twist or torsion occurs at the forward edge of cutting as a result of an increase in the cutting resistance. Thus, the cutting accuracy is reduced.
Further, the cutting blade has also the following problems. Since manufacturing of a metal base exceeding 3.5 meter in diameter is extremely difficult, there is a limit in thickness of the object capable of being cut, as described previously. Moreover, such large cutting blade is extremely inconvenient for handling and transporting or the like; also the noises due to vibration at cutting are severe.
On the other hand, in the band saw, the metal base is thin and long in length, and the cutting loss is of the order of 4 mm to 8 mm which is relatively small. Thus, the yield is superior. However, the band saw is wound around a pair of large-diameter rotating wheels, and accordingly, the cutting apparatus increases in size, and a large equipment space is required.
Furthermore, the band saw has the following problem. That is, bending stress is repeatedly applied to bent sections of the metal base wrapped around the rotating wheels and metal fatigue is apt to be accumulated in the metal base. Thus, the metal base is broken relatively prematurely, and the service life of the metal base is short.
In the wire saw, since the chips in the abrasive-grain-layer are large in diameter, the cutting allowance must be large in comparison with the size of the cutting blade or the band saw. Further, the wire saw is circular in cross-section, and has, by itself, no means for restricting the cutting direction. Accordingly, the wire saw is inferior to other cutting methods in flatness and surface roughness of the cut surface. Furthermore, in the wire saw, since large bending stress is applied to both end portions of each of the abrasive-grain-layers during cutting, the service life is short. Breakage of the wire is dangerous because the ends of the wire jump up and down like a whip.
A cutting apparatus for cutting a workpiece according to the preamble of claim 1 is disclosed in BE-A-518164. This known cutting apparatus comprises an endless chain body, a plurality of sprockets and a rigid backplate supporting the chain body towards a workpiece. Further, a rotating means for rotating the sprocket is provided as well as a moving means for moving the workpiece or the chain body towards each other to cut said workpiece with said chain body.
Further, US-A-614003 discloses a cutting apparatus comprising an endless chain body having a plurality of plate-like flaps connected to each other for angular movement in a common plane. A plurality of sprockets are provided supporting said chain body in tension and a means for activating the rotational movement of the sprockets in cooperation with the chain body is further provided.
An object of the invention is to provide a cutting apparatus having improved performance characteristics with respect to the above discussed problems. This object is solved by a cutting apparatus according to claim 1.
This cutting apparatus provides cutting action by rotating the chain body equipped with cutting devices around at least a pair of sprockets to drive the chain body which is supported at the linear section of the chain body by means of a chain guide disposed on a rigid backplate. The cutting is carried out by moving either the chain cutter and sprockets towards the object or the object to the chain body.
Because the thickness of the flap and the backplate is thinner than that of the cutting devices, the depth of cut is not limited by the thickness of the cutting device of the equipment.
According to the chain cutter, since the flaps, each in the shape of a plain plate, are connected to each other for angular movement in the cutting plane to form the endless chain body, it is possible to obtain sufficient tension-resisting force by using the flaps of relatively thin thickness. The thickness of each of the cutting devices can be reduced, thus, the cutting cost of the object can be reduced leading to improved yield.
Further, since the flaps are flexibly connected to each other, stress fatigue does not occur in the curved region of the chain cutter, and it is possible to use the chain cutter with a higher applied tension force than in conventional cutting devices. Accordingly, the cutting service life is longer than in the conventional cutting tools, and it is possible to enhance cutting efficiency.
Furthermore, since the chain cutter is supported at the inner straight section of the chain by a support section of the rigid backplate, it is possible to support a high load required for large cutting bite.
Moreover, by merely changing the number of connected flaps, the length of the chain body can be freely increased or decreased. Thus, the object capable of being cut is not restricted in size or dimension. The individual flaps are small in size and the same in configuration as each other. Accordingly, the flaps can be mass produced thereby reducing the cost of the entire chain cutter.
Further, since the advancing direction of the cutting is restricted by the plate-shaped flaps, the flatness and surface roughness of the cut surface are superior, and no one-sided wear occurs on the cutting devices. Thus, the service efficiency of the cutting devices is high.
Furthermore, since the flaps are moving in the same plane as the cutting plane while being wound around the sprockets or the like, there is an advantage that the working space for the apparatus can be reduced.
Moreover, since the chain cutter is in the shape of a chain, and is relatively light in weight, handling and transportation or the like are easy. Vibration due to cutting is attenuated at the connecting sections between the flaps. Thus, it is possible to reduce the noises as compared with other cutting tools.
Figs. 1 is a front view of the cutting apparatus.
Fig. 2 is a plan view of the cutting apparatus with a partial horizontal cut-away.
Figs. 3 and 4 are a sectional front view and a cross-sectional view taken along the line D-D, respectively, from a first preferred embodiment of the invention.
Figs. 5 and 6 are a front view and a left side view, respectively, of the flap from the first preferred embodiment.
Fig. 7 is a left side view of a modified flap from the first preferred embodiment.
Figs. 8 and 9 are a front view and a left side, respectively, of the flap from a second preferred embodiment.
Fig. 10 is a left side view of a modified flap illustrated in Figs. 8 and 9.
Figs. 11 and 12 are a front view and a left side view, respectively, of the flap from a third preferred embodiment.
Fig. 13 is a left side view of a modified flap illustrated in Figs. 11 and 12;
Fig. 14 is a front view showing a mounting and demounting method of a flap from an fourth preferred embodiment.
Figs. 15 and 16 are a front view and a left side view, respectively, of the flap from a fifth preferred embodiment.
Fig. 17 is a left side view of a modified flap illustrated in Figs. 15 and 16;
Fig. 18 is a front view showing a mounting and demounting method of the flaps according to the fifth preferred embodiment.
Figs. 19 and 20 are a front view and a left side view, respectively, of the flap from a sixth preferred embodiment.
Fig. 21 is a front view of the flap from a seventh preferred embodiment.
Fig. 22 is a cross-sectional view taken along the line E-E showing a mounting and demounting method for the flaps illustrated in Fig. 21.
Fig. 23 is a cross-sectional view of a cutting apparatus from a eighth preferred embodiment.
Fig. 24 is a plan view of a cutting apparatus from a ninth preferred embodiment.
Fig. 25 is a cross-sectional view of the sprocket and the chain cutter from a tenth preferred embodiment.
Fig. 26 is a cross-sectional view to illustrate the construction of the backplate from an eleventh preferred embodiment.
Fig. 27 is an angle view of a modified backplate shown in Fig. 26.
Various embodiments of the invention will be described next with reference to the drawings.
Figure 1 is a front view and Figure 2 is a plan view with a partial cut-away of the column section of a cutting apparatus for according to a first embodiment of the invention.
In these figures, C represents a chain of cutters (hereinafter referred to as the chain cutter) and is a primary component of the cutting apparatus. The details of this component will be explained in the following.
The chain cutter C is comprising an endless chain body 2 in which a plurality of flaps 1, each in the shape of a plain or flat plate, is connected to each other, as shown in Fig. 3, to provide a flexible angular movement within a cutting plane (hereinafter the cutting plane is defined by the path of the chain cutter). A plurality of abrasive-grain segments or cutting device 4 is firmly mounted to the outer ends of the respective flaps 1.
Each flap 1 is in the shape of a rectangular plate having a constant thickness, and is made of metal such as SK steel, stainless steel, SKD steel, SUP steel, SNCM steel or the like. It is desirable that the hardness of the flap 1 is brought to HRc 30 to 65 by hardening treatment or the like. If the hardness of the flap 1 is less than HRc 30, it is impossible to obtain a sufficient strength, while, if the hardness is higher than HRc 65, forming of the flap 1 becomes difficult.
The dimension or size of the flap 1 varies depending upon the use of the chain cutter. In a case where the flap is utilized in cutting of normal large stone, for example, it is preferable that the flap 1 has its thickness of the order of 2 mm to 6 mm, its height H of the order of 50 mm to 150 mm, and its width W of the order of 40 mm to 100 mm. If the dimension of the flap 1 is within these ranges, it is possible to cut a large stone with high efficiency using sufficient tensioning force. In this connection, the invention is not limiting to these dimensions quoted.
Next, Figs. 3 and 4 show the first embodiment which is characterized in that the connecting tab 8 and the connecting cut-out 10 between each pair of adjacent flaps 1 are formed respectively into a semi-circular configuration.
The connecting tab 8 has its peripheral surfaces 8A and 8B at both side edges thereof which are identical in arc with each other. As shown in Fig. 5, the central angle alpha between the peripheral surfaces 8A and 8B is set equal to or larger than 120^o. If the central angle alpha is less than 120^o, the connecting strength between the flaps 1 is reduced.
The connecting recess 10 has a pair of peripheral surfaces 10A and 10B which corresponds respectively to the aforesaid peripheral surfaces 8A and 8B. The central angle beta between a pair of opening ends 10C of the connecting cut-out 10 is formed larger than the central angle beta between the pair of constricted sections 8C of the connecting tab 8.
In connection with the above, under the condition that the flaps 1 are connected to each other, a slight gap is left between the connecting cut-out 10 and the connecting tab 8. However, insertion of the thickness gage into the gap enables the quantity of wear of each of the connecting cut-out 10 and the connecting tab 8 to be judged.
Furthermore, the mounting recess 18 is provided with a narrow slit 22, one end of whose opening is directed toward the outer periphery. This end of the slit 22 has one end which opens to a portion of the mounting recess 18 near to the forward edge of the flap 1. The slit 22 has at its terminal end a circular bore 24 for stress relieving. A portion to the forward edge of the slit 22 is an elastic engaging part 26, a deflection of which in the forward direction enables mounting and demounting of the cutting device 4.
The cutting device 4 is composed of a metal chip support 28 having its thickness the same as that of the flap 1, and a rectangular cutting bits 30 firmly mounted to the outer end face of the chip support 28.
The cutting bits 30 has its thickness which is set to be 0.5 mm to 4 mm thicker than the chip support 28. If the excess thickness of the cutting bits 30 is less than 0.5 mm, a possibility exists that the chip support 28 and the flap 1 are in frictional contact with a cut surface of an object. On the other hand, if the excess thickness of the cutting bits 30 is larger than 4 mm, the cutting loss is high and the yield is reduced unnecessarily.
The cutting bit 30 has a metal-bonded abrasive layer containing particles of diamond, CBN or the like, and is firmly mounted to the chip support 28 by means such as soldering, unit sintering, laser welding, electron beam welding or the like. In this connection, the grain or particle size, the degree of concentration and the thickness of the abrasive grains should be determined according to the use of the chain cutter.
The chip support 28 is integrally formed with a projection 28A complementary in configuration with the mounting recess 18. The projection 28A has a convex V-shaped cross-sectional configuration. The projection 28A is formed so that the projection 28A can be fitted in the segment-mounting recess 18 when the slit 22 is opened, and the projection 28A is firmly engaged in the segment-mounting recess 18 when the elastic engaging part 26 returns to its original position.
A torsion- or twist-preventing structure for the flap 1 will next be described. Both the forward and the rear end surfaces of the flap 1, as shown in Fig. 3, are made parallel to each other. On the forward end face of the flap 1 is formed a V-shaped cross-sectional engaging groove 38 extending perpendicularly to the vertical forward end face of the flap 1.
Corresponding to the above tab an engaging projection 40 having its cross-sectional configuration complementary to the aforesaid engaging groove 38 is formed on the opposite side to the foregoing projection 38 of the flap 1. When the flaps are lined up tightly in a straight line next to each other, the engaging groove 38 and the engaging projection 40 of the adjacent flaps 1 are locked together with each other without gap so as to be immovable in the thickness direction of the flap 1.
A structure for driving the chain cutter will next be described. Each flap 1 has, on the forward and rear corners, a pair of driving recesses 6A and 6B.
These driving recesses 6A and 6B are curved in configuration and are disposed respectively at forward and rear corners of the inner peripheral end of each flap 1. Each of the driving recesses 6A and 6B has its central angle which is of the order of 90^o.
Each of the driving recesses 6A and 6B (Fig. 3) has its radius of curvature which is identical with a radius of each of pins 126 firmly mounted respectively to outer peripheries of respective sprockets 88 and 112 of a cutting apparatus subsequently to be described. Further, portions extending respectively from the recesses 6A and 6B to the inner end faces of the flap 1 are rounded.
A distance between centers of the respective driving recesses 6A and 6B is equal to a distance between the pins 126. Under the condition that the flaps 1 are wound around the outer peripheries of the respective sprockets 88 and 112, the driving recesses 6A and 6B of the adjacent respective flaps 1 produce an identical curved surface, and the pins 126 are so arranged as to fit in the curved surface without gap.
An engaging structure with respect to a back plate 118 subsequently to be described will next be described. The inner end face of each flap 1 is formed with a sliding groove 42 having in a V-shaped cross-section, which extends along the entire length of the end face of the flap 1. It is desirable that the angle of the V shaped sliding groove 42 is in a range of 60^o to 160^o. If the V-angle is smaller than 60^o, there is a fear that cracks occur in the flap 1 due to a wedging action of the back plate 118, while, if the V-angle is larger than 160^o, the twist-preventing force due to the back plate 118 in the thickness direction is reduced.
Figs. 1 and 2 will next be utilized to describe the cutting apparatus which uses the above-described chain cutter. In this connection, the descriptions such as the upper, lower, left- and right-hand side used in the following description are in reference to the orientation of the cutting apparatus as shown in Fig. 1.
The reference numeral 50 in the figures denote a pair of columns spaced apart suitably to provide the main support to the cutting apparatus. As shown in Fig. 2, mounted respectively to these columns 50 are a pair of rectangular bases 54A (left-hand side) and 54B (right-hand side) which permit vertical motions along the column 50, but the keys 52 extending through vertically along the column prevent the rotation of the bases about the column.
A top plate 56 is firmly mounted across the upper ends of the respective columns 50 horizontally. An elevating motor 58 is mounted to the left-hand end of the top plate 56. The motor 58 is so designed as to rotate a screw shaft 60 (Fig.2) arranged along the rear face of the left-hand column 50, through a gearbox (not shown). An elevating element 62 firmly mounted to the rear face of the left-hand base 54A is mounted to the screw shaft 60.
On the other hand, a gearbox 64 (Fig. 1) is firmly mounted to the right-hand end of the top plate 56. A rotor shaft 66 is laid across or extends between the gearbox 64 and the aforesaid gearbox, so that power of the motor 58 is transmitted also to the gearbox 64. The gearbox 64 has its output shaft which is connected to a screw shaft 68 arranged along the rear face of the right-hand column 50. An elevating element 70, which is firmly mounted to the rear face of the right-hand base 54B, is mounted to the screw shaft 68. When the elevating motor 58 is operated, both the bases 54A and 54B are moved vertically while always maintaining the same relative height.
On the front of the left-hand base 54A, is a disc section 74 and a round-shaped groove 72 whose centers are at the center of the front-face. A tilting plate 76 is arranged along the front face of the disc section 74, and a pair of pawl sections 76A formed respectively at both sides of the tilting plate 76 are fitted respectively in both sides of the round-shaped groove 72. The pawl sections 76A are rotated within the round-shaped groove 72, causing the tilting plate 76 to rotate coaxially with the disc section 74.
The tilting plate 76 has on its front face a rectangular guide rail 78 extending in the right- and left- hand direction. The arrangement is as follows. That is, mounted to the guide rail 78 is an L-shaped support plate 80 having its right-hand end bent forwardly so that the L-shaped support plate 80 is movable in the left- and right-hand directions. The support plate 80 is pulled with a constant force to the left by a biasing mechanism (not shown).
Further, the front face of the tilting plate 76 has a center which is formed with a shaft section 82 projecting forwardly. The shaft 82 projects forwardly through an elongated bore 84 which is formed in the support plate 80 and which extends in the left- and right-hand directions. Mounted to the shaft 82 for rotation is a pulley 86 and a sprocket 88 which are connected to each other in a coaxial manner.
A drive motor 92 is mounted to the left-hand front side face of the base 54A through an attaching plate 90 adjustable in height. A pulley 94 is firmly mounted to a rotary shaft of the drive motor 92. A belt 96 passes around and extends between the pulley 94 and the aforesaid pulley 86. The tension force of the belt 96 is adjustable by vertically moving the attaching plate 90.
On the other hand, on the front-face of the right-hand base 54B are a pair of curved grooves 98 extending vertically and an circular segmental plate 100 having a uniform width. The pair of curved grooves 98 and the circular segmental plate 100 share the same center of arc as the center of the left-hand sprocket 88.
A support plate 102 is arranged at the front face of the segment section 100. The segment section 100 has its both sides which are formed with a pair of pawl sections 104 inserted respectively in the curved grooves 98. By doing so, the support plate 102 is capable of being inclined through an angle equal to or larger than 5^o about the center of the left-hand sprocket 88 along the section 100. If the tilting angle is less than 5^o, cutting into the object W will become difficult to start.
The support plate 102 has on its front face a slide-rail 106 extending in the left- and right-hand direction or the lateral direction. A pulley mounting plate 108 is attached to the slide-rail 106 for movement in the left-and right-hand direction. At the front center of the pulley mounting plate 108 is a shaft 110 which extends forwardly and coaxially. A driving sprocket 112 is rotatably mounted to the shaft 110 through a bearing. A hydraulic cylinder 114 is firmly mounted to the right-hand end-face of the support plate 102 and is directed toward the left. The hydraulic cylinder 114 has its rod which is connected to the pulley mounting plate 108.
In connection with the above, an operating panel 116 is firmly mounted to the right-hand end face of the right-hand base 54B, and each section is controlled by the operational panel 116.
The left-hand end of the support plate 102 is bent in the forward direction in the shape of a letter L. A rectangular back plate 118 extends between the support plate 102 and the right-hand support plate 80 in a plane common to the sprockets 88 and 112. The back plate 118 is made of a material such as SUP steel, SNCM steel, SKD steel, SK steel, stainless steel or the like. The back plate 118 has its thickness which is the same as the flap 1. Further, the vertical distance of the back plate 118 is made equal to the winding diameter of the chain cutter C which is driven by the sprockets 88 and 112. Furthermore, the upper and lower edges of the back plate 118, along its entire length, are formed respectively into a convex V-shaped cross-section complementary with the sliding groove 42 formed on the inner peripheral end of the chain cutter C.
The chain cutter C extends between and is wound about the sprockets 88 and 112. In the linear section of the chain, the upper and lower edges of the back plate 118 are fitted, respectively, in the sliding grooves 42 and into the flaps 1 for sliding movement.
As shown in Fig. 4, the sprockets 88 and 112 are made with a pair of discs 120 and 122 bonded together to form a slit 124. The slit 124 has its opening width which is slightly larger than the thickness of the flap 1. The plurality of cylindrical pins 126 is firmly mounted to the interior of the slit 124 at equal intervals in the peripheral direction. An occluded angle between the pair of adjacent pins 126 defines a sprocket angle S.
Turning to the bases of the apparatus, on the floor surface is formed a shallow gutter 128 at a location between the columns 50, extending in the front and rear directions. A pair of guide rails 130 is mounted at the center of the gutter 128 in parallel relation to each other. A work platform 134 (hereinafter referred to as table 134) having its lower surface provided with two pairs of wheels 132 rests on the pair of guide rails 130. Further, a traction wire 136 connected to a drive machine (not shown) is connected to the longitudinal ends of the table 134, so that the table 134 is movable along the guide rails 130.
Now, the above-described various devices or instruments are used to cause the chain cutter C to perform cutting in the following manner. First, the elevating motor 58 is operated to move the bases 54A and 54B upwardly, and the object W such as stone or the like resting on the table 134 is positioned longitudinally, i.e. along the chain cutter C.
Subsequently, the support plate 102 is moved downward along the curved plate section 100, to tilt the entirety including the chain cutter C and the back plate 118. The support plate 102 is fixed at this lowered position. Further, the left-hand support plate 80 is adjusted to apply an adequate tension to the back plate 118. The hydraulic cylinder 114 is operated to pull the attaching plate 108 toward the right. In this manner, the tension force of the chain cutter C is set to an adequate value.
Under this condition, the drive motor 92 is operated. The elevating motor 58 is operated while rotating the chain cutter C in the direction shown by the arrows in Fig. 1, to lower the entire chain cutter C at a predetermined cutting speed. Thus, the chain cutter C is cut into the object W from the lowered right-hand corner. If a certain degree of cutting depth is reached in due course, the support plate 102 is raised along the curved plate 100, and the chain cutter C is returned to its horizontal position and is locked in place. Cutting proceeds further until the operation has been completed on the object W.
According to the chain cutter C constructed as above, there are produced the following advantages:

1. Since the thickness of the flap 1 and the backplate 118 is less than that of the cutting device 4, the depth of cut is not restricted by the presence of the sprockets 88 and 112, and the chain cutter is able to cut deeply into the object W. Also, the cutting apparatus does not limit the width of the object, i.e. the size in the direction perpendicular to the cutting plane.
2. Since the plurality of metallic flaps 1, each in the shape of a plane plate, is connected flexibly to form the chain body 2, a sufficient cutting force can be obtained by the chain cutter by using relatively thin cutting device 4, compared with the conventional cutting methods such as larger-diameter metal saw or wire saw. It is also possible to reduce the thickness of the cutting bits 30 as compared with the conventional large-diameter cutting blade, wire saw or the like. Thus, the cutting loss can be reduced, and therefore, the product yield from the object W is improved.
3. Since the flaps 1 are connected to each other for angular movement, stress fatigue is difficult to occur, even in the regions around curved sections such as the sprockets 88 and 112, after prolonged used of the cutter. Therefore, it is possible to use the chain cutter C with a high cutting force, thus permitting higher settings of tension and bite than allowable in conventional cutting methods, leading to improved cutting efficiency.
4. Since a rigid back plate 118 is provided on the inner peripheral end of the chain cutter C, the cutting load is supported mainly by the backplate 118, thus permitting straight-line cutting at high applied load.
5. Since the individual flaps 1 can be added or taken off to change the total length of the chain, the chain length can be easily adjusted to custom requirements.
6. The flaps can be mass produced to lower the overall cost of the equipment as well as the cost of cutting operation.
7. Since the linked chain assembly does not permit deflection in the transverse direction (to the cutting plane), there is little vibration of the individual flaps during cutting, and since the bit 30 cuts into the object while being supported by the flap 1 to keep its straightness, cutting action of the chain is stable and accurate, and the resulting cut surface is smooth and has high plainness. At the same time, since the cutting bit 30 is worn off uniformly along its entire length, the abrasive grains are used efficiently, leading to lower cutting cost.
8. Since the chain cutter C operates in the same plane as the plane of rotation of the sprockets 88 and 112, the equipment space needed is less than that of the conventional cutting means, such as a band saw.
9. Vibration occurring during cutting is attenuated at the connecting sections between the flaps 1, so that noises are lower compared with conventional cutting methods.
10. Since the flap connections wear, the chain gradually lengthens with use to make the chain unusable, there is no danger of sudden breakage of the chain. Therefore, this chain offers a high degree of operational safety in comparison to a wire saw.
11. The cutting device 4 are detachable from the flaps 1 so that the worn cutting bits 30 can be replaced readily while the chain is in the curved region of the cutter without demounting the whole chain from the sprockets 88 and 112, thus permitting improved efficiency of the operation.
12. Since the connecting sections between the respective flaps 1 are made flush with each other, shavings and other machining debris are not easily accumulated on the connecting sections, to cause wear and binding of the mechanisms. Thus, the chain construction is made simple as compared with other connecting structures and the manufacturing cost is low.
13. Since the driving recesses 6A and 6B in the flap 1 are present, it is difficult for idle running by the sprockets 88 and 112 to occur during the operation so that cutting which presents high cutting resistance can be done without problem. Furthermore, since the driving recesses 6A and 6B are present respectively at both ends of the flap 1 on the inner end, the opening width between the adjacent recesses 6A and 6B is enlarged in the straight line section than in the curved region of the chain cutter C. Therefore pins 126 of the respective rotating sprockets 88 and 112 can enter into and disengage from the recesses 6A and 6B smoothly. Thus, there is no case where the pins 126 interfere with the opening edges of the respective recesses 6A and 6B.
14. Since the engaging groove 38 and the engaging projection 40, which are machined on the opposite sides of the flap 1, mesh with each other in the straight line section of the chain cutter, and since the flaps 1 are firmly mounted on a rigid single plate, distortion of the chain C perpendicular to the cutting plane does not occur, and the cutting accuracy is raised. Furthermore, since the slit 22 of each flap 1 is firmly closed in the straight line section, there is no danger that the cutting device 4 will fall off during cutting.

In connection with the above-described embodiment, the recesses 6A and 6B were formed, respectively, at both sides of the inner face of the flap 1 as an engaging/driving components. They can be substituted with a semi-circular recess in the center area of the inner face of the flap 1. Moreover, the arrangement may be such that a projection is formed on the inner face of the flap 1 while a recess to mesh with the projection can be formed on suitable locations of the sprocket.
Furthermore, the cutting bit may be firmly mounted to the flap so as to be incapable of being demounted, by means such as brazing or the like. Alternatively, the cutting bit may be firmly mounted by any suitable detachable means.
Further, in the above-described first embodiment, the sliding groove 42 for the backing plate 118 was formed in the flap 1. However, the arrangement may be such that a projection is formed on the end face of the flap 1, while a sliding groove is formed on the end face of the backing plate 118.
Moreover, it is also possible to apply one of the following surface treatments to appropriate portions of the flap 1 or the cutting apparatus, to raise its corrosion resistance and wear resistance.

(a) One or more materials selected from the group consisting of carbides such as TiC, nitrides such as TiN, borides such as BN, oxides such as Al₂O₃, and other hard materials such as diamonds, are coated on the entire surface or a sliding surface of the flap 1 by the use of ion plating method, PVD method, CVD method or the like. In this connection, the sliding surface referred here indicates the outer peripheral surface of the connecting tab, the inner peripheral surface of the connecting cut-out 10, the inner surfaces of the respective driving recesses 6A and 6B, the inner surface of the sliding groove 42, the end faces of the back plate 118, the outer peripheral surface of the pin 126, and other surfaces of high wear.
(b) Powder plasma cladding, weld cladding, or the like is used to form a wear-resistant material coating layer such as ceramic, cobalt alloy or the like on the entire surface or the sliding surface of the flap 1.
(c) A thin plate or the like high in wear resistance comprising cemented carbide, high-strength ceramics or the like is firmly mounted to the inner surface of the sliding groove 42 or the end faces of the back plate 118, by attaching means such as brazing, staking fixing or the like. If possible, the thin plate or the like may be firmly mounted to other sliding surfaces.
(d) Kanizen plating, hard chromium plating, nickel plating or the like is applied to the entire surface or the sliding surface of the flap 1.
(e) Nitriding treatment or carburizing treatment is applied to the entire surface or the sliding surface of the flap 1 within a vacuum heat-treatment furnace or the like.

According to the first embodiment, since the connecting tab 8 and the connecting cut-out 10 are made in a semi-circular configuration, the quantity of projection of the connecting tab 8 and the depth of the connecting cut-out 10 can remain small, even if the size of the parts is increased. Accordingly, it is possible to decrease the width of the flap 1 in the connecting direction, and the strength of the connecting cut-out 10 can be raised to improve the connecting strength, to counter the reduction in depth of the connecting cut-out 10.
In connection with the above, Fig. 7 shows a modification of the above-described first embodiment, in which each of the flap 1 and the chip support 28 is formed into a three-layer construction.
The chain cutter comprises a plurality of flaps 1, in each of which a pair of outer plates 1A and 1C and an inner plate 1B formed by punching process or the like are bonded to each other in three layers by means of spot welding or the like. The inner plate 1B and the outer plates 1A and 1C have their respective configurations which are partially different from each other, thereby forming the engaging projection 40 and the sliding groove 42 for the back plate, as well as the groove 18A in the segment mounting recess 18, which has a C-shaped cross-sectional configuration.
As shown in Fig. 3, the engaging groove 38 and the engaging projection 40 are engaged with each other against movement in the thickness direction in the case where the connecting angle between the adjacent flaps 1 is equal to or less than the sprocket angle S. When the connecting angle is made slightly larger than the sprocket angle S, the engaging groove 38 and the engaging projection 40 are disengaged from each other.
In this embodiment, the respective configurations of the mounting recess 18 and the mounting projection 28A of the cutting device 4 are elliptical configurations elongated in the connecting direction of the flaps 1.
According to this embodiment, since the flap 1 is made in a three-layer construction, mere punching process and spot welding of the thin plates enable the sliding groove 42, the engaging groove 38, the engaging projection 42 and the groove 18A to be formed easily and at high precision. Thus, it is possible to reduce the processing cost as compared with the construction in which they are formed by grinding processing. Further, since the depths of the respective grooves 38 and 42 and the quantity of projection of the engaging projection 40 are made large, it is possible to raise the torsion preventing effects of the flaps 1 correspondingly.
In connection with the above, in order to replace the flaps 1 by new ones in the above embodiment, the chain cutter C is loosened, and a part of the chain cutter C is bent more than the sprocket angle S. By doing so, the engaging groove 38 and the engaging projection 40 are disengaged from each other, so that it is possible to freely remove the flap 1.
Next, Figs. 8 and 9 show a second embodiment of the invention, which is characterized in that a mounting recess 300 and the slit 22 are formed in the bit support 28 of the cutting device 4, while a mounting projection 304 is formed on the flap 1.
Furthermore, in this second embodiment, an engaging groove 306 is formed in the end face of the straight line section of the connecting tab 8. An engaging projection 308 is formed in the end face of the connecting cut-out 10 which corresponds to the engaging groove 306.
According to the second embodiment, even in the case where the elastic engaging part 26 is possibly broken or deformed, no effect or influence is imparted upon the flap 1. Since mere replacement of the cutting device 4 by new one completes repair, the service life of the flap 1 can be prolonged.
Further, when the chain cutter C is extended in a straight line manner, the engaging projection 308 and the engaging groove 306 of each adjacent flaps 1 are engaged with each other. Thus, torsion of the flaps 1 in the thickness direction is further prevented. Accordingly, the arrangement is also possible in which the engaging projection 38 and the engaging groove 40 for prevention of torsion are omitted. Of course, also in this second embodiment, the flap 1 can be brought to a three-layer construction, as shown in Fig. 10.
Next, Figs. 11 and 12 show a third embodiment of the invention. The third embodiment is characterized as follows. That is, a pair of projections 310 and a pair of grooves 312 in the shape of a V-shaped cross-section, complementary with each other, are formed in the respective peripheral surfaces 8A, 8B, 10A and 10B of the connecting tab 8 and the connecting cut-out 10. The projection 310 and the groove 312 are fitted in each other for sliding movement, but against movement in the thickness direction of the flap 1.
An angular-movement angle theta (Fig. 11) of the connecting tab 8 within the connecting cut-out 10 is larger than the sprocket angle S when the flaps 1 are arranged in a straight line manner. An extension line of the end face 10D of the connecting cut-out 10 on the inner peripheral end thereof is set to be in contact with the end face 10C of the connecting cut-out 10 on the outer peripheral end thereof.
Furthermore, in the third embodiment, the mounting projection 28A of the bit support 28 and the mounting recess 18 in the flap 1 have their respective configurations each of which is formed into a shape in which a pair of arcs are connected to each other by a straight line. The shape has such an advantage that the mounting recess 18 can easily be processed by an end mill.
According to the third embodiment, since the flaps 1 are prevented from separation in the thickness direction by engagement between the projection 310 and the groove 312, the flaps 1 are difficult to be separated from each other during cutting or transportation of the apparatus.
On the other hand, when the flaps 1 are replaced by new ones, as shown in Fig. 14, large yielding of the chain cutter C toward the inner periphery enables the connecting tab 8 to be remove from the connecting cut-out 10 in the direction of the arrow. Thus, replacement of the flaps 1 can be done easily and quickly.
In connection with the above, also in this fourth embodiment, the flap 1 can be brought to a three-layer construction as shown in Fig. 13.
Figs. 15 and 16 show a fifth embodiment of the invention. In the fifth embodiment, the arrangement is such that, as shown in Fig. 15, the size of the projection L of the connecting tab 8 does not reach the center O1. Each of the curved peripheral surfaces 8A and 8B is formed with a projection 160, and each of the pair of curved peripheral surfaces 10A and 10B of the connecting cut-out 10 is formed with a groove 312 only at a portion having a predetermined length from the opening edge.
In this fifth embodiment, as shown in Fig. 18, shortening of the connecting length of the flaps 1 enables the projection 310 and the groove 312 to be disengaged from each other, making it possible to separate the flaps 1 from each other in the thickness direction.
According to the fifth embodiment, the flaps 1 are not disconnected from each other regardless of the connecting angle between the flaps 1, during such a period that tension is applied to the flaps 1. Once the chain cutter C is shortened or contracted, however, there is produced an advantage that the flaps 1 can easily be cut off.
In connection with the above, also in this embodiment, the flap 1 may be formed into a three-layer construction, as shown in Fig. 17.
Furthermore, although, in the above-described fifth embodiment, the connecting tab 8 has its forward end face which is set to the rear of the curved center O1, it is also possible that the forward end face is set forwardly of the center O1. In this case, the depth of the connecting cut-out 10 should be enlarged, and a room should be formed in which the connecting tab 8 can be moved forwardly within the connecting cut-out 10.
Next, Figs. 19 and 20 show a sixth embodiment of the invention. In the sixth embodiment, when the flaps 1 are not connected, the peripheral surfaces 10A and 10B of the connecting cut-out 10 are so that only portions from the thickness center of the flap 1 toward the rear face thereof are made into tapered surfaces 314, while portions from the thickness center toward the front face are made respectively into vertical surfaces 316.
Further, the front face of the flap 1 is formed with a pair of curved staking grooves 318 at their respective remote locations through a predetermined distance from the vertical surface of the connecting cut-out 10.
The connecting tab 8 is fitted in the connecting cut-out 10 from the side of the front face of the flap 1, each of the pair of staking grooves 318 is enlarged along the entire length, and a pair of projecting sections 320 on the insides of the respective staking grooves 318 are deformed inwardly, whereby the connecting tab 8 is supported by the connecting cut-out 10 for angular movement, but against separation in the thickness direction of the flap 1.
According to the sixth embodiment, after the chain cutter has been assembled, the connecting tab 8 can not be removed from the connecting cut-out 10, so long as the projection 320 is not deformed. Thus, the sixth embodiment is suitable in the case where it is not desirable to have the connection between the flaps 1 become loose during handling.
Next, Figs. 21 and 22 show a seventh embodiment of the invention, which is characterized in that the curved peripheral surfaces 8A and 8B of the connecting tab 8 and the curved peripheral surfaces 10A and 10B of the connecting cut-out 10 are formed respectively into spherical surfaces which are complementary with each other.
According to the above construction, the engaging groove 40 and the engaging projection 38 of the adjacent flaps 1 are disengaged from each other, and the flap 1 is twisted as shown in Fig. 22, whereby the connecting tab 8 can easily be disengaged from the connecting cut-out 10. Accordingly, replacement of the flaps 1 and adjustment in the length of the chain can easily be done.
Figure 23 shows an eighth embodiment of the invention concerning the cutting apparatus. In the apparatus shown in Fig. 1, both the upper and the lower edges of the back plate 118 was in contact with the upper and the inner peripheries of the cutter C. In this embodiment, only the lower edge of the backplate is in contact with the lower peripheral region of the cutter C in the linear section.
The vertical distance between the upper and the lower edges of the backplate 118 is smaller than the winding diameter of the chain cutter, and the lower edge of the backplate is equipped with a protrusion 118A, which is inserted into the sliding groove 42. Other mechanisms remain the same as in Figure 1.
Fig. 24 shows a ninth embodiment of this invention. The components which are the same as in Fig. 1 are not explained further in this section. This embodiment is characterized in that there are four sprockets in stead of two. The additional sprockets 400 and 402 are disposed in the same vertical plane as the plane joining the sprockets 88 and 112.
The left-hand shaft 50 has a movable base 404A which is separated some distance from the base 54A, and which can move freely vertically on the shaft 50. From the base 404A projects a shaft section 406A, upon which shaft is disposed a freely rotatable sprocket 400.
The right-hand shaft 50 has a movable base 404B which is separated some distance from the base 54B, and which can move freely vertically on the shaft 50. From the base 54B projects a shaft 406B, upon which shaft is disposed a freely rotatable sprocket 402.
The distance between the bases 54A and 404A is fixed and maintained by a spacer rod 408, and the pair of bases 54A and 404A moves vertically along the shaft while maintaining the constant separation.
The separation distance is adjustable with a hydraulic pressure from a hydraulic pump 410, which is located between the bases 54B and 404B.
The other components such as the backplate 118 located between the bases 54A and 54B, and the support plate 80 are the same as in Fig. 1.
According to this arrangement of the sprockets, it is possible to keep the upper straight section X of the chain C, which does not take part in the cutting operation, away from the lower straight section which is performing the cutting. This is useful in cases of cutting large objects, since the diameter of the sprockets, 88, 112, 400 and 402, need not be correspondingly large, thus making it possible to cut large objects with a compact cutting machine.
Therefore, when the size of the object to be cut changes, it is only necessary to alter the separation of the sprockets 400 and 88 in cooperation with sprockets 402 and 112. Thus, the chain cutter arrangement shown in Fig. 24 enables cutting of objects of varying sizes without changing the sprockets. This is important since changing the sprocket diameter changes the relative fit of the bit groove with the sprocket teeth, and consequently, a new sprocket requires a new flap. The versatility of this chain cutter permits a cost efficient operation.
Although in the above preferred embodiment, four sprockets were used, other arrangement such as 3 or over 5 sprockets can also be used. If it is necessary to cut with the upper straight section X of the chain, relocate the sprockets 400 and 402 below the sprockets 88 and 112, and operate the cutter by pressing from the top onto the bottom surface of the object.
Fig. 25 shows a tenth preferred embodiment, in which the cutters are arranged in plurality. In this illustrious, four cutters are arranged in a multi-sprockets configuration effected by stacking several plates 88A-88E forming a cylindrical rod extending in the axial direction. There are plurality of slits 124 on the circumference of the sprockets, and inside each slit is a corresponding chain cutter C to be driven with the pins 126 which penetrate through the plates 88B, 88C and 88D disposed at equal distances around the circumference.
According to this multi-bladed chain cutter, it is possible to produce several cut sections of rocks and objects in a similar way to a gang-saw, permitting a high efficiency operation. In contrast to the reciprocating action gang-saw, however, the chain cutter moves in one direction only, thus, the wear of the rear region of the cutting area does not occur. Excessive wear of the supporting region of the abrasive area is thus avoided, and there is little loss of cutting media from the abrasive bits. The cutting movement is more efficient since the cutting direction is unidirectional, unlike a reciprocating gang-saw.
In this preferred embodiment 17, it is possible to provide for mechanisms within each sprocket for adjusting the chain tension and for adjusting the distance of separation of the cutting bits.
Fig. 26 is an eleventh preferred embodiment of this invention, characterized in that the provision of a pair of protrusions 500, protruding perpendicularly to the thickness direction, is made on the rear area of the backplate 118. The thickness T1 of the protrusion 500 is two times the thickness of the cutting device 4. The tapered protrusion extends along the back plate towards the center of the backplate 118 continuously and smoothly.
According to this preferred embodiment, when the cutting depth into the object W is deeper than the radius of the chain cutter C, the protrusion performs the function of separating the two cut surfaces so that the upper cutting edges will not interfere with said surfaces. In particular, as shown by the double-dot broken line in Fig. 2, the protrusion 500 is designed to prevent the bottom edge 30a of the cutting device 4 will not interfere with the edge W₁ of the cut surface of the work piece W to cause breakage of the work piece or of the bits 30.
In reference to the above, it is not necessary to have the protrusion 500 extending continuously along the backplate 118, it can be disposed periodically along a suitable path.
Fig. 27 shows a variation of the protrusion 500 on the backplate 118. The protrusions are made alternately on each side surface of the backplate 118.
Such protrusions 500 can be made easily from simple plate shape materials. In comparison with the shape of the protrusion shown in Fig. 26, this shape is able to lessen the impact shock, because the latter shape is more elastic than the former.
Some modifications of the chain cutter are presented below.

i) Instead of lowering the cutter C, raise the table 134 towards the object W by providing the table with a lifting mechanism.
ii) Instead of tilting the cutter C, tilt the table 134 to adjust the angle of cut of the object W.
iii) In addition to sprockets 88 and 112, provide a separate tension adjusting mechanism by means of a pulley attached to the inside surface of the cutter C.
iv) Use a driving mechanism to tilt the cutter C.
v) Automate all the cutter drives with the use of numerical control (NC).
vi) Place the object W horizontally, for example, so that the cutting is carried out horizontally. Other configuration of the object W is also possible but they will not be listed here.

Claims

A cutting apparatus for cutting a workpiece (W), comprising:
a) a flexible endless chain body (2) having a plurality of cutting devices (4) located at the outside edge thereof;

b) a plurality of sprockets (88, 112) supporting said chain body (2) for movement on an endless path extending around a given area and in a common plane;

c) a rigid backplate (118) provided within said common plane and in said given area, said backplate (118) supporting said chain body (2) towards said workpiece (W);

d) a rotating means (92, 94, 96) for rotating at least one of said sprockets (88, 112) and driving said chain body (2) around said endless path; and

e) a moving means (58, 64, 66) for moving said workpiece (W) or said chain body (2) toward each other to cut said workpiece (W) with said chain body (2);
characterized in that
f) said chain body (2) comprises a plurality of generally planar flaps (1), each of said flaps (1) having a connecting protrusion (8) and a connecting recess (10) at first and second opposite ends thereof, said connecting protrusion (8) having a semi-circular shape and including a first pair of arc-shaped outer peripheral surfaces (8A, 8B), said connecting recess (10) having a second pair of inner peripheral surfaces (10A, 10B) having shapes matching the shapes of said first pair of outer peripheral surfaces (8A, 8B) of said connecting protrusion (8);

g) said first pair of outer peripheral surfaces (8A, 8B) of said connecting protrusion (8) facing toward the first end of the flap (1) on which the connecting protrusion (8) is formed;

h) said second pair of inner peripheral surfaces (10A, 10B) of said connecting recess (10) facing toward the center of the flap (1) in which the connecting recess (10) is formed;

i) wherein said connecting protrusion (8) of each one of said flaps (1) is fitted into said connecting recess (10) of an adjacent flap with said first pair of outer peripheral surfaces (8A, 8B) of said one of said flaps abutted against said second pair of inner peripheral surfaces (10A, 10B) of said adjacent flap, so that the abutted peripheral surfaces (8A, 8B, 10A, 10B) support the tensile force applied to said chain body (2), said connecting protrusions (8) and said connecting recesses (10) of said flaps (1) connecting said plurality of said flaps together for angular movement in a common plane, and at least some of said flaps (1) having said cutting device (4) located at the outside edge of said flap (1).
The cutting apparatus according to claim 1, wherein the outer peripheral surfaces of said sprockets (88, 112) contain a support means (124) for maintaining said chain body (2) in a plane perpendicular to the sprocket axis.
The cutting apparatus according to claim 1, with a plurality of chain bodies (2) and rigid backplates (118), wherein the outer periphery of each of said plurality of sprockets (88, 112) contains a plurality of support means (124) for supporting the chain bodies (2), respectively, in a plane perpendicular to the sprocket axis, and wherein each of said chain bodies (2) is provided with a rigid backplate (118), respectively.
The cutting apparatus according to claim 1, wherein said backplate (118) has an end opposite to the end supporting said chain body (2) towards said workpiece (W), each surface of the backplate at said opposite end having at least one protrusion (500) respectively, and the distance between said protrusions (500) in the direction perpendicular to said backplate (118) is greater the the thickness of said cutting device (4).
The cutting apparatus according to claim 1, wherein the backplate (118) is provided with an elongating means (114) to adjust the longitudinal tension of said backplate (118).
The cutting apparatus according to claim 1, wherein a tilting means (102) is provided to independently tilt said chain body (2) or the workpiece (W), and thereby to vary at least some relative angles of cut between the workpiece (W) and the chain body (2) within the common plane of cut.
The cutting apparatus according to claim 1, wherein
- each flap (1) has an inside edge on said inner edge of said chain body;

- each flap (1) has a pair of driving recesses (6A, 6B) at first and second opposite ends of said inside edge of said flaps (1) forming engaging means, said engaging means (6A, 6B) of said chain body (2) arranged at equal intervals when said chain body (2) is bent in an arc; and

- at least one of said sprockets (88, 112) has a plurality of driving protrusions (126) provided at equal intervals in a circumferential direction on the periphery of one of said sprockets (88, 112), and each driving protrusion (126) engages with the corresponding engaging means (6A, 6B) of said chain body (2) to drive said chain body (2) around said endless path.
The cutting apparatus according to claim 1, wherein:
- said first end of each flap has a first engaging means (38), and said second end of each flap has a second engaging means (40); and

- in linearly elongated portions of said chain body (2), said first engaging means (38) engages said second engaging means (40) of a flap adjacent to said each flap in order to prevent disengagement of said flaps (1) in the elongated portions of chain body (2) in the direction perpendicular to said common plane.
The cutting apparatus according to claim 1, wherein: each of said flaps (1) consists of a center plate (1B) and a pair of side plates (1A, 1C) bonded to both sides of said center plate (1B), said connecting protrusion (8) having at least a first engaging portion (306, 310) formed by a peripheral surface of said center plate (1B), and said connecting recess (10) having at least a second engaging portion (308, 312) formed by an inner peripheral surface of said center plate (1B) of said flap (1).
The cutting apparatus according to claim 1, wherein each said cutting device is an abrasive cutting bit (30).
The cutting apparatus according to claim 1, wherein each said cutting device comprises saw teeth (250).
The cutting apparatus according to claim 1, wherein each of said cutting devices (4) includes a mounting projection (28A), the outside edge of each one of selected said flaps (1) forming a mounting recess (18) for receiving said mounting projection (28A) of said cutting device (4) connected to each one of the selected said flaps, and each of said mounting recesses (18) including an elastically movable section (26) for selectively engaging and releasing said mounting projection (28A) received in each said mounting recess (18).
The cutting apparatus according to claim 1, wherein the relative position of the backplate (118) with respect to the chain body (2) is adjustable through a positioning device.
The cutting apparatus according to claim 1, wherein
- said connecting protrusion (8) of each flap (1) has a pair of first engaging portions (310) on said first pair of peripheral surfaces (8A, 8B) thereof, said first engaging portions (310) being elongated in a circumferential direction of said first pair of peripheral surfaces (8A, 8B);

- said connecting recess (10) of each flap (1) has a pair of second engaging portions (312) on said second pair of peripheral surfaces (10A, 10B) thereof, said second engaging portions (312) being elongated in a circumferential direction of said second pair of peripheral surfaces (10A, 10B) on said connecting recess (10);

- said first engaging portions (310) of said connecting protrusion (8) of each flap fitting with a corresponding second engaging portion (312) of said connecting recess (10) of an adjacent flap to prevent disengagement of said flaps (1) from each other in a direction perpendicular to said common plane.
The cutting apparatus according to claim 14, wherein said first engaging portion (310) of said connecting protrusion (8) of each flap disengages from said corresponding second engaging portion (312) of said connecting recess of the adjacent flap when a connecting length of each said flap and said adjacent flap is shortened, and each said flap and said adjacent flap become detachable from each other in a direction perpendicular to said common plane.