Note: Descriptions are shown in the official language in which they were submitted.
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DEVICE FOR MEASURING BENDING STRENGTH OF SHEET MATERIAL
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a device for measuring
bending strength of sheet material, such as corrugated f fiberboard
or paperboard, at a crease (score) portion or a blank portion
thereof.
DESCRIPTION OF THE PRIOR ART
For manufacturing corrugated fiberboard containers, in
general, a base board for corrugated fiberboard is processed into
a continuous band-shaped corrugated fiberboard by passing it
through a corrugator. The obtained sheet is cut into a plurality
of corrugated fiberboard sheets having a predetermined length
and then stocked to keep for further processing. After that,
each of the stocked sheets is subjected to a printing process
and also cut into a desired shape by means of a die board which
also makes the slits and creases to be required built into the
container. Then each die cut sheet (die cut box) is formed into
a designated corrugated fiberboard container and stocked in a
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folded state. In case of need, furthermore, the folded
corrugated fiberboard container is extended and built into an
assembled container in the shape of a box. Hereinafter, the
assembled corrugated fiberboard container will be referred as
a corrugated box.
Referring now to Fig. 1, there is shown a device for the
purpose of explaining one of the examples of the conventional
methods for making creases in corrugated fiberboard. In this
case, the creased portions can be provided as lines for folding
f laps of the corrugated f fiberboard container to make a corrugated
box. According to the conventional method, as shown in the figure,
A crease I06 can be shaped by constant pressing through a
combination of an anvil 102 having a protrusion 101 and an
extrusion die 104 having a edge portion 103 corresponding to that
protrusion 101. In the case of making a crease by using a
flexopri.nter folder Bluer (FFG) or the like, an anvil having a
flat surface without any protrusion is used. Recently,
furthermore, it has been known that a crease can be prepared as
a series of holes bored through one liner and corrugating media
of corrugated fiberboard, the remaining liner stays intact, by
means of a laser beam with a pulse oscillation mode.
Regarding the aforementioned crease of the corrugated
fiberboard, the warping force of the creased portion varies among
the methods to be selected for making the crease, for example
at the time of bending the flap. In addition, the warping force
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of the creased portion also varies among the materials of the
corrugated fiberboard and with the conditions of the formed
crease, for example the warping force of the creased portion
varies with a large or small amount of clearance between the edge
portion 103 and the protrusion 101 (or the anvil's surface if
it is not provided thereon) when the crease is shaped by forcing
with the extrusion die 104 having the edge portion 103. When
the crease is prepared as a series of holes by means of the laser
beam as described above, the warping force of the creased portion
varies with the differences in size of each hole or in spacing
between adjacent holes.
Consequently, the following problems can be occur in
accordance with the aforementioned variations in the warping
force of the creased portion.
In a case where the corrugated boxes are used for packing
a wide variety of commodity products or the like on packing lines
under automatic control, the step of fixing the top and bottom
flaps of each corrugated box together by an adhesive tape is
performed as a last step in the packing process. Thus the height
of the empty corrugated box depends on the warping force of the
creased portion, the box' s own weight, the symmetry or proportion
of the box's shape or dimensions, and so on. When the warping
force of the creased portion is too big, each flap of the
corrugated box tends to extend higher than the acceptable height
or width of the box with respect to the packing line. As the
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corrugated box is too high, it is difficult.to place the empty
corrugated box correctly on the line and to keep the box on the
line without bumping into something, resulting in the above
packing line being stopped. Recently, in particular, automatic
high-speed packaging apparatuses have been introduced
increasingly in the fields of the food and drink industries and
the like, so that wrap around cases made of paperboard or
corrugated fiberboard to be used in those fields suffer serious
damages arising out of qualities of the creases formed thereon.
Therefore the amount of money for the damage may increased
enormously. Accordingly, manufacturers of paper containers and
corrugated fiberboard have been poured all their energies into
a quality-control method with a particular emphasis on the
strength of the crease.
A conventionally well-known method for measuring the
bending strength of creases will be described hereinafter with
reference to Fig. 2. The method comprises, as shown in Fig. 2,
the steps of holding one end of a corrugated fiberboard 105 having
a crease 106 by a holder 107, loading a weight on the other end
of the corrugated fiberboard 105, and making an assessment of
the strength of the crease 106 at the time of folding by means
of the heaviness of the weight 108. .Therefore, the above method
is able to estimate yield strength of the creased portion but
not to estimate warping force thereof.
Strength of any portions of the corrugated fiberboard
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except the creased one is directly related to the strength of
the corrugated box, so that it is very important to understand
the bending strength of the corrugated fiberboard easily from
the point of quality control. It is noted that this point is
also important for various kinds of sheet materials including
paperboard, plastic sheet, film, metal thin plate, honey-comb
sheet, and so on.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a device
providing for easily measuring the bending strength of corrugated
fiberboards, various kinds of sheet materials including
paperboard and the like, or creased portions thereof.
Another object of the present invention is to provide a
device having excellent portability for measuring the bending
strength of sheet material in any location at any time.
There is provided a device for measuring bending strength
of a sheet material in a predetermined direction, comprising:
a clamp having a tip that extends in a direction
perpendicular to said predetermined direction and holds one end
portion of said sheet material;
a load sensor which is positioned relatively below another
end portion of said sheet material being held by said clamp;
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a revolving means for revolving said clamp, which is
provided on one end in a direction along said tip of said clamp;
a data-processing means for storing the resistance force
to be detected by said load sensor by contacting with said sheet
material during a period of revolving said clamp and information
concerning the position of said clamp traveled by said revolving
means, by which stored data is processed and outputted as output
data in a predetermined form; and
a data-displaying means for displaying said output data.
Here, said revolving means may be a handle for manually
revolving said clamp.
The revolving means may be capable of revolving said clamp
in a predetermined angle between over 90° to nearly 180°.
The data-displaying means may be removably connected with
a connector for connection and disconnection to a main body.
The said connector is capable of being connected with a
personal computer.
The said data-displaying means is a printer.
The said sheet material is a corrugated fiberboard.
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The said sheet material is a paperboard.
By using the device of the present invention, bending
strength of corrugated fiberboard, paperboard, or creased
portion thereof can be easily measured in any location at any
time, so that the measuring device of the present invention
extremely contributes to the control qualities of these sheet
materials and also to facilitate sales thereof and so on.
The above and other objects, effects, features and
advantages of the present invention will become more apparent
from the following description of embodiments thereof taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic sectional view of the device for
carrying out the process of making a crease on the corrugated
fiberboard;
Fig. 2 is a schematic sectional view of the device for
carrying out the conventional way of making an assessment of the
creased portion of the corrugated fiberboard;
Fig. 3 is a plane view of the device for measuring the
bending strength of sheet materials for illustrating a preferred
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embodiment of the present invention;
Fig. 4 is a front view of the device for measuring the
bending strength of sheet materials for illustrating one of the
preferred embodiment of the present invention;
Fig. 5 is a partial cutaway view of the device shown in
Fig. 4;
Fig. 6 is a graphical representation with a table of the
results obtained by the measurement performed by the device of
the preferred embodiment;
Fig. 7 is a graphical representation of the results
obtained by the measurement performed by the device of the
preferred embodiment;
Fig. 8 is a graphical representation of the results
obtained by the measurement performed by the device of the
preferred embodiment;
Fig. 9 is a plane view of the device for measuring bending
strength of sheet materials for illustrating another preferred
embodiment of the present invention;
Fig. l0 is a graphical representation of the results
obtained by the measurement performed by the device of another
preferred embodiment;
Fig. 11 is a graphical representation of the results
obtained by the measurement performed by the device of another
preferred embodiment;
Fig. 12 is a graphical representation of the results
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obtained by the measurement performed by the device of another
preferred embodiment; and
Fig. 13 is a graphical representation of the results
obtained by the measurement performed by the device of another
preferred embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention will be described in detail with
respect to preferred embodiments, and it will now be that changes
and modifications may be made without departing from the
invention in its broader aspects, and it is the invention,
therefore, in the appended claims to cover all such changes and
modifications as fall within the true spirit of the invention.
Figs. 3 to 5 illustrate a device for measuring bending
strength of corrugated fiberboard as one of the preferred
embodiments of the present invention, in which Fig. 3 is a plane
view, Fig. 4 is a front view, and Fig. 5 is a partial sectional
front view of the device. The device shown in these figures is
designed as compact and lightweight so as to be easily carried
or moved to any place at any time.
As shown in the figures, the device comprises a base 11
in which a data-processing unit (not shown) is imbedded. The
data-processing unit is provided for processing the results
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obtained by measurement to print them as characteristic values
including a yielding value (gf), a yielding angle (deg), an
initial gradient (gf/deg), and a graph representing the
relationship between a revolution angle (deg) and a resistance
value ( gf ) . On one end portion of the base 11, there is provided
a clamp 12 for clamping one end of the corrugated fiberboard D
as a test sheet. The clamp 12 is rotatably connected to a shaft .
13 as the center of the rotation. In addition, the shaft 13 is
rotatably supported by bearing pads 14, 15 which are fixed on
both-sides of the clamp 12, respectively. The clamp 12 comprises
a fixed click 12a being secured to the shaft 13 and a movable
click 12b that performs closing and opening with respect to the
fixed click 12a. The movable click I2b is supported by a pair
of pins 16 and a clamp-adjusting screw 17 so as to be movable
only in the direction of opening and closing. Thus the movable
click 12 be can be opened or closed by revolving the clamp-
adjusting screw 17. The clamp 12 of the present embodiment is
in the type of a ratchet, so that the force exerted on the movable
click 12b toward the fixed click 12a does not exceed a
predetermined level. According to such construction, therefore,
the corrugated fiberboard D held by the clamp I2 of the present
embodiment does not become flat.
As shown in the figures, furthermore, one end portion of
the shaft 13 is protruded from the bearing pad 14 to outside the
device and equipped with a handle 18 for revolving the clamp 12.
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The handle 18 can be fixed to an end portion of the shaft 13 in
the direction of revolution by means of a handle-fixing screw
19. Nearly in the center of the base 11, there is provided a
load sensor 20 having a load-sensing portion 20a. As shown in
the figures, the load sensor 20 protrudes upward from the surface
of the base 11, while the load-sensing portion 20a extends in
the direction corresponding to the width of the test sheet.
Furthermore the load sensor 20 is secured on a mobile platform
21 which is able to shift its position along a guide rail 22 toward
the right and left sides of the figure when viewed from the front
thereof . After the movement, the mobile platform 21 can be fixed
at a predetermined position by mean of a fixing screw 23.
For measuring bending strength of the corrugated
fiberboard by using the device described above, a test sheet of
the corrugated fiberboard, with a size of 50 mm in width and the
measuring length plus 40 mm or more in length, is prepared as
a sample. Then one end thereof is held by the clamp 12. In this
condition, the handle 18 is in the position shown in Figs . 4 and
5, while the free end portion of the test sheet D having the end
portion held by the clamp 12 is in the position part from the
load sensing portion 20a of the load sensox 20 so as to be spaced
therefrom (see Fig. 5). Then the handle 18 is revolved in a
predetermined angle between over 90° to nearly 180° in a
counterclockwise direction. As the handle 18 starts to revolve,
the other end of the test sheet D touches to the load sensing
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portion 20a of the load sensor 20. The measurement can be
completed by further revolving the handle in the predetermined
angle from that position. A force f (a resistance value) applied
on the load sensor 20 is measured so as to correspond to the
revolving angle.
According to the present embodiment, as shown in the
figures, there is provided a printer 24 on the opposite side of
the base 11 with respect to the handle 18 equipped thereon. The
printer 24 is able to print out the results processed by the
aforementioned data-processing unit in accordance with the data
obtained by the measurement. The results may be printed out as,
for example in the form of a table showing the characteristic
values or of a graph showing the relation between the revolution
angle (deg) and the resistance value (gf). According to the
present embodiment, furthermore, the printer 24 is detachable
and attachable for easily taking on the road. The connector for
the printer 24 is in the type of RS-232C for general purpose use,
so that it can be connected to a personal computer or the like
for the purpose of not only easily displaying at-a-glance charts
of the characteristics values and the characteristic graghs as
shown in Figs . 6 to 12 but also editing, comparing, and storing
the data, for easily carrying out an advanced analysis thereof
and so on.
For the sake of attaining the objectives of the present
invention, in spite of with or without the printer, the device
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must be equipped with means for recognizing the data in any
location at any time if required. Such means is not restricted
to the printer but also for example a data-displaying device such
as a liquid crystal display may be used.
Accordingly, we performed the measurements for estimating
bending-strength of the corrugated fiberboard by using the
measuring device of the present embodiment. In addition, we
inputted a plurality of obtained results of several samples into
a personal computer for data-processing to make an assessment
of bending strength. For further consideration, several examples
of the outputs from the personal computer are shown in Figs. 5
to 8.
The data shown in Fig. 6 is of the measurement for bending
strength of a blank portion ( not the creased portion ) of the test
sheet ( 5 . 0 cm in width ) , in which ten samples are used. In this
measurement, furthermore, the measuring length of the blank
portion under the measurement is 6. 0 cm which corresponds to the
distance between the tip of the click portion 12a and 12b of the
clamp 12 and the load sensing portion 20a of the load sensor 20.
In this embodiment, the blank portion is of a score of the
corrugated fiberboard (class B), wherein the score is in the
direction perpendicular to a flute.
The obtained results of the measurement are shown in the
table including a yielding value (gf), a yielding angle (deg),
and an initial gradient ( gf /deg ) and in a graph representing the
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relationship between a revolution angle (deg) and a resistance
value (gf).
Each of the characteristic values and its definition will
be explained as follows.
Yielding value (gf)
The yielding value represents a load at the time of bending
the sheet material by revolving the handle from the position where
the test sheet is horizontal or nearly horizontal after placing
the test sheet in the measuring device. Zn addition, the yielding
value is dependent on the stiffness of the material, so that a
higher the stiffness of the sheet material, the likelier it
becomes that the higher yielding value has been attained. As
for the corrugated fiberboard, the yielding value may vary by
the effect of bonding conditions (i.e., bonding requirements,
amount of applied paste, or the like ) in spite of using the same
flute and the same material.
Yielding angle (deg)
The yielding angle represents an angle corresponding to
the yielding value. In the process of bending the blank sheet,
the higher the stiffness of the sheet material, the likelier it
becomes that the lower yielding angle has been attained.
Initial gradient (gf/deg)
The initial gradient represents variations in the
resistance just after starting the measurement ( i. e. , at the time
that the revolution angle is almost at zero). It is readily
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calculated from the gradient of the tangent to the leading edge
of the data by processing the data obtained within a period
between the instant when the measurement is started and the
instant when yielding angle is attained. Therefore, the initial
gradient can be obtained with respect to the bending of the
corrugated fiberboard, paperboard, or the like, so that it stands
for capableness of being bent with ease or it stands for
difficulty to bend (i.e., bending strength).
The data shown in Fig. 7 corresponds to the results of the
measurement for making an assessment of bending strength of the
creased portion of each test sheet (5.0 cm in width and 6.0 cm
in measuring length), in which the data No. 1 is of the blank
portion and the data Nos . 2 to 4 are of the creased portions of
the corrugated fiberboard (class B).
The data shown in Fig. 8 corresponds to the results of the
measurement for making an assessment of bending strength of the
score of each test sheet ( 5 . 0 cm in width and 12 . 0 cm in measuring
length) prepared from the corrugated fiberboard (class B). In
this measurement, eight samples are used.
In the measuring device of the present embodiment, the
handle 18 is manually revolved. However, the results of the
measurement are not affected by the bending rate when the speed
of revolution is in the range of 50 degree/second or less. Just
as in the case of the aforementioned embodiment, it is possible
to make an assessment of yielding strength of the creased portion,
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warping force of the folded creased portion, mechanical
characteristics of the creased portion, and so on.
By accumulating the data in an appropriate storage means,
furthermore, a box strength can be estimated by using the yielding
value of the bending of the blank portion. Thus the measuring
device of the present invention will be able to support the design
of the packaging with corrugated fiberboard.
For measuring bending strength of the paperboard, Fig. 9
shows a bending-strength measuring device as another preferred
embodiment of the present invention. The measuring device is
constructed in the same way as that of the aforementioned
embodiment with the exception that follows. In the present
embodiment, that is, an allowable load of the load sensor 20A
is maintained within narrow limits and also the load sensor 20A
is positioned at a point closer to the clamp 12A, compared with
that of the first preferred embodiment. In addition, the clamp
12A of the present embodiment is not a ratchet type but a normal
clamp.
Referring now to Figs . 10 to 13, there are represented the
results of the measurement of the bending strength of the
paperboard by using the measuring device of the present
embodiment.
In these figures, Fig. 10 shows the results of the
measurement under the condition that a test sheet (2.5 cm in
width) of the paperboard is bent in a vertical position with
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respect to cross-grain. The results are obtained from eight
samples with the measuring length of 1.5 cm.
Fig. 11 shows the results of the measurement under the
condition that a test sheet of 2 . 5 cm in width is bent in a parallel
position with respect to cross-grain. The results are obtained
from nine samples with the measuring length of 1.5 cm.
Fig. 12 shows the results of the measurement under the same
condition as that of Fig. 10 except that the results are obtained
by measuring bending strength of the blank portion (data No. 1 ) ,
creased portion ( data Nos . 2 and 3 ) , and perforated portion ( data
Nos. 4 and 5) of the paperboard.
Furthermore, Fig. 13 shows the results of the measurement
under the same condition as that of Fig. 11 except that the results
are obtained by measuring bending strength of the blank portion
( data No . 1 ) , creased portion ( data Nos . 2 and 3 ) , and perforated
portion (data Nos. 4 and 5) of the paperboard.
