Nagasawa, Kaneko and Adachi, Journal of Advanced Mechanical Design, Systems, and Manufacturing, Vol.13, No.1 (2019)
In order to make a smooth folding, a paperboard is usually scored by using a creaser at the pre-stage and make a localized delamination. (Kirwan, 2005). When the creased part is folded, the topside layers of fiber on the coated side are extended and require an adequate tensile strength and stretch, while the backside layers are compressed and bulged. In order to make a smart folding under forming the bulged zone, a scoring is processed before folding the paperboard. Table 2 In-Plane tensile properties of white-coated paperboard in Machine direction (MD). Tensile feed velocity was 0.33 mm s (strain rate: 0.00183 s ). Based on the procedure of JIS-P8113. Ultimate Tensile Strength V B MPa 41.1 (40.2~42.7) Breaking true strain H B % 1.71 (1.62~1.81) Young’s modulus E GPa 5.72 (5.53~5.91) The specimen was scored using a round-edge knife (a creaser) and rubber blocks as shown in Fig.2. Here, the creaser was set across MD of the specimen. Figure 3 shows a scoring state (crease forming) of a paperboard specimen using the creaser with a radius of r = 0.355 mm, thickness of b =0.71 mm. When the creaser is indented to the paperboard, the expression: tan G = (2 d B ) = J is the average shearing strain. This quantity J is defined as the normalized indentation depth (Nagasawa et al., 2001). Also, using the paperboard thickness t and the thickness of creaser b , the groove width B was empirically chosen as 2 t + b = 1.3 mm, the height of groove H was 1.5mm and the indentation of creaser d was chosen as d < H . Regarding the time-dependent response of bending moment resistance (Nagasawa et al., 2014, 2015), the scored state of crease part was investigated as J = 0.2~1.0, while the previous work (Nagasawa, et al., 2016) mainly discussed with the scored state of J = 0.6. This was also chosen here owing that the indentation depth was empirically designed as J = 0.4~0.6 ( d ൎ t ). The scoring condition (using a rubber height of 7 mm by the hardness of 40(A) and a creaser height of 5.6 mm) was empirically chosen from a commercial based production. All the specimens were formed without warpages. The feed velocity of creaser was chosen as V = 0.0167 mm s 1 for scoring. 2.2 Folding and release of scored specimen Figure 4 illustrates a conceptual mechanism of crease folding. When the paperboard is scored by a creasing knife, the intermediate layers are damaged as shown in Fig.4(a). Since the paperboard consisted of laminated plies, a certain extent of de-lamination damage is generated in the scored zone. When the paperboard is folded with this scored position, the damaged layers are further de-laminated and its inside (lower) layers are bulged as shown in Fig.4(b) (Hine, 1959; Nagasawa, 2004). The bending moment resistance of the creased zone appeared to consist of three mechanisms: (i) a tensile resistance of the outside (upper) layers, (ii) a compressive resistance of the inside (lower) layers, and (iii) a detaching (peeling) resistance of the middle layers (Nagasawa et al., 2011). The third item (detaching) affects only the transient folding resistance in the early stage, while the first (tensile of outside) and second (compression of bulged layers) items behave as the bending moment resistance in the full stage of folding test. Figure 5 shows a general view of bending test apparatus (CST-J-1, 2003). Figure 6 shows a conceptual illustration of the folding process and rotating method used in the bending test.
b =0.71
(Unit: mm)
Paperboard
Creasing rule tan Creaser knife G
Blade holder
B d 2
Creaser knife
¸ ¹ ·
¨ © §
Paperboard
40HS(A) Hardness
b
18
J
r
d
t
G
Rubber 7
5
5.6
5
7
Groove on face plate B H
t =0.3
Paperboard
B =1.3
Figure 2 Layout of out-of-plane scoring by creaser
Figure 3 Schematic of scoring state and parameters
© 2019 The Japan Society of Mechanical Engineers
[DOI: 10.1299/jamdsm.2019jamdsm0004]
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