Apparatus and method for folding a sheet of material

An apparatus for folding a sheet of relatively brittle material in which an articulated frame assembly is mounted relative to a support structure in a manner so that two portions of the frame assembly can pivot relative to each other in an angular direction to fold the sheet about a fold line intermediate the ends of the sheet. Each portion of the frame assembly includes a movable portion which is adapted to fold the outer end portion of the sheet about an additional fold line intermediate the first fold lines and the outer edge portion. The sheet is heated along the fold lines prior to the folding operations.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus and method for forming an envelope 
from a sheet of a relatively brittle material and, more particularly, to 
such an apparatus and method for forming such an envelope for use as a 
battery separator. 
Traditionally, wet cell batteries employ at least one pair of opposite 
polarity planar electrodes, normally referred to as plates, which are 
closely spaced in a parallel relationship and immersed in a liquid 
electrolyte to form an electro-chemical couple. A great majority of these 
type batteries employ a plurality of pairs of the opposite polarity plates 
with the plates being normally arranged in an upstanding face-to-face 
relation, and with the exact number of pairs in a particular battery 
depending upon the capacity and/or voltage desired. 
To avoid adjacent opposite polarity plates from coming into direct physical 
contact and thereby causing arcing and/or short circuiting, it is 
necessary to electrically insulate the adjacent plates from each other. To 
achieve this insulation, electrically insulative material, usually in the 
form of sheets similar in size to the electrode plates, and commonly 
referred to as separators, have been positioned between the opposite 
polarity plates, with the insulative material being permeable or 
semipermeable to the liquid electrolyte to sustain the ionic conduction 
required for the battery action. In older designs, the separators were 
formed of rubber, wood, and glass while more recent designs have used 
plastic materials. 
Although these types of separators were adequate in many applications, some 
deficiencies in their insulating capability did develop, especially in 
connection with relatively heavy-duty industrial-type batteries such as 
traction batteries, etc. In particular, it has been discovered that, by 
reason of the close proximity of the exposed side edges of the adjacent 
plates, dendrites form on and project out from the edge portion of one or 
the other of the plates, especially after the battery had been in use for 
a relatively long period of time. These dendrites cause short-circuiting 
and/or arcing between the adjacent plates which, of course, reduces the 
capacity and/or output voltage of the battery. 
In order to overcome this problem, recent battery designs have included an 
open ended envelope-type separator of an insulating material which covers 
the side edge portions of the plates and prevents the above-mentioned 
short circuiting and arcing. 
In a parallel sense, the state of the art has also developed with respect 
to the materials used for the separators. In particular, recent designs 
have formed separators of a microporous plastic material, including 
polyethylene, vinyl resin, and the like, which has excellent insulating 
capability yet is relatively low in weight and cost. An example of this 
type of separator is disclosed in U.S. Pat. No. 3,696,061, issued Oct. 3, 
1972 in the name of Selsor et al., the disclosure of which is hereby 
incorporated by reference. The Selsor et al. patent is assigned to the 
same assignee as the present application. And although battery separators 
of the type disclosed in the aforementioned Selsor et al. patent have 
found widespread commercial acceptance, these separators suffer from the 
disadvantage of being brittle and consequently, heretofore have been 
incapable of being folded into the desired envelope configuration on a 
high production, relatively inexpensive basis. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an 
apparatus and method for forming a relatively brittle plastic sheet into 
an envelope. 
It is a more particular object of the present invention to provide an 
apparatus and method for forming an envelope by folding a plastic sheet 
about an intermediate fold line and then about two additional fold lines 
while selectively heating the sheet along localized regions thereof 
defined essentially by the fold lines to prevent cracking of the sheet. 
It is a further object of the present invention to provide an apparatus and 
method which forms an envelope of the above type suitable for use as a 
battery separator. 
Toward the fulfillment of these and other objects, the apparatus of the 
present invention comprises an articulated support assembly for supporting 
the sheet of material, the assembly comprising two portions adapted for 
pivotal movement relative to each other to fold the sheet about a fold 
line intermediate the ends of the sheet, each portion including two 
members adapted for relative movement for folding the sheet about two 
additional fold lines each intermediate the first fold line and the end 
portions of the sheet, and means for selectively heating the sheet 
material along localized regions thereof defined essentially by the fold 
lines in a sequence corresponding to the folding operations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1-3 of the drawings, the reference numeral 10 refers in 
general to a support table formed by front and rear plates 12 and 14, 
respectively, and a pair of side plates 16 and 18 connected to the front 
and rear plates and spaced inwardly from the outer edge portions of the 
latter plates. A pair of horizontal plates 20 and 22 are supported in a 
spaced relationship on the upper edges of the plates 12, 14, 16, and 18. 
A pair of spaced parallel rods 24 and 26 extend between the plates 12 and 
14 inwardly from the plates 16 and 18, and are journalled in bearings 28 
extending through the plates 12 and 14, as better shown in FIG. 2, to 
permit rotation of the rods relative to the plates. 
As shown in FIGS. 1 and 2, two pairs of spaced crank levers 30 and 32 are 
fixedly secured to the rods 24 and 26, respectively, and extend in a 
generally upward direction from the rods. Two additional pairs of levers 
34 and 36 are also fixed to the rods 24 and 26, respectively, and extend 
in a generally downward direction from the rods. The levers 34 and 36 are 
spaced slightly from their corresponding levers 30 and 32 and are attached 
at their free ends to the ends of two pairs of springs 38 and 40, 
respectively. Two pairs of pins 42 and 44 extend from the plates 16 and 18 
of the table 10, and are fixed to the other ends of the springs 38 and 40, 
respectively. As a result, the levers 30 and 32 are urged to the positions 
shown by the solid lines in FIG. 1 for reasons that will be explained in 
detail later. Two pairs of bolts 46 and 48 may be threadedly mounted 
relative to the plates 20 and 22 as shown in FIG. 1 in order to limit the 
movement of the crank levers 30 and 32, respectively, in this direction. 
As better seen in FIGS. 1 and 3, a pair of spaced parallel rods 50 and 52 
extend through corresponding openings formed in the levers 30 and 32, 
respectively, with the rod 50 being journalled at its respective ends 
within a pair of spaced parallel arms 54 and 56 which normally extend in a 
horizontal direction, and the rod 52 being journalled at its respective 
ends within a similar pair of arms 58 and 60. 
As shown in FIGS. 2 and 3, the arms 54 and 58 are pivoted at their ends 
over a pair of eccentric shafts 62 and 64, respectively, extending from 
opposite faces of a disc 66 which, in turn, is fixedly secured within a 
support assembly 68, by means of a set screw 70 and extending through a 
base plate 68a of the support assembly and engaging the disc 66. In a 
similar manner, the arms 56 and 60 are pivoted at their ends over a pair 
of eccentric shafts 72 and 74, respectively, extending from a disc 76 
which, in turn, is fixedly secured with a support assembly 78 by means of 
a set screw 79 extending through a base plate 78a of the support assembly 
and engaging the disc 76. 
An elongated anvil member 80 extends between the base plates 68a and 78a 
and is bolted at its end portions to the latter plates. As better shown in 
FIG. 4, the anvil member 80 includes a flange portion 82 extending from 
its upper surface and along its entire length for reasons that will be 
explained in detail later. 
Referring to FIGS. 3 and 4, a bar 84 extends between the arms 54 and 56 and 
is bolted at its ends to the free ends of the latter arms, and a bar 86 is 
bolted at its ends to the other ends of the arms 58 and 60. Three spring 
loaded pins 90 are mounted at spaced intervals in openings formed in the 
upper surface of the bar 84 and three spring loaded pins 92 are mounted in 
a similar manner in the bar 86. Each of the spring loaded pins 90 and 92 
is urged by its spring to a position where an end portion projects a 
relatively small distance outwardly from the corresponding surfaces of the 
bars 84 and 86, respectively. Three L-shaped fold bars 94 are mounted to 
the upper surface of the bar 84, and three fold bars 96 are mounted to the 
upper surface of the bar 86. The fold bars 94 and 96 have upstanding leg 
portions 94a and 96a, respectively, for reasons that will be explained 
later. 
As shown in FIG. 4, an angle iron support bar 98 is mounted at its ends of 
the arms 54 and 56 and extends in a spaced parallel relation to the bar 
84, while a support bar 100 is mounted in a similar manner to the arms 58 
and 60 and in a spaced parallel relation to the bar 86. One leg portion of 
each of a pair of elongated hinge assemblies 102 and 104 is mounted to the 
support bars 98 and 100, respectively, with the other leg portion of each 
hinge assembly defining a horizontal support surface. 
A fold plate 106 extends between the bar 84 and the bar 98 and is supported 
along its end portions by the pins 90 and by the hinge assembly 102, 
respectively. In a similar manner, a fold plate 108 extends between the 
bar 86 and the bar 100 and is supported by the pins 92 and the hinge 
assembly 104. 
A mandrel, or forming blade, 110 fabricated from a heat-resistant, 
non-conductive material such as for example, laminated phenolic sheet, is 
supported above the support table 10 by means of a guide assembly shown 
better with reference to FIGS. 1-3. The guide assembly includes a pair of 
vertically extending guide rails 112 and 114 which are bolted to the inner 
surface of the rear plate 14 of the support table 10. Each of the guide 
rails 122 and 124 comprises three plates bolted together with an inner 
plate having a reduced width to define a groove for receiving a slide 
plate 116. A plurality of bolts 118 attach the slide plate 116 to the rear 
face of the forming blade 110 for supporting the blade in the position 
shown in FIG. 2. 
A pneumatically operated cylinder 120 is supported by a bracket 122 located 
at the top of the guide rails 112 and 114. The cylinder 120 has a threaded 
piston rod 124 which is secured in a threaded opening formed in one end 
portion of a mounting block 126. A notch is formed in the other end 
portion of the block 126 and receives the upper end portion of the slide 
plate 116. A pin 128 extends through corresponding openings formed in the 
mounting block 126 and the slide plate 116 to fix the slide plate relative 
to the rod 124. Air is selectively admitted and discharged from the 
cylinder 120 in a manner to be described later to reciprocally drive the 
piston rod 124, and therefore the slide plate 116 and the forming blade 
110, in a generally upwardly and downwardly direction as viewed in FIG. 2. 
A support bracket 129 is secured to the rear of the guide rails 112 and 114 
and supports an additional pneumatically operated cylinder 130 having a 
piston rod 131. Air is also selectively admitted to and discharged from 
the cylinder 120 to reciprocate the rod 131 for reasons to be described in 
detail later. 
An additional slide plate 132 is slidably disposed in the groove defined 
between the guide rails 112 and 114 below the slide plate 116. A vertical 
plate 113 is attached to the slide plate 130, extends out of the 
above-mentioned groove, and is connected to a horizontal plate 134 which, 
in turn, is bolted to the base plate 78a of the support assembly 78, with 
the set screw 79 of the latter assembly also extending through the plate 
134. 
As better seen in FIGS. 1 and 2, a threaded rod 136 extends through a 
threaded opening in a plate 138 affixed to the lower portion of slide 
plate 116, and is adapted to engage the plate 134, for reasons that will 
be explained in detail later. 
As shown in FIGS. 2 and 5, a vertically extending plate 140 is mounted to 
the rear of guide rail 112 and supports three vertically spaced limit 
switches 142, 144, and 146, which are sequentially engaged by a blade 148 
attached to the rear of the slide plate 116 during downward movement of 
the latter plate. The limit switches 142, 144, and 146 operate to 
sequentially stop the movement of the slide plate 116, and therefore the 
forming blade 110, in a manner to be described in detail later. 
The piston rod 131 extends through an opening in the blade 148 and receives 
a nut 150 which is engaged by the blade at its lowermost position. As a 
result, upward movement of the rod 131 by the cylinder 130 will also move 
the blade 148, and therefore the slide plate 116 and the forming blade 
110, in the same direction. 
As shown in FIG. 1, a heating element 152, preferably of the electrical 
impulse type, is mounted on the folding blade 110 along its lower edge 
portion, and a pair of similar heating elements 154 and 156 are mounted on 
the blade along its upper corners, with the heating elements functioning 
in a manner to be described in detail later. 
The control system for operating the heating elements 152, 154, and 156 on 
the forming blade 110 and the pneumatic cylinders 120 and 130 is shown 
schematically in connection with FIG. 6. In particular, a control console 
160 is provided which has two actuation buttons 162 and 164 associated 
with three timer switches 166, 168 and 170. The timer switch 166 is 
electrically connected, by a conductor 172, to the heating element 152, 
while the timer switch 168 is electrically connected by conductors 174 and 
176 to the heating elements 154 and 156, respectively. The timer switch 
170 is connected, via a conductor 178, to an air cylinder control unit 180 
which operates in a conventional manner to control the intake and output 
of air to and from the cylinders 120 and 130, respectively, and thus 
reciprocally drive their respective piston rods 124 and 131. In this 
connection, an additional control console 182 is provided having four 
actuation buttons 184, 186, 188, and 190 which are connected, via lines 
192 and 194, to the air cylinder control unit 180 to operate the cylinders 
120 and 130 in the specific manner to be described later. 
The limit switches 142, 144, and 146 are also electrically connected to the 
air cylinder control unit 180 by the lines 196, 198 and 200, respectively, 
to also control the operation of the cylinders 120 and 130. 
It will be appreciated that the aforementioned electrical connections are 
part of electrical circuits that are not shown in their entirety in the 
interest of brevity, and that such circuits would include various 
components such as resistors, relays, etc., as needed to effect the above 
operations. The details of these control circuits are conventional and 
form no part of the present invention; suffice it to say, that only those 
features thereof which are deemed necessary for a complete understanding 
of the present invention are described herein. 
The operation of the apparatus of the present invention will be described 
in connection with the folding of a workpiece 202 of relatively brittle 
plastic material of the type disclosed, for example, in the 
above-identified Selsor et al. patent to form the envelope shown in FIG. 
9. The workpiece 202 which initially is in the form of a relatively thin, 
substantially flat sheet is placed over the fold plates 106 and 108, which 
are in their normal horizontal position as shown in FIG. 4, with a piece 
of relatively soft resilient backing material 204 such as, for example, a 
mat of a silicone sponge rubber, extending between the workpiece and the 
fold plates. It is noted that the ends of the material 204 extend flush 
with the projecting leg portions 94a and 96a, respectively, of the fold 
bars 94 and 96, and the ends of the workpiece 202 extend slightly 
outwardly from or beyond the ends of the material 204. 
To commence the operation, an operator presses button 184 which, through 
the air cylinder control unit 180, introduces air into the cylinder 120 
causing its piston rod 124, and therefore the slide plate 116 and the 
forming blade 110, to move from the position shown in FIG. 2 downwardly to 
a position where the rod 136 engages the plate 134, the lower edge portion 
of the forming blade engages in an abutting manner the workpiece 202 along 
a line halfway between its two ends and urges this portion of the 
workpiece against the flange 82 of the anvil 80. During this downward 
movement, the end portion of the blade 148 operatively engages the limit 
switch 142 which, through the air cylinder control unit 180, terminates 
the operation of the air cylinder 120 and therefore stops movement of the 
piston rod 124 and the forming blade 110 in the latter position. 
The operator then pushes the button 162 which actuates the heating element 
152 and the timer switch 166. The heating element 152 is thus energized 
for a predetermined time to apply heat to and thereby softening that 
localized region or portion of the workpiece 202 with which it is in 
contact, after which predetermined time the heating element is deenergized 
by the timer switch 166. The operator then pushes button 186 which causes 
the air cylinder 120 to move the forming blade 110 further downwardly 
against the resistance provided by the anvil 80 by virtue of the upwardly 
directed force applied against the anvil by the springs 38 and 40 acting 
through the levers 32, 34, 35, 38, the rods 54, 56, 58, and 60 and the 
support assemblies 68 and 78. This movement through the action of the 
support assemblies 68 and 78, the arms 54, 56, 58 and 60, and the levers 
30 and 32, results in a pivoting movement of the arms 54 and 56 about the 
rod 50, as well as a pivoting movement of the arms 58 and 60 about the rod 
52 along with movement of the arms 58 and 60 about the rod 52 along with 
movement of the rods 50 and 52. During this movement, the blade 148 
engages the limit switch 144, which, through the control unit 180, stops 
further movement of the forming blade 110 the arms 54, 56, 58 and 60 
attain a substantially vertical position as shown in FIG. 7 and by the 
dashed line in FIG. 1. The workpiece 202 is thus folded about a fold line 
extending along and within the localized region of the workpiece which had 
been softened by the heat generated by heater element 152. It is noted 
that, in the position of FIG. 7, the fold blades 106 and 108 urge the 
upper surfaces of the respective corresponding portions of the workpiece 
202 against the side faces of the forming blade 110. 
The operator then presses button 164 which activates the heater elements 
154 and 156 on the upper edge portions of the folding blade 110, as well 
as the timer switches 168 and 170. The heat generated by heater elements 
154 and 156 thus softens the workpiece 202 along localized regions spaced 
slightly inwardly from the ends of the workpiece and are deactivated after 
a predetermined time interval by the timer switch 168. The timer switch 
170 controls the operation of the air cylinder control unit in a manner to 
be described later. 
After the heating elements 154 and 156 have been deactivated by the timer 
switch 168, the operator then presses button 188 which, through the air 
cylinder control unit 180, causes the air cylinder 120 to move the forming 
blade 110 further downwardly a relatively short distance until the blade 
148 engages the limit-switch 146 to terminate further movement. This 
movement causes movement of the rods 54 and 56 and therefore the bar 84 
inwardly towards the forming blade 110 and a similar movement of the rods 
58 and 60 and therefore the bar 86, which, in turn, compresses the spring 
loaded buttons 90 and 92. This, in turn, causes the projecting portions 
94a and 96a of the fold bars 94 and 96, respectively, to urge the end 
portions of the material 204 and therefore the workpiece 202 outwardly and 
downwardly as shown in FIG. 8 to fold them. The timer switch 170, which 
had been actuated in a previous step as discussed above, functions, 
through the control unit 180, to maintain the assembly in the position 
shown in FIG. 8 a predetermined time, to permit the workpiece to cool 
properly. Upon the timer switch 170 turning off, the operator can push 
button 190 which actuates the air cylinder 130 through the control unit 
180, and causes the piston rod 131 to move upwardly with the nut 150 
engaging the blade 148 to force the forming blade 110 to its uppermost 
position, with this movement being assisted by the springs 38 and 40 and 
limited by the pins 46 and 48 engaging the levers 30 and 32, respectively. 
The workpiece can then be removed and its folded end portions overlapped to 
produce the finished product shown in FIG. which is readily adaptable to 
receive a battery plate, as discussed above. If desired, the overlapped 
ends of the envelope may be adhesively secured together utilizing known 
means, such as adhesives, sonic welding techniques, and so on. 
It will further be appreciated that the predetermined time intervals 
controlled by the timer switches 166, 168 and during which the heater 
elements 152, 154 and 156 are energized will depend upon the thickness of 
the workpiece material and the composition of this material. The same is 
true with respect to the predetermined time interval controlled by timer 
switch 170. Accordingly, these timer switches 166, 168, and 170 should be 
adjustable over a relatively wide range to enable the apparatus of the 
present invention to accommodate various thicknesses of various materials. 
In one exemplary embodiment of the invention, polyvinyl chloride based 
sheets were folded into the envelope shape of FIG. 9, suitable for use as 
a battery separator, wherein the sheets had a minimal thickness of about 
0.030 inches, the predetermined timing interval of heating elements 152, 
154, and 156 was about 1.5 seconds each, and the cooling-off cycle 
determined by switch 170 was in the range of about 30 to about 60 seconds. 
The resulting envelopes exhibited no sign of cracking in the localized 
regions corresponding generally to the fold lines thereof. 
Without limiting the present invention, it is thus seen that the apparatus 
described hereinabove enables a relatively brittle plastic workpiece to be 
folded along a plurality of fold lines subsequent to being selectively 
heated in localized regions thereof corresponding generally to said fold 
lines to prevent possible cracking of the material, all in a precise yet 
high-speed and economical manner. 
It is understood that variations of the apparatus and method disclosed 
above can be made by those skilled in the art without departing from the 
invention as defined in the appended claims.