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BACKGROUND OF THE INVENTION
This invention relates to the heat welding of thermoplastic expanded foam
materials in the form of essentially rigid sheets or blocks to form
articles such as trays or other cushioning pads or shapes.
SUMMARY OF THE INVENTION
As embodied in a tray forming machine, the invention includes a die cavity
in alignment with a mandrel that is reciprocable therethrough. A supply
hopper for preformed tray blanks is mounted adjacent the die cavity on a
table that also mounts a feed or kicker plate that is reciprocable through
the hopper to singly thrust one blank out of the hopper into an indexed
position over the die cavity.
The power means for the mandrel and kicker plate are coupled together in a
control system to effect a retraction of return stroke of the kicker plate
concurrently with the tray forming stroke of the mandrel into the die
cavity and, also, to cause the kicker plate to dwell in a retracted
position until the mandrel has been retracted out of the die cavity to a
dwell position in readiness for another cycle of reciprocation. The
control system includes an adjustable timer to vary the frequency of a
cycle of operation of the apparatus.
During an initial increment of movement of the mandrel into the die cavity,
at an initial relatively high velocity, opposed die plates of the cavity
fold the opposite side walls of the blank around the edges of the mandrel
into an erect position in which one pair of opposite side walls of the
blank, each having opposite end foldable corner tabs, have their tabs
projecting outwardly beyond the other erected pair of side walls. Voids
are defined at the corners of the die cavity by the opposed pairs of die
plates for the positioning of a radiant heat source in the vicinity of
each corner of the erected tray, in confronting spaced relationship to
those surfaces of the projecting corner tab and the adjacent corresponding
side wall which are to be heat welded together. The rate of advance of the
erected blank past the heat sources by the mandrel is selectively
controllable so that the duration of application of heat is just
sufficient to plasticize those areas which are desired to be welded
together while minimizing or preventing heat transfer into the foamed
material. Customarily, the rate of advance of the mandrel through the
heating phase is at a lower velocity than the initial sidewall erecting
velocity of the mandrel.
After the heating phase, the mandrel moves the tray through a corner tab
folding station at a higher velocity, the tab folding being accomplished
by a camming means co-acting with the mandrel. With this arrangement, the
heated areas to be welded together are brought into mutual contact,
without relative sliding movement therebetween, and, due to the increased
velocity of the mandrel, the open time between the heating and welding
phases is held to a minimum to minimize dissipation of heat from the
plasticized surfaces. Immediately upon completion of the tab folding
phase, the mutually contacting and heated surfaces are biased together
during decelerating movement of the mandrel, during which the welding
process is completed. Thereafter, the mandrel is retracted out of the
completely formed tray and out of the die cavity while the completed tray
is stripped from the mandrel by stripper bars positioned at the exit end
of the die cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an apparatus embodying the invention, with
portions thereof being broken away to reveal certain interior details of
construction.
FIG. 2 is a longitudinal sectional view taken on the line 2--2 of FIG. 1.
FIG. 3 is an end view of the tray forming section of the apparatus of FIG.
1, portions being cut away to reveal interior components thereof.
FIG. 4 is a schematic, exploded perspective view of certain elements of the
tray forming section of the apparatus.
FIG. 5 is a partial perspective view illustrating the configuration of a
corner area of the tray blank after passage through the sidewall erecting
phase and during passage through the radiant heating station, the heater
being illustrated in phantom outline.
FIG. 6 is a schematic, partial perspective view of a corner area of the
tray during the welding dwell phase and immediately after passage through
the tab following station.
FIG. 7 is a perspective view of the completed tray produced by the
apparatus of FIG. 1.
FIG. 8 is a partial sectional view on the line 8-8 of FIG. 4, on an
enlarged scale, showing details of the tray blank construction.
FIG. 9 is a schematic diagram of an electromechanical control circuit for
the apparatus of FIG. 1.
FIG. 10 is a schematic diagram of the mandrel power and control system.
Referring to the drawings, the apparatus illustrated in FIG. 1 is
especially adapted for the manufacture of protective trays 10, of the
configuration illustrated in FIG. 7, made from foamed polystyrene sheet
stock. However, the invention may be embodied in other forms of apparatus
for the production of articles of different configurations made from
sheets, slabs or blocks of other essentially rigid foamed thermoplastic
materials such as expanded polyethylene, expanded polypropylene, expanded
polyurethane or expanded polyvinyl chloride, or material provided with an
extremely thin film coating of a thermoplastic material such as
polyethylene. Accordingly, it is to be understood that the following
description of the presently preferred embodiment of the invention is
illustrative, and not limitative.
FIG. 4 includes a perspective view of the planform of a tray blank 11 that
is made of foamed polystyrene which may be on the order of 45-60 mils in
thickness. The blank 11 is preformed with two opposite pairs of hinge line
grooves 12 and 13 on both surfaces which define those areas of the blank
which will constitute two opposite pairs of sidewalls 14 and 15. The tray
blank 11 is also formed with four notches 16 to define foldable corner
tabs 17 which are extensions of those portions of the blank which will be
turned up to make the walls 14. FIG. 5 represents an intermediate step in
the formation of the tray in which the corner tabs 17 remain coplanar with
the corresponding wall 14. At this phase of the operation, a source of
heat plasticizes the adjacent confronting skin or surface A of the corner
tab 17 and a corresponding area B on the confronting surface of the wall
15 by radiation. As is illustrated in FIG. 6, the heated areas A and B are
thereafter immediately brought into mutually contacting abutment to permit
welding solidification thereof to occur while the mutually contacting
areas are briefly pressed together.
Referring to FIG. 1, the apparatus generally comprises a hopper and feed
section 20 and a forming section 21 for converting a blank 11 into the
tray 10 illustrated in FIG. 7. A base frame for the machine includes an
opposite pair of side frame members 22 having their ends adjacent the
forming section 21 rigidly interconnected by a cross bar 23. The hopper
and feed section 20 of the apparatus includes a sheet member 25 rigidly
secured on top of the framework providing a table on which a supply hopper
26 and a feeder or kicker plate 27 are mounted.
As is shown in FIG. 1, the supply hopper 26 is adapted to contain a stack
of the tray blanks 11. Preferably, the hopper is open sided, comprising
four corner posts 28 having their lower ends rigidly secured to the table
25. A front pair of the posts may be rigidly interconnected at their upper
ends by a girder strap 29 and the hopper may be partially closed at its
opposite sides by plates 30 each of which extends between a corresponding
pair of side posts. The rear pair of posts 28, at least along a major
portion of the rear face thereof, are provided with retainer straps 31,
which confront vertically extending retainer straps 32 secured to the
front pair of posts 28. The retainer straps 31 have their lower ends
terminating at the surface of the table 25 to prevent rearward
displacement of blanks as the kicker plate is retracted.
A vertically adjustable material thickness gauge is provided at the front
of the hopper 26 to prevent all but the lowermost one of the stack of
blanks 11 within the hopper from being fed into the forming section by the
kicker plate 27. This may take the form of a vertically extending strap 34
having its uppermost end adjustably secured to the midpoint of the
transverse hopper strap 29 and having its lower end similarly secured to a
transverse girder strap adjacent the lower end of the hopper. It will, of
course, be understood that the framing elements of the hopper 26
internally define a cross sectional area and planform to closely
complementarily receive a stack of horizontally disposed tray blanks 11.
Because of the low density of the expanded foam material, a column of the
blanks may not provide sufficient gravitational force to bias the
lowermost one into flat conforming relationship to the surface of the
table 25. Accordingly, a weight plate 35 may be placed within the hopper
on top of a stack of the blanks 11, the weight plate being provided with a
handle 36 to facilitate its removal and replacement upon periodic
replenishment of the diminishing supply of blanks within the hopper.
The kicker plate 27 is slideably secured to the top of the table 25 for
rectilinear reciprocation. Thus, the table 25 is centrally longitudinally
formed with an elongated slot 39 and a parallel pair of slots, not shown,
flanking the central slot and longitudinally offset therefrom. Each of the
latter slots slideably mounts a slider clamp 41. Similarly, the central
slot 39 is provided with a slider clamp 42 of inverted T-shape
configuration having its central stem portion secured to a rear portion of
the underside of kicker plate 27. Secured to the underside of the table
25, by means of a bracket 43, is a pnuematic cylinder 44 having a piston
rod 45 reciprocating through the rearwardly facing end thereof to have its
rear end connected, through a clevis 46, to the central slider clamp 42.
As will be apparent, upon reciprocation of the pneumatic piston within the
cylinder 44, kicker plate 27 is reciprocated into and out of the lower end
of the hopper 26 to singly feed a tray blank 11 into the forming section
21. Along its forward edge, the kicker plate is provided with a spaced
pair of tray blank pick up and pusher elements 47. Preferably each of
these is formed with a knife edge projection 48 extending forwardly beyond
the forward end of the kicker plate 27 and tapering rearwardly to a
forwardly facing shoulder 49, which may be given a forwardly inclined rake
angle so as to securely wedgingly engage the rearmost edge of a tray blank
11 for pushing it into the forming section 21.
Referring to FIG. 4, the die cavity comprises an opposed pair of side die
plates 50 and an opposed pair of a front die plate 51 and a rear die plate
52. The four die plates have identical vertical cross sectional profiles,
being of inverted L-shaped cross sectional configuration having horizontal
and vertical flanges joined by an arcuate section along a predetermined
radius in order to effect a folding of the tray wall sections 14 and 15 at
a desired rate as the mandrel forces the tray blank into the die cavity.
From FIG. 4 it will be observed that the forming curve sections of the
pair of die plates 50 are shorter than the tray wall portions 14 and that
the curved forming sections of the front and rear die plates 51 and 52 are
shorter than the wall portions 15 of the tray blank. Voids or clearance
spaces are thus provided at each corner of the die cavity to receive the
heater, corner tab folding, and welding dwell elements.
Referring to FIG. 3, each of the pair of side die plates 50 has its
horizontal flange secured to a corresponding one of the side frame members
22 by a suitable fastener means 55. As is best seen in FIG. 1, the lower
end of each die plate 50 has a framing strap 56 rigidly secured thereto,
externally of the die cavity, and the extremities of the pair of straps 56
are rigidly interconnected by a pair of framing straps 57 which are
secured to the front and rear die plate 51 and 52 externally of the die
cavity. As is indicated in FIG. 1, the horizontal flange of the forward
die plate 51 may comprise an integral rearward extension of the frame
member 23. The rear die plate 52 may have its horizontal flange formed as
an integral forward extension of the table 25 or, alternatively, may be
secured in the desired location by a transverse framing members of the
base framework of the apparatus. In any event, it will be understood that
the die plates 50, 51 and 52, when assembled in the apparatus, constitute
a rigid box-like die cavity structure having voids at the four corners
thereof.
The upwardly facing surfaces of the horizontal flanges of all four die
membes are coplanar with the upper surface of the table 25 and, in effect,
provide a coplanar extension thereof. In order to index a tray blank 11 in
the desired position over the die cavity, a stop member 60 is affixed to
the top of and extends across the length of the horizontal flange of the
forward die member 51, while one of a pair of side guide members 61 is
secured on top of each of the pair of opposite side die members 50. In
order to prevent rebound of a tray blank 11 from the front stop member 60,
the hopper 26 is provided along its lower end front exit with an elongate
hold down member 62 (FIG. 2) comprising a thin sheet of a flexible
material, e.g., half hard stainless steel, whose forward edge is adapted
to lightly bias the trailing edge of a tray blank onto the upper face of
the horizontal flange of the rear die member 52. As is shown in FIG. 3,
each of the pair of side guides 61 is formed with an inwardly directed lip
61a adapted to overlie a corresponding side edge of the tray blank 11. At
the forwardmost ends of each of the side guides 61, a forwardly tapering
member 64 may be secured to initially deflect corresponding forwardmost
portions of the wall areas 14 upwardly out of the plane of the body of the
tray blank.
The framework for mounting the mandrel and its power and control system
includes an opposed pair of side plates 67, each of which is secured to an
inner face of one of the side frame members 22 to project upwardly
thereabove. As is shown in FIG. 1, each of these side plates is formed
with an aperture to permit the extension therethrough of the corresponding
one of the side die members 50. The apex areas of the upper ends of the
pair of side plates 67 are rigidly interconnected by a box beam structure
68 to provide a rigid framework for supporting the power and control
components and, also, a sheet metal housing 69, the front panel of which
comprises a hinge supported door 70.
Internally of the housing 69, the beam 68 centrally supports a vertically
disposed double acting fluid (e.g., pneumatic) cylinder 72 having a
downwardly extending piston rod 73 whose lower end is rigidly secured to
the center of a rectangular mandrel 74. On opposite sides of the cylinder
72 the beam 68 provides bearing support for a pair of vertically
reciprocable mandrel stabilizing and guide rods 75 and 76 which also have
their lower ends rigidly secured to the mandrel 74.
The mandrel 74 has a planform that is substantially congruent to the
planform of the floor of the completed tray 10 and, preferably, an edge
thickness or depth at least as great as the height of the erected side
walls 14 and 15 of the tray. In addition, the inner vertical faces of the
die plates 50, 51 and 52 are spaced from the periphery of the mandrel 74 a
distance which is substantially equivalent to the thickness of the sheet
stock of the tray 11. Accordingly, referring to FIG. 3, when the mandrel
74 descends it engages that area of the blank 11 bounded by the hinge
lines 13. Upon further advance of the mandrel into the die cavity, the
side walls 14 and 15 are cammed or turned upwardly into the erect position
by the curved portions of the die plates 50, 51 and 52 and, upon further
advance of the mandrel into the die cavity, are constrained into the erect
position against the edges of the mandrel 74 by the surrounding interior
surfaces of the four die plates.
The initial increment of movement of the mandrel 74 into the die cavity
thus transports the blank 11 through a side wall erecting phase.
Immediately thereafter, an additional increment of movement of the mandrel
carries the blank through a heating station in which the areas A and B of
each corner are subjected to a source of radiant heat, as indicated in
FIG. 5. Further extension of the mandrel into the die cavity carries the
tray blank through a corner tab folding station and into a station at
which the areas A and B at each corner, having been brought into mutual
contact, are biased together for a sufficient period to permit welding
solidification of the plasticized surfaces.
The heating station is provided by four electrical resistance heating
elements 80, each of which is mounted from a bracket 81 secured to the die
cavity framework and from which it is electrically and thermally insulated
by suitable means. Thus, referring to FIG. 3, a pair of the brackets 81
may be secured at one end to the underside of the horizontal flange of the
front die plate 51 to project angularly relative to the vertical flange
thereof and into the open corner area of the die cavity. Preferably, the
heater elements 80 take the form of resistance heating elements of
cylindrical form, e.g., sealed "Calrod" units, having their longitudinal
axes equidistantly spaced from the areas A and B exposed thereto when the
side walls 14 and 15 of the tray blank have been erected to the positions
shown in FIG. 5. While not specifically illustrated, it will be understood
that the brackets 81 for the rear pair of heaters 80 may be secured to the
underside of the horizontal flange of the rear die plate 52, in locations
symmetrically corresponding to that of the front pair of heater elements
80, for heating the corresponding areas A and B during the downward
passage of the tray blank therepast after the corresponding wall portions
14 and 15 have been erected.
After the areas A and B have been plasticized, the corner tab 17 at each
corner is turned through 90.degree. by a camming means, which may take the
form of a curved rod 83. Each of the four rods 83 may be secured at one
end to the side frame member 56 at the lower end of the die cavity to
extend upwardly therefrom, thence to curve inwardly to intercept the lower
edge of the tab and deflect the corresponding corner tab 17 to bring the
plasticized areas A and B into abutment against the corresponding edge
area of the mandrel 74. At each open corner of the die cavity, a spring
band 84 has one end secured to an end portion of one of the transverse
frame members 57 to extend through approximately 270.degree. of arc to
present a free end with a surface confronting one side of the mandrel 74
and spaced therefrom approximately twice the thickness of the sheet stock
material from which the tray is made but with the spacing such as to
provide a slight interference whereby those portions of the side walls 14
and 15 including the areas A and B are compressed between the operative
face of the spring 84 and the side wall of the mandrel.
The front die plate 51 and rear die plate 52 are each externally provided
with a means for stripping the formed tray from the mandrel 74. Thus, as
is shown in FIG. 3 with respect to the front die plate 51, a laterally
spaced pair of stud bolts 86 have their shanks rigidly secured to the
external face of the vertical flange of the die plate 51 and each is
provided with a compression spring 87 between a head of the stud and one
surface of a stripper plate 88 that is mounted on the pair of studs 86.
The springs 87 normally bias the plate 88 into flush engagement with the
external face of the die plate 51. At opposite ends, the plate 88 projects
laterally beyond vertical edges of the die plate 51 terminating in
stripper tabs 89 having lowermost edges projecting inwardly relative to
the die cavity sufficiently to interfere with the passage of the
corresponding side wall 15 therepast. Upon such interference, the stripper
plate 89 is biased or cammed outwardly, sliding on the studs 86,
permitting passage of the corresponding side wall 15 whereupon the tray
enters the welding dwell station depicted in FIG. 6. After the welding of
the corner tabs has been completed, and upon retraction of the mandrel 74,
the stripper tabs 89 have returned to engagement with the upper edges of
the side walls 15, preventing return movement of the completed tray with
return movement of the mandrel.
As is shown in FIG. 10, both the mandrel cylinder 72 and kicker cylinder 44
have communication with a source of compressed air via a conduit 91 which
incorporates a pressure regulator 92. A conduit 93, out of a Tee fitting
94 in the supply line, has communication with a control valve 95 through
which the compressed air is supplied by conduits 96 and 97 to opposite
ends of the housing of the kicker cylinder 44 to effect controlled
reciprocation of the kicker plate 27. It will, of course, be understood
that the kicker cylinder 44 has a stroke greater than the corresponding
dimension of the tray blank 11 to be fed out of the hopper 26. The control
valve 95 is provided with a pair of exhaust flow restrictors 98 and 99 for
adjusting the velocity of the piston rod extension and retraction strokes
of the cylinder 44.
Similarly, another conduit 100 out of the Tee fitting 94 has communication
with a mandrel cylinder control valve 101 having conduits 102 and 103 to
opposite ends of the housing of the mandrel cylinder 72, the control valve
101 also being equipped with adjustable exhaust flow restrictors 104 and
105. The latter flow restrictor is connected in series, via a conduit 106,
with a cam actuated dump valve 107 which is also provided with an
adjustable exhaust flow restrictor 108.
Referring to FIG. 3, it will be seen that the mandrel cylinder control
valve 104 and kicker cylinder control valve 95 are mounted on top of the
box beam 68, within the housing 69. The dump valve 107 is mounted on the
beam 68 adjacent the mandrel control valve 104 and is provided with a
pivotally mounted control arm 110 whose free end mounts a roller 111. The
mandrel support rod 76 has the upper end of a strap 112 secured thereto,
the lower end of this strip being secured to the upper face of the mandrel
74. As is indicated in FIG. 2, the strap 112 is forwardly offset from and
parallels the support rod 76. The front face of this strap vertically
adjustably mounts a cam plate 113 by a pair of fasteners 114, carried by
the strap 112, and extending through a central longitudinally extending
vertical slot 115 of the cam plate. The cam plate 113 is disposed in the
same vertical plane as the dump valve roller 111 and, on one edge, is
formed with a downwardly facing cam edge 116 which develops upwardly into
a vertically extending roller track edge of predetermined length.
In FIG. 3, the mandrel 74 is shown in a fully raised position with a tray
blank 11 indexed over the die cavity. Upon actuation of the mandrel
control valve 104 to admit compressed air to the upper end of the mandrel
cylinder 72, the mandrel 74 is caused to descend at a relatively high
velocity to carry the mandrel through the side wall erecting station of
the die cavity. This first station of the cavity may be viewed as the
vertical distance between the solid outline position of the mandrel 74
shown in FIG. 3, and a lower position in which the lower face of the
mandrel occupies a plane intersecting upper ends of the heaters 80 or a
plane beneath a junction of the curved surfaces of the four die plates and
the internal vertically extending flat surfaces of the die plates. A
relatively high velocity of the mandrel through this first station is
attained since the area of the underside of the piston is less than the
upwardly facing or topside area of the piston, due to the presence of the
cross sectional area of the piston rod 73 while, at the same time, the
lower end of the cylinder 72 is vented to atmosphere through the exhaust
orifice 105.
As the mandrel 74 approaches the terminal portion of its passage through
the first station of the die cavity, the internal pressure within the
housing of the cylinder 72 under the piston increases until a desired
predetermined imbalance of the pressure differentials acting on the piston
is achieved. The desired degree of imbalance may be attained by
appropriate adjustment of the flow regulator 105. The mandrel 74 then
proceeds downwardly through the die cavity for the length of the heaters
80 and so passes through the heating station illustrated in FIG. 5 and at
a lower velocity than its velocity through the first station. The velocity
of the mandrel through the heating station may be adjusted by adjustment
of the exhaust flow orifice 105.
Upon or immediately after the lower face of the mandrel 74 passing through
the plane of the lower ends of the heaters 80, the cam surface 116 of the
cam plate 113 engages and depresses the pivotally mounted dump valve
roller 111. As a result, air pressure is relieved from the lower end of
the mandrel cylinder 72 through the exhaust orifice 108 at a more rapid
rate than the rate permitted by the exhaust orifice 105 alone. As will be
apparent, the duration of this accelerated rate of exhaustion is a
function of the length of the track of the member 113. Preferably, the
track length is substantially the same as the spacing between the plane of
the lower ends of the heaters 80 and the plane of the downwardly pointing
stripper tabs 89, which spacing includes the tab folding elements 83 and
spring biasing elements 84. Because of the increased velocity, the open
time between the radiant heating station and tab folding station of the
die cavity is minimized to minimize dissipation of heat from the
plasticized surfaces A and B.
Conventionally, pneumatic power cylinders (e.g., Wabco Task master) are
provided with cushion adjustment valves at each end. Accordingly, as the
mandrel 74 reaches the extremity of its extension stroke, the cushion
adjustment valve (which may be adjusted as desired) effects a deceleration
of the downward velocity of the mandrel, just prior to reversal of the
stroke. The formed tray is then in the position relative to the pressure
spring 85 illustrated in FIG. 6, wherein the tab 17 has been turned
through 90.degree. to bring the plasticized areas A and B into mutual
contact for their welding solidification. Accordingly, as a result of
proper adjustment of the cushion adjusting valve of the cylinder 72, the
mandrel downward velocity through the welding pressure phase of the
mandrel stroke is at a greatly decelerated rate, as compared to the
passage of the mandrel through the tab folding station in the open time
period, thus maximizing efficient utilization of the heat which has been
transferred to the areas A and B.
Referring to FIG. 9, the control system for the apparatus includes a power
circuit 120 having a master switch 121. Opposite sides 123 and 124 of the
heater power circuit are connected directly to the master switch so that
the heaters 80 are energized downwardly upon closing of the master switch.
A conductor 125 extends from one side of the master switch 121 to one side
of a mode selector switch 126. As is indicated in the figure, the selector
switch 126 is provided with hand feed, off, and automatic feed positions.
When the selector switch is in the hand feed positions, either one of a
manual mandrel "up" switch 128 and a manual mandrel "down" switch 130 may
be closed to close one side 127 of a circuit controlling actuation of the
mandrel valve 104. The mandrel valve 104 includes a pair of solenoids 132
and 134 having a common line connection 136 to the side 124 of the power
circuit. With this arrangement, either of the parallel switches 128, 130
may be closed to effect extension or retraction of the mandrel. Thus, in
the event that any of the tray blanks 11 becomes jammed within the die
cavity during the forming process, the selector switch 126 may be turned
to the hand feed mode and the mandrel manipulated as desired to accomplish
unjamming.
When the selector switch 126 is turned to the automatic mode, power is
supplied to one side 129 of a circuit to effect synchronous, properly
phased reciprocation of the mandrel cylinder 72 and the kicker cylinder
44. The kicker valve 95 includes solenoids 138 and 140 having a common
line 142 comprising a parallel extension of the common line 136 for the
mandrel valve solenoids and constituted the other side of the circuit for
automatic operation of the kicker valve.
The side 129 of the automatic circuit includes a conductor 131 to a
parallel pair of terminals of a material stop switch 144. The solenoid 132
of the mandrel valve, when energized, effects operation of the valve to
divert compressed air into the lower end of the mandrel cylinder 72. The
solenoid 132 is connected to the side 129 of the automatic circuit by a
conductor 133 that includes a normally open mandrel return switch 146.
Through a position 13 of a terminal strap the mandrel "up" solenoid 132 is
also connected in series with the side 127 of the hand feed circuit so
that the solenoid 132 may be energized by depression of the manual switch
128.
The material stop switch 144 has another pair of parallel terminals. A
conductor 135 from a normally open one of the pair of terminals extends
through a position 9 on the terminal strap (which is in series with the
side 127 of the hand feed circuit) to have the mandrel "down" solenoid 134
and kicker "out" solenoid 140 connected thereto in series by conductors
137 and 139.
The remaining terminal of the material stop switch 144 is connected by a
conductor 137 through a position 11 of the terminal strap to a parallel
pair of terminals of an adjustable automatic timer 148. When the material
stop switch 144 is in the normally closed position shown, the conductor
137 and its parallel pair of terminals within the timer 148 are normally
connected to the side 129 of the automatic circuit. Another terminal of
the timer 148 is connected to the other side of the power circuit by a
conductor 150 through a position 2 of the terminal strap. One of the
parallel pair of terminals of the timer 148 includes a normally closed
switch 152 whose duration of closure can be adjusted to vary the time
period during which the kicker "in" solenoid 138 is held in an open
condition. After the preset period of time, the switch 152 contacts a
fourth terminal of the timer which is connected to a conductor 139,
passing through terminal strap position 7, for connection to a terminal of
the kicker "in" solenoid 138.
Referring to FIG. 3, the material stop switch 144 is mounted on the front
face of the box beam 68 and is provided with a downwardly depending switch
actuating arm 156. As is shown in FIG. 2, the switch arm 156 is normally
biased to the substantially vertically extending position indicated in
phantom outline but is deflectable to the full line position by the
leading edge of a tray blank 11 being thrust into indexed position over
the die cavity. In order to provide clearance for the movement of the
switch arm 156 between the indicated positions, the mandrel 74 is formed
with a notch 157 in its forward edge and the front die plate 51 is formed
in both its horizontal and vertical flanges with a slot 158 to register
with a clearance notch 159 formed in the rear edges of the stop member 60.
Still referring to FIG. 3, the mandrel return switch 146 is also mounted on
the front face of the beam 68 and at its upper end is provided with a
switch arm 161 that is disposed in vertical alignment with a switch
actuator 162 carried at the upper end of the mandrel support rod 75. Thus,
when the mandrel descends under the force of the cylinder 72 the normally
open mandrel return switch 146 is closed upon the actuator 162 coming into
engagement with and depressing the switch arm 161, to initiate a return
stroke of the piston of the cylinder 72.
With the power switch 121 in the "on" position and with the mode selector
switch 126 in the "automatic" position, the sequence of operations of the
apparatus is as follows.
The timer 148 is of a type, e.g., Industrial Solid State Controls
(I.S.S.C.) model 1017 B-1, which automatically resets itself to a zero or
start position upon deenergization or by operation of the material stop
switch. Such restart or zero position is indicated by the solid line
position of the switch arm 152 in FIG. 9, bearing against a limit post and
out of contact with the terminal of the timer for the conductor 139. At
the same time, it will be understood that the timer circuit is closed on
the side 129 through conductors 131 and 137 and on the other side through
the conductors 124 and 150. Accordingly, after lapse of the preset period
of time for which the timer 148 is set, e.g., one tenth of a second, the
switch arm 152 will come into electrical contact with the timer terminal
for the conductor 139, as shown by the dotted line position.
Upon closing of the switch arm 152, the kicker "in" solenoid 138 is
energized to operate the kicker valve 95 for admission of compressed air
through the conduit 97 to effect movement of the kicker plate 27 into the
lower end of the hopper 26 to feed a tray blank 11 into indexed position
over the die cavity. The leading or front edge of the tray blank 11 moves
the switch arm 156 to the left, as viewed in FIGS. 2 and 9, thus opening
the conductor 137 of the timer circuit and closing the conductor 135 to
effect simultaneous energization of the mandrel "down" solenoid 134 and
the kicker "out" solenoid 140. As a result, the mandrel valve 104 is
operated to admit compressed air into the upper end of the pneumatic
cylinder 72 to carry the mandrel 74 downwardly into the die cavity. At the
same time, the kicker valve 95 is operated to admit compressed air through
the conduit 96 into the kicker cylinder 44 to move the piston rod 45
outwardly to withdraw the kicker plate 27 from the hopper 26. The material
stop switch 144 returns to the right hand position indicated in FIG. 9 to
close the conductor 137, reenergizing the timer 148 with the switch
element 152 having been returned to the restart position shown in solid
line in the figure.
The mandrel 74 descends through the stations of the die cavity at different
velocities in the manner previously described until the tray 10 has been
formed, whereupon the actuator 162 carried by the mandrel guide rod 75
engages the switch arm 161 to operate the mandrel return switch 146. As a
result, the conductor 133 is closed to energize the mandrel "up" solenoid
132, effecting operation of the mandrel valve 104 to admit compressed air
into the lower end of the mandrel cylinder 72. The mandrel is thus raised
to uppermost position, after which the automatic cycle of operation
recommences after expiration of the time period set into the timer 148,
which again closes element 152 on the timer terminal for the conductor
139.
Foamed thermoplastics such as polyethylene, polypropylene, polystyrene,
polyurethane and polyvinyl chloride have use temperatures within a range
of about 150.degree. to about 290.degree. F. Such materials, if subjected
to temperatures of over 300.degree. F., will melt, vaporize or decompose.
However, wit | | |
