Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to an apparatus for welding
plastic foils of the type comprising an essentially U-shaped
housing formed from two arms and a bridge piece that joins
the two arms together, the arms being rotatable relative to
each other about the longitudinal axis of the bridge piece, a
powered pressure roller arranged on each of the unattached
ends of each arm, a pressing mechanism pressing the pressure
rollers together, and a heating element.
DE-GM 83 01 191 describes a welding apparatus with an
essentially U-shaped housing, in which at the ends of the two
housing arms that lie in different planes, and the angular
position of which can be varied relative to each other, there
is an over-hung pressure roller. Each of the pressure
; rollers is connected through an appropriate gearing system to
a dedicated motor or to a releasable coupling through a
common motor. The welding apparatus incorporates two pairs
of rollers to support the lower of the two plastic foils that
are to be welded together or the base or sublayer.
DE-OS 35 35 760 describes another mobile welding apparatus
with an essentially U-shaped housing, from which the rollers
have been eliminated in order to save weight. In this
welding apparatus, each of the pressure rollers that is
arranged at the end of each housing arm has a dedicated motor
and a dedicated reduction gearing. The motors and the
gearing are arranged coaxially to the appropriate pressure
rollers. Since the motors project from the sides of the
housing arms, this particular welding apparatus is bulky and
awkward.
It is an object of the present invention to provide a mobile
apparatus for welding plastic foils, which not only weighs as
little as possible but is also of compact construction and
particularly convenient to use.
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According to the present invention there i5 provided in an
apparatus for welding plastic foils comprising a
substantially U-shaped housing formed from two arms, a bridge
piece joining said arms together, said being rotatable
relative to each other about the longitudinal axis of the
bridge piece, a powered pressure roller arranged on each of
the free ends of each arm, a pressing mechanism for urging
the pressure rollers together, and a heating element, the
improvement wherein a geared motor is arranged on the bridge
piece to drive both of the pressure rollers, said motor
having two opposing outputs which drive the two pressure
rollers in opposite directions through a gear system.
Because of the fact that a geared motor that is used to drive
the pressure rollers and which has two opposing outputs that
are each connected through gears to the associated pressure
roller is arranged on the cross-piece of the U-shaped
housing, it has been possible, on the one hand, to reduce the
weight of the apparatus by eliminating one motor and, on the
other, to arrive at a more compact construction by
eliminating parts that project beyond the sides of the
housing. As a consequence of these two advantageous
characteristics, the welding apparatus configured according
to the present invention is particularly suitable for the
production of tunnel linings, in which, when welding is being
carried out on vertical walls or overhead, the whole weight
of the welding apparatus has to be borne by one operator.
The use of a single motor for both pressure rollers entails
the added advantage that the pressure rollers always run
synchronously with each other.
An even more compact construction can be achieved by
arranging the geared motor within the tubular bridge piece
that is closed in around its periphery, which entails the
additional advantage that the geared motor is encapsulated
and th~s protected against dirt and damage.
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If the drive motor for the pressure rollers is arranged
within a tubular pressure element of the pressing mechanism
at a distance from and parallel to the bridge piece of the U-
shaped housing and the drive motion of the motor to the two
geax systems that are connected with the pressure rollers is
split with the help of a shaft that is supported within the
bridge piece, it is possible to use a geared motor with only
one output as the drive motor. A geared motor that has only
one output is narrower by the length of the gearing that has
been eliminated, which makes it possible to make the housing
of the apparatus, i.e., the bridge piece and the pressure
element correspondingly narrower. Even though the saving in
weight brought about by the elimination of one gear system
for the geared motor may be balanced out by the shaft in the
bridge piece that is now required and the additional gearing
that connects the shaft with the geared motor, the reduction
in the length of the bridge piece, of the pressure element,
and of the bearings for the pressure rollers will result in a
further and perceptible reduction in weight of the whole
system.
However, of even greater signi~icance is the advantage that
because of the reduction in the weight of the housing the
apparatus can be made much narrower and thus, overall, more
compact and consequently considerably more convenient.
By making the operating lever adjustable into a position that
is essentially parallel to the housing arm that supports it,
once the arms have been moved into the working position, it
is also possible to arrive at a comparatively flat
construction for the apparatus.
The invention will now be described in more detail, by way of
example only, with reference to the accompanying drawings in
which:-
Figure 1 is a plan view of the welding apparatus;
Figure 2 is a cross sectional drawing taken on the line II-II
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in figure l;
Figure 3 is a cross section taken on the line III-III in
figure l;
Figure 4 is a plan view of the welding apparatus of a second
embodiment;
Figure 5 is a further view of the welding apparatus;
Figure 6 is a side view of the welding apparatus;
Figure 7 is a sectionized plan view of the welding apparatus
in a third embodiment;
Figure 8 is a partially cross-sectioned side view of the
welding apparatus;
Figure 9 is a side view of the pressure arm clamped onto the
pressure element; and
Figure 10 is a cross sectional view of the adjusting
. 15 mechanism for the pressure arm, taken on the line IV-IV in
: figure 2.
The welding apparatus shown in figures l to 3 has an
essentially U-shaped housing 1 that consists of two arms 2
and 3 and of a bridge piece 4 that connects these arms with
each other. The arms 2, 3 are hollow and each has a
removeable side wall 5, 6.
The bridge piece 4 is formed from two bearing sleeves 7, 8
that can telescope into each other, of which the outer
bearing sleeve 7 is rigidly c'onnected to the arm 2 and the
inner bearing sleeve 8 is rigidly connected to the arm 3.
The inner bearing sleeve 8 consists of an annular part 9, a
pipe section lO and an extended hub 11, these parts being
connected rigidly to each other by welds. The hub 11
incorporates a flange 12, a base part 13 with relatively
thicker walls, and an extension 14. At the end of the outer
bearing sleeve 7 there is a stepped extension 15, and at the
other end there is a cylindrical extension 16.
- The extension 16 of the outer bearing sleeve 7 lies on the
; hub 11 and together with this forms a bearing 17. A ball
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bearing 18 is arranged on the extension 14 of the hub 11 and
the extension 15 of the outer bearing sleeve 7 rests on this.
The two bearing sleeves 7 and 8 are supported on each other
so as to be able to rotate through the bearings 17 and 18,
whic:h means that the arms 2 and 3 can also be rotated
relative to each other.
Within the bearing sleeve 8 there is a known geared motor 19
that consists of a centrally arranged motor section 20 and
two epicyclic gears 21, 22 that are installed outside. Each
epicyclic gear 21, 22 has an output shaft 23 or 24,
respectively. The geared motor 19 is connected ta the inner
bearing sleeve 8 through the bearing plate 25 so as to be
unable to rotate independently of this, in that the epicyclic
gear 22 is bolted up with the bearing plate 25 and this is
bolted up with the annular part 9. The other end of the gear
motor 19 is supported in a bearing plate 26 that is bolted up
with the epicyclic gearing 21 and rests with one section (not
described in greatsr detail herein) on the extension 14 of
the hub 11 so as to be radially supported. A shoulder 27 of 20 the bearing plate 26 presses against the inner ring of the
ball bearing 18 and thus holds the outer ring of the ball
; bearing 18 in contact with a shoulder of the extension 15 of
the outer bearing sleeve 7 and, on the other hand, acts as a
contact surface for the face of the extension 16 on the
flange 12.
A notched-belt pulley 28 is secured to the shaft 23 and a
notched belt 29 passes over a notched-belt pulley 30 that is
secured on a shaft 31 that floats in the arm 2. A pinion 32
is secured to the shaft 31 and this engages with a similarly
floating shaft 33. A notched-belt pulley 35 is secured to
the shaft 33~ The notched belt 36 also passes over the
notched-belt pulley 37 that is secured to one end of a shaft
38. The shaft 38 is accommodated in a bearing sleeve 39 that
is secured to the arm 2 and supports at its other end a
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pressure roller 40 that is rigidly secured to this. The two
pinLons 32, 34 form a reversing gear 41.
A notched-belt pulley 42 is secured to the shaft 24 and a
notched belt 43 runs around this. The notched belt 43 also
passes over a notched-belt pulley 44 that is secured to the
end of a shaft 45. The shaft 45 is accommodated in a bearing
sleeve 47 that is secured on the arm 3 and supports at its
other end a pressure roller 47 that is connected rigidly to
it.
An electrically heated heating wedge 49 is arranged on the
arm 3 with the help of a parallel crank mechanism 48 that can
be moved back and forth between the retracted rest position
shown in figure 1 and a working position that is tight
against the pressure rollers 40, 47, by means of a handle 50
that is connected to the parallel crank mechanism 48.
Two spring rods 51 that are parallel to each other are
secured in the base part 13 of the hub 11 and these extend
through an opening 52 in the outer bearing sleeve 7 and
extend essentially along the arm 2. The two spring rods 51
are enclosed by two opposing double profile rollers 53, 54
that are so supported on a first supporting plate 55 as to be
freely rotatable. The first supporting plate 55 is arranged
so as to be adjustable on a second supporting plate 58,
transversely to the longitudinal axis of the spring rods 51,
this being done with the help of vertical slots 56 and
corresponding screws 57. The second carrier plate 58 is
arranged so as to be adjustable on a retaining plate 61,
parallel to the longitudinal axis of the spring rods 51 with
the help of horizontal slots 59 and corresponding screws 60.
The retaining plate 61 is arranged rigidly on the arm 2
through an interposed piece 62, which means that the carrier
plate 58 can be moved on the retaining plate 61 by one or
more multiples of the distance between the drilled holes.
The components 51 to 62 form a pressing mechanism 64.
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Runners 65, 66 that are triangular and rounded off at the
prolecting tip are arranged on the ends of the arms 2 and 3
tha~ are ad;acent to the bridge piece 4.
The method of operation of the welding apparatus will now be
described.
The welding apparatus is used to produce overlapping seams in
plastic foils, this being done particularly when lining
tunnels in which the welded seams are to be made mainly in a
vertical plane and overhead.
The welding apparatus is so arranged between the plastic
foils that are to be welded together that one plastic foil
runs beneath the bridge piece 4 and the heating wedge 49 and
the other plastic foil runs above the bridge piece 4 and the
heating wedge 49, so that they lie directly one on top of the
other between the pressure rollers 40, 47.
The welding pressure between the pressure rollers 40, 47,
which is required to complete the welding procedure, is
generated by the pressing mechanism 64. When the two
supporting plates 55, 58 are appropriately adjusted the two
spring rods 51 shown in figure 2 are tensioned downwards by
the upper double profile roller 53, when a turning moment is
exerted on the base part 13 that supports the spring rods 51
and thus on the inner bearing sleeve 8 and the arm 3 that is
connected with it, which means that the uppermost pressure
roller 47 is pressed against the pressure roller 40 that is
located beneath it.
The pressing mechanism 64 can accommodate two basic
adjustments, namely, on the one hand, the magnitude of the
initial stressing force and on the other hand, the degree of
the springing effect of the spring rods 51. The initial
stressing force is adiusted by moving the supporting plate 55
transversely to the longitudinal axis of the spring rods 51.
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The stiffness of the springing action of the spring rods 51
can be adjusted by moving or displacing the supporting plate
58 parallel to the longitudinal axis of the spring rods 51,
when the effective length of the spring rods 51 is changed.
Thus, optimal operating conditions can be adjusted for
specific foil materials and foil thicknesses by the two
, different adjusting possibilities of the pressing mechanism
? 64. So, for example, when welding HDPE foils, it is
necessary to use relatively high pressure. At the same time,
in addition to the initial stressing it is also desirable to
have a very stiff spring action so that when welding is being
done on a construction site, dirt such as grains of sand and
small stones which could accidentally get between the foils
are pressed into the softened foil so that the necessary
welding pressure can be maintained at these points as well.
In contrast to this, insofar as larger transition points such
as, for instance, transverse seams, are to be crossed during
the welding process, the springs are set for a high degree of
initial stressing in order that the initial stressing force
' 20 does not have to be reduced when negotiating these cross-over
points.
; Should a particularly low welding pressure be required, then
work can be carried out using only one spring rod 51. In
contrast to this, if extremely high welding pressure is
required, then spring rods of a greater cross section can be
used.
Since the whole pressing mechanism 64 as shown in figure 2
does not extend beyond the upper and lower sides of the arm 2
that supports it, the overall welding apparatus is kept very
compact and convenient.
Once the welding pressure has been adjusted, the heating
wedge 49 that has been heated to the required welding
temperature is moved into the welding position. As soon as
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this heating wadge 49 reaches the required welding position,
the geared motor 19 is switched on, whereupon the welding
apparatus moves relative to the foil with the help of the
driven pressure rollers 40, 47, whereupon the softened areas
of foil are bonded to each other so as to form a welded seam.
The welding apparatus that is shown in figures 4 to 6 is
identical to the welding apparatus described in the first
embodiment as far as the housing and the drive systems are
concerned. The essentially U-shaped housing 1 also consists
of the two arms 2, 3 as well as the bridge piece 4 that
hinges these together and in which the geared motor for the
pressure rollers 40, 47 (not shown in this instance) is
arranged. The welding apparatus also has a heating wedge 49
that is mounted on a parallel crank mechanism 48. Further,
triangular runners 65, 66 that are rounded over at the
projecting tips are secured to the adjacent ends of the arms
2, 3.
; In contrast to this, the pressing mechanism 80 that is used
to generate the welding pressure is of a completely different
construction to the pressing mechanism 64 used in the first
embodiment. The pressing mechanism 80 incorporates a rod-
like pressure element 81 that is secured to the runner 65 of
the arm 2 and this extends parallel to the bridge piece 4, at
a distance thereto, parallel to its longitudinal axis. An
angle piece 82 is secured to the unattached end of the
pressure element 81 and this incorporates an L-shaped
horizontal angle plate 82a. The pressure element 81 and the
angle piece 82 together form a pressure beam 83. A threaded
spindle 85 is secured within a rotary piece 84 that is
accommodated in the runner 66 and this spindle extends
through a drilled hole 86 in the runner 66 and through a
drilled hole (not shown herein) in the plate 82a. Within the
part of the threaded spindle 85 that is above the plate 82a
there is a handle 87 and a plurality of disk springs 88 that
rest on the plate 82 through the medium of a washer 89. The
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components 85, 87, 88, and 89 together form a spring
mechanism 90. A stop washer 91 that has a corresponding
internal thread, and which can be adjusted for height, is
arranged beneath the plate 82a on the threaded spindle 85.
On the arm 3 there is an angle bracket 92 on which a handle
93 or 94 that extends transversely to the arms 2, 3 is
secured. A rod 95 that can be moved longitudinally is
accommodated in the angle bracket 92 and the lower end of
this supports a pressure piece 96 and is also connected with 10 a toggle joint system that incorporates a handle 97. The
components 92 and 95 to 98 together form an adjusting
mechanism 99.
Up to the point of adjustment of the welding pressure, the
remaining functions of the welding apparatus are the same as
in the welding apparatus described in the first embodiment,
so there is no need for a more detailed description of these.
The level of the welding pressure is adjusted with the help
of the handle 87. Turning the handle 87 down presses the
disk springs 88 more strongly against the plate 82a and thus
press the pressure beam 83 downwards as a whole. The
pressure that acts on the pressure beam 83 causes a turning
moment that acts in a clockwise direction as in figure 6 to
be exerted on the runner 65. Because of this turning moment,
the arm 2 is pivoted in a clock~ise direction as shown in
figure 6, which means that the pressure roller 40 is pressed
upwards against the pressure roller 47.
The overall angle between the àrms 2, 3 that are in the
welding position can be limited by means of the stop washer
91, i.e., the arms or the pressure rollers 40, 47 cannot be
moved further towards each other if the angle plate 82 is
resting on the stop washer 91. In this way, it is possible
to adjust the thickness of the welding seam within very
precise limits.
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The arms 2, 3 can be moved apart with the help of the
adjusting mechanism 99, whereupon two new foils can be
introduced without any problem between the pressure rollers
40, 47. To this end, the handle 97 is swung downwards and
thus the rod 95 is also moved downward. In the course of
this movement, the pressure piece 96 comes into contact with
the angle plate 82 that is resting on the stop washer 91 and
causes the pressure beam 83, which acts in this case as a
two-arm lever, to be pivoted as a whole about the stop washer
91 that now acts as a pivot axis, this pivoting movement, as
shown in figure 4, taking place in a counter-clockwise
direction. The pivoting movement leads to an elastic
deflection of the pressure element 81 that is connected
rigidly to the runner 65, whereupon a turning movement that
acts in a counter-clockwise direction as in figure 6 is
exerted on the runner 65 which together with the arm 2 can be
pivoted about the longitudinal axis of the bridge piece 4.
As soon as this turning movement is stronger than the turning
movement that is generated by the spring mechanism 90 in the
opposite direction, the arm as in figure 6 is pivoted
counter-clockwise, whereupon the prçssure roller 40 is moved
away from the pressure roller 47.
The welding apparatus of the third embodiment has an
essentially U-shaped housing 100 that consists of two arms
- 25 101, 102 as well as a bridge piece 103 that joins these with
each other. The arms 101, 102 are hollow and each has a
removeable side wall 104, 105.
The bridge piece 103 is formed from two bearing sleeves 106,
- 107 that can telescope into each other, of which the outer
io bearing sleeve 106 is connected with the arm 102 and the
inner bearing sleeve 107 is connected rigidly with the arm
101. The outer bearing sleeve 106 is supported through two
needle bearings 108~ 109 so as to be able to rotate on the
inner bearing sleeve 107, which means that the arms 101, 102
can rotate relative to each other.
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The needle bearing 108 rests on one side on an extension 110
of the inner bearing sleeve 107 and on the other side on a
safety ring 111 that is arranged within the outer bearing
sleeve 106. The needle bearing 109 rests on one side on a
safety ring 112 that is arranged within the inner bearing
sleeve 107 and at the other end on a bearing plate 113 that
is bolted to the arm 102.
A continuous shaft 115 is supported in two bearing sleeves
114 in the inner bearing sleeve 107. A notched-belt pulley
116 and immediately adjacent thereto a pinion 117 are secured
on the end of the shaft 115 that extends into the arm 101;
this pinion rests at its side on the inner side of the arm
101. On the other end of the shaft 115 that extends into the
arm 102 there is a notched-belt pulley 118 that is adjacent
to the bearing plate 113 at the side. The notched-belt
pulleys 116, 118 that are secured to the shaft 115, and the
pinion 117 form an axially acting mounting for the arms 101,
102.
,, The pinion 117 engages with the pinion 119 that is secured on
a shaft that floats in the arm 101. In addition, a notched-
belt pulley 122 is secured to the shaft 120 and a notched
belt 123 passes over this. The notched belt 123 also passes
over a ~otched-belt pulley 124 that is secured at the end of
a shaft 125. The shaft 125 i's accommodated in a bearing
sleeve 126 that is secured to the arm 101 and supports at its
other end a pressure roller 127 that is rigidly connected to
this. The components 117, 119 to 124 together form a first
gearing system 128 that can be reversed.
A notched belt 129 runs over the notched-belt pulley 118 and
also passes over a notched-belt pulley 131 secured to the end
of a shaft 130. The shaft 130 is accommodated in a bearing
sleeve 132 that is secured on the arm 102 and supports at its
other end a pressure roller 133 that is connected rigidly to
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it. The components 118, 129 and 131 together form a second
gearing system 131 that runs in one direction only.
A pressure element 135 is secured on the end area of the arm
101 that is opposite the pressure roller 127 and this is a
component part of a pressing mechanism 136 that is described
in greater detail below. A known geared motor 137 is secured
to the arm 101 and this extends within the pressure element
135 without, however, coming into contact with this. The
geared motor 137 consists of a motor section 138 and an
epicyclic gear train 139 that is flanged onto the side
thereof. The epicyclic gear train 139 incorporates a shaft
140 that forms the output of the gearing system.
A notched-belt pulley 141 is secured to the shaft 140 and a
notched belt 142 passes over this. The notched belt 142 also
passes over the notched-belt pulley 116 described heretofore.
The components 116, 141, and 142 together form a gear system
143 that forms a positive drive connection between the output
of the epicyclic gear train 139 and the shaft 115.
A pressure arm 144 is clamped onto the pressure element 135
so as to be unable to rotate independently thereof, and as is
shown in figure 3. This consists of a slotted adaptor sleeve
145, an arm 146 of rectangular cross-section, which extends
above the arm 102 and parall~l thereto, and an extension 147
that extends transversely to this.
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A narrow supporting plate 148 is secured on the end of the
arm 102 that is opposite the pressure roller 133. A threaded
spindle 150 is arranged so as to be able to pivot on the
supporting plate 148 with the help of a collar screw 149, and
this threaded spindle passes through a drilled hole 151
(figure 3) in the extension 147. In that part of the
threaded spindle 150 that is above the extension 147 there
are a handle 152 and a plurality of disk springs 153, that
rest through the medium of a washer 154 on the extension 147.
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The components 150, 152, 153, and 154 together form a spring
mechanism 155.
A stop washer 156 that can be adjusted for height and which
- incorporates an inside thread is arranged on the threaded
spindle 150 beneath the extension 147.
A bracket 157 that is of U-shaped cross section is secured to
the arm 102 and the arm 146 extends into this. A shaft 159
is supported in the bracket 157 above a flat extension piece
158 of the arm 146; at one end, this shaft 159 incorporates a
collar 160 and at the other a clamping ring 161. An
eccentric 162 is secured to the shaft 159 and this acts in
conjunction with an extension piece 158 of the arm 146. In
addition to the eccentric 162, an operating lever 163 is also
mounted on the shaft 159 so as to be able to rotate. A pin
164 that extends to the side in the direction of the
eccentric 162 is arranged within the operating lever 163.
Within the eccentric 162 there is a plurality of drilled
holes 165, the diameter and distance from the shaft 159 of
i which are so dimensioned that the pins 164 can fit into them.
A compression spring 166 that is arranged on the shaft 159
: holds the operating lever 163 in contact against the
eccentric 162. The pin 164, the drillings 165, and the
compression spring 166 together form a releasable coupling.
Within the console 157, abové the eccentric 162, there is a
cut- out 167 that makes it possible for the operating lever
163 to be pivoted in a position that extends perpendicular to
the arm 102. The components 159 to 166 together form an
adjusting mechanism 168.
An electrirally heated heating wedge 170 is arranged on the
arm 102 with the help of a parallel toggle lever 169 that can
be moved by a handle 171 that is connected to the parallel
toggle lever 169, back and forth between a rest position that
is at a distance from the pressure rollers 127, 133 and into
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a working position, shown in figure 1, that is close to the
pressure rollers 127, 133.
The welding apparatus is used to produce overlapping seams in
plastic foils, this being done, in particular, when lining
tunnels in which the welded seams are mainly made in a
vertical plane and overhead.
The welding apparatus is so arranged between the plastic
foils that are to be joined together that one plastic foil
runs beneath the bridge piece 103 and the heating wedge 170
and the other plastic foil runs above the bridge piece 103
and the heating wedge 170, and at the same time they lie
directly one on top of the other between the pressure rollers
127, 133.
The welding pressure between the pressure rollers 127, 133
that is required to execute the welding process is effected
by means of the pressing mechanism 136.
The level of the welding pressure is adjusted with the help
of the handle 152. By rotating the handle 152 downwards the
disk springs 153 are pressed more strongly against the
extension 147 which means that the pressure element 133 is
pressed downwards. The contact pressure that acts on the
pressure element 135 means tnat a turning moment in a
clockwise direction, as in figure 2, is exerted on the arm
101. Because of this turning moment, the arm, as in figure
2, is pivoted in a clockwise direction, whereby the pressure
roller 127 being pressed downwards against the pressure
roller 133 thereby.
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Because of the stop washer 156, the common angle subtended
between the arms 101, 102 that are in the welding position
can be limited, i.e., the arms or the pressure rollers 127,
133 cannot be moved further towards each other if the
~ xtension is lying on the stop washer 156. In this way, the
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thickness of the welded seam that is to be produced can be
: adjusted within very precise limits.
Using the adjusting mechanism 168, the arms 101, 102 can be
moved away from each other, whereupon two new foils can be
introduced between the pressure rollers 127, 133 without any
problem. To this end, the operating lever 163 is moved
upwards from the position that is shown in figure 2. The
eccentric 162 that is thus rotated by the pin 164 tilts the
arm 146 in a counter- clockwise direction, whereupon the
extension 147 of the pressure arm 144 rests against the stop
washer 156. Since the pressure element 135 and the pressure
arm 144 are connected rigidly to each other, and thereby form
a continuous pressure beam 172, the adjusting movement that
comes from the adjusting mechanism 168 ensures that the
pressure beam 172, which in this case acts as a supporting
two-arm lever, is pivoted as a whole about the stop washer
156 that now acts as a pivot axis. The pivoting movement
leads to an elastic deformation of the pressure element 135
that is connected rigidly with the arm 101, whereby a turning
moment is exerted on the arm 101. As soon as this turning
moment is stronger than the turning moment generated by the
spring mechanism 155 in the opposite direction, the arm 101,
as in figure 2, is pivoted in a counter-clockwise direction,
whereby the pressure roller 127 is moved away from the
pressure roller 133.
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