Vacuum assisted web drive for corrugator double backer

A double backer for curing the web bonding adhesive and drying the corrugated paperboard web utilizes a web holddown apparatus for maintaining the web in intimate drying contact with the lower heating units which does not require the use of a driven holddown belt. The web is pulled through the double backer by a downstream vacuum conveyor section comprising a single belt or a series of transport belt sections to the upper surfaces of which a vacuum is applied. The vacuum drive belt may have portions which are unsupported between laterally spaced vacuum slots, supported on a reduced friction support surface, or supported by air bearings to reduce friction and drive power requirements.

BACKGROUND OF THE INVENTION 
The present invention pertains to a double backer for the production of 
corrugated paperboard and, more particularly, to a double backer in which 
the conventional driven web holddown belt is eliminated and replaced with 
a unique vacuum traction device. 
In a typical prior art double backer, a liner web is brought into contact 
with the glued flute tips of a single face corrugated web, and the freshly 
glued double face web is then passed over the surfaces of a number of 
serially arranged heating units, usually steam chests, to cause the 
starch-based glue to set and to drive moisture from the web. Double face 
web travel over the flat heated surfaces of steam chests is typically 
provided by a wide driven holddown belt in direct contact with the upper 
face of the corrugated web. The top face of the belt, in turn, is held in 
contact with the traveling web by any of several types of weight or force 
applying devices, well known in prior art. For example, the holddown belt 
may be engaged by a series of weighted ballast rollers, it may be forced 
into contact with the web by air pressure from a system of nozzles located 
over the web, or an arrangement of inflatable air bladders may be operated 
to press the moving holddown belt into contact with the double face web. 
It is also known to provide means for varying the ballast load applied to 
the holddown belt and web, both longitudinally in the machine direction 
and laterally in the cross machine direction. 
The use of a driven holddown belt in a double backer has a number of 
attendant disadvantages. The holddown belt must be mounted for continuous 
travel in the manner of the conventional continuous conveyor belt system 
and, therefore, must also include a separate belt drive means. The 
holddown belt also must necessarily overlie the entire surface of 
corrugated web, at least in the heating section, and, as a result, may 
inhibit the escape of moisture from the board as it dries. Also, the edges 
of the belt which overhang the edges of the corrugated web run in contact 
with surfaces of the steam chests or other heating surfaces and are 
subject to wear. 
SUMMARY OF THE INVENTION 
A double backer is provided in which the driven holddown belt is 
eliminated. Stationary holddown strips, extending parallel to one another 
in the direction of web movement, are supported from above to contact the 
entire web across its width and along the heating section. A separate 
downstream vacuum assisted conveyor, in accordance with the present 
invention, is used to pull the corrugated web through the heating section. 
The vacuum assisted conveyor apparatus includes a continuous web transport 
belt which underlies and supports the web across its lateral width, and 
means are provided for driving the belt. In its most basic embodiment, the 
vacuum assisted conveyor apparatus of the present invention may utilize a 
generally flat surface belt for the vacuum conveyor, which belt is 
provided with a series of openings to direct a vacuum applied from below 
to the corrugated web or other web being pulled by the belt. In the basic 
embodiment, the lower belt support structure may include a flat plate 
underlying the entire vacuum belt and provided with two patterns of holes, 
one comprising lines of vacuum openings aligned with the belt openings to 
apply vacuum air flow from plenums attached to the lower surface of the 
plate and a series of apertures between the vacuum openings to modulate or 
prevent the propagation of vacuum force against the underside of the belt. 
The belt may include spaced raised protrusions on the upper belt surface, 
which protrusions have flat surface portions defining a web contacting 
surface, said protrusions defining open channels therebetween. Openings in 
the belt provide communication between the lower belt surface and the 
upper belt surface, including the channels, if present. A vacuum source is 
operatively connected to the openings to supply negative pressure to the 
upper belt surface or the channels sufficient to hold the web to the 
moving belt. 
In one embodiment, the raised protrusions comprise a series of discrete 
support elements, and the channels extend between the support elements 
both longitudinally and laterally over the belt. The channels are 
interconnected in this embodiment. 
In a presently preferred embodiment, the channels in the web transport belt 
are defined by a series of laterally spaced raised longitudinal ribs. The 
ribs are continuous along the length of the belt and, thus, define 
continuous channels therebetween. The belt openings comprise laterally 
spaced lines of apertures, each of which lines of apertures is positioned 
within a channel. 
The apparatus also includes a support structure which underlies the belt 
and provides sliding support for the driven belt. In one embodiment, the 
support structure includes a series of parallel laterally spaced support 
surfaces which extend the length of the conveyor, a longitudinal vacuum 
distribution slot in each support surface connected to the vacuum source, 
and the belt openings comprising a line of apertures aligned with each 
vacuum distribution slot. In this embodiment, each of the vacuum slots 
includes a recessed vacuum surface which is positioned below the support 
surface. A series of spaced vacuum openings is provided in the vacuum 
surface of each slot. Preferably, the support structure includes a vacuum 
plenum for each vacuum slot, and control means are provided for 
selectively connecting the vacuum source to each of said vacuum plenums. 
Conveniently, pairs of corresponding plenums on opposite sides of the 
centerline are arranged so each pair is commonly controlled. The upper 
surface of the belt may include a gridwork of adjoining frame sections, 
each of which is defined by an enclosing rib having a flat outer surface 
coplanar with the web contacting surface portions of the protrusions, each 
frame positioned to be bisected by the longitudinal centerline of a 
support surface. 
In the presently preferred embodiment of the invention, the support surface 
comprises a foraminous plate which includes a series of laterally spaced 
lines of vacuum openings, each of which lines of vacuum openings is 
aligned with certain of the openings in the belt. In the embodiment in 
which the channels are defined by a series of spaced, longitudinally 
extending ribs, a line of vacuum openings in the support plate is aligned 
with a line of apertures in the belt. In this embodiment, each line of 
vacuum openings in the support plate includes a vacuum plenum connected to 
the vacuum source. Appropriate control means are provided to selectively 
connect the vacuum source to each of said plenums, either individually or 
in similarly positioned laterally spaced pairs. In this embodiment, the 
support plate preferably includes patterns of air pressure equalization 
holes which are positioned between the vacuum openings in the plate and, 
by providing a controlled leakage of ambient outside air, prevent the 
propagation of vacuum across the entire underside of the belt. 
The apparatus of the present invention is particularly adapted for moving a 
double face corrugated paperboard web through the heating section of a 
double backer, and the apparatus broadly comprises a web supporting 
conveyor belt positioned downstream of the heating section, means for 
driving the belt in the direction of web movement through the heating 
section, a belt support structure which includes a vacuum plenum and a 
vacuum source operatively connected to the plenum, and openings in the 
belt providing communication between a web contacting surface on the belt 
and the vacuum plenum. The belt includes a series of discrete raised 
support elements having flat surface portions which define the web 
contacting surface, with said support elements defining therebetween a 
network of open channels, and the openings extending through the belt and 
in communication with the channels. In the preferred embodiment, the 
support elements comprise laterally spaced longitudinally extending ribs. 
The belt may also be provided with a gridwork of adjoining frame sections 
which extend longitudinally and laterally thereover, the longitudinally 
extending frame sections defining a plurality of rows, each frame section 
defined by an enclosing rib which has a flat outer surface coplanar with 
the flat surface portions of the raised support elements, and wherein the 
openings comprise laterally spaced lines of apertures which extend along 
the belt, each line of apertures positioned to bisect a row of frame 
sections. 
In another embodiment, the vacuum conveyor includes a plurality of 
laterally spaced parallel belt sections, means to drive the belts, and a 
vacuum source operatively connected to the transport surfaces of the 
belts. Each vacuum belt section may include laterally extending (cross 
machine direction) ribs having flat face portions defining the web 
contacting surface and channels therebetween defining the vacuum openings 
at their ends. The vacuum source is operative to supply negative pressure 
to longitudinally extending (machine direction) spaces between the belt 
sections, which spaces are positioned in open communication with the 
channels in the surface of the belt to distribute the vacuum uniformly 
over the undersurface of the web. The apparatus may also include a source 
of pressurized air operatively connected to the underside of belt sections 
to provide belt supporting air bearings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring initially to FIGS. 1 and 2, there is shown in generally schematic 
form a double backer 10 including web drive of one embodiment of the 
invention. In the double backer, a double face corrugated web 11 is formed 
by joining a single face corrugated web 12 and a liner web 13. The glue 
tips of the corrugated medium 14 of the single face web 12 are covered 
with a starch-based adhesive in an upstream glue machine (not shown) and 
the adhesive bond between the glue tips and the liner 13 is cured by the 
application of heat and pressure in the double backer 10. 
Heat is supplied by a series of heating units 15 having flat, coplanar 
heating surfaces 16 over which the web 11 travels through the double 
backer. The heating units typically comprise individual steam chests which 
are fabricated of a heavy-walled cast iron or steel construction, but may 
as well comprise any suitable flat heated surface. Each steam chest has an 
open interior to which high pressure steam is supplied in a known manner 
and utilizing a supply system which is not shown in the drawings. Each 
heating unit 15 may be 18 to 24 inches (about 45-60 cm) in length (in the 
direction of web movement) and have a width in the cross machine direction 
sufficient to fully support the maximum width of corrugated web to be 
processed, e.g. 96 inches (about 245 cm). The total length of the heating 
section provided by a series of heating units may be, for example, 30 feet 
(approximately 9 m). 
A series of flexible parallel metal strips 17 is suspended above the 
heating section in a manner such that the sag or catenary in the strips 
allows them to lie atop the double face web 11 and provide the holddown 
force necessary to facilitate uniform heating and drying of the web and 
curing of the adhesive. The strips 17 may, for example, be made of 
stainless steel with a width of 1 inch (about 2.5 cm) or greater and a 
thickness of 0.040 inch (about 1 mm). A sufficient number of strips must 
be utilized to provide an overall holddown width in the cross machine 
direction sufficient to cover the full width of web being processed. The 
strips are preferably mounted to be quite closely spaced so that 
substantially full coverage of the web 11 is provided. The upstream ends 
18 of the strips are attached to a common upstream support 20 and the 
downstream ends 21 are attached to a common downstream support 22. 
In the FIG. 1 embodiment, the upstream support 20 is positioned just 
upstream of the upstream-most heating unit 15 just above the incoming 
single face and liner webs 12 and 13. In this manner, there is only a very 
short catenary portion which sags downwardly under the influence of 
gravity and is not in contact with the web 12 in the heating section. The 
downstream support 22 may extend a greater distance downstream of the 
downstream-most heating unit 15 to a point over the web drive conveyor 23, 
to be described in greater detail hereinafter. The downstream support 22 
may also be positioned at a somewhat elevated position with respect to the 
upstream support 20, such that a downstream catenary portion 24 does not 
contact the web along the drive conveyor 23. Either or both of the strip 
supports 20 and 22 may be mounted for adjustable vertical movement, as 
indicated by the arrows in FIG. 1. By raising one or both of the supports, 
the respective ends 18 and 21 of the strips may also be raised to vary the 
length of the strips resting upon and in contact with the double face web 
11. In this manner, the amount of heat transferred to and the amount of 
holddown force imposed upon the moving double face web 11 may be adjusted 
as desired. 
FIGS. 3-5 show details of the construction and operation of one embodiment 
of the drive conveyor 23 which may be used with the previously described 
double backer. The drive conveyor comprises a series of parallel, 
laterally spaced transport belt sections 46. The drive surface of each 
belt section 46 is ribbed to define laterally extending grooves or 
channels 47 between generally flat topped web supporting crowns 48. The 
spaces between adjacent vacuum belts 46 are defined by a series of shallow 
slots 50, the bottom surfaces of which are provided with a line of vacuum 
supply holes 51. The slots 50 provide open communication between the 
grooves 47 in the transport belts and the vacuum supply holes in the slots 
which define the upper surfaces of a series of vacuum plenums 52. The 
vacuum plenums are connected to a suction blower 53 to provide the 
required negative pressure. With the traveling double face web 11 in 
contact with the crowns 48 in the transport belts, the negative pressure 
is distributed evenly through the channels 47 and across the whole width 
of the web. If the web being processed is narrower than the full width of 
the vacuum drive conveyor 23, appropriate valving can be utilized to shut 
off the vacuum supplied to the vacuum slots 50 laterally outside the outer 
edges of the web. 
The transport belt sections 46 operate over and in sliding contact with 
belt support surfaces 54 between the vacuum slots 50. In order to reduce 
sliding friction and corresponding drive power requirements, the transport 
belts may be operated upon air bearings formed between the support 
surfaces 54 and the flat undersides of the belts 46. Thus, the surfaces 54 
may be provided with air supply holes 55 through which pressurized air 
from lower air plenums 56 is supplied to provide the air bearing support. 
In order to provide an adequate air bearing support, the positive air 
pressure supporting the belts must be greater than the negative pressure 
supplying the holddown force for the corrugated web. A second blower 57 
may be used to provide the positive air pressure for the air bearings. As 
shown schematically in FIGS. 3 and 5, the vacuum plenums 52 are suitably 
connected to the suction side of blower 53, while the air plenums 56 are 
operatively connected to the outlet of blower 57. 
The vacuum assisted web drive 23 of another embodiment is shown somewhat 
schematically in the top plan view of FIG. 2 and additional details are 
shown in FIGS. 6-10. In this embodiment, a single web transport belt 92 
operates around a driven head pulley 93 and an idler tail pulley 94. 
Between the pulleys 93 and 94, the belt is carried on a support structure 
95 which includes a vacuum plenum arrangement somewhat similar to the 
previously described embodiment. 
With reference particularly to FIGS. 6 and 7, the support structure 95 
includes a series of longitudinally extending and laterally spaced vacuum 
plenums 96. The uppermost surface of each plenum provides a support 
surface 97 for the belt 92. The plenums 96 and support surfaces 97 
provided by the plenums extend nearly the full distance in the machine 
direction between the head and tail pulleys 93 and 94. Centered in each 
plenum support surface 97 and running nearly the full length thereof is a 
recessed vacuum distribution slot 98. The bottom of the slot 98 is defined 
by a plate 100 provided with a series of spaced vacuum openings 101. The 
openings 101 provide direct communication to the interior of the plenum 
96. 
The vacuum slots 98 do not run the full length of the support surface 97, 
but rather are closed on the upstream and downstream ends with end plates 
102. The end plates lie coplanar with the support surface 97 and provide 
additional support for the belt 92 which travels thereover. The end plates 
102 also prevent or minimize vacuum loss from the ends of the vacuum 
slots. By placing the vacuum openings 101 in the bottoms of the recessed 
distribution slots 98, the holddown force provided by the vacuum is better 
distributed through the belt 92 as will be described. 
The bottom of the web transport belt 92 is essentially flat. The upper 
surface of the belt, however, is specially configured to support the 
double face web 11 and to evenly distribute and control the loss of the 
vacuum applied to the under surface of the web. Specifically and referring 
also to FIGS. 9 and 10, the top surface of the belt (as the belt moves 
through its horizontal active conveying run) is provided with a pattern of 
discrete upstanding support elements 103. In the embodiment shown, the 
support elements are of a generally oblong shape in the cross machine 
direction. The tops of the elements are flat, lie in a common plane, and 
provide a web contacting surface upon which the lower liner 13 of web 11 
is directly supported (see, for example, FIG. 1). The base surface 104 of 
the belt and the sides of the support elements 103 define an 
interconnected network of channels 105 through which the vacuum is 
distributed to the entire underside of the web 11 resting on the surfaces 
of the support elements 103. 
The belt is provided with laterally spaced lines of apertures 106, each of 
which lines extends the full length of the belt, and overlies and is 
aligned with a vacuum distribution slot 98. Thus, as the belt 92 travels 
over the support surfaces 97 provided by the plenums, vacuum force will 
constantly be applied through the apertures 106, distributed throughout 
the network of channels 105, and provide a uniform holddown force for the 
web 11. 
As is best shown in FIGS. 6 and 8, the apparatus of the present invention 
includes means for controlling the application of vacuum to the vacuum 
plenums 96 and to selectively seal off lateral portions of the belt 
surface to accommodate webs of varying widths and at the same time avoid 
the loss of or need to use excessive negative vacuum pressure. A vacuum 
distribution header 107 is used to supply negative pressure to the vacuum 
plenums 96 from a suction blower 53. Preferably, the system includes an 
odd number of vacuum plenums, including a central plenum 108 on the 
longitudinal centerline of the system and pairs of corresponding plenums 
on opposite sides of the centerline, each of which pairs is progressively 
more distant from the central plenum 108. See for example outermost plenum 
pair 109, as shown in FIGS. 6 and 7. In this manner, as a centered 
paperboard web 11 of a narrower width is being processed, pairs of plenums 
may be progressively shut off laterally inwardly from the outermost pair 
so that vacuum is only being applied to those plenums over which the web 
is traveling. As may be seen best in FIG. 6, the system is arranged such 
that a single control valve 110 controls the supply of negative pressure 
to one pair of plenums 96 supplied by a common vacuum lateral 114 
connected to the header 107. 
In order to prevent excess negative pressure loss, either via the lateral 
edges of the web or longitudinally as the belt wraps around the head or 
tail pulleys 93 or 94, the belt surface may be provided with a gridwork of 
adjoining frame sections 111. Each frame section is defined by an 
enclosing rib 112 projecting above the base surface 104 of the belt and 
having a flat outer surface 113 which lies coplanar with the web 
contacting surfaces of the support elements 103. The frame sections 111 
are positioned in the longitudinal direction to be centered on a line of 
belt apertures 106. The vacuum applied to a line of apertures 106 from the 
plenum 96 directly below will thus be confined to the row of frame 
sections 111, assuming the sections are covered by a portion of the web. 
On the other hand, it has been found that elimination of the ribs 112 and 
frame sections 111 which the ribs define may provide a beneficial cooling 
of the web being processed. This is because ambient air will be more 
readily drawn into the network of channels 105 on the belt surface 92 if 
there is no blocking obstruction of the frame sections 111. However, the 
energy requirements to generate additional compensating vacuum pressure 
may be increased. 
In FIGS. 11 and 12, there is shown the presently preferred embodiment of a 
web transport belt 115 and belt support structure 116. The belt may be 
driven and carried by the same pulley arrangement previously described. In 
this embodiment, the web transport belt 115 is provided on its upper 
surface with a series of laterally spaced raised longitudinal ribs 117, 
each of which is continuous along the full length of the belt. The ribs 
have flat surfaces 118 which are coplanar and define a contacting surface 
for supporting the web. 
Alternate adjacent pairs of ribs 117 are relatively closely spaced to 
define therebetween longitudinal channels 120. In each channel, the belt 
is provided with a line of apertures 121 which provide open communication 
through the belt to the lower surface thereof. The belt support structure 
116 comprises a flat metal plate 122 which provides sliding support for 
the belt 115 traveling over it. The underside of the plate 122, in 
alignment with each of the channels 120 formed on the belt surface, 
includes a vacuum plenum 123. The plate 122 is provided with a line of 
vacuum openings 124 along the length of each vacuum plenum 123, which 
vacuum openings are aligned during belt movement with the line of 
apertures 121 in the belt. Thus, vacuum applied to the vacuum plenum 123 
(in generally the same manner described with respect to the embodiment of 
FIGS. 6-10) will be applied to the belt channel 120 via the apertures 121 
and will provide a holding and drive force to the double face corrugated 
web 11 supported on the flat surfaces 118 of the ribs 117. The ribs 117 
confine the vacuum pressure to the channels and help seal the channels 
against entry of excessive air at ambient pressure. As in the previously 
described embodiment, the vacuum source may be connected to the plenums 
123 to provide selective application of negative pressure to laterally 
spaced pairs of plenums or in any other convenient arrangement. 
The longitudinal belt ribs 117 are more widely spaced between the channels 
120 and, in the supporting plate 122 which underlies these intermediate 
portions of the belt, the plate is provided with a pattern of vacuum force 
dissipation holes 125. These vacuum dissipation holes extend through the 
plate and are open to ambient air beneath the plate and between adjacent 
vacuum plenums 123. The use of a flat metal plate 122 for the belt support 
structure requires some means to dissipate the propagation of vacuum force 
from the vacuum openings 124 under the belt 115. The flat interface 
between the underside of the belt 115 and the upper surface of the plate 
122, adjacent the respectively aligned belt apertures 121 and vacuum 
openings 124, will not provide a complete seal to prevent the vacuum force 
from being undesirably applied to the belt as well as being desirably 
applied to the web 11. Thus, the vacuum dissipation holes 125 in the 
supporting plate 122 provide a controlled ambient air leakage which could 
otherwise impose an intolerable vacuum force on the belt. In the 
previously described embodiment (FIGS. 6-10) the regions between the 
plenums where the belt is unsupported provide the same effective relief 
from vacuum force. The controlled leakage of air provided by the vacuum 
dissipation holes 125 in the supporting plate 122 may require some 
increase in the size of the vacuum supply (e.g. blower 53 in FIG. 6). The 
same principle which results in propagation of the vacuum force to the 
underside of the belt 115, if no relief is provided, can be utilized to 
hold the web 11 to the upper surface of the belt without the need to use 
special raised ribs or protrusions. In other words, the upper belt surface 
may be flat and provided with lines of openings or apertures 121 without 
the need for confining ribs. The vacuum will nonetheless be distributed 
quite uniformly over the underside of the web allowing the same to be 
pulled through the system. Again, some upsizing of the vacuum source may 
be required. If necessary, it is even possible to provide the underside of 
the foraminous support plate 122 with a source of positive pressure to 
provide an air bearing effect such as previously described with respect to 
the embodiment of FIGS. 3-5. The vacuum openings 124 and the vacuum 
dissipation holes 125 are all preferably circular and of the same diameter 
for convenience of manufacture.