Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
The present invention relates to improvements in dryer
drum~ for continuousl.y dryirlg a web of paper in a papermaking
machine, and more particulary to an improved condensate removal
structure.
In a papermakin~ machine a plurality of dryer drums are
arranged in sequence for carrying a continuous web of paper in a
serpentine fashion ~hrough the dryer section~ The dryer drums
are steam heated, and the drums are usually constructed of a
cylindrical outer shell with a smooth outer sur~ace for carrying
the paper web with heads at the ends of ~he drum shell which are
provided with supporting bearings for rotatably mounting the
drum. Means are provided at the bearings for directing steam
into the dru~ and as heat is transferred to the web supported on
the surface of the shell, condensate tends to form which must be
removed so that it will not have an insulating effect and reduce
the heat trans~er from the steam to the shell.
In a typical construction so that the heat transfer
abilit~;r of the drum is increased, the shell is made as thin as
possible, and for strength, a plurality of annular raised ribs
are located on the inner surface of the shell with grooves
therebetween. The condensate collects in these grooves, and it
is imperative that it be effectively removed for increasing the
eficiency of the dryer drum, and in high speed papermaking
machines, it is imperative that heat transfer be maintained at
maximum efficiency and that the insulating effect of condensate
collected within the drum be maintained at a minimum and be
immediatel~ and effectively and un.iormly removed.
In accordance with a provision of the present invention,
there are provided a plurality of elongate tubes which suck the
condensate from the base of the grooves and the tube~ are
uniquely constructed and supported for removal of the
`~
condensate.
In order to obtain good operation and a high coefficien~
of ~he transmission of heat ~o the paper web on the outer
s~rface of the drum~ it is advi~able tha~ ~he thickness of the
condensates which accumulates in the bottom of ~he drum be
maintained at a minimum, and it is also imperative that this
thickness remain the same in all o~ ~he grooves to maintain the
same coefficient of heat transmission over the whole length of
the surface of the drum.
Presently known drums can be generally categorized in
two types. One type has condensate collectors which are fixed
to the inner surface of the shell, and the other type has
condensate collectors which are fixed and suppor~ed to the
central shaft of the drum. The first type insures the
maintenance of the distance between the collector tubes within
the drum and the bottom of the grooves, but has the disadvantage
that with rotation of the drum, centrifugal forces generated by
the mas, of the collectors make the shell deform resiliently
causing it to be polygonal because of the concentration of such
forces at the location of the collectors.
Drums which have collectors that are supported on the
central shaft have the disadvantage that there is no good
control over the distance between the open ends of the collector
tubes and the bottom of the grooves particularly because
dimensions change with thermal deformation of ~he parts as
temperatures change. There is thus a need for control over the
depth or th~ckness of the condensate which rims at ~he bottom of
the grooves. Another problem is encountered tha~ small tubes
cannot be mounted with a very small spacing between their open
ends and the inner surfaces of the shell because contact can
occur between the tubes and the bottom of the grooves in
operation generating wear and stresses on the shell.
An object of the pre~ent inventlon is to provide a steam
dryer drum and condensate removal structure which will avoid the
aforementioned disadvantages.
A further object of the invention is to provide a
condensate removal sys~em utilizing individual tubes for the
grooves wherein the tu~bes can be readily and accurately adjusted
relative ~o the bottom of the groove for uniformity o spacing
between the ends of ~he tubes and the groove.
A still further object of th invention is to provide a
condensate removal system ~or a grooved or ribbed dryer drum
wherein the radial spacing between the open receiving ends of
condensate collectvr tubes and the bottom of the grooves remains
constant independent of deformations of the shell during
opération and independent of changes of dimensions due to
thermal deformation.
In accordance with the principles of the invention,
there is provided a rotary steam dryer drum for a continuous
traveling web of paper wherein the drum is supplied with steam
for drying the web and has a cylindrical shaped shell with a
smooth outer surface and with heads at the end of the shell to
support the drum in rotation~ Within the shell on the inner
surface are a plurality of ribs with circumferential grooves
therebetween, and a plurality of axially extending collectors is
supportd and disposed within the interior of the drum to receive
and take up the condensation resulting from the steam and to
convey it out of the drum. The axially extending collectors are
provided with a plurality of small elastically deflectable tubes
which project in both circumferential directions from the
collectors in such a way as to have~the base end securely
mounted on the collector for the flow of cvndensate from the
tube to the collector and having the free end biased toward the
bottom of the groove but provided with a lugged tube positioning
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element which rests on the inner surface of the ribs adjacent
the grooves in order ~o maintain the free end a predetermined
accurate controlled distance from the bo~tom of the groove.
Other objects, advantages and features will become more
apparent with the teaching of the principles of the invention in
connection with the disclosure of the preferred embodiments
thereof in the specification, claims and drawings in which:
DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a sectional view on a plane perpendicular to
the axis of rotation of the dryer drum;
FIGURE 2 is a partial sectional view taken on a plane
extending parallel to the drum axis;
FIGUÆ 3 is a sectional view taken substantially along
line III-III of Figure 2;
FI~URE 4 is a partial sectional view taken substantially
along line IV-XV of Figure 3;
FIGURE 5 is as fragmentary detailed sectional view taken
substantially along line V-V of figure 4;
~ IGURE 6 is a fragmentary detailed sectional view taken
substantially along line VI-VI of Figure 5;
FIGURE 7 is a fragmentary detailed sectional view taken
substantially along line VII-VII o~ Figure 6 and showing a
modified for~ of support; and
FIGURE 8 is a detailed view, partly in section, taken
~ubstantially along line VIII-VIII of Figure 2.
DESCRIPTION
The dryer drum incorporating the features of the present
invention includes a cylindrical shell la having a smooth outer
surface which ~upports the continuously traveling web of paper
to be dried. The drum has at its ends heads 1 which with the
shell define an inner cavity which receives steam and in which
the other components of the device are housed. Within the shell
'~ f~
are axiallY extending collectors 2 which extend parallel to the
central rotational axis of ~he drum and which are of a slightly
less length than the drum. The heads at the ends of the drum
are provided with suitable support bearings, not shown, so that
the drum can rotate during drying operation.
Each of the collectsrs 2 is held by mean~ of four radial
arms 3 which a e supported at their inner ends on an annular
wall 4 which is part of the central shaft 5 or hub of the
drum. The hub is provided in the form of a hollow annular
casting formed in sections and providing two cavities 6 and 7
which are separated from one another by a wall 8. Each of the
radial arms 3 is also circumferentially supported by four pairs
of struts or tie rods 9 which struts are fixed both to the hub
and to the radial outer ends of the arms 3. The tie rods
circumferentia:Lly support the arms. but also provide radial
support and absorb part of the circumferential tension force
created by the mass of the collectors which is subjected to
centri~ugal force during the rotation of the drum.
The central shaft, shown generally at 5, has an axial
connection for the delivery of steam into the interior, and the
hub 4 has a plurality of radial holes 13 which permit the steam
to flow into the cavity 14 to come in contact with the shell.
Within the hub 4 is constructed a cylindrical wall 15 which
de~ines a cavity 16 for the receipt and transmittal of
condensate which flows axially outwardly through the end of the
drum through an outlet hole 17~
Each collector 2 is in communication with ~he condensate
cavity 16 by means of its o~n tube 18 in such a manner that
under a given pressure differential or suction created by a pump
or suitable suction device outside the drum, a flow of
condensate will be caused from ~he collectors 2 into the cavity
16 and outwardly of the drum.
-5
As is shown in Figures 1, 2 and 3, the outer surface of
the shell 1 is smoot~ and cylindrical in shape for providing
support for the paper web and for goQd heat transmission. The
inner surface of the shell is circumferentially grooved to
increase the area for heat exchange, to reduce the distance to
the outer surface of the shell, to strengthen the shell, and to
create a series of collection channels for condensate which
forms during operation. The grooves are formed by integral ribs
on the inner surface of the shell, and the grooves are shown at
19 separated by the ribs 20~
The axially extending collectors 3 are positioned
closely adjacent the shell and supported by arms 3 with the
connection between the collector and its supporting arms
provided by means shown at 23 (Figure 3~. This includes a plate
24 provided with a lug 25 fixed to the collector, and a fork 26
fixed to the radially outermost end of the arm 2 and recei~ing
the lug 25. A pair of pins 27 (Figure 4) pivotally fix the lub
to the fork 26. Between the sides of the fork, there is a
spacer washer 28 of a thickness so as to allow axial play of the
collector 2 by allowing small displacements of the lug 25 as
axial expansion and contraction of the collection occurs due to
temperature variations
In the arrangement illustrated in Figure 3, each arm 3
is hollow, and its radially innermost end is fixed and supported
by means of a flange 29 ~o flange parts 30 of the central shaft
5.
As ~h~wn in Figure 4, each collector 2 has a
sub~tantially rectangular section with flat walls 33a, 33b. The
upper wall 33a is fixed to ~he pla~e 24 of connection means
while the lower plate 34b is located a short distance inwardly
from the ribs 20. As shown in Figure 4, the wall 34a and parts
of the walls 33a and 33b are constructed from a shaped integral
section of ~heet metal, and the other parts of the walls are
provi~ed by bars 35 having a greater thickness than that of the
wall as illustrated in the sectional view of Figure 4. These
bars provide a rigid base for supporting tubes 36.
From the walls 33a and 33b of each collector 2, small
tubes 36 extend in a ~ubs~antial tangential direction with
respect to the shell 1. These tubes lead from each of the
grooves to the interior of the collector 2. The base cr support
end 38 of each of the tubes passes through one of the walls 33a
and 33b of the associated collector and is inserted into a
bushing 39, the threaded outer surface of w~ich is screwed into
a corresponding threaded hole formed in the bar 35 of the
a~sociated wall 33at 33b. A ring nu~ 40 locks this bushing and
the associated small tube to the wall. The outer free end of
each of the tubes 36 projects into a radial groove 19 as
illustrated in Figure 4. The tube is shaped so that it
diminishes in diameter from the base end 38 toward the free
end. ~ne free end is cut at a bias so as to be parallel to the
inner surface of the base of the groove, and therefore suction
flow of the condensate into the tube is enhanced
Each of the tubes 36 is made from an elastically
deflectable material which is resistant to the temperature of
the steam within the cylinder. Preferably, the tubes are formed
of metal~ and the tubes in effect are a cantilever elastic beam
~upported on the associated collector with a natural bias or
bend so as to cause the free end to spring toward the hase of
the groove.
At the free end of each tube is secured a small guide
plate 45 (Figures 4 and 5) preferably having a substantially T~
shaped form. This guide plate is a tube positioning element and
has a central lug 46 with a hole therethrough into which
projects the tubeO The lug is ~ufficiently narrow so that it
fits within the groove. ~he lug has at least one, but
preferably, a pair of laterally extending arms 47 which rest on
the top of the adjacent ribs 20. In this way, the free open end
44 o each tube is held a predetermined very small distance from
the bottom surface 19 of the groove as indicated at g in Figures
4 and 60
While other forms of bias may be used, it is preferred
that the tube be con~tructed of a resilient material so that it
can be mounted at its base to be biased alon~ its length to urge
its free end toward the base of the groove. The bias is such
that a preload or stress exists in the tube which is
counteracted by the tube positioning e~ement 45.
The element rests on the top of the ridges and the
ridges' top surface is parallel to the base of the grooves so
that essentialLy with expansion or contraction due to
temperature difference, the element 45 can slide on the rib
without binding.
In the end regions of the headst there is a formed a
radial groove :L9a (Figure 2~ of axial width greater than the
grooves. In this groove l9a there is inserted a tube 36, the
free end of which is rigidly positioned with respect to the
bottom of this groove by a plate 45a (Figure 6) fixed to the rib
20 adjacent the groove, such as by qcrews 48. The plate 45a has
a hole to receive the tube 43 and allow a limited amount of
radial play.
Each discharge tube 18 (Figures 1 and 2) for the
discharge of condensate from each collector 2 has a structure
such as shown in Figure 8 and includes a first section 49a
fitted into the collector itself bylmeans of a sealing assembly
50. This incl~des a pair of flanges 51 and a sealing element
S2. Also included is a second section 4gb passing through the
wall 15 and connected to the preceding part by means of a ball
.J~r..~
joint 53 of a known ~ype. The discharge tube 18 is guided and
maintained in position along the sha~t 5 by means of a bushing
assembly 54 provided with a flange 55 connected to the wall 4 of
the shaft.
Any configuration of tubes 36 projecting from each
collector 2 can be employed. Preferably, the tubes are
constructed to project alternately in opposite circumferential
directions with respect to the supportin~ collector, but
different arrangements can be adopted.
In operation steam is supplied to the interior of the
drum through the cavity 14 through the hole 12, the cavity ~ and
the radial holes 13 for heating the shell. As heat is extracted
from the steam for evaporating water from the paper sheet, this
causes condensation within the drum which collects at the bottom
of the grooves 19 (Figure 3). Through the holes 17 and the
cavity 16 a suction is applied which rreates a lowered pressure
within the interior of the collectors 2. The condensate, or a
mixture of condensate and steam is drawn through the small tubes
36 through the free open ends ~3 having their collection
surfa~es 44 in close proximity to the base of the grooves. It
is, therefore, apparent that a spacing g between the surfaces 44
and the base is very small, and the condensate can almost
completely be sucked up with the intended advantaye of
increasing the coef~icient of heat transfer between the steam
and the metal of the shell~
During operation of the devicer the shell o one of the
cylinders is subjectd to deformations produced by thermal
expansion due to the heat within the drum and the removal of
heat by the water evapora~ing from the w~b on the ou~er surface
of the drum and these circumstances~:will vary during
operation. As a consequence of this deformation of the shell,
the substantially cylindrical form of the shell and its
J~
associated grooves 19 varies~ Such a variation in form does not
have any nega~ive effect on the sucking action exerted on the
condensate in the bottom of the grooves 19 by the tubes. In
fact, whatever the dimensional and form variations of the
groove, the clearance space g between ~he surface 44 of a given
tube in the bottom surface of the associated groove is
maintained constant. This favorable resul~ i5 obtained because
the free end of the tube is positioned in a fixed manner with
respect to the bottom of the groove both by the action of the
plate 45 and by the resilient preloading of ~he tube. Whatever
the displacement of the bottom surface of the groove which is
located beneath the end surface 44 of the tube, the same
displacement occurs on the ribs on either side of the groove.
Because of the abutment on the plate 45 on these ribs, this
causes a corresponding displacement of the end of the tube.
The con~densate drawn up into the various collectors is
conveyed through the discharge tubes 18, the cavity 16 and the
hole 17 out of the drum7
Because of the form of the section of each collector
which is rectangular, it can be arranged in a radial position
very close to the inner surfaces of the shell with the advantage
of improving effectiveness of the suction.
Each tube 36 can be accurately positioned with respect
to the associated collector by means of the bushing and ring 39
and ring nut 40 for the purpose of positioning in a correct
manner the end 44 of the tube with respect to the bottom surface
of the associated groove 19.
While the pre~erred form is illustrated, it will be
apparent fro~ the foregoing teaching of the description that
various parts of the embodiment of the present invention can be
varied without departing from the spirit and scope of the
invention.
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