Suction roll with deflector pieces in the holes, for a dryer group of a paper making machine

The suction roll of a dryer group is in the path of the web and of the web support belt from an upstream dryer cylinder to a downstream dryer cylinder. The suction roll has an annular roll shell having a plurality of radial holes and being free of stationary inserts at least over the predominant part of the length of the roll shell. A hollow roll journal at at least one end of the suction roll connects vacuum into the suction roll and to the radial holes. In at least some of the holes there are respective deflector pieces. Each extends a short radial distance into the inside of the roll shell over a short radial portion. The deflector piece has a continuous channel which extends radially inward through the hole toward the inside of the roll in a direction substantially parallel to the direction of extension of the hole and the radially inward portion of the channel is curved in the direction contrary to the direction of rotation of the roll shell.

BACKGROUND OF THE INVENTION 
The present invention relates to a suction roll, which is particularly 
useful for a single-wire dryer group of a paper making machine. In such a 
dryer group, a web, for instance, a paper web, which is to be dried 
travels, together with a porous support belt, alternately over dryer 
cylinders and suction rolls. The suction rolls serve primarily as 
reversing rolls for the support belt and for the web which is carried 
along by the support belt. The web of paper is pressed against the dryer 
cylinders by the support belt. As the support belt travels over the 
reversing rolls, however, the support belt is between the outside of the 
reversing rolls and the paper web. At the reversing rolls, the web must be 
drawn by suction against the support belt and in opposition to the 
centrifugal force which acts on the web. For this reason, the reversing 
rolls are developed as suction rolls. 
The invention relates to a suction roll which does not include the usual 
suction box. In known box suction rolls, a stationary suction box extends 
through the hollow roll body. A suction box-less suction roll, of which 
the invention is an example, is known from EP-A 0332599 which is 
equivalent to U.S. Pat. No. 5,022,163. With this type of suction roll, it 
has been found that the consumption of energy for producing a given vacuum 
on the outside of the shell of the roll increases with the operating speed 
of the machine that is, increases with the speed of rotation of the 
suction rolls. 
SUMMARY OF THE INVENTION 
The object of the invention is to develop a suction box-less suction roll 
to reduce the consumption of energy needed to generate the necessary 
vacuum or suction on the outside or periphery of the shell of the roll, 
particularly at the high operating speeds of modern paper making machines, 
namely about 1,000 to 2,000 meters per minute. 
Another object is to eliminate or at least reduce the generation of a 
potential vortex within the roll shell as a result of the air blowing into 
the rotating shell. 
The invention is based on the discovery that as the speed of rotation of 
the suction roll increases, the consumption of energy for producing the 
suction or vacuum at the periphery of the annular shell of the roll is 
considerably increased because the air flowing radially through the 
suction air inlet holes in the shell of the roll is also imparted a 
circumferential component in the direction of rotation of the roll shell 
which is of approximately the same order of magnitude as the radial 
velocity of flow. The resultant of the radial and circumferential 
components of the velocity of the incoming air flow produces a potential 
vortex within the suction roll which causes a considerable increase in the 
power required for the blower. 
The production of the potential vortex can be at least substantially 
prevented by inlet air deflector pieces placed in at least some of the 
holes in the roll shell. The annular roll shell is provided with a 
plurality of radial suction air inlet holes through it which are arrayed 
circumferentially around the roll shell and at least over the predominant 
part of its length. In at least some of the holes, there is held, e.g. by 
force fitting or by bonding, a respective deflector piece which extends at 
least partially through the hole and extends a relatively short radial 
distance into the inside of the annular roll shell. Through each deflector 
piece there extends a continuous channel which communicates from the 
outside of the roll shell into the inside. The part of the channel that 
passes through the roll shell extends at least substantially parallel to 
the hole in the shell. In at least the radially inward part of the 
deflector piece inside the roll shell and possibly a short distance 
radially into the hole in the shell, the channel has a rounded curvature 
that is directed contrary to the direction of rotation of the roll shell. 
The curved section covers an angle of between 50.degree. and 90.degree., 
preferably between 65.degree. and 75.degree. and particularly 70.degree.. 
The deflector pieces and their curved channels provide a direction of 
emergence of the air from the channels, which direction is approximately 
opposite the direction of rotation of the roll shell, and is a so-called 
"relative emergence direction". The relative emergence direction of the 
air and the circumferential direction of roll shell rotation produce an 
absolute emergence direction which is approximately radial. This so 
greatly reduces the speed of rotation of the potential vortex that the 
vortex impedes the radial movement of the air only slightly if at all. Up 
to 40% less blower power than previously is required in order to produce a 
given vacuum on the periphery of the suction roll. 
Other objects and features of the invention are described below with 
reference to an embodiment shown in the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT 
In a single tier single wire dryer group of a paper making machine, the web 
passes through a dryer section having a plurality of dryer cylinders in a 
generally aligned straight row which alternate with reversing suction 
rolls, and the web, carried by a support belt or wire, moves from each 
dryer cylinder, over a subsequent reversing roll to the next dryer 
cylinder. In the portion of such a dryer group shown in FIG. 1, a suction 
roll 10 is arranged between two dryer cylinders 11 and 12. The direction 
of rotation of each dryer cylinder is indicated by respective arrows. The 
dryer cylinder 11 is arranged in front i.e. upstream, of the reversing 
suction roll 10. A support belt 9, developed as a porous wire screen, 
known as a wire, travels in a known manner from the dryer cylinder 11 onto 
the annular shell 13 of the suction roll 10 and from there to the 
following dryer cylinder 12. A web of paper (not shown), which travels 
together with the support belt 9, is disposed on the side of the belt 9 
which has direct contact with the two dryer cylinders 11 and 12. In the 
region of the suction roll 10, the web of paper is on the outside of the 
support belt 9. 
The suction roll 10 is free of stationary inserts within the roll and has 
at least one hollow roll journal 14 which is open radially outward toward 
the inside of the roll shell. A source of vacuum can be connected to the 
journal. The annular roll shell 13 has a plurality of radial holes 15 in 
the roll shell through which vacuum is propagated to the outside of the 
roll shell. The holes 15 are continuous holes through the shell and are 
arrayed circumferentially around the shell and at least over the 
predominant part of the axial length of the shell. Simple continuous holes 
can be provided, as indicated at one arcuate segment, at 13' in FIG. 1. As 
an alternative, circumferential grooves 8 can be provided in the outer 
surface of the roll shell 13, into which grooves the holes 15 debouch, as 
indicated at another arcuate segment in FIG. 1. 
A respective deflector piece 16, shown in detail in FIGS. 2 to 4, is 
preferably inserted in each hole 15. Each deflector piece 16 is 
predominately cylindrical in cross-section, with the shape corresponding 
to the size and shape of the hole 15 in which the deflector piece is 
disposed. The deflector piece has a collar 161 developed on its inlet, 
radially outer end to cooperate with the radially outer side of the shell 
at the hole 15 and hold the piece 16 in position. Toward its outlet, 
radially inner end, the deflector piece 16 extends for a distance into the 
inside of the roll. There the piece 16 has a few barbs 16b which hold the 
deflector piece against moving outward under centrifugal force from within 
the rotating roll shell 13. The barbs 16b can be developed as annular 
beads. 
The deflector pice 16 has a continuous channel 17 through it which extends 
radially of the roll shell in the direction toward the inside of the roll. 
The radially outward part of the channel extends approximately parallel to 
the radial hole 15. The channel gradually curves in the direction opposite 
the direction 18 of rotation of the roll shell 13 starting where the piece 
16 is inside the roll shell and extending through the part of the piece 
that extends radially inside the roll shell. The curved part of the 
channel 17 has a center about which it has a curvature angle of between 
50.degree. and 90.degree., preferably between 65.degree. and 75.degree. 
and as shown, of, for instance, 70.degree.. This produces the relative 
emergence direction of the air indicated by the arrow 19. With due 
consideration of the direction of roll shell rotation shown by arrow 18, a 
substantially radial absolute direction of emergence of the air results. 
The hole 15 has an axis through the center of its cross section. In FIGS. 2 
and 4, the part of the channel 17 that is substantially parallel to the 
hole 15 is displaced with respect to the axis of the hole downstream in 
the direction of rotation 18 of the roll shell 13. The emergence opening 
at 20 of the deflector piece 16 is preferably approximately rectangular in 
cross section, as seen in FIG. 3. At the transition between the straight 
and the curved parts of the channel 17 or in front, i.e. upstream, or 
behind, i.e. downstream, of this transition, a step-like increase in the 
cross section, in the form of a step 21, can be provided. This step 21 is 
present substantially only in the region on the inside of the curvature of 
the channel and, therefore, on the side of the channel which is opposite 
the direction of rotation 18. The channel wall does not have a step in the 
region of the outside of the curvature. As a result, the center line of 
the channel effects a "jump". In the region of the inside of the 
curvature, a vortex-like secondary flow is produced, which is indicated by 
dashed line 22. This secondary flow effects a well defined detachment of 
the primary flow of air from the channel wall downstream of the step 21 
and thus reduces the pressure losses. 
The deflector piece 16 is made of an elastic plastic material It is 
force-fitted or glued in the hole 15. In FIG. 2 the diameter D of the hole 
15 amounts to about 10 mm. The diameter d of the channel 17 is about 4 mm. 
Although the present invention has been described in relation to particular 
embodiments thereof, many other variations and modifications and other 
uses will become apparent to those skilled in the art. It is preferred, 
therefore, that the present invention be limited not by the specific 
disclosure herein, but only by the appended claims.