Note: Descriptions are shown in the official language in which they were submitted.
2026954
LITHOGRAPHIC PRINTING PRESS
Background of the Invention
The present invention relates to an offset printing
press.
During operation of a an offset printing press, an ink
pattern is applied to sheet material by a blanket on a
blanket cylinder. The pattern is applied to the blanket by
a plate cylinder. Any vibrations which may be present in
either the plate or blanket cylinders during operation of
the press promotes smearing of the ink pattern and is
detrimental to the quality of the printing. Known blanket
cylinders have an axially extending gap in which opposite
ends of the blanket are secured. When the blanket cylinder
gap is located at a nip between the plate and blanket
cylinders, vibrations tend to be induced in the cylinders.
These vibrations detrimentally affect the quality of the
printing and contribute to smearing of the ink pattern.
Smearing of the ink pattern is also promoted by
slippage between the surfaces at the nip where the ink
202695~
--2--
pattern is transferred to the blanket. Thus, if the speed
of the blanket surface is either greater or less than the
speed of the surface transferring the ink pattern to the
blanket the surfaces will slip relative to each other which
smears the ink pattern.
Summary of the Invention
The present invention is directed to improving the
quality of printing obtained from an offset printing press
by eliminating or at least minimizing smearing of an ink
pattern. The offset printing press includes a blanket
cylinder which carries a blanket which applies the ink
pattern to the sheet material. An ink transferring surface
on the plate cylinder applies the ink pattern to the
blanket. The ink transferring surface on the plate
cylinder and blanket are disposed in rolling engagement at
a nip formed between the plate and blanket cylinders.
In accordance with the present invention, the blanket
is in the form of a tube having continuous outer and inner
surfaces which are free of any gaps. The blanket is
removably mounted on the outer peripheral circumferential
surface of the blanket cylinder. The outer surface of the
blanket is disposed in rolling engagement with the ink
transferring surface on the plate cylinder at a nip formed
therebetween. Since the outer peripheral circumferential
surface of the blanket is continuous and free of gaps,
2D~s5ll
--3--
smooth and vibration free rolling engagement is obtained
between the blanket and the ink transferring surface on the
plate cylinder to thereby promote the transfer of an ink
pattern to the blanket without smearing of the ink pattern.
The blanket is at least partially formed of a
compressible material which is compressed by the plate
cylinder at the nip between the printing cylinder and
blanket cylinder. By compressing the compressible material
at the nip, the outer surface of the blanket has a surface
speed which is substantially the same at locations
immediately before the nip, at the nip, and immediately
after the nip. This prevents slippage between the surfaces
of the printing plate and blanket before, at, and after the
nip to prevent smearing of the ink pattern.
The tubular blanket has a cylindrical outer layer of
incompressible material and a cylindrical layer of
compressible material on an inner layer of rigid material.
The outer layer of the blanket is deflectable to compress
the compressible layer of the blanket. The compressible
layer of the blanket contains a plurality of voids which
are relatively large before the compressible layer is
compressed and which are relatively small in the portion of
the compressible layer which is compressed by deflection of
the outer layer of the blanket at the nip.
The rigid inner layer of material is stressed in tension
by the blanket cylinder to provide a tight pressure
2026954
--4--
relationship between the blanket and the blanket cylinder.
This pressure relationship fixes the blanket on the blanket
cylinder so that there is no relative movement therebetween
during operation of the press. The press includes means
for effecting radial expansion of the tubular blanket while
on the blanket cylinder to relieve the pressure relationship
between the blanket and blanket cylinder. When the pressure
relationship is relieved, the blanket may be manually moved
axially off of the blanket cylinder. Also, the blanket must
be expanded radially (tensioned radially) outwardly in order
to move the blanket axially onto the blanket cylinder. The
press is also provided with structure for performing this
function.
In order to provide access to one end of the blanket
cylinder to enable a blanket to be moved axially onto and
off of the blanket cylinder, in a preferred embodiment a
portion of the frame adjacent one axial end of the blanket
cylinder may be moved out of the way. The tubular blanket
may be moved axially through the opening in the frame
created by movement of the frame portion out of the way.
To expand the blanket so that it can be placed on the
cylinder, the cylinder interior may have air pressure
applied thereto. Passages to the outer peripheral surface
of the blanket cylinder communicate with the interior of
the blanket cylinder. Air pressure applied to the interior
of the blanket cylinder is thus communicated to the
2~2695~
--5--
interior of the blanket to expand same as it is inserted
onto the blanket cylinder. After the blanket is located on
the outer periphery of the blanket cylinder, the air
pressure may be removed. The blanket then contracts around
the blanket cylinder and tightly engages and grips the
cylinder periphery throughout the axial extent of the
blanket and throughout the circumferential extent of the
inner surface of the blanket. This pressure relationship
between the blanket and the blanket cylinder can be
relieved by again applying air pressure to the interior of
the blanket cylinder to enable the blanket to be manually
moved off the cylinder.
Brief Description of the Drawings
The various features of the present invention will
become more apparent to one skilled in the art upon reading
the following description taken in connection with the
accompanying drawings, wherein:
Fig. 1 is a schematic illustration of an offset printing
press;
Fig. 2 is an enlarged schematic illustration of the
manner in which a blanket formed of an incompressible
material is deformed at a nip between plate and blanket
cylinders of the printing press of Fig. l;
Fig. 3 is an enlarged fragmentary sectional view of a
portion of a blanket constructed in accordance with the
20~6954
present invention and mounted in the printing press of Fig.
l;
Fig. 4 is an enlarged schematic illustration of the
manner in which an incompressible outer layer of the
blanket cylinder of Fig. 3 is deflected to compress a
compressible inner layer at a nip between the blanket
cylinder and a plate cylinder; and
Fig. 5 is a schematic illustration of the manner in
which a portion of a frame of the printing press of Fig. 1
is movable to an open condition to provide access to the
blanket cylinder.
Description of Specific
Preferred Embodiments of the Invention
The present invention may be embodied in a number of
different constructions and applied to a number of different
offset printing presses. By way of example, the drawings
illustrate the present invention as applied to an offset
lithographic perfecting printing press 10.
The lithographic printing press 10 prints on opposite
sides of a sheet material web 12. The lithographic
printing press 10 includes identical upper and lower
blanket cylinders 14 and 16. Blankets 18 and 20 are
mounted on the blanket cylinders 14 and 16-and apply ink
patterns to opposite sides of the web 12. Upper and lower
plate cylinders 22 and 24 support printing plates which are
disposed in rolling engagement with the blankets 18 and 20
2~2~9~4
at nips 26 and 28. Ink patterns are applied to the
blankets 18 and 20 by the printing plates on the plate
cylinders 22 and 24 at the nips 26 and 28. These ink
patterns are, in turn, applied to opposite sides of the web
12 by the blankets 18 and 20.
The printing press 10 includes upper and lower dampener
assemblies 30 and 32 which apply dampening solution to the
printing plates on the plate cylinders 22 and 24. In
addition, upper and lower inker assemblies 34 and 36 apply
ink to the printing plates on the plate cylinders 22 and
24. A drive assembly, indicated schematically at 38 in
Fig. 1, is operable to rotate the blanket cylinders 14 and
16 and plate cylinders 22 and 24 at the same surface
speed. The drive assembly 3~ also supplies power to drive
the dampener assemblies 30 and 32 and inker assemblies 34
and 36. It is contemplated that the printing press 10
could have a construction other than the illustrated
construction. For example, the printing press 10 could be
constructed to print on only one side of the web 12.
To prevent smearing of the ink pattern, the blanket 18
has a continuous cylindrical outer surface which is free of
gaps. By forming the blanket 18 with a continuous outer
surface which is free of gaps, the rolling engagement
between the blanket and printing plate on the plate cylinder
22 tends to be smooth and relatively vibration free. In
addition, smearing of the ink pattern is prevented by making
~269~4
the blanket 18 so that it is compressible at the nip 26.
This results in the blanket 18 having the same surface speed
as the printing plate on the plate cylinder 22 at locations
immediately before the nip, at the nip, and immediately
after the nip to prevent slippage between the outer surface
of the blanket 18 and the outer surface of the printing
plate on the plate cylinder 22.
A cylindrical outer surface 40 of the blanket 18 is
continuous and free of gaps to promote smooth rolling
engagement with the cylindrical outer surface 42 of the
printing plate on the plate cylinder 18. The absence of
gaps in the smooth cylinderical outer surface 40 of the
blanket 18 eliminates bumps or vibrations as compared to
having a gap which rolls into and out of engagement with
the surface 42 of the printing plate on the plate cylinder
22. The elimination of bumps or vibrations tends to
minimize smearing of the ink pattern as it is applied to
the surface 40 of the blanket 18 by the printing plate on
the plate cylinder 22.
By providing the blanket 18 with a cylindrical outer
surface 40 which is continuous and free of gaps, the
diameter of the blanket 18 and the diameter of the blanket
cylinder 14 can be minimized. Thus, an ink pattern can be
applied to the surface 40 of the blanket throughout the
entire area of the surface 40. The ink pattern can extend
across an area where a gap was previously formed in the
surface of known blanket cylinders.
In addition, by providing the blanket 18 with a
cylindrical outer surface 40 which is continuous and free
of gaps, the amount of the web 12 which is wasted during a
printing operation is reduced. In one specific embodiment
of the invention, approximately 0.25 inches of the web is
saved on each revolution of the blanket cylinder 14.
The blanket 18 is at least partially formed of a
compressible material. When a force is applied to the
compressible material of the blanket 18, the volume of the
compressible material decreases. The material of the
blanket 18 is compressed at the nip 26 by the rigid plate
cylinder 22. Since the blanket 18 is at least partially
formed of compressible material, the blanket yields
radially inwardly without any radially outward deformation
of the blanket at the nip 26.
Since the blanket 18 is at least partially formed of a
compressible material, the surface speed of the blanket is
the same at all locations immediately before the nip 26, at
the nip, and immediately after the nip between the blanket
cylinder 18 and plate cylinder 22. Since the speed of
points on the surface 40 of the blanket is the same at
opposite sides of the nip 26 and at the center of the nip,
there.is no slippage between the surface 40 of the blanket
cylinder and the surface 42 of the printing plate on the
plate cylinder 22 at the nip 26. This prevents smearing of
the ink pattern as it is applied to the blanket 18 by the
printing plate on the plate cylinder 22.
2~26954
--10--
If the blanket 18 was formed of an incompressible
material, as is a blanket 18a of Fig. 2, the incompressible
material of the blanket would be deflected radiaIly
outwardly and circum,ferentially sidewardly at a nip 26a by
pressure applied against the blanket by a printing plate on
the plate cylinder 22a in the manner shown schematically in
Fig. 2. The incompressible material of the blanket 18a
which is displaced by deflecting the blanket at the nip 26a,
forms bulges 46a and 48a on opposite sides of the nip 26a.
The bulges 46a and 48a (Fig. 2) are formed because the
volume of incompressible material forming the blanket 18a
remains constant even though the incompressible material is
deflected at the nip 26a. Therefore, the volume of
material which is displaced by the printing plate on the
plate cylinder 22a is equal to the volume of material in
the bulges 46a and 48a. The volume of material displaced
by the printing plate on the plate cylinder 22a is the same
as the volume of material contained in overlapping portions
of the spatial envelopes of the cylindrical outer side
surface 40a of the blanket 18a and the cylindrical outer
side surface 42a of the printing plate on the plate 22a.
This volume of material is contained between the arcuate
plane indicated by the dashed line 50a in Fig. 2 and the
arcuate outer side surface 42a of the printing plate on the
plate cylinder 22a and extends throughout the axial extent
of the plate and blanket cylinders.
The speed of a point on the surface of the
incompressible material of the blanket 18a (Fig. 2) varies
as the point moves from one side of the nip 26a to the
opposite side of the nip. Thus, as the material in the
bulge 46a moves into the nip 26a, the material accelerates
and the surface speed of the material increases. As the
incompressible material leaves the nip 26a and moves into
the bulge 48a, the material decelerates and the surface
speed decreases.
At a given instant, a point 52a on the surface of the
bulge 46a is moving slower than a point 54a at the center
of the nip 26a. Similarly, a point 56a on the surface of
the bulge 48a is moving slower than the point 54a at the
center of the nip 26a. The magnitude of the difference in
the surface speed of the incompressible material of the
blanket 18a at the bulges 46a and 48a and the center of the
nip 26a is a function of the extent of deflection of the
incompressible material of the blanket cylinder at the nip.
As the surface speed of the incompressible blanket
cylinder material moving through the nip 26a (Fig. 2) first
increases and then decreases, ink pattern smearing slippage
occurs between the outer side surface 40a of the blanket
18a and the outer side surface 42a of the printing plate on
the plate 22a. Thus, at locations remote from the nip 26a,
the surface 40a of the blanket 18a and the surface 42a the
printing plate on the plate cylinder 22a have the same
-12- 2~2~9~4
speed. However, as a point on the surface 40a moves onto
the bulge 46a during rotation of the blanket 18a in a
counterclockwise direction (as viewed in Fig. 2), the speed
of the point on the surface of the blanket decreases to a
surface speed which is less than the surface speed of the
printing plate on the plate cylinder 22a.
As a point on the surface 40a of the blanket 18a moves
from the bulge 46a (Fig. 2) toward the center of the nip
26a, the speed of the point increases to a speed which is
greater than the surface speed of the printing plate on the
plate cylinder 22a. As the blanket 18a continues to
rotate, the speed of movement of the point decreases as it
moves from the center of the nip 26a to a point on the
bulge 48a. The speed of a point on the surface of the
bulge 48a is less than the surface speed of the printing
plate on the plate cylinder 22a.
It should be understood that the blanket 18 of Fig. 1
does not have the same construction as the blanket 18a of
Fig. 2. Thus, the blanket 18a of Fig. 2 is formed of an
incompressible material. The blanket 18 of Fig. 1 is at
least partially formed of a compressible material.
Therefore, the blanket 18 of Fig. 1 will not deform in the
manner illustrated schematically in Fig. 2.
The blanket 18 has a hollow tubular construction. The
tubular blanket 18 is fixedly connected with the blanket
cylinder 14 and rotates with the blanket cylinder under the
-13- 2~269~4
influence of the drive assembly 38. However, the tubular
blanket 18 can be removed from the blanket cylinder 14 and
replaced as will be discussed below.
Although the tubular blanket 18 could have many
different constructions, in the specific embodiment of the
invention illustrated herein, the blanket 18 has a
laminated construction. Thus, the blanket 18 includes a
cylindrical outer layer 66 (Fig. 3) upon which the smooth
continuous outer side surface 40 of the blanket is
disposed. The cylindrical outer layer 66 is formed of a
resiliently deflectable and incompressible polymeric
material, such as natural or artificial rubber.
A second or intermediate cylindrical layer 68 (Fig. 3)
is disposed radially inwardly of the outer layer 66. The
intermediate layer 68 has a cylindrical outer side surface
70 which is fixedly secured to a cylindrical inner side
surface 72 of the outer layer 66. In accordance with one of
the features of the invention, the cylindrical intermediate
layer 68 is formed of a resiliently compressible polymeric
material, such as a natural or artificial rubber.
A cylindrical third layer 74 is disposed radially
inwardly of the second layer 68. The third layer 74 has a
cylindrical outer side surface 76 which engages and is
fixedly connected to a cylindrical inner side surface 78 of
the second layer 68. Although the third layer 74 may be
formed of a different material, in the illustrated
-14- 2~26~54
embodiment of the invention, the third layer 74 is formed
of the same incompressible material as the outer layer 66.
The third layer 74 is fixedly secured to a hollow rigid
metal inner layer comprising a mounting sleeve 80 which is
fixedly connected to the blanket cylinder 14. A cylindrical
inner side surface 82 of the third layer 74 is fixedly
secured to a cylindrical outer side surface 84 of the sleeve
80. A cylindrical inner side surface 86 of the sleeve 80
engages a cylindrical outer side surface 88 of the cylinder
14. The sleeve 80, in the illustrated embodiment of the
invention, is formed of nickel and is releasably fixedly
connected with the blanket cylinder 14 to enable the entire
blanket 18 to be slid axially onto and/or off of the rigid
metal blanket cylinder 14 (Fig. 1). This construction
enables the blanket 18 to be replaced after a period of use.
The sleeve 80 is stressed in tension by the blanket
cylinder 14 to provide a tight pressure relationship
between the blanket 18 and the blanket cylinder 14. This
pressure relationship fixes the blanket 18 on the blanket
cylinder 14 so that there is no relative movement
therebetween during operation of the press. The press
includes means for effecting radial expansion of the
tubular blanket while on the blanket cylinder to relieve
the pressure relationship between the blanket 18 and
blanket cylinder 14, as will be described hereinbelow.
When the pressure relationship is relieved, the blanket 18
202~95~
may be manually moved axially off of the blanket cylinder
14. Also, the sleeve 80 must be expanded radially or
tensioned radially outwardly in order to move the blanket
18 onto the blanket cylinder 14. The press is provided
with a means for performing this function, as will be
discussed below.
Although the tubular blanket 18 has been described
herein as having first and third layers 66 and 74 formed of
an incompressible material and a second layer 68 formed of
a compressible material, the tubular blanket 18 could have
a greater or lesser number of layers if desired. For
example, another layer of compressible material could be
provided. This additional layer of compressible material
could be placed immediately adjacent to the layer 68 and
formed with a stiffness which is either greater or less
than the stiffness of the layer 68.
When the plate cylinder 22 and blanket cylinder 18 are
spaced apart from each other prior to a printing operation,
that is, when the press 10 is in a thrown-off condition,
the tubular blanket 18 is in the unrestrained or initial
condition of Fig. 3. At this time, each of the coaxial
layers 66, 68 and 74 has a cylindrical configuration.
When a printing operation is to be undertaken, the
blanket 18 and a printing plate on the plate cylinder 22
are moved into engagement with each other in the manner
shown in Fig. 4. As the blanket 18 and printing plate on
2~6g5~
-16-
the plate cylinder 22 engage each other, the outer layer 66
of the blanket is resiliently deflected radially inwardly
at the nip 26. The distance which the outer layer 66 is
deflected radially inwardly is determined by the amount by
which the initial spatial envelope of the cylindrical outer
side surface 40 of the blanket 18 overlaps the cylindrical
spatial envelope of the outer side surface 42 of the
printing plate on the plate cylinder. Thus, the outer side
surface 40 of the outer layer 66 is deflected radially
inwardly from the position indicated in dashed lines at 88
in Fig. 4 to the position shown in solid lines.
The cylindrical outer layer 66 is formed of an
incompressible material. When the outer layer 66 is
deflected radially inwardly, the volume which is enclosed
by the surface 40 of the outer layer is decreased by the
volume enclosed in the space between the dashed line 88 and
the side surface 40 of the deflected outer layer 66. Since
the outer layer 66 is formed of an incompressible material,
the volume of the outer layer itself does not change when
the outer layer is resiliently deflected by the plate
cylinder 22 in the manner shown in Fig. 4.
In accordance with one of the features of the
invention, the inner layer 68 of the blanket 18 is formed
of a compressible material. When the outer layer 66 is
deflected by the printing plate on the plate cylinder 22,
the inner layer 68 is resiliently compressed. Thus, the
~02695~
-17-
volume of space occupied by the second layer 68 decreases
from an initial or uncompressed volume (Fig. 3) to a second
or compressed volume (Fig. 4) which is less than the
initial volume.
Since the second layer 68 is compressed by the printing
plate on the plate cylinder 22, the outer layer 66 deflects
without bulging radially outwardly at opposite sides of the
nip 26, in a manner similar to that shown in Fig. 2 for the
blanket 18a. Thus, when the outer layer 66 of the blanket
18 is deflected by the printing plate on the plate cylinder
22 (Fig. 4), bulges corresponding to the bulges 46a and 48a
of Fig. 2 are not formed in the outer layer 66. This is
because the inner layer 68 is compressed by an amount
sufficient to accommodate the deflected material of the
outer layer 66.
As a result of the compression of the inner layer 68
and the lack of bulges in the outer layer 66, the speed at
locations on the surface 40 of the outer layer immediately
before the nip 26, at the center of the nip, and immediately
after the nip are substantially the same as the speed of
the surface of the printing plate on the plate cylinder
22. Therefore, there is smooth rolling engagement between
the blanket 18 and printing plate on the plate cylinder 22
at the nip 26 without slippage between the surfaces 40 and
42. Of course, this promotes the transfer of an ink
pattern from the printing plate on the plate cylinder 22 to
the blanket 18 without smearing the pattern.
2~fi~5~
-18-
The compressible second or inner layer 68 is formed from
a resilient foam which contains voids. When the outer layer
66 is deflected and the inner layer 68 is compressed (Fig.
4), the voids are reduced in size or eliminated. As the
voids in the polymeric foam forming the second layer 68 are
compressed, the volume of the compressible material forming
the second layer 68 is reduced.
Prior to deflection of the outer layer 66 of the blanket
18 and compression of the inner layer 68 (Fig. 3), the
tubular blanket 18 and blanket cylinder 14 occupy a
relatively large first volume which is enclosed by the
continuous cylindrical outer surface 40 of the outer layer
66. At this time, the cylindrical intermediate layer 68
contains relatively large voids and occupies a relatively
large first or initial volume. Upon engagement of the
blanket 18 and printing plate on the plate cylinder 22
(Fig. 4), the outer layer 66 of the blanket 18 is deflected
radially inwardly. Deflection of the tubular outer layer
66 results in the blanket 18 occupying a volume which is
less than its original or undeflected volume. However, the
total volume of the outer layer 66 remains constant and the
outer layer does not bulge outwardly adjacent to opposite
sides of the nip 26 in the manner shown in Fig. 2 for the
blanket 14a.
As the outer layer 66 is deflected, the inner layer 68
of the blanket 18 is compressed to a volume which is less
2 ~
than the initial volume of the layer 68. The difference
between the initial volume of the second layer 68 (Fig. 3)
and the compressed volume of the second layer tFig. 4) is
equal to the volume between the dashed line 88 in Fig. 4
and the outer side surface 40 of the outer layer 66.
Therefore, the reduction in volume of the space occupied by
the blanket 18 is accommodated by compressing the second
layer 68 and the only deflection of the outer layer 66 is
in a radially inward direction.
It is contemplated that the blanket 18 could have a
construction which is different than the specific
construction illustrated in Figs. 3 and 4. For example, a
deflectable fabric or inextendable material could be
provided between or in each of the layers 66, 68 and 74.
The number of layers could be either increased or decreased.
Although it is preferred to form the compressible second
layer 68 from a polymeric foam of uniform stiffness, the
second layer could be formed with cylindrical inner and
outer sections of void-containing foam having different
stiffnesses. The compressible inner layer 68 could also be
formed of a material other than foam, for example, a
resiliently deflectable mesh or fabric.
The blanket 18 is formed by spraying adhesive on the
cylindrical outer side surface 84 of the metal sleeve 80.
Preformed strips of material are then wrapped in layers
around the sleeve. The strips include strips of the
~-26~15~
- 2~ -
incompressible material of the outer layer 66, the
compressible material of the second layer 68 and the
incompressible material of the third layer 74. The rubber
material of the strips is then vulcanized to form a solid
body which encloses the metal sleeve 80. Alternatively,
the blanket could be made in a flat planar piece of
material which is then wrapped around sleeve 80 and adhered
thereto. The opposite ends of the piece of material would
abut each other.
Although the construction of only the blanket 18 is
shown in Figs. 3 and 4, the blanket 20 has the same
construction as the blanket 18. Thus, the blanket 20
cooperates with the printing plate on plate cylinder 24 at
the nip 28 in the same manner that the blanket 18 cooperates
with the printing plate on the plate cylinder 22 at the nip
26.
As noted above, the tubular blanket 18 can be
telescopically mounted on and removed from the blanket
cylinder 14 while the blanket cylinder remains in the
printing press 10. Access is provided to one axial end
portion of the blanket cylinder 14 by preferably having a
portion 94 of a side frame 96 of the printing press 10
movable between open and closed conditions. When side
frame portion 94 is in the closed condition, it engages a
bearing assembly 98 to support one end of the blanket
cylinder 14.
2~26~
_2~ _
When it is desired to remove a blanket 18 from the
blanket cylinder 14 and replace it with another blanket, the
portion 94 of the frame is moved from the closed condition
to the open condition illustrated in Fig. 5. This provides
an opening 102 in the frame 96 through which the blanket 18
can be moved. In the embodiment of the invention
illustrated schematically in Fig. S, the movable portion 94
of the frame is mounted for pivotal movement about a
vertical axis by a hinge (not shown) which interconnects
the movable portion 94 and the frame 96. However, the
movable portion 94 could be mounted in a different manner
if desired.
When the movable portion 94 is pivoted to the open
condition of Fig. 5, the end of the blanket cylinder 14
opposite from the side frame 96 supports the entire weight
of the blanket cylinder. To enable the blanket cylinder to
be supported at only one end, a relatively strong bearing
arrangement may be mounted in the opposite side frame or a
counterpoise may be connected with the end of the blanket
cylinder 14 opposite from the side frame 96.
When the movable portion 94 of the side frame 96 has
been moved to the open condition of Fig. 5, a blanket 18
can be manually moved axially off of the blanket cylinder
14 through the opening 102. A new blanket 18 is then
axially aligned with the blanket cylinder 14 and slid onto
the blanket cylinder. Once the new blanket 18 has been
2~26~4
z~
slid onto the blanket cylinder 14, the movable portion 94
of the side frame is moved back to its closed condition in
engagement with the bearing 98 to support the blanket
cylinder for rotation about its horizontal central axis.
An alternative to having a removable portion of the
frame for removal of the blanket is to completely remove
the blanket cylinder from the press by a crane and replace
the blanket at a location away from the press.
Alternatively, the blanket cylinder could be hinged at one
end in such a manner that it could be pivoted into a
position at which the blanket could be removed from the
blanket cylinder.
The blanket 18 and the blanket cylinder 14 have a
metal-to-metal interference fit between the cylindrical
metal sleeve 80 (Fig. 3) on the inside of the blanket 18
and the outer circumference of the metal blanket cylinder
14. Thus, the inner side surface 86 (Fig. 3) of the
cylindrical sleeve 80 has a uniform diameter which is
slightly less than the uniform diameter of the cylindrical
surface 88 on the outside of the metal blanket cylinder
14. The extent of interference required between the sleeve
80 and blanket cylinder 14 must be sufficient to enable the
blanket 18 to firmly grip the blanket cylinder outer
circumference during operation of the press 10 so that the
blanket does not slip relative to the blanket cylinder.
In order to manually slide the blanket 18 onto the
2~2fi~
-23-
by fluid pressure. Thus, the blanket cylinder 14 is
provided with radially extending passages 106 (Fig. 3).
The radially extending passages 106 are evenly spaced apart
in a large number of radial planes which extend through the
blanket cylinder 14 throughout the length of the blanket
cylinder.
The blanket cylinder 14 is hollow and is connected with
a source of fluid (air) under pressure by a conduit 110
(Fig. 5). The air pressure conducted through the conduit
110 to the interior of the blanket cylinder 14 flows
outwardly through the passages 106 (Fig. 3) and presses
against the inner side surface 86 of the metal sleeve 80.
The air pressure causes the metal sleeve 80 to resiliently
expand circumferentially an amount sufficient to enable the
blanket 18 to be manually slid onto the blanket cylinder 14
with a miminum of difficulty.
Once the blanket 18 has been positioned axially on the
blanket cylinder 14, the interior of the blanket cylinder
14 is vented to atmosphere. The sleeve 80 and the blanket
18 then contracts to securely grip the outer surface 88 of
the blanket cylinder 14. The sleeve 80 is then maintained
in tension by the blanket cylinder 14. In one specific
embodiment of the blanket 18, an air pressure of
approximately 60 psi is necessary to effect the expansion
of the sleeve 80. Of course, the magnitude of the air
pressure required to effect the necessary resilient
2~26~5~
-24-
expansion of the sleeve 80 may vary as a function of the
radial thickness of the sleeve 80, the material from which
the sleeve is made and the extent of interference between
the sleeve and the blanket cylinder 14.
The present invention is directed to improving the
quality of printing obtained from an offset printing press
by eliminating or at least minimizing smearing of an ink
pattern applied to sheet material 12 by the printing
press. The printing press includes a blanket cylinder 14
which carries a blanket 18 which applies the ink pattern to
the sheet material. An ink transferring surface on the
plate cylinder 22 applies the ink patteen to the blanket
18. The ink transferring surface and the blanket are
disposed in rolling engagement at a nip 26 formed between
the two cylinders.
The blanket 18 has an outer peripheral circumferential
surface 40 which is free of an axially extending gap. A
blanket 18, in the form of a tube having continuous outer
and inner surfaces 40 and 86, is removably mounted on the
outer peripheral circumferential surface 88 of the blanket
cylinder 14. The outer surface 40 of the tube is disposed
in rolling engagement with an ink transferring surface on
the plate cylinder 22 at a nip 26. Since the outer
peripheral circumferential surface 40 of the blanket 18 is
continuous and free of gaps, smooth and vibration free
rolling engagement is obtained between the ink transferring
2026~
-25-
surface of the plate cylinder and blanket to thereby
promote the transfer of an ink pattern to the blanket
without smearing of the ink pattern.
The blanket 18 is at least partially formed of a
compressible material which is compressed by the printing
plate at the nip 26. By compressing the compressible
material at the nip 26, the outer surface 40 of the blanket
18 has a surface speed which is substantially the same at
locations immediately before the nip 26, at the nip, and
immediately after the nip. This prevents slippage between
the ink transferring surface of the plate cylinder and the
blanket before, at, and after the nip to prevent smearing
of the ink pattern.
The blanket 18 is a tube with a cylindrical outer layer
66 of incompressible material and a cylindrical inner layer
68 of compressible material. The outer layer 66 of the
blanket 18 is deflectable to compress the inner layer 68 of
the blanket. The inner layer 68 of the blanket contains a
plurality of voids which are relatively large before the
inner layer of the blanket is compressed and which are
relatively small in a portion of the inner layer of the
blanket which is compressed by deflection of the outer
layer of the blanket.
The blanket 18 is manually slid onto the blanket
cylinder 14 from an axial end thereof. In order to provide
access to one end of the blanket cylinder 14, preferably a
2~26~54
-26-
portion of the frame adjacent one axial end of the blanket
cylinder may be moved out of the way. The tubular blanket
18 is inserted axially through the frame 96 onto the
blanket cylinder 14 which is aligned with the blanket.
To facilitate insertion of the blanket 18 onto the
cylinder 14, the cylinder interior may have an air pressure
applied thereto. Passages 106 to the outer peripheral
surface 88 of the blanket cylinder 14 communicate with the
interior of the blanket cylinder. Air pressure applied to
the interior of the blanket cylinder 14 is thus communicated
to the interior of the blanket 18 to expand same as it is
inserted onto the blanket cylinder. After the blanket 18
is located on the outer periphery of the blanket cylinder
14, the air pressure may be removed. The blanket 18 then
contracts around the blanket cylinder 14 and tightly engages
and grips the blanket cylinder periphery throughout the
axial extent of the blanket and throughout the
circumferential extent of the inner surface 86 of the
blanket 18.
