Screen roller printing frame improvements

A silk screen printing frame having screen tensioning rollers which are rotatable to stretch a printing screen edgewise across the frame and are mounted on the frame by improved roller mounting assemblies that secure the rollers to roller mounting members at the roller ends. Each roller mounting assembly has an end block portion fixed within the adjacent roller end, a wrench engaging portion beyond the roller end by which the roller may be turned and which may be integral with or a separate part from the end block portion, a bolt extending axially through the end block and wrench engaging portions and the adjacent roller mounting member, and a lock nut threaded on the outer end of the bolt for releasably securing the roller against turning. A head on the inner end of the bolt engages the inner side of the end block portion to restrain the bolt against being pulled outwardly through the assembly when the lock nut is tightened to secure the roller against turning.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
This invention relates generally to the silk screen printing art and more 
particularly to a novel printing screen stretch frame. 
2. PRIOR ART 
Simply stated, a printing screen stretch frame comprises a rectangular 
frame structure having a central rectangular opening and screen tensioning 
means along the sides of the frame opening for gripping edges of printing 
screen placed across one side of the frame and stretching the screen 
edgewise. One type of printing screen frame has screen tensioning draw 
bars which are movable laterally in the plane of the frame to stretch and 
release the printing screen. Another type of screen frame, referred to 
herein in places as a roller frame, has screen tensioning rollers which 
are rotatable to stretch and release the screen. 
Two basic types of roller frames are known in the art. One type comprises 
four rigid frame members arranged along the four sides of a rectangle and 
joined end to end at the corners of the rectangle to form a rigid 
rectangular frame part and screen rollers rotatably mounted on the frame 
members. The other basic type of roller frame lacks such a rigid frame 
part and includes only corner brackets at the four corners of the frame, 
screen rollers extending along the four sides of the frame between the 
adjacent corner brackets, and roller mounting means securing the rollers 
to the corner brackets. This latter type of screen frame comprises only 
the corner brackets, rollers, and roller mounting means and is rigidized 
by rigidly securing the rollers to the brackets. The present invention is 
concerned with roller screen frames of this latter kind. 
A number of roller screen frames with and without separate rigid frame 
members have been devised. Among these known frames are those illustrated 
in FIGS. 5-7 of the attached drawings and those described in the patents 
listed below. 
The roller frame illustrated in FIGS. 5-7 of the attached drawings includes 
screen rollers 20 attached to corner brackets 22 by bolts 24 having outer 
heads 26 which are accessible for tightening and releasing the bolts and 
threaded shanks 28 which extend inwardly through the corner brackets, 
wrench heads 30 for turning the rollers, and end blocks 32 fixed within 
the roller ends into threaded engagement with nuts 34 fixed within the end 
blocks. 
U.S. Pat. No. 3,601,912 dated Aug. 31, 1978, to Dubbs discloses a screen 
frame having screen rollers 14, 16 joined by corner brackets 18. 
U.S. Pat. No. 3,908,293 dated Sep. 30, 1975 to Newman discloses a screen 
frame having screen rollers 18, 20 extending between corner brackets 26. 
Secured within the roller ends are end blocks 58 having integral wrench 
heads 86 for turning the rollers and integral threaded studs 72 which 
extend through the corner brackets into threaded engagement with outer 
lock nuts 84 for securing the rollers against rotation. 
U.S. Pat. No. 4,430,814 dated Feb. 14, 1984, to Wulc discloses a screen 
frame having screen rollers 16, 18 extending between corner brackets 24 
and secured to the brackets by threaded studs 34 which are press fitted 
within the roller ends and mount inner nuts 36 for turning the rollers and 
outer nuts 40 for securing the rollers against rotation. 
U.S. Pat. No. 5,018,442 dated May 28, 1991, to Hamu discloses a screen 
frame having screen rollers 16 extending between corner brackets 14. 
Threaded studs 34, 34a are press fitted (FIG. 2) or threaded (FIG. 5) in 
end blocks 28, 28a fixed within the roller ends and mount inner nuts 38 
for turning the rollers and outer nuts 40, 40a for securing the rollers 
against rotation. 
The screen frames referred to above and other existing screen frames have 
certain deficiencies which this invention overcomes. The frame arrangement 
of FIGS. 5-7, for example, requires complex and costly machining of the 
end blocks 32 to fixedly receive the nuts 34. In the Dubbs, Hamu, and Wulc 
patents, tightening the lock nuts on the studs to secure the rollers 
against turning exerts substantial stress on the press-fitted or threaded 
joints between the studs and the rollers. In order to prevent their 
failure by rupture of the press-fitted joints and stripping of the 
threaded joints, the joints must have a relatively long axial length 
sufficient to resist such rupture or stripping. This, in turn, increases 
the mass of metal in and thereby the weight and cost of the rollers. Also, 
the threaded joints require internal threading of the end blocks and 
increases the frame cost. The use of cross bolts in Newman to secure the 
end blocks in the rollers requires machining of the rollers which 
increases the roller cost and renders the rollers prone to fluid leakage 
around the bolts into the rollers. 
SUMMARY OF THE INVENTION 
This invention provides an improved roller screen frame and an improved 
roller mounting means for the frame. The improved roller screen frame 
comprises a rectangular frame structure having a central rectangular 
opening and composed of tubular screen tensioning rollers along the sides 
of the opening, roller mounting members at the four corners of the frame 
opposite the adjacent roller ends, and improved roller mounting assemblies 
according to the invention securing the roller ends to the adjacent 
mounting members. Each roller has a longitudinal rotation axis and means 
for gripping an edge a printing screen placed across one side of the frame 
and is rotatable in one direction on its rotation axis to wind the screen 
on the roller and thereby stretch the screen across the frame. 
The improved roller mounting assembly of the invention includes an end 
block portion fixed within the adjacent roller end, a wrench engaging 
portion between the roller end and the adjacent roller mounting member, 
and a bolt. This bolt has a shank extending along the roller axis through 
the end block portion, the wrench engaging portion, and the adjacent 
roller mounting member, and a lock nut threaded on the outer end of the 
shank at the outer side of the mounting member. 
Each roller is rotatable in one direction by engagement of wrenches with 
the the wrench engaging portions of the roller mounting assemblies to 
stretch the printing screen across the frame. The roller lock nuts are 
rotatable into and from engagement with the adjacent roller mounting 
members to releasably secure the rollers against turning in the opposite 
direction and thereby retain the stretched screen in its taut condition. 
According to one feature of the invention, the bolt of each roller mounting 
assembly has a shoulder at its inner end which engages the inner side of 
the end block portion to positively restrain the bolt against outward 
endwise movement through the block portion when the outer lock nut is 
tightened against the roller mounting member to secure the roller against 
turning. This shoulder carries the entire axial load exerted on the bolt 
when its outer lock nut is tightened. As a consequence, the joint failure 
and thread stripping problems referred to earlier in connection with prior 
roller mounting arrangements are avoided and the axial length of the end 
block portion within the roller may be substantially reduced without risk 
of failure of the joint between the bolt and end block. 
According to another feature of the invention, the bolt of each roller 
mounting assembly is pressed axially through, rather than threaded in, its 
respective end block portion. This eliminates the need of internally 
threading the end block portion. Relative rotation of the bolt and end 
block portion is prevented by engaging formations on the bolt and block 
portion. According to the preferred practice of the invention, for 
example, the bolt is made of a harder material than the end block portion, 
and its shank is formed with axial serrations or ridges which bite or cut 
into the softer end block material when the bolt is pressed through the 
block portion to prevent turning of the bolt in the end block portion. 
In two presently preferred embodiments described herein, the end block 
portion and wrench engaging portion of each roller mounting assembly are 
separate parts. The bolts of these preferred assemblies are pressed 
through the separate end blocks in the manner mentioned above. In one of 
these two embodiments, the separate wrench engaging part is a roller 
turning nut which is threaded on the bolt in the manner explained in my 
earlier mentioned U.S. Pat. No. 5,018,442. Rotation of the nut in the 
direction in which the roller turns to stretch the printing screen jams 
the nut against the end of the roller so that further rotation of the nut 
in this direction rotates the roller to stretch the printing screen. In 
the other of these two preferred embodiments, the bolt is pressed through 
both the end block part and the separate wrench engaging part. In a third 
presently preferred embodiment, the end block and wrench engaging portions 
of the roller mounting assembly are integrally formed as a single unitary 
part through which the bolt is pressed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to these drawings and first to FIGS. 1-4, the illustrated 
roller screen printing frame 40 comprises a rectangular frame structure 
(only one full side and two partial sides of the frame structure shown) 
having a central rectangular opening 42, screen tensioning rollers 44 
along the four sides (only three sides shown) of the opening, roller 
mounting members 46 at the frame corners between the adjacent roller ends, 
and improved roller mounting means 48 according to the invention securing 
the rollers to the mounting members. The screen rollers 44 have screen 
gripping means 50 like those shown in my above mentioned U.S. Pat. No. 
5,018,442. In use, a printing screen 52 is placed across one side of the 
frame. The screen edges are attached to the screen gripping means 50, and 
the rollers are rotated in directions to wind the screen on the rollers 
and thereby stretch the screen edgewise across the frame. During screen 
printing, the frame is positioned with the screen side of the frame 
lowermost and with the printing screen in contact with the work to be 
printed. 
Except for the roller mounting means 48, the roller frame 40 is 
conventional. That is to say, the frame rollers 44 and roller mounting 
members 46 are conventional and thus need be described only in sufficient 
detail to enable a full and complete understanding of the invention. With 
this in mind, each screen roller 44 comprises a tube having the 
cross-sectional configuration shown in FIG. 4. Along the top of the roller 
in FIG. 4 is a channel receiving a pair of screen gripping rods 54 to form 
the screen gripping means 50. Each roller mounting member 46 is an 
L-shaped bracket like that shown in my U.S. Pat. No. 5,018,442 and having 
a pair of right-angle bracket arms 56 extending across the ends of the 
adjacent rollers 44 normal to their rotation axes. 
Each end of each roller 44 is secured to the adjacent mounting member 46 by 
a roller mounting means 48 of this invention. Each roller mounting means 
comprises a mounting assembly including a roller end block portion 58, a 
wrench engaging portion 60, a bolt 62, and a lock nut 64. The end block 
portion 58 of each roller mounting assembly is shaped to complement the 
internal cross-section of its roller and is adhesively bonded, welded, or 
otherwise rigidly fixed within the adjacent roller end. The wrench 
engaging portion 60 is coaxially disposed beyond the end of the roller. 
The mounting assembly bolt 62 has a head 66 at the inner side of the end 
block portion 58 and a shank 68 which extends along the rotation axis of 
the roller 44 through the end block portion 62, the wrench engaging 
portion 60, and the adjacent arm 56 of the adjacent roller mounting 
bracket 46. The lock nut 64 is threaded on the outer end of the bolt shank 
at the outer side of the bracket arm. 
In the particular inventive embodiment illustrated in FIGS. 1-4, the end 
block portion 58 and wrench engaging portion 60 of each roller mounting 
assembly 48 are separately formed parts. The end block 60 has an annular 
generally disc-like shape and is disposed in a plane transverse to the 
rotation axis of its roller 44. The head 66 of the assembly bolt 62 seats 
against the inner side of the block. The bolt shank 68 has an inner 
unthreaded portion adjacent the head 66 which is press fitted within a 
central hole in the end block. According to one feature of the invention, 
the end block 58 and the bolt 62 have engaging formations 70 which secure 
the bolt against rotation relative to the end block. In the preferred 
embodiment illustrated, the engaging formations 70 include longitudinal 
spline-like serations or ridges which are circumferentially spaced about 
the bolt shank 68 within the end block. The bolt is made of a harder 
material than the end block so that when the bolt is pressed axially 
through the block, the ridges 70 cut into the material of the block to 
firmly fix bolt against turning in the block. The engaging formations 70 
could be a polygonal portion of the bolt engaging in a mating polygonal 
opening in the end block. 
In the embodiment of FIGS. 1-4, the wrench engaging portion or part 60 of 
each roller mounting assembly 48 is a hexagonal roller nut. This roller 
nut is threaded on the shank 68 of the assembly bolt 62 in the manner 
described in my U.S. Pat. No. 5,018,442, such that rotation of the nut on 
the bolt in the direction in which the respective roller 44 turns to 
stretch the printing screen 52, jams the nut against the end of the 
roller. This prevents further rotation of the nut in this direction 
relative to the roller. Accordingly, the rollers 44 may be rotated to 
stretch the printing screen 52 across the frame 40 by turning the roller 
nuts 60 with wrenches. The rollers are secured against reverse rotation to 
retain the stretched screen in its taut condition by threading the lock 
nuts 64 tightly against the adjacent mounting bracket arms 56 to firmly 
grip these arms between the lock nuts and the roller nuts 60. 
The modified screen printing frame 40a of FIGS. 8-10 is identical to the 
frame 40 just described except for the following differences between the 
roller mounting assemblies 48a of the modified frame and those of the 
frame 40. The wrench engaging portion or part 60a of each roller mounting 
assembly 48a is not a nut threaded on the assembly bolt 62a as in the 
frame 40, but rather a member of hexagonal nut-like shape having a central 
hole. The bolt shank 68a has a relatively long unthreaded portion which is 
pressed through, and has ridges 70a which extend through, both the end 
block 58a and the wrench engaging member 60a to secure the bolt against 
turning relative to the block and member. 
The modified screen printing frame 40b of FIGS. 11-13 is identical to the 
frame 40 first described except for the following differences between the 
roller mounting assemblies 48b of the modified frame and those of the 
frame 40. The end block portion 58b and wrench engaging portion 60b of 
each roller mounting assembly 48b are not formed as separate parts as in 
the frame 40, but rather as a single integral part. This integral part has 
an inner end portion which is fixed within the respective roller and forms 
the end block portion 58b of the mounting assembly and an outer end of 
hexagonal cross-section which forms the wrench engaging portion 60b of the 
mounting assembly. The shank 68b of the assembly bolt 62b has a relatively 
long unthreaded portion which is pressed through, and has ridges 70b which 
extend through, both the end block and wrench engaging portions of the 
integral part to secure the bolt against turning relative to the part. 
The modified screen printing frames of FIGS. 8-13 are otherwise identical 
to and used in the same way as the frame of FIGS. 1-4. If desired, the 
wrench engaging portions of the roller mounting assemblies may be welded 
to the adjacent roller ends about the full circumference of the rollers, 
as shown, to seal the ends of the rollers against liquid leakage into the 
rollers. In the case of FIGS. 1-4, the weld between the wrench engaging 
portions or nuts and the rollers may be omitted to permit removal of the 
nuts. These nuts may be constructed of a harder material than the rollers 
to permit the nuts to be jammed against the rollers with sufficient force 
to form a seal between the nuts and rollers. 
The improved screen printing frames and roller mounting assemblies of the 
invention have the following important features. Engagement of the heads 
of the roller mounting assembly bolts with the assembly end blocks 
eliminates the need for threaded or press fit joints to support the axial 
loads exerted on the bolts when the outer lock nuts are tightened to 
secure the screen rollers against rotation. As noted earlier, these joints 
are prone to failure by rupture or stripping when the bolts are axially 
stressed by tightening the lock nuts. The bolt holes in the end blocks 
need not be internally threaded, which results in a cost saving. Another 
advantage of locating the bolt heads within the rollers for engagement 
with the end blocks is the elimination of the cost of internally shaping 
the end blocks to fixedly receive nuts, as in the prior art screen frame 
arrangement of FIGS. 5-7. The improved screen frames of the invention are 
thus characterized by relative simplicity of construction and reduced cost 
of manufacture.