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BACKGROUND OF THE INVENTION
This invention relates to a novel and improved corner bead for drywall
construction and the like, and to a novel and improved method for
producing such corner bead.
PRIOR ART
Corner bead is usually installed at outside corners in drywall
construction. Such corner bead is formed, generally by roll-forming, from
an elongated strip of sheet metal, and provides a rounded nose and two
mounting flanges extending at right angles from the opposite sides of the
nose. The mounting flanges are often knurled or embossed to provide a
rough surface so that the joint compound will adhere when the corner is
finished.
The corner bead is installed by securing the mounting flanges along the
surface of the drywall panels adjacent to the corners by a clench or nail
connection. Thereafter, joint compound is applied over the flanges to the
nose and a finished, smooth corner is provided.
Such corner bead is generally produced in high-speed rolling mills which
produce the corner bead bY bending and forming flat sheet metal strips.
Because such corner bead is produced by rolling processes, the labor
content of the product is minimal, and the material costs of the product
constitute by far the largest cost in producing the corner bead.
In order to reduce cost, corner beads have been produced in which the
flanges are slit and expanded laterally to provide expanded metal-type
flanges. It is also known to produce corner bead with a narrow metallic
nose combined with stiff paper mounting flanges. Such products can be
produced at reduced material cost but have not achieved significant
acceptance in the marketplace, possibly because users have felt that the
corner bead was not sufficiently strong and because it is difficult to
handle and install in a perfectly straight condition necessary for a
satisfactory finished corner.
SUMMARY OF THE INVENTION
The present invention provides a novel and improved corner bead for drywall
corners and the like which has a reduced material content and cost. The
present invention also provides a novel and improved method for producing
such corner bead.
The finished metal corner bead of this invention provides a rounded nose
having one metal thickness and two mounting flanges extending at
substantially right angles from the nose having a reduced metal thickness.
The corner bead has the appearance, handling and installation
characteristics which are substantially identical to existing corner bead
structures of uniform thickness. However, the material content, and
consequently the cost of the corner beads incorporating this invention, is
substantially reduced.
The corner bead is produced from a strip of flat sheet metal having a
uniform thickness. The corner bead provides a nose portion which retains
the original thickness of the strip of metal. The flanges, however, are
substantially thinned by shear deformation to increase the width of the
metal forming the flanges. Therefore, a finished corner bead is produced
having the same overall dimensions as typical prior art corner bead, but
is manufactured from a narrower strip of sheet metal stock. With the
present invention, material savings of about 21% can be achieved. For
example, a corner bead in accordance with this invention can be produced
from a strip of metal 1.925 inch wide that has the same overall dimension
of a prior art corner bead requiring a strip of identical metal 2.4375
inch wide.
The shear deformation of the metal forming the mounting flanges is
accomplished in the illustrated embodiment, by a method and apparatus
disclosed in the copending application for U.S. Pat. Ser. No. 07/019,214,
filed Feb. 26, 1987, now U.S. Pat. NO. 4,770,018 assigned to the assignee
of the present invention. Such application is incorporated herein in its
entirety to provide a more detailed disclosure of the method and apparatus
for shear deformation of elongated strips of metal.
The flanges of the illustrated embodiment each provide three laterally
spaced, longitudinal bands of substantially reduced thickness. The
portions of each flange between each band of reduced thickness and the
edge thereof remote from the nose have substantially the same thickness as
the nose. The flanges are knurled or embossed to provide a rough surface
to which joint compound provides a good mechanical bond. Further, the
flanges are provided with spaced openings which may be used for nailing
the corner bead into position during installation, and which also improve
the interlocking with the joint compound.
In accordance with the illustrated method of producing the corner bead, a
strip of metal is first passed through a rolling mill which progressively
applies shear deformation forces to the metal along opposite sides of the
central portion of the strip which ultimately becomes the nose of the
corner bead. These shear forces are applied so that the metal which
ultimately becomes the flanges is shear deformed in a direction
perpendicular to the length of the strip and without any substantial
longitudinal deformation.
These shear forces produce narrow bands of reduced thickness, and, by
sequentially applying shear forces to adjacent unthinned portions, the
width of the bands are increased. The amount of thinning achieved in such
sequential applications of shear forces tends to decrease, probably due to
work-hardening of the material. Therefore, after a first sequence of
sequential thinning operations is performed, a portion of the strip
immediately adjacent to the thinned band is skipped over and a second
sequence of shear deformation force applications is applied which again
produces substantial thinning. In the illustrated embodiment three
sequences are used to produce an increase in the width of the metal
forming the flange by thinning the metal of the bands by about fifty
percent.
Preferably, the final shear deformation and consequent thinning are
terminated while leaving a narrow band about 1/8 inch wide of original
metal thickness along the edge of the flange remote from the nose. This
unthinned edge band provides stability to the flange, and tends to hold
the flanges straight. Further, since clinches are often formed in the
edges of the strip to mount the corner bead the unthinned edges provide
additional strength.
In practice, it has been found that the thinned bands tend to elongate a
very small amount and result in a waviness or non-straight condition
because the central portion of the strip is not correspondingly increased
in length. Therefore, subsequent forces are applied which cause a very
slight increase in the length of the unthinned central portion to increase
the straightness of the strip.
The strip is thereafter punched and passed through rolls which emboss or
knurl the flange portion of the strip to provide an embossed irregular
surface so that the joint compound will form a strong mechanical bond with
the flanges Also, the nails sometimes used to mount the corner beads can
be inserted through the punched holes. These holes also provide an
improved interlocking bond with the joint compound. Further, the embossing
and the punching of the holes also function to improve the straightness of
the strip, which is then roll-formed to its final shape and cut to length.
With this invention, substantial savings in costs of production of corner
beads are achieved, while providing a corner bead structure which is
functionally equal to existing prior art corner beads.
These and other aspects of the invention are illustrated in the
accompanying drawings and are more fully described in the following
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the sequential steps of producing
corner bead in accordance with this invention;
FIG. 2 is a cross section of the strip of metal from which the corner bead
is formed;
FIG. 3 is a cross section illustrating the first intermediate strip shape
after the preliminary nose is formed thereon;
FIG. 4 is a cross section illustrating the second intermediate strip shape
after shear deformation has been completed to reduce the thickness of the
flanges;
FIG. 5 is a side elevation of one of the flanges of a third intermediate
strip shape after the bands closest to the nose have been subjected to a
second thinning step which causes a slight elongation of the unthinned
nose to improve the straightness of the strip;
FIG. 6 is a cross section of the strip after it has been flattened to
position the flanges coplanar for subsequent operations;
FIG. 7 a side elevation of one of the flanges of the subsequent
intermediate strip formed after the flanges have been punched;
FIG. 8 is a side elevation of one of the flanges of a subsequent
intermediate strip after the knurling or embossing operation;
FIG. 8a is an enlarged, fragmentary view illustrating the shape of the
embossments formed in the flange illustrated in FIG. 8 during the knurling
operation;
FIG. 8b is a fragmentary section, taken along line 8b--8b of FIG. 8a;
FIG. 8c is a fragmentary section, taken along line 8c--8c of FIG. 8a;
FIG. 9 is a cross section with the embossments eliminated for purposes of
illustration of a subsequent intermediate strip in which the nose has been
reformed to its final shape;
FIG. 10 is a cross section similar to FIG. 9 of the final strip of corner
bead prior to its being cut to length;
FIG. 11 is a schematic side elevation of the apparatus for producing the
shear deformation of the strip to produce thinned bands along the flanges
thereof;
FIG. 12 is a schematic lateral view of the apparatus of the first shear
deforming station in which initial shear deformation occurs;
FIG. 13 is a schematic, lateral view of the apparatus of the last shear
deformation station;
FIG. 14 is a lateral view of the apparatus for producing additional
thinning of the band adjacent to the nose which operates to slightly
increase the length of the nose and improve the straightness of the strip;
FIG. 15 is a schematic side elevation of the knurling rolls which emboss
the flanges; and
FIG. 16 is a schematic side elevation of a set of straightening rolls which
may be substituted for or provided in addition to the straightening
operation illustrated in FIG. 14.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates, with a block diagram, the sequential steps which are
performed to produce a corner bead structure in accordance with the
present invention. These sequential steps are performed in the illustrated
embodiment by a rolling mill through which a flat strip 10 of metal,
initially having a uniform thickness, progressively moves. Preferably, the
strip 10 is hot dip galvanized, cold-rolled, common quality 1006 steel
which provides a thin corrosion-resistant zinc coating. Such coating,
which is not illustrated, because it is very thin, remains substantially
undamaged during the various forming operations.
In the first operation, the strip of metal 10 is bent along its center to
provide a preliminary nose 11 and coplanar flanges 15. The preliminary
nose is formed during the first operation illustrated at the box 12 by
simple bending and does not result in any change in the thickness of the
metal forming the strip 10. The preliminary nose 11 is provided with a
generally U-shaped profile, as best illustrated in FIG. 3.
In the subsequent rolling operations, the metal of the flanges 15 along
each side of the preliminary nose 11 is thinned by shear deformation
without any significant longitudinal deformation. This shear deformation
of the strip is represented by the second box 13 and results in a strip,
in the illustrated embodiment, having three discrete thinned bands 16, 17,
and 18 along the flanges 15 on each side of the preliminary nose 11. The
bands 16 and 17 are separated by a first unthinned portion 19 and the
bands 17 and 18 are separated by a second unthinned, longitudinal portion
21.
At the completion of the shear deformation or flange reduction operation,
the preliminary nose 11 continues to have a thickness equal to the
original thickness of the strip 10 and the metal forming the bands 16, 17,
and 18 is preferably reduced so that the bands have a thickness equal to
about one-half of the original thickness of the material forming the
bands. Also, the lateral extremities of the strip 22 are not thinned and
remain at the original thickness of the strip.
The apparatus for producing the shear deformation and the thinning of the
flanges is schematically illustrated in FIGS. 11 through 13. Such
apparatus includes a plurality of Work stations 23, schematically
illustrated in FIG. 11. FIG. 12 schematically illustrates the apparatus at
the first work station 23 where the initial shear deformation is
performed. At such work station, the strip 10 passes between a rotating
mandrel 27 and a pair of similar but opposite, laterally abutting pressure
rolls 28 and 29. The mandrel 27 is provided with opposed conical surfaces
31 and 32 and a central peripheral portion 33 shaped to mate with the
interior of the preliminary nose 11 Which supports the preliminary nose
11.
The two pressure rolls 28 and 29 are provided with narrow, conical working
faces 34 and 36, respectively, each having the same cone angle as the
associated conical faces 31 and 32 of the mandrel 27. Between the two
working faces 34 and 36, the rolls are shaped to mate with the exterior
preliminary nose and confine the metal thereof without causing thinning of
the preliminary nose. The two pressure rolls are journaled on a shaft 37
connected to a pair of piston and cylinder actuators 38. Pressure supplied
to the actuators 38 produces a downward force F urging the pressure rolls
28 and 29 toward the mandrel 27 to produce shear deformation of the metal
forming the strip 10 between the working face 34 and the conical surface
31 on one side of the preliminary nose 11 and between the working face 36
and the conical surface 32 on the other side of the preliminary nose 11.
The pressure rolls and the mandrel operate to apply forces to the opposite
surfaces of the strip 10 in a lateral direction with respect to the strip,
and without any appreciable longitudinal component. Such forces function
to produce lateral shear deformation of the material of the strip and
produce a narrow, thinned band 16a extending longitudinally of the strip
on each side of the preliminary nose 11. In the illustrated embodiment,
the reduction of thickness of the material forming the band 16a is almost
fifty percent. Therefore, it has a thickness of about one-half the
thickness of the material forming the preliminary nose 11 and also the
remainder of the strip.
The thinned band 16a formed on each side of the preliminary nose 11 is
substantially narrower than the required thinned band 16 illustrated in
FIG. 4. Therefore, in the next work station 23 a similar apparatus is
provided which thins the portion of the metal along the sides of the bands
16a remote from the preliminary nose 11 to increase the width of the
thinned band, and such procedure is repeated at subsequent work stations
23 until a thinned band having a width of the thinned band 16 is formed on
each side of the preliminary nose, as illustrated in FIG. 4. After the
thinned band 16 is formed, similar apparatus at subsequent work stations
of the same type progressively forms thinned bands 17 and 18. However at
the completion of the thinned band 16 the apparatus is sized to skip over
the unthinned portion 19 and commence the thinning operations to produce
the thinned band 17. Such skipover is provided to re-establish a thinning
in material of the strip which has not been work-hardened by previous
thinning operations. Similarly, a skip is made at the location 21 after
the completion of the thinned band 17, and in multiple passes, the thinned
band 18 is produced.
FIG. 13 illustrates the final thinning operation in which the thinned band
18 is completed. Here again, the strip 10 is passed between pressure rolls
28a and 29a which cooperate with a mandrel 27a to increase the width of
the band 18 to its final width. The pressure rolls 28a and 29a are
preferably formed with conical containment surfaces 35a which are relieved
back slightly from the working surfaces 34a and 36a. These containment
surfaces 35a function to apply sufficient pressure to the previously
thinned portion of the band 18 to prevent back flow of metal into the
previously thinned portion. This ensures that the flow of metal is in a
lateral direction toward the edges of the strip.
The number of sequential thinning operations performed between each skip is
determined by the material being thinned and, in the illustrated
embodiment, involves three progressive thinning stations for each band 16,
17, and 18.
Reference should be made to the application Ser. No. 07/019,214,
incorporated by reference above, for a more detailed description of the
manner in which the thinning operations are performed and the apparatus
for performing such operations.
In the illustrated embodiment, the production of the three thinned bands
16, 17, and 18 on each side of the preliminary nose 11 results in an
increase in width of the strip by about twenty-one percent. However, even
if the thinning results in a smaller increase in the width of the strip,
for example, a fifteen percent increase in strip width, substantial cost
savings ar achieved.
The thinned band 18 extends to an unthinned portion 22 at each extremity of
the strip. This portion which is unthinned tends to maintain straightness
of the strip and is therefore left at its original thickness. Also when
clinches are used to mount the corner bead, they are formed in the
unthinned edges.
With this shear deformation, virtually all of the displacement of the metal
occurring during the thinning operations is laterally with respect to the
length of the strip. However, even if very minute amounts of elongation
deformation occur, for example, less than one percent the resulting strip
is not completely straight. It is believed that this is because the metal
of the preliminary nose portion does not elongate during the thinning
operations, but that very slight amounts of elongation occur along the
thinned bands 16, 17, and 18.
Since it is necessary that the ultimate corner bead be very straight and
the flanges planar, a straightening operation is performed, as illustrated
in FIG. 14 and as represented by the box 41 in FIG. 1. In this operation,
a pair of relatively wide pressure rolls 42 and 43 cooperate with a
mandrel 44 to perform a slight amount of additional thinning of the bands
16.
In this work station, the pressure rolls 42 and 43 are provided with
conical working faces 46 and 47, respectively, having a width
substantially equal to the width of the previously thinned band 16. Such
rolls having such wide working faces produce deformation which includes
longitudinal flow of the material forming the two thinned bands 16, and
produce an intermediate strip as illustrated in FIG. 5, in which the
thinned band 16 has been further thinned and subjected to longitudinal
deformation. This creates shallow ripples 48 along the thinned band
between the preliminary nose portion 11 and the first unthinned portion
19. These internal stresses producing these ripples 48 also stretch the
material forming the preliminary nose 11 a small amount so as to reduce
the non-straightness of the two flanges 15 on each side of the preliminary
nose.
The next sequence of operation involves the flattening represented by the
box 51, in which the strip 10 is passed between rolls which bend the
flanges 15 to a substantially coplanar condition illustrated in FIG. 6
without significantly changing the shape of the preliminary nose 11, and
while bending the unthinned portions 22 to a position substantially
coplanar with the flanges 15.
In the next operation, holes 62 and 63 are punched in the two flanges 15 at
intervals along the length thereof as represented by the box 61. The
apparatus for performing these punching operations can be of any suitable
type capable of producing a pattern of openings 62 and 63 (illustrated in
FIG. 7) at intervals along the length of each of the flanges 15. These
openings, which are typically formed in corner beads at intervals along
the flanges thereof, function to provide an interlocking structure to
better lock the joint compound in position. Further, in instances in which
nails are used to mount the corner bead, nails can be inserted through the
openings 62 or 63. However, typically, a clench is formed in the flanges
by a clench tool when the corner bead is installed. These openings 62 and
63 are believed to provide even further straightening of the flanges and
of the strip, which is believed to be the result of further stress relief
and stress redistribution in the material forming the strip.
Thereafter, the strip illustrated in FIG. 7 is passed through knurling
rolls represented by the box 56 and illustrated at 57 and 58 in FIG. 15.
These knurling rolls are formed with mating projections 57a and recesses
58a which emboss the two flanges 15 and provide an intermediate strip
having flanges 15, best illustrated in FIGS. 8 through 8c. The knurling
rolls are shaped so that during the knurling operation, they do not engage
the preliminary nose 11, but only engage the flanges 15 on the opposite
sides of the preliminary nose 11.
In the illustrated embodiment, the flanges are embossed with a multiplicity
of small, square projections 59 located in laterally and longitudinally
aligned rows of closely spaced projections. As best illustrated in FIGS.
8a through 8c, the projections 59 are square, provide rounded corners 61
and an offset, planar wall portion 62. It should be understood that other
shapes and patterns of projections can be used, and that the present
invention is not limited to the particular embossed projections
illustrated.
It has been found that by embossing or knurling the flanges 15, further
straightening of the intermediate strip occurs. This is because the
deformation performed during the knurling operation redistributes the
internal stresses in the material of the flanges in a more uniform manner
and compensates for variations in longitudinal length of the various
elements of the flanges and the nose. The embossing, in the illustrated
embodiment, extends to the edge of the strip, as best illustrated in FIG.
8, and includes the unthinned portions 22. This embossing operation not
only improves the straightness of the intermediate strip, but also
provides a roughened surface to which the joint compound can better adhere
when the corner bead is installed for use and the corner is finished with
joint compound.
In the next operation, represented by the box 66, the strip is passed
through rolls which finish-form the preliminary nose to the final nose
configuration 67, illustrated in FIG. 9, to accurately size and shape the
nose. The projections 59 are not illustrated in FIG. 9 to simplify the
drawings.
In the last forming operation, represented by the box 71, the two flanges
15 are bent to extend at substantially right angles relative to each other
to produce the final cross section of the finished corner bead 72
illustrated in FIG. 10. Preferably, the flanges extend at an angle
slightly less than 90.degree.. Here again, the projections are not
illustrated to simplify the drawings. Thereafter, the strip is cut off at
the desired lengths, as represented by the box 76, to complete the
manufacturing operation of the corner bead 72.
If desired, a straightening operation can be performed by passing the
flattened strip formed in the operation of the box 51, and illustrated in
FIG. 6, through straightening rolls illustrated schematically in FIG. 16.
Such straightening rolls include a plurality of rolls 77 which engage one
face of the strip and a plurality of rolls 78 which engage the opposite
face on opposite sides of the associated rolls 77. The two sets of rolls
77 and 78 are positioned so that the strip is flexed back and forth in a
direction normal to the flanges 15 as the strip passes between the rolls.
The rolls of the set 77 which engage the side of the strip from which the
preliminary nose 11 extends are notched out so as to prevent the
flattening of the nose.
Such straightening rolls tend to stretch the preliminary nose 11 and the
flanges to a uniform length, and function to improve the straightness of
the intermediate strip being processed. The straightening rolls of FIG. 16
can be substituted for the straightening operation illustrated in FIGS. 1,
5, and 14, or can be performed in addition to such operation.
The finished corner bead in accordance with the present invention is
preferably formed from a hot dip galvanized strip of metal on which a zinc
corrosion coating has been previously applied and can be produced
utilizing the exact material and coating which have heretofore been used
to produce conventional prior art corner strip. However, with the present
invention the initial strip can be about twenty-one percent narrower while
producing a finished corner bead having exactly the same overall
dimensions as a prior art conventional corner bead. This substantial
savings in the material required to produce the corner bead is achieved
without degrading in any way the functional qualities of the finished
corner bead and without resulting in any material change in the manner in
which the corner bead is installed.
Such savings in material costs are extremely important, since it is
conventional to form corner bead in rolling mills with substantially no
labor expense. Further, the rolling mill for producing corner bead in
accordance with the present invention, although somewhat more complex than
conventional rolling mills, can be operated at the same line speeds
previously employed during the manufacture of conventional prior art
corner bead.
The corner bead produced in accordance with this invention is identical to
some prior art corner bead except for the fact that the flanges 15 are
each formed with thinned bands extending lengthwise of the corner bead.
The finished nose 67 remains at the original thickness of the strip, and
therefore provides the same strength and rigidity present in the prior art
corner beads.
Although the preferred embodiments of this invention have been shown and
described, it should be understood that various modifications and
rearrangements of the parts may be resorted to without departing from the
scope of the invention as disclosed and claimed herein.
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