BACKGROUND OF THE INVENTION

The fabrication of expanded titanium mesh is well known. Since the fabrication of expanded titanium mesh usually involves considerable cold-working of the titanium, it has been the usual practice, to employ grade 1 titanium which, apparently because of its higher purity, has the highest formability. Thus, when quantities of expanded mesh articles are prepared, one is more likely to encounter a much higher* percent of off-spec ^" or faulty articles when using grade 2 titanium than when using grade 1 titanium. By "off-spec" or "faulty" it is meant that the articles have broken, split, or otherwise damaged portions due to their inability to withstand the extensive cold-working of the titanium during fabrication of the expanded mesh articles. Grade 1 titanium is appreciably more expensive than grade 2 and the available quantity of grade 1 is appreciably less than that of grade 2.

There is an economic incentive to find ways of using grade 2 titanium in expanded mesh articles in place of the more expensive grade 1 titanium. There is also an incentive to find ways for efficiently using the more abundant grade 2 titanium in the preparation

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of expanded mesh, thereby broadening the field of usage of the grade 2 material.

As a convenient source of information to show the composition and properties of not only grades 1 and 2, but also other grades (3 through 12) of titanium, one may refer to American National Standard Institute's ASTM-B-265-79, published in February, 1980 in the Annual Book of ASTM Standards.

SUMMARY OF THE INVENTION Grades of titanium which have less formability than grade 1 titanium are more efficiently used in fabricating expanded mesh articles by employing expander dies which provide expanded slit openings wherein the long way dimension/short way dimension (LWD/SWD) ratio ^" of the openings is at least about 2.5, preferably at least about 2.7.

DETAILED DESCRIPTION

Figures 1 through 4, none of which are drawn to scale, are provided for use as visual aids for describing the preparation of expanded mesh, using techniques which are well known to practitioners of the art. Figures 1-A through 1-E illustrate steps taken in preparing expanded mesh titanium. Figure 2 illustrates a portion of the expanded mesh before being flattened. Figure 3 illustrates a portion of an expanded sheet after being flattened. Figure 4 illustrates a sheet levelling operation.

In a general sense, the present invention is applicable to all grades of titanium which have less formability than grade 1 titanium. The preferred grade

is grade 2 and for purposes of conciseness the descrip¬ tions provided here are, for the most part, directed to grade 2 in contrast to grade 1. The descriptions, properties, and.identities of the grades are those which conform essentially to ASTM-B-265-79.

Some of the paramount differences between grade 1 and grade 2, at least some of which contribute to the better formability ("workability") of grade 1, are:

1. Grade 1 normally contains lower levels of impurities, especially iron and oxygen;

2. Grade 1 has lower tensile strength, lower yield strength, and higher elongation, all of

" which contribute to, or are indicative of, its better formability; and

3. ^'* Grade 1 can be bent cold through an angle of

105° (without fracture in the outside of the bent portion) on a bend diameter less than that of grade 2.

Figures 1-A through 1-E illustrate steps taken in preparing expanded mesh titanium. In Fig. 1-A there is a base (1) having a tool steel shearing edge (2), a titanium sheet (3) and die (4). For purposes of discussion there is shown an index point (5) on die (4). The titanium sheet is shown as having been advanced by one strand width (6) to protrude past edge (2) to beneath die (4). Figure 1-B illustrates that the die has been pressed downward, shearing plate (3) in places governed by the width and depth of the die points which

protrude downwardly;- this also stretches the strands and provides "expansion" of the sheet. The die travel is set so that the die, acting along edge (2), does not shear the sheet completely. Fig. 1-C illustrates that die (4) has been raised back to its starting position and moved sideways (indexed) as shown by the arrow and the sheet advanced by one strand-width. Figure 1-D shows the die has been brought down again, the die points shearing the sheet as shown by downward movement of the index point. In Figure 1-E it is shown that the die has been raised back ^' to its starting position, indexed back to the left to its original position, and the sheet (3) advanced another strand width; it is ready to perform another shearing cycle. The shearing cycles are repeated until the sheet-expanding operation is completed. The expansion process generally expands the length of the titanium sheet in an amount of from about 1.5 to about 5 times its original dimension.

Figure 2 illustrates a portion of the ex- panded mesh before being flattened. In Figure 2 the strand width (W), the sheet thickness (T), the long way dimension (LWD), the long way opening (LWO), the short way dimension (SWD) and the short way opening (SWO) are shown. The LWO is the length of the opening along its "long way" and the SWO is the width of the opening along its "short way". The LWD is the length between bond centers along the long way and SWD is the length between bond centers along the short way; thus the LWD and the SWD take into account the width of the bonds, which are determined principally by the strand width. Note, as viewed in Figure 2, that two strands of a given bond are bent downward, and two strands of the same bond are bent upward. The expanding process,

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which bends and stretches strands out of the plane of the original flat sheet, subjects the titanium to considerable "working". Expanded sheets may be several feet wide and several feet long. The flattening process also subjects the metal to additional "working".

Figure 3 illustrates a portion of an expanded sheet after passing through flattening rollers (not shown) which compress or flatten the expanded, mesh so that all the strands and bonds essentially lie in the same plane, even though the plane is generally arcuate. The bond areas (10) are the areas where the strands intersect. For illustration purposes bond-sheared edges (11) are contrasted with random-sheared edges (12). The flattening process subjects the metal to additional "working"

Figure 4 illustrates a sheet levelling operation. In order to get the flattened expanded mesh to lie in a flat plane it is generally best to run the mesh through a levelling operation, such as shown in Figure 4. Figure 4 depicts a plurality of upper rollers (R) banked above lower rollers (R ), the lower rollers being along a plane (Pi) or centerline and the upper rollers being along a plane (P ₂ ) or centerline which is oblique with respect to plane (P _x ). As the expanded mesh is passed through the rollers in the direction indicated by the arrow, the rollers "work" the mesh in a progressively lessening corrugated manner until it emerges from the effects of the last roller as a flat sheet of expanded mesh. This levelling process also subjects the metal to additional "working".

In many applications the expanded mesh is subjected to even more stringent "working" when it is bent to provide a desired configuration. This even includes, in some applications, being bent into a U-shape or V-shape, using an infinitely small bend- diameter.

It has been found that one can employ titanium of grade 2 for making flattened, levelled expanded mesh (or other grades which ordinarily are less "workable" than grade 1) if one uses a die which produces openings which have a ratio of LWD/SWD of at least about 2.5, preferably at least about 2.7. Most preferably a ratio of LWD/SWD in the range of about 3 to about 6 is used, with the W/T ratio being preferably in the range of about 1 to about 2. The openings in the mesh so-produced generally comprise about 40% to about 60% of the total area of the mesh, as computed from the amount of the expansion. The thickness (T) of the strands is preferably in the range of about 0.07 cm to about 0.77 cm, most preferably in the range of about 0.07 cm to about 0.2 cm.

The grade 2 ( or other grades less "workable" than grade 1) titanium meshes so-prepared withstand the rigors of the expanding, flattening, and levelling described above, without there being a substantial number of rejects, and also may be bent using infinitely small bend-diameters if the above LWD/SWD ratio is employed: The bending may be done along a centerline lying in the long way dimension or the short way dimension, and, in most cases can be bent diagonally.

The following data is for comparative illus¬ tration purposes, but the invention is not limited to the particular embodiments illustrated.

Example 1

The following comparisons between grade 1 and grade 2 titanium are made employing the expanding, flattening, and levelling steps such as described above, using dies appropriate for making the opening sizes and strand widths shown in following Table I. In Table I, the measurements shown are the dimensions after expanding, but before flattening and levelling. The "Remarks" column shows results obtained by bending the flattened, and leveled mesh beyond 90° (i.e., about 105°) using a small bend radius.

TABLE I

Strand Ratio Approx. Ti Sheet width SWD LWD LWD/ % Grade T(cm) W (cm) (cm) (cm) SWD open Remarks

1 0.16 0.16 0.635 1.27 2.0 48 no cracks

1 0.16 0.16 0.711 1.27 1.79 60 no cracks

2 0.16 0.16 0.737 1.27 1.72 60 cracked

2 0.16 0.16 0.737 2.67 3.6 60 no cracks

2 0.09 0.15 0.508 2.67 5.3 40 no cracks

2* 0.16 0.15 0.737 2.67 .3.6 60 no cracks

2** 0.16 0.20 0.737 2.67 3.6 45 no cracks

2 0.152 0.152 0.711 1.27 1.79 60 cracked

2 0.152 0.152 0.737 2.54 3.45 60 no cracks

2 0.102 0.152 0.508 2.54 5.0 40 no cracks ψ This specimen had SWO of 0.5 cm.

^' * This specimen has SWO of 0.4 cm.

In Table II below, approximate measurements of the first seven of the above specimens are shown, in the same sequence, to demonstrate that a small change in LWD and SWD is usually obtained during flattening and levelling.

TABLE ir

Ti SWD LWD Ratio of Compared with Ratio Grade (cm) (cm) SWD/SWD of LWD/SWD of Table I

1 0.69 1.37 1.99 2.0

1 0.81 1.42 1.75 1.79

2 0.81 1.35 1.67 1.72

2 0.86 2.73 3.17 3.6

2 0.64 2.74 4.28 5.3

2 0.86 2.73 3.17 3.6

2 0.86 2.75 3.20 3.6

Thus flattening and levelling processes can also cause small changes in the thickness and width of the strands and bonds.

Example 2 The following Table III illustrates data for grade 2 titanium compared with grade 1 titanium in order to demonstrate effect of LWD/SWD ratio on bend- ability after flattening and levelling. • In these, the W/T ratio is about 1/1 before flattening and levelling.

TABLE III

Sample T Ratio of No. cm LWD/SWD Results of Bending After Levelling*

1* 0.11 1.88 bent double (180°) without cracking bent along length, width, 4 diagona using very small bend radius.

2 0.11 1.88 some cracking during levelling, broke completely apart when bent beyond 90°.

3 0.11 2.73 bent double (180°) without crack¬ ing when bent through about zero radius along length and width; small amount of cracking when bent 180° diagonally through about zero radius.

4 0.16 3.0 bent double (180°) through zero radius, without cracking, along width, along length, and diag¬ onally.

* Sample No. 1 is grade 1 titanium for comparison; other samples are grade 2.

** "Zero radius" means the tightly bent, double- back (180°) has been mashed so tightly along the bend ^' that there is essentially no distance between the folded sheets; they are disposed tightly against each other; this is a very severe test for bendability.

LWD/SWD ratios of as much as 6 or more may be used, but there is generally no additional benefit, within the purview of the present invention, for exceeding a ratio of about 6.