1. Technical Field
This invention is in the field of nails with integral locking means comprising protrusions on the shank in the form of longitudinal ribs. Class 411, subclass 452 appears to be an appropriate classification.
2. Background
Nails have been around for thousands of years. During that time they have been made using different methods. One-way of forming a nail was to start with a bit of steel and shape it by hand on an anvil. Another way was to cut elongated rectangles from a sheet of steel. During these earlier times, nails were a high tech item and were quite valuable. It was not uncommon to burn down old buildings in order to collect the nails from the ashes.
In the early 1800s there was a change in the way nails were made. Wire making had been developed to a point that wire was readily available and round shaped nails, made from wire, began to appear. These nails were made from a length of wire that had a flattened cylindrical head hammered on one end and a point cut on the other. This form of nail was very easy to make from wire and has not changed in any fundamental way for over one hundred years. Some minor features such as enlarged heads, cement coatings, or surface textures have been added in order to improve the holding power when used in specific applications such as dry wall or roofing operations.
There are some disadvantages to a round cylindrically-shaped nail.
First, a round cylindrical nail uses the maximum amount of steel for a given cross-section. The cost of the steel wire is between 50 and 80 percent of the total expense in making nails, and any decrease in the steel used in each nail would lead to a significant increase in potential profit.
The second disadvantage of a round cylindrical nail is that it has a tendency to wedge the wood apart. Assuming the wood is not split, a common occurrence, the wood fibers spread apart in such a way as to form an eye-shaped opening around the nail. This shape decreases the holding power of a round nail by reducing the amount of surface area, the nail perimeter times its length, which is in contact with the wood. As a corollary to the first disadvantage, a round nail has the smallest amount of surface area for any amount of steel.
The disadvantages of a round nail have not gone unnoticed. U.S. Pat. No. 340,692, issued Apr. 27, 1886 to Bailey for a “Wire Nail,” discloses a nail with a dozen or so longitudinal ridges and channels on the shank. In the illustrations, the height of the ridges and depths of the channels are not large, but the nail is useful as a furniture nail because it will not turn on its axis. Also, the strength to weight ratio is increased.
The invention described herein is not in the field of rail spikes. Rail spikes, rather than join two pieces of wood, hold down an iron rail. The traditional rail spike has an almost square cross-section. However, there have been a large number of attempted improvements in this field as well. An example is U.S. Pat. No. 927,301, issued Jul. 6, 1909 to Walcott for a “Spike.” This patent discloses a modified rail spike with a shank that has a half-round shape opposite the rail side and, on the rail side, three longitudinal convex flanges with two intervening concave grooves. The inventor emphasizes that “The curves of the concave grooves run smoothly and continuously into the convex flanges without angles.” This has special value in avoiding splitting of the tie and increasing holding power.
U.S. Pat. No. 2,014,746, issued Sep. 17, 1935 to Robergel for “Method of Making Nails,” discloses a nail having a “cross-shaped or, more generally, star shaped” shank. FIG. 3 illustrates the cross-shaped version as having rectangular arms of equal length. The method of making this particular part of the nail is not specified, but it is pointed out that the beginning and ending cross-section have the same area.
U.S. Pat. No. 4,637,768, issued Jan. 20, 1987 to Rabe for a “Nail-Type Fastener . . . ,” discloses a nail having a shank cross-section with three four-sided V-like grooves disposed at 120° around the nail shank. This cross-section is manufactured with three cold-rollers at 120° followed by a second set to deepen the grooves. The purpose of the grooves is to increase the ratio of frictional surface to weight so as to increase pull grip. The ribs between grooves increase flexural rigidity. The cold-rolling operation is designed to produce material flow in both longitudinal and transverse directions. The transverse flow is to increase strength.
U.S. Pat. No. 4,755,091 issued Jul. 5, 1988 to Potucek et al. for “Star Fasteners” and U.S. Pat. No. 4,973,211 issued Nov. 27, 1990 to Potucek for “Star Fastener,” disclose non-round nail shapes. The preferred embodiment appears to be a nail with a five pointed star-like cross-section. These nails performed as well as, or in some cases better than, traditional nails and were made using 50 percent less steel. These patents also discuss a 15% increase in surface area compared to a round nail of the same overall diameter and a 60% increase in holding power due to wedging and compression of fibers in the cups between the star points. As illustrated in U.S. Pat. No. 4,800,746, issued Jan. 31, 1989 and U.S. Pat. No. 4,833,906, issued May 30, 1989, both to Potucek, five pointed nails could be produced by cold rolling five grooves longitudinally down round wire feedstock.
U.S. Pat. No. 5,836,826, issued Nov. 17, 1998 to Haraminac for a “Machine for Making Star Nails”, attempted to overcome some problems with the previous approaches by using form rollers, but on conventionally formed nails as opposed to wire bar feedstock. These grooves displaced 50 percent of the steel during the forming process, producing a nail with a finished outer diameter larger than the starting wire. Although the new shape appeared to be promising, attempts to manufacture nails of this shape for a commercial market have not yet been successful. There appears to be several reasons for this.
First, the rolling system required to produce this shape is not common to the nail industry. Beyond that, the star nail rolling system proved to be difficult and expensive to build and maintain. The rollers in test machines had rolling edges which would not hold their shape long enough to be economically viable, and the machines could not be made to operate fast enough to be competitive.
Second, the displacement of the wire during the rolling process was hard to control or predict. Displacing fifty percent of the material in order to achieve a 50% steel savings was a significant feature of the Potucek patents, but moving such a large amount of material created technical problems that have not been overcome to date.
The preferred embodiment in Potucek's Star Fastener(s) patents is quite clearly a nail shank having a circular central shaft with five radial fins (rather like a starfish with thinner arms than the animal.) Although the number of fins can vary from three upwards, they are always radial. Even though the new star shape appears to be a significant improvement on a round nail, the very star shape may have hindered development of practical production machinery.
Lastly, U.S. Pat. No. 5,143,501, issued to Leistner et al. for a “Grooved Nail and Strip” discloses three different nail shank cross-sections. One has four symmetrically disposed concave quarter-circle grooves with radii the same or less than the half-width of the shank from ridge top to ridge top. Two opposing ridge tops are flat to facilitate forming a nail strip. Another cross-section has three similar, but larger radii, grooves and ridges at 120° and the third cross-section is essentially square. Compared to other non-circular cross sections, these are relatively smooth.
This patent teaches that “the holding power of a nail is simply the degree to which the wooden fibers are displaced transversely to, i.e., across the axis of the grain of wood,” see FIG. 5. Thus, it states that, in practice, teeth or notches and various forms of knurlings or serrations have produced very little, if any, increase in holding power. It goes on to state that, although “some manufacturers still insist on achieving the sharpest possible teeth or notches,” teeth or notches would tear the wood and reduce holding power. Therefore, the object of this invention is to provide increased wood separation for the same weight nail in a shape that also allows forming into nailing sticks. The cross-sections can be produced by extruding through a die with additional pointing and heading operations.
To add to the debate, one trick that experienced carpenters use to avoid splitting wood with common nails in some situations, is to blunt the point. This breaks some of the fibers so that it is easier to separate the remaining ones. Holding power should be reduced, however.
In spite of some inventive effort over many years, nails with non-circular cross-section shanks (or non-square ones in the case of rail spikes) as discussed in these patents are not in widespread use. Part of the problem is probably the difficulty in manufacturing.
Therefore, what is needed is a nail shank design that, compared to a round one, provides reduced weight but has the same or increased holding power and can be manufactured using practical forming apparatus.
The invention comprises a shank cross-section for a reduced material fastener that is selected to provide a parting line. Having a parting line means that the fastener may be made using two opposing dies to cold form the cross-section. The cross-sections do not have to be symmetrical with respect to the parting line as long as hypothetical dies can be separated. Typical fasteners include common nails.
Cross-sections having parting lines may have fin-like protuberances that result in less material being used for the same overall outline as a round cross-section. Intervening valley-like regions between the fin-like protuberances are connected to the tops of adjacent protuberances with substantially straight lines. Although not essential, it is preferably that the valley regions and fin tops are rounded. Sometimes it may be desirable to use a conical transition from the shank to the head as described herein.
Although not necessary to practicing the invention, cross-sections can be conveniently designed by following a process described herein that uses computer aided design to produce a desired overall diameter and cross-sectional area.
Although not necessary to produce a reduced material fastener employing the shank described herein, a particular quarter-circle rolling die design, also described herein, could work on wire feedstock to produce a headed and pointed nail and separate the finished nail in an integrated operation.
The invention will now be described in more detail with reference to preferred forms of the invention, given only by way of example, with reference to the accompanying drawings, in which:
Second, on each side of the parting line are a series of fin-like protuberances (fins) 2 that are separated by valley-like indentations (valleys) 3. Usually, for aesthetic reasons at least, the shape would be symmetrical about the parting line.
The third general design feature, perhaps the most important, is that the fin and valley shapes should not undercut each other relative to the parting line.
Fourth, the fin and valley designs may be produced from any combination of straight or curved lines, but in the preferred embodiment, the top of the fins and bottom of the valleys should have a non-negligible radius of curvature to reduce tool wear. For simplicity in a design process, as described below, part circles can be used and connected with straight lines.
In a radial nail, the bending characteristics are essentially the same for any direction in which the bend occurs. With the design concept present in this invention, the bending moment can be greater in all directions using less material. This is because the bending strength of a beam is proportional to a dimension perpendicular to the bend and the square of a dimension in the plane of the bend. As applied to nails, for the same amount of material, fins increase the effective diameter perpendicular to the bend in all directions. This is easy to comprehend with Potucek's star shapes, but is also true for most of the cross-sections of the present invention
For a typical design,
After forming as in
Computer-Aided Design Process:
As shown in
The next step is to decide how many fins are desired and place that number of starting circles equally around the bounding diameter as shown in
Since, for 12 fins, the desired shape will be symmetrical to the vertical and horizontal axis, it is sufficient to conduct all further operations on only one quadrant.
The next step is to determine how deep will be the valleys between fins. As an example, assume a depth of half way as will be explained with reference to
As shown in
The fillet radii 19a and 19b require an extra step. The radius 19b must be moved away from radius 19a so that the two radii can be connected with a tangent line. To move 19b, begin by creating vertical construction lines 20 as shown in
In
To increase the area slightly, offset the lower valley arc away from the vertical axis by an estimated amount (here it was 0.0024 in.), as in
Trim away the replaced sections and recalculate the area of the new shape,
Lastly, mirror the new shape along both the vertical and horizontal axis and remove the axis lines resulting in the complete shape shown in
Compared to a round nail 24 using the same amount of material, the new design has a bounding diameter that is 35% larger and a perimeter of that is 365% larger. Moreover, the bending moment is larger because the same material has been converted into structure that is thinner but has a larger effective diameter. Since beam strength is proportional to the square of the dimension in the plane of bending, the new design will be stronger.
There are so many possible variations of the improved nail described herein that it is impossible to anticipate how a nail designer will create each embodiment. Before a shape is created, the designer will need to consider many factors. The starting metal shape may be round or some other shape, the number of fins may be few or many, the desired amount of material reduction may be great or small, the fins may be sharp or rounded and the nails may be large or small. With all that in mind, the preceding design process yields what is currently thought to be one of the better designs for an ordinary nail.
Although the 45% material savings in the example is fairly substantial, this amount is by no means necessary. Since raw material is a large part of nail costs, a savings of 15% or even 10% is commercially attractive.
Nail Pointing:
After the two part die is separated, conventional point making cutters could be used in a separate operation to form a pointed nail. Although not an essential feature of the invention, another method utilizing a modified split die to form a point may be advantageous.
As illustrated in the cross-sectional drawing in
In operation, first, the split die parts 30a and 30b are brought together with sufficient pressure to form the bilateral nail shape. Then, with the partially formed nail still held by the split die 30a and 30b, head forming die 34 would be pressed into the cavity 35 to form the head 36 (illustrated without a transition). At this point, the lower end of the wire 37 would still be part of the continuous spool of wire.
A pointed finished nail 38 can be formed by rotating the die parts 30a and 30b as illustrated in
Making the entire nail requires that dies 30a and 30b execute a transverse movement wherein they are squeezed together followed by a rotational movement. The rotation may not be about a fixed axis. However, since all movements are in a plane, it should not be difficult to construct a series of cams or use four or more hydraulic actuators that would carry this out. The curvature of the surfaces 32a and 32b in the plane of the paper need not be circular, but could be tailored to simplify die rotation. At least one practical solution to all of these problems is believed to be straightforward and well within the skill of nail making machine designers.
Working Examples:
The end of the nail in the photomicrograph was produced by cutting with a saw blade. The original wire diameter was about 0.14 inches and 6 inches long. The dies were compressed with a small 50 ton hydraulic press, but this was not enough force to close the gap between the two dies. It is estimated that at 150 ton press would have been adequate.
Based on data for the roller cross-section, the area is 0.013 inches. An equivalent round nail would have a diameter of 0.13 inches and a perimeter of 0.404 inches. The perimeter of this cross section is 0.724 inches, about 80% more, and the approximate diameter is 0.155 inches, a 20% increase. (The actual shank in
The method that is used to produce the nails in commercial production quantities will depend on a number of production factors. Either die stamping short pieces or rolling wire with additional cutting, pointing and heading operations could be used. This art is old and fairly well developed so that it would not be difficult for one of ordinary skill to adapt these or other methods to produce nails having the shapes of this invention.
While the best mode for carrying out the invention has been disclosed, it should be understood that the description is only illustrative of a range of equivalents. For example, nothing herein limits the invention to nails made from steel or aluminum or those designed purely for wood.
While nails usually have heads and points, the novel fastener cross-sectional design disclosed herein may be applied to fasteners that lack one or more of these structures. Those skilled in the art will be able to apply unforeseeable equivalents of the invention disclosed herein to a range of applications.
Thus, the limits on the invention are set out in the following claims. In the claims, it should be understood that a “parting line” puts inherent limitations on the structure on both sides of it as discussed above with respect to
This application claims priority to provisional application no. 60/434,351, filed on Dec. 18, 2002 by the same inventor, the entire contents of which are incorporated herein by reference.
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Number | Date | Country | |
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60434351 | Dec 2002 | US |