SELF-CLEANING TUBULAR SCREEN
United States Patent 3667615
A self-cleaning tubular screen adapted for de-watering or classifying particulates and the method of making such screen. The screen embodies a slotted construction to provide a self-cleaning "V" slot that enlarges in the outward radial direction. The support rods for the tubular screen are located on the inner periphery of the tubular screen and attached to the wide face of the wedge-shaped wire in a manner so as to preclude any interference with the slot opening. This is accomplished by utilizing a wire having a ridge portion on the wide face thereof to prevent the weld connecting the wire to the rods from disturbing the edges of the wide face.
Application Number:
05/077944
Publication Date:
06/06/1972
Filing Date:
10/05/1970
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Export Citation:
Assignee:
Universal Oil Products Company (Des Plaines, IL)
Primary Class:
Other Classes:
228/904, 166/231
International Classes:
B01D29/11; E21B43/08; E21B43/02; B01D29/22
Field of Search:
210/497.1,497H 209/393,395,407 166/231,232,233 29/488
Primary Examiner:
Zaharna, Samih N.
Assistant Examiner:
Calvetti, Frederick F.
Parent Case Data:
This application is a continuation-in-part of my copending application Ser. No. 787,708, filed Dec. 30, 1968 now U.S. Pat. No. 3,561,605.
Claims:
I claim
1. A self-cleaning tubular screen comprising a plurality of spaced apart longitudinal support rods and a wedge-shaped wire wound helically about said support rods and attached thereto, said wedge-shaped wire forming a resulting continuous "V" slot of increasing cross-sectional area in the outward radial direction, said wedge-shaped wire having ridge means on the base thereof facing said support rods for attaching the wire to said support rods in a manner to maintain the edges of the base of said wire free from irregularities.
2. The tubular screen of claim 1 further characterized in that said longitudinal support rods are straight and that said support rods are spaced equal distance apart around the inner periphery of said tubular screen.
3. The tubular screen of claim 2 further characterized in that said longitudinal support rods are parallel to the longitudinal axis of the said tubular screen.
4. The tubular screen of claim 1 further characterized in that said ridge means is a continuous ridge.
5. The tubular screen of claim 1 further characterized in that said ridge means is a projection provided only at spaced intervals corresponding to the junctions with the support rods.
6. In a method of making a tubular screen which comprises winding a wedge-shaped line helically about a plurality of support rods and fusing the wire to said support rods to form a resulting continuous "V" slot of increasing cross-sectional area in the outward radial direction, wherein the improvement comprises forming a ridge on the base of said wedge-shaped wire prior to fusing of the wire to the support rods and fusing the ridge portion of said wire to the support rods in a manner to maintain the edges of the base of said wire free from irregularities.
7. In the method of claim 6 wherein said ridge is formed continuously along the base of said wire.
8. In the method of claim 6, wherein said ridge is formed in spaced intervals along the base of said wire corresponding to the junctions with the support rods.
1. A self-cleaning tubular screen comprising a plurality of spaced apart longitudinal support rods and a wedge-shaped wire wound helically about said support rods and attached thereto, said wedge-shaped wire forming a resulting continuous "V" slot of increasing cross-sectional area in the outward radial direction, said wedge-shaped wire having ridge means on the base thereof facing said support rods for attaching the wire to said support rods in a manner to maintain the edges of the base of said wire free from irregularities.
2. The tubular screen of claim 1 further characterized in that said longitudinal support rods are straight and that said support rods are spaced equal distance apart around the inner periphery of said tubular screen.
3. The tubular screen of claim 2 further characterized in that said longitudinal support rods are parallel to the longitudinal axis of the said tubular screen.
4. The tubular screen of claim 1 further characterized in that said ridge means is a continuous ridge.
5. The tubular screen of claim 1 further characterized in that said ridge means is a projection provided only at spaced intervals corresponding to the junctions with the support rods.
6. In a method of making a tubular screen which comprises winding a wedge-shaped line helically about a plurality of support rods and fusing the wire to said support rods to form a resulting continuous "V" slot of increasing cross-sectional area in the outward radial direction, wherein the improvement comprises forming a ridge on the base of said wedge-shaped wire prior to fusing of the wire to the support rods and fusing the ridge portion of said wire to the support rods in a manner to maintain the edges of the base of said wire free from irregularities.
7. In the method of claim 6 wherein said ridge is formed continuously along the base of said wire.
8. In the method of claim 6, wherein said ridge is formed in spaced intervals along the base of said wire corresponding to the junctions with the support rods.
Description:
This invention relates to an improved form of self-cleaning screen for use in separating fluids from solid particulates and the method of making said screen. More specifically, this invention relates to a self-cleaning tubular screen formed by helically winding a wedge-shaped wire about a plurality of support rods and attaching the same thereto in a manner to provide for radial outward flows. In other words, the cross-sectional area of the resulting continuous "V" slot increases in the outward radial direction to give a self-cleaning effect when the flow of material initiates from the center of the tubular screen. The screen is susceptible to being rotated about its longitudinal axis so as to centrifugally force the material introduced into its interior, radially outward.
It is recognized that "wedge-form" separation screens are known and are used in various services such as well screens, vibrating or shaker screens, ore classifiers, and the like. Screens of tubular shape also have been used in a rotating action to centrifugally force a fluid from slurry materials. However, it is to be noted that tubular screens of the self-cleaning type are generally fabricated to accommodate out-to-in flows. If an in-to-out flow screen is to be manufactured, it is generally fabricated as an out-to-in flow screen and then reformed in a reverse manner in order to have the "V" slot increase in an outward radial direction. This procedure is, of course, expensive and generally prohibitive.
It is thus a principle object of this invention to provide for an in-to-out flow tubular screen, suitable for rotation, having the benefit of a self-cleaning, but inexpensive construction.
It is also an object of this invention to provide a method for making such a screen.
Broadly, this invention is a self-cleaning tubular screen comprising a plurality of spaced apart longitudinal support rods and a wedge-shaped wire wound helically about said support rods and attached thereto, said wedge-shaped wire forming a resulting continuous "V" slot of increasing cross-sectional area in the outward radial direction, said wedge-shaped wire having ridge means on the base thereof facing said support rods for attaching the wire to said support rods in a manner to maintain the edges of the base of said wire free from irregularities.
The means by which this type screen can be fabricated is generally known and is described in Johnson U.S. Pat. Nos. 2,046,457, 2,046,458, 2,046,459, 2,046,460, and 2,046,461. Summarizing, these patents cover the apparatus and process whereby a wedge-shaped wire is helically wound about support rods and fused or spot welded at each junction of wire and rod. The welding operation is described as an electrical resistance weld that fuses the two pieces together, the wire sinking into the rod some predetermined distance. Thus, the improved method comprises forming a ridge on the base of the wedge shaped wire prior to fusing of the wire to the support rods and fusing the ridge portion of said wire to the support rods in a manner to maintain the edges of the base of said wire free from irregularities.
The resulting screen of this invention may be used for separating a flow or slurry of material which is introduced into the interior of the tubular screen. The fluid part of the slurry would be drawn off and thusly separated from solid particulates through the continuous slot by means of gravity, by means of maintaining a pressure differential between the interior and the exterior surfaces of the screen, or by means of rotational force; the particular means, however, not being a subject of this invention. In the simplest embodiment, the longitudinal flow of slurry is effectuated by maintaining the screen at a slope.
The solid particulates contained in the slurry of material are prevented from clogging in the continuous "V" slot because the narrowest part of the "V" slot is at the entry point on the interior periphery of the screen, and there is no depressed zone to permit particle bridging effects. Even in the event that a particulate would temporarily catch itself at one point of the slot, other particulates would tend to free it because of the continuity of the "V" slot. Of course other uses of the novel screen are contemplated, as for example, as distributor means in a fluid contacting chamber.
In this present invention, as previously noted, the wedge shaped wire is wound initially around the support rods to form the "V" slot with a cross-sectional area increasing in the outward radial direction. If conventional wedge-shaped wires are welded or otherwise fused to the support rods, the edges of the wide part or base section of the wedge would be disturbed with irregularities, and the continuous feature of the resulting "V" slot would be interrupted. Clogging would more likely take place, and any classification operations would be interferred with. Thus, the novel cross-sectional profile for the wedge-shaped wire is used as a means of fabricating the present in-to-out flow screen. As set forth, this novel profile includes a ridge means along the central portion of the wide face of the wire, which is used to assist in effectuating a weld to the longitudinal support rods; however, it is not intended to limit the ridge means to any one shape or cross-section. Any shape chosen should be large enough to take a weld at the junction of a support rod and also have the dimensional requirements to prevent the weld from disturbing the edge of the wire.
The support rods will generally be equally spaced around the inner periphery of the tubular screen but may be spaced in any desirable manner. Preferably, the rods are arranged to be made parallel to the longitudinal axis of the screen. Also, the cross-sectional profile of the support rods may be of most any shape but consideration must be made in order to facilitate a strong weld. Round, oval, square, rectangular and all possible combinations may be considered probable cross-sectional profiles. In choosing a proper shape, the overall strength of the screen must be taken into account, in addition to the strength of the weld.
Reference to the accompanying drawing and the following description will serve to more fully illustrate the design and construction of the various embodiments of the present invention, as well as to assist in pointing out advantageous features in connection therewith.
DESCRIPTION OF DRAWING
FIG. 1 is a schematic longitudinal elevational view of the one embodiment of the tubular screen with the slot formed to increase in area radially outwardly.
FIG. 2 is the schematic end view of the embodiment of FIG. 1.
FIG. 3 is the schematical representation of the novel method of making a tubular screen.
FIG. 4 is a cross-section of a portion of the screen shown in FIG. 3 as taken along section line 4--4.
FIGS. 5a, 5b, 5c, 5d, and 5e are various cross-sectional configurations of support rods.
FIGS. 6a, 6b, 6c, and 6d are various cross-sectional configurations of wedge-shaped wires.
Referring now particularly to FIGS. 1 and 2 of the drawing, there is shown a tubular screen 1 formed by having a wedge-shaped wire 2 wound helically around a plurality of spaced apart, longitudinal, support rods 3. The wire 2 is wound in such a way so to form a continuous slot 4; however, because of the wedge-shape of wire 2, the slot 4 increases in cross-sectional area in a radial outward direction. This feature provides a self-cleaning type slot. Longitudinal support rods 3 are shown equally spaced around the inner periphery of the screen 1 and parallel to the longitudinal axis of the screen. The wedge-shaped wire has a projecting portion or ridge means 7 on the wide face or base thereof. Thus, when wire 2 is attached to rods 3, the projecting portion 7 provides means for attaching the wire in a manner to maintain the edges 12 and 13 of the base free from irregularities.
The improved method of making a self-cleaning screen is schematically illustrated in FIG. 3 and 4 of the drawing. The method may include placing the support rods 3 around a cylindrically shaped mandrel, form, or other suitable holding means 10 and holding them in position by means not shown. The form 10 is rotated about its axis of rotation and the wedge-shaped wire 2 is helically wound around and attached to the rods 3. The fusing or attaching may be accomplished by using electrical resistance or ultra-sonic welding. The wire 2 is pressed against the support rods 3 by a pressure applying means 11. If electrical resistance welding is used for attaching the wire and rods, an electrical current may be applied through the pressure applying means 11 to weld the wire to the rods. If ultra-sonic welding is utilized, the pressure applying means may be vibrated by conventional ultra-sonic means not shown to fuse the wire to the rods. The improved method includes forming a ridge 7 on wire 2 prior to the attachment to rods 3. This may be accomplished during the initial forming of the wire by conventional means such as drawing or extruding. The ridge portion 7 of wire 2 is fused to the rods 3 in a manner to maintain the edges 12 and 13 of the wire free from irregularities.
The tubular screen 1 of FIGS. 1 and 2 is adapted to receive a slurry of materials to the open interior zone 6. The fluid in the slurry can be drawn off through the continuous slot 4 via suction, gravity, or centrifugal means. The power means for effectuating the suction or for effectuating the rotation of the tubular screen is not shown but may be provided in any conventional manner. Also, the screen can be supported at a slope to establish flow of slurry from the inlet to outlet of interior zone 6.
FIGS. 5a, 5b, 5c, 5d, and 5e show various alternative cross-sectional profiles of longitudinal support rods than can be used for various embodiments of the tubular screen. A wedge-shaped wire 18 is schematically shown in each figure to indicate where attachment would take place at the junction of support rods and wire. Also shown is a slight sinking or embedment 24 of the various support rods 19, 20, 21, 22, and 23 into the ridge portion 17 of wire 18 which takes place when the junction is subjected to the pressure of electrical resistance or ultra-sonic welding and is thus a characteristic of the method of fabrication. FIG. 5a shows a sufficiently rectangular shaped profile, FIG. 5b, a tear drop shaped profile, FIG. 5c, a wedge-shaped profile, FIG. 5d, an oval-shaped profile, and FIG. 5e, a square profile. A typical round profile is shown in FIG. 2. By illustrating these various profiles it is, of course, not the intention to limit the choice of design to those shown.
In FIGS. 6a, 6b, 6c, and 6d there are shown various alternative cross-sectional profiles of a wedge-shaped wire used to form a continuous slot. A support rod 25 is schematically shown in each instance to indicate where attachment would occur between wound wire and support rod means. Again, the sinking or embedment 26, characteristic of the method of fabrication, is shown. The profiles of the wires 27, 35, 37, and 38 are shown as a simple wedge; however, this should not be a limiting factor with respect to this invention since other wedge-shapes are also contemplated within the scope of the improvement.
In FIG. 6a the profile of a wedge-shaped wire without the novel ridge means is shown. It can be seen that if wire 27 is helically wound about a plurality of support rods 25, a "V" slot 28 of increasing cross-sectional area in the outward radial direction 29 will be formed, however, there will be welding irregularities and a resulting non-uniform slot. To be self-cleaning and uniform, the opening 30 of the "V" slot 28 should be uninterrupted, i.e., if the wedge-shaped wire is merely shaped as shown in FIG. 6a, then weld irregularities would form along the entire breadth 31 of the wire, when that particular junction is subjected to an electrical resistance welding means. This would have the affect of interrupting the continuity of the edges 32 and 33 of the wire at every junction of the wire and rod, thereby creating disturbances or irregularities along the edge of the wire, which would impair the ability of the screen to be self-cleaning.
To provide for an uninterrupted opening, a novel ridge 34 is incorporated into the profile, as shown on wire 35 in FIG. 6b. This ridge 34 will most likely be continuous over the circumferential length of the rod 35, but alternatively, may be broken and only occur where needed for attachment purposes. The ridge 34 serves as a means for attaching the wire in a manner to maintain the edges 42 and 43 free from irregularities. In other words, at this contact point a welding operation is possible without disturbing the edges 42 and 43, consequently leaving an uninterrupted opening 44. Other possible shapes of ridges 39 and 40 are shown in FIGS. 5c and 5d respectively but should not be considered as limiting designs. The important considerations in shaping each of these ridges are strength of weld and the prevention of disturbances along the edges of the wire.
Although I have described my invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be restored to without departing from the spirit and the scope of the invention as hereinafter claimed.
It is recognized that "wedge-form" separation screens are known and are used in various services such as well screens, vibrating or shaker screens, ore classifiers, and the like. Screens of tubular shape also have been used in a rotating action to centrifugally force a fluid from slurry materials. However, it is to be noted that tubular screens of the self-cleaning type are generally fabricated to accommodate out-to-in flows. If an in-to-out flow screen is to be manufactured, it is generally fabricated as an out-to-in flow screen and then reformed in a reverse manner in order to have the "V" slot increase in an outward radial direction. This procedure is, of course, expensive and generally prohibitive.
It is thus a principle object of this invention to provide for an in-to-out flow tubular screen, suitable for rotation, having the benefit of a self-cleaning, but inexpensive construction.
It is also an object of this invention to provide a method for making such a screen.
Broadly, this invention is a self-cleaning tubular screen comprising a plurality of spaced apart longitudinal support rods and a wedge-shaped wire wound helically about said support rods and attached thereto, said wedge-shaped wire forming a resulting continuous "V" slot of increasing cross-sectional area in the outward radial direction, said wedge-shaped wire having ridge means on the base thereof facing said support rods for attaching the wire to said support rods in a manner to maintain the edges of the base of said wire free from irregularities.
The means by which this type screen can be fabricated is generally known and is described in Johnson U.S. Pat. Nos. 2,046,457, 2,046,458, 2,046,459, 2,046,460, and 2,046,461. Summarizing, these patents cover the apparatus and process whereby a wedge-shaped wire is helically wound about support rods and fused or spot welded at each junction of wire and rod. The welding operation is described as an electrical resistance weld that fuses the two pieces together, the wire sinking into the rod some predetermined distance. Thus, the improved method comprises forming a ridge on the base of the wedge shaped wire prior to fusing of the wire to the support rods and fusing the ridge portion of said wire to the support rods in a manner to maintain the edges of the base of said wire free from irregularities.
The resulting screen of this invention may be used for separating a flow or slurry of material which is introduced into the interior of the tubular screen. The fluid part of the slurry would be drawn off and thusly separated from solid particulates through the continuous slot by means of gravity, by means of maintaining a pressure differential between the interior and the exterior surfaces of the screen, or by means of rotational force; the particular means, however, not being a subject of this invention. In the simplest embodiment, the longitudinal flow of slurry is effectuated by maintaining the screen at a slope.
The solid particulates contained in the slurry of material are prevented from clogging in the continuous "V" slot because the narrowest part of the "V" slot is at the entry point on the interior periphery of the screen, and there is no depressed zone to permit particle bridging effects. Even in the event that a particulate would temporarily catch itself at one point of the slot, other particulates would tend to free it because of the continuity of the "V" slot. Of course other uses of the novel screen are contemplated, as for example, as distributor means in a fluid contacting chamber.
In this present invention, as previously noted, the wedge shaped wire is wound initially around the support rods to form the "V" slot with a cross-sectional area increasing in the outward radial direction. If conventional wedge-shaped wires are welded or otherwise fused to the support rods, the edges of the wide part or base section of the wedge would be disturbed with irregularities, and the continuous feature of the resulting "V" slot would be interrupted. Clogging would more likely take place, and any classification operations would be interferred with. Thus, the novel cross-sectional profile for the wedge-shaped wire is used as a means of fabricating the present in-to-out flow screen. As set forth, this novel profile includes a ridge means along the central portion of the wide face of the wire, which is used to assist in effectuating a weld to the longitudinal support rods; however, it is not intended to limit the ridge means to any one shape or cross-section. Any shape chosen should be large enough to take a weld at the junction of a support rod and also have the dimensional requirements to prevent the weld from disturbing the edge of the wire.
The support rods will generally be equally spaced around the inner periphery of the tubular screen but may be spaced in any desirable manner. Preferably, the rods are arranged to be made parallel to the longitudinal axis of the screen. Also, the cross-sectional profile of the support rods may be of most any shape but consideration must be made in order to facilitate a strong weld. Round, oval, square, rectangular and all possible combinations may be considered probable cross-sectional profiles. In choosing a proper shape, the overall strength of the screen must be taken into account, in addition to the strength of the weld.
Reference to the accompanying drawing and the following description will serve to more fully illustrate the design and construction of the various embodiments of the present invention, as well as to assist in pointing out advantageous features in connection therewith.
DESCRIPTION OF DRAWING
FIG. 1 is a schematic longitudinal elevational view of the one embodiment of the tubular screen with the slot formed to increase in area radially outwardly.
FIG. 2 is the schematic end view of the embodiment of FIG. 1.
FIG. 3 is the schematical representation of the novel method of making a tubular screen.
FIG. 4 is a cross-section of a portion of the screen shown in FIG. 3 as taken along section line 4--4.
FIGS. 5a, 5b, 5c, 5d, and 5e are various cross-sectional configurations of support rods.
FIGS. 6a, 6b, 6c, and 6d are various cross-sectional configurations of wedge-shaped wires.
Referring now particularly to FIGS. 1 and 2 of the drawing, there is shown a tubular screen 1 formed by having a wedge-shaped wire 2 wound helically around a plurality of spaced apart, longitudinal, support rods 3. The wire 2 is wound in such a way so to form a continuous slot 4; however, because of the wedge-shape of wire 2, the slot 4 increases in cross-sectional area in a radial outward direction. This feature provides a self-cleaning type slot. Longitudinal support rods 3 are shown equally spaced around the inner periphery of the screen 1 and parallel to the longitudinal axis of the screen. The wedge-shaped wire has a projecting portion or ridge means 7 on the wide face or base thereof. Thus, when wire 2 is attached to rods 3, the projecting portion 7 provides means for attaching the wire in a manner to maintain the edges 12 and 13 of the base free from irregularities.
The improved method of making a self-cleaning screen is schematically illustrated in FIG. 3 and 4 of the drawing. The method may include placing the support rods 3 around a cylindrically shaped mandrel, form, or other suitable holding means 10 and holding them in position by means not shown. The form 10 is rotated about its axis of rotation and the wedge-shaped wire 2 is helically wound around and attached to the rods 3. The fusing or attaching may be accomplished by using electrical resistance or ultra-sonic welding. The wire 2 is pressed against the support rods 3 by a pressure applying means 11. If electrical resistance welding is used for attaching the wire and rods, an electrical current may be applied through the pressure applying means 11 to weld the wire to the rods. If ultra-sonic welding is utilized, the pressure applying means may be vibrated by conventional ultra-sonic means not shown to fuse the wire to the rods. The improved method includes forming a ridge 7 on wire 2 prior to the attachment to rods 3. This may be accomplished during the initial forming of the wire by conventional means such as drawing or extruding. The ridge portion 7 of wire 2 is fused to the rods 3 in a manner to maintain the edges 12 and 13 of the wire free from irregularities.
The tubular screen 1 of FIGS. 1 and 2 is adapted to receive a slurry of materials to the open interior zone 6. The fluid in the slurry can be drawn off through the continuous slot 4 via suction, gravity, or centrifugal means. The power means for effectuating the suction or for effectuating the rotation of the tubular screen is not shown but may be provided in any conventional manner. Also, the screen can be supported at a slope to establish flow of slurry from the inlet to outlet of interior zone 6.
FIGS. 5a, 5b, 5c, 5d, and 5e show various alternative cross-sectional profiles of longitudinal support rods than can be used for various embodiments of the tubular screen. A wedge-shaped wire 18 is schematically shown in each figure to indicate where attachment would take place at the junction of support rods and wire. Also shown is a slight sinking or embedment 24 of the various support rods 19, 20, 21, 22, and 23 into the ridge portion 17 of wire 18 which takes place when the junction is subjected to the pressure of electrical resistance or ultra-sonic welding and is thus a characteristic of the method of fabrication. FIG. 5a shows a sufficiently rectangular shaped profile, FIG. 5b, a tear drop shaped profile, FIG. 5c, a wedge-shaped profile, FIG. 5d, an oval-shaped profile, and FIG. 5e, a square profile. A typical round profile is shown in FIG. 2. By illustrating these various profiles it is, of course, not the intention to limit the choice of design to those shown.
In FIGS. 6a, 6b, 6c, and 6d there are shown various alternative cross-sectional profiles of a wedge-shaped wire used to form a continuous slot. A support rod 25 is schematically shown in each instance to indicate where attachment would occur between wound wire and support rod means. Again, the sinking or embedment 26, characteristic of the method of fabrication, is shown. The profiles of the wires 27, 35, 37, and 38 are shown as a simple wedge; however, this should not be a limiting factor with respect to this invention since other wedge-shapes are also contemplated within the scope of the improvement.
In FIG. 6a the profile of a wedge-shaped wire without the novel ridge means is shown. It can be seen that if wire 27 is helically wound about a plurality of support rods 25, a "V" slot 28 of increasing cross-sectional area in the outward radial direction 29 will be formed, however, there will be welding irregularities and a resulting non-uniform slot. To be self-cleaning and uniform, the opening 30 of the "V" slot 28 should be uninterrupted, i.e., if the wedge-shaped wire is merely shaped as shown in FIG. 6a, then weld irregularities would form along the entire breadth 31 of the wire, when that particular junction is subjected to an electrical resistance welding means. This would have the affect of interrupting the continuity of the edges 32 and 33 of the wire at every junction of the wire and rod, thereby creating disturbances or irregularities along the edge of the wire, which would impair the ability of the screen to be self-cleaning.
To provide for an uninterrupted opening, a novel ridge 34 is incorporated into the profile, as shown on wire 35 in FIG. 6b. This ridge 34 will most likely be continuous over the circumferential length of the rod 35, but alternatively, may be broken and only occur where needed for attachment purposes. The ridge 34 serves as a means for attaching the wire in a manner to maintain the edges 42 and 43 free from irregularities. In other words, at this contact point a welding operation is possible without disturbing the edges 42 and 43, consequently leaving an uninterrupted opening 44. Other possible shapes of ridges 39 and 40 are shown in FIGS. 5c and 5d respectively but should not be considered as limiting designs. The important considerations in shaping each of these ridges are strength of weld and the prevention of disturbances along the edges of the wire.
Although I have described my invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be restored to without departing from the spirit and the scope of the invention as hereinafter claimed.