MX2008007593A - Liner system for forming concrete panels - Google Patents

Abstract

A form (10) for creating a pattern in uncured concrete during a casting process includes a support frame (12) and a perforated reinforcing structure (14) coupled adjacent to at least a portion of the support frame. The perforated reinforcing structure includes a plurality of apertures (16) defined therein. A pliable liner (20) is disposed at least partially within the plurality of apertures and at least partially about the perforated reinforcing structure adjacent the support structure. The pliable liner has a patterned surface (22) formed thereon for creating a corresponding pattern in uncured concrete poured adjacent the form.

Description

LINING SYSTEM TO FORM CONCRETE PANELS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a lining system to be used in order to form concrete panels in fences, walls and related concrete structure.

Related Technique Vertically oriented concrete panels have been used for a number of years in afflictions including fences, walls against sound, partitions, etc., of concrete. Concrete panels are often poured and cured in a central manufacturing area and shipped as cured panels to work sites, where the panels can be assembled into a fence or similar structure. It is often convenient to apply a decorative, textured finish to such concrete panels to improve the appearance of the panels. Decorative finishes such as brick simulated finishes, rock wall finishes, etc., give concrete panels a more aesthetically pleasing appearance, and in some cases, such as wall-to-sound applications, can increase the effectiveness of concrete panels.

A type of system developed for pouring into concrete panels uses vertically oriented molds between which the uncured concrete is poured and allowed to cure. As concrete panels are formed and cured in a vertical orientation, this type of system is known as a vertical pouring system. Some of said systems, for example, that described in the Patent Application Publication of E.U.A. No. 20050067551, uses pattern molds, vertically oriented, which are secured within a support structure and filled with uncured concrete. As the uncured (or wet) concrete is poured into the mold, the weight of the wet concrete ensures that the concrete fills the indentations in the pattern mold to accurately form a pattern on the finished panel. Such systems have been found to be advantageous over the horizontal mold systems because very few voids appear in the final product, resulting in an aesthetically pleasing product with superior physical integrity. While systems that pour concrete into vertical shapes have been successful in creating the decorative patterns on both sides of the vertical concrete panel, the shapes used to create these panels have had several operational problems. For example, forms are very expensive to form because they can be made of a material that i) does not adhere to the cured concrete, ii) is not deformed to a greater degree under the weight of uncured concrete, and iii) is sufficiently foldable so that it can be easily removed from the pattern created in the cured concrete . Additionally, the shapes used to create the decorative pattern on the panels are exposed to, and must be able to withstand, severe environmental conditions such as frequent cyclical loading between concrete spills, rough handling during the removal of cured concrete, and caustic chemical reactions for cure concrete. These environmental conditions have caused the liners used in vertical concrete forms to prematurely degrade and / or prematurely separate from the adjacent support structure. As a result, relatively expensive lining has had a short useful life and it has been necessary to produce new forms on a relatively frequent basis. These problems have increased both the costs of materials associated with several pouring systems, and with the number of manpower hours needed to maintain a constant manufacturing cycle.

SUMMARY OF THE INVENTION It has been recognized that it could be advantageous to develop forms for use in concrete panels that they include lining systems that are physically robust and that can withstand the severe environmental conditions involved in the formation of concrete panels vertically. The invention provides uniform to create an uncured concrete pattern during a casting process, including a support frame, and a perforated reinforcement structure, coupled adjacent to at least a portion of the support structure. The perforated reinforcement structure may have a plurality of apertures defined therein. A collapsible liner may be disposed at least partially within the plurality of openings and also around the perforated reinforcing structure adjacent to the support structure. The foldable liner may have a pattern surface formed thereon to create a corresponding uncured corresponding pattern poured adjacent to the shape. According to another aspect of the invention, a system of shapes for creating a particular uncured pattern during a concrete casting process is provided including a base, and a pair of opposite end wall shapes extending upwards from the base and defining surfaces of extreme walls of a vertical mold cavity for uncured concrete. A pair of opposite sidewall shapes can extend upwards from the base and can define the sidewall surfaces of the vertical mold cavity. Each of the opposite sidewall shapes may include the perforated reinforcing structure having a plurality of openings defined therein, and a collapsible liner, disposed at least partially within the plurality of openings and around the reinforcing structure. perforated The foldable liner may have a pattern surface formed thereon to create a corresponding uncured corresponding pattern poured adjacent to the shape. The present invention also provides a method for creating a form for vertically molding concrete including placing a support structure to support a shape. A perforated reinforcing structure that may have a plurality of apertures disposed therein may be coupled to at least a portion of the support structure. A foldable liner may be disposed at least partially within the plurality of openings. The foldable liner can also be arranged around the perforated reinforcement structure and the support structure. A pattern surface can be created in the foldable liner in order to form a corresponding uncured corresponding pattern poured adjacent to the shape. The additional aspects and advantages of the invention will be apparent from the following description detailed, taken together with the accompanying drawings, which illustrate together, by way of example, features of invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a vertical concrete panel shape according to one embodiment of the invention; Fig. 2 is a partial, front view, of the vertical concrete panel shape of Fig. 1; Fig. 3 is a sectional view of the shape of the vertical concrete panel of fig. 2, taken throughout section 3-3 of Fig. 2; Fig. 4 is a perspective view of a vertical concrete panel form system according to an embodiment of the present invention, shown in a partially assembled configuration; and Fig. 5 is a perspective view of the vertical concrete panel form system of Fig. 4, shown in an assembled configuration. DETAILED DESCRIPTION Reference is now made to the illustrative embodiments illustrated in the drawings, and specific language will be used herein to describe the same. However, it will be understood that there is no limitation of the scope of the invention as claimed herein. Further alterations and modifications of the invention aspects illustrated herein, and further applications of the principles of the inventions as illustrated herein, which could occur to someone skilled in the relevant art and who have possession of this description, they should be considered within the scope of the invention. An example of a shape, shown generally at 10, is illustrated in Fig. 1 to create a particular uncured pattern during a curing casting process with an aspect of the invention described herein. As discussed in more detail below, the shape 10 can be used in conjunction with other shapes such as end wall shapes and retaining structure, to form concrete panels (e.g., 11 in Fig. 4) that can be Use in vertical applications such as bars, retaining walls, and the like. An illustrative system with which form 10 can be used was described in Patent Application Publication of U.S.A. No. 20050067551, filed September 30, 2003, which is incorporated herein in its entirety. The vertical concrete panels 11 created in the form 10 of the present invention are used in a variety of applications, including residential and commercial fences, wall-to-sound applications, etc. Additionally, the concrete panels formed in accordance with this invention usually require little or no maintenance, provide superior strength, and can be assembled relatively quickly at the work site on a fence or other structure. The assembly of the panels in a wall structure is generally achieved by installing or forming posts (not shown) that include structure of slots in which the panels are placed and maintained in a secure manner. The shape 10 can mold a decorative pattern on sides of the concrete panels 11 to give the concrete panels an aesthetically pleasing appearance such as a rock wall, a brick wall, or other convenient patterns. As used herein, the term "decorative pattern" is understood to mean a pattern applied to concrete panels and may be decorative or functional in nature, or both. In addition to the decorative pattern applied to the panel, the concrete panel can be dyed or colored in a particular color scheme to improve the aesthetically pleasing appearance of the panel. In some embodiments, the term "decorative pattern" may refer to a relatively uniform, featureless pattern that has a decorative nature. As illustrated in Figs. 2-3, the shape 10 may include a sopote structure 12. The support structure 12 may be a structurally important material, such as metal, and can be sized and configured to withstand the load of uncured concrete poured into a mold system as described below. In one aspect, the support structure 12 can be formed substantially from a plurality of elongated tubular members 13 that can be welded or in some way coupled together in an integral frame. In one embodiment, the support frame 12 can also be formed of relatively flat sheet-like materials such as reinforced three-layer sheets, metal sheets, etc. The support frame can be configured in a variety of ways to ensure that sufficient support is provided to allow the connection of a liner (discussed in greater detail below) to the support frame. The shape 10 may also include a perforated reinforcement structure 14. The perforated reinforcement structure 14 may be coupled adjacent to at least a portion of the support frame 12. The perforated structure may include a plurality of apertures 16 defined therein. The openings can have a variety of shapes and can include a variety of shapes in cross section, such as square, circular, diamond shape, etc. Also, the openings can be separated from one another and arranged through the reinforcing structure in a variety of shapes and spatial relationships, in regular repetition patterns and in random patterns. The openings 16 can be holes 18 that extend through the perforated reinforcing structure 14 and form the perforations in the reinforcing structure. In one aspect, the perforated reinforcement structure 14 can be an expanded sheet metal. As is known in the art of metal manufacturing, expanded metal is a product generally formed of a single sheet of metal that is cut or punched and stretched to "expand" the cuts in diamond-shaped perforations in the metal sheet. A series of "knuckles" are formed in the bodes of each of the perforations as a result of stretching and serve to distribute loads applied to the metal through the sheet. Expanded metal can be formed from a variety of materials, such as steel, stainless steel, brass, aluminum, etc. Since the expanded metal can be manufactured relatively easily and obtained at a relatively low cost, it has been found to be an effective reinforcing structure for the liner 20 (discussed in greater detail below). Also, the expanded metal can be welded by gluing and another connection to the support frame (eg, stapled in the case where the support frame includes wood), it can be securely connected to the support frame.

As discussed above, the shape 10 may also include a foldable liner 20 that can be placed at least partially within a plurality of apertures 16. The foldable liner 20 can also be disposed at least partially around the adjacent perforated reinforcement structure 14 to the support structure 12. The foldable liner 20 may include a conformable polymeric material, such as polyurethane or 2070 SX polymer. In one aspect of the invention, the foldable liner is applied around the reinforcing structure adjacent to the support structure while in an uncured liquid state. As the liquid fills between and around each of the perforations or openings 16 when applied adjacent to the support frame, an excellent bond is achieved between the liner and the perforated reinforcement structure (and between the liner and the structure). support). In this embodiment of the invention, the foldable liner substantially comprises the perforated reinforcement structure. As the perforated reinforcement structure 14 can be independently attached to the support frame 12, the reinforcing structure helps retain the liner 20 securely connected to the support frame so that repeated casting and demolition cycles can be accomplished without requiring that the liner is replaced frequently. It has been found that the present invention can produce a shape that can hold up to 1,000 casting cycles before requiring the liner to be replaced or discarded. Since the liner does not need to be replaced at frequent intervals, a higher quality polymer, which is generally more expensive than lower quality materials, can be used to provide a superior finish to the concrete panels without significantly increasing the cost of each concrete panel. The foldable liner 20 can also be stiff enough to mold the uncured concrete in a decorative pattern. The foldable liner may also be foldable to allow the form 10 to flex when assembled into a system of shapes as described below. Advantageously, the flexibility of the foldable liner can extend the useful life of the form 10 since the shape can be flexed instead of broken during rough handling of the form during assembly and disassembly procedures. Advantageously, the support structure 12 and the perforated reinforcement structure 14 can reduce the amount of shaped polymer that is necessary, so that sufficient polymer is present to seal the mold cavity, but it is prevented from deforming to undesirable bonding. by the reinforcement structure. In addition to the modality shown, the reinforcing structure can be placed on, on or adjacent to the support package to give reinforcement to the support package. The perforated reinforcement structure can also be formed of perforated metal, rolled wire sheets, welded mesh sheets and the like. As such materials can be easily obtained and cut to preferred sizes, they have been found suitable as a reinforcing structure. In addition, conventional sheet material can also be used with perforations formed in the sheet material in a variety of forms, such as perforation, pitting, etc. The foldable liner 20 may have a pattern surface 22 formed over the same. The pattern surface can be a reverse decorative pattern that can form a corresponding decorative pattern on a surface of a cast concrete wall. Specifically, the pattern surface 22 can create a corresponding uncured corresponding pattern poured adjacent to the shape 10 when the shape is used in a system of shapes as described below. The inverse decorative pattern 22 may be of a variety of inverse patterns including brick, rock, or other simulated structure that provides the concrete panel with a decorative or functional advantage. The inverse decorative pattern 22 can be formed on or in the form 10 by a number of methods. In a aspect, the inverse decorative pattern 22 is provided in the form 10 by the application of the folding frame 20 to the shape 10. The foldable lining 20 can be formed by preparing a "master" shape in which it can be placed to the support frame and structure of the frame. reinforcement. A polymer or cure can be poured onto the support frame, reinforcing structure and master form. The uncured polymer can flow around and through the support frame and the openings or perforations in the perforated reinforcement structure. When the viscous polymer is cured, the resulting collapsible liner can be removed from the master form and bonded or cured around the reinforcing structure. Once prepared, the shape 10 can be used numerous times to apply the decorative pattern to a number of concrete panels poured into cavities defined at least partially by the shapes 10. By preparing many such forms 10 of the same master form, multiple panels which have identical surfaces can be formed concurrently. Therefore, in use, a wet concrete is poured adjacent to the shape 10, the weight of the wet concrete ensures that the concrete is filled in and around the textured surface of the reverse decorative pattern as a decorative pattern, such as an appearance of brick wall, rock wall appearance, etc.

The form 10 of the present invention can also be used to form concrete panels of a variety of sizes. For example, shapes can be sized to create concrete panels with a length of 3.6 m, a height of 1.8 to 2.4 meters, and a thickness of 10 cm. As described in more detail below, shapes can be used in a system of shapes to create panels of variable width, including panels with widths of 10, 12.7 or 15.24 cm. The shapes can be adapted to fit into shape systems that can create a number of vertical concrete panels of varying size and shape with minimal adjustments to the system in ways that are necessary to effect the formation of panels of different sizes. Referring now to Fig. 4, a system of shapes, shown generally at 100, is shown with a pair of shapes 10 forming at least partially a mold cavity to create a concrete pattern not cured during a concrete casting process. according to the present invention. The system of shapes 100 may have a base 130 that is placed on a support surface, such as the floor or a cast floor. The system of shapes 100 may also have a pair of opposed end wall shapes 140 each extending upward from the base 130 and defining end wall surfaces 142 of a vertical mold cavity (150 in Fig. 5) for concrete not cured. The shapes of end walls 140 may have a perforated reinforcement structure 144 with a plurality of apertures (not shown). A foldable liner 148 may be placed at least partially within the plurality of openings, and around the perforated reinforcement structure 144. A pair of shapes 10, described above, may define opposite sidewall shapes 110 that extend upward from the base 130. The side wall shapes 110 can define sidewall surfaces 112 of the vertical mold cavity. The shapes of the side wall 110 can be separated by a desired distance, which corresponds to a desired thickness of the particular panel that will be formed. As described above, each shape 10 may have a perforated reinforcement structure 14 having a plurality of openings (not shown) and a foldable liner 20 placed at least partially within or through the plurality of openings and around the reinforcing structure. perforated 14. The foldable liner 20 may have a pattern surface 22 formed thereon to create a corresponding uncured corresponding pattern poured adjacent to the forms 10. The form system 100 may also have a lower support package 160 which can placed on the base 130 to define at least partially a lower surface 162 of the vertical mold cavity. He bottom support gasket may have a perforated reinforcement structure 164 with a plurality of openings (not shown). A collapsible liner 168 may be placed at least partially within the plurality of openings, and around the perforated reinforcing structure 164. Together the end wall shapes 140, the sidewall shapes 110, and the infomeric support packaging 160 may operably positioned to form a tetragonal mold cavity 150, as best seen in Fig. 5. The vertical mold cavity 150 may correspond to a substantially vertical concrete panel. In one aspect the tetragonal vertical mold cavity 150 can extend a smaller rectangular cross section through an upper surface 152, and a larger rectangular cross section through a front surface 154. Advantageously, the shaped polymer of the collapsible liners 20, 148 and 168 can provide an effective seal between the lower support package 160, and each of the end wall shapes 140 and side wall shapes 110. Since the mold cavity 150 is filled with wet concrete, it can be Allow the different shapes to flex slightly outward to form a seal that increases effectiveness with the addition of more wet concrete. Therefore, wet concrete can be maintained within the mold cavity 150 even when larger panels are poured which may generally require larger amounts of wet concrete. Referring now to Fig. 5, the form system 100 may also extend a security structure, generally shown at 170, associated with the end wall shapes 40 and the side wall shapes 110 which retain and secure the wall shapes. end portions 140 and side wall shapes 110 in the tetragonal mold cavity configuration in order to receive concrete in a non-curled state within the vertical mold cavity. The security structure 170 may include various tension and restriction devices, as shown in the art, to ensure that the mold shapes are not displaced by the introduction of uncured concrete, or "wet" in the mold cavity. Once each mold cavity is defined, and any retaining or securing structure 170 has been applied, wet concrete can be poured into each mold cavity. Vibrations or other agitation devices can be used when pouring wet concrete to reduce voids and ensure that wet concrete fills each cavity to the desired degree. Therefore, the mold cavity 150 can be defined by movable concrete shapes constrained by the securing structure 170 in order to maintain the vertical mold cavity 150. As an example of the present invention in use, the first sidewall shape 110 can be placed in a desired location within the securing structure 15. The lower support packing 160 can be placed adjacent to the shape of side wall 110, abutting against sidewall shape 110. End wall shape 140 may be placed within the safety structure associated with sidewall shape 110. A second sidewall shape 110 may be moved in its position in a manner that the end side wall shape 140 is oriented within the safety structure 170 associated with the second side wall shape 110. In this way, the end wall shape 140 is secured in place between the side wall shapes 110 ensuring the structure 170. If desired, the additional side wall shapes 110 can be similarly placed with the shape of end wall 140 and lower support packs 160 form end and a bottom, respectively, of a vertical mold cavity 150. The width of the concrete panels thus formed can be easily altered by the use of alternate end wall shapes and bottom support gaskets. If a wider panel is required, the wider end wall shapes and support gaskets can be used. If a panel with a narrower width is required, it can be use narrower end wall shapes and support gaskets. Once each end wall form 140, sidewall shape 110 and bottom support pack 160 are placed, the shapes may be restricted in their position in a number of ways. Due to the substantial weight of uncured concrete, the different shapes will tend to move outwardly from the defined mold cavity when introducing wet concrete into the cavity. As discussed above, the shapes of end walls 140 can be secured in place by securing structure 170. In addition, as illustrated in FIG.

Fig. 5, the sidewall tension members 240 may be coupled to the different shapes of sidewalls 110 to restrain the shapes of sidewalls to move in reaction with the forces introduced by humerus concrete poured into the mold cavity. The tension members 240 can be a variety of those known in the art and can include threaded ends 242 that can be secured in place by a nut 244. An opposite threaded end 246 can similarly be secured by the nut 248. Each of the ends 244 , 248, can be tightened to have the sidewall shapes together. To provide variation in the number of formed mold cavities, the threaded end 246 can include a length of threads that allow the nut 248 Connect in a variety of positions to ease tension in a variable number of concrete forms. The tension members 240 can be arranged outside the mold cavity so as to retain the side wall shapes in position without displacing the wet concrete in the mold cavity. In this way, the forms are safely held in position without adversely affecting the finished panel by introducing foreign matter into the wet concrete and without leaving the cavities in the concrete, as will be done in the previous methods. In this way, the concrete forms are safely held in place before curing the concrete without compromising the structural integrity of the finished concrete panel's aesthetic appearance. Therefore, in use, as the wet concrete is brazed into the mold cavity 150 and adjacent the shapes 10, the weight of the wet concrete ensures that the concrete fills in and around the molded surface of the inverse decorative pattern. After curing, the inverse of the pattern surface 22 appears on the cured concrete panel as a decorative pattern, such as a brick wall appearance, a rock wall appearance, etc. Because the present invention advantageously forms concrete panels in a vertical orientation, wet concrete can fill the surface textured of reverse decorative patterns on both sides of the mold cavity 150 in the same way, in contrast to horizontal mold systems that generally only apply a well-defined pattern to a lower surface of the concrete panel. After pouring, the wet concrete in the shape system 100 can cure, after which several structures and forms of retention can be removed. The cured panel can then be removed and the process repeated a number of times to create a number of concrete panels. In the case where the appropriate concrete mix is used, the system can form panels in the one-day cycle, that is, the panel can be poured in the morning and left to cure during the night. The next morning, the cured panel can be removed, the forms can be reassembled and the process can start again. The present invention also provides a method for creating a shape for vertically molding concrete including placing a support frame to support a shape. A perforated reinforcing structure having a plurality of apertures disposed thereon can be coupled to at least a portion of the support frame. The perforated reinforcement structure may include a substantially flat sheet of expanded metal. A collapsible liner can be arranged at least partially within the plurality of openings. The foldable liner can also be placed around the perforated reinforcement structure and the support frame. A pattern surface can be created in a foldable liner in order to form a corresponding uncured corresponding pattern poured adjacent to the shape. The foldable liner can be a shaped polymer that can be poured into the plurality of openings and around the perforated reinforcement structure and support frame. The shaped polymer of the collapsible liner can be cured to form a mold surface to retain uncured concrete. It should be understood that the provisions referred to above are illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements can be foreseen without departing from the spirit and scope of the present invention while the present invention has been shown in the drawings and described above in relation to the illustrative embodiments of the invention. It will be apparent to those skilled in the art that numerous modifications can be made without departing from the principles and concepts of the invention as set forth in the claims.

Claims (20)

CLAIMING

1. - A form to create a concrete pattern not cured during a casting process, comprising: a support frame; a reinforced structure, coupled adjacent to at least a portion of the support frame and having a plurality of openings defined therein; and a collapsible liner, disposed at least partially within a plurality of openings and at least partially around the perforated reinforcing structure adjacent to the support structure, the foldable liner has a patterned surface formed therefrom to create a corresponding pattern in the uncured concrete poured adjacent to the shape.

2. - The form of claim 1, wherein the support frame includes a plurality of elongated tubular members.

3. - The form of claim 1, wherein the reinforced structure is formed of a substantially planar sheet.

4. - The form of claim 1, wherein the foldable material further includes a conformable polymer.

5. - The form of claim 1, wherein the foldable material further includes polyurethane.

6. - The form of claim 1, wherein the foldable material further includes expanded metal.

7. - The form of claim 1, wherein the foldable material further includes a material selected from a group consisting of: perforated metal, rolled wire sheets and welded mesh sheets.

8. - A shape system to create a concrete pattern not cured during a concrete casting process, comprises: a base; a pair of opposite end wall shapes, extending upwardly from the base and defining the end wall surfaces of a vertical mold cavity for uncured concrete; and a pair of opposite end wall shapes, extending upwardly from the base and defining the end wall surfaces of a vertical mold cavity, the opposite side wall forms each including at least: a perforated reinforcement structure that it has a plurality of apertures defined therein; and a foldable liner, disposed at least partially within the plurality of openings and at least partially in the perforated reinforced structure, the foldable liner has a patterned surface formed of the same to create a corresponding pattern in the uncured concrete poured adjacent to the shape.

9. - The system of claim 8, further comprising a lower support package available on the base to define at least partially a lower surface of the vertical mold cavity.

10. - The system of claim 8, wherein each end wall includes: a reinforced structure having a plurality of openings defined therein; and a foldable liner, disposed at least partially within the plurality of openings and at least partially with respect to the perforated reinforcing structure.

11. - The system of claim 8, wherein the side walls and end walls are operably positioned to form a tetragonal mold cavity.

12. - The system of claim 8, further comprising securing the structure associated with the shapes of the end wall and the shapes of the side wall and has been configured to retain the shapes of the end wall and the shapes of the side wall in a secure configuration to receive concrete in an uncured state within the mold cavity.

13. - The system of claim 12, further comprising a plurality of the shapes of the side wall, the shapes of the end wall and the lower package disposed within the secured structure, to define a plurality of the vertical mold cavities to allow vertical simultaneous casting of multiple concrete panels.

14. - The system of claim 8, wherein the reinforced perforated structure further includes a material selected from a group consisting of: perforated metal, rolled wire sheets and welded mesh sheets.

15. - A method for making a form for vertical mold concrete, comprising the steps of: a) obtaining a support frame b) coupling a reinforced structure perforated to at least a portion of the support frame, the reinforced structure has a plurality of openings arranged therein; and placing a foldable liner at least partially of openings and at least partially with respect to the reinforced perforated structure adjacent to the support frame.

16. - The method of claim 15, comprising the additional step of: curing the collapsible liner to form a mold surface to retain the uncured concrete.

17. - The method of claim 15, wherein the support frame includes a plurality of elongated tubular members.

18. - The method of claim 15, wherein the step of coupling the reinforced perforated structure further comprises coupling a flat sheet of substantially expanded metal to at least a portion of the support frame.

19. - The method of claim 15, wherein the foldable liner includes a compatible polymer.

20. - The method of claim 15, wherein the reinforced perforated structure further includes a material selected from a group consisting of: perforated metal, rolled wire sheets and welded mesh sheets.