Expansion anchor

Abstract: An expansion anchor capable of being inflated by thrusting a lock plug (30, 68) onto a contracted portion (11, 51, 61) to spread a clamp member (20, 40, 53, 63) having acutely angular peripheral edges (24). When the anchor is inflated within a hole in a rigid material such as concrete, the angular edges (24) of the clamp member (20, 40, 53, 63) bite into the rigid material, so that the anchor is no longer released out of the rigid material.

Description: This invention relates to an expansion anchor capable of being expanded within a hole bored in a rigid material such as a stone and concrete by thrusting a lock plug into inside of the anchor so as to fasten something else onto or reinforce the rigid material. There have been so far a variety of expansion anchors capable of being secured onto a rigid material such as concrete. One expansion anchor which is widely used is shown in Figure 1 as one example. In principle, the anchor of this type comprises a cylindrical anchor body 1, a wedge plug 5 which is forced into the inside of the anchor body 1, and a thread bolt 3 having a clamp nut 7 at one end portion thereof and brought in screwed connection with the wedge plug 5 at the other end portion. After inserting the anchor body 1 in a fitting hole bored in a concrete material or other rigid materials, the wedge plug 5 is forced into the anchor body 1 by turning the thread bolt 3 to thereby inflate the anchor body. Thus, the anchor is fixedly secured within the concrete material in the non-returnable state. The anchor body of this expansion anchor is generally made of relatively soft material and has longitudinal expanding slits in its leading end portion so as to facilitate to inflate the anchor body by forcibly thrusting the wedge plug 5 into the anchor body 1. The anchor body thus inflated inside the hole in the concrete material comes into frictional contact with the inner surface of the concrete hole to be thereby kept in its non-returnable state. In order to heighten the non-returnable effect of the anchor, the anchor body is provided in its outer circumferential surface with checking steps 9 as illustrated. To further improve the non-returnable effect of the anchor expanded within the concrete hole, the degree of permitting the anchor body to be inflated must be increased sufficiently. However, the anchor capable of being sufficiently inflated requires a markedly large thrusting force to be imparted to the wedge plug 5. Moreover, this anchor is disadvantagous in that the frictional clamping force brought about by the checking steps 9 formed in the outer circumferential surface thereof is not sufficient to steadily secure the anchor onto the concrete material. Also, the clamping force depends upon the diameter of the hole bored in the concrete material or the like relative to the outer diameter of the anchor body, and it is difficult to form the hole having a suitable diameter. CH-A-506,720 discloses an expansion anchor having the features of the preamble of Claim 1 or Claim 2. An object of the present invention is to provide an excellent and reliable expansion anchor which can be sufficiently inflated and produce a large clamping force merely by thrusting a lock plug with a relatively small force. The invention provides an expansion anchor according to Claim 1. Upon inserting the expansion anchor into a fitting hole bored in a rigid object such as a stone or concrete base, the lock plug assembled inside the anchor body is thrust into inside the contracted portion to thereby inflate the contracted portion. The contracted portion thus expanded causes the clamp member fitted to the circumferential retaining groove to be spread in diameter and bite into the inner surface of the hole in the rigid object. Owing to the acutely angular edges on the peripheral portion of the clamp member, the anchor inflated in the hole can no longer be released out of the hole and is reliably fixed onto the rigid object. The objects and features of the present invention will be explained in detail with reference to the accompanying drawings, wherein Figure 1 is a partially sectioned perspective view showing one example of conventional expansion anchors; Figure 2 is a perspective view showing one embodiment of an expansion anchor according to this invention; Figure 3 is a sectioned side view of the expansion anchor of Figure 2; Figure 4 is an enlarged view in section of Figure 2; Figure 5 is a front view of a clamp member in the anchor of Figure 2; Figure 6 is a sectioned side view of the expansion anchor of Figure 2 in the state of effecting a lock plug inside a hole in a rigid material; Figure 7 is a front view of a clamp member used in another embodiment; Figure 8 is a side view in section showing the principal portion of still another embodiment according to this invention; Figure 9 is a sectioned side view of a further embodiment of this invention; Figure 10 is an enlarged view in section showing the principal portion of Figure 9; and Figure 11 is a graph representing the result of the comparative experiment which was conducted to prove the performance of the anchor according to this invention. Figures 2 through 5 represent one preferred embodiment according to this invention. The illustrated expansion anchor of this invention comprises a cylindrical anchor body 10 having a contracted portion 11 which is provided in the circumferential outer surface thereof with a retaining groove 12, a clamp member 20 fitted into the retaining groove 12 formed in the contracted portion 11, and a lock plug 30 contained within the anchor body 10. The contracted portion 11 may be formed by reducing the leading end portion of the anchor body 10 so that the anchor body is composed of a large diameter portion (trunk portion 13) and a small diameter portion (contracted portion 11). The lock plug 30 has a diameter smaller than the inner diameter of the aforementioned trunk portion 13 of the anchor body 10 and larger than the inner diameter of the contracted portion 11, and is placed inside the anchor body 10 slidably in the lengthwise direction. The anchor body 10 can be made of not merely tough material such as stainless steel or other metallic materials of various kinds, but also plastic materials having moderate flexibility together with rigidness and strength. The trunk portion 13 of the anchor body 10 is provided on its rear end with a flange 14 and gradually reduced in diameter from the flange 14 toward the contracted portion 11. In the trunk portion 13, there are formed side openings 15 for allowing fluid such as a sealing agent as described later to flow out therethrough, whereas they are not indispensable constituents of this invention. The clamp member 20 to be fitted into the retaining groove 12 in the contracted portion 11 is formed in a general U- or C-shape as shown in Figure 5. The clamp member 20 has an inner diameter nearly equal to the diameter of the retaining groove 12 formed in the contracted portion 11, and an outer diameter equal to or somewhat smaller than the trunk portion 13 except the flange 14. In the case that the outer diameter of the clamp member 20 is made smaller than the outer diameter of the trunk portion 13, the difference in outer radius between the trunk portion 13 and the clamp member 20 should be made sufficiently larger than the thickness of the contracted portion 11. The clamp member 20 may be made by, for instance, punching a metal plate, or bending a rod material into a general U-shape. It is however required to form acutely angular edges 24 on the circumferential periphery of the clamp member. The clamp member 20 may preferably be secured in the retaining groove 12 by caulking as indicated by the imaginary line in Figure 5. Otherwise, the clamp member may be made of a spring ring which is forcibly fitted into the retaining groove 12. A dike portion 16 formed along the retaining groove 12 has an effect of preventing the clamp member 20 from deviating from the retaining groove. In the contracted portion 11, there are formed expanding slits 17 extending in the longitudinal direction of the anchor body. The lock plug 30 in this embodiment is composed of a rear half part 30a having a larger diameter than the inner diameter of the contracted portion 11, and a front half part 30b having a streamline section like a wedge or bullet. To be more specific, the lock plug 30 should necessarily be designed so that the total of the radius of the rear half part 30a, the thickness of the contracted portion 11 at the retaining groove 12 and the radial width of the clamp member 20 (difference between the outer and inner radii of the clamp member) becomes larger than the radius of the maximum diameter of the anchor body 10 except the flange 14. Now the manner in which the anchor constructed as above is secured inside a fitting hole Hc in a concrete base C shown in Figure 6 will be described below. At the outset, the anchor is inserted from the leading end of the contracted portion 11 into the hole Hc having the inner diameter nearly equal to the outer diameter of the anchor body 10 until the flange 14 of the anchor comes into touch with or only beyond the surface Sc of the concrete base C. Then, the lock plug 30 in the anchor body 10 is thrust toward the contracted portion 11 by using a push rod or other similar tool, consequently to expand the contracted portion 11 as shown in Figure 6 and spread radially the clamp member 20. The clamp member 20 thus spread causes the angular edges 24 to bite into the inner wall surface of the hole Hc in the concrete base C as illustrated. The lock plug 30 is easily moved into the contracted portion 11 with a relatively small force to expand the contracted portion 11 owing to the expanding slits 17. Besides, the contracted portion 11 can be inflated without imparting a large thrusting force to the lock plug 30, because only the clamp member 20 is spread substantially. The clamp member having the acutely angular edges firmly bites into the inner wall surface of the hole Hc so as to steadily secure the anchor in position onto the concrete base. The anchor thus secured is no longer released out of the concrete hole even if being subjected to an intense drawing force. The excellent performance of the expansion anchor according to this invention having the structure noted above could be confirmed experimentally. In the experiment which was conducted actually, an expansion anchor of stainless steel having a length of 70mm, an outer diameter of 6mm, and a thickness of 0.5mm was used with the clamp member made of a stainless steel plate of 1mm in thickness, which is designed to have variation of about 0.25mm. This anchor showed its tensile strength of 300 kg. It was found from the results of the experiment that it is desirable to confer an expanding variation of 0.15mm to 0.3mm upon the same clamp member. The expansion anchor which is provided in its contracted portion 11 with the retaining groove 12 to obtain a sufficient expanding variation of the clamp member was used in the above experiment. However, even the anchor having no contracted portion was found to be nearly equal in ability to the aforementioned anchor with the contracted portion. To secure the anchor expanded inside the hole in the concrete base more steadily, the inner hollow of the anchor body 10 may be filled with a sealing agent such as of epoxy resin in the spread state of the anchor body as shown in Figure 6. The sealing agent filled into the inner hollow of the anchor body flows out through the side openings 15 bored in the anchor body 10 and permeates the entire inner surface of the concrete hole Hc. When the sealing agent filled into the concrete hole and the inner hollow of the anchor body is solidified, the anchor is fixedly secured within the hole of the concrete base in the non-returnable state as if the anchor and the concrete base are united integrally. Shown in Figure 7 is a clamp member 40 provided in its peripheral portion with notches 42 to further heighten the effect of biting into a concrete base. As shown in Figure 8, the retaining groove 12 in the contracted portion 11 at the leading end portion of the anchor body 10 may be formed deeply. According to this embodiment, the dike portion 16 used in the foregoing embodiment can be excluded from the contracted portion 11 of the anchor body. Further, though the expanding slits 17 in the contracted portion 11 in the foregoing first embodiment are not present in this embodiment, the contracted portion 11 can be expanded with a small force if the anchor body 10 is made of a flexible material. In Figure 8, the elements indicated by like reference numerals with respect to those of the first embodiment noted above have analogous structures and functions to those of the first embodiment. Another embodiment shown in Figures 9 and 10 provides an expansion anchor comprising an anchor body 60 having a contracted portion 61 with a plurality of retaining grooves 62. There are fitted a plurality of clamp members 63 into the retaining grooves 62. Similarly to the aforementioned embodiments, the contracted portion 61 is provided with longitudinal expanding slits 67, and a lock plug 68 is inserted inside the anchor body 60 so as to be thrust into the contracted portion 61 to spread the clamp members 63. This anchor has an effect of establishing the engagement with a rigid object such as a concrete base with great strength. The strength of the expansion anchor of Figure 9 with respect to a pull-out force exerted thereon which was obtained experimentally is shown in TABLE 1 below. The experiment was conducted by using the Amsler's tensile test machine. In the experiment there were used a concrete base of 240kg/mm² which is commonly used as a building material, and an anchor according to this invention having an outer diameter of 6mm, a thickness of 0.8mm and a length of 55mm. Figure 11 represents the tensile characteristic of the expansion anchor (M) of this invention shown in Figure 10, comparing with a conventional expansion anchor (N) having an outer diameter of 6mm, a thickness of 0.7mm and a length of 45mm. As is evident from the illustrated graph, the expansion anchor (M) according to this invention has achieved the effect of vigorously maintaining the condition secured onto the concrete base for a relatively long time due to the clamp members, compared with the conventional anchor (N) which was broken away from the concrete base before long. As described above, the expansion anchor according to the present invention can be sufficiently inflated and produce a large clamping force from a relatively small force of thrusting the lock plug into the contracted portion by means of the clamp member having the acutely angular edges.

Claims: An expansion anchor comprising: a cylindrical anchor body (10,60) having a trunk portion (13), said anchor body provided with at least one circumferential retaining groove (12,62) having an inner diameter smaller than that of said trunk portion (13); at least one clamp member (20,40,63) fitted into said retaining groove (12,62) in the leading end portion of said anchor body (10,60), said clamp member having an inner diameter nearly equal to the diameter of said retaining groove in said anchor body and an outer diameter substantially equal to or smaller than the outer diameter of said trunk portion (13); and a lock plug (30,68) having a diameter larger than said inner diameter of said leading end portion of said anchor body (10,60) and being contained slidably within said anchor body, characterized in that said clamp member (20,40,63) is made of a generally U- or C-shaped plate having peripheral angular edges (24). An expandion anchor according to claim 1, characterized in that said anchor body has a contracted end portion (11), and said groove (12) is formed in said contracted portion (11) An anchor according to claim 1 and Claim 2 wherein the outer diameter of the clamp member (20,40,53,63) being smaller than the outer diameter of said trunk portion (13), difference in outer radius between said trunk portion and said clamp member being sufficiently larger than said contracted portion in thickness. An anchor according to Claims 2 and 3 wherein said trunk portion (13) is provided on its rear end with a flange (14) and gradually reduced in diameter from said flange toward said contracted portion (11,51,61). An anchor according to any one of Claims 1 to 4 wherein said trunk portion (13) has at least one side opening (15). An anchor according to any one of claims 2 - 5, wherein said contracted portion (11,51,61) has at least one expanding slit (17,67) extending longitudinally. An anchor according to any one of Claims 2 - 6, wherein said lock plug (30,68) comprises a rear half part having a larger diameter than the inner diameter of said contracted portion (11,51,61), and a front half part having a streamline section. An anchor according to any one of Claims 2 - 7, wherein said lock plug (30,68) has the diameter smaller than the inner diameter of said trunk portion (13) and larger than the inner diameter of said contracted portion (11,51,61). An anchor according to any one of Claims 1 to 8 wherein said clamp member (40) has notches in its outer peripheral portion.

Inventors: YOSHINO YOUSUKE, YOSHINO, YOUSUKE
Applicants: YOSHINO SEIKI KK, YOSHINO SEIKI INC.
Application year: 1991
Main classification: F16B13
IPC codes: E04G23, F16B13, E04B1