IE922765A1 - Anchor with extrusion plastic bonding - Google Patents

Abstract

A method and an anchoring element for high strength solid wall anchorin .in which a solid plastic plug is inserced in a hole in a solid wall of a porous material such as concrete. The invention provides a high strength compressive bonding between the plastic plug and the wall which simulates high strength chemical bonding. In order to effect the high strength compressive bonding, the plug is inserted into a hole in the wall having nominally the same dimension as the plug. A screw of substantia11y the same diameter as the plastic plug is inserted into the plug to provide the anchoring. The plastic of the plug is an extrudible material such as polypropylene, high density polyethylene and co-polymers, which is extruded against and into the solid wall of the hole by the rotary insertion of the screw. Continued rotation of the screw causes a very high compression of the plastic berween adjacent threads of the screw and a thin, very highly compressed film, which substantially covers the threads. The extrusion and the highly compressed areas of plastic provide phenomenally high resistance to pull-out of the plug from the wall. The plastic plug further contains one or more hairline separations or cleavages which serve to guide the screw int a path in the center of the plug to maximize the extent of the circumferential extrusion.

Description

ANCHOR WITH EXTRUSION PLASTIC BONDING This invention relates to solid wall anchors and particularly to plastic plug solid wall anchors.

In US patent No. 4,752,170, with the same assignee as the present application, a solid wall anchor is described in which the anchor, having an overal1 bullet-1 ike or plug appearance, is comprised of interfitting sections which form a solid plug of plastic, i.e. with a starter hole for the screw but without a central hollow. When a screw is inserted, the solid nature of the anchor permits it to support considerably more weight than other similar but hollowed out anchors because of the increase in compacted material within a given hole diameter. These anchors provide holding strength greater than or at least comparable to many types of metai anchors of similar dimension.

It is an object of the present invention to provide an inexpensive method for substantially increasing the holding strength of solid wall plastic anchors .

It is a further object of the present invention to provide a unique combination of plastic and screw which forms a very high strength anchoring element.

These and other objects, features and advantages of the present invention will become more evident from the following discussion and drawings in which: Figure la is an isometric view and Figure lb is a side elevacion view or an anchor of the aforeraentioned patent in the opened and closed positions respec c ively; Figure lc is an alternative embodiment of the anchor of Figures la and 6; Figure 2 is a side elevacion (enlarged for decail) photographic view or Che anchor of Figures la and lb when used in accordance with the method of che prior art and removed from a substrate; INTEL OPEN TO PUBLIC INSPECTION j f -1JNL. No......OF Figure 3 is a aide elevation (enlarged for detail) photographic view of the anchor of Figure 2 when used in accordance with the method of the present invention and removed from a substrate; and Figure 4 ia a aide elevation (enlarged for detail) photographic view of the anchor of Figures la and lb when the inserted screw diameter excessively exceeds that of the anchor and is removed from a substrate.

Generally the present invention comprises a method for high strength compressive bonding of a plastic plug to a solid wall or other substrate which forms an anchoring element. The invention comprises using a substantially solid plug of a plastic material, having specific mechanical properties, into which a screw, of specific dimensions, ia threaded. The present invention further comprises a unique combination of plastic and screw which provides a very high strength anchoring element.

In accordance with Che present invention, a solid, generally tubular plastic plug is inserted into a hole formed in a solid wall or other solid substrate. The hole is of initial depth sufficient to exceed the length of the plastic plug by an amount which will accommodate extrusion elongation of the plug, caused by the insertion of the screw, and to allow for compLete screw engagement. For optimum utilicy, the hole depth should be at least about 302 and preferably at least 502 more chan che original Length of Che plug. The screw should noc however, be longer chan Che combined hole depth and thickness of item to be fastened.

The plastic plug, is preferably of uniform diameter or cross section along a substantial portion of its length, and it is inserted into che hole to a depth, above the bottom of Che hole, sufficient Co accommodate che extrusion elongacion. The plastic plug is substantially equivalent in diameter to che diameter of che hole. In actual practice, drills, particularly for masonry and concrete, form holes very slightly larger -2922765 (.01-.02 (1/4 - l/2mm)) than the nominally called out diameter to permit insertion of items having that diameter, without binding.

A screw of substantially the same diameter (+.02 (l/2mm)) as the plug, is rotatably inserted into the plastic plug to provide the anchoring element. The screw-may be a sheet metal screw, wood screw, lag bolt, (e.g. Type AB and BP tapping screws - ANSI/ASME B18.6.4; wood screws - ANSI/ASME B18.6.1; and lag screws - ANSI/ASME B18.2.1) or other similar screw capable of self tapping the plastic plug and having a thread of sufficient length for engagement with the fully elongated plug for optirum holding strength.

Generally, for maximum holding, the screw should have a lengch of threaded portion at least equal to 302 and preferably 502 more than that of the original plug length. Hole depth should be matched accordingly. Tapping screws having somewhat more threads/inch and screws with larger root sections will provide greater compression and holding strengch. It is preferred that the screw have a head suitable for high torque such as a hex head, to facilitate insertion into the plug. A more substantial head is also preferred to sustain the very heavy loads that the anchor is capable of holding. The screw should also have a relatively sharp point for immediate and easy boring into the plastic of the plug in preference to pushing the anchor down into the hole. A dull point will tend, because of Che very large screw diameter, to push the plug down into the insertion hole before engagement of the screw with the plug.

The plastic plug is preferably of substantially uniform outer dimensions along its inserted length to substantially conform with the uniform dimensions of the insertion hole. With highly extrudible materials the plastic plug may initially be slightly out of round with respect to the hole, if it is conformed to the hole with Che insercion of Che screw. The plascic -39Γ27Τ5’ plug is also substantially completely solid in the cross section along a substantial portion of its length.

In accordance with the present invention, the plastic of which the ancuor is comprised oust be a material which is extrudible or flowable under increased pressure and temperature exerted by the screw. This is in contrast to materials, such as the nylon or PVC of many plug anchors which merely stretch somewhat and are just cut by an inserted screw. In addition, the plastic material must also have high shear strength, on a molecular basis, and high compressibility in order to provide holding capability. Examples of such materials are polypropylene, high density polyethylene, and co-polymers thereof. It is preferred, for facilitated screw insertion, that the plastic be of a self lubricating type such as polypropylene. The nylon and PVC of common plug anchors do noc have these qualities and there is a strong tendency of inserted ecrews to detrimentally bind, particularly if they arc of larger sizes within the specified range.

The method of the present invention (comprising the utilization of a plastic plug, of a plastic having the above described characteristics, with a very large screw of specific dimension, relative to the size of the plug) operates, to effect the requisite high strength compressive bonding, it is believed, in the following unique manner. As the screw is inserted by rotary motion, the screw threads apply tremendous pressure to the highly confined plastic with increase in temperature sufficient to make the plastic flew and reshape itself in exact conformity with the wall surface of the hole. The plastic is spirally pressure extruded into many imperfections in the wall surface. In addition, plastic between threads of the screw is almost completely confined between the threads and the adjacent wall surface of the hole and is very highly compressed with extrusion against the wall surface. -49 2 my Only a very small amount of plastic can escape out of this confinement. A small amount plastic becomes a thin film, in very high compression, between the outer periphery of the screw threads and the wall surface of the hole. It has been noted that the forward threads of the screw are flattened during insertion with a plastic film covering the flattened threads. With excessively oversized screws, the threads cut through the plastic before flattening thereby negating the utility of the anchor. Residual plastic Is extruded forward of the screw. Because of the high extrusion pressures, the plug elongates to as much as 50Σ of its original length. Longitudinal hairline separations or cleavages in the plastic serve to guide the screw to ensure that plastic extrudes over a substantial circumference of the inserted screw threads. In particular, Che alternating teeth of the anchor, shown in the above identified patent, tend to substantially completely surround and lock the screw into a proper central direction. Since the plastic remains capable of reshaping itself into conformation with the screw, the anchor can be re-used, without loss of holding power, if the original screw is unthreaded from the anchor.

It has not been considered possible to be able to provide a useful anchorage with an insertion hole, a plug anchor and a screw, all of substantially the same diameter or cross section, in a non-yielding material such as concrete. It is expected chat either the screw cannot be inserted because of insufficient room for the screw, or if inserted, it will be unable to be rotated, and will lock up with resultant shearing of the screw. Alternatively, increased pressure, without relief, is expected to result in J splitting of the substrate with considerable loss of holding power. With common plug anchors made of non-extrudible materials such as nylon or ?VC , screws, when capable of being inserted, do indeed lock up and shear or the -59 2 2 7 6 5 * substrate cracks to provide room for expansion, even though the plugs already have central hollows which would tend to relieve some of the pressure.

All screw anchors, whether for solid walls or hollow walls, are marketed with instructions to utilize screws which have smaller diameters than that of the' insertion hole. It has however been discovered, with anchors of materials such as polypropylene, and such as those made in accordance wi^h Che teachings of US Patent No. 4,752,170, the teachings of which are incorporated herein by reference thereto, that substantially matching screw size (+.02 (l/2mm)) with anchor diamecer in a hole nominally having a diameter Che same (up to +.02 (l/2mm)) as that of the anchor, provides unexpectedly high .trength anchoring without problems of screw insertion, shearing or substrate breaking. With such utilization, the anchor undergoes a unique transformation in which Che anchor becomes considerably elongated, the area beeween the threads of the screw are completely filled in with the material of the anchor in highly compressed form and a thin film of plastic covers a substantial portion of the outer edges of the screw threads. The thin film of pLastic such as polypropylene also fills adjacent interstices of the walls of the insertion hole, in solid materials such as porous concrete. Utilization of a larger (by more chan a minimal amount) screw than that of the insertion hole and the anchor, however, results in slicing through of the anchor macerial by the screw thread, and significant loss of holding power.

With anchors having the matched screw and which are removed from the concrete substrate, the diameter of the anchor is from about 10-20Z greater than the initial diameter of the anchor and that of Che hole. Accordingly, when the anchor is contained within Che hole, Che polypropylene is compressed to this extent, thereby providing a very high compression strength at the molecular level. The holding power of the anchoring element of the present invention, with the high strength compressive bonding and high compression, -6greatly exceed· Chit of similarly dimensioned metal anchors and is equivalent Co or even better ·\ιη high cost chemically bonded anchors. Dense materials having little yield capability such as Che nylon of which plug anchors are generally formed, do not permit such extensive ompression. Use of plastic plugs of such materials with matched size screws results in Che inability to fully insert the screw, with the screw becoming locked-up in position such that additional turning pressure causes the screw itself to shear. Alternatively, with plugs of such materials, forced insertion of a screw causes che substrate, even high density concrete, to split.

In addition to Che above characteristics, it has been discovered that plastic plug anchoring elements of che present invention are re-usable without significant loss of holding power. The extruded plastic, when re-extruded, simply reforms itself to che newly inserted screw with Che same plastic compression and film formation even after the application of a substantial load. Other plastic anchors are simply cut to shreds by re-inserted screws.

It is also very important that :he plastic plug be held in position in a manner sufficient to prevent spinning or forcing of the plug to the bottom of che insertion hole. Very large screws, upon initial insertion, are most likely Co cause detrimental spinning which renders further insertion of che screw difficult, if not impossible. However, an excessively strong interface of Che plastic plug with Che wall of the hole will prevent insertion of the plug into the hole in the first instance. It is accordingly preferred thac minimally dimensioned anti-rotationa1 means, such as two or more small peripheral fins, be provided at the outer end of the plug, which wedge against the surface of the wall of the hole and thereby fix the plastic plug into position for rotational insertion of the screw without spinning or -7s ink ing.

With reference co Che drawings, Figure la depicts prior art plastic plug anchor 10 with anna 4 in cheir molded, outstretched condition. The surfaces of the arms 4 are each configured in two sets (a and b) of successive wave create 10a and 10b and troughs 11a and 11b which extend in direction parallel to che lengths of the arms 4. The sets of wave crests and troughs are staggered with respect to each other so that the wave crests 10a are aligned transversely on each arm with the troughs lib, and the crests 10b being similarly transversely aligned with the troughs 11a, across che width of Che arm. The wave crests and troughs or. each arm 4 are thus positioned in a keyed relationship with the troughs and wave crests on the other arm 30 that, when che arms are folded together, as ehown in FIG. lb, che crests 10a of each arm incerfit with the troughs ’.la of che other arm, and the crests lCb of each arm interfit with the troughs lib of the other arm. Thus, above che base 1, the anchor 10 is substantially completely solid in cross section.

The plastic plug anchor 10 has a central rib 15 formed, on each of che arms 4, by transversely spacing apart the sets of wave crests and troughs on each arm. The hairline split or cleavage between juxtaposed portions of central rib 15 (the height of each portion of the rib being half Che height of the wave trough to wave crest) serve to provide a narrow guide for the insertion of the screw 16. Thus, after the screw is inserted, it is thereby cencrally oriented between the secs of wave crests 10a and 10b. Additionally, except for che narrow hairline cleavage between che juxtaposed portions of rib 15, a substantially solid material front is presented to an advancing' screw. As shown in Figure lb, anti-rotation fins 6 are provided to serve che dual purpose of preventing rotation when a screw is inserted into the anchor through insertion starting hole 2, and they also wedge against the walls of a / hole to prevent sinking when pressure is exerted bv the screw on the anchor. -8rmr' Figure lc depicts an alternative embodiment of the anchor of Figurea la and b, wherein the arms 4' to base flange 5'. As with the anchor of Figures la and b, wave crests 10a' and 10b' fit into troughs 11a1 and lib1 respectively to provide a substantially completely solid plug.

As shown in photographic Figure 2, the anchor of Figure lb with an inserted screw of normal size, as used in the prior art, is extracted intact * from a wall. The anchor is shown as being elongated to some extent with Che exterior surface of Che anchor remaining roughly cylindrical in substantially the same configuration as that of Che anchor initially. In contrast thereto the anchor of photographic Figure 3, in which the screw is matched co bcth Che anchor and the hole, is elongated and a chin film with hooplike indentations is formed at the confining areas of Che screw threads. The chin film covers the edges of Che screw threads. Because of Che high compression, the chin film becomes cranslucenc and almosc transparent in such regions. The raised areas between the hooplike indentations become highly compressed and, in the photograph shown, are about 152 greater in diameter Chan the hole from which the anchor was extracted.

As shown in Figure 4, utilization of a screw, with an excessively larger diameter than that of the anchor, results in the edges of the screw threads slicing through Che anchor with macerial remaining only within the threads of the anchor. There is a substantial loss of holding power since the effectiveness of the anchor is negated by the segmentation of the anchor.

Only residual holding becween screw threads and the wall of Che hole retain the screw in position.

In order to more fully appreciate the nature of the present invention the following examples are presented for illustrative purposes. It is understood thac Che examples are illustrative in nature and that details contained therein are not to be construed as limitations on the present invention. -99?27g5 EXAMPLE ΙΑ (PRIOR ART) A polypropylene anchor ae shown in Figure lb with an outer diamecer of 8na and a length of 39no is inserted into an 8raa hole (having a depth in excess of 60nn) in 24.1 N/mm^ (3500 psi) concrete block. A 6ram screw (the recommended metric size) is threaded into the anchor and an increasing tensile load is applied to the screw head. The anchor begins to loosen at about 563kg. Figure 2 is a photograph ot this anchor with inserted screw.

EXAMPLE IB (PRIOR ART) A 1/4 (6.35on) screw (the largest recommended UNC size) is inserted into a second 8mm diamecer anchor with the same anchor and hole dimensions. There is no significant increase in pull-out value over the anchor of Example 1A.

EXAMPLE 1C (PRIOR ART) An anchor with an outer diameter of 5mm and a length of 24ram is inserted into a 5mm hole (having a depth of at least 36mm) in Che same block and a 4mm screw is threaded into the anchor. With a tensile load applied, the anchor begins to loosen at about 360kg.

EXAMPLE 2 A polypropylene anchor as ir. Examples 1A and IB with an outer diameter of 2 8mm is inserted into an 8mm hole in 24.1 N/mm concrete block. An 8mm hex-head screw is easily threaded into the anchor (no block cracking or screw shearing) and an increasing tensile load is applied. The anchor begins to loosen at about 885kg, a nearly 60Z increase in holding power over the anchors of Examples 1A and IB. Figure 3 is a photograph of this anchor with inserted screw.

EXAMPLE 2A (MODIFIED PRIOR ART) A nylon plug anchor having a central slotted hollow and original dimensions equivalent to Che anchor of Example 2 is inserted into an 8mm hole -109 2 2 7 6 5-4 io 24.1 N/mm concrete block. An 8mm hex-head screw is threaded into the anchor and before the screw is fully seated, the screw shears in half.

EXAMPLE 3 A polypropylene anchor as Example 1C with an outer diameter of 5mm is 2 inserted into a 5mm hole in 24.1 N/mm concrete block. A 5mm ecrew is threaded into the anchor and an increasing tensile load is applied. The anchor begins to loosen at about 500kg, a nearly 40Z increase in holding power over the anchor in Example 1C.

EXAMPLE 4 A polypropylene anchor as in Example 2 with an outer diameter of 8mm is inserted into an 8mm hole in 24.1 N/mm concrete block. An 8mm hex-head screw is threaded into che anchor and an increasing tensile load is applied. At 225kg (about 1/4 che ultimate load of Che anchor in Example 2 to simulate Che standard 4:1 safety load ratio) the load is released, and the screw is backed out. A second screw is re-Chreaded into Che anchor and a second load is applied. The anchor holds in excess of 950kg before beginning Co loosen.

EXAMPLE 5 (PRIOR ART) A polypropylene anchor as shown in Figure 1A with an outer diameter of 6mm and a length of 29mm is inserted into a 6mm hole (with a depth of 45mm) in 24.1 N/mm concrete block. A 5mm screw is threaded into the anchor and an increasing tensile load is applied. The anchor begins to loosen at about 620kg.

EXAMPLE 6 A polypropylene anchor as in Example 5 with an outer diameter of 6mm is 2 inserted into the 6mm hole in 24.1 N/mm concrete block. A 1/4” (6.35mm) screw is threaded into che anchor and an increasing tensile load is applied. -119 ? 2 7 6 5 * The anchor begins Co loosen sc abouc 270kg. Examination of che anchor afcer removal from Che concrete block reveals that Che threads of Che screw had completely cut through the plastic of the anchor as is more clearly seen in Figure 4.

It is understood that the above examples are illustrative in nature and Chat changes in material and dimension may be made without departing from th scope of Che present invention as defined in the following claims. -12922765 ‘

Claims (13)

1. Vhac is claimed is:

1. A method for the formation of a high strength anchoring element in a solid wall substrate, comprising Che steps of forming a hole in said solid wall substrate; fully inserting a substantially solid, generally tubular shaped plastic plug into said hole; and rotatably inserting a screw into said • r plastic plug anchor; characterized in chat said plastic is comprised of a ¥ material which is extrudible under increased pressure and temperature exerted by the screw and which has a high shear strength; said plastic plug anchor having a diameter substantially eqaual to the diameter of said hole; and wherein said screw has a diameter substantially equal Co Che diameter of said plug anchor; whereby rotational insertion of said screw causes pressure co be exerced on che plastic and further causes Che plascic Co become sufficiencly heated whereby the plastic extrudes with: a) plascic between adjacent threads of said screw becoming very highly compressed; b) a very highly compressed film of plastic being formed around a substantial portion of che outer edges of the threads of said screw; and « c) plastic extruding into imperfections in che surface of che wall of che hole .

2. The method of claim 1 wherein che hole has a diameter up Co .02 (l/2mm) larger Chan Che diamecer of che plascic plug and che screw has a diameter +.02 (l/2iaa) relative co Che diamecer of Che plastic plug.

3. The method of claim 1 wherein said hole has a depth at least 30Z more than che original length of che plascic plug.

4. The method of claim 2 wherein said screw has a sharp point whereby ic penetrates che plascic plug in preference co pushing che pLug cowards che bottom of che hole. 9227651

5. The method of claim 4 wherein said acrew haa a hex-head configuration to facilitate said rotational insertion.

6. The method of.claim 1 wherein said plastic is selected from the group consisting of polypropylene, polyethylene and co-polymers of polypropylene and polyethylene.

7. The method of claim 1 wherein said plaatic plug further comprises means Co prevent rotation thereof with rotational insertion of said screw.

8. The method of claim 7 wherein said means to prevent rotation comprise! two or more small extending fins at a peripheral edge of said plastic plug anchor exposed to insertion of said screw, with said fins adapced co be wedged between the plug and ehe wall of Che hole, upon insertion of the plug anchor into Che hole.

9. The method of claim 8 wherein said wedged fins further provide means to prevent sinking of the anchor within the wall caused by pressure of screw insert ion.

10. The method of claim 1 wherein said plug anchor further comprises longitudinal cleavages whereby an inserted screw is substantially guided thereby into a substantially central insertion within said plug and wherein the cleavages permit Che plastic Co substantially circumferentially enclose ' f Che screw.

11. The method of claim 10 wherein said cleavages comprise an interface between longitudinal elements of said plug anchor which interfic with each other to form said substantially solid, generally tubular shaped plastic plug.

12. An anchoring element comprising a plastic plug and a screw made in accordance with the method of claim I. -14922765

13. A method for the formation of a high strength anchoring element in a solid wall substrate according to any preceding claim with reference to and as illustrated in Figures 2,3 and/or 4 of the accompanying drawings.