US 3244055 A
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April 5, 1966 F. SCHUERMANN ETAL 3,244,055
DETACHABLE ANCHOR BOLTS Original Filed March 15, 1961 2 Sheets-Sheet 1 @mmm Edwina/QM amp April 5, 1966 F. SCHUERMANN ETAL 3,244,055
DETACHABLE ANCHOR BOLTS Original Filed March 15, 1961 2 Sheets-Sheet 2 /NVENI'0,PS 7' @ZA Wu 4). Jim
United States Patent 3,244,055 DETACHABLE ANCHOR BOLTS Fritz Schuerrnann, Baimlerstras'se, Essen-L redeney, Germany, and Rudolf Novotny, 22 @stpreussenstrasse, Essen-Heisingen, Germany Continuation of application Ser. No. 95,925, Mar. 15, 1961. This application Mar.26, 1964,Ser.N .sssnza 2 illaims. (Cl. 85-1) This is a continuation application of an earlier filed application Serial Number 95,925, filed March 15, 1961, now abandoned.
This invention relates to anchor bolts which are used, for example, for the support of mine workings, for securing overhanging rock walls above ground and in building for reinforcing foundations or the like.
Such anchor bolts are secured by their tips in the bottoms of drill holes and are braced against the rock or the like by means of a plate secured to that end of the bolt which projects from the drill hole.
Substantially more advantageous than purely mechanical fixing, which is conventionally obtained in anchor bolts by forcing an expansible tip against the wall of the drill hole, is a recently developed method in which securing of the tip of the anchor .bolt in the bottom of the drill hole is effected by cementing the same in the hole by means of cement, cement mixtures or hydraulic mortar introduced into the drill hole in front of the anchor bolt, for example by a pressure pipe or in a cartridge contain ng synthetic resin, hardener and accelerator in a plurality of compartments. In the known method, the cartridge is destroyed by the tip of the anchor bolt penetrating into it when the anchor bolt is introduced into the hole, preferably with a rotating action, so that intimate mix ng of the synthetic resin, hardener and accelerator and, thereby, rapid hardening of .the previously viscons resin occurs. This method of securing an anchor bolt in the bottom of a drill hole allows the use of bolts of substantially simpler design than the conventional expansible bolts and permits a cementing of the anchor bolts in the drill holes so that the release thereof, i.e. later withdrawal of the bolts, is generally impossible.
The invention relates to anchor bolts secured by cementing material in the bottom of a drill hole. According to a first feature, the object of the invention is to permit removal of at least part of the anchor bolt. According to the invention, this is achieved in that the anchor bolt consists of two parts, a tip and a shank extending beyond the mouth of the drill hole, which are detachably connected to one another by means of screw threads, a coupling or other connecting elements having a reversible action, the location of the connection of the .parts being such that the tip is shorter than one half of the total length of the anchor bolt.
The proportioning of the length of the tip While maintaining said length shorter than one half of the length of the complete anchor bolt depends mainly on the length of the cementing or adhesion surface provided in the bottom of the drill hole. Generally, the length of such cement ng surface in the method in which the constituents of the cement are introducedinto the bottom of the drill hole in a destructible cartridge is between -40 cm. according to the rock conditions. As the normal total length of an anchor bolt is at least two meters, it is possible to recover practically 80% of the anchor bolt, that part (the shank) which has been screwed out being immediately ready for use again by screwing on a new tip, and thus to reduce the cost of anchor-bolt supports by the cementing method by 40-60%.
Another advantage which is obtained in the cementing method owing to the two-part construction of the an- 3,Z44,55 Patented Apr. 5, 1956 chor bolt according to the invention is the possibility of screwing bolt tips of suitable diameter and length, which may be varied as desired, on to the longer section or shank of the anchor bolt.
The diameter of that part of the bolt which is disposed towards the mouth of the drill hole is thus entirely independent of the diameter of the drill hole, so that the latter is no longer subiect to limitations because of considerations of the amount of material in the anchor bolt and can therefore be enlarged, which enables an enlargement in the area of adhesion for the same cementing-in length of the tip or the possibility of making the cementing-in length smaller. In addition, the detrimental effect of the expansion of a steel anchor bolt on the cementingin length, .i.e. the loss of effective cementing-in length, which increases with the expansion, is eliminated if a screwed-on tip made of a cast steel which expends very little is employed. The result is that the available cementing-in length is utilized to substantially better advantage than heretofore and this also can result in a reduction in the length of the cartridge and thereby of the cost thereof.
The detachable tip may consist of material other than that of the main part of the anchor b0 t, for example of a polyester resin, a phenolic resin or the like reinforced with glass fiber, which results in improved adhesion of the tip to the synthetic resin introduced into the drill hole as the cementing material. It is also possible to manufacture the shank which is to be recovered of synthetic resin.
The anchor bolt tip, which may be provided with an external thread to enable it to be screwed into the synthetic resin contained in the bottom of the drill hole or into a cartridge filled with resin, may have so small a length that, when it is manufactured from synthetic resin, it can readily be made by conventional molding or injection method.
The complete independence of the tip of the anchor bolt from the main part of the latter makes it possible to incur heavier expenditure for the manufacture thereof, without the cost of tie complete anchor bolt becoming uneconomic, and so to design the bolt that optimum conditions are obtained for the cementing thereof in the bottom of the drill-hole.
To this end the tip of the anchor bolt may be provided, in the region of the tip to be secured in the drill hole, with encircling thread-like ribs and at its free end with a conical point. Longitudinal grooves may be provided to extend from the conical point over the entire cementing-in length or a part thereof, the grooves having a depth at least equal to that of the thread-like ribs, so that the longitudinal grooves interrupt theperipheral extension of said ribs.
With this design, the penetration of the tip of the anchor bolt with rotary action into the cartridge takes place with the smallest possible resistance and, after the cartridge has been destroyed, the charge thereof is moved by the conical point of the tip mainly transversely of the direction of the penetration of the tip andtowards the wall of the drill hole, without an undesirably high pressure being generated in the undestroyed part of the cartridge to oppose the tip penetration.
Even in the event of the cartridge being already completely destroyed when the tip of the anchor bolt first strikes it, the major portion of the cementing material is still pressed against the wall of the drill hole and only a small quantity thereof is compressed against the bottom of the drill hole.
The spiral turns on the tip act as a scr w press which compresses the cementing mixture towards the bottom of the drill hole, but the grooves which extend longitudikeying surfaces.
7 partying nally of the tip and interrupt the ribs in the peripheral direction prevent this pressing action becoming undesirably 'drill hole intercepts cracks and fissures into which the cementing material could penetrate too far on being strongly compressed so that the amount of cementing material left in the bottom of the drill hole would no longer be sufficient to fill the cavity.
In addition to the longitudinal slotshaving the effect of achieving a certain equalization of pressure between the bottom of the drill hole and the adjacent region of the periphery of .the hole which is to be cemented to the anchor bolt, they also act to improve the mixing when the tip of the anchor bolt is screwed into the cartridge.
As small a pitch as possible of the thread formed by the encircling spirals has been found to be desirable to avoid an undesirable increase in pressure, and the pitch is preferably of the order of magnitude of between 2 and mm., preferably 3 mm., per turn. With this small pitch, even when the directionof rotation of the thread and of the shank are the same, the compression of the cementing materialin the bottom of the drill hole does not exceed a desired value when the tip is introduced.
When opposite directions of rotation of the thread and shank are used, the rotation of the anchor bolt has the effect of conveying the materialaway from the bottom of the drill hole, i.e., so that, if desired, all compression of the cementing material in the bottom of the drill hole can be avoided.
The invention also provides the possibility of applying, when the anchor bolt has penetrated almost completely into the cartridge and the mixing of the constituent has been completed, an increase in the compressing pressure which may then be desirable by means ofv a disc mounted on the anchor bolt so as to seal off the space in the drill hole which is filled with the cement and to prevent the cement flowing down in upwardly directed drill holes. The disc is arranged at so small a distance from the tip of the anchor bolt that, after the cavity surrounding the tip of the anchor bolt has been completely filled with the cement, the disc acts on the latter as a piston as the anchor bolt is further screwed in, the disc compressing the cement evenly in the direction of the bottom of the drill hole.
The design of the tip of the anchor bolt described above is also advantageous if the tip is not detachably connected to the shank but forms one structural part therewith.
The above-described manifold possibilities, provided by the design of the tip of the anchor bolt in accordance with the invention, of varying the pressure efiect on the cebottom of the drill hole, are dependent to a considerable extent on the uniformityof the rotating or striking movement imparted to the anchor bolt when it is driven in.
4 In FIGURE 1 the reference 1 indicates the tip anchor bolt which isdetachably connected to the shank 2 of the anchor bolt by means of arscrew thread 3; the tip 1 terminates in a conical point 9 having a semi-spherical.
angle of about To improve the adhesion and the mixing effect when the bolt tip 1 is screwed into a cartridge containingthe plastic, the tip 1 comprises, over the major part of'it s length, an external thread 4 and, adjacent its rear end, an annular groove 5 in which an annular disc 6 is inserted for sealing off the bottomof the drill hole which is filled with the cement. The sealing disc 6 preferably consists of hard rubber or a material equivalent thereto and is of According to the preferred embodiment of the invention, the disc 6 is ar the same diameter as the drill hole;
ranged at such'a distance from the point 9 that, after the cartridge containing the constituents of the cement has been completely destroyed, the disc 5 exerts a compressing pressure on the mixture contained in the bottom'of the drill hole when the anchor bolt is further screwed in.
The shank '2 is provided at its outer end with a thread 7 which enables the anchor bolt to be braced against the rock by means of a base plate and nut. The shank terminates in a squared ends with a plain base or end sur-- face 3- on which a device which turns the anchor bolt,
i.e., screws it in when it is being set and screws the shank 2 out when it is being removed, can act. The plain base or end surface 8' also enables the anchor bolt to be driven in by means of a hammering action on saidend surface instead of with a rotating action.
FIGURES'Z and 3 showeven more clearly than does FIGURE 1 the external thread on the tip 1 with a pitch of the turns of between 2 and 10 mm. The turns may be either left-handed or right-handed, i.e., they may be formed so that they correspond to the direction of rotation of the anchor bolt when it is driven in or are opposite to said direction of rotation.
The spiral thread turns are interrupted by a plurality of longitudinal grooves 10 distributed uniformly over the periphery and of a depth at least equal to the depth of the turns 4 of the thread. If required, the grooves may of the drill .hole which is to be filled with cement or.
- mortar mixture. The disc 6' is mounted, prefer-ably ee- According to a feature of the invention, in order to obtain such uniformity and for the purpose of transmitting movements from a rotary tool, for example a rotary drilling machine, employed for the drive, keying surfaces are provided on that part of the anchor bolt which projects from the drill hole and keys, spanners, or sockets which a can be inserted in the head of the tool are engaged on said The presence of these keying surfaces 7 anchor bolt constituting a first embodiment,
FIGURE 2 is a similar view to FIGURE 1 of a second embodiment, and
FIGURE 3 is a similar view of a third embodiment.
merited, on the tip at a distance from the point 9 which is chosen in dependence on the cementing-in length of the tip provided with a thread. a
The embodiment shown in FIGURE that shown in FIGURE 2 only in that the longitudinal grooves 10 do not extend beyond the sealing disc 6", but are arranged only in the front region of the anchor bolt, i.e. only on a part of the intended cementing length, and
act to produce an equalization of pressure over this most important region.
In FIGURE 3, the direction of twist of the spiral turns ferentiation'of the adhesion of the cement mixture to the; a
periphery of the tip as compared with its adhesion to the wall of the drill hole, as a result of which, if a certain I loading of the braced anchor bolt is exceeded, the adhesion of the cement mixture ceases in the region of this of an differs from plain part, whereas it is maintained at the wall of the drill hole, so that the cement mixture is compressed elastically and compacted transversely of the direction of the anchor bolt.
The invention is not limited to the embodiments described in detail above and illustrated in the drawings, and numerous modifications thereof are possible without departing from the scope of the following claims. Thus, in particular, the design of the tip of the anchor bolt according to FIGURES 2 and 3 is also applicable with similar advantages to anchor bolts whose tip part is not separable from the shank of the anchor bolt.
What we claim is:
1. In an anchor bolt assembly adapted to support mine workings, rock walls, foundations and the like by being secured in a drill hole having a transverse cross sectional dimension larger than the transverse cross sectional dimension of the anchor bolt assembly by means of a cementing material, said assembly including:
an anchor bolt tip portion and a shank portion detachably secured thereto, said tip portion being generally cylindrical and terminating at one end in a cone, the other end of said tip portion having an internal- 1y threaded bore, an external helical cement material mixing groove extending from the cone of said tip portion toward the said other end of said tip portion, at least one external longitudinal groove extending from the cone of said tip portion toward said other end and terminating within said mixing groove, said helical mixing groove intersecting said longitudinal groove and together forming flow and mixing channels for the cementing material, a sealing washer disposed outwardly beyond said longitudinal groove, said sealing washer including a pair of threaded nuts threadably engaging the helical groove with an annular sealing member therebetween;
and said shank portion including a threaded portion at one end adapted to be threadably received in the internally threaded end of the tip portion, and means at the other end of said shank portion for rotating the assembly in a drill hole.
2. In an anchor bolt assembly adapted to support mine workings, rock walls, foundations and the like by being secured in a drill hole having a transverse cross sectional dimension larger than the transverse cross sectional dimensicn of the anchor bolt assembly by means of a cementing material, said assembly including:
an anchor bolt tip portion and a shank portion detachably secured thereto, said tip portion being generally cylindrical and terminating at one end in a cone, the other end of said tip portion having a smooth cylindrical outer wall surface and an internally threaded bore formed coaxially thereof, an external helical cement material mixing groove extending from the cone of said tip portion toward the said other end of said tip portion, at least one external longitudinal groove extending from the cone of said tip portion toward said other end and terminating in the smooth cylindrical outer wall surface inwardly of the outermost end thereof, said helical mixing groove intersecting said longitudinal groove and together forming flow and mixing channels for the cementing material, sealing means secured to the smooth cylindrical outer wall surface and disposed inwardly of the termination of said longitudinal groove; and said shank portion including a threaded portion at one end adapted to be threadably received in the internally threaded end of the tip portion, and means at the other end of said shank portion for rotating the assembly in a drill hole.
References Cited by the Examiner UNITED STATES PATENTS 569,235 10/ 1896 Rockwell --14 2,573,498 10/1951 Scott 85-82 2,690,879 10/ 1954 Snyder 85--23 2,829,502 4/1958 Dempsey 85-23 2,890,845 6/ 1959 Kiekhaefer.
FOREIGN PATENTS 3,012 2/ 1889 Great Britain. 70,309 6/ 1915 Switzerland.
CARL W. TOMLIN, Primary Examiner.