GB2095355A

GB2095355A - Securing anchor rods in boreholes

Info

Publication number: GB2095355A
Application number: GB8138770A
Authority: GB
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1981-03-20
Filing date: 1981-12-23
Publication date: 1982-09-29
Also published as: AU8096182A; SE8201425L; ES272562U; BE892540A; FI72786B; NL8200936A; SE453854B; FI814147L; IT1150640B; FR2502268A1; AT383192B; JPS57161297A; FI72786C; ATA42082A; IT8220051A0; GB2095355B; CA1197716A; CH652806A5; ES272562Y; FR2502268B1

Abstract

A threaded anchor rod 3 is secured in a borehole 2 by driving it at an elevated temperature, into a rod-like plastics body 1 consisting of a thermoplastic or thermosetting granular plastics material, the shape of the body 1 being achieved by sintering or by enclosing the granules in a frangible container. The heat from the rod softens the body 1 and causes it to adapt itself to the interior of the borehole 2 and the exterior of the rod 3. <IMAGE>

Description

SPECIFICATION Afastening device This invention relates to a fastening device comprising an anchor rod and a plastics body which is meltable under the action of heat supplied by means of the anchor rod.

To anchor a fastening element, such as an anchor rod, in a borehole, basically two possibilities exist.

According to the first possibility, anchorage is achieved by mechanical expansion in the borehole.

For this, substantial forces have to be applied in order to achieve the necessary high expansion pressure in the borehole. Because of these pressure conditions, the use of such dowels in certain locations is not possible. For example, in the case of a fastening required to be effected close to the end edge of receiving material the danger exists that the receiving material may break away.

In such and similar instances of use in which the creation of a high expansion pressure in the borehole is not desired, so-called composite or adhesive anchors are used. In this respect, the components of a hardenable mixture are introduced, usually in separate destructible containers, into the borehole and are mixed with one another in the borehole along with destruction of the containers.

This type of anchorage is very complicated and expensive mainly on account of the separate packaging of the components, and the necessary intermixture of the components in the borehole is not without problems. Moreover, the hardening time during which leading may not be applied to the dowel is highly dependent upon the ambient temperature.

In order to avoid the above-described difficulties in relation to composite or adhesive anchors, it is already known to insert into the borehole a hollow body made of plastics material which is meltable at a specific temperature, and to melt same at least partially by introducing the fastening element into the borehole at an elevated temperature. However, such a hollow body has the disadvantage that its inside diameter has to be co-orindated to the fastening element that is to be introduced. Production of the hollow body is relatively expensive and can be complicated. Moreover, the melting of the plastics hollow body, which may be relatively large, can involve a lot of energy.

The problem underlying the invention is to provide a simple fastening device which comprises an anchor rod and a plastics body meltable under the application of heat, and which is universally usable and requires only relatively moderate melting heat.

In accordance with the invention, this is achieved in that the plastics body is composed of thermoplast or duroplast granulate.

The plastics body is preferably designed as a solid body and is, thus, suitable with a specific outside diameter for a specific bore for the reception of anchor rods of different sizes. The plastics body consisting of granulate is more easily meltable than a corresponding solid body. Upon softening, the individual granulate grains can shift relative to one another without their being completely melted. The introduction of the heated anchor rod serves to force the plastics material into the depths of the borehole and againstthe walls thereof, so as to be compacted.

In the case of a duroplast, such as for example epoxy resin or polyester resin, hardening takes place during the fastener-setting procedure by the pressure applied and the heat also supplied in so doing. In this respect, the plastics mass adapts itself to the geometry of the borehole. The air volume possibly existing between the individual granulate grains is taken up, by the anchor rod. The introduction of the anchor rod can be effected, for example, by means of a hammer drill operating in impacting or rotaryimpacting manner.

The plastics body may be designed in various ways. For convenience of handling, and also for cost reasons, it is advantageous for the granulate to be sintered. Such sintering of the granulate can be effected by compressing the body whilst it is at an elevated temperature. As a result of the pressure produced in so doing and the heat, the individual granulate grains "stick" together or agglomerate into a body of stable shape.

A further advantageous possibility consists in that the granulate is arranged in a destructible container.

This destructible container may be, for example, of plastics foil, paper or glass. The granulate is filled loosely into the container and this is then sealed.

Upon driving-in the heated anchor rod, the container melts or is mechanically destroyed.

The plstics material must satisfy certain practical requirements. Thus, on the one hand it needs to have a relatively low melting point and, on the other hand, it should have high strength. In orderto improve its strength, it is advantageous for the plastics body to contain an additive; such an additive may be present in the granulate itself or be admixed therewith.

The additive may be fibrous, flake-shaped or spherical in configuration and it may be metallic, organic or inorganic. For example, glass fibres, asbestos fibres or carbon fibres, or steel wire, or a combination thereof, may be used as a fibrous additive. All these substances have a certain resistance to heat, and after hardening of the plastics material the fibres form a reinforcement. Talc and mica are examples of suitable flake-shaped additives. Suitable spherical additives are, for example, powdered quartz, glass spheres or steel shot. Spherical additives have the advantage that they do not result in a notch effect.

Various thermoplasts or duroplasts may be used as the plastics materials. Particularly suitable are thermoplasts, such as polyamide or polyphenylsulphide (PPS), also known under the trade name of "Rayton". The proportion, by volume, of the additive can amount to about 15 to 60 percent. The density of the plastics body may be varied depending on the desired eventual strength of the fastening. Correspondingly, the extent by which the plastics body is compacted upon the introduction of the anchor rod can be selected to be greater or lesser to achieve a stronger or not so strong fastening. Plastics bodies of high density may be used for reception materials having high strength.

The invention will be described further, by way of example, with reference to the accompanying drawing which illustrates a preferred embodiment by way of example and in which: Fig. 1 is a sectional side view illustrating a plastics body, which forms part of the preferred embodiment of the fastener in accordance with the invention, during insertion into a borehole; and Fig. 2 is a view comparable with Fig. 1 but illustrating the driving-in of a heated anchor rod of the fastener into the borehole in which the plastics body has been fully inserted.

Fig. 1 shows a plastics body 1, which forms part of a fastener in accordance with the invention, which body is composed of a thermoplast or duroplast granulate, being inserted into a borehole 2. The plastics body 1 has a cylindrical shape and its outside diameter corresponds substantially to the diameter of the borehole 2. The granulate grains have been sintered together. The plastics body 1 may, moreover, contain additives, such as glass fibres or asbestos fibres. These additives increase the strength of the plastics body 1. The density of the plastics body 1 may be selected so as to be any practical desired value, depending on the intended use.

In orderto avoid confusion, the granulate of the plastics bodies of different densities may be dyed differently in accordance with their suitabilities for different uses, for example for making fastenings in concrete, brick or aerated cement.

Fig. 2 shows the driving-in of an anchor rod, designated as a whole by the reference numeral 3, into the plastics body 1 after the latter has been fully inserted into the borehole 2. The anchor rod 3 is provided, over its entire length, with a thread 3a and has, at its front end, a convergent cutting edge 3b.

Both the thread 3a and the cutting edge 3b are, however, merely advantageous versions and are not absolutely necessary for the functioning of the fastening device. Instead of the thread 3a, to achieve a firm connection, bead-shaped ribs may, for example, be provided on the shank of the anchor rod 3. Prior to the anchor rod 3 being driven into the plastics body 1, the anchor rod 3 is heated to a temperature just under the melting point of the granulate of the body 1. Upon the driving-in of the anchor rod 3, heated for example to a temperature in the range of 180 to 350 C, into the plastics body 1, the granulate is softened and brought into a plastic state, without actually melting. The driving-in of the anchor rod 3 is effected by means of a setting tool, 4 of which part is illustrated at 4 in striking or rotary-striking manner.

Upon the driving-in of the anchor rod 3, the softening granulate is compacted in the borehole 2, and thus adapts itself on the one hand to the geometry of the borehole 2 and on the other hand to the shape of the anchor rod 3. Because of this adaptation, any fairly large dimensional discrepancies or deviations, both of the borehole 2 and of the anchor rod 3, can be present without giving rise to any significant dis advantage to the eventual fastening.

In addition to or instead of sintering the granulate grains together into a shaped body, such grains may be arranged in a destructible container consisting for example, of foil, paper or glass.

The plastics body 1 may contain, besides the granulate, greater or lesser proportions of additives consisting, for example, of glass fibres, asbestos fibres or the like, to increase both the strength and the temperature stability of the anchorage. A con sidemble advantage of the fastening of the invention consists in the problem-free storing of the plastics body and introduction thereof into the borehole as well as in the immediate loadability of the fastening after the setting operation.

Claims

1. Afastening device comprising an anchor rod, and a plastics body meltable underthe action of heat supplied by means of the anchor rod, characterised in that the plastics body is composed of thermoplast or duroplast granulate.

2. A device as claimed in claim 1, characterised in that the granulate is sintered.

3. A device as claimed in claim 1 or 2 characterised in that the granulate is arranged in a destructible container.

4. A device as claimed in claim 1, 2 or 3, characterised in that the thermoplast or duroplast granulate contains an additive.

5. A fastening device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.