PLASTIC TIE-ROD FOR CONSTRUCTION FORMWORK

The present patent relates to equipment for building constructions and in particular concerns tie-rods, which are used in construction formwork, with which structures in reinforced concrete are built. The most advanced formwork consists of panels with a metal frame (steel, aluminium etc.) which contain a multi-ply timber panel, and/or of one-piece panels in plastic. To resist the considerable pressure which concrete exerts when it is poured into the inside of the formwork, tie-rods are used, consisting of threaded bars, onto the ends of which are screwed accessories, which lock the formwork in the desired position. This avoids it being displaced and/or deformed as a result of the pressure which is created when it is filled with concrete. Currently the tie-rods are in metal and consist of a threaded bar, predominantly of the "diwidag bar" type. The accessories which are screwed onto them are also made of metal, and have various conformations. The most widely-used of these is called a "nut plate" or "flanged nut". The current tie-rods represent an excellent and tested means of opposing the pressure of the concrete, but have the defects of weighing a lot, of being expensive and of requiring more work than necessary, because an accessory needs to be screwed on and unscrewed at both extremities. And it is precisely to obviate all the above-mentioned disadvantages, that a new tie-rod has been conceived and researched, which presents two important novelties:

the first is that at, one extremity, it incorporates integrally one of the accessories which lock the formwork; the second is that, preferably, it can be made of plastic (synthetic resin and/or polymers), by the technique of moulding, a technique which is very widely used to produce a very large number of objects, but never utilised for the production of tie-rods. This technique provides for the use of a machine, called a press, and of a mould constructed in steel and/or other metal. The press receives the raw material (synthetic resin and/or polymers), in the solid state, meters it, melts it till it is brought to a liquid state and injects it at high pressure (approx. 2 kg per cm ² ) into the mould, implementing precisely the parameters (temperature of the plastic, temperature of the mould, sequence of opening the nozzles, injection pressure, cooling time for the mould etc.) which have previously been set and memorised (as a result of careful research and many practical tests) on an electronic board, floppy disk or other media. Besides metering and injecting the plastic, which could already contain other materials, such as fibres, for example (of glass, carbon etc.) .and/or mineral additives (calcium carbonate, talc, mica etc.) which increase its strength, the press can meter and inject other materials capable of correcting possible defects (physical and/or chemical expanders and/or nucleating agents called internationally Foaming Agents, Blowing Agents and Nucleating Agents), or materials capable of adding characteristic benefits to the plastic (protection from ultraviolet rays for example) or, again, capable of adding useful characteristics (for example, colourants). These are some of the substances which may be used for making the new tie-rod. The fibres and the mineral additives serve to increase the strength of the plastic, for example its resistance to traction, the expanders serve to ensure that the plastic which forms the tie-rod does not deform in the cooling and solidification phase, and to ensure homogeneous shrinkage, or even, if useful and/or

advantageous, to further reduce the weight. The protective agents against ultraviolet rays improve the characteristics of the plastic, which has the defect of being attacked by them. It should be borne in mind that tie-rods are used on building sites, therefore in the open air. Consequently they are exposed to the rays of the sun and therefore to ultraviolet rays. If they were not enriched with this substance, in the short space of a few years they would be attacked and begin to degrade through the phenomenon of "chalking". The tie-rods would thus lose one of their principal characteristics, which consists in their durability. The colourants perform a function of great usefulness. In fact, for a cost which consists only of their purchase price, without there being any additional cost for subsequent processes (as occurs

V for example with painting and zinc-plating metal), they allow the operator to easily and intuitively identify the class to which the tie- rods belong, in terms of its capacity. For example, the tie-rod with a capacity of 4.0 tons can be coloured red, the one with a capacity of

6.5 tons can be coloured green, and so on.

This innovative tie-rod is distinguished from those currently in use, principally by the following characteristics: - universality, that is to say that it can be used, throughout the world, in any kind of formwork for building;

- lightness, since the plastic material used has a very low specific gravity, about a sixth of the specific gravity of metal;

- low cost, since the material used, the production technique and the fact that the threaded bar already incorporates an accessory for locking the formwork, allow a significant lowering of the costs of production and consequently of the prices of sale;

- durability, since the material employed does not rust; - ease of cleaning, since the material used, being smooth, does not lend itself to clinging by the concrete. Also, since it is not

affected by water, it can easily be washed even by using a high-pressure spray cleaner, and since it is unaffected by heat, hot water can be used with no problems, even water at 100 ⁰ C;

- ease of disposal, since the material used is recyclable; - ease of identification and maximum safety, since it can be manufactured in various colours, for the purpose of identifying with ease and certainty the class to which the tie-rod belongs, in terms of its capacity;

- high productivity, since much time is saved by the fact that it is no longer necessary to screw and unscrew an accessory at one extremity, because the new tie-rod contains it incorporated integrally. Furthermore, being very light, the new tie-rod does not fatigue the workers who handle it, and allows them to maintain constant productivity over the course of the day.

An object of the present invention is to produce a tie-rod for construction formwork in plastic, which incorporates, at one extremity, the accessory for locking the formwork, in order to simplify and speed up the operations of setting up the formwork and dismantling it. \

Another object is that the tie-rod should be light and that it should not fatigue the workers who use it.

Another object is that it should be inexpensive and that it should be usable throughout the world and with every type of formwork. Another object is that it should be made from recyclable materials and/or that it should be able to be made from recycled materials. Another object is that it should promote safety on building sites, in other word that it should be easily identifiable, with different colour-schemes depending on the capacity, without the possibility of error.

Another object is that it should be easy to clean.

The principal elements of the new tie-rod in plastic are described below, with reference to the attached drawings, by way of example and without limiting effect. Figure 1 shows one of the many types of tie-rod (Ta) currently in use in construction formwork and how it is made up of a threaded bar (Bd) onto which are screwed, at one extremity, the nut plate (Pd) and, at the other extremity, the nut with three wings (Da) which divides the force reacting to the pressure of the concrete on the plate (Pr). Figure 2 shows, by way of example but without limiting effect, the new tie- rod in plastic (NT), and it can clearly be seen how the accessory for locking the formwork (DFI) is incorporated integrally into the threaded bar (BF), while the other accessory for locking the formwork (DF), which is screwed onto the threaded bar (BF) by means of the threaded hole (FF), is separate. ^particular, it is possible to see, in both the locking accessories, the hole (FL) into which a lever is inserted to forcibly tighten up the formwork, and the hexagon (EB) which is used alternatively to forcibly tighten up the formwork, using a spanner if necessary. It is also possible to see the plates (PAC) which are used to bear on the formwork and to divide up over a large surface the reaction force to the pressure exerted by the concrete.