FI93671B - Device and method for tightening a bolt - Google Patents

Abstract

Device and method for tightening a bolt, based on the dimensional changes of two-way memory metal at certain transformation temperatures and on its capacity to generate very large forces, which are transmitted to the tightening of the bolt 1 by means of a device, which is placed inside the bolt 1 and utilises the collet 2, 2a as tightening device. <IMAGE>

Description

93671

Apparatus and method for biasing the screw - Anordning och metod att förspänna en skruv. 5

The invention relates to a biasing device for a screw or the like, which is used in the art, especially in the case of biasing larger screws during installation.

It is preferable to perform prestressing by stretching the screw with a certain pre-calculated force before tightening the nut. To carry out this operation, prestressing tools have been developed, for example hydraulic prestressing devices, such as, for example, in the Swedish publication 7701049-4, in which the screw is stretched by means of hydraulic pressure and then the nut is tightened. When the pressure is removed, the connection tightens and the desired prestress remains in the screw 15.

In the above case, the stretching takes place at the end of the screw to be stretched, but often a piston-like part is also placed in the hole drilled inside the screw, at one end of which hydraulic pressure can be applied. In this case, the tensile force is applied by the piston 20 0 directly to the ends of the screw, between which a prestressing elongation is also generated.

German publication OS 3733243 uses a piston element placed in a hole drilled inside the screw, which can also be heated. In some cases, a steel rod placed inside the screw, for example electrically heated, has been used, which stretches the biased screw by the thermal expansion caused by the heat introduced into it.

U.S. Pat. No. 4,450,616 discloses a unidirectional memory metal washer which is cup-shaped and elastic and which is intended to seal and secure the screw tension after the phase change of the memory metal. Due to its shape, the washer of the present publication is not able to cause prestressing elongation of the screw, nor is it required by the invention.

93671 2 SU patent publication 1523761 discloses a hook-shaped memory metal tool by means of which two flanges can be tightened against each other and then bolted to each other.

Japanese Patent Publication No. 60-188608 discloses a memory metal screw made of a Ni-Ti alloy 5 having a starting point of deformation temperature lower than the operating temperature of the screw.

All of the above methods require complex equipment and tools, which often have to be manufactured for each screw size separately or which, although applications of memory metal, are not within the scope of the invention.

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In the biasing device according to the invention and defined in the preamble of the claims, most of the inconveniences associated with the devices in use have been eliminated and the device itself is remarkably small in size.

The device according to the invention is based on the use of memory metals known per se. In the crystal structure of the memory metal, a phase change occurs under the influence of temperature. The phenomenon is called the marten sperm reaction. The shapes of the pieces made of memory alloys, when heated to a relatively low temperature after deformation caused by an external force, return exactly to the original. Recovery is typically typically 0 0 after 4 to 8% deformation. The martensite reaction starts and takes place in a rather narrow temperature range, typically about 20 ° C, which can generally be adjusted to the desired point in the temperature range -30 to + 100 ° C. The martensite reaction is crystallographically completely reversible under certain conditions. Changes in memory metals are not based on thermal expansion, but on a phase change in the crystal structure triggered by a change in temperature.

2 5 Deformation occurs rapidly when the transformation temperature is reached. Change in temperature. due to the low level, it is not necessary to transfer large amounts of heat to the piece to be heated.

There are two main groups of memory metals, one of which is a one-way memory phenomenon and the other a two-way one. For those memory metals based on the one-way memory phenomenon, the deformation triggered by a certain transformation temperature is irreversible. In the case of a bidirectional memory phenomenon, the deformation is reversible when the body cools below a certain temperature 93671 3. Hereinafter, a memory metal based on a one-way memory phenomenon will be referred to as a one-way memory metal, and a memory metal based on a two-way memory phenomenon will be referred to as a two-way memory metal. Similarly, in the following, the terms upper transition temperature and lower transition temperature will be used for the above-mentioned temperatures.

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With bidirectional memory metal, the upper transformation temperature is typically in the range of 80 to 100 ° C, and the body does not recover until the body cools or cools to a lower transformation temperature, which is typically -20 to + 200 C. The above cycle can be repeated several times, up to about 10,000 times and depending on the load.

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Many memory metal alloys can withstand very high stresses, up to 800-1000 N / mm2, without being plasticized and without losing their memory properties, so that a body made of such a metal is capable of producing high forces during deformation.

In the device according to the invention, as defined in claims 1 to 6, in the device and in the method shown in claims 7-8, a phase change initiated in a certain change temperature range of the so-called memory metal is used as the source of the stretching force. This causes a dimensional change in the piece of memory metal, in which the force generated is used to stretch the screw. The deformation capacity of the bidirectional memory metal is typically about 4%, while the pre-tension elongation of a steel screw is typically only about 0.2% of the elongation.

The invention will now be described in detail with reference to the accompanying drawings: Figure 1 shows a screw biasing device according to the invention, in which biasing is performed by a memory metal cartridge placed inside a screw.

Figure 2 shows an alternative according to the invention for performing prestressing using a memory metal cartridge and in which part of the cartridge has been replaced by a steel rod.

Figure 3 shows a third embodiment according to the invention, in which the memory metal cartridge 30 93671 4 is moved outside the hole of the screw and a steel rod is placed in the hole as a force transmitter.

According to Figure 1, a hole (5) is drilled in the center of the screw (1) to be pre-tightened, into which a memory metal cartridge (2) can be inserted. A heating element (3) is placed inside the cartridge, which may be, for example, an electrically heated electric heater. At the other end of the screw, a stop screw (4) can be attached to the thread (6) inside it, hereinafter referred to as a stop, and into which the electrical wires (8) going to the cartridge (2) through the drilled hole (7) pass through the stop (4). The hole (5) drilled in the screw (1) generally extends through the entire area which must be stretched during the prestressing of the screw (1).

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The device works as follows: Insert the pre-tensioning screw (1) and insert the memory metal cartridge (2) into the screw hole (5). The stop (4) is screwed into the thread (6) so that the wires (8) of the cartridge heating element (3) pass through the hole (7) of the stop (4). By suitable rotation of the stopper, a clearance (9) can be left between the cartridge (2) and the stopper (4), which is dimensioned so that the change in the length dimension of the memory metal cartridge (2) minus the clearance is equal to the desired elongation of the screw. When the memory metal cartridge (2) is heated to the upper transformation temperature by the heating element (3), a deformation takes place in the cartridge, which also manifests itself as an increase in the length of the cartridge. This in turn stretches the screw (1) via the cartridge base (10) and the stop (4). When the screw is stretched, tighten the screw or nut (11). When the 20 0 memory metal cartridge (2) cools to a lower transition temperature, it returns to its original gauge and the screw (1) is prestressed. The stop (4) and the cartridge (2) can now be removed. The screw (1) is removed in a similar way.

In the above description, the screw (1) is heated by an electric heater. It is clear to a person skilled in the art 25 that the heating can also take place in other known ways.

The memory metal cartridge (2) can be dimensioned separately for each screw length and force required to stretch the screw (1). However, it is practical for the cartridge to be dimensioned to a length sufficient to stretch a screw of a certain length. If the elongation required by the screw to be pre-tightened is less than the elongation of the memory metal cartridge (2), a clearance (9) can be left between the memory metal cartridge (2) and the stop, thus using 1 · 93671 5 of the same cartridge to pre-tighten screws of several lengths. The clearance can be measured by first turning the stop (4) closed and then opening it a certain number of revolutions or by measuring the distance coming out of the stop in some known way.

Figure 2 shows another alternative for performing prestressing. Screw the stop (4) into the bore (6) made at one end of the biasing screw (1). A memory metal cartridge (2) is inserted into the non-threaded bore extension (6a). From the cartridge (2) comes a metal rod (12) placed in the bore (5) entering the screw, the purpose of which is to transmit the force caused by the deformation of the memory metal cartridge to the other end of the screw (1). The device 10 operates as described above.

Figure 3 shows a third alternative in which the memory metal cartridge (2) is moved outside the screw hole and a steel rod (12) longer than the hole drilled in the screw (1) is inserted in the hole and dimensioned to withstand the force required to stretch the screw (1). A nut (11) is threaded into the threads at the end of the screw (1) and then a stop nut (4a) corresponding to the stop (4) of Fig. 1, hereinafter collectively referred to as the stop, and containing at least one cylindrical piece of memory metal corresponding to the memory metal cartridge (2) of Fig. 1 ( 2a) so that it rests on the rod (12) and on the other side the stop 20 (4a). Heating of the memory metal cylinder (2a) to an upper transition temperature can take place. with a heating element inserted therein or the heating element can be placed in the space (13) inside the stop. Heating can also be performed by heating the restrictor (4a) from the outside, whereby heat is conducted along the restrictor to the memory metal cylinder (2a), initiating a desired phase change thereby transmitted by the deformation screw 25 from the memory metal cylinder (2a) via the restrictor (4a). ) at one end and. through the rod (12) to one end of the screw (1) by stretching the screw. When the screw is thus prestressed,. · Tighten the nut (11). Once the memory metal cylinder (2a) has cooled or is cooled to its lower transition temperature, it returns to its original dimension and the biasing means, stop (4a), memory metal cylinder (2a), possible heating element and rod (12) can be removed. The screw is removed in a similar way.

93671 6

In the embodiment according to Figure 3, it is also possible to use a clearance (9) so that the deformation of the memory metal cartridge (2) or the cylinder (2a) and the desired screw elongation can be matched, as previously described.

In the embodiment according to Figure 3, instead of one memory metal cylinder (2a), two or more cylinders of the same or different lengths can also be superimposed and thus their common deformation can be adapted to the desired elongation in the screw (1).

If a memory metal cartridge (2, 2a) made of unidirectional memory metal 10 is used in the device, it is difficult to remove it after prestressing. If a cartridge made of bidirectional memory metal is used, it can be easily removed after preloading the cartridge and reused to preload the other screws.

It will be clear to a person skilled in the art that the invention can also be applied to biasing fastening means other than those shown in Figures 15 and the description, and it is not essential for the operation of the device how the heat is introduced into the memory metal cartridge.

Memory metals are generally alloys and are known in a variety of forms, e.g. nickel-titanium alloy doped with additives. The invention is not limited to any currently known or later discovered memory metal.

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Claims (8)

93671 A device for biasing a screw or similar fastening means, wherein in the device 5 a space (2, 2a) for biasing the screw is placed in the space delimited in the hole (5) drilled inside the bolt (1) and the stop (4, 4a) fixed to the screw end, and if necessary its rod-like extension (12), characterized in that the cartridge (2, 2a) is made of memory metal. Device according to claim 1, characterized in that the cartridge (2a) rests at one end on a stop (4, 4a) and at the other end on a rod (12) extending to the bottom of the hole as an extension of the cartridge. Device according to claim 1, characterized in that the cartridge (2a) is inside the stop 15 (4a) but outside the end of the screw (1) and rests at one end on the stop (4a) and at the other end on the bottom of the hole (5) as an extension of the cartridge up to the rod (12). Device according to Claims 1 to 3, characterized in that the cartridge is made of 20 bidirectional memory metals. Device according to Claims 1 to 4, characterized in that a heating element (3) is connected to the cartridge, to which thermal energy is introduced, for example, through a restrictor (4, 4a). 25 Device according to Claims 1 to 4, characterized in that the cartridge (2a) is arranged relative to the restrictor (4a) so that heat can be conducted to the cartridge through the restrictor. A method in which the biasing of a fastening member, for example a screw (1), is performed by tensioning the screw with a cartridge (2, 2a) placed in a hole drilled in it and fixed to the end of the screw (1) 33671 and in the space defined by the bottom of the hole (5) as such or via a rod-like extension (12), characterized in that the cartridge (2, 2a) made of bidirectional memory metal is heated to its upper transition temperature, whereby due to the phase change 5 it expands and stretches the stop (4, 4a) and the hole bottom (5). ), whereby the screw (1) or nut (11) can be screwed on and after which the cartridge (2,2a) is allowed to cool or is cooled to a lower transition temperature, whereby the cartridge (2, 2a) returns to its original dimension and the restrictor (4, 4a), the cartridge (2, 2a) and its possible extension (12) as well as the heating element 10 (3) can be removed. A method according to claim 7, characterized in that the desired prestressing elongation in the screw (1) and the expansion change of the memory metal cartridge (2, 2a) are matched by leaving the stop (4, 4a) and the cartridge (2, 2a) or cartridge (2, 2a) 15 and a clearance (9) between its extension (12). 20 25 «30 93671