FI93893B - Bolt-pretensioning device and method for performing the pretensioning - Google Patents

Abstract

Pretensioning device for a bolt or a similar fastener 2 and method for pretensioning the bolt, which is based on the deformation of the sleeve 4, made from two-way memory metal, at a certain transformation temperature, and on the capacity of the sleeve to generate very large forces. The sleeve is placed between the piece 1a that is to be fastened or tightened, and the locking piece 5, the locking piece transmitting the force generated in the deformation of the sleeve to the bolt that is to be pre- tensioned. <IMAGE>

Description

, 93893

Screw biasing device and method for performing biasing - Skruvens förspänningsanordning och förfarande för genomförande av förspänningen.

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 in connection with installation.

It is advantageous to perform prestressing by stretching the screw before tightening the nut with a certain pre-calculated force. To perform this operation, 10 pre-tensioning tools have been developed, such as hydraulic pre-tensioning devices, for example 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 preload 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 directly to the ends of the screw, between which a prestressing elongation is also generated.

20 0 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 screw has been used. , a steel rod placed inside, for example electrically heated, which, by thermal expansion caused by the heat introduced into it, stretches the prestressed screw. All of the above methods require complex equipment and tools, which often have to be fabricated 2 5 for each screw size separately.

U.S. Pat. No. 5,248,233 discloses a type of screw attachment removal device in which, using a memory metal fabricated, thermocouple, cylindrical phase change to remove a segmented nut without shocking the structure. This patent 30 does not involve bolting the screw by means of a memory metal cylinder.

U.S. Patent 4,450,616 comprises a memory metal plate in which the properties of the memory metal 2 93893 are used to ensure the tightness of the nut or screw, not to provide bolt prestressing elongation.

In the biasing device according to the invention, most of the difficulties associated with the devices in use have been eliminated. 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 martensite reaction. The shape and volume of the pieces made of memory alloys in the heating after the deformation caused by the external force to a relatively low temperature are restored to exactly the original. Recovery is typically still complete after 4-8% deformation. The martensite reaction starts and takes place over 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. The deformation occurs rapidly when the transformation temperature is reached. Due to the low change in temperature, it is not necessary to transfer large amounts of heat to the part to be heated.

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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 a one-way memory phenomenon, the deformation triggered by a certain change temperature is irreversible. In the case of a bidirectional memory phenomenon, the deformation is reversible when the body cools below a certain temperature. Hereinafter, a memory metal based on a one-way memory phenomenon is referred to as a one-way memory metal, and a memory metal based on a two-way memory phenomenon is referred to as a two-way memory metal. Also in the following, 7 of the above temperatures, the terms upper transition temperature and lower transition temperature will be used.

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With bidirectional memory metal, the upper transition temperature is typically in the range of 80-100 ° C, and the body does not recover until the body cools or cools to the lower 3 0 transition temperature, which is typically -20 ° C + 200 C. The above cycle can be repeated several times, even in the order of 10,000 times depending on deformation and load.

Il 3 93893

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

The device according to the invention, as defined in the characterizing part of claims 1 to 4, uses a phase change caused by a screw in a certain temperature change range of the memory metal, which causes a dimensional change in the memory metal body in connection with which the force is used to stretch the screw. The deformation capacity of the bidirectional memory metal is typically about 4%, while the prestressing elongation of the steel screw 10 is typically about 0.2% of the elongation.

In addition, claims S and 6 set out the characteristics of the method.

The invention will now be described in detail with reference to the accompanying drawings:

Figure 1 shows an arrangement and a device according to the invention for biasing a screw.

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Figure 2 shows a lock piece according to the invention and the actual tightening nut according to Figure 1.

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In the arrangement according to Figure 1, the parts (1a, Ib) to be joined together are connected by means of a screw (2). ... In the case shown in Fig. 1, the screw is shown to be fastened by a thread (8) to the pieces (Ib) to be fastened to each other and to pass through the upper piece (1a). For example, a nut (3) is screwed into the thread (9) at the upper end of the screw and a locking piece (5) is placed on it in the same thread, within which the nut (3) can move freely. An annular sleeve (4) made of a bi-directional memory metal strip is placed between the skirt (13) of the locking piece (5) and the body (1a) to be fastened. The device works as follows: The sleeve (4) is heated in some way, for example by a heat blower, to the upper change temperature of the memory metal. In this case, a phase change takes place in it and it also expands in the direction of the screw 30 and stretches the screw (2) by means of the locking piece (5). The nut (3) can then be tightened with a tool known per se through the openings (7) in the lock body (5) by means of notches (10) in the nut (3). When the nut (3) is tightened, the memory metal sleeve 4 93893 (4) is allowed to cool or is cooled to a lower change temperature, whereby the sleeve (4) returns to its previous dimension and the screw is tightened. The lock piece (5) can now be removed and the memory metal sleeve (4) removed.

5 The memory metal sleeve can be dimensioned separately for each screw length and force required to stretch the screw. However, it is practical that the sleeve is dimensioned in such a way that it is sufficient to stretch the screws of different lengths up to a certain maximum length. If the elongation required by the biasing screw is less than that of the memory metal sleeve (4), a clearance (11) is left between the memory metal sleeve 10 (4) and the hem (13) of the lock piece, dimensioned so that the elongation of the memory metal sleeve minus the required prestressing stretch. The clearance can be measured with a measuring device known per se.

The memory metal sleeve (4) can be heated to an upper transition temperature in a manner known per se using, for example, a heat blower or an electric heater, which may be ready around the sleeve. Because the transition temperature is relatively low, the amount of heat required: ·, is not very large. A sleeve made of bidirectional memory metal returns to its original dimension when its temperature drops below the lower transition temperature. If it is below ambient temperature, cooling to a lower transition temperature can take place, for example using carbon dioxide ice.

. . . The device according to the invention has the great advantage that quite ordinary cap screws or stud screws can be used. Also, the space required by the devices for performing the prestressing is small and no measuring devices are necessarily required to perform the prestressing. The screw can be removed using the same device.

By making a plurality of adapter rings (12) in the lock piece (5), in which the inner thread (6) is fitted according to the corresponding thread (9) of the screw (2) and the outer thread (14) is attached to the lock piece (5). 0 screws.

It is clear to a person skilled in the art that if a long screw and one memory

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5 The deformation of the 93893 metal 1 sleeve is not sufficient to give the screw sufficient prestressing elongation, two or more memory metal sleeves can be placed on top of each other under the lock piece. The bushings can then be of standard height, so that by using one or more slings on top of each other, the desired elongation required for the bolt is achieved.

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The sleeve (4) can also be divided into several parts. In this case, it is advantageous for the locking body (5) to have two or more separate legs instead of a skirt (13), under which the memory metal pieces are placed.

From the point of view of the invention, it does not matter in which way the change temperature required by the memory metal is achieved. Likewise, the invention is not limited to any currently known memory metal.

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Claims (6)

93893 A device for biasing a fastening member, for example a screw, in which a locking body (5) is placed on the same thread at one end of the bolt (2) to be bolted to the actual nut or the like (3), the hem-shaped edge (13) and the body to be fastened ), at least one annular sleeve (4) is interposed, characterized in that the sleeve (4) is made of bidirectional memory metal, the at least upper transition temperature of which is above the installation temperature. 10 Device according to Claim 1, characterized in that the locking element (5) has a fitting ring (12) for fitting it to the prestressed screw. Device according to Claim 1, characterized in that the lock piece has two or more legs under which memory metal pieces are placed. Device according to Claims 1 to 3, characterized in that the sleeve (4) or pieces made of memory metal are fastened to the locking piece (5). A method in which prestressing of a fastening member, for example a screw (2), is performed by tightening the screw between one or more sleeves (4) placed between the skirt (13) of the lock piece (5) fastened to the free end (9) of the screw and the fastening or tightening piece (1a) characterized in that the sleeve made of memory metal is heated to its upper transition temperature, whereby due to the phase change it expands and stretches the screw (2) by means of the 2nd locking piece (5), whereby the nut (3) can be tightened, after which the sleeve ( 4) allowed to cool or cool to a lower transition temperature, whereby. it returns to its original size and the lock piece and sleeve can be removed. • « Method according to Claim 5, characterized in that the desired prestressing elongation 3. of the screw (2) and the expansion of the sleeve are matched by leaving a clearance (11) between the sleeve (4) and the skirt (13) of the locking piece. Il 93893