ITTO20090757A1 - SELF-LOCKING NUTS. - Google Patents

Description

"Self-locking nuts"

Technical sector

The present invention relates, in general, to self-locking nuts in which the presence of one or more components is provided to prevent, in use, the loosening of the nut.

In particular, the present invention relates to self-locking nuts in which a cylindrical end is compressed by a helical spring and these types of nuts are preferably referred to here.

Note Art

Various types of self-locking nuts are known.

For example, from US Patent 4,893,977 a self-locking nut is known in which "V" or "U" grooves are provided in the cylindrical end, suitable for being elastically compressed by an external helical spring acting in a radial direction.

From US Patent 5,160,227 a self-locking nut of the type mentioned above is also known in which, in order to improve its corrosion resistance performance and to allow its use at temperatures above 250 ° C, that the helical spring is made in stainless steel for springs, such as the steel called AISI (American Iron and Steel Institute) 302.

The Applicant has observed, in general, that following technological and market evolution, there is an increasing need for nuts having, in particular, a constant braking moment on disassembly (braking torque in unscrewing) for a high number of cycles. screwing / unscrewing on screws, for example 30 cycles, and diversified according to the type of application.

The known nuts, in fact, are sized in such a way as to guarantee, for example in accordance with technical standards or manufacturing standards, braking moment values on disassembly that are higher than the minimum predefined values.

The known nuts, however, are not sized in such a way as to guarantee constant performance and braking moment values on disassembly differentiated in a predetermined way and such as to guarantee not only minimum values higher than the minimum predefined values, but also maximum values not higher than maximum values predefined.

A common problem with this situation is that in the face of different types of needs there is no guarantee, for those who buy the nuts, that these have braking moment values on disassembly that do not exceed the predefined maximum values and in any case included in a predefined range. and corresponding to the actual needs of a buyer.

For example, for applications in which there are screws or studs fixed to a metal body, in which the braking torque of the stud must be higher than that of the nut, the nut must not exceed braking torque values upon disassembly such as to cause the possible unscrewing of the prisoner from the body.

The same type of phenomenon could occur in devices with fixed parts or parts in slow motion, with low vibrations and low working temperatures where nuts with low braking moment values at disassembly are required. In these applications, nuts with high braking moment values on disassembly, in addition to being useless, can cause damage to the screws used or to the devices themselves, due to excessive rigidity.

On the contrary, for applications in devices with moving parts at high speed, high vibrations and high temperatures, the need for nuts with braking moment values on disassembly higher than the minimum predefined values is equally strong as, otherwise, there would be the risk of loosening of the nut with possible damage to the device and / or, possibly, to whoever uses the device.

The Applicant therefore observed that, with the evolution of the applications of self-locking nuts, the need not only for constant performance, but also for the performance to have predefined minimum and maximum limits, has been increasingly highlighted.

In particular, the Applicant observed that, following technological evolution and market demands, it is no longer sufficient to guarantee braking moment values on disassembly that are higher than the minimum predefined values, but it is necessary to prepare nuts with braking moment values on disassembly. diversified from each other and included within predefined minimum and maximum values or predefined ranges.

Description of the Invention

The purpose of the present invention are self-locking nuts which, while maintaining the structure of the known nuts, allow to realize diversified braked torques in a controlled way, so as to allow to obtain the advantages of:

- be selectable according to actual application needs;

- there is no risk of having too high or too low braking torque values when unscrewing;

- guarantee in a predefined range a substantial constancy of the braked torques in screwing and unscrewing for a high number of screwing / unscrewing cycles, for example for at least 30 cycles.

The self-locking nuts and the related manufacturing method as claimed achieve the purpose.

The claims form an integral part of the technical teaching provided herein regarding the invention.

According to a characteristic of a preferred embodiment of the present invention, the self-locking nuts comprise a threaded upper collar provided with suitably shaped longitudinal slots and defining in the collar itself a plurality of circular arc segments, and an external helical spring, suitable to compress the segments, made of precipitation hardening stainless steel and configured in such a way that the nuts produce braked unscrewing torques differentiated from each other and obtained by suitably modifying, for the same diameter of the nuts, at least one dimensional parameter of the spring.

In accordance with a further characteristic of the present invention, the spring is configured in such a way that the nuts produce a plurality of partially overlapping braked torques in unscrewing and able to cover respective differentiated ranges of braked torque in unscrewing.

In accordance with yet another characteristic of the present invention, the Applicant has identified three ranges of partially superimposable braked torques in unscrewing, such as to cover an extremely wide range of braked torque in unscrewing and therefore, consequently, an equally wide range. applications otherwise not possible with the nuts of the known art.

Brief Description of the Figures

These and other characteristics and advantages of the present invention will become clear from the following description of preferred embodiments, made by way of non-limiting example, with the aid of the attached figures, in which elements indicated with the same or a similar numerical reference indicate elements which have the same or similar functionality and construction and in which:

Fig. 1A represents a perspective view of an example of a self-locking nut with a helical spring;

Fig. 1B represents a spring usable on the self-locking nut of Fig. 1A;

Figs. 2-4 represent the braking moment values in Newton per meter (Nm) measured on a sample of nut M10 as the number of screwing / unscrewing cycles increases by varying the dimensional parameters associated with the spring;

Figs. 5-7 represent the braking moment values in Newton per meter (Nm) measured on a nut sample as the number of screwing / unscrewing cycles increases by varying the dimensional parameters associated with the spring in an M20 nut;

Figs. 8-9 represent braking moment values in Newton per meter (Nm) measured on a nut sample as the number of screwing / unscrewing cycles increases using a stainless steel spring (AISI 302) in M10 and M20 nuts, respectively;

Description of Preferred Forms of Realization

With reference to Fig. 1A, a nut 1, made in accordance with a preferred embodiment according to the present invention, is able to be screwed onto a threaded rod, not shown in the figure, inside the nut itself and is able to for example, to fix consumable parts of devices.

The nut has a known type of structure which comprises a collar 3 on which a helical spring 5 is wound, acting by radial pressure on the collar 3 and, through this, on the threaded rod on which the nut is screwed.

The structure of the nut 1 comprises a plurality of slots 7, preferably "U" shaped, provided in the collar 3 itself.

Of course, the slits, in other embodiments, can be "V" or "U" with sharp edges.

The slits 7 form on the collar 3 a plurality of segments in a circular arc 9 having an external upper rib 11.

In the preferred embodiment, a recess 13 is provided on the upper face of the structure of the nut 1; a certain number of coils 6 (Fig. 1A and 1B) of the helical spring 5 is housed in this seat, so as to wrap the collar 3 and radially compress the segments 9 which in turn exert a certain pressure or force against the threaded rod on which the nut is screwed.

The spring 5 is preferably made with a wire 5a having a diameter Φj which varies according to the size of the nut and has an internal diameter Φd which, according to the preferred embodiment, is diversified, with the same of dimensions or diameter of the nut, to allow, as will be described in detail below, to differentiate the minimum and maximum values of braking moment upon disassembly (braking moment or braking torque) in a predetermined way.

In use, the spring is preferably mounted in the opposite position to the fixed part, for example a consumable part, so that, as easily understood by a person skilled in the art, it is generally subjected to temperatures lower than those reached by the parts. fixed.

In the preferred embodiment, the spring 5 is made of precipitation hardening stainless steel also called PH (Precipitation Hardening steel) in which the presence of hardening compounds or elements, for example aluminum or an aluminum compound, soluble to high temperatures.

Even more preferably, the spring is made of semi-austenitic PH steel, such as 17-7 PH steel, also called AISI 631.

The Applicant first of all observed, for example by carrying out tests with steel springs of the 17-7 PH type, that the nuts, made using precipitation hardening stainless steel, have braking moments upon disassembly with high constancy of characteristics, even for repeated screwing cycles. / unscrewing, for example at least 30 cycles.

In particular, the Applicant has observed that the constancy of the braking moment characteristics upon repetition of the screwing / unscrewing cycles occurs both in the case of use at room temperature, for example at temperatures between -50 ° C and 100 ° C, and at high temperature, for example at temperatures between 300 ° C and 400 ° C.

In summary, the Applicant has observed a high constancy of braking moment characteristics upon the repetition of screwing / unscrewing cycles for temperatures between -50 ° C and 400 ° C, so that the nuts according to the invention are particularly convenient in contexts in which which requires their reliable reuse.

The Applicant has also observed that the constancy of characteristics is also maintained by modifying, for the same diameter of the nut, one or more dimensional parameters of the spring 5.

The detection of this phenomenon made it possible to carry out experimental tests by preferably modifying a dimensional parameter of the spring with the same diameter of the nut and to obtain nuts having differentiated values of braked torques in unscrewing and included between predetermined minimum and maximum values.

The dimensional parameters, which can be modified with the same diameter of the nut are:

- the internal diameter Φd of the spring 5;

- the diameter Φj of the wire 5a;

- the number, even if not an integer, of the coils 6.

In the preferred embodiment, the internal diameter Φd of the spring 5 was chosen as the dimensional parameter to be modified since its modification seemed to have less implications on any dimensional changes (lengthening or shortening) of the collar 3 of the nut 1 and therefore, in the continuation of the description reference is made preferentially to the internal diameter Φd of the spring 5 as a dimensional parameter subject to modifications.

In conducting the experimental tests on nuts of different diameters, a torque having as a minimum value the minimum value of the braked torque at the 5th unscrewing provided for in the ISO_2320 standard was taken as a reference as the braked torque in unscrewing.

Nuts having such an average torque were considered as nuts with standard characteristics (standard nuts or nuts with standard or average torque) and the dimensional parameters of the spring 5 used were considered as reference parameters (Fig. 3 and Fig. 6) .

Having taken the standard nuts as a reference, the diameter Φd of the spring 5 was modified.

In view of the experimental measurements carried out, the Applicant has found that, by increasing the diameter Φd of the spring 5 and keeping the other dimensional parameters of the same unchanged, it is possible to obtain average, minimum and maximum braking torque values in unscrewing which are decidedly lower than those of nuts with standard characteristics, while maintaining constant characteristics for repeated screwing / unscrewing cycles, for example 30 cycles (Fig. 2 and Fig. 5); in this case the nuts which have this type of characteristics are defined here as low torque nuts.

The Applicant has also found that, by decreasing the diameter Φd of the spring 5 and keeping the other dimensional parameters of the same unchanged, it is possible to obtain average, minimum and maximum braking torque values in unscrewing that are higher than those of nuts with standard characteristics, while maintaining constant characteristics for repeated screwing / unscrewing cycles, for example 30 cycles (Fig. 4 and Fig. 7); in this case the nuts that have this type of characteristics are defined here as high torque nuts.

In summary, the Applicant has found that, by suitably varying the diameter Φd for each type of nut of predefined dimensions, a plurality of values or ranges of braking torque values can be obtained which partially overlap, but which in any case have average values , minimum and maximum differentiated as shown below in table 1, obtained on the basis of measurements made on class 8 nuts and limiting the range of values to three.

Φ Nut Low Torque Medium Torque High Torque M08 0.3 à 1.0 0.6 à 2.0 1.0 à 3.0 M10 0.5 à 1.7 1.0 à 2.8 2.0 à 4.0 M12 1.0 à 2.5 1.6 à 4.0 3.0 à 5.0 M14 1.2 à 3.0 2.3 à 7.0 3.5 à 8.0 M16 1.5 à 4.0 3.0 à 8.0 4.5 à 10.0 M20 3.0 à 8.0 5.3 à 11.0 7.0 à 14.0 M22 3.5 à 9.0 6.5 à 13.0 8.5 à 17.0 M24 4.0 à 10.0 8.0 à 15.0 10.0 à 20.0 M27 5.0 à 12.0 10.0 à 18.0 12.0 à 25.0 Table 1

In particular, in the example the variations of the dimensional parameters of the spring 5 were directed to obtain the following effect:

- that the maximum braking torque value associated with the low torque nuts is in any case higher than the minimum braking torque value of the standard torque nuts;

- that the maximum braking torque value associated with the standard or medium torque nuts is in any case higher than the minimum braking torque value of the high torque nuts; which, as easily understood, corresponds to the fact that the minimum braking torque value of the high torque nuts is lower than the maximum braking torque value of the standard torque.

We have thus obtained to cover, with each die of predefined dimensions:

- an extremely wide range of braking torque performance in unscrewing and therefore, consequently, an equally wide range of applications otherwise not possible with the nuts of the known art.

Furthermore, the result obtained does not change the consistency of performance for repeated screwing / unscrewing cycles. Preferably, the wide range of coverage obtained by means of low, medium and high torque nuts also entails, for each nut of predefined dimensions, as shown below in Table 2 for class 8 nuts, that:

- the average value of the braked torque when unscrewing the low torque nuts is between about 45 - 55% of the braking torque when unscrewing the standard torque nuts;

- the average value of the braked torque when unscrewing the standard torque nuts is between about 75 - 85% of the braking torque when unscrewing the high torque nuts.

Φ Nut Low Torque Medium Torque High Torque M08 0.6 1.3 1.5 M10 1.1 2.0 2.6 M12 1.6 3.0 3.5 M14 1.8 4.0 5.0 M16 2.7 5.1 6.0 M20 3.7 7.5 10.0 M22 5.0 11.0 13.0 M24 7.0 12.0 15.6 M27 8.5 13.1 17.4

Table 2

The braking torque values shown in Table 1 and Table 2, in particular, are obtained preferably: - using, for example, an increased diameter as the internal diameter Φd of the low torque spring 5, compared to that of the torque spring standard, with values between about 8 - 10% for nuts smaller than M20 and increased by values between about 2 - 4% for nuts larger than or equal to M20;

- using, for example, as the internal diameter Φd of the high torque spring 5 a diameter which is reduced by values between about 2 - 4% compared to that of the standard torque spring.

In summary, the Applicant has found that to obtain high torque nuts it is generally sufficient to reduce the diameter Φd of the spring, with respect to that of the spring of standard torque nuts, by substantially constant percentage values and that a similar rule It is applicable, in the case of nuts with a sufficiently large diameter, to obtain low torque nuts, but increasing the diameter Φd of the spring with respect to that of the spring of standard torque nuts.

Finally, the Applicant noted, with surprise, that with the same dimensional parameters of the standard torque spring, by replacing the material with which the spring is made, for example the precipitation hardening stainless steel AISI 631, with a stainless steel for springs such as, for example, AISI 302 steel, the same values of braked torque in unscrewing are obtained, with the same constancy of characteristics, of the low torque nuts shown in Tables 1 and 2.

In summary, the Applicant has found that in order to obtain nuts with low torque with high constancy of characteristics, it is sufficient to choose a stainless steel for springs as, for example, AISI 302 steel, as the material with which the spring is made. keeping the dimensional parameters provided for the springs of the standard torque nuts substantially equivalent.

The term "substantially equivalent" is here intended to indicate dimensional parameters having identical values within the tolerances of use in the technical sector considered here.

By way of example and for clarity, Figures 2, 3 and 4 show the braking moment characteristics of samples of nuts M10 measured as the diameter Φd varies as described.

Figures 5, 6 and 7 also show, by way of example and for clarity, the braking moment characteristics of samples of nuts M20 measured as the diameter Φd varies as described.

The experimental tests whose measurements are shown in figures 2 to 7 were carried out, at room temperature, on Class 8 nuts using precipitation hardening stainless steel springs, for example AISI 631 steel.

Experimental tests were also conducted on Class 10 nuts and INOX nuts with substantially equivalent results.

The results of these tests are not reported as they did not involve significant deviations from those obtained with the more commonly used Class 8 nuts.

In all cases the measurements were taken in repeated screwing / unscrewing cycles (35 cycles).

Finally, Figures 8 and 9 show the braking moment characteristics of samples of M10 and M20 Class 8 nuts carried out, at room temperature, using stainless steel springs for springs, for example AISI 302 steel, with dimensional parameters identical to those of the springs used for the standard torque nuts and made of AISI 631 steel.

Thanks to the invention it is not only possible to use the nuts according to the invention several times and without risk on parts that require a high number of replacements during their life period, but it is also possible to select, within the nuts range, different diameter, the range of braking torque characteristics in unscrewing more suited to the fixing needs of the same parts.

The present description has used the self-braking nuts of Fig. 1A as a reference, but, as easily understood by a person skilled in the art, it is also foreseeable that a wide range of unscrewed braked torques can be obtained with self-locking nuts with axial effect metal insert and truncated cone nuts with calibrated deformation of the conical part on the thread by suitably varying the dimensional parameters of the metal insert or the calibrated deformation of the conical part.

Of course, obvious modifications and / or variations are possible to the above description, in the dimensions, shapes and components as well as in the details of the illustrated construction and method of operating without departing from the invention as specified in the following claims.

Claims (10)

CLAIMS 1. Self-locking nuts (1) comprising a threaded upper collar (3) provided with longitudinal slots (7), V-shaped or U-shaped also with sharp edges, defining in the collar itself a plurality of arc-shaped segments (9) compressed by a certain number of coils (6) of an external helical spring (5) made with a metal wire (5a), said slots having such width as not to allow mutual contact of said arc-shaped segments (9), characterized by fact that - said wire (5a) of said spring (5) is made of precipitation hardening stainless steel; and from what - said nuts have differentiated braking torque values in unscrewing, obtained by modifying, for the same diameter of the nuts (1), at least one dimensional parameter (Φd, Φj, 6) of said spring. 2. Self-locking nuts (1) according to claim 1 wherein said at least one dimensional parameter (Φd, Φj, 6) is selected from the group consisting of: - internal diameter (Φd) of the spring (5); - diameter (Φj) of the wire (5a); - number of turns (6) of the spring. 3. Self-locking nuts (1) according to claim 1 or 2 wherein said at least one dimensional parameter is constituted by the internal diameter (Φd) of the spring (5). 4. Self-locking nuts (1) according to any one of claims 1 to 3 wherein said at least one dimensional parameter is selected so as to obtain: - a first braked torque or standard or average torque having, as a minimum value, a predetermined minimum value of braked torque at a given loosening and a determined maximum value of braked torque; - a second braked torque in a range lower than that of the first braked torque, called second braked torque or low torque, having as a maximum value a maximum braked torque value higher than the minimum value of the standard torque; - a third braked torque in a range higher than that of the first braked torque, said third or high torque, having as a minimum value a minimum braked torque value lower than the maximum braked torque value of said standard torque; therefore, said dimensional parameter is selected in such a way as to obtain partially superimposable braking torque values capable of covering, respectively, differentiated braking torque ranges in unscrewing. 5. Self-locking nuts according to claim 4 wherein said low torque is obtained by selecting, in place of said spring made of precipitation hardening stainless steel, a spring made of stainless steel for springs having dimensional parameters substantially equivalent to those selected to obtain said standard pair with said precipitation hardening stainless steel. 6. Self-locking nuts according to claim 5 wherein said substantially equivalent dimensional parameters are constituted by the internal diameter (Φd) of the spring (5). 7. Method for making self-locking nuts comprising the steps of - making a nut structure (1) comprising a threaded upper collar (3) provided with longitudinal slots (7) shaped like a V or a U, also with sharp edges, defining in the collar itself a plurality of segments (9) in a circular arc adapted to be compressed by a determined number of coils (6) of an external helical spring (5) made with a metal wire (5a); - making said wire (5a) in precipitation hardening stainless steel; - modify at the same diameter of the nut (1) at least one dimensional parameter (Φd, Φj, 6) of said spring to obtain nuts (1) having different values of braking torque in unscrewing. 8. Method according to claim 7 wherein said step of modifying at the same diameter of the nut (1) at least one dimensional parameter (Φd, Φj, 6) of said spring (5) comprises the step of - modify at least one dimensional parameter (Φd, Φj, 6) chosen from the group consisting of: - internal diameter (Φd) of the spring (5); - diameter (Φj) of the wire (5a); - number of turns (6) of the spring. Method according to claim 7 or 8 comprising the step of - select said at least one dimensional parameter (Φd, Φj, 6) in order to obtain: - a first braked torque or standard or average torque having, as a minimum value, a predetermined minimum value of braked torque at a given loosening and a determined maximum value of braked torque; - a second braked torque in a range lower than that of the first braked torque, called second braked torque or low torque, having as a maximum value a maximum braked torque value higher than the minimum value of the standard torque; - a third braked torque in a range higher than that of the first braked torque, called third braked torque or high torque, having as a minimum a minimum braked torque value lower than the maximum braked torque value of said standard torque. Method according to claim 9, wherein the step of - choosing, in place of said spring made of precipitation hardening stainless steel, a spring made of stainless steel for springs having dimensional parameters substantially equivalent to those used to obtain said standard torque with said precipitation hardening stainless steel.