Safety Anti-loosening screw–nut system

Abstract

The aim of the present invention is to solve or significantly reduce the phenomenon of unintentional unscrewing in bolt mechanics as a result of vibrations, forces or rotations This aim can be achieved by applying the following technical solution: the use of a screw characterised by the presence of two threaded stems separated by an unthreaded stem with a smaller diameter than the other stems, and a special nut, which is matched to the final thread of the screw. The nut is free to slip, rotate and misalign itself from the screwing axis when it reaches the unthreaded stem, making unintentional unscrewing impossible. This technical solution can be applied in the context of industrial accident prevention, related to the unintentional unscrewing of fasteners.

Description

[0001] Safety anti-loosening screw-nut system

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The present invention belongs to the technical field of fastening mechanics. More specifically, the invention relates to nuts and cylindrical screws for joining plates, walls, surfaces or, more generally, bodies of various kinds and for preventing accidental loosening.

[0005] PRIOR ART

[0006] As is well known, a bolt is a detachable fastening element between two mechanical parts, consisting of a male element (a screw) and a female element (a nut).

[0007] A typical bolt comprises a male part formed by a hexagon-head screw and a female part formed by a nut, usually hexagonal, whose hole carries a thread complementary to that of the screw.

[0008] The male part has a smaller-diameter portion (the shank) that passes through the parts to be joined and, at one end, a larger portion (the head) that bears on and compresses the parts. The parts are drilled, the male part is inserted through the common hole and is then coupled with a female part on the side opposite the head. The holes need not be threaded and must allow the bolt to pass freely.

[0009] The screw thread is normally absent along that portion of the shank lying within the thickness of the joined parts, since the connection is obtained by compressing the parts against each other; a partly unthreaded shank also gives greater shear strength.

[0010] The characteristic data of a bolt are its diameter (the outside diameter of the screw thread, identical to that of the unthreaded cylindrical part) and its length (the length of the shank).

[0011] Apart from the nut, the other principal component is the screw, which consists of three parts:

[0012] • Head - bears against the part to be joined and supplies the clamping force; its shape depends on the required tightening force, on the tool used and on the space available.

[0013] • Shank - cylindrical, and partially or entirely threaded.

[0014] • Shank end - in common applications is chamfered or rounded to aid insertion and protect the first thread.

[0015] The nut is normally hexagonal; according to its height it is classified as high, regular or thin. A bolted joint is useful whenever two or more purpose-designed parts must be joined without welding or interference fit, allowing rapid disassembly and re-assembly without damage.

[0016] TECHNICAL PROBLEM

[0017] The problem arises when a bolted joint is subjected to repeated loads or vibrations that cause the nuts to rotate, so that the joint slackens and the nuts back off. Commercial countermeasures (locknuts, washers, lock plates, prevailing-torque nuts, thread-locking compounds, welding, etc.) all have limitations. The phenomenon of loosening is still the subject of mechanical-engineering and physical research aimed at preventing industrial accidents.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] • FIG. 1 - schematic view of a first embodiment of the safety cylindrical screw together with the main clamping nut (7) and the safety anti-loosening nut (8).

[0020] • FIG. 2 - schematic view of a first embodiment of the safety anti-loosening nut.

[0021] • FIG. 3 - schematic view of the fastening assembly comprising the cylindrical safety screw (9), the parts to be clamped (10), the main clamping nut (11) and the antiloosening safety nut (12).

[0022] • FIG. 4 - schematic view of the safety cylindrical screw that is completely threaded.

[0023] • FIG. 5 - schematic view of another embodiment of the safety cylindrical screw having shanks with the same thread direction and identical diameter.

[0024] • FIG. 6 - schematic view of a first embodiment of the safety anti-loosening nut; the upper (13) and lower (14) faces are shown with respect to the screwing axis (15) and the plane orthogonal to that axis (16). In this specific embodiment a triangular profile is chosen solely to place the centre of gravity off-axis.

[0025] FIG. 7 shows further embodiments of the safety anti-loosening nut. In these examples the upper and lower faces are parallel but carry protrusions (17), wedges and / or irregularities that offset the nut axis (18) from the screw axis when the nut is supported, during back-off, by another nut with parallel faces.

[0026] FIG. 8 shows the fastening assembly consisting of a safety cylindrical screw (20), parts to be clamped (21), a main nut (22) and a safety anti-loosening nut (23) provided with protrusions and / or wedges. The anti-loosening nut (23) rests on the main nut (22) under gravity, but the protrusions / wedges (17) make it tilt and thus offset it from the screw axis.

[0027] FIG. 9 shows the assembly in operation without the main nut (22). The safety cylindrical screw (25) has multiple shanks of the same thread and diameter (26) and multiple smooth shanks of smaller diameter (27).

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] With reference to FIG. 1, the safety cylindrical anti-loosening screw comprises a head (1); a first shank (2) having a smooth zone (3) followed by a threaded zone (4); a second smooth shank (5) whose outside diameter is smaller than that of the other shanks (2, 6); and a third, final threaded shank (6). The final shank (6) mates with the thread of the safety anti-loosening nut (8). The second shank (5) allows the anti-loosening nut (8) to rotate, slide and tilt freely under forces and vibration. The first shank (2) may be entirely threaded (FIG. 4). The outside diameter of the first shank (2) is larger than that of the second shank (5). In FIG. 1 the thread of the first shank (2, 4) differs from that of the final shank (6), but in other embodiments (FIG. 5) their threads and diameters may coincide.

[0030] With reference to FIG. 2, a possible embodiment of the safety anti-loosening nut is shown. It is illustrated as a hexagonal nut with a triangular profile and inclined upper and lower faces. The nut is configured so that its centre of gravity is offset from its screwing axis, although other shapes are possible. With reference to FIG. 3, the bolt assembly is shown. The safety cylindrical anti-loosening screw (9) passes through the hole in the two plates (10). A standard nut (11) slides over the final shank (6, FIG. 1), over the second smooth shank (5, FIG. 1) and screws onto the threaded zone (4) of the first shank (2, FIG. 1). The safety anti-loosening nut (12) screws onto the final shank (6) and then occupies the second smooth shank (5), where it can rotate, slide and tilt. Because the thread diameter of nut (12) is larger than the diameter of shank (5), the nut offsets itself from the screw axis under its own weight or centrifugal force, preventing unscrewing. When the standard nut (11) begins to back off, it is blocked by the tilted antiloosening nut (12). This occurs because, while the anti-loosening nut is on the second smooth shank, rotational forces or gravity misalign it with the screwing axis; when it is supported by the main nut its non-parallel faces or protrusions keep it misaligned. Right-hand and left-hand threads are shown, but are not essential to the invention.

[0031] With reference to FIG. 4, the safety cylindrical screw is fully threaded along the first shank (2).

[0032] With reference to FIG. 5, another embodiment of cylindrical anti-loosening screw is shown. Here the first shank (2, 4) and the final shank (6) have identical threads and diameters, so the anti-loosening nut can screw onto either of them, and the main nut has the same internal thread and the same diameter as the anti-loosening nut.

[0033] With reference to FIG. 6, the upper (13) and lower (14) faces of the anti-loosening nut are not parallel but inclined so that they intersect, thereby shifting the nut’s centre of gravity away from the screwing axis (15). Whenever the anti-loosening nut is supported by a flat surface, such as when the main nut backs off, its screwing axis misaligns with that of the cylindrical screw. The faces are not orthogonal to the screwing axis (15) and therefore are not parallel to the plane orthogonal to that axis (16).

[0034] With reference to FIG. 7, other embodiments of the anti-loosening nut are illustrated in which the upper and lower faces are parallel but provided with wedges or protrusions (17) or other irregularities that offset the nut axis (18) from the screw axis. If the anti-loosening nut had flat faces parallel to those of the main nut, it could be supported by the main nut during back-off; in that case its axis (18) would coincide with the screw axis and could re-engage the thread and unscrew. The irregularities or wedges (17) keep the nut tilted even when supported.

[0035] With reference to FIG. 8, the mechanism by which the wedge-equipped anti-loosening nut (23) becomes offset is depicted. As the main nut (22) loosens it travels up the safety screw (20) and meets the anti-loosening nut (23); the wedges of nut (23) offset its axis from that of the screw, creating a mechanical lock that prevents loosening. If gravity causes nut (23) to rest on the final shank, its offset centre of gravity makes it tilt and remain misaligned.

[0036] With reference to FIG. 9, the fastening assembly is shown without the main nut (22). Even alone, the anti-loosening nut (29) prevents separation of the plates (28), demonstrating that the system can operate without a main nut. In this embodiment multiple smooth shanks (27) of smaller diameter than the others (26) are provided along the screw to further hinder loosening.

Claims

AMENDED CLAIMS received by the International Bureau on 15 November 2025 (15.11.2025)

1. A safety anti-loosening screw-nut system for clamping at least one member (10,21 ,28), comprising: a cylindrical anti-loosening screw (9,20,25) provided with a head (1) and a shank extending from the head (1), the shank comprising:- an initial shank portion (2,4) that is partially or fully threaded;- at least one intermediate smooth shank portion (5,27); and- a final threaded shank portion (6,26); a main clamping nut (11 ,22) configured, in use, to clamp the at least one member (10,21 ,28) between the head (1) and the main clamping nut (11 ,22) upon tightening on the shank; and an anti-loosening nut (8,12,23,29) having an internal thread complementary to a thread of the final threaded shank portion (6,26); characterised in that: the intermediate smooth shank portion (5,27) has an outer diameter smaller than an outer diameter of the initial shank portion (2,4) and of the final threaded shank portion (6,26); the internal thread of the anti-loosening nut (8,12,23,29) has a minor diameter larger than the outer diameter of the intermediate smooth shank portion (5,27), such that, when the anti-loosening nut (8,12,23,29) is arranged on the intermediate smooth shank portion (5,27), the anti-loosening nut does not form an operative threaded engagement with any threaded portion of the screw (9,20,25) and is free to rotate, slide and tilt relative to the intermediate smooth shank portion (5,27); the anti-loosening nut (8,12,23,29) has an outer geometry configured such that a centre of gravity of the anti-loosening nut is offset with respect to a screwing axis (15,18) of the antiloosening nut; and in an operating condition, the anti-loosening nut (8,12,23,29) is arranged on the intermediate smooth shank portion (5,27) at a position to be contacted by the main clamping nut (11 ,22) when the main clamping nut (11 ,22) tends to unscrew, so that, under the effect of gravity and / or vibrational or centrifugal forces, the anti-loosening nut (8,12,23,29) adopts a tiltedposition in which the screwing axis (15,18) of the antiloosening nut is misaligned with an axis of the cylindrical screw (9,20,25) and the internal thread of the anti-loosening nut (8,12,23,29) cannot engage the final threaded shank portion(6.26), contact between the main clamping nut (11 ,22) and the tilted anti-loosening nut (8,12,23,29) thereby acting as a mechanical stop limiting loosening of the main clamping nut (11 ,22) and preventing separation of the at least one member (10,21 ,28) clamped between the head (1) and the main clamping nut (11 ,22).

2. The system according to claim 1 , wherein upper and lower end faces (13,14) of the anti-loosening nut (8,12,23,29) are not parallel to each other and are not orthogonal to the screwing axis (15,18) of the anti-loosening nut.

3. The system according to claim 1 or 2, wherein at least one of an upper end face and a lower end face (13,14) of the antiloosening nut (8,12,23,29) comprises projections, wedges and / or irregularities (17) configured such that, when the antiloosening nut (8,12,23,29) is supported on a plane surface (16) or on the main clamping nut (22), a screwing axis (18) of the anti-loosening nut is kept misaligned with respect to the axis of the cylindrical screw (9,20,25).

4. The system according to any one of claims 1 to 3, wherein the initial shank portion (2,4) and the final threaded shank portion(6.26) have the same diameter and the same thread.

5. The system according to claim 4, wherein the main clamping nut (11 ,22) has the same internal thread as the anti-loosening nut (8,12,23,29).

6. The system according to any one of claims 1 to 5, wherein the shank of the cylindrical screw (9,20,25) comprises a plurality of intermediate smooth shank portions (27) of reduced diameter, spaced along a length of the shank.

7. The system according to any one of claims 1 to 6, wherein the system is configured such that the anti-loosening nut (29), arranged on one of said intermediate smooth shank portions (27), is sufficient to prevent separation of the members (28) to be clamped even in the absence of the main clamping nut (22).[0001]STATEMENT UNDER ARTICLE 19 (1)[0002]This statement accompanies the amendments to the claims filed under Article 19 PCT.[0003]The amendments to claim 1 are intended to clarify the contribution of the present invention over the prior art cited in the international search report, in particular documents DI and D2, and to make explicit the co-operation between the geometry of the anti-loosening nut and the specific configuration of the screw shank as already disclosed in the description.[0004]Amended claim 1 now clearly defines that the cylindrical anti-loosening screw comprises, in addition to a head, an initial shank portion, at least one intermediate smooth shank portion of reduced outer diameter and a final threaded shank portion. The claim further specifies that the internal thread of the anti-loosening nut has a minor diameter larger than the outer diameter of the intermediate smooth shank portion, so that, when the anti-loosening nut is located on the intermediate smooth shank portion, it no longer forms an operative threaded engagement with any threaded portion of the screw and is free to rotate, slide and tilt with respect to that portion. These features are supported, inter alia, by the detailed description of Figures 1, 3 and 9, which describe the second smooth shank of smaller diameter, the free rotation, sliding and tilting of the anti-loosening nut on that shank, and the presence of multiple smooth shanks of smaller diameter along the screw.[0005]In addition, amended claim 1 explicitly recites that the anti-loosening nut has an outer geometry such that its centre of gravity is offset with respect to its screwing axis and that, in an operating condition, the anti-loosening nut is arranged on the intermediate smooth shank portion at a position to be contacted by the main clamping nut when the latter tends to unscrew. Under the effect of gravity and / or vibrational or centrifugal forces, the anti-loosening nut adopts a tilted position in which its screwing axis is misaligned with the axis of the screw and its internal thread cannot engage the final threaded shank portion. In this misaligned state, contact between the main clamping nut and the tilted anti-loosening nut provides a mechanical stop which limits the loosening travel of the main clamping nut and prevents separation of the clamped members. This co-operation is described, for example, in connection with Figures 3 and 8, which explain how the tilted anti-loosening nut blocks the back-off of the main nut and creates a mechanical lock.[0006]By defining this co-operation, amended claim 1 makes clear that the anti-loosening effect in the claimed system is not based on a conventional prevailing-torque or frictional lock between threads, but on a geometric and kinematic interaction between an off-axis anti-loosening nut and an intermediate smooth shank portion of reduced diameter on which the nut is free to tilt and act as a mechanical stop against loosening. This distinguishes the claimed system from prior-art arrangements in which the lock nut remains in continuous threaded engagement with the screw in its locking position and where the anti-loosening effect is essentially achieved by increased friction between threads.[0007]The dependent claims have been adapted accordingly and now explicitly recite features already disclosed in the description, such as the non-parallel, non-orthogonal end faces of the anti-loosening nut, the presence of projections or wedges on such faces, the embodiment in which the initial and final threaded shank portions share the same diameter and thread, and the embodiment with multiple intermediate smooth shank portions, including a configuration in which the anti-loosening nut alone can prevent separation of the clamped members even in the absence of the main clamping nut. No modification of the drawings is required as a result of these amendments.

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