GB2066401A

GB2066401A - A slack-resisting bolt

Info

Publication number: GB2066401A
Application number: GB8027011A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-12-26
Filing date: 1980-08-19
Publication date: 1981-07-08
Also published as: IT8049566A0; ES258155Y; ZA804869B; DE3032166C2; CH637450A5; NL8004673A; ES261798Y; IT1127881B; JPS6261805B2; AU543177B2; FR2472687A1; ES261798U; DE3032166A1; SE8005970L; FR2472687B1; BE885332A; JPS5694019A; ES258155U; FI802610A; DD153174A5

Abstract

A slack-resisting bolt comprises two parts 2, 3 which are separable at the clamping position of a nut 7. An internally threaded hole 4 is bored in the part 3 of the shank, and on externally threaded projection 5 is formed on the head part 2 and the projection 5 is screwed into the hole 4 so as to join the two shank parts together and form the complete shank. A screw driver slot or squared end portion 11 for rotating the part 3 is provided at the free end thereof. After the bolt is secured in position by the nut 7, the part 3 of the shank is turned in a direction so as to unscrew it from the body part 2 and thereby securely lock the nut 7 on the shank. The projection 5 may be formed in the separable part 3 and the bore 4 in the head part 2 (Figure 1 not shown). Two nuts may be used, the outer one being locked by the two-part shank. <IMAGE>

Description

SPECIFICATION A slack resisting bolt The present invention relates to a slack resisting or slack-proof bolt and, more particularly, to a slack-proof bolt enabling a nut to be locked in its clamping position.

Generally, when a nut is tightened, a tensile force is produced in the bolt thereby imparting a clamping force to a body to be clamped. The phenomenon of a reduction in the clamping force is called "a slack of the thread". This phenomenon is represented by a slackening of a nut relative to a bolt, and various devices have been introduced over many years for preventing such slackening.

Even if a nut is sufficiently secure when initially tightened, it is frequently rotated in the slackening direction by vibrations thereby rendering it impossible for the bolt to accomplish its primary object.

Conventionally, a double nut has been used in order to prevent rotation in the slackening direction. Although this is one of the simplest methods of precluding slackening of a nut, the outer nut is not prevented from loosening and there is no insurance against slackening of the nut.

As is commonly known, between the torque T required for tightening a nut on a bolt and the torque T' required for unscrewing the nut there is established an interrelation of T < T'.

Theoretically, therefore, a nut once tightened is never loosened except when an external force is applied thereto. In reality, however, there frequently occurs a case in which the nut rotates until it works off the bolt. This phenomenon is generally caused by vibrations or intermittent shocks, either to a greater or lesser degree, the static friction coefficient being reduced to a far smaller dynamic friction coefficient, the friction coefficient of the thread face being also reduced.

As a result, if an external force, small as it may be, is applied in the loosening direction, the aforesaid torque interrelation is upset resulting in < 0, thereby permitting the nut to rotate in the slackening direction.

Thus, countermeasures against slackening comprise the following: - (1) Use of a fine screw thread: (2) Increasing the friction on the end face of the nut: (3) Increasing the friction coefficient of the thread interface: The present invention is based on measure No. 3 above.

The invention has for an object to provide a bolt "having a construction enabling it to preclude or resist slackening of a single or double nut by increasing the friction coefficient.

Fundamentally, the bolt according to the invention achieves the above object by a two part shank construction of the bolt.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which: - Fig. 1 is a sectional view illustrating one embodiment of the invention, Fig. 2 is an end view of the separable part of the shank of Fig. 1, Fig. 3 is a sectional view illustrating another embodiment of the invention, Fig. 4 is an end view of the separable part of the shank of Fig. 3, Fig. 5 is a fragmentary sectional view, on an enlarged scale, of the portion designated by a circle in Fig. 1 or Fig. 3.

Referring to Figs. 1 and 2, the bolt 1 comprises a shank formed in two parts, that is, a main or head part 2 and a separable part 3. In the center of the head part 2 there is axially bored an internally threaded hole 4 and a small diameter externally threaded projection 5 on the separable part 3 is screwed into this internally threaded hole so as to join the head part and separable parts together to form an integrated shank or bolt.

The numeral 6 designates a first nut, 7 designating a second nut. It is essential that the joint 8 between the head part 2 and the separable part 3 of the shank be located intermediate opposite ends, and preferably approximately in the center, of either of the two nuts. In the embodiment shown in Fig. 1, the joint 8 is located in the center of the second nut 7. It is preferable that the joint 8 be located in the center of the second nut on the outside rather than in the center of the first nut on the inside.

The thread on the projection 5 is cut in the same direction as that on the bolt 1 , that is, in the right-hand direction. The numerals 9 and 10 designate clamped members and 11 designates a screw driver slot provided at the free end of the separable part 3 to permit turning of that part.

When it is to be used, the bolt 1 is first inserted into a through hole 12 in the members 9, 10 to be clamped together and the first and second nuts 6, 7 are tightened from the opposite side. Then the separable part 3 of the shank is rotated in the left hand direction, utilising the slot 11 notched at the end of this part, until a slight clearance is produced between the head part 2 and the separable part 3 at the joint 8. Since the second nut 7 has a different pitch with the joint 8 as a borderline, the friction coefficient of the thread face is greatly increased thereby enabling the nut to be held in a securely locked state.

Fig. 5 is a magnified view showing this locked state wherein the internal thread is held in a securely locked state by the clamping force a of the external thread of the head part 2 and by the clamping force b of the external thread of the separable part 3 applied in the opposite direction.

Referring now to the embodiment shown in Figs. 3 and 4, the bolt 1 comprises a shank formed in two parts, that is, a main or head part 2 and a separable part 3 similarly to Fig. 1. Unlike Fig. 1, however, an internally threaded hole 4 is bored in the center of the separable part 3, where a small diameter threaded projection 5 on the head part 2 is screwed into the internally threaded hole 4 in the separable part. In this state of engagement, the head part 2 and the separable part 3 constitute an integrated shank. In the embodiment shown in Fig. 3, only a single nut 7 is utilised and this single nut should be fastened in such manner that the center thereof is located on the joint 8 between the head and separable parts of the shank.

The thread on the projection 5 is cut in the same direction as that of the bolt 1 , that is, in the right-hand direction. The numerals 9 and 10 designate clamped members and 11 designates a squared end portion of the separable part 3 which is engageable by a suitable tool to permit rotation of the part 3.

As hereinbefore described the bolt 1 is first inserted into a through hole 12 in the members 9, 10 to be clamped together, the nut 7 is fastened from the reverse side, and then the separable part 3 of the shank is rotated in a lefthand direction by means of the squared end portion 11 until a slight clearance is produced between the head part 2 and the separable part 3, as shown in Fig. 5. Thus, the nut is held in a secured locked state since the pitch thereof differs from the pitch of the threads joining the two shank parts together, thereby greatly increasing the friction coefficient of the thread face. To be more precise, the internal thread of the nut 7 is sustained in a securely locked state by the clamping force a of the external thread of the head part 2 and the clamping force b of the external thread of the separable part 3 applied in the opposite direction to the clamping force a.

A slack-proof bolt, as described above, is capable of sustaining a securely locked state not only at the time of initial tightening or clamping but also during use accompanied by vibrations, inasmuch as the rotation of the nut in the loosening direction is precluded by the clamping forces a and b applied in opposite directions.

Claims

1. A slack-resisting bolt comprising a two-part shank separable into its two component parts at the fastening position of a nut screwed onto the shank, an internally threaded hole being provided in one of the parts and an externally threaded portion being formed on the other part and being screwed into sid internally threaded hole so as to join the two parts together, and means disposed at the free end of the shank for enabling relative turning of the two shank parts.

2. A bolt as claimed in claim 1 , wherein the thread joining the two shank parts is the same as the external thread of the bolt.

3. A bolt as claimed in claim 1 or 2, wherein the means enabling relative turning of the two shank parts is a slot.

4. A bolt as claimed in claim 1 or 2, wherein the means enabling relative turning of the shank parts is a projection.

5. A slack-resisting bolt constructed substantially as hereinbefore described with reference to Figs. 1, 2 and 5 or Figs. 3, 4 and 5 of the accompanying drawings.