RU2419733C1 - Procedure for threaded connection with uniform distribution of load along turns of thread - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: threaded connection is made at initial zero contact in last 2 pair of turns (relative to support end of nut). The rest turns of the nut are made at successively increasing dimension of gaps (in the direction to the support end). Connection is made at successively increasing force of tightening. Turns are successively "engaged" and load onto "engaged" turn rises from zero and is levelled starting from the first one on all turns, (except pair of turns, the last from the support end) in accordance with a preliminary specified parametre of gap increment and value of tightening force increment.

EFFECT: uniform distribution of load on turns of thread.

1 dwg

Description

The invention is intended for use in mechanical engineering. The method affects the strength, reliability and installation of threaded connections.

When loading a threaded connection, each pair of turns perceives a different load. In an idealized joint design, the load increases towards the lower turns relative to the support end face of the nut. The gaps (technological properties) between the surfaces of the screw and nut turns significantly affect the load distribution between the threads.

Known methods for influencing the law of the distribution of contact forces over the turns of threaded joints at the design stage of their various structural parameters.

Closest to the claimed technical solution, a method for obtaining a uniform load due to previously provided increased clearances in the thread is suitable. Such clearances can be created by increasing the average diameter of the nut thread. The average diameter of the nut should vary according to the law of the parabola. Each rated load corresponds to its own curve of the average diameter of the nut (see Birger I.A., Iosilevich GB, Threaded and flange connections. - M.: Mashinostroenie, 1990. - 368 p.).

This method of obtaining the design load does not take into account the sequence of “turning on” the threads. The determination of the load from the threads in the presence of gaps can be considered in the aspect of the calculation of systems with one-way connections, in which the sequence of "inclusion" of connections (turns) is of fundamental importance.

SUMMARY OF THE INVENTION

A threaded connection is made with the initial zero contact in the last (with respect to the nut end face) two pairs of turns. The remaining turns of the nut are performed with a successively increasing (in the direction of the supporting end) gap, and the installation of the connection is achieved with a sequentially increasing magnitude of tightening, the turns are “turned on” sequentially, the load on the “turned on” turn increases from zero and is equalized from the 1st to all turns (excluding the last pair of turns from the support end) in accordance with the pre-set parameters of the increment of the gap and the magnitude of the increment of the tightening force.

The claimed technical solution is aimed at regulating contact forces, depending on the manufacturing technology of the thread and the method of mounting the connection. With gradual loading and a controlled tightening force, the turns are sequentially “turned on” and then the contact forces are equalized.

According to the claimed method, the threaded connection contains (see the drawing) a nut 1 and a bolt 2. The initial zero contact is achieved in the last (in relation to the supporting end) two pairs of turns k and k-1, where k is the number of loaded turns of the connection. In turns k-2, the gap h, and in subsequent (towards the 1st turn), the gap increases sequentially by the same value of h.

When tightening the threaded connection at all stages of loading, the load values and the displacements of the “turn-on” turns are controlled, which is established based on the calculation of linear equation systems of order k + 1. In the matrix notation, the system of equations will take the form:

Where

, мм - условное смещение; Р, Н - усилие затяжки (см. журнал «Вестник машиностроения», 2002, №5, с.22-23).Here: w, mm - joint unit displacement of the contacting threads; d, mm - the total unit displacement of tension and compression of the body of the screw and nut; h _{i = 1-k} , mm - interference in the rod between the threads; X _{i = 1-k} - unknown contact forces;

, mm - conditional displacement; P, N - the tightening force (see the journal "Bulletin of mechanical engineering", 2002, No. 5, p.22-23).

The gaps in the connection are set so that the initial zero contact is achieved in the last two (relative to the nut end face) pairs of turns k and k-1. In the remaining turns, the gaps gradually increase in the direction of the supporting end.

When establishing the value of the parameter h, technological capabilities of ensuring the size of the gaps and the strength of the joint materials are taken into account.

With a uniform tightness (between all threads), the relationship between the parameter h and the tightening force P is established by

The number of turns is not limited; the parameter h can be small. The parameter h is interpreted as an interference fit in the bolt shaft between turns i and i-1. When choosing a gap by the value of h, the “turn-on” of i-2 occurs, the value is entered in the Δ column of equation (1). At the moment of “turning on” the coil, the magnitude of the contact force is zero. The size of the technological gap is set taking into account the kinematic displacement of the bolt.

The initial tightening force is established from equation (1) according to the results of the calculation of the connection for two pairs of turns (k and k-1) with zero clearance 1 from the condition that the displacement of the turns k-1 is equal to h. When “turning on” the turn k-2, the parameter h is entered in the column Δ as an interference between turns k-1 and k-2.

Installation of the connection is achieved with a sequentially increasing value of tightening, the turns are sequentially “turned on”, the load on the “turned on” turn increases from zero and is equalized starting from the 1st for all turns (excluding the last pair of turns from the support end) in accordance with a pre-set increment parameter the gap h and the magnitude of the increment of the tightening force.

соответствующем смещениюThe alignment of contact forces is achieved in a final way after the "turn on" of the 1st (from the support end) coil with the force

corresponding offset

Sequence listing

The proposed method is implemented in the following sequence.

1. Taking into account dependence (2), the gap increment parameter h is set.

2. For two pairs of turns (k = 2) according to dependence (1), the initial tightening value is established from the condition that the displacement of the turns k-1 is equal to the parameter h.

3. According to the parameter h, the 3rd turn is “turned on” and then all the other turns are respectively calibrated with respect to each “switched on” turn of the tightening torque. When calculating the tightening values, equations (1) are used with the corresponding value of the “turned on” turns k.

и окончательном значении усилия затяжки Р, определяемыми на основе расчета соединения по зависимости (3) и (1) соответственно.4. The alignment of contact forces is achieved after the "turn on" of the 1st (with respect to the support end face of the nut) coil with the magnitude of the displacement

and the final value of the tightening force P, determined on the basis of the calculation of the connection according to dependencies (3) and (1), respectively.

Claims (1)

A method of obtaining a threaded connection with the possibility of evenly distributing the load along the threads, characterized in that the threaded connection is made with the initial zero contact in the last (with respect to the nut end face) two pairs of turns, the remaining nut turns are performed at a sequentially increasing (towards the reference end) the size of the gaps, and the installation of the connection is achieved with a sequentially increasing value of tightening, the turns are sequentially "turned on", the load on the "turned on" turn It melts from the ground and aligned, starting from the 1st, all coils (excluding the last from the face a couple of turns), in accordance with a predetermined gap increment parameter and value increment tightening efforts.