RU2414339C1 - Method of assembling threaded joints - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machine building and may be used in assembling threaded joints. Proposed method comprises pre-tightening, converting mechanical oscillations into electric signal, recording joint quality parametre and final tightening to reference quality parametre. In producing the joint, threaded joint is hammered on. Logarithmic decrement of joint oscillation is used as quality parametre.

EFFECT: higher quality of threaded joints.

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Description

The invention relates to mechanical engineering and can be used in the assembly of threaded joints.

Known methods of assembling threaded connections, including pre-tightening by exposure to forced vibrations on the threaded connection and final tightening with quality control of the connection (Patent RU No. 2228256 C1, B25B 21/00, 05/10/2004, Bull. No. 13), [1].

A disadvantage of the known methods is the low reliability of the connections.

The closest in technical essence is a method of assembling threaded joints, including pre-tightening, which is carried out with the action of forced vibrations on the threaded connection, the conversion of mechanical vibrations into an electrical signal, registration of the connection quality parameter and final tightening with quality control of the obtained threaded connection to achieve the reference value of the parameter quality (Patent RU No. 2277041 C1, B25B 21/00, B23P 19/06, 05/27/2006, Bull. No. 15), [2].

The disadvantage of this method is the low quality of the formed threaded connection.

The technical result of the invention is to improve the quality of the formed threaded connections.

The technical result is achieved by the fact that in the method of assembling threaded connections, including pretightening, which is carried out with the action of forced vibrations on the threaded connection, the conversion of mechanical vibrations into an electrical signal, registration of the quality parameter of the connection and the final tightening with quality control of the obtained threaded connection to achieve the reference value quality parameter, during the assembly process additionally carry out impact on the threaded connection, and as a quality parameter, use the logarithmic decrement of vibrations of the formed compound.

A distinctive feature of the proposed assembly method is the combination of ultrasonic and shock effects in the process of forming a threaded joint and analysis of the reaction of a mechanical oscillatory system to these effects. The simultaneous use of shock mechanisms with a frequency of 3-40 beats per second and high-frequency ultrasonic vibrations, the working frequency range of which is about 20,000 impacts per second, makes it possible to obtain new opportunities, both in technological and in information aspects.

The technological advantages of the developed method are that due to the action of forced vibrations together with shock effects in the joint, changes in the kinematic conditions of contacting the surfaces occur, a significant decrease in the friction forces, and the nature of the stress state of the metal in the friction zone changes. The impact of forced vibrations is accompanied by a reduction in the load on the process equipment and a reduction in energy costs without impairing the load-bearing capacity of threaded joints, in addition, vibration leads to a change in both the physicomechanical properties and the microgeometry of the contacting parts. As a result of changing the quality parameters of the surface layer of the contacting parts, the bearing capacity of the formed threaded connection becomes higher.

The informational advantages of the developed method are to increase the reliability of quality control of the formed threaded connection by increasing the amount of diagnostic information received. An application to a mechanical system of forced oscillations from an information point of view is considered as a test harmonic effect, by the reaction to which the amplitude-frequency characteristics of the analyzed system in the frequency domain can be determined. From an information point of view, the impact application is considered as a test signal supplied to the input of the analyzed system, the reaction of which will be damped oscillations, the parameters of which carry diagnostic information about the properties of the analyzed mechanical system in the time domain [3]. Impact impact has a much wider spectrum compared to the frequency impact of ultrasonic vibrations. “In practice, when the input process is artificially introduced, the quality of identification can be improved by simply increasing the maximum width of the spectrum of the input process” (Bendat J., Pirsol A. Application of correlation and spectral analysis: Translated from English. - M.: Mir, - 1983. - 312 p. P.139), [4], and the shock effect has a wider spectrum than the harmonic vibrational effect.

A change in the normal pressure in the contact zone during the tightening of the threaded connection leads to an increase in the contact area of the parts and a change in the stiffness and damping of the oscillating mechanical system, to a change in the acoustic contact in the working zone and is reflected in the function of such interrelated quantities as attenuation decrement, absorption coefficient, quality factor and etc.

Impulse (shock) exposure allows you to identify the internal vibrational properties of a mechanical system, which are most fully expressed with its free vibrations. Features of reducing the amplitude of free vibrations over time are determined by the dissipative characteristics of energy dissipation in a mechanical system and can serve as the basis for obtaining integral characteristics of the quality of the assembly. Most often, in the experimental assessment of the vibrational properties of systems, the logarithmic decrement of oscillations [3] is used, which characterizes the rate of damping of free oscillations in the system and is determined by the natural logarithm of the ratio of two consecutive maximum values of the variable:

,

,

where A _mi , A _{mi + 1} are successive values of decreasing amplitudes.

The logarithmic decrement of oscillations shows the attenuation rate of free oscillations excited by a shock pulse and for most engineering structures ranges from a few hundredths to several tenths of a unit and serves to assess the dynamic quality of a mechanical system.

The drawing shows a structural diagram of a device for implementing the proposed method.

The device comprises a hammer 1 and anvil 2, connected with the spindle 3 and a wrench 4, worn on a nut 5. The assembled parts 6 and 7 are pulled together by a bolt 8, with which an ultrasonic vibrations concentrator 9 interacts, the piezoceramic transducer 11 is pressed against the opposite end of it 10, recruited from discrete washers of axial polarization. The piezoceramic transducer 11 is sandwiched between the concentrator 9 and the frequency-reducing element 12 (damper).

A vibration sensor 13 is mounted on one of the assembled parts 6, the output of which is connected to an analog-to-digital converter (ADC) 14, which is connected to the input of a personal computer 15, the output of which is connected to a digital-to-analog converter (DAC) 16, connected to the input of an ultrasonic generator 17, connected to the piezoelectric transducer 11.

The method of assembly of threaded joints is implemented as follows.

The main details of the striking mechanism are the striker 1 and the anvil 2. During successive striking interactions, the striker 1 and the anvil 2, the impacts are transmitted through the spindle 3 and key 4 to the nut 5, which is tightened with the necessary force. Under the action of the tightening force, the bolt 8 is stretched, and the contracted parts 6 and 7 are compressed. This process allows to obtain significant tightening forces with low drive power, small size and weight of the wrench.

At the same time, in the controlled product, consisting of the assembled parts 6 and 7, during make-up, vibrations are additionally excited and accepted, achieving resonance. Oscillations are excited by the piezoceramic transducer 11 and amplified by the concentrator 9 in amplitude. Mechanical vibrations from shock effects are superimposed on the forced vibrations excited by the piezoceramic transducer 11, converted by the vibration sensor 13 into an electrical signal, which is digitized in an analog-to-digital converter 14 and processed in a personal computer 15.

For automatic tuning to resonance from the output of a personal computer 15, the signal is digitally fed to the input of a digital-to-analog converter 16, from the output of which an analog signal is supplied to an oscillation excitation unit, which is a frequency-tunable ultrasonic oscillator 17.

и определяется натуральный логарифм этого отношения, который и будет являться текущим значением логарифмического декремента колебаний формируемого резьбового соединения. В персональном компьютере 15 предварительно устанавливают эталонные значения логарифмического декремента колебаний для данного типа резьбового соединения и при достижении текущим значением логарифмического декремента колебаний эталонного значения процесс затяжки прекращают.In the personal computer 15, the maximum value of the variable (envelope of oscillations) A _{mi is extracted} and stored (fixed). Then the following maximum value of the variable A _{mi + 1} is determined and stored, their ratio is calculated

and the natural logarithm of this relationship is determined, which will be the current value of the logarithmic decrement of vibrations of the formed threaded connection. In the personal computer 15, the reference values of the logarithmic decrement of vibrations for a given type of threaded connection are pre-set, and when the current value of the logarithmic decrement of vibrations of the reference value is reached, the tightening process is stopped.

As the vibration sensor 9, sensors of the KV-10 or KD-35 type with a piezoelectric plate working in bending were used, due to its high sensitivity and favorable shape, the sensor provides separate determination of differently directed components of the vibration.

To convert analog signals to digital form, we used a 12-bit analog-to-digital converter type JIA-2USB-12 (Russia, Moscow, Rudnev-Shilyaev firm), which allows you to connect up to 32 single-pole channels to the USB port of a personal computer. The JIA-2USB-12 also has a digital-to-analog converter. The available software allows the simultaneous analysis of frequency and time signals using a personal computer, which significantly increases the reliability of the quality control of connections.

The simultaneous effect of forced vibrations and shock influences increases productivity and reduces the energy intensity of the assembly process of threaded joints.

Joint analysis of the system in the time and frequency domains increases the reliability of assessing the quality of the formed threaded connection due to the more complete use of diagnostic information, and the obtained information can be used both to assess the quality of the formed connection and for the operational control of the assembly process.

The proposed method of assembling threaded joints allows to ensure the guaranteed quality of each joint without tightening the manufacturing technology and assembly of parts due to appropriate control means.

Information sources

1. Patent RU No. 2228256. IPC V25V 21/00. The method of assembly of threaded connections / Shuvaev V.G., Shtrikov B.L., Shuvaev I.V. No. 2002124027/11; Claim 09.09.2002; Publ. 05/10/2004. Bull. No. 13.

2. Patent RU No. 2277041 C1, B25B 21/00, B23P 19/06. Assembly method of threaded connections / Shuvaev V.G., Shtrikov B.L., Shuvaev I.V. 05/27/2006, Bull. No. 15.

3. Panovko Y. G. Introduction to the theory of mechanical vibrations: Textbook. - 2nd ed., Revised. - M .: Science. The main edition of the physical and mathematical literature, 1980. - 272 p.

4. Bendat J., Piersol A. Application of correlation and spectral analysis: Per. from English - M.: Mir, 1983 .-- 312 p.

Claims (1)

A method of assembling threaded joints, including pre-tightening, which is carried out by acting by forced vibrations on the formed threaded connection, converting mechanical vibrations into an electrical signal, registering the quality parameter of the connection and final tightening with quality control of the obtained threaded connection to achieve a reference value of the quality parameter, characterized in that in the process of forming the compound additionally carry out shock effects on the threaded soy Inonii, and as a quality parameter using a logarithmic decrement of oscillations of the formed compound.