RU2139510C1 - Process testing hydraulic cylinders for leaks - Google Patents

Abstract

FIELD: evaluation of technical state of hydraulic cylinders. SUBSTANCE: pressure differential of tested medium in which capacity air is used is created to ensure authenticity of diagnosis and to increase accuracy of evaluation of leak and leak through seals is determined. Pressure differential through seals is created as result of travel of rod and pressure of tested medium driven out of high-pressure space and volume of tested medium coming into low-pressure space with rod being immobile are measured. After leak of tested medium is calculated by formulas presented by inventors. EFFECT: provision for authenticity of testing process. 3 dwg

Description

 The invention relates to the assessment of the technical condition of hydraulic cylinders and can be used to establish the degree of leakage of their sealing units during the test.

 To make a decision on the technical condition of hydraulic cylinders, it is necessary to carry out an exact technical diagnosis, indicating, if necessary, the place, type and causes of defects. The result of wear of the friction surfaces of the hydraulic cylinder is the occurrence of leaks in its sealing units, leading to a decrease in volumetric efficiency and the loss of expensive working fluid. Therefore, the process of diagnosing a hydraulic cylinder in most cases can be considered as the task of determining the characteristics of leaks.

 Most of the known methods for testing the tightness of sealing assemblies are based on leakage monitoring of a working or controlled environment. At the same time, a method of testing the tightness of sealing units and determining the number of working fluid leaks is quite well known (see GOST 18464-87. Hydraulic cylinders. Acceptance rules and test methods).

 The main disadvantages of the known methods include low reliability and accuracy, the subjectivity of the assessment of the state of the sealing units, the use of expensive working fluid (the recommended brand of fluid for each type of hydraulic cylinder), the immobility of the rod, the presence of a high-power pump station, energy consumption, low safety, low environmental friendliness due to fluid leakage, uneconomical. In addition, in the known methods can not be taken into account many operating factors that affect the amount of leakage, for example, the different state of the sealing unit with a movable or stationary rod or piston of the hydraulic cylinder.

 Closest to the proposed invention according to the technical solution is a method for checking the tightness of pneumatic cylinder seals by purging the cylinder cavities and determining the number of air leaks through the sealing units (see Wang Gu Qong. Method to diagnose pneumatic cylindrs, Hydraulics and Pheumetics, 1993, January. PRChina) .

 The known method adopted as a prototype has several advantages over the analogue, namely, that air is used as a controlled medium, therefore, the use of expensive working fluid is eliminated, the energy consumption of this method is reduced due to the absence of a high-power hydraulic pump station, but this method has several disadvantages, namely, low reliability and accuracy, the presence of a compressor station, low security. Since the test is carried out with the piston rod and piston stationary, the prototype method mentioned above does not take into account the fact that unevenly worn seals that give a large leak in movement, in a static position, as a rule, do not have leaks, which is its main drawback.

 This is explained by the effect of "collapse" of lip seals, especially at high pressures of the working fluid (see SP Eresko. Study of the influence of the loading regime of single-bucket excavators on the reliability of the working equipment hydraulic cylinder and their sealing assemblies. Diss. On the research station. the so-called - L .: LISI, 1982.- 360 p.).

 In this regard, the decision on the technical condition of the sealing unit when using the method of the prototype is difficult.

 The aim of the invention is to ensure the reliability of the diagnosis by improving the accuracy of leakage estimates.

 This goal is achieved by creating a pressure differential of the controlled medium, which is used as air, and leakage through the seals is determined. The differential pressure through the seals is created as a result of the movement of the stem, and the pressure of the controlled medium in the low-pressure cavity, the volume of the controlled medium displaced from the high-pressure cavity and the volume of the controlled medium entering the low-pressure cavity with a fixed rod are measured. The rod is moved using a traction device.

 The invention is illustrated by drawings, where in FIG. 1 shows a schematic diagram of a device; in FIG. 2 shows a diagram of a device for testing a piston seal; FIG. 3 shows a diagram of a device when testing a piston and rod seal.

 The device (Fig. 1) for diagnosing sealing nodes of hydraulic cylinders that implements the inventive method consists of valves 1-4, manovacuometers 5, 6, gas flow meters 7, 8, connecting lines 9, 10 and outlet 11 and inlet 12 pipes.

 A method for diagnosing rod and piston sealing units is carried out in ten stages.

 The first stage: attaching a diagnostic device to the test cylinder (Fig. 2).

Second stage: valve 2 is open; valves 1, 3, 4 are closed; the rod is extended by the traction device to the length Z _i at a speed of Z '₁; at the end of the movement, the air pressure P _5i in the piston cavity (pressure gauge 5) and the volume of gas V _7i displaced from the rod cavity into the atmosphere through the pipe 11 (flow meter 7) are measured.

Third stage: valve 3 is open; valves 1, 2, 4 are closed; the stem is stationary; measured - the pressure drop of the gas in the piston cavity for an arbitrary time t _i to the pressure value P _5j ( _{manovacuum meter} 5) and the volume of air V _8i coming from the atmosphere through the pipe 12 into the rod cavity during time t _i (flow meter 8).

 The fourth stage: valves 2, 4 are open: valves 1.3 are closed; the rod with the traction device is pulled into the extreme position (Fig. 3).

Fifth stage: valve 1 is open, valves 2, 3, 4 are closed; the rod is pulled by the traction device into the body by the length Z _j at a speed Z ' _j , at the end of the movement the air pressure P _6i in the rod cavity (manovacuum meter 6) and the volume of gas V _7j displaced from the piston cavity into the atmosphere through the pipe 11 (flowmeter 7) are measured )

Sixth stage: valve 4 is open, valves 1, 2, 3 are closed; the stem is stationary; measured are the air pressure drop in the rod cavity over time t _i to the pressure value P _6j (manovacuum meter 6) and the volume of gas V _8j received from the atmosphere through the nozzle 12 into the piston cavity during time t _i (flow meter 8).

расположенными со стороны поршневой полости цилиндра, по формуле

в динамическом режиме при движении штока, а также в статическом режиме при неподвижном штоке теми же уплотнителями соответственно по формулам:

Восьмой этап: количественно оценивается объем газа, пропущенный штоковыми уплотнителями в динамическом режиме по формуле:

в статическом режиме по формуле:

где P₀ - атмосферное давление, МПа;
V₀₁ - невытесняемый объем поршневой полости, м³;
V₀₂ - невытесняемый объем штоковой полости, м³;
P_5i, P_5j, P_6i, P_6j V_7i, P_7j, V_8i, V_8j - измеряемые на 1-6 этапах диагностирования параметры.Seventh step: the volume of gas passed through piston seals located on the side of the rod end of the cylinder is quantified by the formula

located on the side of the piston cavity of the cylinder, according to the formula

in dynamic mode during the movement of the rod, as well as in static mode with a stationary rod with the same seals, respectively, according to the formulas:

The eighth stage: quantitatively estimated the volume of gas passed through the rod seals in dynamic mode according to the formula:

in static mode according to the formula:

where P ₀ - atmospheric pressure, MPa;
V ₀₁ - displaced volume of the piston cavity, m ³ ;
V ₀₂ - displaced volume of the rod cavity, m ³ ;
P _5i , P _5j , P _6i , P _6j V _7i , P _7j , V _8i , V _8j - parameters measured at 1-6 stages of diagnosis.

для поршневых уплотнителей, расположенных со стороны поршневой полости цилиндра, по формуле:

для штоковых уплотнителей по формуле

Удельная объемная утечка газа в статическом режиме составляет: для поршневых уплотнителей, расположенных со стороны штоковой полости, по формуле:

для поршневых уплотнителей, расположенных со стороны поршневой полости, по формуле:

для штоковых уплотнителей по формуле:

Однако установление эквивалента сравнения удельных объемных утечек газа и жидкости через одинаковые микрозазоры при диагностировании гидроцилиндров всегда вызывают затруднения. Массовые удельные утечки различаются значительно меньше (см. Кондаков Л.А., Голубев А.И., Овандер В.Б. и др. Уплотнения и уплотнительная техника: Справочник, М.: Машиностроение, 1986. -484 с). Удельная массовая утечка газа в динамическом режиме составляет: для поршневых уплотнителей, расположенных со стороны штоковой полости, по формуле:

для поршневых уплотнителей, расположенных со стороны поршневой полости, по формуле:

для штоковых уплотнителей по формуле:

Удельная массовая утечка газа в статическом режиме составляет: для поршневых уплотнителей, расположенных со стороны штоковой полости:

для поршневых уплотнителей, расположенных со стороны поршневой полости, по формуле:

для штоковых уплотнителей по формуле:

где ρ - плотность воздуха, кг/м³.Ninth stage: specific volumetric and mass air leaks through diagnosed seals are quantified. The specific volumetric gas leak in dynamic mode is: for piston seals located on the side of the current cavity of the cylinder, according to the formula:

for piston seals located on the side of the piston cavity of the cylinder, according to the formula:

for rod seals according to the formula

The specific volumetric gas leak in static mode is: for piston seals located on the side of the rod cavity, according to the formula:

for piston seals located on the side of the piston cavity, according to the formula:

for rod seals according to the formula:

However, the establishment of an equivalent comparison of the specific volumetric leakages of gas and liquid through the same micro-gaps when diagnosing hydraulic cylinders always causes difficulties. Mass specific leakages differ significantly less (see Kondakov, L.A., Golubev, A.I., Ovander, V.B. The specific mass gas leak in dynamic mode is: for piston seals located on the side of the rod cavity, according to the formula:

for piston seals located on the side of the piston cavity according to the formula:

for rod seals according to the formula:

The specific mass gas leak in static mode is: for piston seals located on the side of the rod cavity:

for piston seals located on the side of the piston cavity according to the formula:

for rod seals according to the formula:

where ρ is the air density, kg / m ³ .

 Tenth stage: specific air leaks are compared with the experimentally obtained dependence of air leaks and a specific working fluid, on the basis of which a diagnosis is made about the condition of cylinder seals and their compliance with standard requirements. In addition, sharp changes in the readings of the manovacuum meters 7, 8 during the movement of the rod indicate the presence of damage to the sealing surface of the rod and the cylinder body. For example, scratches, dents, badass. Correlation of the readings of the manovacuum meters 7, 8 with the stroke length of the rod allows localizing these damages without developing the cylinder and timely sending it for repair.

где φ - параметр цилиндра, рассчитываемый по формуле:
φ = D $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ (D $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ -D $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ )^-1,
где D₁ - диаметр поршня;
D₂ - диаметр штока.It remains to add that for the test it is necessary to withstand the following conditions:
- the ratio of the piston strokes for the cylinder with a one-sided rod when it is extended Z _i when it is extended Z _j
Z _i = Z _j φ ^-1 , [m]
- the ratio of the speeds of the rod in either case is

where φ is the cylinder parameter calculated by the formula:
φ = D $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ (D $\genfrac{}{}{0ex}{}{\text{2}}{\text{1}}$ -D $\genfrac{}{}{0ex}{}{\text{2}}{\text{2}}$ ) ^-1 ,
where D ₁ is the diameter of the piston;
D ₂ - the diameter of the rod.

выбирается из условия, что давление в полостях цилиндра не превышает 0,09-0,1 МПа, при котором возможны "захлопывания" уплотнителя. Перемещение Z_j выбирается произвольно в зависимости от интересующего участка уплотняемой поверхности.In this case, the speed

is selected from the condition that the pressure in the cylinder cavities does not exceed 0.09-0.1 MPa, at which "sealing" of the sealant is possible. The displacement Z _j is chosen arbitrarily depending on the area of interest of the sealing surface.

 The advantages of the proposed method for testing the sealing nodes of the hydraulic cylinders in comparison with the prototype is as follows.

 The proposed method provides high accuracy due to the insignificant dependence of air viscosity on temperature and its high permeability, the reliability of the diagnosis: dynamic for cylinders operating cyclically and static for support cylinders, the possibility of localizing damage to sealing surfaces, low power consumption, since a pressure differential is created the movement of the rod and the overlap of the cavity, and does not require high test pressure, safety, simplicity of design and control, lack of sweat ry working fluid, environmental friendliness, profitability.

Claims (1)

 A method of testing hydraulic cylinders by creating a differential pressure of a controlled medium, which is used as air, and determining air leaks through gaskets, characterized in that the differential pressure is created by moving the rod of the tested hydraulic cylinder, and the amount of leakage is determined by measuring the pressure of the controlled medium in the low pressure cavity, the volume of the controlled medium displaced by the moving piston from the high-pressure cavity, and the volume of the controlled medium received in the low-yes cavity Lenia with stationary rod.

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