RU2279579C2 - Method of heating and cooling brake pulleys of belt-block brake of draw-works at estimation of their thermal balance - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: belt-block brake has hollow pressurized brake pulleys filled with low-melting metal (potassium, sodium, lithium) where heating elements are located over perimeter of cavity. Thermocouple wires are connected to outer surfaces of brake pulleys. Surfaces of first brake pulley are fully heat-insulated from surrounding medium and surfaces of second brake pulley are engageable with it when heating elements are connected to external current source to ensure heating of brake pulleys by molten low-melting metal. Then heating elements are disconnected from external current source and part of heat scattered into surrounding medium by radiation is determined by ratio of measured temperatures of first (t₁) and second (t₂-t₀) brake pulleys. According to second version, belt-block brake is provided with friction linings located over brake band embracing arc; thermocouple wires are passed through them. Projection of first brake pulley is heat-insulated from drum flange and projection of second brake pulley is not heat-insulated. Interaction of friction units of brake is ensured through cyclic braking and brake pulleys are heated by low-melting metal to its molten state. Part of heat of its total amount is estimated by ratio of measured temperatures [(t₁-t₀)/(t₂-t₀)] of first and second brake pulleys at different intensity of radiation and convective heat exchange from their surfaces; heat is drawn to drum flange by conductive heat exchange. Provision is made for estimation of losses of heat in brake pulley of belt-block brake by temperature method for determination of heat transfer coefficients at natural and forced convection and radiation, as well as at conductive heat exchange for proper selection of materials of friction linings and operation at surface temperatures below permissible limits.

EFFECT: enhanced efficiency; possibility of operation at surface temperature below permissible limits.

4 cl, 5 dwg

Description

The invention relates to mechanical engineering and can be used in heavily loaded tape-shoe brakes, for example, in drilling winches.

Known methods for determining the amount of heat (the so-called calorimetry), which include the use of various types of calorimeters, namely:

- an ordinary variable temperature calorimeter with an isothermal shell;

- a massive variable temperature calorimeter with an isothermal shell;

- a variable temperature calorimeter with an adiabatic shell;

- differential calorimeter with variable temperature;

- constant temperature calorimeter [1, prototype].

However, the presented methods for determining the fraction of generated, accumulated and dissipated heat into the environment by the brake pulley of the drawbar brake of the drawworks cannot be used for the following reasons:

- due to the large weight of the brake pulley;

- it is not possible to separately evaluate the intensity of natural and forced convective cooling of the surfaces of the brake pulley;

- it is impossible to accurately assess the heat loss from radiation heat transfer from the surfaces of the brake pulley;

- it is not possible to take into account heat losses from conductive heat transfer in the brake pulley.

Known methods for solving problems of thermal conductivity, which include: analytical, numerical, analog, graphic and experimental. Using these methods, determine the temperature values in the studied objects by calculation or experimentally [2, analog]. In the dependencies used, in order to calculate the amount of heat that is removed from the brake pulley of the band brake, it is necessary to know not only the temperature difference (t _n -t _o ), where t _n , t _o are the temperatures: heating the surface of the brake pulley and the environment, but and process intensity factors, i.e. heat transfer during natural and forced convection, as well as during radiation heat transfer. As for the determination of heat loss from the brake pulley by conductive heat transfer, it is almost never determined. This is because no one simply takes it into account. Knowing the surface temperature of the friction pairs of the brake during its operation allows you to make the right choice of material for the friction linings as the weakest link in the friction unit.

The disadvantage of calculation methods is that when determining heat losses in the studied object, it is necessary to know two parameters: surface temperatures and heat transfer and radiation emission coefficients. The former are calculated, and the latter are accepted from the reference literature as some averaged values.

The objective of the invention is the determination of heat loss in the brake pulley of the drawbar brake of the drawworks using a temperature method for determining heat transfer coefficients for natural and forced convection and radiation, as well as conductive heat transfer for the correct choice of materials for friction linings and work in the surface temperature ranges below acceptable.

The task is achieved by the fact that under laboratory conditions they heat the insulated (first) from the environment and the non-insulated (second) pulley with molten low-melting metal located in the pulley cavity using an electric heating device operating for the same period of time and through the ratios of their averaged surface temperatures (t ₁ / t ₂ -t ₀ - measured by thermocouples) determine the heat loss from the surfaces of the second pulley by radiation heat transfer. Then, for a certain period of time, the second pulley is allowed to cool from the obtained thermal state to ambient temperature, and the heat transfer coefficient is determined by natural convection from the surfaces of the brake pulley from the obtained data.

After that, the insulation and thermocouples are removed from the brake pulleys, but the protrusion of the first one is insulated, the pulleys are installed and bolted to the winch drum flanges. At the same time, brake tape with linings is equipped with thermocouples. After that, the heat load of the friction pairs of the brake is similar to that which was in laboratory conditions (either by cyclic braking or by heating fusible metal using electric heating devices). Then, through the ratio of their average surface temperatures (t ₁ -t ₀ / t ₂ -t ₀ ), heat losses are determined from its total amount, which is removed from the pulley to the drum flange by conductive heat transfer. After that, the surfaces of the brake pulleys for a certain period of time at various constant frequencies of their rotation are allowed to cool from the obtained thermal state to the ambient temperature and the obtained data determine the family of heat transfer coefficients by forced convection from the surfaces of the brake pulley.

A comparative analysis of methods for assessing heat loss in belt pulley brakes pulleys, based on the prototype and analogue, showed the following advantages of the proposed temperature method:

- the possibility of a phased determination of the heat loss of the brake pulley in laboratory and industrial conditions;

- the heat introduced into the brake pulley having a cavity with fusible metal is delivered by electric current using a heating device;

- determination of heat loss caused by radiation heat transfer is made for the same time by comparing the heated non-heat-insulated and heat-insulated brake pulley in the laboratory;

- determination of the heat transfer intensity of the natural convection of the brake pulley is carried out when it is cooled from a given thermal state to the ambient temperature in laboratory conditions;

- determination of heat loss caused by conductive heat transfer is made for the same time by comparing the heated brake pulley and brake pulley with a thermally insulated protrusion in an industrial environment;

- determination of the intensity of heat transfer of forced convection of the heated brake pulley is made for the same time at different constant frequencies of its rotation in an industrial environment.

Figure 1 shows the design of a thermally insulated brake pulley with a heating device; figure 2 shows the design of non-insulated brake pulley from the environment with a heating device; figure 3 illustrates the friction unit with thermocouples; figure 4 shows a view of figure 3 - installation of a thermocouple with electrodes in the details of the friction unit; figure 5 shows a General view of the tape-shoe brake, in which the first brake pulley has a thermally insulated protrusion.

When assessing their heat balance, the methods for heating and cooling brake pulleys of a drawbar brake of a drawworks are to determine the heat loss from the surfaces of the brake pulley by radiation heat exchange, natural and forced convection, and also by transferring heat by heat conduction (conductive heat transfer) from the protrusion of the brake pulley to the flange drum winch.

Methods of heating and cooling the brake pulleys of the tape-shoe brake is carried out in laboratory and industrial conditions in four stages.

First step. In laboratory conditions, heat losses are determined by radiation heat transfer from a heated brake pulley. To do this, take two serial brake pulley 1 having protrusions 2 and a cavity 3 in its rim. The latter is filled with low-melting metal 4 (potassium, sodium, lithium). In the same place in the cavity 3 there are heating devices 5 installed around its perimeter and connected to the terminals 6 of the electric circuit. Moreover, the surfaces of the first of the brake pulleys 1 are completely covered by thermal insulation 7, i.e. insulated from the environment. On the working surface of the brake pulley 1, thermocouples 8 are installed with thermoelectrodes 9 connected to recording equipment (not shown in the drawing) for fixing the thermopower, and according to the calibration schedule, it is converted to temperature.

Before heating the brake pulleys 1 they are installed on supports made of a material with low thermal conductivity, for example hard rubber or textolite.

Then at the same time connect the heating device 5 in the two pulleys 1 using the terminals 6 in the electrical network. The heating devices 5 are turned on for the same time in order to melt the low-melting metal 4, so that the temperature of the working surface of the second brake pulley 1 reaches at least 1000 ° C.

доля теплоты, которая рассеивается в окружающую среду радиационным теплообменом от поверхностей тормозного шкива, составляет 22,2%.Subsequently, the heating devices 5 are disconnected from the electrical network and after averaging the measured temperatures on the surfaces of the brake pulleys 1, their ratio is established. The latter characterize the ratio of the surface temperature of the first (t ₁ ) to the second (t ₂ -t ₀ ) brake pulleys, which determines the fraction of heat dissipated into the environment by a radiation heat exchanger. So, for example, when the ratio of these temperatures

the proportion of heat that is dissipated into the environment by radiation heat transfer from the surfaces of the brake pulley is 22.2%.

Second phase. In laboratory conditions, heat loss is determined by natural convective heat transfer from the surfaces of the heated first brake pulley.

As a result of the steady-state thermal state of the brake pulley 1 obtained in the first stage, the time interval of natural convective cooling is fixed. Then determine the intensity of natural convective heat transfer, i.e. heat transfer coefficient from the surfaces of the brake pulley 1 in predetermined temperature ranges.

So, for example, Q = IUτ, kJ (the amount of heat spent warming up the first brake pulley); I is the current strength, A; U is the voltage, V; τ is the time, s. On the other hand, a given amount of heat (Q) dissipated from the surfaces (F) of the brake pulley 1 during time (τ) at a temperature difference (t _n -t _o ) (t _n , t _o is the initial temperature of the surface of the heated brake pulley and the surrounding medium, ° C). In this case, the heat transfer coefficient will be equal to

The third stage. In industrial conditions, heat losses are determined by conductive heat transfer from the protrusions of the brake pulleys into the body of the winch drum flange.

To implement the third stage, thermoelectrodes 9 of thermocouples 8 are disconnected from the brake pulleys 1, as well as the electric wires going from the heating devices 5 to the terminals 6. In addition, the thermal insulation 7 is removed from the second pulley 1, leaving it only on its protrusion 2. Then the brake pulleys 1 is mounted on a drawworks, seating them on the flange of the drum 23 and securing the protrusions of the 2 pulleys 1 to the flange 23 with the fixing bolts 24.

доля теплоты, которая передается кондуктивным теплообменом во фланец барабана 23 лебедки составляет 4,7%.To measure the surface temperatures of the friction pairs of the drawbar brake of the drawworks, thermoelectrodes 17 of thermocouples 18 are placed in its friction pads (see Fig. 4). A two-channel ceramic tube 16 is installed in the hole 14 of the friction lining 12 and is brought out almost flush with its working surface 13. Thermoelectrodes 17 of thermocouple 18 made of chromel-alumel wire with a diameter of 0.8 mm are laid in the pipe 16 with a diameter of 4.0 mm. The positive thermoelectrode 17 is the chromel wire, and the negative is the alumel wire. The head of the thermocouple 18 (in the form of a sphere), which interacts with the working surface 15 of the brake pulley 1, is formed of high-temperature copper solder in the form of a junction with a diameter of 3.0 mm and is installed in the restrictive ring 19. The latter prevents the failure of the head of the thermocouple 18, contributing to it work until complete wear and tear. A two-channel ceramic tube 16 (a ceramic tube consists of two parts) is installed with insulating sleeves 20 and 21, in the hole 11 of the brake tape 10. The length of the thermoelectrodes 9 and 18 was chosen so that during the experiments the cold junction does not have time to warm up, and equals 200- 350 mm Conclusions to the recording equipment were carried out with copper wires. Thermocouples 8 and 18 were calibrated together with connecting wires before installation. After that, the drilling winch is turned on and cyclic braking is performed by the tape-block brake by applying and removing the force on the control lever (not shown in the drawing), pressing the friction linings 12 with their working surfaces 13 against the working surface 15 of the brake pulleys 1 using brake tape 10 . In the process of braking on the surfaces of the friction pairs of the brake a significant amount of heat is generated, which is used to heat the body of the brake pulley 1 and the low-melting metal 4 in its cavity until the molten state i. In addition, in the second pulley 1, heat from its protrusion 2 is transferred to the flange of the drum 23 and therefore the temperature of the working surface 15 of the first pulley 1 will be greater than the second. This circumstance will contribute to different intensities of radiation and forced convective heat transfer from the surfaces of the brake pulleys 1. Then, by the ratio of the measured surface temperatures (t ₁ -t ₀ / t ₂ -t ₀ ) of the first and second brake pulleys 1 of the band brake and judge the proportion heat from its total amount, which is transmitted to the flange of the winch drum 23, i.e. conductive heat transfer. So, for example, when the ratio of these temperatures

the proportion of heat that is transferred by conductive heat transfer to the flange of the winch drum 23 is 4.7%.

The fourth stage. Under industrial conditions, heat losses are determined by forced convective heat transfer from heated brake pulleys.

At various constant frequencies of rotation of the lifting shaft 25 of the winch, and with it the brake pulleys 1, their surface temperatures are fixed by sliding thermocouples for equal periods of time. For this, thermocouples are mounted on the flange of pulleys 1 and are connected through a current collector to recording equipment (not shown in the drawing). Then determine the intensity of the forced convective heat transfer of the surfaces of the pulleys 1 (heat transfer coefficient) in the given intervals of surface temperatures. In this case, it is necessary to withstand the conditions for heating the brake pulley of the tape-shoe brake, corresponding to the second stage of research. In this case, we determine the heat transfer coefficients from the surfaces of the brake pulley 1 during its free rotation according to a dependence similar to that given for the second stage.

Thus, in laboratory and industrial conditions, heating and cooling of the brake pulleys of the band brake is carried out, which made it possible to determine the heat loss with radiation, natural and forced convective heat transfer from its surfaces to the environment, as well as conductive heat transfer from the protrusions of the brake pulleys to the drum flanges winches.

Information sources

1. Kirillin V.A., Sheindlin A.E. Fundamentals of experimental thermodynamics. - M. - L .: State Energy Publishing House, 1950. - 310 p. (prototype).

2. Volchenko A.I. Thermal calculation of brake devices. Lviv: Higher School, 1987. - 133 p. (analogue).

Claims (4)

1. The method of heating and cooling the brake pulleys of the drawbar brake of the drawworks to assess their heat balance, containing hollow, sealed brake pulleys filled with low-melting metal (potassium, sodium, lithium), in which there are heating devices around the cavity, and to the outside thermocouple thermoelectrodes are connected to the surfaces of the brake pulleys, characterized in that the surfaces of the first brake pulley are completely insulated from the environment, and the surfaces of the second brake pulley in they interact with it when the heating devices are separately connected for the same period of time to an external source of electric current, providing heating of the brake pulley body by means of molten low-melting metal, after which the heating devices are disconnected from the external source of electric current and according to the ratio of the measured surface temperatures of the first (t ₁ ) and the second (t ₂ -t ₀ ) brake pulleys determine the fraction of heat that is dissipated into the environment by radiation heat transfer. 2. The method of heating and cooling the brake pulleys of the drawbar brake of the drawworks for evaluating their heat balance according to claim 1, characterized in that the time interval of natural convective cooling of the surfaces of the second brake pulley is fixed from the obtained thermal state as a result of electrical heating to ambient temperature and determine the intensity of convective heat transfer of the surfaces of the second brake pulley in predetermined temperature ranges. 3. The method of heating and cooling the brake pulleys of the drawbar brake of the drawworks for evaluating their heat balance, containing hollow pulleys attached to the flanges of the drum, the cavities of which are filled with fusible metal with heating devices located in them, and the friction linings are located on the arc of the brake band , through the body of which thermocouple thermoelectrodes are passed and at the same time all the elements of the brake mounted on the lifting shaft, as well as the drive, characterized in that the protrusion of the first brake kiva are insulated from the flange of the drum, and the protrusion of the second brake pulley is not insulated, after which, by cyclic braking, ensuring the interaction of the friction brake assemblies, the brake pulleys with fusible metal are heated to its molten state and according to the ratio of measured surface temperatures

the first and second brake pulleys at different intensities of radiation and convective heat transfer from their surfaces judge the fraction of heat from its total amount, which is removed to the drum flange, i.e. conductive heat transfer. 4. The method of heating and cooling the brake pulleys of the drawbar brake of the drawworks for assessing their heat balance according to claim 3, characterized in that at different constant frequencies of free rotation of the heated brake pulley for the same periods of time, its surface temperatures are fixed with sliding thermocouples, and then determine the intensity of forced convective heat transfer of the surfaces of the pulley in the given intervals of its surface temperatures.

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