RU2250816C2 - Method for hydro-abrasive working of surface - Google Patents

Abstract

FIELD: deactivation of surfaces by removing radioactive impurities.

SUBSTANCE: method comprises steps of acting upon flow of hydro-abrasive suspension at speeds of compressed gas flow more than 200 m/s at relation of mass flow rates of hydro-abrasive suspension and compressed gas no more than 1 : 2; setting flow rate of hydro-abrasive suspension for each value of compressed gas flow speed due to measuring distance between outlet cross section area of gas nozzle and outlet cross section area of end of needle of sprayer for supplying hydro-abrasive suspension to zone of nozzle where hydro-abrasive aerosol particles are formed.

EFFECT: enhanced efficiency of cleaning, finishing and deactivating surfaces.

1 dwg, 1 note, 1 tbl

Description

The invention relates to the field of mechanical engineering and nuclear energy for waterjet processing of parts, namely to waterjet cleaning and surface finishing of parts, and can be used for decontamination of surfaces from radioactive contamination.

A known method of waterjet cleaning of surfaces of parts, which provides for the creation of a waterjet aerosol stream consisting of aerosol particles of liquid, abrasive particles and air and surface treatment with such an aerosol stream [1].

The three-component stream obtained in this way (compressed air, abrasive particles and aerosol particles of a liquid) has a significant drawback which consists in the presence of a large number of free, non-liquid abrasive particles in an aerosol stream. In this case, the abrasive particles interact directly with the treated surface, and not through a protective (damping) layer of liquid, which contributes to more intense damage to the surface of the workpiece.

There is also known a method of hydroabrasive cleaning of surfaces of parts, selected as a prototype, which provides for the creation of a hydroabrasive aerosol stream, where an aqueous suspension consisting of water and abrasive particles is used as hydroabrasive particles [2]. Such a suspension is obtained by pre-mixing the abrasive particles with a liquid. An abrasive aerosol stream for surface treatment is obtained by exposing the suspension to an air stream at a speed of 200 to 500 m / s. The ratio of the mass flow rate of the suspension and air does not exceed 1:10.

The disadvantage of this method is the decrease in the efficiency of surface treatment of parts at speeds of exposure to a jet of compressed air with an aqueous suspension of more than 500 m / s. The limitation of the values of the air velocity to 500 m / s does not allow to increase the cleaning performance for this cleaning method. The absence of a positive effect for this method is associated with the peculiarity of the interaction of the air flow inside the gas nozzle and its effect on the ejection coefficient of the aqueous suspension through the atomizer needle. So, for fixed geometrical parameters of the gas nozzle and the atomizer needle, an increase in the air flow rate above the calculated one leads to an unbalanced flow of compressed air inside the nozzle channel. So, for example, for the geometric parameters of the nozzle given in the description of the prototype [2], the calculated speed of the air stream from the nozzle corresponds to a velocity value of ≈ 450 m / s. With an increase in the gas flow outflow rate above the calculated one, the air pressure redistributes (which is a function of the gas velocity P _g = ƒ (V _g )) along the axis of the air inside the nozzle. A change in the pressure value of the compressed air inside the gas nozzle affects the ejection coefficient and, therefore, the flow rate of the aqueous suspension through the atomizer needle.

To solve the problem of maintaining the required flow rate of the aqueous suspension through the needle of the atomizer, depending on the change in the speed of the air flow inside the gas nozzle, several technical solutions are possible.

Option 1. Use a replaceable set of gas nozzles, each of which is designed for a given, boundary for the given nozzle geometry, gas flow rate. In this case, to change the operating mode of the nozzle mode, it is necessary to stop the device for waterjet cleaning, and then replace one nozzle with another. It is also necessary to carry out a subsequent check and adjustment of its operating characteristics, in particular, the amount of flow of the aqueous suspension. In production conditions, this leads to a decrease in the productivity of the device for waterjet cleaning, as well as to additional financial costs associated with the manufacture of replaceable sets of nozzles.

Option 2. Use a forced supply of an aqueous suspension. This option can be implemented by creating an adjustable pressure head for supplying an aqueous suspension, for example, using a pump or by changing the height difference between the suspension tank and the sprayer needle. When using a forced supply of an aqueous suspension, for example, using a pump, it is necessary to synchronize the flow rate of the aqueous suspension through the needle of the atomizer with the air velocity. The fulfillment of this condition is associated with the need to maintain a certain ratio of the mass flow rates of the suspension and air, at which the process of crushing the suspension by high-speed air flow into aerosol particles, as well as the acceleration of these particles to speeds sufficient to perform the cleaning process. Therefore, when using forced feeding of a suspension through a needle, a spray gun requires a special self-adjusting system to automatically control the ratio of the mass flow rates of the suspension and air. The creation of such automatic control systems is associated with certain technical difficulties due to the speed of the crushing process of the suspension flowing from the atomizer needle (≈10 ⁵ s), and also due to the inertia in the control systems themselves. According to preliminary estimates, the inertia (i.e., the time the process of crushing and dispersing aerosol particles of the suspension into the specified operating mode) of such a system can be 10-30 seconds. At the same time, there is one more problem, namely, the time of stable retention of the system in the given operating parameters.

The objective of the present invention is to increase the productivity and functionality of a hydroabrasive method for cleaning surfaces of parts based on the use of a high-speed hydroabrasive aerosol stream of an aqueous suspension of abrasive particles, which is created inside a gas nozzle when a stream of compressed air is applied to an aqueous suspension by increasing the range of variation of the air flow rate, beyond due to which the productivity of surface cleaning is increased.

The problem is solved due to the fact that in the method of hydroabrasive cleaning of the surfaces of parts, including the action of a stream of compressed gas to form aerosol particles on the flow of a hydroforming suspension, according to the invention, the effect on the flow of a hydroforming suspension is carried out at a flow rate of compressed gas of more than 200 m / s, while the ratio of the mass flow rates of the waterjet slurry and compressed gas does not exceed 1: 2, and for each value of the flow rate of the compressed gas, the flow rate of the waterjet is determined Penzov by changing the distance between gas nozzle outlet section and the outlet section of the needle butt nebulizer for supplying gidroobrazivnoy slurry nozzle into a zone where the formation of aerosol particles gidroobrazivnyh.

The drawing shows one of the possible installation schemes for implementing the method.

Installation for implementing the method of waterjet cleaning includes a tank 1 with an aqueous waterjet suspension, which is equipped with a device 2 for mixing the suspension, a needle 3 for feeding a waterjet suspension, the position of the spray zone (outlet end of the needle) which can be installed in the subsonic or supersonic part of the gas nozzle 4.

An example implementation of the method.

From the tank 1, inside which is located and is constantly mixed (to maintain the suspension solid particles in suspension) with the help of device 2, the hydroabrasive suspension, the suspension, due to ejection, through the needle 3 enters the spray zone of the gas nozzle 4. Gas velocity V _g , in in this case, the compressed air exiting the nozzle exceeded 200 m / s and varied in the range from 280 to 720 m / s, which corresponded to the change in the pressure of compressed air at the inlet to the nozzle in the range from 0.28 to 0.6 MPa. The control of the gas pressure was carried out using a manometer connected to the internal cavity of the gas nozzle. In the indicated range of changes in the air flow velocity, the hydroabrasive suspension is crushed into liquid droplets with a diameter of (4-50) × 10 ⁶ m and containing abrasive particles no larger than 5 × 10 ⁵ m in size.

As the experimental results showed, with a decrease in the size of the particles of the suspension, their specific surface area and their amount per unit volume of the aerosol stream increase, which improves the cleaning efficiency.

The results of the efficiency of the cleaning processes for the ranges of parameter changes indicated in the example are given in the table that is attached.

Sources of information

1. A.S. 1237403 1984.

2. A.S. 1740142 1987.

Table
Experimental results of the performance of cleaning the surfaces of control metal samples from scale with a fixed and variable position of the outlet end of the atomizer needle and the outlet section of the gas nozzle Compressed air pressure at the gas nozzle inlet, MPa 0.28 0.32 0.4 0.45 0.5 0.55 0.6 Airflow rate at the nozzle exit, m / s 280 350 430 500 580 650 720 The distance L (mm) between the outlet section of the gas nozzle and the fixed end of the needle 3 3 3 3 3 3 3 The flow rate of the working fluid (waterjet suspension) through the needle of the sprayer, liters / min 0.52 0.38 0.3 0.18 0.12 0.06 0.01 The performance of cleaning the surface of the sample size of 25 cm ² from scale, seconds 63 thirty 12 25 36 52 90 The distance L (mm) between the exit section of the gas nozzle and the end face of the needle nine 7 4 3 1 0 -2 * The flow rate of the working fluid (waterjet suspension) through the needle of the sprayer, liters / min 0.3 0.3 0.3 0.3 0.3 0.3 0.3 The performance of cleaning the surface of the sample size of 25 cm ² from scale, seconds 38 twenty 12 10 8 5 4 * - the end face of the needle is extended 2 mm from the nozzle

Claims (1)

A method of hydroabrasive treatment of surfaces of parts, including the action of a jet of compressed gas to form aerosol particles on the flow of a hydroabrasive suspension, characterized in that the impact on the flow of a hydroabrasive suspension is carried out at a flow rate of compressed gas of more than 200 m / s, while the ratio of the mass flow rate of the hydroabrasive suspension and compressed gas does not exceed 1: 2, and for each value of the compressed gas flow rate, the flow rate of the hydroabrasive slurry is established by changing the distance between the outlet th section of the gas nozzle and the outlet section of the nozzle needle end face for supplying the slurry waterjet nozzle into a zone where the formation of aerosol particles hydroabrasive.