SU1660894A1 - Method of determination of the degree of wear for a nozzle of a plasma-arc cutting torch - Google Patents

Abstract

The invention relates to plasma arc cutting, for example sheet metal, and can be used in all industries where mechanized metal cutting is used. The purpose of the invention is to improve the cutting accuracy and increase the productivity of the cutting process. The method allows to determine the degree of wear of the nozzle during the cutting process from the change in voltage of the cutting arc between the electrode and the product by comparing it with the reference voltage determined when the nozzle is worn out based on the allowable deviation of the dimensions of the cut out parts. Stabilize other parameters of the mode: current, cutting speed, plasma gas consumption, height of the cutter above the product. Productivity is increased by reducing the time spent on assembling and welding parts of various metal structures cut out with nominal accuracy (reducing the time spent on fitting work) and on welding work in connection with the reduction of gaps in the welded joints. 1 il.

Description

The invention relates to the field of plasma arc cutting, such as sheet metal, and can be used in all areas where mechanized metal cutting is used.

The purpose of the invention is to improve the accuracy of cutting and productivity of the cutting process.

The drawing shows a block diagram of the device for implementing the method

During the cutting process, under the influence of the plasma arc, the forming channel of the nozzle is destroyed, as a result of which its diameter increases, which leads to an increase in the width of the cut and a decrease in accuracy. Therefore, determining the degree of wear of the nozzle is an important task.

As is known, the width of the cut b depends on the diameter of the forming channel of the nozzle d and the distance from the cut (end) of the nozzle to the surface of the product h and is expressed by the formula

 (0.1-0.3) h. (1)

In the process of mechanized plasma cutting, the operator is forced to periodically turn off the equipment in order to measure the cutting width and assess the nozzle wear degree, while there are unproductive losses of working time and cases of deviation of the cutting width from the allowable are not excluded.

The dependence of the change in arc voltage on various parameters is also known.

U C -I- K- G + D U (Go with + $ s.), (2)

ABOUT

oh oh

with y

where G is the plasma gas flow rate;

1 - cutting arc current;

E. - the length of the nozzle forming channel, which does not change during the cutting process;

d is the diameter of the forming channel; the gradient of the voltage of the open part of the arc;

Ro is the length of the open portion of the arc, determined by the value of h;

RS. - the length of the working section of the column, determined by the location of the anode area of the arc on the frontal cutting edge and depending on the current of the cutting arc I and the cutting speed v.

From the above dependence it can be seen that a change in the diameter of the nozzle changes the arc voltage.

Before starting the process of cutting this metal, the parameters I, v, G, h, a and the nominal diameter d of the forming channel of the nozzle 1 are chosen optimal from the point of view of productivity and quality of the cutting edges. The maximum permissible diameter of the forming channel due to wear di is determined by calculation from permissible deviation of the dimensions of the parts to be cut out, and in the mode chosen earlier, experimental cutting of this metal is performed using a nozzle with a diameter di. In this case, the voltage of the cutting arc, burning between the electrode 2 and the product 3, provided by the power source 4 is measured. This voltage value is taken as the reference U0n.

In the process of cutting this metal, stabilizing the mode parameters and using a nozzle with a diameter d, the arc voltage is compared with the reference source provided 5. In the case when Ug Don, the nozzle wear does not exceed the maximum allowable. When the voltage value becomes less than the reference one, the device 6 issues a command to turn on the device 7, the output signal of which registers the state of the nozzle wear limit and stops the cutting process.

Example. Air plasma cutting of steel sheet with a thickness of 6 mm was performed. The mode parameters were adopted in accordance with the recommended standards for which the requirements for cut quality and productivity are met: mm, l / min, m / min, A, mm.

These parameters stabilized, the stabilization accuracy was: h 11 mm, 5 l / min, v ± 0.1 m / min, A.

The arc voltage, which was 140 V., was measured. Cutting was performed on a computer with a software control Crystal which, according to the passport, ensured dimensional accuracy of the drawn contour with a tolerance of ± 0.5 mm (D m) and stabilization of speed ± 2.5%. Determine the deviation of the dimensions of the width of the cut caused by fluctuations in the parameters of the cutting mode: speed

DU ± 0.15 mm, transducer ± 025 mm, the gas flow rate D0o 0, the height of the DHP cutter 0. The limiting absolute value of the size deviation of the cut out part was

 / Lm | + | abv | + / Lb | / 0,9mm.

In accordance with GOST 147I2-80 for parts with nominal dimensions, for example, no more than 630 mm, the absolute value of deviations, dimensions when received is the 2nd

accuracy class is 1.4 mm

Consequently, the dimensional deviation caused by the wear of the nozzle should be no more than 0.5 mm, i.e. wear diameter is equal to .5 mm.

The change in the width of the cut in accordance with formula (1) with a stabilized value of h is equal to the change in the diameter of the nozzle

Using a nozzle with a diameter of the forming channel, 5 mm, the arc voltage was measured at the previously accepted cutting parameters, which was B.

Claims (1)

As can be seen, the change in arc voltage with increasing diameter of the forming channel of the nozzle is significant, which allows using this change as a signal for the operation of an automatic device. This method allows to increase the accuracy of the cut parts and reduce the amount of fitting work, reduce the overhead of working time, save welding wire. Claims The method of determining the degree of wear of a nozzle of a plasma arc torch, which consists in measuring the voltage of a cutting arc, characterized in that. in order to increase cutting accuracy and increase the productivity of the cutting process, the measured cutting arc voltage in the cutting process with stabilized parameters is compared with the reference voltage, for which the cutting arc voltage is taken when the diameter of the nozzle forming channel ensures the tolerance of the dimensions of the cut parts from nominal, and stop the process when the reference voltage exceeds the value of the measured voltage of the cutting arc. ///////////// &