Electric heating – Metal heating – By arc
Reexamination Certificate
2001-02-16
2002-01-01
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121540, C219S121390
Reexamination Certificate
active
06335505
ABSTRACT:
The present invention relates to an automatic plant, for cutting or welding using a jet of gas, comprising a line for supplying a torch with pilot gas and a line for supplying the torch with a cutting or welding gas, which plant comprises, in addition, control means enabling the pressure of the cutting or welding gas to be controlled according to the pressure of the pilot gas.
Plasma-arc cutting of metal, such as steel sheets, using a torch delivering a plasma jet is a very widespread process from the industrial standpoint.
Usually, a cutting operation, for example involving a steel sheet, breaks down into two distinct phases, namely an ignition phase and an actual cutting phase.
During the ignition phase, an ignition gas, otherwise called the pilot gas, is used to strike, i.e. ignite the electric arc in the torch.
More specifically, the pilot gas is ionized within the torch and an electric arc, called the pilot arc, forms within said torch.
Next, during the cutting phase, the torch is supplied with a main gas, otherwise called the cutting gas, which in general has a flow rate of about 10 to 500 l/min, which cutting gas is ionized in the electric arc which forms between the plasma torch electrode, acting as cathode, and the workpiece to be cut, acting as anode.
Depending on the circumstances, the pilot gas may be identical to or different than the cutting gas, for example, argon can be used as pilot gas and oxygen, nitrogen or a gas mixture, such as an argon/hydrogen mixture, as cutting gas.
However, in all cases, the ignition phase and the cutting or welding phase are executed one after the other and in that order.
In general, the flow rates of the pilot gas and of the cutting gas are set at the desired levels by adjustment of the pressure of these gases, respectively.
Moreover, the pilot-gas circuit and the cutting-gas circuit are usually independent of each other and the operation of the cutting torch is increasingly often controlled by automatic control means, especially control means with a microprocessor card running one or more computer programs.
However, for some types of gas, such as oxygen or hydrogen, the use of electrically-controlled pressure-reducing devices is not possible or recommended during the cutting phase, for obvious safety reasons.
Consequently, for this type of gas, the pressure-reducing devices or the pressure-reducing valve that can be used are usually of the manual-adjustment type or, depending on the circumstances, pressure-reducing valves remotely controlled by an inert gas such as hydrogen or argon, which makes it possible to alleviate the aforementioned safety problem but requires the presence of an additional source of pilot gas.
Conversely, the phase of igniting the torch is usually carried out with an inert gas with a high ionizing power, such as argon, with which the use of an electrically-controlled pressure-reducing valve does not, by contrast, pose any safety problem.
However, there is a growing demand for devices for simultaneously and automatically adjusting the pressure of the pilot gas and of the cutting gas, for example from the same operator console or via parameter tables included in computing systems, for example digital control systems.
This is because, given that the adjustments of the pilot-gas and cutting-gas pressures depend, in particular, on the metal sheets to be cut, that is on the type of material, on its thickness, on its geometric shape, etc., it is usually difficult for an operator to find, quickly and with certainty, the appropriate parameters for adjusting the pressure of these two gases.
In other words, the problem which is posed is that of being able to automatically adjust the pressure of the cutting gas and the pressure of the ignition gas in complete safety, whatever type of gas is used and without using an external source of pilot gas from the pressure-reducing valves fitted in the lines or circuits conveying, on the one hand, the pilot gas and, on the other, the cutting gas.
The solution provided by the present invention is based on control of the pressure-reducing valve fitted in the cutting-gas circuit, directly on the basis of the pressure of the pilot gas flowing in the pilot-gas circuit.
In other words, the present invention relates to an automatic plant for cutting or welding by a cutting or welding gas jet, especially by plasma jet, comprising at least:
a torch for cutting by gas jet, preferably a plasma torch;
a first line for supplying said torch with a pilot gas;
a second line for supplying said torch with a cutting or welding gas;
control means;
first means for adjusting the pressure of the pilot gas flowing in the first line, said first adjusting means being fitted in the first line and being controlled by the control means;
second means for adjusting the pressure of the cutting or welding gas flowing in the second line; and
a pneumatic control line pneumatically connecting the first line to the second adjustment means in order to enable the pressure of the cutting or welding gas in the second line to be adjusted on the basis of the pressure of the pilot gas in the first line by acting on said second adjustment means.
Depending on the case, the plant according to the invention may comprise one or more of the following characteristics:
the torch is a plasma jet cutting torch;
the first adjustment means are electrically controlled, preferably first adjustment means are chosen from electrically-controlled pressure-reducing valves;
the control means are chosen from numerical control systems;
the second adjustment means are chosen from pneumatically-controlled pressure-reducing valves;
at least one solenoid valve is fitted in the first line and/or the second line, preferably at least one solenoid valve is fitted in each of said first and second lines;
at least one solenoid valve is controlled by the control means;
the control line is connected to the first line, downstream of said first adjustment means.
According to another aspect, the present invention also relates to a process for cutting or welding by a cutting or welding gas jet, in particular plasma jet, capable of being implemented by an automatic plant, such as the aforementioned plant, comprising means for adjusting the pressure of the cutting gas flowing in a line for supplying a cutting torch with cutting or welding gas, in which the means for pneumatically adjusting the cutting or welding gas are controlled on the basis of the pressure of the pilot gas.
REFERENCES:
patent: 5290995 (1994-03-01), Higgins et al.
patent: 5614110 (1997-03-01), Shintani et al.
patent: 5844201 (1998-12-01), Dibacco et al.
patent: 6054669 (2000-04-01), Warren, Jr.
patent: 195 36150 (1997-04-01), None
patent: 2 237 720 (1975-02-01), None
Paschall Mark
Safmatic
Young & Thompson
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