Data processing: generic control systems or specific application – Specific application – apparatus or process – Chemical process control or monitoring system
Reexamination Certificate
1998-08-03
2001-09-04
Gordon, Paul P. (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Chemical process control or monitoring system
C700S282000
Reexamination Certificate
active
06285922
ABSTRACT:
The invention relates to a control device of a gas/air mixture regulating system for a gas flame treatment for the coating of surfaces with at least one burner according to the preamble of claim
1
.
In the coating of surfaces, for example the decoration of plastics or the printing or lamination of foils, the materials concerned are mostly nonpolar and—regardless of their other advantages—show no tendency to exhibit adhesion to other materials such as, for example, lacquers, printing inks, adhesives and the like. It is therefore necessary to activate the surfaces to be treated, in order to make possible a sufficient wetting and adhesion of the coating. For this, besides a corona discharge process and a low pressure plasma process, a gas flame process is used.
In such gas flame processes, the surface to be coated is treated with a gas flame produced by a burner. In this pretreatment, it is not only a thermal process which is concerned, in which an improved adhesion is attained by means of a deformation of the surface and the resulting surface enlargement, but also a chemical process is concerned, by means of which an increase in the surface energy can be attained. The surface energy is in general a prerequisite as a measure for a satisfactory adhesion, in which the surface energy of the base material is larger, for example by an amount of 10 mN/m, than the surface tension of the medium to be applied.
It has been shown that a flame having the highest possible temperature and a stable form is obtained with a purely stoichiometric gas/air mixture for a gas flame treatment, but showed no effect as regards improvement of adhesion. A reduction of the proportion of oxygen had the result that the flame became unstable, since the lacking oxygen was replaced with oxygen from the surrounding air. Such a flame thus has a reducing action, which is likewise not advantageous. With an increase of the proportion of oxygen over the stoichiometric amount, the excess oxygen likewise takes part in the reaction at the surface to be treated, so that—after the gas has been combusted without residue—the excess oxygen remains in the combustion product in the form of radicals and various ions, so that an oxidizing flame results.
Surface treatment with a flame whose oxygen content exceeds the stoichiometric amount has the effect that molecular chains of the material to be coated are broken by the action of heat and the oxygen components are bonded to these break points. Polar molecules thus arise in the originally nonpolar material, so that good adhesion to the coating material results. The proportion of the gas/air mixture is an important aspect for the action of the gas flame treatment.
Apparatuses for gas flame treatment have heretofore been disclosed in which the proportion of the gas/air mixture can be determined. However, such apparatuses have the disadvantage that they can only give information on the mixing ratio of oxygen to gas, but not on the output relating to the flow of gas and oxygen, which likewise contributes to the result of the treatment. Furthermore, there are problems in setting the desired output at the burner. An expensive manual setting is therefore necessary, which first requires an equalization of the flow of the gas/air mixture to the output required for the pretreatment, and then a setting to the corresponding mixing ratio between gas and air, where the proportion of oxygen is to exceed the stoichiometric amount, or an additional measurement of the burner output. Such apparatuses cannot be used with automatic production such as preferably provided for example in the automobile industry, in which fenders made of plastic are lacquered in various sizes.
Moreover an apparatus for burner control is also known in the prior art, in which a measurement of the flame temperature is used as a criterion for the setting and regulation of the mixture proportions. This apparatus has the disadvantage, however, that a precise determination of the mixing ratio is not possible. This is because the highest temperature of the flame is obtained with a stoichiometric gas/air mixture. However, a temperature lower than the highest temperature results from setting the required excess of oxygen, and has to be passed to a regulator as a reference value. It then cannot be determined whether the temperature reduction is due to an excess of oxygen or to an excessive proportion of gas, which likewise results in a fall of the flame temperature. Thus a precise determination cannot result, since either an excess of oxygen or else an excessive proportion of gas can be present at the same temperature.
The invention therefore has as its object to provide a control device for a gas flame treatment system such that both the mixing proportion of gas to air and also the output to be delivered at the burner can be set, regulated, and monitored.
This object is attained according to the invention by the characterizing part of claim
1
.
By the use of a central computer unit, which determines the flow rates of air and gas in dependence on the mixing proportion of the gas/air mixture which was entered and also in dependence on the output to be delivered by the burner, the central computer unit can output control variables as reference values to a regulator for control of an air quantity regulating valve, and to a regulator for control of a gas quantity valve, so that a required setting of the gas flame for the treatment is given directly after starting up the control device or after the entering of new parameters. The present setting of the regulating valves, and thus the actual flow quantities, can be determined by the simultaneous measurement of the flow quantities of air and gas by means of a flow measuring device, so that on the one hand the precise mixing ratio of gas: air can be determined, and on the other hand the output delivered at the burner can be determined. The measurement data which are determined as regards the flow quantities are passed as reference values to the regulators for control of the regulating valves, so that these can carry out an equalization to the reference values obtained from the central computing unit, in order to be able to set the mixing proportion exactly and to be able to output new control values to the actuators of the regulators. An optimum performance result for the improvement of adhesion can thereby be attained, since the proportion of oxygen exceeding the stoichiometric amount can be set and regulated with certainty.
The embodiment of the control device according to the invention furthermore has the advantage that several standard mixing proportions are stored in the central computer unit, and can easily be called up in dependence on the gas used, for example, natural gas (methane), propane, or butane. Depending on the output to be delivered at the burner, the central computer unit can then output the corresponding control variables to the regulators, so that an optimum gas flame is present at the burner by exact setting of the valves. Furthermore, the required flow quantities can be set to given parameters, such as for example the kind and the surface of the material to be treated, and also the speed of travel with the burner over the surface to be treated. Then, specifically to the application, a quick and simple changeover can be made for the treatment of a new material, as regards the parameters for the treatment, which can also be encapsulated in an automatic process control. It can furthermore be insured that an incorrect setting can be prevented from causing damage to a material to be treated.
This embodiment furthermore makes it possible for a higher operating convenience, which can be adjusted to each application, to be provided by means of a simple entering of the parameters for the material to be treated.
According to an advantageous embodiment of the invention, it is provided that the air and gas quantity regulating valves are respectively followed by a device which measures the flow. The flows of air and gas can thereby be determined exactly, corresponding to the ac
Cabrera Zolla
Gordon Paul P.
LandOfFree
Device for controlling a gas-air mixture for a gas flame... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for controlling a gas-air mixture for a gas flame..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for controlling a gas-air mixture for a gas flame... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2537682