Fluid handling – Systems – With flow control means for branched passages
Reexamination Certificate
2001-03-28
2002-12-17
Fox, John (Department: 3753)
Fluid handling
Systems
With flow control means for branched passages
C137S906000, C251S335200
Reexamination Certificate
active
06494231
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims priority of German Application Serial No. 198 48 358.9 filed Oct. 21, 1998, and PCT/DE99/07936 filed Oct. 19, 1999.
The invention relates to a valve device for low-viscosity to high-viscosity fluids, especially for fluid plastic components of plastic mixtures consisting of one or more components. The device includes a valve housing having a fluid inflow and a dosing valve. The dosing valve has a dosing nozzle that can optionally be closed or opened by a closing element, as well as a pressure control device which acts on the fluid in the fluid inflow.
Such valve devices are used particularly in the processing of plastics with mixing heads, with the help of which the different plastic components are mixed and then ejected as a processable plastic mixture through an outlet and, for example, are immediately moulded onto a part as a seal. The valve devices are arranged at the inlets of the mixing head for the individual plastic components and serve to stop the supply of a component when the dosing valve is closed. The valve devices ensure, when the dosing valve is opened, that the supplied component is introduced into the mixing head not only with a constant volume flow, but also with a previously set, constant fluid pressure.
A valve device according to the above-mentioned type is known from DE-OS 195 42 797. With this valve device, the pressure control device is formed essentially from a compression spring which is arranged in the housing. The compression spring acts on the closing element which is formed as a valve needle. The compression spring pretension can be adjusted manually by adjusting an adjusting screw from the outside of the housing. The fluid pressure exerted by the spring on the nozzle needle is in equilibrium with the fluid pressure. The fluid pressure acts on the frontal area of the nozzle needle which lies transversely to its shift direction. The pressure of the spring and the pressure exerted on the nozzle needle due to the fluid pressure are in equilibrium when operated, so that it is possible to control the fluid pressure in the fluid inflow by adjusting the spring pretension.
The '797 device is relatively complicated with regard to the adjustment of the correct pressure ratios in the fluid inflow. The adjustment of the correct pressure ratios takes place manually from the outside of the housing. Small adjustments of the adjusting screw result in relatively large pressure changes in the fluid, as the effective frontal area at the nozzle needle, which transfers the spring force to the fluid, is small due to its design. A particular disadvantage of the known device is that an operation at a constant fluid pressure, with the volume flow supplied by a dosing pump, is only guaranteed as long as the nozzle needle maintains its relative position in the valve housing when the valve is open. If the cross section that is opened by the nozzle needle is reduced in this relative position, for example by deposits of solidified plastic components or other build-up of material, the nozzle needle has to be opened further against the force of the spring, so as to maintain the steady cross section which is necessary for the constant volume flow of the fluid. A small movement of the nozzle needle already results in a large change in the spring tension and the spring force, so that the fluid pressure increases by a large amount, even when only a small build-up of material occurs.
SUMMARY OF THE INVENTION
It is the object of the invention to avoid the aforementioned disadvantages and to design a valve device of the above-mentioned type in such a way that a constant fluid pressure can be adjusted easily. The fluid pressure is essentially independent of the position of the closing element when the dosing valve is opened, and therefore is also maintained when contaminations occur at the nozzle cross section.
This object will be solved by means of the invention in that the pressure control device consists essentially of a pneumatically pretensionable control membrane which acts on the closing element.
The use of a pneumatically or servo-pneumatically pretensionable control membrane, which replaces the compression spring used in the state of the art, allows a particularly simple pressure control of the fluid dosed by means of the device. The air pressure for changing the membrane pretension can easily be adjusted automatically. By using a suitable pressure accumulator for the compressed air which pretentions the membrane, movements of the closing element which arise from contaminations at the nozzle outlet, result in practically no or only a negligible increase of pressure of compressed air and subsequently no change of the fluid pressure. In particular, the design of the valve device according to the invention also facilitates its automatic control by means of a computer-aided adjustment or change of the air pressure acting on the control membrane.
In a preferred design of the invention, there can also be arranged a recirculation valve in the valve housing in such a way that the dosing valve is optionally opened for the supply of fluid to a processing device or the recirculation valve is opened for the return of the fluid to a storage vessel. With this configuration, the supplied fluid is either supplied to for example the mixing head by the dosing valve of the processing device, or is conveyed in the cycle back to the storage vessel by the recirculation valve. The compact unit of dosing and recirculation valve in a common housing avoids difficulties in the starting phase of the subsequent processing device, as this is always completely filled due to the circulation of fluid in the cycle, and fresh fluid is always added as soon as the dosing valve opens.
The control membrane is preferably part of a pneumatically chargeable pressure control chamber and acts on the closing element designed as a valve needle by means of a plunger which can be moved in the housing. The pressure control chamber thereby forms the pressure storage for the compressed air which acts on the fluid in the fluid inflow by means of the control membrane. The force exerted by the compressed air is transferred to the valve needle by means of the plunger essentially without friction losses. The pressure control device is preferably arranged separately from the fluid inflow by means of a shut-off membrane, whereby it is ensured that no fluid can reach the sensitive control membrane. The shut-off membrane is preferably arranged between the closing element and the plunger, so that the plunger is also separated from the fluid inflow and that its very accurate, mainly frictionless mounting in the valve housing is not adversely affected by the entry of fluid.
The plunger can be charged by the control membrane by means of a pressure pin mounted at the control membrane, which is supported at the plunger by means of a ball bearing element. The ball bearing element, which preferably consists simply of a single ball, effects an even central transfer of the forces acting between the plunger and the pressure pin essentially without friction losses, so that an exact pressure balance can take place between the air pressure at the control membrane and the fluid pressure in the fluid inflow.
The closing element is preferably pretensioned in the direction of the plunger by means of a spring which is supported in the housing. When the dosing valve is opened, the spring draws the dosing element in the dosing nozzle back at least to such an extent that the fluid pressure of the supplied fluid can act on the closing element. The closing element of the dosing valve can be moved by an actuating device for closing or opening the dosing nozzle. The actuating device consists in a particularly advantageous manner essentially of an actuating lever that can be actuated in the actuating cylinder. The actuating lever is mounted pivotally in the housing and acts on the closing element or the pressure cylinder against the spring. In particular, with the particularly advantageous design of the inv
Fetz Dietmar
Hausbichler Hannes
EDF Polymer-Applikation Maschinenfabrik GmbH
Fay Sharpe Fagan Minnich & McKee
Fox John
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