GB2170731A

GB2170731A - Time-controlled fluid mixers

Info

Publication number: GB2170731A
Application number: GB08603154A
Authority: GB
Inventors: Paul Phillip Hope
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-02-09
Filing date: 1986-02-10
Publication date: 1986-08-13
Also published as: GB2170731B; GB8603154D0

Abstract

A time-controlled mixer for mixing two or more fluid components from separate supplies has a mixing chamber (1), separate conduits (2) connecting each supply to the chamber (1), with each conduit having an on/off valve (3), and an electronic controller (4) which operates each valve (3) for a proportion of a timed cycle, in accordance with the supply pressures and the pressure drop/flow rate characteristic of each fluid component in its conduit (2), to provide a required mixture in the chamber (1). The supply pressures may be sensed by pressure sensors (7) located in each conduit (2) and connected to the controller (4). The mixer operates accurately, and is particularly useful in mixing gases for gas-shielded electric arc welding. <IMAGE>

Description

SPECIFICATION Time-controlled fluid mixers This invention relates to time-controlled fluid mixers for mixing two or more fluid components.

Mixers of this kind are used to mix liquids or gases, and control the flow rate of each component to provide a mixture with the required proportions of the components. Direct and accurate measurement of flow is expensive and cumbersome, so instead the flow of each component through a flow regulator must be predicted. Mechanical flow regulators of sufficient accuracy are expensive, and do not allow the composition of the mixture to be changed easily.

In order to overcome this problem the mixer may have a common flow regulator for the components, but this is not suitable for mixing components of very different densities. Further, maintaining the accuracy of a given mixture depends on the components being supplied at constant pressures, and the accurate pressure regulators required may not be available or convenient to use.

According to our invention, a time-controlled mixer for mixing two or more fluid components from separate supplies has a mixing chamber, separate conduit means connecting each supply to the mixing chamber, each conduit means having a single control valve means to control passage of the fluid component through its conduit means, and a controller which operates each valve means for a part of a timed cycle, in accordance with the supply pressures and the pressure drop/flow rate characteristic of each fluid component in its conduit means, to provide the required proportion of the fluid components in the mixing chamber.

Because the controller takes the flow characteristics of the fluid components into account, the accuracy of the mixtures will be improved.

Preferably the controller is electronic, and any mixture that is required can be programmed into it.

Each valve means may comprise an on/offvalve which is operated electrically by the controller.

Each conduit means preferably includes a pressure sensing means for sensing the supply pressure of the fluid component, which is transmitted to the controller. Any fluctuations in the supply pressures can therefore be taken into account, so that accurate pressure regulators for the supplies are not required.

The mixing chamber may also have a pressure sensing means connected to the controller, such that the controller permits fluid flow to the mixing chamber only when the pressure in the mixing chamber is below a threshold level.

Each conduit means may also have a flow restrictor between the valve means and the mixing chamber. The valve means and the restrictor are chosen to ensure a suitable flow rate for the component in its conduit means.

The mixture may also include extra sensing means, such as temperature sensors, which provide further information for the controller. The controller may also operate the valve means in response to information fed to it from an external device, such as an operator, and provide information for the operator.

The mixer is particularly useful for mixing gases. It may be used for mixing helium, argon and carbon dioxide, which are used in gas-shielded electric arc welding, as it can provide, with accuracy, the variety of mixtures needed for welding different metals or different thicknesses of metals. The mixer can also be used for liquids.

One embodiment of our invention is shown, by way of example only, in the accompanying drawing, the single Figure of which is a schematic representation of a time-controlled fluid mixer.

The mixer shown is adapted to mix three fluid components, in this case the gases helium, argon and carbon dioxide which are used in gas-shielded electric arc welding. The mixer comprises a mixing chamber 1, which may be a large conduit or vessel, connected to a supply (not shown) for each gas by separate conduit means 2, 2' 2", each of which has a single control valve means in the form of an on/off valve 3, 3', 3", together with an electronic controller 4 which operates the valves 3, 3', 3" for a part of a time cycle, in response to the supply pressures and the pressure drop/flow rate characteristic of each gas in its conduit means 2, 2', 2", to provide a required mixture in the mixing chamber 1. The mixture is then supplied to welding apparatus (not shown) through an outlet conduit 5 which includes a variable flow restrictor 6.

The electronic controller 4 works in timed cycles, and provides the required gas mixture by determining the proportion of each cycle that each valve 3, 3',3", is open (the valves being operated independently) in response to the information supplied to it.

The controller 4 is programmable to provide different mixtures, and the information supplied to it may be entered manually as fixed data, or be provided from variable sources, such as sensors. Thus, the pressure drop/flow rate characteristic of each gas is measured or calculated and entered as fixed data.

The information about the supply pressures is provided by pressure sensors 7,7',7", which are located in a respective conduit means 2, 2',2" between the supply and the valve, so that the proportions of each cycle for which the valves are open can be varied in accordance with any fluctuations in the supply pressures. The controller 4 also receives information from a pressure sensor 8 for the mixing chamber 1 such that the controller 4 will operate the valves 3, 3',3", if the pressure in the mixing chamber 1 is below a threshold level, and will stop operation if it is above the threshold level. Fixed flow restrictors 9,9',9" are also provided in the respective conduit means between the valve and the mixing chamber 1.These restrictors and on/off valves 3,3',3" are chosen to ensure that the proportion of a cycle that a valve is open or closed is not too short, as this tends to affect the accuracy of the mixture.

The controller 4 can also be programmed to receive information from an operator or another device (not shown), and to provide output information back to the operator. The output information can be a warning of high or low input pressures, a display of the mixture selected, or the mixing chamber pressure, or the total gas used or any other information available.

In gas-shielded electric arc welding the use of a particular gas mixtures enhances significantly the welding speed and quality for a given metal and thickness of metal. In use, therefore, the required mixture is set, from the selection contained in the controller, by the operator, or by an automatic robot welder (not shown) connected to the controller 4. If the pressure in the mixing chamber 1 is below the threshold level the controller 4 operates the valves 3,3',3" in timed cycles in accordance with the supply pressures and the pressure drop/flow rate characteristics for each gas to provide the required mixture in the chamber 1. If the mixing chamber pressure rises above the threshold level the controller 4 closes all the valves 3, 3',3" at the end of the next cycle.

In a modification (not shown) the output from a current sensing device on an automatic robot welder may be used to vary the mixture.

The mixer may also have other modifications (not shown). Thus, if the fluid supplies are fitted with accurate pressure regulators the pressure sensors 7, 7', 7" are not required, and the controller 4 works on the basis of fixed supply pressures. It should be noted though that accurate pressure regulators may be too expensive to be used in applications such as welding.

In a further modification the flow restrictor 6 may be a fixed restrictor. In this case the controller 4 is arranged to alter the threshold level, and thus the average operating pressure in the chamber 1, which will control the flow rate through the outlet conduit 5. More than one outlet conduit may be provided Additional sensors such as temperature probes may also be included, and these will feed information to the controller 4 to enable itto operate the valves 3, 3', 3" more accurately.

The mixer may be adapted to mix liquids rather than gases.

The fluid mixer described will therefore mix two or more fluids accurately, and also enables the proportions of the mixture to be changed easily.

Claims

1. Atime-controlled mixer for mixing two or more fluid components from separate supplies has a mixing chamber, separate conduit means connecting each supply to the mixing chamber, each conduit means having a single control valve means to control passage of the fluid component through its conduit means, and a controller which operates each valve means for a part of a timed cycle, in accordance with the supply pressures and the pressure drop/flow rate characteristic of each fluid component in its conduit means, to provide the required proportion of the fluid components in the mixing chamber.

2. Atime-controlled mixer as claimed in claim 1, in which the controller is electronic, and programmable with the required mixtures.

3. Atime-controlled mixer as claimed in claim 1 or claim 2, in which each valve means comprises an on/off valve operated electrically by the controller.

4. A time-controlled mixer as claimed in any preceding claim, in which each conduit means has a pressure sensing means for sensing the supply pressure of the fluid component, each pressure sensing means being connected to the controller.

5. Atime-controlled mixer as claimed in any preceding claim, in which the mixing chamber has a pressure sensing means connected to the controller.

6. Atime-controlled mixer as claimed in any preceding claim, in which each conduit means has a flow restrictor between the valve means and the mixing chamber.

7. Atime-controlled mixer as claimed in any preceding claim, in which each conduit means has a temperature sensing means connected to the controller.

8. Atime-controlled mixer as claimed in any preceding claim,in which the controller provides information for an operator.

9. Atime-controlled mixer for mixing two or more fluid components substantially as described herein with reference to and as illustrated in the accompanying drawings.