WO2003087583A1

WO2003087583A1 - Vacuum operated ink pump

Info

Publication number: WO2003087583A1
Application number: PCT/GB2003/001506
Authority: WO
Inventors: Robert Snedker
Original assignee: Printco (Uk) Limited
Priority date: 2002-04-06
Filing date: 2003-04-07
Publication date: 2003-10-23
Also published as: GB0207987D0; AU2003219318A1; GB0307991D0; GB2389877A

Abstract

The pump has a first chamber (1) with an ink intake (4) connected via a first valve (3). A second chamber (2) is connected to the first chamber (1) via a second valve (7). An ink outlet (8) is connected to the second chamber (2). The pressure in the first chamber (1) may be varied either so to reduce it that ink is taken into the first chamber (1) through the intake (4), or to raise it so that ink is delivered from the first chamber (1) to the second chamber (2) and thence to the ink outlet (8).

Description

VACUUM OPERATED INK PUMP

The present invention relates to a pump for delivering ink, varnish, adhesive, paint or the like (hereinafter referred to generally as ink).

Apparatus requiring such a supply of ink (as defined) may be those wherein a rotating transfer or anilox roll applies the ink to a rotating plate roll which transfers the ink to the surface of a web of material. Alternatively, an engraved printing cylinder may directly transfer ink to a web of material. In such apparatus a reverse angle doctor blade assembly meters ink onto the anilox roll or printing cylinder from a reservoir to which ink is fed and which communicates with the roll or cylinder.

In such apparatus, as the rotational speed of the transfer roll increases the roll may become unevenly wetted. In operation, this results in a "starvation" phenomenon wherein ink or other liquid is unevenly transferred to the web and printing is therefore incomplete. In systems which employ a sealed reservoir to apply ink to a rotating transfer roll it is important to maintain a constant, relatively even level of ink within the reservoir and a constant flow of ink through the reservoir. A constant flow is required to avoid settling of constituents of the liquid, particularly when water based inks are used. A constant supply of fresh liquid at a modest flow rate is also useful in eliminating or reducing foaming of the liquid within the reservoir and in minimising the volume of ink required to supply the reservoir.

One such apparatus is a chambered doctor blade printer such as described in US Patent No. 4590855.

One method of delivering printing ink is by means of a double diaphragm pump. However, this suffers the disadvantage that it delivers a pulsed flow of fluid. In some circumstances, this can be so serious a problem that it is necessary to install a shock blocker into the delivery line, and the addition of this equipment can materially increase the cost of the installation.

It is also known to utilise a peristaltic pump. Again, this delivers a pulsed flow of ink, although to a lesser extent than the double diaphragm pump. However, since the pump operates by rollers acting on a flexible pipe, the ink is subject to shear forces. Furthermore, should the pipe burst, the entire mechanism will be coated in printing ink which entails a lengthy shutdown for cleaning. Finally, such a pump has many moving parts subject to wear and therefore requiring frequent replacement. A more commonly used form of printing ink pump is a centrifugal pump. This is simpler and cheaper than the pumps mentioned above, but subjects the ink to cavitation and shear forces, and causes foaming of the ink.

This is true even of solvent based inks, but with water based inks the problem is considerably worse.

It is an object of the present invention to provide a pump, especially for use with printing inks, which overcomes the above disadvantages and enables a smooth flow of foam free ink to be delivered.

According to the present invention, there is provided a pump for ink as defined herein, comprising first chamber means, ink intake means connected thereto via first valve means, second chamber means connected to the first chamber means via second valve means, ink outlet means connected to the second chamber means, and pressure varying means operatively connected to the first chamber means and adapted either so to reduce pressure in the first chamber means that ink is taken into the first chamber means through the intake means, or to raise pressure therein so that ink is delivered from the first chamber means to the second chamber means and thence to the ink outlet means.

The first valve means of the intake means and the second valve means between the first and second chambers means may each be a check valve, adapted to permit flow only into the first chamber means and only into the second chamber means, respectively. Preferably, the ink outlet means is provided with flow regulating means.

Advantageously, the flow regulating means is an adjustable flow control valve.

The pressure varying means preferably comprises a pneumatically operated vacuum generator, such as a venturi tube.

A common compressed air supply may then be applied operatively either to the vacuum pump to reduce pressure in the first chamber means or directly to the first chamber means to raise pressure therein.

The first chamber means may be provided with an upper ink level sensor means and a lower ink level sensor means.

Control means may then be adapted so that the pressure varying means is switched from its pressure reduction mode to its pressure-raising mode when the level of ink in the first chamber means rises to the level of the upper ink level sensor.

The control means may further be adapted so that the pressure varying means is switched from its pressure-raising mode to its pressure reduction mode when the level of ink in the first chamber means falls below the level of the lower ink level sensor.

The second chamber means may be provided with baffle means separating inlet means from the first chamber means from the ink outlet means. The pump may be provided with additional inlet means through which cleaning media may be introduced into the pump, particularly into the chamber means thereof.

The pump may be mounted to a frame, optionally to a wheeled frame for ease of movement.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which:-

Figure 1 shows a front elevation of a pump system embodying the invention; Figure 2 is a side elevation of the system; and Figure 3 is a plan view thereof.

Referring now to the drawings, there is shown a transportable pump system which comprises a first, upper ink chamber 1 and a second, lower ink chamber 2. A first inlet check valve 3 is mounted to,an underside, in use, of the upper ink chamber 1, and an inlet pipe 4 is detachably mounted to the first check valve 3. In the embodiment shown, the inlet pipe 4 is inserted into a tub 5 of ink 6. The pump system may be used with a range of sizes and forms of ink containers, with an appropriate connector (for example a flexible hose) substituted for the inlet pipe 4 shown.

The upper ink chamber 1 and the lower ink chamber 2 are connected via a second check valve 7. An outlet pipe 8 is provided with a flow control valve 9 and a connection piece 10, by which it may be connected to a device requiring a supply of ink. A control box 11 contains control equipment for controlling a compressed air supply to supply air either to an air-operated vacuum generator, such as a venturi tube or orifice plate, or to an upper part of the upper ink chamber 1. A solenoid valve directs compressed air from the supply either to the vacuum generator, in which case "vacuum", pressure reduction, is applied to the upper ink chamber, or directly to the upper ink chamber, so that increased pressure, typically at 4 bar, is applied thereto. Connector 22 supplies the compressed air at 4 bar and alternately applies vacuum to the upper chamber 1. (The details of the compressed air supply and, the vacuum generator are omitted from the drawings for clarity). An upper ink level sensor 12, preferably in the form of a float valve, and a lower ink level sensor 13 , preferably in the form of a tuning fork level switch, within the upper ink chamber 1 each sends its output signal to the control equipment.

The "tuning fork" level switch 13, relies on a difference between the density of air and that of ink. As the prongs of the tuning fork become exposed, the vibration frequency changes to indicate a low level of ink, when the control system reverts to application of vacuum. Hence the sensor is independent of the exact density or colour density of the ink to determine a switching level.

In operation, compressed air is initially supplied to the vacuum generator, which causes a reduction in air pressure within the upper ink chamber 1 to draw ink 6 from the tub 5 through the inlet pipe 4 and the first check valve 3 into the upper ink chamber 1, as shown by arrow 14. The second check valve 7 remains closed, so ink accumulates in the upper ink chamber 1, passing the level of the lower level sensor 13, until it reaches the level of the upper float valve or other level sensor 12. At that point, the control equipment switches the compressed air supply from the vacuum generator to the upper chamber 1 to increase the pressure therein. The first check valve 3 closes and ink ceases to flow into the upper chamber 1. The increased air pressure in the upper chamber 1 now causes the second check valve 7 to open and ink flows into the lower ink chamber 2, as shown by arrow 15.

The lower chamber 2 is supplied with air at a pressure of 2 bar - half that supplied to the upper chamber 1 - by means of inlet 20, which also contains a pressure relief valve (not shown) set at 2 bar. A float valve 21 is fitted to the inlet 20 to prevent back flow of ink at a pressure greater than 2 bar.

With the check valve 7 open, the lower chamber 2 then fills with ink under pressure of 4 bar in the first chamber. The flow control valve 9 may now be opened to a desired setting, allowing ink to flow out of the lower chamber 2, through the exit pipe 8 and the connecting piece 10, to a printing apparatus. A baffle 16 within the lower chamber 2 prevents a direct flow of ink from the upper chamber 1 to the exit pipe 8 and ensures that turbulence does not affect the outflow.

As ink is pushed from the upper chamber 1 to the lower chamber 2, the level of ink in the upper chamber 1 falls, until it passes the level of the lower level sensor 13. In response to its signal the control equipment shuts off the compressed air supply to the upper chamber 1 and redirects it again to the vacuum generator, which once more lowers the pressure in the upper chamber. The second check valve 7 thus closes, preventing flow of ink and/or air back from the lower chamber 2 to the upper chamber 1, while the first inlet check valve 3 opens, allowing further ink to enter the upper chamber 1 from the tub 5.

Meanwhile, the air pressure within the lower chamber 2 provides sufficient energy to continue to drive ink out of the lower chamber 2 at a substantially constant flow rate as permitted by the flow control valve 9. The additional supply of compressed air at a pressure of 2 bar provided to the second lower chamber maintains the air pressure therein as the ink flows out.

The upper chamber 1 refills with ink, as described above, until the ink level once more reaches the upper level sensor 12. The upper chamber 1 is then once again pressurised, and ink flow from the upper chamber 1 to the lower chamber 2 is re-established.

The rate at which the upper chamber 1 refills with ink is substantially greater than that at which ink may be delivered through the flow control valve 9. The proportion of the pump's operating cycle during which the upper chamber 1 is being replenished is thus relatively small, and an almost steady state is achieved during the remainder of the cycle with ink flowing from the upper chamber 1 into the lower chamber 2 and out of the lower chamber 2 through the flow control valve 9. At any stage of the cycle, the pressure exerted on the ink in the lower chamber 2 is sufficient to push it through the flow control valve 9 at the desired constant rate. The ink delivery is thus almost totally isolated from the pressure changes in the upper chamber as it fills and then empties. The process does not involve shear forces on the ink, and therefore a steady supply of non-foamed ink may be delivered.

The pump system described does not require large amounts of compressed air for its operation. It has been found that at an airflow of 7-8 ft³/min, the system should deliver approximately 10 litres/minute of ink.

The pump system may be emptied after use by turning the compressed air supply to the upper chamber 1 full on, until substantially all ink from the upper chamber 1 is driven into the lower chamber 2 and thence out through the exit pipe 8. The control box 11 may have settings for "RUN", "OFF" and "EMPTY". On "EMPTY", the lower level sensor 13 is disabled, and the system may be washed out by replacing the tub 5 of ink with a container of cleaning fluid and running the pump as described above. Alternatively, for a more thorough cleansing, cleaning fluid may be introduced to either or each chamber 1,2 through a cleaning inlet 17 connected to an upper face of each chamber 1,2 via a corresponding manual valve 18. In this case, the pump is not operated, and the used cleaning fluid is drained out of the pump under gravity through the exit pipe 8.

The pump system is conveniently mounted to a wheeled trolley 19 so that it may be transported between the printing machines to be fed with ink. It is alternatively envisaged that such a pump system could be permanently attached to such a machine. While the above description refers throughout to compressed air and to atmospheric pressure, it is clear that, if necessary (for example with highly flammable solvent-based inks and the like) an inert gas could be substituted for air. References above to "air" should be interpreted accordingly.

Similarly, although the pump system described is particularly suited to pumping inks, paints, varnishes and the like, it may also find use with other industrial process fluids with similar requirements for being pumped without foam generation.

Claims

1. ' A pump for ink as defined herein, comprising first chamber means, ink intake means connected thereto via first valve means, second chamber means connected to the first chamber means via second valve means, ink outlet means connected to the second chamber means, and pressure varying means operatively connected to the first chamber means and adapted either so to reduce pressure in the first chamber means that ink is taken into the first chamber means through the intake means, or to raise pressure therein so that ink is delivered from the first chamber means to the second chamber means and thence to the ink outlet means.

2. A pump as claimed in claim 1, wherein the first valve means of the intake means and the second valve means between the first and second chamber means may each be a check valve, adapted to permit flow only into the first chamber means and only into the second chamber means, respectively.

3. A pump as claimed in either claim 1 or claim 2, wherein the ink outlet means is provided with flow regulating means, preferably an adjustable flow control valve.

4. A pump as claimed in any one of the preceding claims, wherein the pressure varying means comprises a pneumatically operated vacuum generator, such as a venturi tube.

5. A pump as claimed in claim 4, wherein a common compressed air supply may be applied operatively either to the vacuum generator to reduce pressure in the first chamber means or directly to the first chamber means to raise pressure therein.

6. A pump as claimed in any one of the preceding claims, wherein the first chamber means is provided with an upper ink level sensor means, preferably a float valve, and a lower ink level sensor means, preferably a tuning fork type sensor.

7. A pump as claimed in claim 6, further comprising control means adapted so that the i pressure varying means is switched from its pressure reduction mode to its pressure- raising mode when the level of ink in the first chamber means rises to the level of the upper ink level sensor.

8. A pump as claimed in claim 7, wherein the control means is further adapted so that the pressure varying means is switched from its pressure-raising mode to its pressure reduction mode when the level of ink in the first chamber means falls to the level of the lower ink level sensor.

9. A pump as claimed in any one of the preceding claims wherein the second chamber means may be provided with baffle means separating inlet means from the first chamber means from the ink outlet means.

0. A pump as claimed in any one of the preceding claims further comprising additional inlet means through which cleaning media may be introduced into the pump, particularly into the chamber means thereof.