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CIRCULATION APPARATUS FOR A LIQUID MIXTURE OF SUBSTANCES IN A CONTAINER

20210347182 · 2021-11-11

    Inventors

    Cpc classification

    International classification

    Abstract

    The invention relates to an apparatus for circulating a liquid mixture of substances, for example a solution, emulsion or suspension, between a container and a pressure-sensitive component which is supplied from the container, for example for circulating an ink between an ink storage container and a print head of a printing system, comprising a pump, which allows the liquid mixture of substances to circulate in the container through an external conduit circuit, a Venturi tube, the main conduit of which is connected into the external conduit circuit, and also a conduit which connects the output connection of the pressure-sensitive component to the suction connection of the Venturi tube.

    Claims

    1. An apparatus for circulating a liquid mixture of substances (5) that is stocked in a container (2), for example a solution, emulsion or suspension, comprising a circulation pump (7), which allows the liquid mixture of substances (5) to circulate in the container (2) through an external conduit circuit (6), so that a separation is prevented within the container (2), even if a mechanical stirring device is not arranged in said container; characterized by a) a Venturi tube (11), the main conduit of which (12, 13) is connected into the external conduit circuit (6); as well as b) a line (15) which connects an output connection (16) of the pressure-sensitive component (4) to the suction connection (14) of the Venturi tube (11).

    2. The apparatus according to claim 1, characterized in that the external conduit circuit (6) is not closed via the pressure-sensitive component (4), rather is closed directly, i.e., constitutes virtually a bypass to the pressure-sensitive component (4).

    3. The apparatus according to claim 1, characterized in that the conduit circuit between the container (2) and the pressure-sensitive component (4) is not closed via the circulation pump (7), but constitutes a bypass to the circulation pump (7).

    4. The apparatus according to one of claim 1, characterized in that the main conduit (12, 13) of the Venturi tube (11) is connected downstream of the circulation pump (7) into the external conduit circuit (6), in particular into the pressure conduit (9, 10) of the circulation pump (7).

    5. The apparatus according to claim 1, characterized in that the pressure-sensitive component (4) is supplied at the input connection (17) thereof from the container (2).

    6. The apparatus according to claim 1, characterized in that a return line from the pressure-sensitive component (4) to the container (2) is switched via the Venturi tube (11).

    7. The apparatus according to claim 1, characterized in that the circuit closed via the pressure-sensitive component (4) is free of pumps.

    8. The apparatus according to claim 1, characterized in that the flow within the circuit closed via the pressure-sensitive component (4) is maintained only via a pressure gradient, which can be attributed to the suction power of the Venturi tube (11).

    9. The apparatus according to claim 1, characterized in that a non-return valve (19) is provided in the suction line (15) between the output connection (16) of the pressure-sensitive component (4) and the suction connection (14) of the Venturi tube (11), which non-return valve prevents a reverse flow to the output connection (16) of the pressure-sensitive component (4).

    10. The apparatus according to claim 1, characterized in that a reducing device is provided in the suction line (15) between the output connection (16) of the pressure-sensitive component (4) and the suction connection (14) of the Venturi tube (11), in order to limit the flow quantity from the output connection (16) of the pressure-sensitive component (4).

    11. The apparatus according to claim 10, characterized in that the reducing device is embodied as an adjustable reducing valve (18).

    12. The apparatus according to claim 1, characterized in that the inlet and/or outlet line(s) (3, 8, 10) discharge(s) at the storage container (2) in the region of the housing base thereof.

    13. The apparatus according to claim 1, characterized in that a stirrer is not arranged in the storage container (2), rather that the storage container (2) is free of movable elements in the interior.

    14. The apparatus according to claim 1, characterized in that the circulation pump (7) is a continuously conveying pump, for example a membrane pump or propeller pump.

    15. The apparatus according to claim 1, characterized in that the container (2) is an ink storage container.

    16. The apparatus according to claim 1, characterized in that the pressure-sensitive component (4) is an ink print head.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0038] Additional features, details, advantages and effects based on the invention are yielded from the following description of a preferred embodiment of the invention as well as on the basis of the drawing, which shows:

    [0039] FIG. 1 A schematic tubing plan of an ink printing system according to the invention; and

    [0040] FIG. 2 An ink printing system according to the prior art.

    DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

    [0041] As a part of a printing system 1 according to the invention, an ink storage container 2 is provided, which supplies a print head 4 with ink 5 via a line 3.

    [0042] However, a stirring mechanism is not provided in the ink storage container 2. Instead, a separation of the ink 5 is prevented in that said ink is kept in continuous motion via an external circuit 6. A circulation pump 7 is used for this, which pump is connected via the suction line 8 thereof as well as via the pressure conduit 9, 10 thereof respectively with the ink storage container 2 so that the ink 5 circulates through the external circuit 6.

    [0043] In the pressure conduit 9, 10 of the circulation pump 7, in other words, downstream of same, a Venturi tube 11 is connected in so that the ink 5 circulating in the circuit 6 flows through it.

    [0044] The Venturi tube 11 consists of a smooth-walled tube piece, the inner lumen of which narrows at a point in the cross section, for example to 90% of the normal internal cross section of the tube or less, preferentially to 80% of the normal internal cross section of the tube or less, preferably to 60% of the normal internal cross section of the tube or less, in particular to 40% of the normal internal cross section of the tube or less, or even to 30% of the normal internal cross section of the tube or less. Even greater narrowings are conceivable, for example to 25% of the normal internal cross section of the tube or less, preferentially to 20% of the normal internal cross section of the tube or less, preferably to 15% of the normal internal cross section of the tube or less, in particular to 10% of the normal internal cross section of the tube or less.

    [0045] The narrowing of the cross section of the Venturi tube 11 can be effectuated for example by two opposing tube segments 12, 13, which are conical or which taper in another manner from the peripheral ends thereof towards the other ends thereof that face each other, and which are connected to each other at the point of the smallest diameter thereof. At this point, a third lateral connection 14 is provided, at which a negative pressure is applied during the operation of the Venturi nozzle 11, and which therefore should be designated as a suction connection 14.

    [0046] The Venturi tube 11 preferably has no other openings besides the peripheral discharges of its two tube segments 12, 13 and the suction connection 14, in other words, in the interior space, it is independent of the surrounding atmospheric pressure.

    [0047] The Venturi tube 11 should consist of a solid material, such as for example metal or a solid structurally stable plastic so that it is not deformed under the influence of a pressure difference between the external and interior space.

    [0048] In addition, the sheath of the Venturi tube 11 should be both liquid-tight so that no ink can escape, as well as gas-tight so that so, in the case of an internal negative pressure, neither air nor other gas can diffuse into the interior space.

    [0049] A further special feature of the invention is that the central, tapered region of the Venturi tube 11 should preferably lie at the same level as the two tube segments 12, 13. This can be effectuated for example in that the Venturi tube. 11 is aligned horizontally as shown in FIG. 1.

    [0050] The peripheral ends of the conical tube segments 12, 13 are connected into the pressure conduit 9, 10 of the circulation pump 7 and form the main conduit of the Venturi nozzle or of the Venturi tube 11. The suction connection 14 of the Venturi tube is connected via a suction line 15 with the outlet side connection 16 of the print head 4 so that the negative pressure with respect to the normal operating pressure at the inlet side connection 17 of the print head 4 causes a pressure difference, which results in a flow.

    [0051] In order to be able to adjust this pressure difference precisely to the value required by the print head 4 in question, a reducing device can be connected into the suction line 15. In doing so, this can be an adjustable reducing valve 18.

    [0052] Furthermore, the invention provides that a non-return valve 19 still be connected into the suction line 15 in order to prevent a backflow of ink in the suction line 15, even if the circulation pump 7 is turned off or fails.

    [0053] Because the pressure difference p.sub.A via the print head 4 from the height of the liquid level 20 of the ink 5 is in the ink storage and/or supply container 2, this container 2 can be operated without refilling as long as the lines 3, 8 do not dry out.

    [0054] The Bernoulli equation applies to the Venturi tube 11, wherein the index 1 refers to the parameters in the inlet connection or the tube segment 12, and index 2 refers to the parameters in the suction connection 14:


    (p.sub.1−p.sub.2)+p*g*(h.sub.1−h.sub.2)=½*p*v.sub.2.sup.2*[1−(A.sub.2/A.sub.1).sup.2],

    wherein p is the pressure at the respective location, h is the height at the respective location, A is the clear flow cross section at the respective location, v is the flow rate at the respective location, and p is the density of the ink and g is the gravitational acceleration,
    or:


    p.sub.2−=p.sub.1*g*(h.sub.1−h.sub.2)−½*p*v.sub.2.sup.2*[1−(A.sub.2/A.sub.1).sup.2];


    p.sub.2=p.sub.1+p*g*(h.sub.1−h.sub.2)−½*p*v.sub.2.sup.2*[1−(A.sub.2/A.sub.1).sup.2].

    [0055] If the height difference (h.sub.1−h.sub.2) is negligibly small, in other words, in particular if the Venturi tube 11 is aligned horizontally or if the dimensions thereof are small, the formula is simplified to:


    p.sub.2=p.sub.1−½*p*v.sub.2.sup.2*[1−(A.sub.2/A.sub.1).sup.2],

    [0056] In the following, it should be assumed that the density p of the ink is approximately 1 kg/dm.sup.3.

    [0057] Furthermore, is can be assumed that the pressure p.sub.1 in the case of a running circulation pump 7 is greater than the weight pressure p.sub.t at the base of the ink storage container 2 and also greater than the surrounding atmospheric pressure p.sub.a. In particular, the following applies with the pressure increase p.sub.z stemming from the power of the circulation pump 7:


    p.sub.1=p.sub.t+p*g*(h.sub.t−h.sub.1)+p.sub.z.

    [0058] The weight pressure p.sub.d at the inlet side connection 17 of the print head 4 is a function of the height h.sub.d of the inlet side connection 17 of the print head 4 in proportion to the height h.sub.t of the outlet at the base of the ink storage container 2:


    p.sub.d=p.sub.t+p*g*(h.sub.t−h.sub.d).

    [0059] However, a negative pressure p.sub.2 should be applied at the suction connection 14, such that at the outlet side connection 16 of the print head 4, a negative pressure p.sub.Δ<0 prevails with respect to the weight pressure p.sub.d at the inlet side connection 17 of the print head 4:


    p.sub.2=p.sub.d+p.sub.Δ=p.sub.t+p*g*(h.sub.t−h.sub.d)+p.sub.Δ,

    and specifically reduced by more than the difference p*g*(h.sub.2−h.sub.d):


    p.sub.2+p*g*(h.sub.2−h.sub.d)=p.sub.d+p.sub.Δ=p.sub.t+p*g*(h.sub.t−h.sub.d)+p.sub.Δ,

    [0060] In other words:

    [00001] ⁢ p 2 + ρ * g * ( h 2 - ⁢ h d ) = p t + ρ * g * ( h t - ⁢ h d ) + p Δ , ⁢ ⁢ p 2 = p t + ρ * g * ( h t - ⁢ h d ) - ρ * g * ( h 2 - ⁢ h d ) + p Δ , ⁢ ⁢ p 2 = p t + ρ * g * ( h t - ⁢ h 2 ) + p Δ . ⁢ ⁢ p 2 = p 1 - 1 2 * ρ * v 2 2 * [ 1 - ( A 2 A 1 ) 2 ] = p 1 + ρ * g * ( h t - ⁢ h 2 ) + p Δ . ⁢ p 2 = p t + ρ * g * ( h t - ⁢ h 1 ) + p z - 1 2 * ρ * v 2 2 * [ 1 - ( A 2 A 1 ) 2 ] == p t + ρ * g * ( h t - ⁢ h 2 ) + p Δ .

    [0061] If h.sub.1≈h.sub.2 is, the following applies:

    [00002] p 2 ≈ p t + ρ * g * ( h t - ⁢ h 2 ) + p z - 1 2 * ρ * v 2 2 * [ 1 - ( A 2 A 1 ) 2 ] == p t + ρ * g * ( h t - ⁢ h 2 ) + p Δ . ⁢ ⁢ p z - 1 2 * ρ * v 2 2 * [ 1 - ( A 2 A 1 ) 2 ] = p Δ . ⁢ ⁢ 1 2 * ρ * v 2 2 * [ 1 - ( A 2 A 1 ) 2 ] = p z - p Δ . ⁢ ⁢ v 2 2 * [ 1 - ( A 2 A 1 ) 2 ] = 2 * ( p z + .Math. p Δ .Math. ) ρ . ⁢ ⁢ v 1 2 * ( A 1 A 2 ) 2 * [ 1 - ( A 2 A 1 ) 2 ] = ( p z + .Math. p Δ .Math. ) * 2 ρ . ⁢ ⁢ v 1 2 * [ ( A 1 A 2 ) 2 - 1 ] = ( p z + .Math. p Δ .Math. ) * 2 ρ . ⁢ ⁢ [ ( A 2 A 1 ) 2 - 1 ] = ( p z + .Math. p Δ .Math. ) * 2 ( ρ * v 1 2 ) .

    [0062] Accordingly, the cross-section relationship (A.sub.1/A.sub.2) between the inlet 12 of the Venturi tube 11 and the suction connection 14 thereof can be determined in accordance with the above formula from the pump pressure p.sub.z of the circulation pump 7, the desired pressure difference p.sub.Δ via the print head 4 and the flow rate v.sub.1 in the supply line 12 taking the density p of the ink into account.

    [0063] Various modifications of the arrangement according to the invention are possible. In particular, various valves and/or cross section reductions can respectively also be inserted at another location of the circuit in question. In addition, according to this principle, a plurality of print heads of a printing system can also be connected to a common Venturi tube or every print head is connected to a separate Venturi tube.

    TABLE-US-00001 List of Reference Numbers 1 Printing system 2 Ink storage container 3 Line 4 Print head 5 Ink 6 Circuit 7 Circulation pump 8 Suction line 9 Pressure conduit 10 Pressure conduit 11 Venturi tube 12 Inlet side tube segment 13 Outlet side tube segment 14 Suction connection 15 Suction line 16 Outlet side connection 17 Inlet side connection 18 Reducing valve 19 Non-return valve 20 Liquid level 21 Printing system 22 Ink storage container 23 Line 24 Print head 25 Ink 26 Stirrer 27 Shaft 28 Housing