METHOD FOR COMPENSATING LEAKAGE LOSSES AND CONVEYOR SYSTEM FOR CONVEYING A DEFINED VOLUME OF A LIQUID

Abstract

A method and a device for compensating leakage losses in a line system, in which at least one positive displacement pump and at least one shut-off member are provided, wherein the method and device can be used for the isobaric metering of liquid plastic components and wherein the actual liquid pressure in the system is determined by way of a pressure measuring device and, when the shut-off member is closed is regulated to a pressure target value by actuation of the positive displacement pump, wherein the conveying loss rate of the positive displacement pump, which ensues to maintain the pressure target value when the shut-off member is closed is added to a target delivery rate in order to compensate for the leakage loss occurring at the corresponding pressure target value.

Claims

1-7. (canceled)

8. A method for compensating leakage losses in a line system for liquids having at least one positive displacement pump and at least one shut-off member, in particular in the at least largely isobaric metering of liquid plastic components, wherein an actual liquid pressure in the line system is ascertained by a pressure measuring device and is regulated to a pressure target value by actuation of the at least one positive displacement pump with the at least one shut-off member closed.

9. The method according to claim 8, wherein a conveying loss rate of the positive displacement pump which ensues to maintain the pressure target value when the at least one shut-off member is closed is added to a target delivery rate in order to compensate for the leakage loss occurring at the corresponding pressure target value.

10. The method according to claim 8, wherein the at least one positive displacement pump includes a rotary displacement machine.

11. The method according to claim 10, wherein the rotary displacement machine includes a geared pump.

12. The method according to claim 8, wherein the line system has a substantially constant volume at least between the at least one positive displacement pump and the at least one shut-off member.

13. The method according to claim 8, wherein in order to compensate for a thixotropic flow behaviour of the liquid the pressure target value with the at least one shut-off member closed is increased by comparison with the pressure target value during a conveying operation with the at least one shut-off member open.

14. The Method according to claim 13, wherein a regulation for raising and/or lowering the pressure target value takes place as a function of time in the manner of a PT1 element.

15. A conveyor system in particular for isobaric conveying of a definitive volume of a liquid per unit of time, in particular for metering a liquid plastic component, the conveyor system comprising a line system having at least one positive displacement pump and at least one shut-off member, as well as a pressure measuring device which ascertains an actual liquid pressure in the line system and a control system which acts on the at least one positive displacement pump as a function of the ascertained actual liquid pressure, including means for determining a conveying loss rate of the positive displacement pump with the at least one shut-off member closed to maintain a target liquid pressure in the line system and means for adding the conveying loss rate to a target delivery rate with the shut-off member open.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0013] The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail and illustrated in the accompanying drawing which form a part hereof and wherein the single FIGURE shows a conveyor system according to the invention on a dynamic mixer head for mixing polyurethane or silicone plastic components for the production of a foaming sealing material in a flow diagram.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] Referring now to the drawing wherein the showings are for the purpose of illustrating preferred and alternative embodiments of the invention only and not for the purpose of limiting the FIGURE shows a conveyor system 10 that serves for metering of two liquid plastic components A, B to a mixer head 11, in which the two components A, B are mixed together by means of a driven stirrer 12 in a precisely fixed quantitative ratio and are then discharged with an overpressure prevailing in the system by comparison with the ambient pressure as a reactive mixture via an outlet 13. Only as the mixture exits from the outlet is it subjected to the ambient pressure, i.e. the pressure in the interior of the mixer head is at least somewhat higher than ambient pressure. With such systems, for example, foaming seals are produced which are formed directly on a structural part.

[0015] A line system 14 of substantially the same construction is provided for each of the two components A, B. This system has a motor-driven geared pump 15 and a shut-off member 16 arranged on the mixer head 11 in the form of an electromagnetically switchable valve, by which the inlet for the respective component A, B into the interior of the mixer head can be opened or closed.

[0016] For starting of a metering operation the two valves 16 are opened, so that by means of the geared pumps 15 the components A, B are conveyed out of their respective storage containers 17 in the required mixing ratio and into the mixer head 11, where they are mixed together by the stirrer 12, whilst maintaining the pressure prevailing in the line system 14, and are then discharged via the outlet 13 as a reactive plastic mixture.

[0017] In order to compensate for leakage losses which occur in the line system 14 due to unexpected leaks, for example in the region of the pump 15, and which are represented in the schematic drawing by the arrows on the broken lines as Qv, the line systems 14 are in each case provided with a pressure measuring device 17 which ascertains the system pressure in the line system 14 with the valve 16 closed. This actual liquid pressure 18 is compared with a pressure target value 20 in a comparator 19. As soon as a pressure drop is detected, and thus the actual liquid pressure drops relative to the pressure target value, the geared pump 15 is actuated, even with the valve 16 closed, at a correspondingly lower conveying (loss) rate, in order to deliver to the line system 14 precisely the quantity lost from the system due to the leakage Qv.

[0018] This conveying loss rate which is produced by the pump 15 with a few revolutions per unit of time is also taken into consideration during the process of conveying to the mixer head with the shut-off member open, i.e. in order to compensate for the leakage losses Qv the geared pump is operated at such a speed that it withdraws from the storage container for the component concerned a mass flow which corresponds to the sum of the leakage loss Qv ascertained with the valve closed and the target delivery rate Qs of the component concerned. In this way the leakage loss is also taken into account during the metering of the components to the mixer head.

[0019] While considerable emphasis has been placed on the preferred embodiment(s) of the invention illustrated and described herein, it will be appreciated that other embodiments, and equivalences thereof, can be made and that many changes can be made in the preferred embodiment(s) without departing from the principles of the invention. Furthermore, the embodiment(s) described above can be combined to form yet other embodiments of the invention of this application. Accordingly, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.