GB2466705A

GB2466705A - Paint mixing device having a viscometer

Info

Publication number: GB2466705A
Application number: GB0922459A
Authority: GB
Inventors: Monika Renner; Thilo Koeder
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-12-30
Filing date: 2009-12-22
Publication date: 2010-07-07
Also published as: CN101766970A; GB0922459D0; DE102008055179A1

Abstract

Paint mixing device 10 comprises a stirring apparatus which can be driven by a motor 24 and has at least one stirring element 32 for intimately mixing paint 12, wherein a viscometer 30 is provided for determining the viscosity of the paint 12. The viscometer 30 may be a rotational viscometer and both the viscometer 30 and the stirring apparatus may be driven by the same motor 24. The stirring element 32 and viscometer 30 may be formed separately with a clutch 28 provided to couple and uncouple the rotational movement of a drive train.

Description

Paint mixing device The present invention relates to a paint mixing device comprising a stirring apparatus which can be driven by a motor and has at least one stirring element for intimately mixing paint.

Paint mixing devices of this kind are already known in the prior art in various configurations. They are normally used to blend desired shades from a plurality of paints.

Furthermore, it is often necessary to thin a paint to a predetermined degree before it is used, as is particularly important in the case of spray applications, for example.

For this purpose a thinning agent is added to the paint which is to be thinned and then mixed with the paint using the stirring apparatus. The viscosity of the composition is then detected by measurement techniques. If the viscosity corresponds to the desired viscosity, then the thinning operation is concluded. However if the viscosity remains higher than desired, then the steps described previously must be repeated until the desired viscosity is obtained.

A viscosity cup is normally used at present to determine the viscosity by measurement techniques, this ending conically at the bottom in a hole with an accurately defined diameter. In order to carry out a measurement, paint is poured into the viscosity cup and the length of time which is needed for the paint to flow off is measured.

The viscosity of the paint can then be determined by calculation on the basis of the cup capacity, the hole diameter and the measured length of time.

A significant disadvantage of this viscosity measuring method lies in the fact that it is very time-consuming. In addition, paint must be removed from the paint container in order to pour this into the viscosity cup, which involves a significant expenditure and also makes it more difficult to automate the viscosity measurement. Furthermore, it is frequently necessary to move the paint mixing device away from the paint container in order to be able to take paint out of the paint container, which is likewise linked with additional expenditure.

An object of the present invention is to provide a paint mixing device which enables paint to be thinned to a predetermined degree without any problems or a high expenditure of time and preferably in an automated manner.

In order to achieve this object, the present invention provides a paint mixing device of the type initially mentioned which has a viscometer for determining the viscosity of the paint as an integral component. Therefore it is possible both to intimately mix paint and to determine its viscosity with the device according to the invention, so that it is not necessary to carry out paint sampling in order to determine the viscosity in a viscorneter provided separately.

The viscometer is preferably a rotational viscometer with a test element which can be driven by a motor. The test element is rotated in the paint in order to detect the viscosity, with the torque required for rotation being measured. The dynamic viscosity of the liquid can then be determined on the basis of the detected torque and of the geometry of the test element and its rotational speed.

Generally speaking, separate drives can be used for the stirring apparatus and the viscometer. However a single motor is preferably provided to drive both the stirring apparatus and the rotational viscometer, as a result of which costs can in particular be saved.

According to one configuration, the stirring element and the test element are formed integrally. For this purpose extensible stirring elements, for example, can be provided on the test element, these enabling the paint to be intimately mixed in the extended state.

The stirring element and the test element are alternatively formed separately, in which case a clutch is provided in order to couple and uncouple the rotational movement of a drive train, in particular the rotational movement of the stirring element.

The clutch can be, for example, a free-wheel clutch, in the case of which both the stirring element and the test element are driven in a first direction of rotation, whereas just the test element is rotated in the other direction of rotation. It is alternatively also possible to use a centrifugal clutch, in the case of which just the test element is rotated at low rotational speeds, whereas both the stirring element and the test element are driven at higher rotational speeds. For this purpose the motor can be provided with two speed stages, for example. The use of change-speed gearboxes is also conceivable.

An evaluation unit is preferably provided, this being formed such that a quantity of a thinning agent to be added can be calculated on the basis of a viscosity measurement which has been carried out. A user can accordingly receive instructions as to how much thinning agent still has to be added to the paint in order to obtain the desired viscosity.

It is of advantage to provide a thinning agent receptacle with a metering mechanism for the metered delivery of a thinning agent contained in the receptacle, so that the addition of the calculated quantity of thinning agent can be automated.

The paint mixing device is preferably formed such that it can be positioned on a paint container and/or fastened to such a paint container. For this purpose the paint mixing device can have a base plate, for example, which is simply placed from above on the edge of a paint container.

The paint mixing device preferably also comprises an operating unit which has, for example, input means in the form of keys and output means in the form of a display, so that a user can input instructions and read out information.

The subclaims as well as the following description of an embodiment, with reference to the accompanying drawings, are to be referred to with regard to further configurations of the invention. In the drawings Figure 1 is a schematic view of a paint mixing device according to an embodiment of the present invention; Figure 2 is a perspective view of the stirring element and the measurement element of the paint mixing device which is represented in Figure 1 and Figure 3 is a scaled-up sectional plan view of the arrangement which is represented in Figure 2, showing a clutch structure for transmitting a torque from the motor to the measurement element and/or the stirring element.

Figure 1 shows a paint mixing device 10 which is positioned on a paint container 14 filled with paint 12. The paint mixing device 10 comprises a base plate 16 with a downward projecting circumferential rim 18, which embraces the top edge of the paint container 14, so that the paint mixing device 10 is secured to the paint container 14. A thinning agent receptacle 20 containing thinning agent 22, such as, for example, water or the like, is fastened to the top side of the base plate 16. A motor 24 is disposed in the thinning agent receptacle 20, which motor is likewise fastened to the base plate 16 and is sealed with the aid of sealing means, which are not represented in detail, so that the thinning agent 22 is prevented from penetrating. The shaft 26 of the motor 24 is connected to a clutch 28, via which a torque generated by the motor 24 can be transmitted to a test element 30, which dips into the paint 12, of a rotational viscometer 31, which otherwise is not represented in detail, and/or to a stirring element 32, which dips into the paint 12, of a stirring apparatus 33, in order to drive these in a rotational manner. An evaluation unit 34 is provided in order to calculate the viscosity of the paint 12 contained in the paint container 14 and to calculate a quantity of the thinning agent 22 to be added to the paint 12 on the basis of a viscosity measurement which has been carried out. A metering mechanism 36 in the form of a valve is also disposed in the thinning agent receptacle 20 in order to automatically deliver the calculated quantity of thinning agent into the paint container 14. An operating unit 38 is in addition positioned on the top outside of the thinning agent receptacle 20, which unit can have, for example, input means in the form of keys and output means in the form of a display.

According to Figure 2, the stirring elements 32 consist of two bent stirring rods which are retained at the top at the clutch 28 and at the bottom at a support ring 40, which serves to stabilise the stirring elements 32. The substantially cylindrical test element 30 of the rotational viscometer extends centrally between the stirring elements 32. In this arrangement care must be taken to ensure that the distance between the test element 30 and the stirring element 32 is sufficiently large, so that a viscosity measurement carried out with the aid of the test element 30 is not impaired by the stirring elements 32 of the stirring apparatus.

The clutch 28 is a free-wheel clutch, which is represented in greater detail in Figure 3. The shaft 26 of the motor 24 is connected to an annular inner part 42 in a rotationally rigid manner. Accommodation spaces 44 are formed at regular intervals along the outer circumference of the inner part 42, in which spaces roller-shaped clamping elements 46 are accommodated, these being pressed lightly with the aid of springs 48 against an outer ring 50 of the clutch 28, just one of the springs 48 being represented for the sake of simplicity. If the shaft 26 of the motor 24 now rotates in the direction of the arrow 52, the clamping elements 46 will become wedged in their accommodation spaces 44. As the accommodation spaces 44 taper away from the springs 48, the torque which is being transmitted increases the further the inner part 42 is rotated with respect to the outer ring 50.

The outer ring 50 is accordingly rotated together with the shaft 26 of the motor 24 as from a predetermined torque, so that both the test element 30 and the stirring elements 32 are driven in a rotational manner. If, on the other hand the shaft 26 is rotated in the opposite direction by the motor 24, the clamping force produced by the clamping elements 46 will not be sufficient to drive the outer ring together with the shaft 26. Just the test element 30 is accordingly rotated.

Should a paint 12 contained in the paint container 14 be thinned to a predetermined degree using the thinning agent 22 contained in the thinning agent receptacle 20, for example for a subsequent spray application, a desired viscosity as well as the quantity of paint (for example in litres) contained in the paint container 14 are input in a first step by a user via the operating unit 38. Afterwards the actual viscosity of the paint 12 is detected by rotating the test element 30 of the rotational viscometer in the paint 12. The torque which is required for driving the test element 30 is measured during the rotation. The dynamic viscosity of the paint 12 is determined on the basis of this torque and of the geometry of the test element 30 and the rotational speed. A quantity of the thinning agent 22 to be added is then calculated in the evaluation unit 34, taking account of the established actual viscosity as well as the quantity of paint contained in the paint container 14, and automatically delivered into the paint container 14 via the metering mechanism 36.

In order to mix the added thinning agent 22 with the paint 12 contained in the paint container 14, the stirring elements 32 of the stirring apparatus are subsequently driven in a rotational manner for a predetermined length of time. As soon as a homogeneous intimate mixture is obtained, a viscosity measurement is once more carried out as has been described above. Should the actual viscosity then established correspond to the desired viscosity, then the paint thinning operation is concluded. Should the actual viscosity still exceed the desired viscosity, then the steps described previously are repeated. With regard to the desired-actual comparison, it is of course possible to define limit values within which deviations are admissible or inadmissible.

It should be obvious that a centrifugal clutch or the like can also be used instead of the free-wheel clutch. It should also be obvious that separate motors can also be provided to drive the test element 30 and the stirring elements 32. Furthermore, the test element 30 and the stirring elements 32 can also be formed as a unit. Thus the stirring elements can, for example, be disposed in an extensible manner on the test element such that they allow the paint contained in the paint container to be properly intimately mixed in the extended state.