Metering valve

The present invention concerns an apparatus for gravimetric dosing of powder material from a container. These kinds of powder materials include among others different substances of mortars and fillers These materials have in practice especially difficult flowing properties, whereby they do not flow easily out of the container under gravity, and in case they flow, the mass flow is quite uneven, caused e.g. by the tendency of the material to bridging into the discharging part of the container. This kind of a discharging part is in general the funnel-shaped lower part of a cylinder-shaped storage container, having in its lower portion the discharge aperture for the material, extending downwards.

For providing a more even and secure flow of the material from the funnel-shaped portion in question, the Finnish patent publication No 80430 proposes a construction of a discharge hopper, wherein there are elements provided onto the inner walls of the bottom hopper, through which pressurized air can be led among the material to be discharged. These elements can be weld-fixed plates or plates attached in other ways.

In this way it has been discovered that the material brought into a fluidized condition flows from the hopper substantially as an even flow without problems with the formation of bridges. In these kinds of constructions known in the art, the flow is regulated by means of a control valve located in the discharge aperture, said valve being e.g. a rotary flap valve known in the art. In that case the valve has a flap corresponding to the cross section of the discharge aperture, the flap being rotated about a rotation axis defined by the diagonal diameter of the discharge aperture. With big flow amounts this control valve has proven to operate on a quite satisfactory level.

The dosing with the rotary flap valve is performed so that the rotary flap valve closing the aperture on the bottom of the container opens by rotating about its turning point or turning points and thus releases the material in the container to flow onto a lower level caused by the gravity. This lover level is usually a weighing appliance. The weighing appliance to be used can be meant for continuous weighing

or batch weighing. For example weigh containers are suitable for weighing of powdered or granular materials and fluids. Fields of application include e.g. the metallurgic industry, chemical industry, food processing industry and building material industry.

A problem with the appliances of prior art has been in achieving an adequate dosing accuracy. An improvement for the above mentioned problem has been provided by means of the apparatus in accordance with the present invention, said apparatus comprising, as known in the art, a container and a valve located in a flow channel of material flowing through a discharge aperture of the container, said valve being provided for opening and closing the flow channel and comprising a flow aperture and a shutter movable with a sliding tolerance back and forth in the aperture. According to the basic idea of the invention, the shutter is a plug, movable in the perpendicular direction with respect to the plane of the aperture, and having a length in the flow direction of the valve and an envelope surface forming a sliding surface equivalent to the periphery of the aperture and having on its sliding surface at least one groove expanding in the flow direction of the valve, said groove having a clearance that is in each position of the plug in the flow aperture bigger than the respective opening of the flow aperture.

Special embodiments of the invention are included in the dependent claims of the enclosed set of claims.

The invention will be described in more detail in the following, with reference to the enclosed drawings, wherein

Figure, 1 shows the apparatus in accordance with the present invention as one practical application,

Figure 2 is a more detailed general view of the apparatus of the invention,

Figure 3 is a detailed view of the operational phases of one valve to be used in the apparatus of the present invention, and

Figure 4 illustrates the detailed construction of the shutter of the valve of Figure

3.

Figure 1 shows a schematic view of the lower part of a container 1 for powder material, convergent downwards to a discharge cone having at its lower part a flow ^' • opening for the material to be discharged from the container. In the implementation shown in the figure, a discharge pipe is connected to the flow opening, said pipe being further connected to an inclined flow pipe 7. To the lower end of this flow pipe there is connected a device forming the core of the apparatus according to the present invention for opening and closing the material flow, respectively controlling the flow, denoted in the figure with general reference 8. Essential parts of this device include a valve seat comprising a flow aperture 2 and a plug 3 located in the flow aperture 2.

In the illustrated embodiment, the plug 3 has substantially a cylindrical form and it has a predetermined axial length. The diameter of the plug is dimensioned so that the plug can be moved with a sliding tolerance in the aperture 2. A groove 4 is formed in the envelope surface of the plug 3. The groove 4 starts at or close to the upper edge of the plug. The aperture 2 can be closed with the plug 3 when pressed into its lower position. The groove 4 is formed so that it expands downwards. The expansion can be implemented as shown in the figure as a widening and deepening form, or in some cases as a groove widening only in the circular direction downwards, having a certain depth. The cross-section of the deepening groove 4 can have the form of a circular arc, some other arc form, or a sharp-edged form, like V- form. The groove extends preferably as a regular form, expanding in the predetermined form until the lower edge of the plug 3. For the design of the groove 4 it is essential, that the clearance of the groove downwards from the aperture 2 plane is in all open positions of the plug bigger than the opening the groove exposes above the aperture 2 plane, from which (primary opening) the material to be discharged flows to the groove. The flowing path expanding in the flow direction through the whole valve is especially important with powder materials. Even a small contraction can cause the collapsing of the flow state and the bridging of the material eventually blocking the flow path, or at least disturbing essentially the flow.

Especially significant this problem is with materials that must be kept in a fluidized condition by using fluidization measures.

In the situation illustrated in Figures 1 and 2, the flow aperture 2 of the apparatus 8 is closed, when the plug 3 is in its lower position, and the aperture is secured with a gasket 9. The situation is illustrated in the enclosed Figure 3, phase c). When lifting the plug from the aperture, the upper part of the groove 4 is released over the edge of the aperture 2, whereby the material flow can be started (Figure 3, phase b), when the primary flow opening is opened. By adjusting the depth position of the plug in the aperture 2 the flow can be adjusted as desired. Even the full flow is possible so that the plug releases the whole aperture 2. Correspondingly, by pressing the plug downwards, the flow aperture can be reduced controllably, maintaining the form of the primary flow opening.

The motion of the plug 3 in the aperture 2 can be provided by of a suitable actuator 10, by means of a shaft 11. The actuator can be controlled to provide a stepless motion or motion in predetermined steps. The motion can have steps of the same length or changing progressively or regressively depending on the operational needs. Also the stepless regulating motion can be implemented accelerating/decelerating depending on the application.

Unlike in the embodiment shown in the figures, where the plug 3 is solid, it can be implemented as a tube construction, as a hollow sleeve. In that case the groove 4 in the wall of the sleeve is formed as a split widening towards the lower edge of the plug.

The plug can also be provided with a plurality of grooves 4, and not only the one shown, for example two or more, located on the opposite sides of the plug. A plug with one groove has however, certain flowtechnical advantages in the present embodiment, where the material to be dosed is in general difficultly flowable, and constructions enabling precise additional functions are required from the apparatus for maintaining the fluidity. It is advantageous to have a smooth flowing path to the primary opening from the parts of the flowing path upstream the primary opening, as illustrated in connection with the embodiment with the flow pipe 7.

For achieving and maintaining the fluidized condition of the material, it is substantial to have fluidizing equipment 5 in the lower part of the container, as well as the corresponding equipment 12 in the flow pipe 7. By means of this equipment, the above mentioned gaseous medium like air is blown to the material.

Significant for the operation of the apparatus is that the flow of the material to be discharged through the flow aperture released by the groove 4 of the plug 3 is as undisturbed as possible. For providing and maintaining this flowing condition with materials that are difficultly flowable, the apparatus includes inflow channels 13, through which suitable fluidizing medium, primarily air, can be blown to the flowing material immediately before the flow aperture 2. In many applications it is advisable to install vibrating means 6 beside these inflow channels in connection with the flow aperture 2.

By means of the apparatus in accordance with the invention, the dosing flow from the container 1 can be controlled by following different modes of operation according to the need. In batch dosing, the apparatus ensures the unproblematic fine- adjustment of the flow at the ending stage of the dosing. On the other hand, by choosing the position of the plug 3 in the flow aperture 2 the apparatus can be made to operate in predetermined batches in the optimal flow range of the material. The apparatus is also suitable for controlling the continuous flow of material.

In addition to the cross-sectional form of a circular cylinder, the plug 3 can also be implemented with some other kind of a cross-sectional form, like polygon form, without departing from the scope of the invention.