WO1994007783A1

WO1994007783A1 - A method and a vibration feeder for metering bulk goods

Info

Publication number: WO1994007783A1
Application number: PCT/DK1993/000320
Authority: WO
Inventors: Kim Kristian Davidsen
Original assignee: Skako A/S
Priority date: 1992-10-02
Filing date: 1993-10-04
Publication date: 1994-04-14
Also published as: DK121292D0; AU5148693A

Abstract

A method and a vibration feeder (1) serve to meter bulk goods, such as concrete, fibres, granulates and stone. The vibration feeder comprises a feet trough (7) and at least one vibrator (10) secured on it as well as a plurality of screw springs (13) for flexibly suspending the trough (7) from a supply container (2). A frame (14) is interposed between the supply container and the screw springs (13), said frame being tiltably mounted on the supply container (2) by means of pivots (17) and brackets (18). The feed trough (7) can be caused to assume desired angular positions by means of a drive cylinder (26) which is connected partly with the frame (14), partly with the supply container (2). This means that one and the same vibration feeder (1), even in a restricted size, can work at a considerable metering rate, since the feed trough (7) is then placed in a relatively inclined position. At the end of the metering process the feed trough (7) is rotated up to a slightly inclined, horizontal or negatively inclined position, as desired, whereby the metered amount can be adjusted with great accuracy.

Description

A method and a vibration feeder for metering bulk goods

The invention concerns a method of metering bulk goods, such as concrete, fibres, granulates and stone, by means of a vibration feeder which comprises a feed trough and at least one vibrator secured on the feed trough as well as a plurality of carrier springs, e.g. screw springs, for flexibly mounting the trough on a support, said bulk goods being fed to the feed trough from a supply container arranged above it.

Vibration feeders are extremely suitable for metering bulk goods which are filled from e.g. an overlying supply con¬ tainer down into the feed trough. In operation the bulk goods are then thrown slightly upwards and forwards in the feed trough for each vibration cycle and are transported in this manner forwardly to the end edge of the trough at a rate which depends on the amplitude and frequency of the vibrations. These parameters can be regulated to a certain degree for some vibrators, but only to a limited extent.

For reasons of economy and quality it would be desirable in many cases if the bulk goods could be metered both quickly and economically.

This applies e.g. to the pouring concrete in a mould which should preferably be filled as quickly as possible owing to the production yield, while it is also necessary that the mould is filled completely. If this is not the case, the casting will not be complete and will not obtain the intended quality. If, conversely, too much concrete is metered, this results .. a waste of materials and difficulty in the subsequent removal of the excess concrete from the mould and the surroundings. It is therefore of utmost importance that the mould is filled with a carefully metered quantity of concrete.

However, conventional vibration feeders are not capable of satisfying the speed requirement and the accuracy require- ment at the same time.

Thus, if primary importance is attached to speed, this necessarily means that a suitably big and thus expensive vibration feeder has to be selected. The size in turn means that such a vibration feeder has a correspondingly great capacity, e.g. transports a large amount of bulk goods which are discharged from the end edge of the feed trough per time unit. When metering is to be interrupted, this typically takes place by stopping the vibrators. How- ever, a certain period of time elapses before the trough and the bulk goods in it have come to rest. During this period of time, which is not exactly the same each time, the bulk goods continue running beyond the end edge of the trough, but at a decreasing rate. Therefore, the metered flow of bulk goods cannot be stopped abruptly and precisely when metering is to be interrupted, but only be brought to an end within a tolerance range which increases with increasing capacity.

Instead a relatively small and inexpensive vibration feeder may be selected, by means of which a satisfactory metering accuracy can be obtained much more easily, but now at the expensive of the capacity. If it is attempted to force up the capacity by filling the feed trough with a large amount of bulk goods, these will frequently tend to pack in the feed trough, which frequently results in a considerable reduction in the metering accuracy. In some case the bulk goods may even pack so densely as to clog up the trough, whereby the vibrators might be damaged, and products for which the metered material were to be used, might be destroyed. Once a trough has become clogged up with bulk goods, a not insignificant amount of manual labour is usually required to subsequently loosen and optionally remove the packed bulk goods.

The German Offenlegungsschrift DE 3700270 Al discloses a pivotable trough for transferring granular bulk goods from a supply container to an underlying conveyer. Changing the inclination of the pivotable trough so that its discharge end is directly above the conveyer obviates the previous drawback of dust formation when the bulk goods fall down on the conveyer. When the flow of bulk goods is to be stopped, the pivotable trough is pivoted upwards so that an edge in the outlet from the supply container is lowered into the bulk goods and blocks the flow thereof. This structure does not solve the problem of economically filling e.g. a mould both quickly and accurately.

Accordingly, there is a need for a method of the type men¬ tioned in the opening paragraph which can meter bulk goods from a supply container more quickly and accurately than known before with a relatively small and inexpensive vibration feeder.

This is achieved by the novel and unique features of the invention which are that the feed trough is initially placed in a position of such a great angle that the bulk goods are transported along the feed trough at a great rate, and then in a position of such a small angle that the bulk goods are transported along the feed trough at a small rate.

By means of this method the bulk goods can now be metered quickly and accurately and at relatively low vibrator feeder investment costs. The reason is that the process initially takes place as a rough sorting where gravity is employed to a considerable extent for rapidly filling e.g. a mould, and then the angular position of the feed trough is diminished so much that the bulk goods are substantial¬ ly transported in the feed trough by means of its vibrat¬ ing movements. This switches the feed trough to fine metering which ensures accurate filling of the mould, and at the same time it is just necessary to dimension the vibration feeder for the relatively modest capacity which fine metering requires. It is therefore possible to use a small and inexpensive vibration feeder for filling of bulk goods amounts which previously required much larger vibra¬ tion feeders and/or much greater space of time for the filling.

The invention also concerns a vibration feeder for meter- ing bulk goods, such as concrete, fibres, granulates and stone, and comprising a feed trough and at least one vibrator secured on the feed trough as well as a plurality of carrier springs, e.g. screw springs for flexibly mount¬ ing the trough on a support, and the novel and unique fea- tures of this vibration feeder are that a frame is inter¬ posed between the vibration feeder and the carrier springs, and that the frame is tiltably arranged on the support and can be caused to assume at least two diffe¬ rent, preselected angular positions with respect to it by means of at least one actuator which is connected partly with the frame, partly with the support.

If the vibration feeder, like in the example previously mentioned, is to be used for filling a mould with con- crete, this can now take place in the manner that the feeder is first tilted to a suitable, obliquely downwardly extending angular position where gravity assists the vibration forces applied simultaneously. The bulk goods will therefore partly almost slide down the feed trough and fill the mould in a short time. Then the feed trough is tilted up to another less inclined or horizontal posi- tion in which the metering is-terminated at a small rate and a correspondingly great accuracy. If during filling the concrete should tend to pack in the trough, this can easily be remedied by increasing its inclination.

The actuator may e.g. be a linear motor, but in a pre¬ ferred embodiment it is a pneumatic or hydraulic drive cylinder which may optionally be in the form of a rotary cylinder. If a known, repeating process is involved, it will be advantageous if the angular positions of the trough are determined by means of fixed stops.

If the actuator is e.g. a pneumatic drive cylinder, it is possible that the air pressure fails, so that the tilting movement of the trough will get out of control. This, how¬ ever, is prevented by at least one zero position spring, e.g. a leaf spring, which is connected at one end with the frame and at the other with the support and is biased in a manner such that the frame is forced into its starting position if the air pressure fails and the pneumatic drive cylinder is consequently rendered inoperative.

In very common arrangement the feed trough is located below a lower opening in a supply container for the bulk goods. The supply container hereby acts as a support for the frame, which is tiltably suspended by means of pivots arranged at the respective sides of the supply container in the vicinity of its lower opening.

The invention will be explained more fully by the follow¬ ing description of an embodiment, which just serves as an example, with reference to drawing, in which

fig. 1 is a perspective view of a vibration feeder accord- ing to the invention suspended from a supply container and having a conveyer belt located below the discharge end of the feeder,

fig. 2 is a lateral view of the vibration feeder shown in fig. 1 with the feed trough in an upper angular position, and

fig. 3 is a view of the same, but with the feed trough in a lower angular position.

In figs. 1, 2 and 3 the vibration feeder is generally designated by the reference numeral 1. The vibration feeder is suspended from a supply container 2, which consists of an upper portion 3 and a lower portion 4 which are assembled by means of flanges 5 screwed together with a plurality of screws (not shown). Downwardly the supply container has a lower opening 6 through which the bulk goods (not shown) to be metered can run out to be received by the underlying feed trough 7 of the vibration feeder. The feed trough is reinforced by stiffeners 8 and upper flaps 9. A vibrator 10, which serves to vibrate the vibration feeder, is rigidly connected with the feed trough 7 by means of an attachment 11. A conveyer belt 12 is located below the discharge end of the feed trough to convey the metered material in the direction indicated by the arrow. The feed trough 7 is suspended freely pivotably from a frame 14 by means of four screw springs 13. This frame consists of two opposed side members 15 which are connected by two transverse members 16. Each side member 15 is tiltably suspended from the lower portion 4 of the supply container 2 by means of a pivot 17 and a bracket

18. The screw springs 13 are inserted between the frame 14 and the upper flaps 9 of the feed trough 7 and are secured to the respective parts by means of screws 19, 20. Further, two leaf springs 21 are interposed between the frame 14 and the lower portion 4 of the supply container 2, each of said leaf springs being secured to the lower portion 4 by means of a bracket 22 and extending into a slot 23 in one of the transverse members 16 of the frame 14. Further, the lower portion 4 of the supply container 2 mounts a bracket 24 which, by means of pivots 25, pivot- ably carries a drive cylinder 26 having a piston rod 27 whose outer end is connected with another bracket 28, which is in turn rigidly connected with the frame 14. Further, a first stop boss 29 and a second stop boss 30 are provided on respective sides of the lower portion 4 of the supply container 2 to fix an upper feed trough tilted position and a lower feed trough tilted position, respec¬ tively.

When a batch of bulk goods (not shown) is to be metered for a process, e.g. concrete to be poured into a mould, a suitable amount of the respective bulk goods is placed in the supply container 2, from which it drops down into the feed trough via the lower opening 6 of the container. At this time the feed trough 7 is in a vibrating state, since it is vibrated by the vibrator 10 and is suspended freely pivotably from the springs 13. The vibrations propagate to the bulk goods which are placed in the feed trough 7, and which are therefore transported in small jumps upwards and forwards to the discharge end of the feed trough, from which the bulk goods successively drop down on the con¬ veyer belt 12 which conveys the bulk goods further on to the location of use.

If fast metering is desired, the feed trough 7 is rotated by means of the drive cylinder 26 to the lower position of fig. 3 in which the frame 14 abuts the second stop boss 30. In this position the bulk goods will rapidly be driven out from the feed trough under the simultaneous action of gravity and vibration forces. During the last phase of the metering the frame 14 is rotated by means of the drive cylinder 26 up to the position of fig. 2 in which the frame 14 abuts the first stop boss 29. In this position the bottom of the feed trough 7 is substantially horizon¬ tal, and the bulk goods present in the feed trough are therefore just subjected to vibration forces. This means that the bulk goods can be discharged from the end edge of the feed trough only slowly, thereby making it possible to cut off the flow of material relatively accurately when the vibrator 10 is stopped.

The vibration feeder of the invention can thus work with great capacity as well as with great accuracy during a metering process.

It was assumed in the above example that the feed trough 7 could tilt between a lower fixed position in which meter¬ ing took place at a great rate, and an upper fixed posi¬ tion in which metering took place with a great accuracy. Of course, this is just to be understood as an example of the how the feed trough 7 can be caused to assume posi- tions which are compatible with the requirement that the vibration feeder is to have a great capacity and also is to be able to work with great accuracy.

Instead of fixed stops for determining the angular posi- tions of the feed trough 7, these may be determined selectively by means of a programmable control (not shown) of the drive cylinder 26 or another suitable actuator. Thus, the angular positions may describe a pattern where the trough is initially present in a steeply inclined position and is gradually rotated up to a position of negative inclination at the end of the metering, where gravity and vibration forces neutralize each other so that metering automatically stops. For example concrete can be poured into a mould in this manner in an even very accu- rately metered amount. In the embodiments of the vibration feeder of the inven¬ tion shown by way of example in figs. 2 and 3 the actuator consists of a pneumatic cylinder 26, which may be sub¬ jected to air failure. In this case the feed trough 7 is no longer under control, and it can therefore by itself pivot into positions which may have unfortunate conse¬ quences. To avoid this the two prebiased leaf springs 21 are provided, which always try to urge the feed trough 7 back to its upper angular position in which the frame 14 engages the first stop boss 29.

The vibration feeder of the invention may be used for many different purposes extending from pouring of concrete to metering of e.g. fibres, sand, gravel, pebble, limestone, and rock. In the last-mentioned case difficulties have often been encountered in rock or limestone quarries when conventional vibration feeders are used, since materials of this type tend to get wedged between the sides of the feed trough. This problem is easily remedied by means of the vibration feeder of the invention, whose feed trough is then merely rotated to suitably inclined position.

Claims

P a t e n t C l a i m s:

1. A method of metering bulk goods, such as concrete, fibres, granulates and stone, by means of a vibration feeder which comprises a feed trough and at least one vibrator secured on the trough as well as a plurality of carrier springs, e.g. screw springs for flexibly mounting the trough on a support, said bulk goods being fed to the feed trough from a supply container arranged above it, c h a r a c t e r i z e d in that the feed trough is initially placed in a position of such a great angle that the bulk goods are transported along the feed trough at a great rate, and then in a position of such a small angle that the bulk goods are transported along the feed trough at a small rate.

2. A vibration feeder for metering bulk goods, such as concrete, fibres, granulates and stone, and comprising a feed trough and at least one vibrator secured on it as well as a plurality of carrier springs, e.g. screw springs, for flexibly mounting the trough on a support, c h a r a c t e r i z e d in that a frame is interposed between the support and the carrier springs, and that the frame is tiltably arranged on the support and can be caused to assume at least two different, preselected angu¬ lar positions with respect to it by means of at least one actuator, which is connected partly with the frame, partly with the support.

3. A vibration feeder according to claim 2, c h a r a c ¬ t e r i z e d in that said at least one actuator is a pneumatic or hydraulic drive cylinder.

4. A vibration feeder according to claim 2 or 3, c h a ¬ r a c t e r i z e d in that the preselected angular posi- tions are determined by means of fixed stops.

5. A vibration feeder according to claims 2, 3 or 4, c h a r a c t e r i z e d in that it includes at least one zero position spring, e.g. a leaf spring, which is connected at one end with the frame and at the other with the support and is biased in a manner such that the frame is forced into its starting position if said at least one actuator fails.

6. A vibration feeder according to one more of claims 2- 5, wherein the feed trough is located below a lower open¬ ing in a supply container for the bulk goods, c h a ¬ r a c t e r i z e d in that the frame is tiltably sus- pended from the supply container by means of pivots which are arranged on their respective sides of the supply con¬ tainer in the vicinity of its lower container.