GB2111638A

GB2111638A - Two-mass vibrating system

Info

Publication number: GB2111638A
Application number: GB08235194A
Authority: GB
Inventors: Heimo Macenka
Original assignee: Binder and Co AG
Current assignee: Binder and Co AG
Priority date: 1981-12-10
Filing date: 1982-12-09
Publication date: 1983-07-06
Also published as: GB2111638B; YU271682A; JPS58104814A; ATA529781A; ZA828825B; DE3245223A1; AT370642B

Abstract

A vibrating screen, an oscillating conveyor or anything similar is resiliently supported on a counter-weight 1 which is resiliently supported against a supporting structure or foundation 3. The structure of the counter-weight 1 encloses at least one cavity, filled with loose granulated compound (2) or a mix of granulated compound with a permanently viscous binding agent, the proportion by weight of the empty structure to the material filling the cavities being 1:0.2 to 1:3, preferably 1:2 to 1:2.5. At the operating frequency the granular material forms part of the counter-weight but on passing through the resonance after the drive has been cut off the acceleration separates the granular material from the floor of the cavity and this changes the resonance frequency and effects damping. <IMAGE>

Description

SPECIFICATION Two-mass vibrating system The invention relates to a two-mass vibrating system, especially a vibrating screen, an oscillating conveyor or anything of the sort, in which a mass serving as a counterweight is resiliently supported against a supporting structure or a foundation and a utility mass, for instance a vibrating screen, is resiliently supported against the counterweight.

Such a system, which is used with a frequency higher than its resonance frequency, has become known through DE-PS 2 121 539. Two-mass vibrat- ing systems, which are operated above their first resonance frequency have the disadvantage, after the turn-off of the drive, that they run out in resonance. After the turn-off of the drive the amplitude of the utility - mass multiplies. These big amplitudes put a very big stress on each component of the vibrating system, which is why the components have to be designed stronger than actually would be necessary. Also, these big amplitudes during running down, especially with oscillating conveyors, cause material to be conveyed. This is especially a disadvatange, when a quick turn - off because of an accident or a malfunction of the conveyor has become necessary.Stationary parts, which belong to the whole system, of which the vibrating screen or the oscillating conveyor is a part, have to be fitted far enough from the utility mass, so as not to destroy each other.

To reduce the amplitudes of the utility mass, while running through the resonance area to a manageable size, it has been proposed to connect the counter - weight with the supporting structure through several shock absorbers.

While constructing the system, one has to keep in mind that the counter - weight should swing only with small amplitudes at the operating frequency of the system, so as to keep the losses in the shock absorbers down.

An essential disadvatage of this kind of absorption of vibrations is that, because of the large amplitudes of the vibrating system which arise while the drive is running down on reaching its natural frequency, considerable dynamic loads build up which affect the supporting system.

The shock absorbers, usually hydraulic, are prone to malfunction. So, a small leak leads to a drastic reduction af its function, or may even leave it without function.

l:there is a reduction of the effectiveness of only one of the shock absorbers, the whole system starts to vibrate uncontrolled at this position, whereby considerable damage can occur.

Because of the reasons stated, shock absorbers have to be checked and changed quite frequently in systems which are constructed in accordance with DE-PS 2 121 539.

It was the main aim of the invention, to propose a two - mass vibrating - system, which by its construction, has a sufficient damping in the area of resonance, to suppress dangerous high amplitudes of the utility mass, and which can do without extra equipment, such as shock absorbers, or brakes which influence the drive, which themselves are prone to malfunction.

The invention achieves this, in that the structure of the counter - weight encloses at least one cavity, filled with loose granulated compound or a mix of granulated compound with a permanently viscous binding agent, with the weight proportions of the empty counter - weight structure to the material filling the cavity or cavities being 1:0.2 to 1:3, preferably 1:2 to 1:2.5. The binding agent should preferably show a viscosity of 1000 cp (1 Pass), to have a high absorbing effect At operating frequency the counter - weight usually swings only with a small amplitude, and the acceleration which acts on the counter - weight is comparatively small and is less than the acceleration due to gravity. The granulated compound lies on the floor of the cavity and there is no particular relative movement between the granulated compound and the counter - weight.At operating frequency the granulated compound and the structure of the counter - weight act as one mass or at least as if connected.

If the amplitude of the counter - weight rises, because of getting nearer to the resonance frequency, the acceleration act on the counter - weight rises and exceeds the acceleration of gravity. So the granulated compound loses contact with the floor of the cavity and is taken out of free fall.

Energy is thereby withdrawn from the vibrating system and it is damped. From the moment of the lift - off of the granulated compound until the impact onto the ceiling of the cavity a reduction of the mass of the counter - weight, which determines the resonance frequency, takes place, as a result of which the resonance frequency consistantly changes and so a distinct build up of vibrations of the counter - weight is prevented.

By using this two-mass vibrating - system, the advantage is, that the damping is ineffectual during the normal operation and so no extra energy input is needed, but is increasingly effective when running through resonance areas afterthe drive is turned off, the larger the amplitudes get. Also, this construction does not need any specific control or servicing and there is no danger of the damping suddently failing.

Following a further feature of this invention, it is intended, that the granulated compound should have a pellet size less than 10 mm and a bulk weight of 1.5 to 3 vim3, preferably a pellet size of 1 to 5 mm and a bulk weight of 1.8 to 2.3 t/m3, with which more energy can be absorbed when passing through resonance areas than otherwise.

It is especially advantageous, when the filling percentage of every cavity is 50-95%, preferably 70-80%. In this context it is extremely advantageous, if the pellet form is of a shellyfracture.

The invention will now be further explained with reference to the drawing, in which Fig. 1 and 2 show a vibrating screen according to the invention in front elevation and profile, and Fig. 3 and 4 are sections of a chamber of a counter - weight during normal operation and while operating in the resonance area.

The counter - weight 1 is supported through springs 7 on a foundation, and is mainly made up of two hollow longitudinal boxes, connected by their end faces, which are subdivided into several cham bers by partitions. On counter - weight 1 a vibrating screen 4 is supported through springs 5. Four unbalanced masses 6 driven in counter - rotation are used as vibrators, and are connected to each other and to a drive motor 9 by Cardan shafts 8. It is obvious, that the drive of two of the unbalanced masses does not derive directly from a shaft po wered by a Cardan shaft, but through a gear which reverses the sense of rotation.

As you can see in Fig. 3 and 4, the chambers of the hollow longitudinal boxes of counter - weight 1 are partly filled with granular material 2 giving a filling percentage of 95%, as shown.

The percentage of filling does not have to be as great as this and can lie substantially below, for instance at 50%. The filling material, for instance sand, should have a suitable bulk weight of 1.8 to 2.3 tlm3 and a pellet size of less than 10 mm, with a preferable pellet form a shelly fracture. The relation of the masses of the structure of the counter - weight to its filling should be about 1:2 so that, as soon as the granulated compound 2 lifts off from the floor of the cavity of the counter - weight 1, a noticeable difference in the mass of counter - weight 1 occurs, thus influencing the value of mass for the resonance frequency.As you can see from Fig. 3, accelerating forces which are less than gravitational forces, act on the vibrating screen at the operating frequency, which is above the resonance frequency of counter weight 1, so that the granulated compound 2 stays on the floor of the chambers of the longitudinal boxes and is, so to speak, connected with them.

If, while running through the resonance area of the coupled masses of the granulated material 2 and the counter - weight 1, greater vibrations of the counter weight occur, then the accelerating forces acting on the granulated compound 2 increase and the granulated compound 2 begins to lift off the floor of the chambers of the longitudinal boxes (Fig. 4). So the temporary effective mass of counter - weight 1 changes and also its resonance frequency.

Also the mass of the granulated compound 2 bounces from floor to ceiling of the chamber. So from the vibrating system, which is running down, energy is absorbed to break and decelerate the granular material 2. The effect is, that a high degree of damping is achieved.

Claims

1. Two-mass vibrating system, especially a vibrating screen, an oscillating conveyor or anything similar, in which a mass used as a counter - weight is resiliently supported against a supporting structure or a foundation and a utility mass, for instance a vibrating screen is resiliently supported on the counter - weight, characterized in that the structure of the counter-weight encloses at least one cavity, filled with loose granulated compound or a mix of granulated compound with a permanently viscous binding agent, with the weight proportions of the empty structure to the material filling the cavity or cavities being 1:0.2 to 1:3, preferably 1:2 to 1:2.5.

2. Vibrating system according to claim 1, characterized by a binding agent, which has a viscosity in the area of 1030 cp (1 Pa.s).

3. Vibrating system according to claim 1 or 2, characterized by a granulated compound, which has a pellet size of less than lOmm and a bulkweight of 1.5 to 3t/m3 and a preferable pellet size of 1 to 5 mm and a preferable bulkweightofl.8to 2.3 t/m3.

4. Vibrating system according to claim 1 to 3, characterized by a pellet form of shellyfracture.

5. Vibrating system according to claim 1 to 4, characterized in that the hollow chambers (or chamber) of the counter - weight are filled to 50 to 95%, preferably 70 to 80%, with granulated compound.