EP0358632B1 - Screening device - Google Patents

Description

The invention relates to a sieve device with at least two frame systems which can be moved relative to one another, with grate bars assigned to each system, which engage in pairs and are connected by flexible sieve elements which are attached to them and bridge the distance between the bars and which are connected by means of a means exclusively to the two systems stored and caused by a drive in rotation eccentric shaft relative movement of the two systems can be tensioned and relaxed.

Such a screening device is described in German Patent No. 1 206 372. The eccentric shaft is arranged in the middle of the screen length and the two systems are stabilized against each other by springs. However, this known device does not meet the expectations placed on it.

From DE-A-32 14943 a vibrating sieve has become known in which a box containing at least one sieve bottom and elastically supported at its ends in the area of one of its oscillation centers with a vibrator in the form of an arranged in the longitudinal center plane of the box and provided with an imbalance Shaft is connected.

This creates an uneven vibration field, both across and lengthwise, which causes an intensive loosening of the screenings layer. However, this type of construction cannot be transferred to the screening device mentioned at the outset, in which two frames which swing against one another are provided, the grate bars of which are connected to one another by means of flexible screening elements.

The invention aims to provide a screening device which is simple in construction, inexpensive to operate and has a long service life. Above all, however, it should perform well. According to the invention this is achieved in a screening device of the type mentioned in the introduction in that the eccentric shaft is arranged at one end of the two systems and this at the other end or at a distance therefrom by means of an element which ensures an essentially linear relative movement of the two systems to one another, such as handlebars , Pushing rubber blocks and the like, are connected to one another.

If the eccentric shaft is arranged at the end of the material feed side, the handlebar or handlebar-like connection ensures that the systems initially perform circular vibrations which gradually take the form of ellipses and in the area of the handlebars take the form of a flat circular arc or a straight line. The desired decrease in the vibration effect is achieved in the design according to the invention without further assistance. This also results in the avoidance of unnecessary drive energy, so that a high level of efficiency is achieved.

If the handlebars or the like are moved closer to the eccentric shaft, the frame systems on the screen material discharge side again describe elliptical vibrations, which may be desirable for certain screen material.

It is particularly expedient if the links or the like are arranged in the region of the acceleration pole of the vibration system. In most cases, the distance between the eccentric shaft and the handlebars or the like can be about 60-80% of the screen length.

In the drawing, the subject matter of the invention is shown in an exemplary embodiment. 1 shows the screening device in a side view and partially in section, FIG. 2 shows a cross section, FIG. 3 shows a section along the line III-III in FIG. 1 and FIG. 4 shows a body to which a force acts eccentrically.

The screening device has a first frame system 1, which is supported by spring elements 2 on the foundation or machine frame, not shown. An eccentric shaft 3 is by means of the bearings 4 in the frame system 1 and their Eccentric 5 guided in bearings 6, which are connected to the second frame system 7. 2, the frame system 7 is connected to grate bars 8 which pass through an opening 9 in the frame system 1 and are screwed to the web of the frame 7. The opening 9 is covered on the inside by means of a disk 10 which moves with the system 7.

As can be seen from FIG. 2 below, the frame 1 is also screwed to the grate bars 11, the grate bars 8 and 11 alternating.

At the end of the material discharge side, the two systems 1 and 7 are connected to one another by means of spring links 12. Due to the vibration of the two systems to one another caused by the eccentric shaft, the screen elements 13 are alternately tensioned and relaxed between the grate bars 8 and 11. The mutual relative movement in the longitudinal direction of the screen elements 13 is 2e if e is the measure of the eccentricity of the shaft 3.

By arranging a weight 14 on the eccentric shaft 3, the extent of the oscillating movement of the system 1 in the region of the eccentric shaft can be influenced favorably. For example, can be achieved that the system vibrates almost exclusively parallel to the screen surface, the amplitude being sufficient for self-cleaning of the system 1.

The invention can have yet another embodiment, the physical basis of which is explained with reference to FIG. 4.
4 shows a body K whose center of gravity is P _o . The force _F starts at a point P _F , whereby the body K is given a tangential acceleration a _t and an angular acceleration α around the center of gravity P _o .

$${\text{a}}_{\text{n}}\text{=}\frac{\text{F·S}}{\text{J₀}}\text{r}$$

$${\text{a}}_{\text{t}}\text{=}\frac{\text{F}}{\text{m}}$$

Hiebei bedeuten:

r =

Abstand des Massenpunktes P₁ vom Schwerpunkt P_o

M =

das von der Kraft F hervorgerufene Drehmoment um den Schwerpunkt P_o.

s =

Abstand der Kraft F vom Schwerpunkt P_o

J_o =

Massenträgheitsmoment des Körpers K, bezogen auf den Schwerpunkt P_o

m =

Masse des Körpers K

Die Tangentialbeschleunigung a_t ist für alle Massepunkte des Körpers K gleich groß und gleichgerichtet.The following calculation results for the two accelerations at an arbitrary mass point P 1: $${\text{a}}_{\text{n}}\text{= α · r α =}\frac{\text{M}}{\text{J₀}}\text{M = F · S}$$

$${\text{a}}_{\text{n}}\text{=}\frac{\text{F · S}}{\text{J₀}}\text{r}$$

$${\text{a}}_{\text{t}}\text{=}\frac{\text{F}}{\text{m}}$$

Hiebei mean:

r =

Distance of the mass point P₁ from the center of gravity P _o

M =

the torque caused by the force F around the center of gravity P _o .

s =

Distance of the force F from the center of gravity P _o

J _o =

Mass moment of inertia of the body K, based on the center of gravity P _o

m =

Body mass K

The tangential acceleration a _t is of the same size and the same direction for all mass points of the body K.

The normal acceleration of the mass points increases with the distance from the center of gravity P _o and is perpendicular to the connecting line center of gravity P _o - mass point. For the mass points, which lie in a plane E perpendicular to the force F and passing through the center of gravity P _o , it is parallel to the tangential acceleration a _t . To the left of the center of gravity P _o the normal acceleration is rectified and to the right of it the tangential acceleration.

$$\text{X =}\frac{\text{J₀}}{\text{ms}}$$

Handelt es sich um einen gestreckten Körper mit konstantem Querschnitt und der Länge l, so ist $${\text{J}}_{\text{o}}\text{= m}\frac{\text{ℓ²}}{\text{12}}$$

Ist der Abstand der Kraft F vom Schwerpunkt $${\text{P}}_{\text{o}}\text{S =}\frac{\text{l}}{\text{2}}$$

so ist $$\text{X =}\frac{\text{l}}{\text{6}}$$

There is therefore a point in plane E where the tangential acceleration and the normal acceleration cancel each other out. The acceleration pole P _B is located at this point. Its distance from the center of gravity P _o is X: $$\frac{\text{F · S}}{\text{J₀}}\text{X =}\frac{\text{F}}{\text{m}}$$

$$\text{X =}\frac{\text{J₀}}{\text{ms}}$$

If it is an elongated body with a constant cross-section and length l, then $${\text{J}}_{\text{O}}\text{= m}\frac{\text{ℓ²}}{\text{12th}}$$

Is the distance of the force F from the center of gravity $${\text{P}}_{\text{O}}\text{S =}\frac{\text{l}}{\text{2nd}}$$

so is $$\text{X =}\frac{\text{l}}{\text{6}}$$

If the handlebars 12 or the like are arranged in the region of the acceleration pole, restoring forces acting damping on the drive are eliminated, as a result of which the required drive power is reduced. From the feed side of the screen to the acceleration pole, the system has an accelerating effect on the screened material. From the acceleration pole to the end of the sieve there is an increasing delay of the material to be sieved, so that there is a longer dwell time on the sieve for the sieving of the boundary grains and thus a better sieving in this grain size range.

The mass of the material to be sieved on the sieve can also be taken into account in the determination of the acceleration pole by including the mass of the material to be sieved in the calculation of the moment of inertia around the common center of gravity.

Claims (5)

1. A screening device having at least two frame systems (1, 7) movable relative to one another, with grate bars (8, 11) associated with each system, which engage in one another in pairs and which are connected by flexible screening elements (13) which are secured to the grate bars, span the gap between the bars and are tightened and slackened by the relative movement of the two systems brought about by means of an eccentric shaft (3) mounted exclusively on the two systems and caused to rotate by a drive unit, characterised in that the eccentric shaft (3) is disposed at one end of the two systems (1, 7) and the latter are connected with one another at the other end or at a distance therefrom by means of a member (12) which ensures a substantially linear relative movement of the two systems with respect to one another, such as control rods, rubber thrust blocks etc.
2. A screening device according to Claim 1, characterised in that the eccentric shaft (3) is disposed at the end on the delivery side of the material being screened.
3. A screening device according to Claim 1 or 2, characterised in that the eccentric shaft (3) is provided with a counterweight (14).
4. A screening device according to Claim 1, 2 or 3, characterised in that the distance between the eccentric shaft (3) and the member (12), which ensures a substantially linear relative movement of the two vibrating systems (1, 7), with respect to one another, corresponds approximately to the distance of the acceleration pole (P_B) of the systems from the eccentric shaft.
5. A screening device according to Claim 4, characterised in that the distance is 20% to 40% smaller than the screen length.

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