FIELD OF THE INVENTION

The present invention relates to an apparatus for discharging fine material, such as fiber stock, wood chips or sawdust from a silo or a similar device via an aperture or apertures in the bottom of the silo.

BACKGROUND OF THE INVENTION

Some prior art solutions for discharging material from the bottom of a silo employ a transport screw turning about the center axis of the silo and extending radially from the wall of the silo to a discharge opening in the center of the bottom. The turning movement can be brought about for example, as disclosed in Finnish patent specification no. 51325, by a hydraulic device disposed at the outer end of the transport screw and communicating with a geared step ring provided outside the silo.

Other prior art solutions for discharging material from the bottom of a silo have discharge arms fixed to a drive shaft disposed centrally in the silo which arms are arranged to move material to a discharge opening or openings of the silo while the shaft rotates. The discharge arms are arranged to be rotated continuously to the same direction or to be moved to and fro by a motor or a hydraulic device. An example of this kind of an apparatus is disclosed in Finnish patent specifation no. 47328.

Finnish patent application no. 874889 discloses a discharge apparatus for a silo, comprising a double-ended discharge arm pivoted in an excentric pin of a drive shaft disposed centrally in the silo. The movement of the discharge ^■ arms is controlled by pins provided at the ends of the discharge arms and by pins disposed at the bottom portion

of the silo by means of which rollers are caused to move, when the drive shaft rotates, along a substantially epicycloidal path around the pins thus forcing the discharge arm in a slow "sawing" turning movement.

DISCLOSURE OF THE INVENTION

The object of the invention is to provide an improvement in apparatus having a discharge arm or arms disposed rotatable about the center axis and to move along the bottom of a silo.

An apparatus according to the invention is mainly characterized in that the discharge arm is double-ended and that the movement of the discharge arm is guided by means provided in the ends of the arm and by counter surfaces disposed in the silo and by two cylinders acting on the center of the discharge arm and being disposed substantially perpendicular in relation to each other, so as to move the ends of the arm alternately in the peripheral direction.

In a preferred embodiment of the invention the cylinders are arranged to operate alternately in such a way that one of the cylinders is hydraulically locked with the piston arm in the retracted position or in the extended position while the other cylinder performs a pushing or a pulling motion. The ends of the arm are preferably provided with rollers moving at the outer side of projections from one space between the projections to another, the projections being disposed at the bottom edge of a skirt connected to the wall of the silo.

The most important advantage provided by the discharger of the invention is that the drive means of the discharger is remarkably cheaper than the prior art rotating means. As no rotatable drive shaft is needed also the devices required

for bearings, lead-through and sealing of the shaft and for transmission of the torque are dispenced with.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail, by way of example, with reference to the accompanying drawings in which

Fig. 1 is a plan view of an embodiment of the invention ;

Fig. 2 is a section along line A-A of Fig. 1;

Fig. 3 is a section along line B-B of Fig. 1; and

Fig. 4 is a section along line C-C of Fig. 1.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT

In the figures which illustrate a typical structure according to the invention, the reference numeral 1 refers to a bottom portion of a silo having a cylindrical wall 2 and a planar bottom 3, the bottom having two discharge apertures 4. A skirt 5 is connected to the wall 2 the lower edge of which skirt is formed by adjoining inverted castellations or projections 6 disposed at a distance from each other. The openings between the projections are referred to by reference numeral 7.

A double-ended or double-limbed discharge arm 8 is provided at the bottom of the silo. Rollers 9 and 10 are disposed at the ends and on top of the arm. There is a round hole 11 in the center of the discharge arm and a spherical bearing 12 in the hole 11. The top end of a movable shaft 13 provided under the bottom 3 is pivoted in the spherical bearing. The lower end of the shaft 13 is pivoted in a spherical bearing 16 provided in a lever 15 journalled in a support 14 fixed to the bottom.

Two hydraulic cylinders 17 and 18 disposed substantially in opposite positions relative to each other under the

silo are journalled at their rear ends to the bottom of the silo. A piston arm 19 of the cylinder 17 is connected to a connecting piece 20 provided with a spherical bearing 21 through which the movable shaft 13 passes and to which said shaft has been pivoted. A piston arm 22 of the cylinder 18 is pivoted to the connecting piece 20.

There is a hole 23 in the bottom through which the movable shaft 13 passes. A cover 24 moving with the discharge arm 8 covers the hole.

The apparatus according to the invention operates in the following way:

Stage I: Cylinder 17 is hydraulically locked with the piston arm in the retracted position. Cylinder 18 pushes. Roller 10 lies nearly still between the projections 6. Roller 9 moves at the outer side of the projections substantially in the peripheral direction.

Stage II: Cylinder 18 is hydraulically locked with the piston arm in the extended position. Cylinder 17 pushes. Roller 10 is released from the guidance of the projections 6. Roller 9 moves substantially radially inwards to be guided between the projections 6.

Stage III: Cylinder 17 is hydraulically locked with the piston arm in the extended position. Cylinder 18 pulls. Roller 10 moves at the outer side of the projections 6 substantially in the peripheral direction. Roller 9 lies nearly still between the projections 6.

Stage IV: Cylinder 18 is hydraulically locked with the piston arm in the retracted position. Cylinder 17 pulls. Roller 10 moves substantially radially outwards away from the guidance of the projections 6.

While one of the cylinders is locked alternately in the retracted position or in the extended position and functions as an oscillating arm and the other cylinder pushes or pulls the center of the discharge arm moves around the center of the bottom of the silo along an almost square path.

The invention is not limited to the embodiment described here but it can be modified within the scope of protection defined by the patent claims. Thus the movement of the discharge arm can be guided with the cylinders in such a way that its center moves along a circular path whereby the rollers at the ends of the arm move along an almost epicycloidal path.

The projections can be located in the bottom of the silo as in Finnish patent application no. 881926, Fig. 2.