CA2009076A1 - Drum screen - Google Patents

Abstract

Abstract The invention relates to a drum screen formed by a rotatable drum the shell surface of which is formed by parallel bars (2). Such screens are frequently clogged up when soil is wedged between the bars. In the invention some of the bars (2) are loose so that clods of earth wedged between the bars may be detached when the gap between the bars changes.
(Fig. 3)

Description

20~76 A drum screen The invention relates to a screen drum formed by a substantially cylindrical drum rotatable around its central axis, the shell surface of the drum being formed by parallel bars disposed side by side and at-tached at the ends to drum ends.
Screens of the above type are used for screen-ing various soil types, such as gravel and earth. The drum is typically about 2 to 4 m long while the dia-meter is about 2 m. It is mounted on bearings dis-posed in its ends, so that it can be rotated about its central axis by means of a motor. Soil to be screened is introduced into the drum through its one end by means of a conveyor. Depending on the type of the soil to be screened, the width of the gap between the bars is typically in the range of about 2 to about 5 cm.
A major problem with this kind of screens is that they clog up easily. Wet soil in particular in-termittently clogs up the gaps between the bars, so that the drum has to be cleaned up, which is carried out manually and therefore requires plenty of labour.
The ob;ect of the present invention is to pro-vide a drum screen in which the gaps between the bars do not clog up as easily as in prior art screens. The drum screen according to the invention is character-ized in that some of the bars are attached to the drum ends in such a way that they are movable over a short distance in the transverse direction under the influence of the force of gravity or the weight of the material to be screened.
By replacing some of the bars, usually welded to the ends of the drum, by bars movable in the side-ward direction, that is, by transversely movable 2 ~ 6 bars, the width of gaps bordering on at least one movable bar varies while the drum rotates. Soil stuck in this kind of ~ap may be detached when the bar moves and-the width of the gaps changes so that it passes~--through the -screen or drops back into the inner space of the drum.
- -The bars can be simply made movable in such a way that the ends of the movable bars are left loose in the openings of the drum ends, the size of the openings being greater than the cross-sectional area of the bars.
In the following one preferred embodiment of the screen drum according to the invention will be described in greater detail with reference to the attached drawing, wherein Figure 1 is vertical sectional view of the drum screen;
Figure 2 is an end view of the screen; and Figures 3 and 4 show an enlarged view of a de-tail of the screen in two different positions.
Figure 1 shows a drum screen formed by a sub~
stantially cylindrical drum. The drum is rotatable by means of a motor about its central axis 1 shown in the figure by means of a dot line. The shell surface of the drum is formed by parallel bars 2 disposed side by side and attached at the ends to the ends of the drum. The ends of the drum comprise a metal strap 3 the inner periphery of which is provided with re-cesses disposed close to each other and the open side of which is closed by means of a sleeve-shaped end plate 4 so that openings 5 are formed side by side in the strap for the end portions of the bars. Figure 1 also shows a bottom plate 6 for runner grooves for bands used to rotate the drum.
The attachment of the bars 2 to the ends of the ' 2 ~ t~ 6 drum screen is shown in more detail in Figures 3 and 4. It appears from the figures that the openings 5 taper away from the central axis of the drum. This shape corresponds substantially to the cross-section-al shape of the bars. Some of the bars are conven-tionally welded to the edges of the opening 5 by means of a weld joint 7.
According to the invention some of the bars are attached to the ends of the drum so as to be trans-versely movable, in the sideward and vertical direc-tion, for instance. In the embodiment shown in the drawing, the bars are movable because they have not been welded to the edge of the opening 5 but the bars are freely movable within the opening. As is apparent from Figures 3 and 4, the area of the openings 5 is slightly larger than the cross-sectional area of the bars, so that the bars are movable over a short dis-tance, preferably about 2 to 4 mm in the sideward direction. In that case the width of the slot sur-rounding a movable bar is about 1 to 2 mm. The width preferably corresponds to the width of the weld joint 7. The desired effect is usually obtained when every second or every third bar 2 is movable.
The drum screen according to the invention operates in the following way. Soil to be screened, such as earth or gravel, is introduced into the drum through its one end by means of a conveyor not shown.
While the drum is rotated about its central axis, clods of soil are broken and part of the material drops between the bars below the drum while larger particles remain within the drum. In prior art drums, stones and wet clods of soil are often wedged between the bars, clogging up the screen.
The screen according to the invention is less liable to clogging than prior art screens as some of 2 ~ 7 6 the bars are movable. The movable bars on the sub-stantially vertical sides of the drum rest on the lower edge of the opening, so that their distance from the upper fixed bar is greater than the average distance of the bars from each other. At the top and bottom of the drum the moveable bars are positioned substantially centrally in the opening in cases where the force of gravity only acts on them. Of course, the weight of the material to be screened may also affect the position of the movable bars in the open-ings 5.
Due to the variable width of the gaps between the bars, part of the material which otherwise would be wedged between the bars is detached and either drops back within the screen or passes through the screen.
It is to be understood that the bars can be made displaceable in the sideward direction in some other way than that described above. For instance, resilient material can be provided between the edge of the openings 5 and the bar.

Claims (4)

1. A screen drum formed by a substantially cy-lindrical drum rotatable around its central axis and having a shell surface being formed by parallel bars disposed side by side and attached at the ends to drum ends, part of said bars being attached to said drum ends in such a way that they are movable over a short distance in the transverse direction under the influence of the force of gravity or the weight of the material to be screened.

2. A drum screen according to claim 1, wherein said ends of said movable bars are disposed loosely within openings in said drum ends, the size of said openings being greater than the cross-sectional area of said bars.

3. A drum screen according to claim 2, wherein the width of the slot between a movable bar and the edge of said opening is about 1 to 2 mm.

4. A drum screen according to claim 1, wherein every second or every third bar is movable.