This type of screen crusher is known from the Applicant's patent publication US- 5,405,092. It has proven to be particularly useful in screening and crushing all kinds of soil materials. However, there often also arises a need to crush relatively hard pieces, such as soft types of stone, pieces of lightweight concrete and other construction waste or frozen blocks. Known screen crushers are unable to do this and leave harder material blocks uncrushed in the bucket.

The object of the invention is to develop the said screen crusher further in such a way that it will be suitable for use in crushing pieces of relatively hard material, such as soft types of stone, lightweight concrete and other construction waste or frozen earth.

This object is achieved by means of the invention, on the basis of the characteristics disclosed in the appended claim 1.

The invention is illustrated in greater detail in the following, by means of an embodiment, with reference to the accompanying drawings, in which : Figure 1 shows a screen crusher according to the invention as seen from the side, and Figure 2 shows an enlarged detail of the screen crusher according to the invention in the area of the crushing mouth.

In the illustrated case, the screen crusher is included in an excavator bucket 1, which is a dipper type shovel. Naturally, it is also possible to use a back-acting type of shovel, whereby the structure of the fastening elements 1 b is changed accordingly. The bucket 1 is thus fixed by means of fastening elements 1 b and a pivoting joint 6 on the bucket boom of an excavating machine. The screen crusher relating to the invention can also be constructed in the bucket of a bucket loader.

Between the bottom plate 1 a of the bucket and the pivoting joint 6 is a back wall formed by a crusher screen 2, through which the crushed and screened material flows when the crusher screen is in operation. In this situation, the bucket 1 is turned into a position in which the crusher screen 2 forms the bucket bottom and the bottom plate 1 a faces more or less upwards.

A hydraulic motor 5 rotates the shafts 3 via chains 4, onto which shafts are provided the screening and crushing means formed by spacer plates 7 and crushing teeth 9. The shafts 3 are substantially horizontal, that is, parallel to the shaft of the pivoting joint 6 of the bucket. The spacer plates 7 surrounding the shaft 3 are fixed to the shaft 3 at an axial distance from each other. This distance is selected to match the desired screening coarseness and may thus vary between screen crushers used for varying purposes.

The fastening butts 8 of the crushing teeth 9 are placed between tool holders 8a and fixed into place, for example, by means of through-pins (not shown). The tool holders 8a are in turn welded to the spaces between the spacer plates 7 and to the shaft 3. The position of the crushing teeth 9 may turn in a spiral fashion when progressing in the axial direction of the shaft 3. The tips of the teeth 9 extend beyond the peripheral line of the spacer plates 7 and their circumference of rotation is marked by reference numeral 9'. The diameter of the spacer plates 7 is selected to almost match the distance 3'between the rotating shafts 3, whereby the peripheries of spacer plates 7 on adjacent shafts almost touch each other.

The shafts 3 with their spacer plates 7 thus form a kind of screen mesh, through which the crushing means 9 deliver mass while the shafts 3 rotate.

In the illustrated case, the bucket 1 comprises four pipe shafts 3, which all have the same direction of rotation.

Larger solid pieces, which are too large to pass through the crusher screen 2 and which the teeth 9 are unable to penetrate and grip for the purpose of crushing, are conveyed on top of the crushing screen, pushed by the teeth 9, towards the crushing mouth, which is formed between a wearing plate 10 and the tail end of the crusher screen 2 (as seen in the direction of feed F).

The wearing plate 10 is positioned in such a way that a sharp-angled crusher jaw is formed for the material to be crushed between the wearing plate 10 and the direction of feed F of the material. Although the direction of feed of individual pieces may vary greatly depending on the point of the circumference of rotation at which the tooth 9 touches the piece, as a general or main direction of feed F can be considered a direction which is substantially parallel to the plane which touches the circumferences of rotation 9'of the crushing means 9 on successive shafts 3. When the direction of feed F is thus determined, the angle of the receiving mouth can be said to be within the range from 60° to 25°, most preferably within the range from 45° to 30°. The crusher jaw is then sufficiently sharp-angled for the teeth 9 to break solid pieces against the wearing plate 10 efficiently. Figure 2 shows by means of arrows A how the teeth 9 of successive shafts 3 get a good grip on pieces of different size which wedge into the receiving mouth which decreases in size in the direction of feed F as the teeth 9 crush the pieces smaller. The crushing of the pieces continues until they fit through the apertures of the above-mentioned screen structure. As shown in Figure 2, at the bottom of the receiving mouth, which is V-shaped in cross-section, the circumference of rotation 9'of the crushing means 9 touches the trailing edge of the wearing plate 10 at a slight clearance from it.

During crushing, the bucket 1 is held in a position in which the said direction of feed F is somewhat obliquely upwards. This means that if the rotation of the crushing means jams, the shafts 3 can be swung backwards to change the direction of feed, whereby the piece causing the jamming will flow outwards from the crusher jaw also partly due to the effect of the force of gravity. After this, operation in the direction of feed can be restarted immediately. If, on the other hand, the bucket is held in a position where the material pushes into the crusher jaw due to the force of gravity, it is often not possible to clear the jam simply by means of a rapid back feed period. During crushing, the bucket 1 can be turned in such a way that the direction of feed F is initially relatively sharply obliquely upwards, and as the amount of material in the bucket decreases, the direction of feed F is turned towards the horizontal plane and finally possibly so as to slope slightly downwards.

The wearing plate 10 is made easily replaceable, because it is subjected to considerable stress caused by wear and the plate 10 may wear out within a relatively short time. In the illustrated case, the two-part wearing plate 10 is fixed to frame plates 11 by means of fixing screws 12 which attach from the back of the frame plates to the threaded holes in the wearing plate 10, to which holes the ends of the screws 12 are welded. The point of welding is marked by reference numeral 13. In this way, the wearing plate 10 side of the crusher jaw is made smooth and the partly worn out plate 10 can be easily removed. Reference numeral 10'denotes an extension of the wearing plate 10, which may be an optionally used part, the use of which depends on the material being crushed.

When the wearing plate extension 10'is used, larger pieces than before can be subjected to the crushing action, that is, already the crushing means of the third last shaft begin to crush the largest pieces against the extension 10'. Without the extension 10', the crushing teeth 9 on the last two shafts 3 perform the crushing against the plate 10.

The frame structures required to support the wearing plate 10 can also be arranged to be easily detachable, whereby the crusher jaw can be disassembled

and the device will operate as a normal screening device which does not crush hard materials.

The wearing surface of the wearing plate 10 does not have to be smooth, on the contrary, ribs (e. g. level rods welded on their side edges) parallel to the material flow may be added to it.