The invention relates to an assembly of a pellet press and a pellet breaking device mounted on the pellet press, said pellet press being equipped with a cylindrical outer wall that is provided with a series of radial through holes with a prede fined hole-diameter for radially and outwardly pressing the pel lets from within the press towards and away from an outer cir cumferential contour of the pellet press.

EP-A-2 727 715 discloses a pellet breaking device. The known pellet breaking device is equipped with pellet cutting means and at least one attachment region in which the cutting means are attached on a fixed housing part of the pellet press such that the cutting means can be arranged at a predefined space from the pellet press. The cutting means has a concave ar cuate contour which is substantially helical over at least a re gion of one of the radial through-holes of the ring die of the pellet press, so that a pellet, via the ring die in the radial direction and with a greater length than the distance between the ring die and the cutting means protrudes from the through hole, then in the region of its free end comes to rest on a base body with a concave circular-arc radial guide surface on which the cutting means is mounted, and can move along the circumfer ential direction of the base body such that the pellet is de flected by the cutting means by means of a force having an axial component, so that the pellet kinks in the region of the ring die.

The invention has as an object to depart from the com plicated and heavy design known from EP-A-2727 715, and to pro vide an assembly of a pellet press and a pellet breaking device which is contrary to the known device energy-efficient and reli able in providing pellets of well-defined length within a lim ited length-range. A maximum length of the pellets is approxi mately 40 mm.

FR 3028 446 discloses a machine for manufacturing granules by pressing a pulverulent material, said machine com prising a frame defining an enclosure; a perforated annular die mounted in the enclosure and driven in rotation relative to the frame; at least one pressure roller mounted in the die in the vicinity of an internal face thereof; and a device for cutting granules comprising a grid which extends at least partially around the die opposite an external face thereof.

GB 889,628 discloses an extrusion machine having a plu rality of tapered orifices. Each orifice comprises an inlet and an outlet, and a tapered wall of at least a portion of each ori fice intersects the outer wall of said die in a knife-edge transverse to the flow of material, the inlet of each orifice being larger than the outlet, the intersecting angle between the tapered wall of each orifice and the outer wall of said die be ing no more than 60.

The pellet breaking device of the invention has the features of one or more of the appended claims.

In a first aspect of the assembly of the pellet press and the pellet breaking device according to the invention, the breaking device is shaped as a spiral encircling the pellet press at a predefined distance from the outer circumferential contour of the pellet press, wherein the spiral spans at least a part of the outer circumferential contour of the pellet press along an area that is provided with said through holes, and wherein the predefined distance between the spiral and the outer circumferential contour of the pellet press amounts to at least twice the pre-defined hole-diameter of the through-holes for the pellets.

The spiral surrounding the pellet press thus provides a series of consecutive free-standing windings encircling the pel let press at said predefined distance from the outer circumfer ential contour of the pellet press. The word freestanding as used herein signifies that the windings are substantially free from supports that close the room between the windings. The free-standing windings arrange for a comparatively light design with notable benefits in the limitation of energy consumption, whilst the effectiveness of breaking the pellets at an intended length is safeguarded. It has been found that the invention pro vides that the pellets are all maintained well within a prede fined length-range amounting to 3 to 5 times the pellet diame ter, whereas the occurrence of fines is effectively countered.

It is possible that the mentioned predefined distance between the consecutive free-standing windings of the spiral and the pellet press is a fixed distance or an adjustable distance.

The effectiveness of breaking the pellets at their in- tended length is promoted by arranging that the spiral encircles the outer circumferential contour of the pellet press uninter ruptedly.

One of the appreciable features that support the bene fits of the invention is that the consecutive windings of the spiral define open slots between said windings, wherein the slots are arranged to enable the pellets to escape through said slots.

Preferably the open slots between the windings of the spiral are arranged such that during operation of the pellet press the open slots receive the pellets and that said windings are arranged to subsequently break the pellets growing out of the outer circumferential contour of the pellet press.

Best results may be achieved by embodying the consecu tive windings of the spiral with obliquely slanting surfaces with respect to the outer circumferential contour of the pellet press, wherein said obliquely slanting surfaces are bordering the slots. Preferably the obliquely slanting surfaces are at an angle of about 40° with reference to the outer circumferential contour of the pellet press.

It is preferred that the obliquely slanting surfaces of the consecutive windings of the spiral are arranged to narrow a line of sight between the windings in the radial direction away from the outer circumferential contour of the pellet press so as to prevent that pellets can escape through the slots unhindered and in a straight line, yet can escape through the slots follow ing a bending and breaking motion of the pellets which occurs approximately at the outer circumferential contour of the pellet press.

The invention will hereinafter be further elucidated with reference to a drawing of a non-limiting exemplary embodi ment of the apparatus and its use in accordance with the inven tion.

In the drawing:

-figure 1 shows a pellet breaking device mounted on a pellet press according to the invention in an isometric view;

-figures 2a, 2b, 2c, 2d and 2e show the pellet breaking device of the invention in respectively a frontal view, a side view, an isometric view, a detail view, and a cross-sectional detail side view;

-figure 3 shows a detail of the pellet breaking device mounted on a pellet press according to the invention in a detail cross-sectional view, during operation; and

-figure 4 shows a graphical representation of the pel let quality of the pellets manufactured with the assembly of the invention.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Making first reference to figure 1, it shows a pellet press 1 on which a pellet breaking device 2 according to the in vention is mounted. In a way known to the skilled person the pellet press 1 is equipped with a cylindrical outer wall 3 that is provided with a series of radial through holes 4. These radi al through holes 4 have a pre-defined hole-diameter tailored to the intended diameter of the pellets, and are visible in the cross-sectional view of figure 3. The holes 4 serve for radially and outwardly pressing the pellets from within the press 1 to wards and away from an outer circumferential contour 5 of the pellet press 1. Said outer circumferential contour 5 of the pel let press 1 is the outer surface of the cylindrical outer wall 3 of the press 1.

Figure 1 clearly shows that the breaking device 2 is shaped as a spiral 6, wherein the spiral 6 follows the outer circumferential contour 5 of the pellet press 1 at a predefined distance; see also figure 3. The spiral 6 is equipped with a se ries of consecutive free-standing windings 7, wherein the word freestanding signifies that the windings 7 are substantially free from supports that close the room between the windings 7. The freestanding windings 7 encircle the pellet press 1 at the earlier mentioned predefined distance from the outer circumfer ential contour 5 of the pellet press 1. The predefined distance between the spiral 6 and the outer circumferential contour 5 of the pellet press 1 amounts to at least twice the pre-defined hole-diameter of the holes 4.

Further said free-standing windings 7 of the spiral 6 span at least a part of the outer circumferential contour 5 of the pellet press 1 along an area that is provided with said through holes 4, as will be clear to the skilled person from figure 3 and figure 1 in combination.

In the respective figures 2a, 2b, 2c, 2d and 2e, the windings 7 of the spiral 6 are shown separate from the pellet press 1, and from these figures in combination with figure 1 it is clear that the consecutive windings 7 of the spiral 6 encir cle the outer circumferential contour 5 of the pellet press 1 uninterruptedly .

Particularly figures 2d and 2e show that the consecu tive windings 7 of the spiral 6 define open slots 8 between said windings 7. Figure 3 shows that the slots 8 are arranged to ena ble the pellets 9 to escape through said slots 8. The open slots 8 between the windings 7 of the spiral 6 are arranged such that during operation of the pellet press 1 the open slots 8 receive the pellets 9 and said windings 7 are arranged to subsequently break the pellets growing out of the outer circumferential con tour 5 of the pellet press 1. This breaking action is brought about by a rotational movement of the outer circumferential con tour 5 of the pellet press 1 with reference to the non-moving windings 7 of the spiral 6.

Both figure 2e and figure 3 clearly show a preferable embodiment in which the consecutive windings 7 of the spiral 6 are embodied with obliquely slanting surfaces 7', Ί ' ' with re spect to the outer circumferential contour 5 of the pellet press 1, wherein said obliquely slanting surfaces 7', 1 ' ' are border ing the slots 8. Preferably the obliquely slanting surfaces 7', 1 ' ' are at an angle of about 40° with reference to the outer circumferential contour 5 of the pellet press 1. It is further preferred that the obliquely slanting surfaces 7', 1 ' ' of con secutive windings 7 of the spiral 6 are arranged to narrow a line of sight between the windings 7 as seen in the radial di rection away from the outer circumferential contour 5 of the pellet press 1 so as to prevent that pellets 9 can escape through the slots 8 unhindered and in a straight line, yet can escape through the slots 8 following a bending and breaking mo tion of the pellets 9 occurring approximately at the outer cir cumferential contour 5 of the pellet press 1.

Figure 4 shows a graphical representation of the pellet quality of the pellets manufactured with the assembly of the in vention. The x-axis depicts the distance between the spiral 6 and the outer circumferential contour 5 of the pellet press 1. The y-axis shows the percentage of fines as well as total fines and the pellet durability index as a percentage.

The pellet durability index is measured by taking 100 g of cleansed pellets, i.e. without fines resulting from the manu facturing process, and loading these cleansed pellets during two minutes, and thereafter measuring the percentage of fines. The pellet durability index is then determined by subtracting the fines from the original hundred grams of clean pellets, and ex pressing the remaining weight of pellets as a percentage of the original weight.

The fines determined with the just mentioned test are considered representative for the fines that would emerge during transport of the pellets. The total fines are calculated as the sum total of the just mentioned fines together with the fines that are removed prior to the performance of the above mentioned test.

From figure 4 it is clear that best results are achieved when the predefined distance between the spiral 6 and the outer circumferential contour 5 of the pellet press 1 amounts to at least twice the pre-defined hole-diameter of the holes 4.

Although the invention has been discussed in the fore going with reference to an exemplary embodiment of the pellet breaking device mounted on a pellet press according to the in vention, the invention is not restricted to this particular em bodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall there fore not be used to construe the appended claims strictly in ac cordance therewith. On the contrary the embodiment is merely in tended to explain the wording of the appended claims without in tent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible am biguity in the wording of the claims shall be resolved using this exemplary embodiment.