received by the International Bureau on 28.05.2014

CLAIMS

1. Drum for magnetic separator comprising a cylinder (C) of ferromagnetic material closed at its ends by two flanges (2) having central hubs (3) provided with seats for bearings (4) and locking clamps (5), said central hubs (3) being arranged along the longitudinal axis (A-A) of said cylinder (C), a plurality of longitudinal grooves (6) being formed on the outside of the cylinder (C) and housing permanent magnets (7) arranged in longitudinal rows of a single polarity along a magnetic arc of about 130° to 160° with alternate N-S polarity between adjacent rows, the cylinder (C) being located within a shell (M) of non-magnetic material closed at its ends by two flanges (F) having flanged hubs (MF) provided with seats for said bearings (4), at least one of said flanged hubs (MF) being also provided with means for receiving from a motor the motion to drive into rotation said shell (M), said means being preferably a toothed wheel (R), characterized in that the length (D) of the single dipole of the magnetic circuit is comprised in a range between 100 and 150 mm, being preferably equal to 127 mm.

2. Drum according to claim 1 , characterized in that the magnets (7) are all identical and in a release zone (10) at the end of the magnetic arc they are housed in progressively deeper longitudinal grooves (6).

3. Drum according to claim 1 or 2, characterized in that it further includes a plurality of rotatable ball supports (8) arranged in a chequered pattern among the magnets (7), the balls of said supports (8) projecting by 0,3-0,4 mm with respect to the active surface of the magnets (7).

4. Drum according to claim 3, characterized in that the play (G) between the active surface of the magnets (7) and the internal surface of the shell (M) is < 2 mm.

5. Drum according to any of the preceding claims, characterized in that the external surface of the shell (M) is coated with an epoxy paint that forms a high-friction layer.

6. Drum according to any of the preceding claims, characterized in that an arm (B) for adjusting the position of the magnetic arc of the cylinder (C) is secured to one of the hubs (3).

7. Drum according to any of the preceding claims, characterized in that the magnets (7) are made of a Nd-Fe-B alloy.

8. Drum according to any of the preceding claims, characterized in that the shell (M) is made of AISI 316 stainless steel having a thickness (Sm) of 4 mm.

9. Method for producing a drum for magnetic separator according to any of the preceding claims, comprising the following steps :

a) welding the closure flanges (2) at the ends of the cylinder (C);

b) fixing the hubs (3) at the center of the flanges (2)

c) machining the cylinder (C) on a lathe to achieve perfect coaxiality of the hubs (3) with the outside of the cylinder (C) and to form on the hubs (3) the seats for the bearings (4) and for the locking clamps (5);

- d) milling the longitudinal grooves (6) on the outside of the cylinder (C);

e) fixing the magnets (7) into the grooves (6);

f) introducing the cylinder (C) inside the shell (M) and seajingly mounting the closure flanges (F) of the latter;

characterized in that in step d) the grooves (6) are formed at a distance such that the length of the single dipole of the magnetic circuit is comprised in a range between 100 and 150 mm.

10. Method according to claim 9, characterized in that in step d) there are also formed seats for ball supports (8) which are subsequently fixed in said seats so as to project by 0,3-0,4 mm with respect to the magnets (7).

11. Method according to claim 10, characterized in that in step e) there are also fixed easily removable plugs (9) into the seats for the ball supports (8) and in that it further includes the following steps between steps e) and f):

e') covering the region of the cylinder (C) where the magnets (7) are present with a wrapper sealed with a putty suitable to allow the filling of said wrapper with an epoxy resin;

e") filling the wrapper with an epoxy resin and subsequently removing the wrapper upon hardening of the epoxy resin;

e'") machining the cylinder (C) on a lathe to perform the grinding at the desired diametral size of the surface covered with magnets (7) and of the interspaces filled with resin;

e"") removing the plugs (9) and fixing the ball supports (8).