Device for transporting particles of a magnetic material and tool comprising such a device

A tool for excavating an object, the tool comprising a jetting system arranged to impinge the object to be excavated with a jetted stream of a fluid mixed with abrasive particles comprising a magnetic material, the jetting system being provided with at least an abrasive particle inlet allowing entrance of abrasive particles into the jetting system, the tool further comprising a recirculation system arranged to recirculate at least some of the abrasive particles, from a return stream of the fluid mixed with the abrasive particles downstream impingement of the jetted stream with the object back to the jetting system, the recirculation system comprising a device for transporting particles containing a magnetic material in a selected direction, the device comprising:

• a support member having a support surface for supporting the particles which is exposed to said return stream for transporting the abrasive particles from the return stream to the inlet, the support surface extending in the selected direction;
• a separator magnet arranged to generate a magnetic field for retaining the particles on the support surface whereby the magnetic field on the support surface is arranged to have a high-field band, a low-field band, and a magnetic field gradient in a gradient zone between said high- and low-field bands whereby the magnetic field strength in the high-field band is higher than that in the low-field band;
• means for advancing the high- and low-field bands relative to the support surface in a direction having a component in the direction of the magnetic field gradient on the support surface, whereby the high-field band is followed by the low-field band;
• whereby along said high-field band at least a first magnetic pole and a second magnetic pole of opposite polarity are arranged such that a first magnetic path on the support surface from the first magnetic pole to the second magnetic pole is shorter than a second magnetic path on the support surface crossing the gradient zone from the first magnetic pole to any other nearest magnetic pole of opposite polarity.