Throughput efficiency enhancement of fluidized bed jet mill

A fluidized bed jet mill for grinding particulate material comprising:

• a. a grinding chamber having a peripheral wall, a base, and a central axis;
• b. a plurality of sources of high velocity gas, said gas sources being mounted within said grinding chamber on said peripheral wall, arrayed symmetrically about said central axis, and oriented to direct high velocity gas along an axis intersecting said central axis, each of said gas sources comprising:
• i. a nozzle holder having a central axis and an outside diameter;
• and
• ii. a nozzle mounted in one end of said nozzle holder oriented toward said central axis of said grinding chamber and having an internal diameter;
• and
• c. an annular accelerator tube mounted concentrically about said nozzle holder and having a first end proximal to said nozzle and a second end distal from said nozzle, each of said first end and said second end having an internal diameter, said internal diameter of said first end being larger than said internal diameter of said second end and being larger than the external diameter of said nozzle holder, said accelerator tube and said nozzle holder defining an annular opening therebetween through which particulate material in said grinding chamber can enter and be entrained with a flow of gas from said nozzle and accelerated within said accelerator tube and discharged toward said central axis of said grinding chamber;
• said accelerator tube comprises a cylindrical outlet portion distal from said nozzle and a converging portion proximal to said nozzle.

A fluidized bed jet mill for grinding electrostatographic developer particles comprising:

• a. a grinding chamber having a peripheral wall, a base, and a central axis;
• b. a generally spherical impact target mounted within said grinding chamber and centered on said central axis of said grinding chamber;
• and
• c. a plurality of sources of high velocity gas, said gas sources being mounted in said grinding chamber on said peripheral wall, arrayed symmetrically about said central axis, and oriented to direct high velocity gas along an axis intersecting said central axis within said impact target, each of said gas sources comprising a nozzle haing an internal diamter, said impact target having a maximum periphery in a plane perpendicular to said central axis, said maximum periphery being between 3 and 6 times said internal diameter of said nozzle.

A fluidized bed jet mill for grinding electrostatographic toner particles comprising:

• a. a grinding chamber having a peripheral wall, a base, and a central axis;
• b. a generally spherical impact target mounted within said grinding chamber and centered on said central axis of said grinding chamber;
• and
• c. a plurality of sources of high velocity gas, said gas sources being mounted in said grinding chamber on said peripheral wall, arrayed symmetrically about said central axis, and oriented to direct high velocity gas along an axis intersecting said central axis within said impact target, each of said gas sources comprising a nozzle haing an internal diamter, said impact target having a maximum periphery in a plane perpendicular to said central axis, said maximum periphery being between 3 and 6 times said internal diameter of said nozzle.

A method for grinding particles of electrostatographic developer material comprising the steps of:

• a. introducing unground particles of electrostatographic developer material into a grinding chamber of a fluidized bed jet mill;
• b. injecting high velocity gas from a plurality of sources of high velocity gas;
• c. forming a fluidized bed of said unground particles;
• d. accelerating a portion of said particles with said high velocity gas;
• e. fracturing said portion of said particles into smaller particles by projecting them against a rigid, convexly arcuate body mounted within said grinding chamber;
• f. separating from said unground particles and said smaller particles a portion of said smaller particles smaller than a selected size;
• g. discharging said portion of said smaller particles from said grinding chamber;
• and
• h. continuing to grind the remainder of said smaller particles and said unground particles.

A method for grinding particles of electrostatographic developer material comprising the steps of:

• D. introducing unground particles of electrostatographic developer material into a grinding chamber of a fluidized bed jet mill;
• E. injecting high velocity gas from a plurality of sources of high velocity gas attached to injecting nozzles;
• F. forming a fluidized bed of said unground particles;
• G. accelerating a portion of said particles with said high velocity gas;
• H. fracturing said portion of said particles into smaller particles by projecting them against a rigid, curved body mounted within said grinding chamber, said rigid, curved body having a diameter D which substantially conforms to the equation:
• D=(1+2.multidot.X.multidot.tan (.alpha./2)).multidot.d,
• wherein:
• X=distance from said nozzle to said surface of the rigid, curved body,
• .alpha.=included angle of said portion of said particles, and
• d=internal diameter of said nozzle;
• I. separating from said unground particles and said smaller particles a portion of said smaller particles smaller than a selected size;
• J. discharging said portion of said smaller particles from said grinding chamber;
• and
• K. continuing to grind the remainder of said smaller particles and said unground particles.