Pelleting Apparatus
1,152,061. Tabletting machines. UPJOHN CO. 14 June, 1966, No. 26559/66. Heading B5A. [Also in Divisions G1 and G3] In a rotary table, multiple die, opposed plunger pelletizer machine for producing tablets by compressing powder in a die, the applied force is measured by a first strain gauge, and the force required to eject the tablet by a second strain gauge. As shown (Fig. 2), the powder is fed into a die between an upper punch 1 and a lower punch 2, mounted with others on a rotating table. Compression is produced by pressure rollers 14, 41. The former is eccentrically attached to a shaft 12, carrying at the other end a crank with a roller 21 resting on a crosshead 23. An identical assembly is mounted on the other side of the crosshead 23, and the complete unit is supported by a plunger 24 urged upwards by spring 26 and fluid pressure F, counterbalanced by screws 28, 29 bearing on the rollers 21, 22. As the table is rotated an upper punch 1 is forced down by roller 14 as its mating lower punch 2 is raised by an eccentrically mounted lower pressure roller 41, to compress a predetermined quantity of powder fed between them. During compression, roller 14 is partially rotated, reducing the strain in screw 28, and this change in strain is measured by a semi-conductor resistance strain gauge 31 (Fig. 4) bonded to the screw, and associated with a similar strain gauge 84 and two static resistors 83, 86 in a bridge circuit 32 whose output is indicated on a CRO 39 or a recorder. Ejection of the formed tablet is effected by the lower punch 2 passing along a ramp 51 (Fig. 6) secured to a flange 53. A block 56 is mounted below the flange, carrying screws 59, 61 which protrude through holes in the flange to abut the pump 51. Thus as the lower punch 2 is forced up the ramp, the force needed to eject the formed tablet increases the compression on screws 59, 61 and is measured by a strain gauge resistor 71 mounted on screw 61 and connected in another bridge circuit. The measured compression force in the punches may be averaged and compared with a reference value to regulate (a) the compression force (Fig. 9, not shown) by adjusting the vertical position of roller 41, (b) the volume above punch 2 to be filled with powder (Fig. 10, not shown), by adjusting the vertical position of punch 2 when the powder is introduced, (c) the quantity of powder for each tablet by adjusting the pressure of a fluid controlling the powder feed (Fig. 11, not shown).