Vertical motion mixing drive
A vertical motion mixer has a drive mechanism with two axes of guidance for vertical motion. A reciprocating yoke is fixedly secured to the driving shaft for the mixer, without any guide bearing for the mixer driving shaft. The mixer drive unit is of compact and simplified design with minimal moving parts, and including drive gearing with planetary gears to minimize wear during reciprocating movement.
1. A reciprocating mixer disc assembly for mixing wastewater sludge by cyclical reciprocating motion of the mixer disc within a wastewater digestion treatment tank, with a mixer shaft connected to the mixer disc, comprising:
a housing,
a driving mechanism connected to the housing and to the mixer shaft to drive the mixer disc in reciprocating linear motion in the wastewater sludge within the wastewater digestion tank, the driving mechanism including
a motor-driven crank assembly such that rotation of the crank assembly causes reciprocating linear motion of a yoke driven by the crank assembly, the yoke being within the housing and rigidly attached to the mixer shaft, without any guide structure on the mixer shaft,
a guide assembly for restraining and guiding the movement of the yoke in linear reciprocation in two opposite directions of movement, the guide assembly including a pair of spaced apart linear guide shafts oriented parallel to said directions of movement, the guide shafts being secured fixedly to the yoke for movement therewith, and bearings fixed to the housing, the guide shafts being in contact with the bearings and slidable with respect to the bearings, the two guide shafts being the only said guide shafts and being on two parallel axes which are the only axes of guidance for yoke movement,
the bearings being cylindrical, and the guide shafts being cylindrical and circumscribed by the bearings and reciprocating within the bearings, and
wherein the linear guide shafts define a plane which is offset from the mixer shaft and wherein the plane is offset no more than about four inches from the mixer shaft and the yoke having an axis of reciprocating movement located centrally of the yoke, and said axis of the yoke being aligned with the mixer shaft.
2. The reciprocating mixer disc assembly of claim 1 , wherein the bearings are grease-lubricated bearings.
3. The reciprocating mixer disc assembly of claim 1 , wherein the yoke is a scotch yoke, with a driving roller on a crank arm of the crank assembly, wherein the driving roller, when at positions farthest from said axis of the yoke, is located at one of the linear guide shafts.
4. The reciprocating mixer disc assembly of claim 1 , wherein the yoke is a scotch yoke, with a driving roller on a crank arm of the crank assembly, wherein the driving roller travels on a path limited to a distance from center to center of the two guide shafts.
5. The reciprocating mixer disc assembly of claim 1 , wherein the crank assembly comprises planetary gearing to minimize gear wear.
6. The reciprocating mixer disc assembly of claim 1 , wherein the crank assembly is secured to the housing via a removable back plate which is secured by bolts at an opening in the housing, and to which the crank assembly is connected by bolts, so that the crank assembly is removable from the housing along with the back plate by removing the bolts securing the back plate and pulling the back plate and crank assembly back from the housing.