Large volume twin shaft compulsory mixer

Details Large volume twin shaft compulsory mixer Large volume twin shaft compulsory mixer

2002-07-31

2003-07-08

Soohoo, Tony G. (Department: 1723)

Metal working

Method of mechanical manufacture

Repairing

C366S348000, C366S349000, C366S042000

Reexamination Certificate

active

06588082

ABSTRACT:

This invention relates to so-called twin shaft, compulsory mixers. More specifically, a large volume twin shaft, compulsory mixer having a capacity exceeding 12 cubic yards is utilized in combination with an elevating concrete conveyor to mix and convey concrete from the foundation of a modular portable concrete plant. Problems related to discharge gate deflection and compulsory mixer chamber deformation are disclosed and solved.
BACKGROUND OF THE INVENTION
Concrete mixers in North America are usually of the rotating tilting drum variety. In such mixers, a rotating cylinder that tilts on its axis of rotation is utilized. Initially, the drum is in a tilted orientation to have its open end elevated. Depending on the manufacturer, the drum is filled with the constituents of concrete including cement, aggregate, sand, and water either through its discharge opening or through the opposite end. Paddles are fastened to the interior of the rotating drum. Upon rotation, the constituents act against the paddles and the force of gravity to be stirred and moved within the rotating drum. In part, some of the mixing action is by the concrete being lifted by the mixer paddles then falling to the bottom of the drum into the rest of the concrete. By both interfering flows within the rotating drum and the paddle stirring against the force of gravity, mixing occurs.
Upon completion of mixing, drum tilting occurs about the axis of rotation to dispose the discharge end of the drum generally downward. To enhance discharge of the concrete, on some tilting drum mixer designs, the drum is provided with reverse rotation. During this reverse rotation, the now mixed concrete constituents are moved by the force of gravity interacting with paddles interior of the drum from the closed drum end towards the open drum end. The mixed concrete is discharged from the open end of the rotating and tilted drum.
Rotating drum mixers have their disadvantages. Mixing utilizing the force of gravity takes time. In the case of mixing low slump or optimum moisture materials their mixing efficiency is low. Further, in the usual cases, in order to permit discharge, the rotating drums must be elevated. This requires the elevated support of considerable weight. Further, since the drums are tilted after mixing occurs, considerable torque must be resisted. In the usual case, both foundation structures and upwardly extending structural supports must be supplied to such rotating drum mixers. Rotating drums are unsuitable for use as a foundation for other parts of a mixing plant.
So-called twin shaft “compulsory mixers” for concrete are old and well known. These mixers, invented in 1888, cause the constituents of concrete to be rapidly mixed along interfering paths without rotating drums. Compulsory mixers have counter rotating paddle systems in an otherwise static mixing chamber to enable thorough mixing with great rapidity. In what follows, we will set forth the modem construction and usage of such mixers.
In their modern construction, compulsory mixers have an open top to a static mixing chamber. The static mixing chamber has a bottom defined from two horizontally disposed and interfering cylindrical shapes. A first cylindrical shape formed along a first horizontal axis defines a little over one half the volume and bottom profile of the static mixing chamber. A second cylindrical shape formed along a second horizontal and parallel axis defines a little over a second one half of the volume and remaining bottom profile of the static mixing chamber. The cylinders defining the bottom profile of the mixing chamber overlap or interfere at respective interfering sections interior of the volume of the mixing chamber. This interference occurs along cylindrical segments extending centrally of the volume of the static mixing chamber.
Counter rotating paddle systems effect mixing within such compulsory mixers. Each mixing paddle system rotates co-axially within and along the axis of the interfering cylinders defining the bottom of the chamber. A first paddle system has a first axis of rotation co-axial to the first horizontal axis of the first cylinder defining half the volume of the mixing chamber. A second paddle system has a second axis of rotation co-axial to the second horizontal axis of the second cylinder defining the remaining half of the volume of the mixing chamber. Each paddle system has canted paddles to sweep concrete constituents in their respective cylinders from the sides of the cylinders to and toward the interfering portion of the cylinders defining the volume of the static mixing chamber. Dual spiral motions directed to one static mixing chamber end occurs. During their rotation, the paddles systems overlap and interleave at the interfering portions of the cylinders defining the volume of the static mixing chamber.
The arrangement and rotation of each set of mixing paddles imparts to the concrete constituents a spiral pattern within each half of the volume of the static mixing chamber. The interfering portions of the cylindrical volumes defining the static mixing chamber result in the superimposition of the two spiral patterns. These superimposed and interupted spiral patterns produce a compulsory and interfering concrete constituent flow resulting in a three-dimensional interfering flow path within the static mixing chamber. A high degree of turbulence is promoted. Mixing at the interfering portions of the cylinders is most intensive, resulting in a rapid homogeneity and cement dispersion or thorough mixing of the concrete constituents.
Unlike the rotating drum mixer, the discharge of the mixed concrete constituents from a compulsory mixer does not use or require mixing chamber movement. Instead, it is necessary to supply the bottom of the static mixing chamber with an opening.
To discharge mixed concrete from the static mixing chamber, an elongate rectilinear opening is provided parallel to the axial length of the two cylinders defining the volume and bottom profile of the static mixing chamber. Specifically, at the juncture of the interfering cylinders along the bottom of the mixing chamber, there is placed an elongate rectilinear opening. This elongate rectilinear opening is opened and closed by a rotating gate.
The rotating gate is provided with a sealing surface that is correspondingly elongate and rectilinear with respect to the elongate rectilinear opening. In a first position, the rotating gate at the elongate rectilinear eccentric surface tightly seals the elongate rectilinear opening. When mixing occurs, concrete constituents, especially water, cement and sand, cannot easily escape out the bottom of the compulsory mixer chamber.
When mixing is complete and concrete discharge is desired, the gate is rotated. Rotation occurs from a position that seals the bottom of the chamber to a position that opens the bottom of the chamber. Discharge of the mixed concrete constituents from the interior of the static mixing chamber occurs.
It has been realized that rapid emptying of the mixed concrete is required to reduce mixing cycle times. For this reason, the opening of the rectilinear slot at the bottom of the mixing chamber must be maximized. In order to maximize this opening, the elongate rectilinear portion of the gate is eccentrically mounted with respect to the axis of rotation of the gate. Specifically, the gate defines a chord occupying about one third of the arc produced by the cylinder of rotation of the gate.
With such an eccentric gate, rotation of the gate through an arc of about 120° is required. The top of the eccentrically mounted elongate rectilinear portion of the gate moves out of sealing relation to the rectilinear slot centrally of the static mixing chamber. As rotation continues, the sealing side of the eccentrically mounted elongate rectilinear portion of the gate is no longer disposed to the mixed concrete. Instead, the reverse side of the eccentrically mounted elongate rectilinear portion of the gate forms a mixed concrete discharge chute. This discharge chute forms flow path opening well over one

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