Summer Industrial TRAINING Report

The next major group of components is known as the body assembly, which is that section of the mixer below the hopper assembly and above and bedplate. There are five principal parts:- 1. Chamber sides 2. End frame assembly 3. Rotors 4. Discharge door 5. Dust stops 1. Chamber sides:- The portions of the mixture which enclose the mixing cavity are the sides. This side consists of heavy shells bored with lateral drilled holes for the circulation of steam and or water. The internal surfaces of the sides are treated as indicated on the specifications data sheet in the front of this manual. 2. End frame assembly:- Supporting the chamber sides are the end frames. Each end frame assembly consists of the frame, the rotor bearings, bearing seals and the rotors and end plates. These are the two ends to the banbury mixer: the water end and driver end. The water end is the area through which the heating end/or cooling of the rotors is introduced. The opposite end is the connection point for the machine drive arrangement. 3. Rotors:- The two rotors perform the mixing action by rotating in opposite directions and at slightly different speeds. Each edge of these wings is called a rotor tip. The rotors are set in the mixing chamber so that the long wing of one rotor is opposite the short wing of the other. A two wing rotor has one short wing and one long wing. A four-wing rotor has two of each. With the compact drive design, there are connecting gears on the rotor shafts. With the unidrive design each rotor is independently connected to the drive unit. These are the two types of rotors:- • Four wing rotors • Two wing rotors. The rotors are cooled by steam or water circulating through the center of each shaft. The rotors turn within the chamber toward each other and at unequal speeds. This is done so that the relative wing-to-wing positions are constantly changing. The term mixing as we use it actually involves three separate phases of activity. For each batch to be thoroughly mixer, the ingredients must be... • Blended: - This means that every portion of the batch must contain the same proportion of the ingredients. • Dispersed: - The ingredients must be dispersed homogeneously. This means that every particle of the mix has been distributed uniformly throughout the batch. • Mixed: - In this sense mixing means a combining of the ingredients which been evenly blended and completely dispersed. The rotors of the banbury mixer accomplish the complete mixing job by working the ingredients in three ways simultaneously. We should visualize the batch as a series of layers. As the material is moved within the chamber, these layers work against each other. This action is known as shear. Shearing is the material working itself, thereby effectively dispersing and blending the ingredients. The rotors of the banbury, therefore, are intended to cause this shear. The rotors cause the layers of material to shear against each other in several ways. One mixing action is that of the rotor wing tips shearing or wiping the material against the wall of the chamber. This is similar to what happens between the rolls of a mill. The material as it is being compressed between the two surfaces (the rotor tip and the chamber wall) forms a rolling bank just forward of the rotating wing. Within this rolling bank, the layers of material are shearing against each other further breaking down the batch. Another area of mixing action is termed kneading. The rotor wings function, in a sense, as fingers in the kneading of dough. Since the rotors are running at unequal speeds, the relative positions of the rotor wings change with every revolution. This means, in turn, that the material is worked differently with each revolution of the rotors as the material between the rotors is constantly changing. Because of the shape of the rotor wings, material is always the wall of the mixing chamber and then toward the other rotor. The curvature of the rotor wings causes the material being forced back and forth from one end of the mixing chamber to the other. Since the rotors are running at unequal speeds, the mix is also being pushed from side to side in the chamber. These two mixing actions working simultaneously result in a constant overlap and exchange of material within the chamber from end-to-end, side-to-side and rotor-to-rotor which further the blending and dispersion of ingredients. Discharge door The drop door is mounted on a support shaft which pivots parallel to the rotors. The offset hinge arrangement allows the door to swing down and away from the door opening permitting the finished batch to discharge. A hydraulic rotating device called a Rotac opens and closes the door. When the door is fully closed, a limit switch mounted at the end of the rotac actuates a solenoid valve which operates the door latch. This latch is actually a hydraulic cylinder which looks the door in place and creates a tight seal. The door top has passages with inlet and discharges fittings for the circulation of cooling water or steam. The door top is normally cooled to prevent the sticking of stock at the time of discharge. Cooling or heating the door top is also effective in helping to control batch temperature. The door drop assembly is heavy, fast and positive in its movement. Dust stops There are four stops on each banbury mixer – one at each point where a rotor shaft passes through the body (end frame). They function to steal the mixing chamber around the rotor shafts. The dust stops selected for the machine are the FYH type. The hydraulically levered yoke presses against the gland ring opposing the flow of material trying to seep through the seal area. Oil for lubrication is fed through drilled holes in the gland ring. Lubrication is most critical to satisfactory operation of dust stops.

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The mixer is equipped with a ram consisting of a rod and floating weight. It is held by an air operated piston in a cylinder. In the raised position the ram bottom (floating weight) is above the hopper door allowing for the introduction of material into mixing chamber. The ram is raised by compressing lubricated air. It is lowered by floating (no air) or by regulated air pressure. Normal pressures used are 80 to 100 psi 5.6 to 7.0 kg/cm2 with a maximum design pressure of 200 psi 14.1 kg/cm2. The stroke of the ram is cushioned at both ends. (a)--- Single type, (b)—double type, (c) single type ram in action The tell-tail rod indicates position of the floating weight. During normal mixing the material inside the chamber moves the ram up or down. How much motion there is, is directly indicated by the tell-tail rod to the operator who can thereby gauge the status of the mixing process. When the ram is in the raised position, a weight pin may be inserted under the bottom of the weight to hold it in place. Before attempting to do any work on the mixer, this pin must be inserted. It should be inspected regularly to ensure that it is in good condition. When the pin is in place, turn off the air supply to the cylinder and bleed both the raise and lower ram control valves. There are four type of bottom:- 1. Single slope v bottom 2. Single slope flat bottom 3. Double gable v bottom 4. Double gable flat bottom.

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