Tea World

Lesson 24

Sorting Machines Continued.....

Balanced Tea Sorter

The most attractive feature of the Balanced Tea Sorter is that it can be operated efficiently even while maintaining the best bloom of tea. It is considered most suitable for the dual type of manufacture. Various sieves with different mesh sizes sort tea particles into the required grades. However, the drawback of the Balanced Sorter is that its output is lower than that of other comparable sorting machines.

          A hopper fitted at one end of the Balanced Sorter contains no wearing parts, ensuring even input of tea. A flap easily regulates the thickness of spread.

 In the lower part of the hopper, there is a rubber diaphragm which is subjected to the slight impulse of the beater bar during the upward movement of the trays. The required impact distance is very small, with not more than 1/16 inch being needed for CTC tea and little more for orthodox tea. The action of the beater bar can be adjusted easily while the machine is running. The impact should be kept to a minimum, as this will prolong the life of the diaphragm.

 Two handles on both sides of the hoper are used to control the shutter. Two small glands grip the spindle of the shutter-opening device just tightly enough to prevent self-movement, and thus eliminate the use of any clamping or locking devices.While the hopper can be fed through a conveyor; it can also be hand fed. Since the hopper is stationary in this machine, greying can be avoided.

This machine comes equipped with five trays, with the bottom-most used for producing dust grades. Half this tray's length is fitted with number 40 mesh, and the rest with number 30 mesh. The other trays are normally fitted with number 8,10, 12, 20, 30 and 40 meshes.

Since a simple spring clip automatically holds the trays in position, no clamping device is required to remove or the refit trays. This can easily be done manually.

 The Balanced Tea Sorter receives power from a motor or line shaft belt. A barrel with a cambered portion runs at speeds of 300 rpm. This cambered portion serves as a fixed pulley and imparts Jigger-type motion to the machine's fitted screens via links.

The lower slope of the machine's feed hoper is made of a rubber diaphragm forms. As tea passes over it into the machine, it is subjected to the impulse of the oscillating trays' beater bar. This ensures a uniform feed into the machine.

Benton Density Sorter

The Benton Density Sorter is a small machine that works on the density variations of particles. A small fan that consumes only 30 Watts of electricity powers this machine. Four wheels fitted to the machine make it easy to move the machine to a desired location anywhere within a factory.

The Benton Density Sorter is used for the following operations:

  • Separation of sand from dust tea.
  • Separation of fibre and flaky leaf from other grades.
  • Separation of large foreign matters from dust tea.
  • Separation of stones and broken grades

A feed shutter is used to admit leaf into the machine; the shutter can also control the rate of feed. The rate of feed is controlled at thickness of 0.25 to 0.5 inch.

As soon as leaf is fed into the hopper, it is admitted to the chute through the feed shutter at 0.25 to 0.5 inch thickness. The chute is set at such an angle that the leaf accelerates rapidly down its surface in such a manner that individual particles separate out. At the point where the chute terminates in the gap, the leaf mass is subjected to a current of air supplied from beneath. The heavier particles are least affected by the current of air and pass into the side delivery number 1. Lighter particles float across the gap on the cushion of air and pass into side delivery number 2. Similarly, the lightest particles are carried upward for a short distance and pass into the end delivery.

The chute can be angled from 30° for heave grades to 70° for powdery grades. This change is possible merely by altering the position of a clamp on its rack. The angel of the fan duct can not be changed relative to the angle of the chute; but there is a provision for altering the angle of the fan duct separately to optimise the airflow through the gap. Normally, the machine is operated with the fan duct in the lowest position. The volume of air used in this machine is very small, but that can be adjusted through orifice plates of varied diameter. Orifice plates of 9, 6 or 4 inch diameters can be used in conjunction with the two available fan speeds.

Circular Vibro Screen

 The circular Vibro Screen was introduced into tea industry for the classification of various grades of tea in an efficient and economical way. This machine is designed to work in a continuous manufacturing situation. Essentially, it comprises a circular gyratory screen that is subjected to three-component - horizontal, vertical and tangential - multiplane mechanical vibrations. The vibration is created by a motor with a double extended shaft fitted at both ends with eccentric weights. Both motor shaft and weights are mounted on the screen assembly. The drive assembly, in turn, is mounted on a circular base fitted with rugged springs. The springs not only allow the unit to vibrate freely, but also prevent the vibration from reaching ground where the machine is installed.

A three-component multiplane mechanical vibration is induced by a motor mounted on a vertical axis. The motor has double extended shafts fitted at both ends with eccentric weights. It is suspended from the screen assembly, which is supported on a circular base by rugged springs at its periphery. When leaves are fed into the assembly through a hopper, oversized particles leaves are immediately discharged through a tangential outlet. Smaller particles pass on down to the next screen to produce finer grades.

The machine's horizontal and vertical motion depends on the eccentric weights fitted at the top and bottom. Any increase in the top eccentric weight increases horizontal motion, which increases the machine's output. Similarly, more bottom eccentric weight increases vertical motion, which keeps particles in circulation.

The tangential motion, meanwhile, is controlled by the weights' angular position. It is at a minimum when the top and bottom weights are lined up; there is then virtually no tendency for the material to spiral. But if the weights are not lined up, the particles spiral from the center out to periphery. In this manner the leaf is sorted, with the finest particles spiralling furthest out.

Hammer Mill

The Hammer Mill is used to produce dust teas in a continuous manner. It is normally installed apart from other sorting machines so that the dusty atmosphere can be minimized in the sorting room.

The grinding chamber, which holds the grinding wheel, is made of thick steel. The latter is made of a cluster of carbon steel strikers running at very high speeds of up to 4,500 rpm. The size of the machine is expressed according to its grinding wheel - i.e., 6, 8, 10, 15, 18 or 20 inch.

Collecting chamber is a cylindrical chamber made of steel plate supported by three rods. Dust tea outlets through a vent at the chamber's bottom.

When the coarse product of other sorting machines is fed into the Hammer Mill's grinding chamber through the hopper, it comes into contact with the grinding wheel revolving at 4,500 rpm. The leaf is reduced into a fine power by the striker's sharp cutting edges. The dust tea so produced is directed by a suction fan into a collecting chamber and is directly discharged into the container. The velocity of the dust at the collecting chamber's inlet can be minimized by enlarging the duct through which it travels.

Andrew Breaker

In 1948, a machine was developed for breaking tea. It is called the Andrew Breaker, after its developer H.C. Andrew. Today, this machine is an integral of the modern tea sorting room. Earlier machines used for breaking tea could not solve a critical problem i.e. when leaf is broken into small grades, so is the stalk and this complicates its removal. The Andrew Breaker eliminated this problem in sorting.

The most important part of the Andrew Tea Breaker consists of a pair of fluted rollers.The rollers of 11 inch diameter and 17.5 inch length run in mesh but are not in contact. The rollers rotate at 60 rpm and are spring loaded.A lever is provided to adjust both the gap between the engaged teeth of the rollers as well as the pressure applied to the tea particles passing through.

Three types of rollers are used in the Andrew Breaker. The first kind of roller is the longitudinal fluted roller. These are sub-divided into two types - the 8 and 16 fluted types.Eight-fluted longitudinal rollers are general purpose rollers.The increased number of closer flutes in the 16-fluted longitudinal rollers are used in CTC manufacture for even grading and appearance. The third type of roller is also 8-fluted. But here the roller is fluted circumferentially because of which it is known as the corrugated type. This is a special purpose roller used for the treatment of broken teas or stalky coarse residue.

When rough tea is fed to the Andrew Breaker (fitted with longitudinal fluted rollers) through a conveyor system, it is compressed between the rollers rotating at 60 rpm. The amount of tea broken depends on the degree of pressure applied and the speed at which it is applied. Care must be exercised here to optimise the speed at which pressure is applied; that way there is no damage to the natural bloom of the made tea.

After extracting all normal, worthwhile grades from the bulk, stalky coarse residue can be fed to the Andrew Breaker fitted with corrugated rollers. In these rollers, the flutes run around the periphery of the rollers. These rollers cause a rubbing action that removes the skin from stalk and tends to disintegrate the tough and flaky particles that previously escaped breakage. The speed of the rollers here is maintained at 180 rpm.

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