Tea World

Lesson 24

Machine Used in Withering and Leaf Distoration

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Withering Trough

Withering troughs are generally installed in the first floor of the factory. Green leaves are spread over a wire mesh (No.4/16 16 gauge) which is fitted on plenum chamber. The height of the plenum chamber is 0.6 -0.76 m (201.5 ft).The leaves are placed over the mesh at 20-23 cm (8-9 inch) thickness or 8-9 kg /sq m (2.5-3 kg /sq. ft) of the withering trough.  Normally, the size of the withering trough is 22.9 30.5 -m (75-100 ft) long and 1.8 m (6 ft) wide. Better withering can be achieved with smaller trough of 22.9 x 1.8m (75x 6 ft) size. The trough is fitted with a suitable fan to deliver the required volume of air as per the size of the trough. To achieve proper withering, the fan has to deliver 45 CFM air for every square feet of trough area. For artificial withering, hot air from the drier room is bulked with outside air and used. Fans are arranged in such a way that they can draw air from the drier and cool air from the atmosphere.

Withering Trough

Green Leaf Sifter

It is used to remove extraneous materials such as stone, metal pieces etc. to avoid damage to the CTC rollers. The green leaf sifter consists of a reciprocating tray powered with an electric motor. The reciprocating tray is fitted with a mesh through which leaves are passed and unwanted materials removed. Powerful magnets are fitted in the sifter which removes the iron/steel particles from the leaves.

Rolling Machine

A conventional rolling machine or roller for orthodox rolling consists of three parts viz., the Table, the Hood and the Pressure cap. Rotation of the machine is achieved through three crankshafts attached to the table. The level gear mechanism transmit power to one of the crankshaft at a time, while the other two rotate freely on their bearings and play an auxiliary role. The pressure cap applies pressure to the leaf mass during rolling, imparting the proper twisting and bruising action. It is the pressure applied during orthodox rolling that causes the extraction of sap and imparts twist to the leaf . In some kind of rolling tables, both vertical and lateral pressure may be applied. Vertical pressure is applied with the help of pressure caps whereas lateral pressure is applied by a cone fitted in the middle of the table. The cone also causes greater circulation of leaf than that provided by battens alone.

Rolling Machine


It is the machine used to pre-condition of the withered leaves before putting into the CTC machine. It consists of a cylindrical drum of a diameter of 200 cm (8 inches), 380 cm (15 inches) or 460 cm(18 inches) depending on the capacity. Inside the circumference of the drum, the resistors are fitted at appropriate distances. The main shaft which rotates inside the drum, has vanes at equal intervals. There is a worm arrangement in the main shaft which facilitates forward motion of the leaves into the drum. The leaves are crushed in between the vanes and resistors and discharged through the diaphragm. The RPM of Rotorvane ranges from 30-35.

Rotorvane coupled with CTC machine

CTC Rollers

The CTC roller consists of a main shaft on which the segments are fixed by heat treatment on a mandrel form. The diameter of the roller is generally 200 cm (8 inches) and in the latest Senova models rollers are of 330 cm (13 inches) diameter. The length of the rollers varies from 600 cm (24 inches) to 910 cm (36 inches) depending on the capacity of the rollers. Generally, two rollers are fixed horizontally and parallel to each other and both rotate in opposite directions. The ratio of speed between the low speed and high speed is 1:10 depending upon the requirement of leaf or dust grade.

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