Tea World

Lesson 24

Sorting Machines

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A good number of sorting machines are used in modern tea factories for sorting and grading of tea.

Myddleton

The Myddleton tea stalk extractor is a common machine in all types of tea manufacture. It is used widely in almost all tea growing areas as an initial sorting machine. It performs the operations of grading and making tea free of stalks.

There are two trays in the Myddleton, the top and bottom trays. The top tray is 9ft x 4ft and the bottom tray is 8 ft 5 inch x 3ft 10 inch. The trays are made of thick aluminum sheet, with lines of small bosses, each with a perforation at the top. The trays are easily removable and sieves of different specifications can be fitted into the frames to suit the tea being treated. One of the Myddleton's two sieves is normally has 3/16 inch perforations and 1/8 inch high bosses. Two additional trays are also available; one with 7/32 inch perforations and 1/8 inch high bosses, and the other with 17/64 inch perforations and _inch high bosses.

An oscillating motion is imparted to the sieves with the help of a crankshaft, which revolves at 200 rpm. Leaf is fed to the Myddleton machine at spread thicknesses of approximately 1.3 to 1.9 inches. The tea being sorted in the Myddleton moves down a slopped tray between the bosses. This imparts a slight disturbance to the mass and causes the leaf to hop through the perforations. The stalk and fibre slide over the bosses pass over the end of the tray, and is thus separated.

The Myddleton can also be used for grading by treating fine and coarse teas separately. 

Rotary sifter

The rotary hexagonal sifter, or Ghugi, is one of the most important machines for orthodox operations. This machine has gained popularity for its efficient working. Normally, leaf sorted at the uppermost level of the Myddleton is fed to the Ghugi for selection into other grades.

The important components of the Ghugi are three screens of different mesh combinations - such as 14, 12 and 10 or 10, 8 and 6 - forming a hexagonal body of 5 ft and 3 ft at two ends. The sifter is set on an incline, which can be adjusted according to requirements. The sifter is usually about 10 ft long.

The sifter can be run at 25 to 30 rpm with the help of a motor or a line shaft. Due to the rotation of the sifter at an inclined position, the tea moves from the feeding point to the sifter's discharge end. The tea passes through various separating zones in the sifter according to the size of the particles. Thus, the grading of tea is carried out.

Electrostatic Fibre Extractor

The Electrostatic Fibre Extractor (EFE) is a relatively new machine used for stalk extraction after drying. In this machine, the principle of static electricity is used for extracting fibre and stalk. It can be used in continuous manufacture with the help of a conveyor system after the second drying. The machine is normally 10-12 ft long and 3-4 ft wide and is considered one of the best for extracting fibre in CTC manufacture.

This machine works on the principle of static electricity. There are seven PVC rollers arranged in two rows that run at speeds of 2,000-2,500 rpm. Tea fed into the machine via a conveyor system comes into contact with the PVC rollers, causing friction between the two. As a result, static electricity is produced with the fibre and rollers developing opposite charges. This causes the particles and rollers to attract each other. But the fibre is turned over through centrifugal action and collected in aluminum collecting boxes fixed over the conveyors between rollers. From there it is transferred to other containers.

Electrostatic Fibre Extractor

The Macintosh tea sorter

The Macintosh tea sorter has several outstanding features. It is widely used for both orthodox and CTC manufacture. The unique feature of this machine is that it makes uniform size grading possible. In today's tea market, this is of great importance.

The machine has five trays with seven discharge outlets for various grades of tea. The trays slide into the frame and are each securely fastened with four band-operated screws. All trays are interchangeable, and the mesh used depends on the type of tea to be sorted. The selection of trays too depends on the grades to be produced, but the following broad guidelines may be considered for sorting leaf.

Tray no.

Mesh no.

Grade discharged

1.

30 at closed end

No. 1 Brown Dust

24 at open end

No. 2 Dust

2.

20

No. 3 Fanning

3.

12

No. 4 Broken Pekoe

4.

19

No. 5 Small Pekoe

5.

8

No. 6 Larger Pekoe

No. 7 Pekoe Souchong

In the case of broken grade teas, the arrangement of trays can be made as follows

Trey no.

Mesh no.

Grade discharged

1.

30 at closed end

No. 1 Brown Dust

24 at open end

No. 2 Dust

2.

20

No. 3 Small Fanning

3.

18

No. 4 Larger Fanning

4.

14

No. 5 Small Broken Pekoe

5.

10 to 12

No. 6 Larger Broken Pekoe

No.7 Broken Peko2 Souchong

Tea is fed to the Macintosh through a hoper attached at one end. The rate of feed is controlled by adjusting a mechanically agitated flap valve. A satisfactory rate of feed has to be ensured to suit the different types of tea being sorted in the machine.

The gradient trays are adjustable and quickly interchangeable so that grading can be changes as desired. The machine's frame is connected by a connecting rod to a single crankshaft fitted with heavy duty ball bearings.

The crankshaft rotates at 250 to 270 rpm and transmits a straight oscillatory motion to the trays with the help of spring legs. Due to this motion, tea particles pass through holes according to their size, and are thus classified into various grades within 8 to 10 seconds.

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