# Baer's Comb Sorter

Topics: Cotton, Fiber, Median Pages: 6 (1912 words) Published: November 15, 2012
Baer’s Comb Sorter Diagram
Fibre Length:
The "length" of cotton fibres is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of a cotton is an indefinite quantity, as the fibres, even in a small random bunch of a cotton, vary enormously in length. Following are the various measures of length in use in different countries Mean length:

It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibres present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight. Upper quartile length:

It is that value of length for which 75% of all the observed values are lower, and 25% higher. Effective length:
It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a numerical length distribution
eliminated by an arbitrary construction. The fibres eliminated are shorter than half the effective length. Modal length:
It is the most frequently occurring length of the fibres in the sample and it is related to mean and median for skew distributions, as exhibited by fibre length, in the follwing way. (Mode-Mean) = 3(Median-Mean)

where,
Median is the particular value of length above and below which exactly 50% of the fibres lie. 2.5% Span length:
It is defined as the distance spanned by 2.5% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH". 50% Span length:

It is defined as the distance spanned by 50% of fibres in the specimen being tested when the fibres are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH". The South India Textile Research Association (SITRA) gives the following empirical relationships to estimate the Effective Length and Mean Length from the Span Lengths. Effective length = 1.013 x 2.5% Span length + 4.39

Mean length = 1.242 x 50% Span length + 9.78

Baer’s Comb sorter Method:
For the determination of the length and of the length distribution of cotton fibers in purified cotton the Baer’s Comb Sorter method: These directions describe the mode of procedure that is well adapted to the sorter* most extensively used in the United States at the present time. Apparatus— The sorter

Duplex Cotton Fiber Sorter consists of two banks of combs rigidly mounted side by side on a common base. Each bank of combs consists of at least 12 individual combs spaced 3.2 mm apart, one behind the other, and mounted in grooves so that as they are approached during the fractionating process and no longer needed, they may be dropped below the working plane. Each individual comb has a single row of accurately aligned and sharply pointed teeth, 12 mm long, consisting of needles 0.38 mm in diameter. The teeth are spaced 62 to 25 mm over an extent of approximately 50 mm. Accessory equipment consists of fiber-sorter forceps, fiber-depressing grid, fiber-depressing smooth plate, and velvet-covered plates. The sorter forceps consist of two brass pieces approximately 75 mm long, hinged on one end and slightly curved to present a beaked aspect at the gripping end for gripping the protruding fibers close to the surfaces of the combs. Usually, one of the gripping edges has a leather or other fibrous padding. The gripping edge is approximately 19 mm wide. The fiber-depressing grid consists of a series of brass rods spaced 3.2 mm apart so that they may be placed between the combs to press the fibers down between the teeth. The fiber-depressing smooth plate consists of a polished brass plate approximately 25 × 50 mm,...