1 The machine revolutions per minute is only relevant to a specific machine and machine diameter. A larger-diameter machine, or one having more patterning facilities, would be expected to run at less revolution per minute
2 The circumferential speed in metres per second is a constant for a range of machine diameters of the same model and can be used to calculate the rpm for a particular machine diameter. An average circumferential speed is about 1.5m/sec; 2m/sec is 'high speed'.
Example: A 30-inch diameter machine runs at 40 rpm. Circumference of circle = pd, where p = 3.142, and d = 30 inches. pd = 94.26 inches, or 239.4cm (2.4m).
In one minute the machine turns 2.4 metres x 40 (rev) = 96 m. The circumferential speed is therefore 96/60 = 1.6 m/sec. To convert circumferential speed to rpm: 1.6m/sec x 60 = 96m/min.
96m/min divided by 2.4 = 40rpm for a 30-inch diameter machine.
3 The Speed Factor (SF) is a constant obtained by multiplying the rpm (e.g. 30) by the diameter in inches (e.g. 30) = 900. As can be seen, rpm and diameter vary inversely to each other - when the diameter increases, the rpm decrease.
Modern high-speed fabric machines can operate in factory conditions at speeds of 1.6 to 1.7 m/sec. Under laboratory conditions, speeds of 2.0 m/sec have been achieved.
The number of feeds can be expressed as a total for a particular cylinder diameter or as the number of feeds per inch of the cylinder diameter, in which case the total number of feeds for any cylinder diameter in that particular range of machinery can then be calculated.
Example: A single-jersey 4-track machine with 3 feeds per diametral inch will have 12 x 3 = 36 feeds in a 12-inch diameter, 54 in an 18-inch diameter, 90 in a 30-inch diameter, and 102 feeds in a 34-inch diameter.
The speed of fabric formation expressed in linear metres per hour is equal to (speed of machine in rpm x percent efficiency x number of knitting feeders x 60 minutes) n (number of feeds per face course x face courses per cm x 100).
Example: Calculate the length in metres of a plain, single-jersey fabric knitted at 16 courses/cm on a 26-inch diameter 28-gauge circular machine having 104 feeds. The machine operates for 8 hours at 29 rpm at 95 per cent efficiency.
XT , r , • J- o, 8 x 29 x 104 x 95 x 60 Number of courses knitted in 8 hours =-
Therefore the total length of the fabric in metres =
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