1. To collect the fibres from the cylinder by doffer,
2. To strip off the fibres from the doffer by doffer comb or any roller doffing device
3, To condense them into sliver with the help of calender rollers and trumpets.
4. For deposit them in the form of coils in a can with the help of coiler mechanism.
The doffer is a cast iron cylinder of the same width of the main cylinder 27 " dia.
The doffer bends secured to the upper part of the doffer pedestals at each side of the machine carrying at their forward ends the doffer stripping and grinding brackets.
The fibres doffed from the cylinder are carried on the under surface of the doffer and upwards at the front the machine. On reaching a position just above the doffer centre line, the fibres are stripped from the doffer by an oscillating doffer comb in the form of web.
Assisting factors in the transfer of fibres from cylinder to
doffer are
i) the doffer continuously presents a clean surface to the cylinder at the point of interaction;
ii) the clothing on the doffer is usually 10 counts finer than that on the cylinder, and the increased number of points per square inch increases the retentive power of the doffer clothing
iii) Owing to the curvature of the cylinder and doffer. the working surfaces move rapidly apart after the transfer of fibres to the doffer, so that there is little opportunity of the return of fibres to the cylinder.
iv) Centrifugal force due to the high cylinder speed tends to
throw fibres towards the doffer, whereas the much lower speed of
the latter prevents corresponding forces in the reverse
direction.
v) air-currents may also assists the transfer of fibres to the doffer.
DOFFER COMB:
The comb is an accurately manufactured straight steel plate provided with teeth or serrations on its lower edge. The comb shaft is rocked about its axis by a crank or eccentric drive at one end to impart an upward and downward movement to the comb of about 1 to 1 1/4" in an accurate path. The comb is operated at a speed of from 1200 to 1600 vibrations per minute. The fibres are stripped from the doffer by the downward stroke of the comb acting against the back of the teeth on the upwardly moving doffer surface.
CALENDER ROLLERS:
A collecting trumpet is positioned close to the nip of the calender rollers. The web leaving the doffer comb is collected and passed through the trumpet to the calender roller nip, in the form of a compact sliver.
The surface speed of calender rollers are kept slightly higher than that of doffer so as to maintain slight tension in the web between them.
The top calender roller is gear driven from the bottom roller shaft, and pressure is applied between the two rollers by means of two springs at each end of the rollers.
ASSISTING FACTORS IN THE REMOVAL OF FIBRES FROM DOFFER are
The physical contact of the comb made on the protruding fibres from doffer.
The web tension between calender roller and doffer.
The fanning action of the comb,
THE COILER MECHANISM- The object of this mechanism is condense further the silver delivered by the calender rollers and to lay them in an orderly manner in a cylindrical can for easy withdrawal at subsequent processing.
The coiler gets its drive from the bottom calender roller shaft as shown in fig.
This coiler calender rollers are driven at a surface speed slightly higher than that of the calender rollers so that the sliver is maintained in a taut condition as it passes from the calender rollers through the trumpet and into the nip of the coiler calender roller below the trumpet.
A tube wheel driven by gear on the upright shaft, has an inclined tube with its upper end below the trumpet and coiler calender rollers. The lower end of the inclined tube is provided with an exit for the sliver at a point near to its periphery so that the sliver delivered by the rollers passes down the tube and is led in circular coil into the can. The can is positioned on a plate driven through reduction gearing from the bottom of the upright shaft at a slow speed,
The slow rotation of the can changes the position at which each coil is laid, so that overlapping coils are formed around the can. This continues until the can is full. A stationery coiler plate, which surrounds the tube-wheel, assists in
Dressing the sliver firmly in the can and prevent the sliver from being damaged by the coiling mechanism.
