Flats in Carding Machine: Types, Construction and Movement
Dept. of Textile Technology
Sarvajanik College of Engineering & Technology, Surat, India
FLATS IN CARDING MACHINE
In the nineteenth century, cards were designed with the top flats carried on an endless chain so that they could move continually forward as the card worked. This type of card is called a “revolving flat top” (R.F.T.) card or more commonly a “revolving flat” card. Flats in carding machine are the flexible wire–clothed bars rotating at a very slow speed (8–20 cm/min) compared with the highspeed cylinder. Flats move slowly either in the same direction or in the opposite direction of the cylinder, but the wire points are always backward, which is opposite to the direction of the cylinder wire points. Together with the cylinder (Fig.), the flats form the main carding zone.
Here, the following effects should be achieved:
- Opening of tufts into individual fibers;
- Elimination of remaining fiber impurities;
- Elimination of some of the short fibers;
- Untangling neps (possibly their elimination); dust removal
- High degree of longitudinal orientation of the fibers.
Construction of the Flats:
The bars of the flats are made of cast iron and are somewhat longer than the operating width of the card, since they rest on adjustable (so-called flexible) bends to the left and right of the main cylinder and must slide on these guide surfaces. Each bar is approximately 32 – 35 mm wide (might change to smaller widths). The bars are given a ribbed form (T-shape) in order to prevent longitudinal bending. A clothing strip (108 b) of the same width is stretched over each bar and secured by clamping, using clips (c) pushed onto the left- and right-hand sides of the assembly. Since some space is taken up by the upper edge of each clip, only a strip about 22 mm wide remains for the clothing (hooks or teeth). For this reason, the flats do not enable an absolutely continuous carding surface to be formed above the cylinder; there are gaps between the clothing strips.
The flats as used on the flat type carding machine designed for processing cotton and fibres of similar staple length to cotton may be fixed in relation to the carding cylinder or part of a chain of revolving flats which move around part of the circumference of the carding cylinder.
Types of Flats:
Flats are two types….
- Revolving flat
- Stationary flat
Conventionally, the revolving flat is T-shaped and made of cast-iron, machined to accept a top of card-clothing attached to its flange by steel clips, each end of the flat being machined for correct location of the flat in close proximity to the carding cylinder, against which the card-clothing top has to operate. The rib of the flat is designed to provide the necessary stiffness to enable the flats to span the width of the carding machine and ensure that an equal setting of the card-clothing on the flats to that on the carding cylinder is sustainable over the working width of the cylinder.
Stationary flats can be used in addition to revolving flats or can be entirely substituted for revolving flats, such stationary flats being conventionally also T-shaped in the form of an iron casting or an aluminum extrusion. The flange carries a card-clothing top or other operative element such as a trash extracting knife which is clipped or attached by screws to the surface of the flat, and the rib is designed to support the flat correctly across the width of the carding cylinder. The ends of the flat are machined to accept the setting and securing arrangements for fixing the flat to the carding machine frame in its required relationship to the carding cylinder.
With both stationary and revolving flats, when the card- clothing top or other operative element becomes worn out or damaged, it is removed from the flat and a new top or other element is clipped or screwed to the flat in replacement. Replacement of the card-clothing top which is conventionally clipped or bonded to the revolving flat involves the use of specialized machinery which adds to the cost of the replacement. Replacement of the top which is screwed to the flat requires investment in the specially designed flat adapted to receive a screw-on type of top.
Movement of the Flats
The bars of the flats mesh individually, like an internally toothed wheel, with the recesses in a sprocket gear, and are carried along by rotation of the sprocket. The ends of the bars of the operative flats slide over a continuous bend – with metal-to-metal friction.
As the flats move at a very low speed compared with that of the cylinder in principle, the flats can be moved forward or backward, i.e. in the same direction as or in opposition to the cylinder.
If the flats move with the cylinder (forward), the cylinder assists in driving the flats and the removal of strippings is easier. Forward movement therefore gives design advantages. On the other hand, reverse movement (against the cylinder) brings technological advantages. In this system, the flats come into operative relationship with the cylinder clothing on the doffer side. At this stage, the flats are in a clean condition.
They then move toward the licker-in and fill up during this movement. Part of their receiving capacity is thus lost, but sufficient remains for elimination of dirt, since this step takes place where the material first enters the flats.
At that position, above the licker-in, the cylinder carries the material to be cleaned into the flats. The latter take up the dirt but do not transport it through the whole machine as in the forward movement system; instead, the dirt is immediately removed from the machine (directly at the point where the flats leave the machine).
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