RING FRAME - 2
RING and TRAVELLER COMBINATION:
- The following factors should be considered
- materials of the ring traveller
- surface charecteristics
- the forms of both elements
- wear resistance
- smoothness of running
- running-in conditions
- fibre lubrication
- For the rings two dimensions are of primariy importance. 1.internal diameter 2. flange width.
- Antiwedge rings exhibit an enlarged flange inner
side and is markedly flattened on it upper surface.
This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination.
- Low crown profle has the following advantage. Low
crown ring has a flattened surface top
and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely used ring form now.
- The ring should be tough and hard on its exterior. The running surface must have high and even hardeness in the range 800-850 vikcers. The traveller hardness should be lower (650-700 vickers), so that wear occurs mainly on the traveller, which is cheaper and easier to replace. Surface smoothness should be high, but not too high, because lubricating film can not build up if it too smooth.
- A good ring in operation should have the following
- best quality raw material
- good, but not too high, surface smoothness
- an even surface
- exact roundness
- good, even surface hardness, higher than that of the traveller
- should have been run in as per ring manufacturers requirement
- long operating life
- correct relationship between ring and bobbin tube diameters
- perfectly horizontal position
- it should be exactly centered relative to the spindle
- In reality, the traveller moves on a lubricating
film which builds up itself and which consists primarily
of cellulose and wax. This material arises from material
abraded from the fibres.If fibre particles are caught
between the ring and traveller, then at high traveller
speeds and with correspondingly high centrifugal forces,
the particles are partially ground to a paste of small,
colourless, transparent and extremely thin platelets.
The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on
- yarn fineness
- yarn structure
- fibre raw material
- traveller mass
- traveller speed
- heigh of traveller bow
- Traveller imparts twist to the yarn. Traveller and
spindle together help to wind the yarn on the bobbin.
Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller.
The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behind by the spindle.
- High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited.
- When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength.
- If the traveller speed is raised beyond normal levels , the thermal stress limit of the traveller is exceeded, a drastic change in the wear behaviour of the ring and traveller ensues. Owing to the strongly increased adhesion forces between ring and traveller, welding takes place between the two. These seizures inflict massive damage not only to the traveller but to the ring as well.Due to this unstable behaviour of the ring and traveller system the wear is atleast an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celcius and the danger of the traveller annealing and failing is very great.
- The spinning tension is proportional
- to the friction coefficient between ring and traveller
- to the traveller mass
- to the square of hte traveler speed
and inversely proportional
- to the ring diameter
- and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop.
- The yarn strength is affected only little by the spinning tension. On the other hand the elongation diminishes with increasing tension, for every tensile load of hte fibres lessens the residual elongation in the fibres and hence in the yarn. Increasing tension leads also to poorer Uster regularity and IPI values.
- If the spinning tension is more, the spinning
triangle becomes smaller . As the spinning triangle gets
there is less hairiness.
SHAPE OF THE TRAVELLER:
- The traveller must be shaped to match exactly with the ring in the contact zone, so that a single contact surface, with the maximum surface area is created between ring and traveller. The bow of the traveller should be as flat as possible, in order to keep the centre of gravity low and thereby improve smoothness of running.
- However the flat bow must still
leave adequate space for passage of the yarn. If
the yarn clearance opening is too small, rubbing of the
yarn on the ring leads to roughening of the yarn,
a high level of fibre loss as fly, deterioration of yarn
quality and formation of melt spots in spinning
of synthetic fibre yarns.
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