Cop Shape

• The cop, the typical package shape on the ring spinning machine, consists of three clearly distinguishable buildup sections

• the lower, rounded base (A) • the middle, cylindrical

section (Z) and • the conical nose (S).

Winding and binding coils

• This prevents entire layers from being pulled off during unwinding of the cop in downstream processing

COP BOTTOM

• It is built up from bottom to top from many conical layers (Fig), but constant conicity is achieved only after the formation of the base. In the base portion itself, winding begins with an almost cylindrical layer on the similarly almost cylindrical tube. With the deposition of one layer on another, the conicity gradually increases.

The formation of the conical layers

• The ring rail speed increases during upward movement and falls during downward movement.

• At the tip of each layer the speed is higher than at the base of the layer, i.e. the ring rail does not dwell as long at the tip as it does at the base: less material is wound, and the layer is thinner at the tip. If it is assumed by way of example that the ring rail is moving twice as fast at the top of its stroke as at the bottom of the stroke, the first layer would be half as thick at the top as at the bottom, i.e.b1 1/2 instead of b1, (Fig. 88).

Motion diagram for the working elements: ring (a), balloon checking rings (b) and yarn guide eyelets (c)

THE WINDING MECHANISM

Winding mechanism (an example) not commercially used presently

FORMING THE BASE

• The base is convex in order to accommodate as much yarn as possible on the cop.

• The Dog/ Cam ‘N’ will require to create the base in to round shape.

PREPARATION FOR DOFFINGIf the empty tubes have been prepared for the change and if the ring rail has reached its uppermost position (II)

the ring rail and the     balloon checking rings are lowered (III) in order to reach the cop more easily.

At the same time the yarn guide eyelets are tilted upward (IV),

Underwinding position (b) and piecing position (a) of the ring rail

Reserve winding (1) and underwinding (2)

The forces acting at the travelerThe following forces act on the traveler (1) in the plane of the ring (2):•A tensile force FF, which arises from

the winding tension of the yarn and always acts at a tangent to the circumference of the cop (3).•A frictional force FH between the ring

and the traveler. In the stationary state, i.e. with constant traveler speed, this braking force FH is in

equilibrium with the forward component FT of the yarn tension FF.

Hence we have:

The forces acting at the traveler cont..

• A force FN normal to the surface of the ring

(pulling the traveler in the direction of the cop, diminishing the friction of the traveler at the ring created by the centrifugal force FZ ).

• The frictional force FHarises from this

normal force in accordance with the relation:

The forces acting at the traveler cont..

• A centrifugal force FZ, which is the largest

force acting on the traveler. This force can be calculated in accordance with the relations

• where mL is the mass of the traveler, ωL is the

angular velocity of the traveler, and dR is the

diameter of the ring.

The forces acting at the traveler cont..

• Professor Krause (ETH, Zurich) identifies the following relationships between these forces, solved for the tensile force:

For a rough estimate, the term                        

can be ignored. Approximately, therefore, we have:

• The tensile force (FF) on the yarn; a, with a large cop diameter; b, with a small cop diameter (bare tube)

Continual changes in yarn tension due to winding on larger and smaller diameters

Resolution of forces at the traveler: a, in elevation; b, in plan

The resultant tensile force FL on the yarn

Varying inclination of the traveler on the ring; a) upright; b) inclined

BALLOON TENSION