Tension device

Spandex Fibers. Spandex fibers are suppHed for processing into fabrics in four basic forms as outlined in Table 3. Bare yams are suppHed by the manufacturer on tubes or beams and can be processed on conventional textile equipment with the aid of special feed and tension devices. In covered yams, the spandex fibers are covered with one or two layers of an inelastic filament or staple yam the hard yam provides strength and rigidity at full extension, which faciUtates knitting and weaving. 

Conveyors may be of parallel-chain, mat, slat, woven wire-mesh belt, or cast-alloy type. Automatic tensioning devices are used to maintain belt tension during heating and cooung. The product may rest directly on the conveyor or on special supports built into it. RoUer-conveyors are used for large pieces. Flame curtains are provided for sealing the ends and for protection of special treating atmospheres. 

All chains, boomers, clamps, and tensioning devices used in the guy lines shall satisfy the mast manufacturer s recommendations. In the absence of mast manufacturer s recommendations, the following minimum breaking strengths should be maintained load guy lines—18 tons external guy lines—12 tons racking board guy lines—10 tons. 

A marine riser must be held in tension to prevent the riser from collapsing under its own weight. This can be accomplished by adding buoyant material to the riser pipe, or by mechanical tensioning devices (Figures 4-498, 4-499). Tensioning devices are usually required in water depths greater than 250 ft. 

A diagram showing how rubber sheet, fabric, linings, etc., are let off through tensioning devices into calenders, spreading machines, etc., and finally taken up on box rollers. Direction of travel and position of rubber nips are usually included in such diagrams. 

The bare wire is unwound, sometimes by a controlled tension device, and is preheated to a temperature above the Tg or Tm of the polymer to be extruded this is done so that the layer next to the bare wire adheres to it, and to drive moisture or oils off the conductor surface. The wire is fed in the back of the cross-heat die and into a guider tube. Upon exiting the guider, it meets the molten plastic, which covers it circumferentially. Since the wire speed, which is controlled by a capstan at the end of the line, is usually higher than the average melt velocity, a certain amount of drawdown is imposed on the melt anywhere from a value slightly greater than unity to 4. 

Surface-tension devices consist of wicking or grooved surfaces to direct the flow of liquid in boiling and condensing. 

Single-loop slitting (often referred to as post -loop slitting) is a concept that involves an uncoiler, a slitter, a loop (after the slitter), a tensioning device, and a recoiler. In order to operate in a single-loop mode, the slitter and the recoiler have their own separate drive motors. 

If the mills could roll perfect mill shape (see Fig. I), there would be no need for loops and tensioning devices and, except for some fan-out problems, the tight-line pull-through slitting-line concept would satisfy the tight coiling needs of the industry. 

Each of the de.scribed tension devices has its place and purpose. Because slitting lines are required to handle a variety of materials and applications, in due course, both of the above concepts were married into a single design. This resulted in a unit that can process oily and slippery material using only the pads, dry surface-critical material using the rolls, and many in-between materials combining both in tandem. With the tandem operation, three control variables are available to the operator pad air pressure, roll nip pressure, and brake air pressure (see Fig. 8). 

In most present installations, operators rely upon experience to know when to change the controls. In most cases, the operator limits himself to a few preferred sets of conditions that he finds comfortalbe. These may not be able to produce a finished coil of the best quality. However, computer programs have been developed to advise, and even set, a preferred set of variables. With this modem technology, the line can demonstrate an increased degree of repeatability and, hence, consistency of quality. How can the use of a loop and tension device improve quality of slit coils, and for what quality improvements are we looking ... 

Perhaps the most important expectation of a tension device is to produce uniformly tight coils, every time. When set on the floor or placed in storage, these coils will not sag into an elliptical shape, but rather will remain perfectly round. 

With loop slitting, all of the slit strands are pulled tight against the tension device, resulting in uniform tightness without the need of inserting paper. 

When tension devices are used, the unsupported strand length can be reduced to 8 ft. or less, depending on coil size. The shorter distance, coupled with uniform tension, and aided by fact that strip fan-out is accomplished ahead of the tension device in a free-Ioop state, results in improved sidewall condition. 

The post-loop concept allows the two split strands to hang freely, expend their residual stress, approach the tension device according to their shape, and wind neatly into tight coils on the recoiler drum. Often, it is desirable to provide extra separator disks, perhaps or 5 in., between the strands as they approach the recoiler drum. 

The definition of exit-loop slitting is that the slit strands are driven from the slitter and allowed to fall into a tensionless loop between the slitter and the tension device (see Fig. 14). Approaching the ultimate in the slitting process is not without... 

The most economical type of tensioning device is a wiper-type unit. These are simple to operate and will produce excellent results in rewinding the slit strip. 

Many potential users of this type of tensioning device are reluctant to purchase this design today because surface finish of the strip is becoming more and more critical, and this type of unit has the potential to mar a bright finish if the wipers are not properly maintained. Another deficiency of this type of unit is that it is not possible to operate with any form of slip-core rewinding because this unit is not capable of metering strip flow. However, even with these possible drawbacks, there is no other device that will produce a more uniform tension across the face of the coil and, with care, not mar most material surfaces. 

Another concern in this type of tension device is that if the rolls are diced for varying strip flow, the space in the kerf from the dicing can be an area for... 

Pinch-type tensioning devices will allow for a limited differential in strand speed from strip to strip to compensate for any gauge variation that may exist in the strip being processed. The slip-core rewinding technique is also possible with this type of device, provided that the rolls are driven or braked with a speed-regulated drive system. 

Figure 17 Material flow through an S -wrap tensioning device. This type of tensioning device may consist of two or more tension rolls, depending on the final tension requirements.

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