DoubleTwist Buncher is the fastest and compact solution among other twisting/bunching machines. Layout of Double twist buncher generates two twists per rotation. Cores are pulled through twisting plate over bow (also known as flyer arms). Then, wound on take-up spool. Twisting occurs first at the entrance of the bow and second just before coming off the bow. Doubletwist machine may be used for several different applications. Bare conductors and insulated cable cores can be twisted at comparingly high speed level. Twists per minute is twice the rotation of the bow. A big advantage over not only Single-twist machine and also other twisting machines. Latest models can reach 8000 twists per minute. In General, double twist machines are referred by the size of Take-up spool. "XTC630" for example, points that take-up spool flange size is 630mm.
Various types of bows are used for bare wires, solid or flexible insulated cores. Use of correct bow is important for vibration problem and tension control over twisted material. Light-weight bows are more productive.
Double twist is compact , fast and reliable but still not best solution for large solid bare conductors. Construction of bundle is not as good as a rigid strander. Total weight of take-up spool is limited. Therefore, over 1600mm flange size is not productive. Also, Production speed is decreased drastically by spool size. Vibration is an obstacle for doubletwist bunching. Machine manufactuers use various solutions to that.
Best For: A doubletwist machine is best for one layer stranding. Bunching fine strands of bare conductors and flexible insulated cores.
Versatility: DoubleTwist buncher versatile in terms of product range. Number of strands has no limit as long as finished overall diameter stays within in the range of machine. Total weight of take-up spool is limited. Size of take-up spool is fixed. Application of foil or other wrapping materials is not possible while twisting process. Changing processed material may require bow change. Stranding sector shape conductors is possible with a rotating compacting head installed.
There are two main types of doubletwist.
(1) Direct pull-up.
(2) Double twist with capstan.
(1)Direct pull-up double twist uses take-up spool as pulling force. Take-up spool and bow driven by two seperate motors. Lay-length is adjusted by means of changing take-up spool rotation versus bow speed electronically controlled. Advantages of direct pull double twist machine are precise and constant lay-length, highest speed for twisting, minimum mechanical friction and use of gears minimized.
Therefore maintenance cost and frequency are recuded as well. Precise electronic control of take-up speed also results in precise pitch. Disadvantage of direct pull doubletwist is that requires use of motor driven pay-off units. Without motor driven pay-off units may result unwanted twist construction. Rotating and motor driven pay-off units are necessary to maintain overall quality of final product.
(2) Double twist with capstan use only one main motor. Rotation of bow unit is transferred to captsan via a gear set. Then, take-up spool by means of a clutch. Cores are pulled by capstan. Lay-length is fixed by changing gears that adjust the ratio between bow and capstan.
Low initial cost is an advantage. However, low speed , tension control problem, wearing gears, non-stable pitch problems make this type undesirable. Not to mention "Flower effect" is still there.
Empowering capstan by use of slip rings is possible. By doing that problem of wearing gears and non-stable lay length is solved. However, use of slip rings bring its own set of maintenance headaches.
TIPS:
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Double Twist buncher is good for only a few type of your stranding needs. Multi layer stranding and conductor stranding may lead to quality problems.
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When you make a purchase make sure manufacturer has reliable solution to lay-length stability
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Main bearings for the bow and cradle are right size and compatible with weight of your product.
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A Double Twist buncher might work around the clock but maintenance schedule must be kept well.
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Main bearings for the bow and cradle may produce at high speed. If so they must be ventilated or cooled.
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Pre-Twist must be used for certain products.
