Planetary Strander: A cage strander with backtwist. Planetary strander makes two twist action at the same time. Pay-off cradles rotates around their own axis while cage is rotating in opposite direction. With this backtwist , planetary strander saves the round shape of stranded material. This mean no "flower effect" of finished strand.
Backtwist ratio could be fixed or variable between 0-100 percent and even more upto 135 percent. Cradles also can be locked to rigid mode. Then Planetary strander works as a rigid strander.Disadvantage of Planetary strander is speed and limitation of pay-off units. Cage rotation speed maximum 100-150 rpm range. As the pay-off spool size increase rotation speed decreases to minimum 6-10 rpm range.
A classic Planertary strander line is completed with a caterpuller/capstan and a take-up unit.Other auxiiliary units such as die holder, tape/yarn applicator, lubricating equipment and chalk applicator may added. If necessary more than one cage could be used in one line. It depends on how many cradles are in one cage. Twisting lay is adjusted by the ratio between caterpuller's speed and rotation of cage.
Planetary strander is used for :
Fibre Optic and sub-marine cables
Overhead Lines and conductors
Insulated conductors of power cables iwth Class I or Class II conductor strand
Signal and Special cables.
Best For: Hard drawn bare wire stranding. Insulated conductors where backtwist is a quality issue.
Versatility: In compare to SingleTwist and Doubletwist buncher , Planetary has no weight issue of take-up drum. Auxiliary equipments are easy to add. It can work either with or without backtwist. Aplanetary line project must be configured for possible future needs. Because once whole line is configured , it could be real hastle to add more cradles or changing pay-off spool size. Thus, maximum number of strands has limited at first.
When bunching insulated cores, wire / insulated conductors also twist around thier own axis. Round shape of insulation is ruined because of torsion. In this case, insulation thickness is not constant and cores not circular anymore. Impedance and capacity of the final assembly would not be a constant value by length. Such default bears impedance, capacity and cross talk problems for Communications cables working over 600Mhz. Solution is back-twist or pre-twist depending on what type of twisting machine is used.