Most engineers think of flat cable as inexpensive wiring that runs between computer peripherals. But not all flat cable is created the same. There is a special category of flat cable that excels in uses where space efficiency isn’t the only consideration. What’s called Extruded Silicone cable designed specifically for motion control and automation where flexibility, strength, and space economy carries a premiun.
An Extruded Silicone cable is a collection of wire conductors that has been encased in a silicone jacket by means of a special extrusion process. The most typical form factor for these cables is that of a flat cross section with conductors lined up in parallel. But cables can be extruded in other shapes to handle specific needs, such as to snug-fit into a wiring channel.
Extruded cable technology is unique to Cicoil Corporation, based in Valencia, California.
The basic technology of encasing conductors in silicone jackets has been in use for over 50 years and can be found in diverse applications ranging from jet fighters to industrial motion control equipment. A recent development is the ability to manufacture silicone-jacketed cable in continuous lengths through use of a proprietary extrusion process (Fig. 1). This reduce costs, improved precision, and made it possible to manufacture long cable lengths that were impractical with older methods. These older methods involved molding wires in silicone, and curing the resulting cable for up to two days.
FLAT VERSUS ROUND CABLES
It is also useful to contrast the makeup of Extruded Silicone flat cable with the construction of typical round “flex” cable. Round cables generally are characterized by insulated wires in a bundle which is surrounded by several layers of other material. The bundle is usually wrapped in either a textile material or a polymer chosen to minimize frictional heating as the cable moves. A PVC jacket surrounds these layers. In shielded cables, there is an additional set of layers consisting of another low-friction wrap, braided copper, and an overall jacket of PVC or other material selected for abrasion resistance. A point to note about this construction is its use of multiple layers of insulation and special low-friction materials necessary to reduce the friction that arises as cables go through numerous cycles of repetitive motion (Fig. 2).
For comparison, an Extruded Silicone cable also makes more efficient use of insulating material. It needs no low-friction tapes and fillers because conductors don’t move within the silicone material that forms the outer jacket. And when bent in the plane of its thin cross section, Extruded Silicone has inherently more flexibility than round cable. The flat form factor of Extruded Silicone also provides better heat dissipation that round cables because there is more surface area for a given volume. The larger surface area lets flat cables carry a higher current level for a given temperature rise and for conductors of a given cross section. Conductors in a flat cable also have a fixed geometry that makes for consistent and non-varying electrical qualities. The spacing of conductors in the extruded silicone never changes as the cable moves. Thus cable impedance, inductance, capacitance, time delay, crosstalk, and attenuation all remain constant. Similarly, the conductors in the cable all have the same physical and electrical length. This, coupled with the fact that the dielectric dimensions stay constant, means that signal skewing and differential time delays between signals in the cable stay at a minimum.
Extruded flat cable is available in a wide variety of configurations, enabling engineers to optimize the cable package for the application. The silicone rubber jacket,and the use of high flex conductors, make it twice as flexible as other widely used types of fl at cables, and ideal for flexing, repetitive motion applications. The silicone jacket provides a water proof case resistant to extreme heat and cold.
Finally, flat cables can form an inherently high-density interconnect system. Packing density of flat cable is higher than is possible with round cables. The fact that conductors can be visible in the silicone extrusion simplifies coding, inspection, and tracing circuits for trouble shooting.
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Filed Under: Cables + cable management