White Paper | Cable Chain Capacity

PVC

PUR

CHARACTERISTICS • Easy stripping • Compound material contains chalk; gets lighter when kinking • Economical material

FIRE BEHAVIOR

CHARACTERISTICS

FIRE BEHAVIOR

• Mostly self extinguishing • Releases hydrogen chloride gases, which react with

• Wear resistant • Shrinks after extrusion; harder to strip • Better mechanical protection

• Burns if not specially marked as highest flame retardant • Material gets tacky when burning • Releases toxic gases, such as hydrogen cyanide

moisture to form hydrochloric acid

• Highly toxic

Although PVC is the dominant choice for cable jacket materials, additional materials are also available as jacket choices, such as polyurethane (PUR).

BENDING LOADS Three distinct bending methods include the following. • Simple flexing (tick/tock)—Flexing at a single, defined break point. • Continuous flexing—Flexing that occurs along the entire cable length.

TORSION LOADS Torsion flexing typically occurs in robotic applications. Special torsion-rated cables are designed to withstand increased torsional stresses and feature a different construction than continuous flex cables. While continuous flex cable conductors are stranded tightly to allow relative movement of individual conductors during flexing, robotic cables have significantly longer lay lengths to compensate for more stressful torsional forces. Generally, the following parameters must be considered: Required length of travel; maximum acceleration and speed; minimum bending radii of cables and wires; combined weight of all moving components (including the cable chain and related cables); and desired life expectancy of the complete system. SELECTING THE BEST MATERIALS The molecular structure of a compound determines its fundamental physical characteristics, such as fire resistance and the ability to withstand certain oils. In turn, these attributes determine the material’s suitability as a wire insulator. Polyvinyl chloride (PVC) dominates the cable insulation market, although other materials are also used, such as thermoplastic elastomers (TPE), polyurethane (PUR) and polypropylene (PP). Each material has unique features that makes it suitable for different types of cables. For example, PVC offers relatively high mechanical firmness, good insulation resistance and flexibility at a reasonable price. In comparison, ether-based PUR guarantees microbe resistance and features high abrasion resistance, tensile strength, stability against certain oils and good flexibility. In general, cables and wires in highly dynamic applications must withstand acceleration forces up to 50 m/s². However, acceleration is not the primary factor to consider when choosing materials—abrupt deceleration is far more critical. Within a fraction of a second, the cable brakes to a stop. Because of this, certain rigidity is indispensable, which can only be guaranteed by suitable insulation materials. Choosing the wrong materials will eventually lead to cable chain fractures due to the extreme forces and highly dynamic acceleration and deceleration that the cable experiences on a continual basis.

• Guided flexing—Continuous flexing using a guiding component. (ex. pulleys)

Cables used in chains are exposed to bending along their entire length and are therefore subjected to continuous flexing. When specifying components for this type of use, it is important to choose cable specifically designed to handle these forces. For example, ÖLFLEX ® FD and ÖLFLEX ® CHAIN power and control cables from LAPP are carefully engineered for this purpose.

LAPP 29 Hanover Road, Florham Park, NJ 07932 T. 800 774 3539

www.lappusa.com www.lappcanada.com