Cable and hose carriers prevent the lifelines of automated machinery from tangling and fatiguing prematurely by limiting flexion to a specified radius, and imparting a gentle rolling to feed lines in and out as machinery moves. But there's a lot more to applying cable and hose carriers than just stringing cables through — and picking a carrier out of a catalog is not likely to provide the best possible solution. After all, application variables make it difficult to satisfy weight requirements, travel speeds, environmental conditions, mounting configurations, and space limitations with one standard product. A better tactic than catalog shopping or even developing a custom design from scratch, which can be prohibitively expensive and time-consuming (particularly for limited quantities) is an approach somewhere in the middle.
Assembling standard components (including links, crossbars, and accessories) into configurations that satisfy a specific application often makes for ready-to-install carrier subassemblies, with all the necessary accessories, mounting hardware, brackets, and fabrications. This is a practical way to achieve the results of a custom cable and hose carrier at a reasonable cost.
Choosing which type
Most cable and hose carriers consist of parallel side links joined together by crossbars that support the hoses, where pivot pins and stops allow the links to travel through a predetermined arc. Some designs are open between links, while others are completely enclosed for greater cable and hose protection.
Open, nonmetallic carriers are made of heavy-duty fiber-reinforced nylon, and are most suitable for high speeds and long travels. These carriers are nonconductive and corrosion-resistant, particularly when they incorporate nonmetallic pins or bars. Typical uses include machine tools and industrial robots. Lighter versions are also suited to automation machinery or where quiet operation is necessary.
Completely enclosed carriers are another link-type design that envelops the top and bottom of hoses and cables in environments with abrasive materials. Several enclosure subtypes allow easy access to cables and hoses with removable slide strips or plates.
Metallic link-type carriers consist of metal links joined by hardened steel pins that act as both bearings and lock points. They are suitable for machine tools, cranes, industrial robots, mobile and construction equipment, and steel mill machinery.
Demanding applications
In some applications, carrier design is central to long-term machine operability. One example is aerial boom lifts — built with ever-longer lengths for greater reach. Cable and hose carriers located between telescoping boom sections allow machines to reach greater heights with a smaller retracted boom envelope. By controlling the motion of hydraulic hoses and wiring cables attached between the base and tip of the boom sections, carriers also prevent cable fatigue.
Minimized weight and resistance to environmental conditions are key. Light nylon-based materials are one option. New metal carriers with less steel content are another way to reduce weight, as well as exposure to steel market instability. These light yet strong units can support the longer cantilevered spans increasingly common in aerial lift design.
Underground directional drills are another illustrative application. Here, carriers free operators from having to pace with the machine's carriage, and allow them to remain stationary. But the challenge is managing hydraulic lines to the carriage that feeds drill pipes used in the operation, and electrical cables for controls, speed sensors, and solenoid-operated valves. Dirt, oil, and weather extremes abound; a water and bentonite mud mixture flows during operation, and there is exposure to hydraulic oil during maintenance.
Plated or stainless steel carriers excel here, particularly when internal dividers or bars separate hoses by size. A cost-effective option for protection is textile sleeves.
In contrast, cables on pick-and-place robotics are not abused by dirt and water. Their challenge is the twisting, two-way movement of axes. Here, rollers incorporated into carriers for robotic vacuum, air, and power lines (say, on injection molding machines) minimize hose wear and permit use of unique reverse-bend configurations to fit in a limited space.
Overhead or portal cranes and gantry robots also exhibit complex motion. Here, carriers offer advantages over systems. Unlike festoons, carriers can be center-mounted to accommodate bidirectional ranges of motion. Fluid and electric power lines are easy to combine in a single carrier — difficult or impossible with reels or festoons. Carriers also eliminate the space-consuming third rail effect of bus bars, as they can be mounted without safety guards or isolation.
Subsystems
Several accessories can be added to carriers to boost performance and simplify designs. For example, half-shear lockout systems reduce the need for pins and snap rings: These inserted molded elastomer torsion bearings at link-pivot points significantly reduce noise for equipment used in laboratories, medical and semiconductor equipment, and other applications where quiet operation is required. Other subsystems:
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Hinge or snap-out bars allow easy access and allow installation of cables and hoses with fittings that cannot be fed through carriers.
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Polymer rollers can reduce wear incurred by rubbing cables and hoses, as are window extenders that add more vertical room. Similarly, low-friction sliders added to nonmetallic carriers reduce wear and load on extremely long travels.
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Carriage support systems for plastic link carrier applications support heavier hose and cable loads and speeds. They incorporate major rollers and intermediate supports, which together bear the carrier for the complete length of travel. So, the entire system rolls on channels mounted to the floor or crane bridge for speed to 450 ft. per min. — suitable for overhead crane applications.
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Long-travel support systems with retractable roller systems ride on a simple rail. The carrier doesn't glide on itself; instead, as motion is created as links pass through the radius, rollers are lifted from the guide rail and pulled inwards. On the return travel, roller sets are pushed back out and sit down on the rail for rolling support through the complete travel. This makes for speeds to 5 m/sec, reduction of tow force up to 90%, and friction elimination on carrier links.
Steel vs. plastic
Most carrier manufacturers have concentrated recent development efforts on plastic carriers, but steel remains a useful design option. In fact, some newer steel versions are lighter than previous designs — with the added ability to support longer spans than plastic. Some tips when deciding between metal and nylon carriers:
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Use metal if loads exceed 15 lb per ft.
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Use nylon with speeds over 100 ft per min.
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Metal carriers are most practical for travels up to 50 ft. Beyond that, nylon is more economical and functional.
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Nylon carriers perform best between 0° and 250° F.
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For corrosive environments, plastic carriers might be the logical choice; that said, carriers in stainless or zinc dichromate-plated steel are sometimes better, particularly for longer unsupported spans.
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Appearance should also be considered when choosing carrier material.
The Gortrac Division of A & A Manufacturing Co. Inc. provides CAD drawings at gortrac.com. Also visit motionsystemdesign.com/issue for the latest articles online.
A word on specifications
Collect as much information as possible on your design: This might include cross-sectional size, carrier radius, length of travel, any height and width clearance limitations, travel speeds, as well as number and type of cables, and environmental conditions. Regardless of which carrier type is ultimately best for your application, supplying as much information as possible to manufacturers helps them determine which of their designs is suitable. The total weight per foot of the cables and hoses within the carrier, including the weight of any liquids contained in the hoses, is also relevant information.