Sizing and selecting cable carriers

July 1, 2012
Besides preventing failure, carriers ensure the safe and smooth operation of motion designs. Smart designers use relevant information to match carriers to applications before design finalization.

Carriers guide cable and hoses, and protect them from abrasion, snagging, and overbending during machine movement. They’re more versatile than conductor bars, festoons, and reels, because they can be mounted anywhere along a motion design’s travel. What’s more, in center-mounted applications, carriers only need half the amount of cable/hose to achieve the same travel.

As with other common motion components, carriers are sometimes low-priority bill-of-material items, with price and delivery often the main criteria used for their selection. However, an inappropriate carrier can quickly cost more than its initial cost if failure becomes chronic or noticeable by the end user. In obscured locations, unnoticed carrier degradation an even lead to catastrophic failure.

Step-by-step carrier sizing

Following is a ten-step process for quantitatively determining the most suitable cable carrier size for a given application.

Step 1 — Make a list of all cables and hoses to be carried in the design.

Step 2 — By adding a safety factor to the outer diameter of the largest cable or hose (10% for cables, 20% for hoses), determine the inner height B dimension required.

Step 3 — Determine the inner width A dimension required (shown in the “Installation Dimensions” illustration) by adding the outer diameters plus appropriate safety factors (again, 10% and 20%) of all cables and hoses.

If using vertical cavity separators — inserts that keep cables segregated and organized over the width of the carrier — add that separator width to the equation.

If using horizontal cavity dividers — used to stack layers of cables and hoses in individual vertical compartments, to prevent crossover and entanglement in both X and Y directions — it’s recommended that the designer consult with the manufacturer.

Step 4 — Next, refer to the manufacturer’s sizing chart to identify the
most appropriate carrier model. Here, note that most manufacturers also provide web design assistance including design configuration and automatic 2D or 3D drawing files. The total
ideal fill is 60%.

Step 5 — Check the carrier’s outer width C and outer height D dimensions against potential space restrictions.

Step 6 — Select the minimum bending radius R by consulting the cable and hose manufacturer specifications.

Step 7 — Check the dimensions for the depot K and curve height H
against potential space restrictions.

Step 8 — Determine the amount of travel required by the installation.

Step 9 — Consult manufacturer design guide specifications for curve length CL of the chosen carrier, where CL = (R x π) + (Pitch x 2)

Step 10 — Final carrier length is the total travel/2 + Distance offset from center + CL.

For minimum carrier length, a moving bracket should be mounted
directly above fixed bracket when machine is in center of travel. Offset is the dimension between those brackets at center of travel. Height H is the overall height of the carrier at the loop; clearance should be provided above the carrier (as specified by the manufacturer) for both metal or plastic carriers, to account for built-in camber.

Closer look at design factors

Considerations requiring additional attention are unsupported travel lengths, load, and speed.

Load is the total weight of the cables and hoses within the carrier, typically expressed in pounds per foot. If hoses will contain liquid, that weight should be included in calculations as well. Typically, carriers are designed to support the load of an average cable lineup physically able to fit properly into their geometries.

Consider the load’s interactions with unsupported travel limits. One solution is metal carriers; see the section on the next page that details this technology. Another design element is rolling carriage supports. These are most commonly applied on steel carriers with travels that exceed the limits of fixed roller supports, or when heavy payloads and high velocities are present.

In short, such a carriage support system consists of rollers, conveyor supports, and a moving framework that supports the carrier over the complete length of travel. Channel guides ensure accuracy and dependability, even at high loads and velocities.

Such carriage systems for longtravel plastic carriers also exist. These are lightweight for reduced tow forces versus conventional carriage systems; modular, quickly bolting together or apart; feature urethane wheels for low noise; and are paired with plastic or steel track. These carriage systems are also self-guiding for travels under 50 feet. Channels are required for travels over 50 feet.

Yet another option is modular sliders — removable glide shoes molded from low-friction materials, providing a replaceable, low-wear gliding surface in long-travel applications to reduce tow forces and increase life. Some applications that move very quickly necessitate more customized installations with long-travel carrier supports. Unlike traditional systems in which the carrier glides on itself, one such support system utilizes a retractable roller system that rides on a simple rail.

Using the carrier’s polygonal effect, the rollers are lifted from the guide rail, and pulled inward as the links pass through the radius. On the return travel, the roller sets are pushed back out and sit down on the rail providing rolling support through the complete travel. These systems allow for travels to 2,000 m; speed to 5 m/sec; up to 90% reduction of tow force; and no gliding friction on carrier links.

No matter the design, note when a carrier is used in any arrangement besides horizontal flange-fixed, the manufacturer should be consulted, because the application will likely require specialized supports.

Loading carriers with cable

Cables or hoses that are round or flat should be positioned freely. The stacking or direct side-by-side placement of cables and hoses with arge cross-sectional differences is not recommended. Tip: In situations where stacking is appropriate, ensure that enough slack has been provided to allow cables and hoses to travel freely on top of one another.

As mentioned, a minimal 10% clearance for each cable overall diameter and 20% clearance for each hose overall diameter is recommended. Cables and hoses must not be twisted and should be free of kinks or other irregularities. All cables and hoses should be securely clamped at both the fixed and moving ends, but should not
be pinched. Ensure that cable and hoses are laid into the carrier completely free of twist. When supplied in rolls or reels, they should be unrolled — not pulled sideways or off the top of the coil.

Plastic carriers

In many applications, design parameters are well within off-the-shelf injection-molded polymer carrier capabilities.

One option is all-plastic open-style carriers for light to medium-duty applications. Snap-together construction simplifies installation and maintenance; glass reinforcement boosts durability. Such carriers are often available in specialty materials for challenging applications requiring low wear, a specialty flammability rating, or resistance to severe temperatures and chemicals.

Miniature-link models feature mounting holes as part of the link,
eliminating the need for separate brackets — useful in robotics, pick and- place, and light industrial applications.

For applications requiring multiaxis travel (in three dimensions), some standard carrier systems can be modified with molded elastomer links at alternating locations. These allow virtually unlimited ranges of motion — lateral movement of 90° plus axial rotary motion of 180° with minimal oscillation. Such designs are also useful when an application equires a slight lateral movement due to misalignment. securely clamped at both the fixed and moving ends, but should not be pinched. Ensure that cable and hoses are laid into the carrier completely free of twist. When supplied in rolls or reels, they should be unrolled — not pulled sideways or off the top of the coil.

Open metal carriers

Custom carriers of steel or hybrid construction withstand UV rays, heat and cold, submersion, abrasives, industrial fluids, caustic washdown, long travel, and high acceleration and duty cycle.

Open-style metal carriers are typically constructed from steel. Their advantages are:

• High strength, and
• The ability to carry cables, hoses, and their own weight over long spans with no support.

Useful for mobile construction, mill and foundry, paper converting, and refining equipment, such open metal carriers sport cavity heights from 0.75 to over 24 in. Continuous design improvements have led to the development of lightweight, high-strength versions with significantly more load capacity, and the ability to sustain longer unsupported spans than plastic systems.

Custom-width crossbar options abound, and other custom subcomponents boost performance in the most demanding industries. For example, half shear and extruding technologies eliminate pins and lock-out rings used for pivots and stops. This reduces cost and weight.

In fact, most metal carriers can incorporate polyurethane rollers, horizontal dividers, and vertical separators. The latter provide multiple compartments in a single link — snapping into carrier cross bars. In

both stationary and rolling designs, vertical separators can be installed every link, or staggered for economy.

Enclosed metal carriers

Enclosed carrier systems are the benchmark for fully protected dynamic cable and hose. With the exception of optional cavity separators, they feature all-metal construction. Helically wound extrusions, extensively used in machine tool applications for over 30 years, provide smooth movement, are aesthetically pleasing, and protect against even hot chips and fluids.

Another option is metal carriers with aluminum armor plates to resist heavy debris load and flying parts. Some link-style carriers utilize these links and removable armor-plate-style lids for ruggedness,
easy repairs, and quick length modifications. Both snap-in and bolt-in lids maximize protect against hot chips and heavy debris — particularly suitable in severe machine tool, mill, and foundry applications.

For more information, call (262) 786- 1500. To download a complete design guide on cable carriers, visit www.

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