Cables can degrade if they are not maintained and properly cared for. Cable carriers are designed to guide and protect cables and hoses on moving machinery, ultimately extending the cables life. contributed By Joe Ciringione, Energy Chain Systems Division Manager, Igus.
What Is A Cable Carrier?
Cable carriers guide and protect cables and hoses on moving machinery. They prevent tangling and damage from debris or contact with the machine itself. Using cable carriers extends the service life of both the cables and the machine. Any application involving moving machinery and constant repetitive motion will benefit from a cable carrier system. Typical applications range from machine tools, woodworking machinery and palletisers, to automated robots, cleanrooms and ship-to-shore cranes.
Types Of Installation
The cable carrier is an integral part of any machine design and should be considered early-on in the design process. It can be implemented in a variety of ways depending on the motion of the machine, but the most common is a horizontal, unsupported, short-travel installation. In this type of application, the upper run of the carrier operates without touching the lower run throughout the entire length of travel. The maximum unsupported length is different for every application, but this type of configuration will have the longest service life.
If the length of travel is too long for an unsupported installation, it is considered a gliding, long-travel application in which the cable carrier glides on itself. A guide trough and glide bar must be used to support the carrier. Cable carriers also can be installed vertically or horizontally. Side-mounted, rotary, multiple nested carriers are also quite common.
Nine Steps For Specifying A Cable Carrier System
Here is a step-by-step guide to specifying a cable carrier:
1. Gather data: The first step in choosing a cable carrier is to gather all the necessary technical data prior to contacting a cable carrier vendor. This includes length of travel, what cables or hoses will be installed, the size of cables and hoses and how much they weigh, any environmental factors such as debris, heat or chemicals, and speed and acceleration.
2. The largest cable or hose: The first question any reputable cable carrier manufacturer will ask is, ‘What is the largest cable or hose in your system?’This will determine the minimum size of the cable carrier. To this number, add proper clearance —10 percent for cables and 20 percent for hoses —and the resulting dimension is the minimum inner height of the carrier.
3. Style, style, style: Next, choose the style of carrier. Always choose a snap-open version whenever possible. This type of carrier allows access to cables with crossbars that snap open at any point along the carrier.
If debris or other external conditions are an issue, the tube-style cable carrier replaces the crossbars with lids to fully enclose the carrier and provide complete cable protection. This style is especially useful in applications where woodchips, metal filings and other debris are present.
With a split crossbar, simply press the conduit into the carrier to install and pull straight up to remove. For zipper-like removal of crossbars, the carrier has interconnected lids that are pulled back like a zipper, removing the top section of the carrier. The hinged crossbars are attached to the side links and are made of non-fibre, reinforced nylon to enable the hinge to flex. These designs minimise assembly and disassembly time.
There also are modular cable carriers for heavy-duty, longer-travel applications. They are available with hinged crossbars that are opened on either the inner or outer radius, depending on which is preferable for the application, or with lids to make them into a tube for debris protection. Special cable carriers are available to meet a variety of application requirements. Some are: low-vibration or low-noise carriers, multi-axis carriers for robotic applications, ‘twister’chains for rotational movements, fully enclosed carriers for protection against metal chips and flying debris, and carriers with integrated wheels for longer travels and less wear.
4. The environment: The environmental conditions of an application typically determine which type or style of carrier to use. If debris such as woodchips or metal shards are present, or if the application is in a dirty or contaminated area, an enclosed tube is ideal. An open crossbar carrier is lightweight and facilitates easy inspection and replacement of cables, whereas tube carriers offer removable lids for cable access. Also consider whether the application is underwater or comes in contact with liquids.
Note: Space restrictions
Many applications have a space restriction that will affect the design and selection of the cable carrier system. It is imperative that the performance of the system is not compromised to meet these restrictions. Keep in mind things such as the camber of the carrier when determining how much height is available for the installation. Camber is the curve of the upper portion of the carrier along its unsupported length. Most cable carriers are manufactured with camber, but special, no camber carriers are usually available upon request. Be advised however, that carriers without camber do not have the same load-bearing capacity as those with camber.
5. Bend Radius: All cable carriers have a predetermined radius stopping point on each link. When a number of links are assembled, these stopping points restrict the carrier from fully pivoting and form a curve loop or minimum bend radius. All cable carriers have multiple bend radii to choose from and all manufacturers suggest a minimum bend radius. If this is unknown, the general rule is 8-10 times the outer diameter of the largest cable or hose. The larger the bend radius, the less stress is placed on the cable and the longer the service life will be. Bend radius is measured from the centre of the curve loop to the centre of the pivot pin on the side link. Do not confuse this with the dimension of the overall curve height.
6. Cable and hose packages: Since the primary function of a cable carrier system is to ensure cables bend properly, it is imperative to install the conduits correctly. To ensure maximum cycle life for your machine, the easiest solution is to use cables designed for use in a cable carrier.
7. Cable carrier length: To determine how long a cable carrier your application will require, first determine the position of the fixed end. The ideal and most cost-effective position is at the centre of travel. This will require the minimum amount of carrier to achieve the necessary movement.
Use the following formula to determine the necessary cable carrier length:
S = Maximum machine travel distance
K = Curve length
L K = Carrier length
R = Bending Radius
∆M = Deviation from the centre point
8. Acceleration and inertia: It is critical to ensure that the cable carrier is strong enough to support the application. If it is not, the results can be devastating. The carrier can literally snap in two. In order to ascertain that the carrier is strong enough, use the following formula to determine the force required for your application.
First, determine the acceleration force. Acceleration force is the force required to keep the cable carrier moving once it has started.
Acceleration Force (lb) = Total Weight lb
(carrier and fill) x Acceleration ft/sec2
Then determine the push force. Push force is the force required to get the cable carrier moving and overcome inertia.
Push Force (lb) = Total Weight x COF
Once those numbers are determined, calculate the force of the application by:
Acceleration Force + Push Force = Force Required
The force required must be less than the maximum force for the selected carrier. Cable carrier manufacturers typically do not publish the maximum force allowance for their products, but igus technicians will calculate the force required for your application and select the proper size carrier to meet this requirement.
9. Accessories: A variety of accessories are designed to further facilitate the energy supply system. They can include:
- Interior separators or shelve ensure proper alignment of the cables within the carrier and prevent friction, tangling and corkscrewing. These are available in both vertical and horizontal implementations.
- Mounting brackets are almost always required to attach the carrier system to the machine itself. Plastic or steel brackets made of a single piece are for smaller carriers. Others have aluminium bushings in the bracket to prevent damage when tightening the bolts. These can either pivot for standard applications or lock into place for vertical or side-mounted, gliding applications.
- Guide troughs are available for long-travel applications
- Rollers can be used for even longer-travel applications.
- Extender crossbars enable the use of oversized conduits.
- Strain relief is another common accessory designed to keep cables in position at both ends of the carrier.
Sometimes strain relief at just the moving end is sufficient, depending on the application, and hydraulic or other fluid hoses should only be strain relieved on the moving end.
Strain relief can consist of profile rails, clamps, tie wraps and tie wrap plates. Improper, or lack of, strain relief is a common cause of cable and hose failure. The strain relief clamps hold the cable in the neutral axis of the carrier. This prevents the cables from being pulled against the inner radius of the carrier or pushed against the outer radius of the carrier where it can be damaged or incur wear. While it may seem like an insignificant point, strain relief can often make —or break —the success of an application.