2.2 Chain Selection and Installation
Plain or Detachable Link Chain
Plain chains are usually used in slow speed applications like conveyors. They are rugged, designed to carry heavy loads, and when properly maintained, can offer years of reliable service. They are made up of a series of detachable links that do not have rollers.
The problem is that, if the direction of the chain is reversed, the chain can come apart. When replacing a motor, the rotation of the coupling must be the same before you connect the coupling to the driven unit.
Roller chains are made up of roller links that are joined with pin links. The links are made up of two side bars, two rollers, and two bushings. The roller reduces the friction between the chain and the sprocket, thereby increasing the life of the unit.
Some roller chains come with a double pitch, meaning that the pitch is double that of a standard chain, but the width and roller size remains the same. Double-pitch chains can be used on standard sprockets, but double-pitch sprockets are also available. The main advantage to the double-pitch chain is that it is cheaper than the standard pitch chain. So, they are often used for applications that require slow speeds, as in lifting pieces of equipment in a hot press application.
Sprockets are fabricated from a variety of materials depending on the application of the drive. Large fabricated steel sprockets are manufactured with holes to reduce the weight of the sprocket on the equipment. Since roller chain drives occasionally have restricted spaces for their installation or mounting, the hubs are made in several different styles.
Type A sprockets are flat and have no hub at all. They are usually mounted on flanges or hubs of the device that they are driving. This is accomplished through a series of holes that are either plain or tapered.
Type B sprocket hubs are flush on one side and extend slightly on the other side. The hub is extended to one side to allow the sprocket to be fitted close to the machinery that it is being mounted on. This eliminates a large overhung load on the bearings of the equipment.
Type C sprockets are extended on both sides of the plate surface. They are usually used on the driven sprocket where the pitch diameter is larger and hub classification where there is more weight to support on the shaft. Remember this: The larger the load is, the larger the hub should be.
Type D sprockets use an A sprocket mounted on a solid or split hub. The Type A sprocket is split and bolted to the hub. This is done for ease of removal and not practicality. It allows the speed ratio to be changed easily by simply unbolting the sprocket and changing it without having to remove bearings or other equipment.
When the proper procedures are followed for installing chains, they will yield years of trouble-free service. Use the following procedures perform this task:
1. The first step is to level the shafts. This is done by placing a level on each of the shafts, then shimming the low side until the shaft is level.
2. The next step is to make sure that the shafts are parallel. The shafts must be parallel or the life of the chain will be shortened. To do this, measure at different points on the shaft and adjust the shafts until they are an equal distance apart. Make sure that the shafts are pulled in as close as possible before performing this procedure. The jacking bolts can be used to move the shafts apart evenly after the chain is installed.
3. Before installing a set of used sprockets, verify the size and condition of the sprockets.
4. Install the sprockets on the shafts following the manufacturer’s recommendations. Locate and install the first sprocket, then use a straightedge or a string to line the other one up with the one previously installed.
5. Install the chain on the sprockets, then begin increasing the distance between the sprockets by turning the jacking bolts.Do this until the chain is snug but not tight. To set the proper chain sag, deflect the chain ¼” per foot between the shafts. Use a string or straightedge again, and place it across the top of the chain. Then push down on the chain just enough to remove the slack. Use a tape measure to measure the amount of sag.
6. Do a final check for parallel alignment. Remember: the closer the alignment, the longer the chain will run.