Understanding Various Collar Types and Their Applications
Although they are rather simple devices, collars serve as important mechanical functions in transmission applications. They act as mechanical stops, locating components and load-bearing surfaces. As with many mechanical components, there are various types available. They are used in many industries including auto, medical, packaging, food and beverage, and many others. Let’s review the different types and their applications.
Standard set screw collars, the most commonly used type of shaft collars, are used as locating and retaining components. The set screw locks down the collar by digging into the shaft to hold the collar's position. Therefore, they are most ideal when applied to a shaft made of a material softer than the screw. Set screw collars produce higher holding strength and torque capacity than other methods. They are typically used to lock power transmission components in place, such as gears, sprockets, pulleys, and bearings.
Clamping Shaft Collars
Clamping shaft collars were designed to overcome the issues that set screws present. Rather than damaging the shaft, they are mounted using compression and clamp down to lock into place. There are two styles available, one-piece and two-piece.
One-piece – provides even distribution with only one screw. This allows it to be repositioned as required. However, since it’s placed over the end of the shaft, it must be placed when the assembly is apart.
Two-piece – contains two screws and therefore holds a lot tighter than a one piece. If you remove both screws, you can it place over the shaft and assemble in place without moving other components. The assembly does not need to be pulled apart, saving time, effort and money.
Selecting the Right Collar for Your Application
So, how do you best determine which collar is best for your application? There are three things to consider:
- Holding power
- Operating conditions
- What kind of mechanism
A set screw will hold a lot tighter provided the shaft is softer than the screw. If you need a stronger hold, then the split type is required. Many shafts are made of 303 stainless steel, which has a low Rockwell scale hardness. The set screws are typically heat treated carbon steel with higher hardness ratings, in the higher 30’s.
However, a linear shaft made from case-hardened steel such as carbon or stainless, has a much higher hardness rating, in the 50-60 range. In this case, the set screw would flatten itself out, but a split clamp would be up for the task.
If you need to reposition the collar, then set screw is not recommended, as it damages the shaft.
If your assembly takes effort to pull apart, then two screws would be recommended since it provides ease of use without disturbing the assembly.
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