Couplings

Electric motors are used to "DRIVE" or power some piece of equipment or machinery. In order to do that, the two items MUST be somehow "MECHANICALLY" connected.

For a lot of applications such as fans and blowers, rock crushers, conveyors, and others to many to mention, that means the use of "Belts and Sheaves".

But for many of those SAME applications, under a different set of circumstances, the motor and driven piece of equipment are "DIRECTLY" connected by the use of a COUPLING! A coupling is just that.... a device that "couples" a driver to a driven piece of equipment. 

Couplings are similar to sheaves, in that, depending on size, they can be either "bored to fit" or "bushing type". The bored to fit is just as it says, the mounting hole used to mount the coupling half on the equipment, is bored to the specific size of the shaft on which it will be used. The bushing style of coupling, is one that is large enough to use a tapered bushing with a specific size hole to mount on the equipment. This bushing may be of a size that is capable of numerous bore sizes and therefore can accommodate many different HP motors and driven shaft sizes.

There are numerous types of couplings available with ratings from fractional HP to tens of thousands of HP. On this page we'll outline a few of the more common types and give you an idea of their features.

• Pin Coupling

• Jaw Coupling

• Chain Coupling

• Elastometric Coupling

• Geared Coupling

• Sleeve Coupling

• Grid Coupling

• Flange (Rigid) Coupling

• Fluid Coupling

Pin Coupling - The pin coupling is one that has in one half, multiple PINS protruding that are inserted into the mating holes in a rubber (flexible) member. This flexible member varies in thickness, material composition and physical size depending on the power that it can transmit. The second half of the coupling, that mounts on the other piece of machinery, also has pins protruding that are inserted into other mating holes in this "flexible" member. In this manner, the STEEL coupling halves are totally isolated from each other and the flexibility of the center member allow for some "misalignment".

Jaw Coupling - This coupling has been around for a lot of years, and because of the company that introduced it, is known in many industries as a "Lovejoy" coupling. The two halves of the jaw coupling have protruding "JAWS" machined or cast into them and these coupling halves are symmetrical. When the coupling halves are placed on the equipment to be coupled, a center section of "FLEXIBLE" material referred to as a "spider", is places between them and this spider acts as a "cushion" between the jaws of the two coupling halves. This type coupling allows for some misalignment.

Chain Coupling - It's pretty easy to identify this coupling. The two steel coupling halves have what looks like a "sprocket" on the one edge. When the halves are installed on the equipment to be coupled, the space between the two coupling halves is rather critical. This is because to "COUPLE"  the two halves together, the user wraps a "DOUBLE-STRAND" of roller chain around the two coupling halves and pins them together. This roller chain is standard chain but, of course, the circumference of the coupling halves are designed such that a specific number of links of chain of the proper size, will terminate properly with a full wrap. Once the chain is terminated, a cover is installed around the coupling and the cavity is filled with lubricating grease. This type coupling allows for very limited misalignment.

Elastomeric Coupling - Also referred to as the "RUBBER TIRE" coupling.

Geared Coupling - This coupling is similar in appearance to the chain coupling in that each coupling half has a "GEAR" tooth design cut into the circumference of the casting or steel half. The mating halves are placed on the equipment to be mated. A cover "half", with a mating "GEAR" cut on the inside surface is then pulled over the coupling half to be mated with a second cover "half" on the other piece of equipment. These covers are bolted together and the cavity is filled with lubricating grease. These couplings allow for very limited misalignment but carry some of the highest HP and torque ratings.

Sleeve Coupling - A sleeve coupling is basically a tube of steel, either bored to fit (usually on the smaller sizes) or bored to accept the tapered fit of a bushing. These couplings are totally rigid in use and allow for NO misalignment.

Grid Coupling - The GRID coupling is similar in design to the chain and gear couplings. In the GRID design, the external circumference of each half has "grooves" cut symmetrically and parallel to the direction of the shaft bore, of a thickness and depth so as to accept a steel "GRID" during mounting. Once the coupling halves are mounted on the equipment, a "HERRINGBONE" or "RIBBON" looking GRID is inserted in the grooves of the halves. This grid is made of a steel similar to a spring steel and is VERY tough. This allows it to be FLEXED in a misalignment condition without causing rapid mechanical fatigue of the grid. Once mounted, a cover is placed over the coupling and lubricating grease is used to fill the cavity. This coupling allows for very limited misalignment.

Flange (Rigid) Coupling - This is somewhat self explanatory also. Two mating halves of malleable castings or rolled steel, are bored to fit or fitted with the tapered busing for shaft mounting. The large mating FACE of these coupling halves are precisely machined and when assembled are simply bolted together. This type of coupling allows for NO misalignment.

Fluid Coupling - This is a hybrid of designs. It is actually a two piece cylinder or "can" that has, on it's interior, sets of "turbine type" blades. The "can" is filled with a fluid, usually a viscous oil, and as the driver half of the can is turned the friction and action of the blades serve to drive the second half in the same direction. As the driver speed increases, so does the driven section. The top speed and torque transmitted depends on the amount of fluid added to the "can". This coupling has NO mechanical connection between the driver and driven sections, except for the "can" that holds the oil. So the ONLY thing driving the equipment is the friction of the fluid and action of the blades. These types of couplings have been used in larger equipment to achieve a "SOFT START" and limit mechanical damage from the locked rotor torque of the larger motors. Alignment is still a problem but more of a problem is the physical size and cost .... in comparison to other methods of coupling.