Safety warnings:
1. Cut by sharp blades or burned by hot surfaces.
2. Getting entangled and pulled into rotating surfaces.
3. Being struck by a part or object thrown from a machine.
4. Becoming trapped or being crushed by a moving or rotating machine.
Use the following guidelines while working on or using a rotating machine.
l Be always aware of fingers or hands, lose fitting overalls, jewelry and long hair that can be caught in machine.
l Never work on or try to repair machines you are unfamiliar with.
l Never try to stop revolving machines with your hands.
l Isolate machine from electricity with a lock-out device before you start to dismantle the machine.
l When assembling a machine, make sure you fit the parts correctly in the correct position and that
no part has been left out.
l Spin machine by hand before starting it.
l Replace all safety guards before starting the machine.
l Maintain good housekeeping.
Safety measures for using hand tools:
1. Have all necessary tools at hand before starting any job on couplings
2. Use right size and type of tools for the job at hand.
3. Wear the correct safety equipment for the job.
4. Keep your tools clean, sharp and in good condition.
5. Don’t work with dirty, oily and greasy hands.
6. Handle sharp tools with care
7. Secure small and short work with a vice.
8. Report breaks and malfunctions to your instructor.
9. All couplings must be covered with safety guards.
Introduction to couplings:
A mechanical coupling is a device used to connect two rotating shafts for the purpose of transmitting torque.
Couplings does not change motion or speed and do not contain clutches because they never disengage. The connection is permanent.
Some words that you should know.
l Driving machine: mostly we use electrical motors as driving machines. We can also use diesel,
petrol or steam engines to provide the power.
l Driven machine: the machine using the power to do different tasks. A pump, compressor,
conveyor, shredder, hoist, etc.
l Base: the driving and the driven machines must be placed on and attached to a level base that can carry the combined weight of the two machines. This will assist in the proper alignment of the
two units.
l Machine or motor foot: this is the part of the motor or machine that is bolted to the base.
l Sole plate: the steel plate fitted on the base onto which the motor or machine is bolted.
l Mounting: the act of bolting the machine or motor to the base to prevent movement.
l Shims: spacers that fit between foot ans sole plate to help with leveling the motor/machine.
l Jacking bolts: the jacking bolts help to move the machine horizontally on the base.
l Dowel pin: the pin is inserted in the foot to secure the foot and when the motor has been moved
the pin help to relocate it to the correct position.
Types and applications of couplings:
Couplings are classified into three main groups:
l Rigid or permanent couplings
l Flexible couplings
l Self-aligning couplings.
Rigid couplings.
Rigid or permanent couplings are used when two shafts are in line with each other (coaxial). Rigid
couplings can not compensate for misalignment and are only used where shafts are already aligned. Misalignment will lead to high stresses and overload on bearings.
The following couplings fall under rigid couplings.
Flange coupling:
these couplings consists of two flanges, two keys, two shafts and a number of bolts. A key fixes a flange to each shaft. The flanges are then bolted together.
Marine coupling:
This coupling look similar to the flange coupling but the flange form part of the axial.
The bolts are tapered the same as the holes. These couplings need to withstand very high torques
and thrusts.
The bolts are tapered the same as the holes. These couplings need to withstand very high torques
and thrusts.
Chain coupling:
A chain hub with teeth is attached to each axial. Then a double chain is fitted over the teeth to
keep the two chain hubs in place. No misalignment or shocks can be tolerated.
Gear coupling:
Make use of two hubs with external gears fitting into flanges with internal gears. The clearance
between the meshing teeth allows for small amounts of misalignment. Gear couplings require
lubrication and seals are provided to trap the lubricant.
Oldham coupling:
When the axes of two shafts are not in a straight line but are parallel, you can use the Oldham
coupling. It’s made up of two flanges with a groove in each. The third member of this joint is a
spacer that sandwich between the two flanges. The spacer has two tongues at right angles to each other. The spacer can slide along each groove to take up any misalignment in the shafts.
Flexible Couplings:
Flexible or elastic couplings are usually used to compensate for some misalignment between two
shafts as well as the possibility of shocks in the transmission of the torque. Generally flexible
couplings can tolerate up to 3ยบ of angular and 0.75 mm of parallel misalignment.
Flexible couplings are often revered to as elastomeric couplings because the must also compensate
for temperature changes and axial movement of the shafts.
The following couplings fall under flexible couplings.
Raffard coupling:
Allow for axial and lateral flexibility. Pins in each half of the coupling are coupled together with rubber bands.
Rubber belt Coupling:
