How to make the correct coupling selection?

The guideline to make the right coupling selection

In the power transmission field, there are many different types of couplings that can be used in order to transfer power from the gear side to the machine. Taking into consideration that each specific application has its own features, it is extremely important to analyse and check what characteristics should our coupling have, to ensure a long-life cycle and a successful performance of our machinery.

Huading Product Page

We should take into account the following factors in the coupling selection process:

1. Environmental requirements: temperature, corrosive environment, etc.
2. Accessibility: space required to apply the coupling.
3. Geometry requirements: Type of shafts.
4. Coupling sizes: maximum outside diameter and length to work with.
5. Misalignment requirements: angular, torsional misalignment, angular, etc.
6. Mechanical performance requirements: torque, speed, cushioning capability, etc.

1. Environmental requirements

It is important to analyse the area, the temperature where the coupling is going to be exposed, and also if the device is going to be in a corrosive environment or not.

2. Accessibility

The space might be an issue when placing the coupling. In some applications there is a limited or a difficult access to locate the coupling. Therefore, this is also another key aspect to take into consideration for the coupling selection.

3. Geometry requirements

The type of shafts should be checked, as well as the diameter and the length.

4. Coupling size

As an example; considering the access, space required, and the shaft types, we have to analyse what size would apply best to our installation from our range of products. 

5. Misalignment requirements

The operator should check what types of misalignments should be corrected; parallel, torsional, axial, angular or lateral.

6. Mechanical performance requirements

The main target consists on understanding what kind of performance we want to have with our coupling; high torque, high speed, repeatability or high level of flexibility and cushioning.

Decide which type of coupling will be most appropriate depending on the above aspects.

• Rigid coupling: provides a solid connection between two shafts, high precision, and torque transmission but it has no misalignment capabilities. Explained in another way, it allows no movement between two shafts. Sleeve type coupling, flange type coupling, 

• Flexible coupling: compensates for some misalignment, movement or deflection. It is very useful when having quick and short starts. Normally less torque transfer, but it can absorb misalignments and shocks.

Instructions for coupling selection

In order to determine the type of coupling to be used the following formula should be applied:

M = N hp/ n. . K

M = N kW/ n. . k

M = Nominal torque

N = Driving-motor power (CV or KW)

n = Minimum speed of the connected axles (rpm)

k = Multiplying co-efficient

The value obtained on applying the formula should be less or equal than the indicated in the tables of sizes and powers that refer to the corresponding coupling in the column &#;nominal torque&#;.

k = Multiplying co-efficientElectric motor
Steam turbine
Transmissions11.522.53Steam machine
Gas machine 
Hydraulic Turbine
Diesel 4-6 cylinders1.522.533.2Diesel 2-3 cylinders
4 Stroke motor2.22.52.83.23.5Diesel 1-2 cylinders
4 stroke motor2.62.833.54

Notes:

The values indicated in the above table are by no means applicable to every case. If, for example, one of the machines to be coupled displays such a degree of irregularity that it is judged necessary to carry-out technical investigations of the oscillations, then it is recommended to proceed to the selection of the multiplying co-efficient using the enclosed questionnaire.

The following groups apply to the machines being driven:

K-coefficient calculation guidance for different groups of machines.

1. Continual load machines: Generators (electro genetic group). Conveyor belts. Small hoisting equipment of up to six starts per hour. Low power machinery for working wood. Small fans. Small machines of which principal movement is rotation. Small centrifugal pumps.
2. Generators (electro genetic group). Conveyor belts. Small hoisting equipment of up to six starts per hour. Low power machinery for working wood. Small fans. Small machines of which principal movement is rotation. Small centrifugal pumps.
3. Variable load machines: Small hoists. Generators. Winches. Hoisting equipment of up to 120 starts per hour. Conveyor chains. Crane movement mechanism. Sand blast equipment. Textile machinery. Transmissions. Conveyors Turbo blowers (gas blowers: compressors). Fans. Machine tools in which main movement is rotation. Large winches. Centrifugal pumps.
4. Normal size to heavy machinery: Heavy hoists. Revolving ovens Tannin barrels. Cylinder grinders. Refrigerating drums Continuous Ring Looms. Mechanical mixers. Cutters. Sharpening machines. Washing machines. Looms. Brick presses. Fans Hoisting equipment of up to 300 starts per hour. Translation mechanism.
5. Heavy machinery: Dredge control mechanism. Briquette presses. Rubber rollers. Ventilators for mines. Machinery for sand papering wood. Sand and paper grinders. Pumps with immersible piston. Cleaning drums. Machinery of oscillating movement. Compound grinders. Cement grinders. Drawbenches. Hoisting mechanisms. Hoisting Equipment of more than 300 runs per hour.
6. Heavy machinery of variable energy consumption: Large drilling installations Machinery for glossing sheets of paper. Horizontal and reciprocating vertical saws. Presses. Paper calenders. Roller trains for laminators. Drier rollers Small rollers for metals Centrifuges. Roller equipment for paper.

Key factor for the coupling selection process

Example:

The elevator bucket is driven by a motor of 16 kW; n=1.450 rpm., by means of a reducer whose outlet axle rotates at a speed of n= 180 rpm. The motor and reducer are protected by a UNE-FLEX flexible axle coupling.

1. COUPLING BETWEEN MOTOR AND REDUCER

N = 16 kW
n = rpm
M = NKw/n. . k

Elevator buckets figure in group 2 of the classification. Under &#;variable load machinery&#;. The multiplying co-efficient k = 1,5 figures in the k value table under heading 2 and in the classification of machines driven by &#;electric motor&#;.

M = 16/ x x 1.5 = 158.07 Nm

Contact us to discuss your requirements of Half Gear Half Rigid Couplings. Our experienced sales team can help you identify the options that best suit your needs.

Then, according to the power table. the appropriate coupling for a torque of 158 Nm. is model M-5.

2. COUPLING BETWEEN REDUCER AND ELEVATOR, BUCKET MECHANISM

N = 16 kW
n = 180 rpm
M = NKw/n. . k

M = 16/180 x x 1.5 = Nm

Then, according to the power table, the appropriate coupling for a torque of Nm is the model M-9.

Note: to carry out the correct selection of a coupling, an indication of power and speed is generally sufficient. However, it&#;s better to have the following information as well:

NECESSARY DATA FOR THE SELECTION OF THE APPROPIATE UNE-FLEX COUPLING DRIVEN BY ELECTRIC MOTOR

1. Kind of motor (make, type, running factor in ED %
2. Power of motor: N&#;..kW
3. Speed: n&#;&#;.rpm
4. Input and output shaft diameters
5. Couple of start of the motor: C = Nm
6. Type of machine to be driven
7. Whether operation is continuous or intermittent
8. Number of runs per hour
9. Whether operation conditions are uniform, irregular or special, and if there is any running change
   

Used to connect driving equipment to driven equipment, couplings are a critical machine component that can sometimes be overlooked when it comes to selection and maintenance. These critical components come in many different shapes and sizes, so it can be confusing trying to navigate what couplings are used for, what they do, and which couplings are best for your machinery.

We have put together the essential list of everything you need to know about each different type of Coupling, including their features and benefits and in what machinery you will often find them:

Flexible Couplings

Flexible Couplings come in many different variations, but all of these have 1 thing in common &#; its elastomeric properties. These properties typically come in the form of an elastomer or elastic type element that is often made of a rubber or urethane compound. This element absorbs impact, dampens vibrations, and cushions shock loads, making it ideal for applications with high shaft misalignment. Depending on your application, the type of flexible coupling you use differs and can provide additional benefits to your machine.

Jaw Couplings

Jaw couplings are made up of 3 parts, two metallic hubs and an elastomeric spacing element (also known as a spider) this means depending on your application, these couplings offer different levels of dampening protection. In addition, these versatile couplings have a fail-safe design, meaning that even if the spider fails, the coupling can continue to operate without its dampening properties until the spider is replaced. They also do not require lubrication during operation, making them a low maintenance option that helps to reduce machine downtime for your business.

Tyre Couplings

Tyre couplings have two metal hubs with a tyre shaped spacer positioned in between &#; this enables the coupling to transmit torque. The tyre also gives this coupling outstanding vibration dampening capabilities and excellent resistance to shock loads, helping to extend the life of the connected equipment in a wide range of industries.

Gear Couplings

Gear couplings are a great option for universal use and are often suitable for most applications as they can transmit high torque while working at low speeds.

Curved tooth gear couplings

Curved tooth gear couplings are known for their easy of assembly and their maintenance free operation making them ideal for inhospitable environments. These couplings also have a good resistance to chemicals, meaning they offer a low cost, reliable service for industries such as: Minerals & Mills, Pulp & Paper, Petrochemical, Oil & Gas, Machine Tools and Railway.

Claw Couplings

Claw couplings can be a great option for machinery where either angular, parallel or axial shaft misalignment is an issue. These couplings generally have a short overall length, meaning they are suitable for applications where space on the shaft is limited. Similar to other flexible couplings, a claw couplings elastic element dampens vibration and cushions shock loads, helping to extend the life of surrounding equipment in a range of industries.

Pin & Bush Couplings

Another fail-safe coupling option is pin and bush couplings. These couplings also have fantastic vibration and shock load dampening properties, all while accommodating up to 0.5° of misalignment. Also, their fail-safe design make them ideal for use in safety equipment such as fire pumps and elevator drives.

Grid Coupling

When your application has high levels of vibration and large shock loads, grid couplings are the ideal solution. Due to the grid that runs between the two slotted hubs of the coupling, these components have a high torsional flexibility. This helps to reduce vibration, which aids in prolonging the life of the surrounding drive equipment.

Back-lash Free Couplings

Back-lash free couplings are often found in applications where precision is key. Back-lash occurs because of the spacing of components within an application, this backlash often accumulates in the couplings as the joining piece for components. Using a back-lash free coupling minimises the effects of backlash within the system, helping to increase accuracy levels. These couplings come in the form of:

• Beam Couplings - Machined from a single piece of aluminium or stainless steel, beam couplings offer torsional stiffness while compensating for misalignment and back-lash &#; ideal for high-speed applications that require high accuracy.
• Bellows Couplings &#; These couplings are able to flex while remaining rigid under torsional loads, meaning it can accurately transmit velocity, angular position, and torque. It&#;s ability to flex also allows for parallel & angular misalignment and axial motion.
• Oldham Couplings &#; Oldham couplings are the ideal solution for high levels of parallel misalignment, while also being a highly customisable to suit your specific applications needs. These couplings are often found in a range of industries such as food & beverage, pharmaceutical & medical, and semiconductor applications.

Rigid Couplings

Rigid Couplings are often found in lower speed or lower torque applications and are used where a solid connection is required between two shafts of the same size. They tend to be high strength couplings that are used to maintain alignment between shafts. These couplings are often considered the most basic, but most cost-effective coupling.

One piece, two piece and set screw rigid couplings

There are three different variations of rigid couplings, each provide different features and benefits for applications. These variations include:

• One-piece rigid couplings &#; good holding power but disassembly of surrounding equipment is needed for fitting.
• Two-piece rigid couplings &#; The highest holding power of all rigid coupling with a two-part split design making fitting and removal much easier.
• Set screw rigid couplings &#; This variation is screwed to the shaft but again, requires disassembly of surrounding equipment for fitting and removal.

Torsionally Rigid Couplings

Torsionally rigid couplings are generally suitable for most industrial applications. This category includes disc and composite couplings. These can feature zero back-lash, low-restoring forces, and electrically insulated designs.

Other Couplings

These Couplings can fall into either flexible or rigid depending on the requirements of your application.

Flywheel Couplings

Flywheel couplings, also known as flange couplings, is a torsionally rigid coupling that provide maintenance free operation that&#;s free from resonance. This makes them ideal for applications such as cranes, harvesting machines and floor conveyors.

Chain Couplings

Chain couplings have flanges that are linked with duplex roller chains, meaning they are a high strength coupling option. Not only this, but these couplings can transmit high levels of torque AND accommodate up to 2° of misalignment, helping to protect surrounding equipment from damage.

Fluid Couplings

Where vibration in machinery is high, you may find a fluid coupling. This is because these couplings have an excellent level of vibration dampening and provide a controlled soft start up. Commonly found in applications such as conveyors, mills, shredders, crushers and agitators, fluid couplings can withstand the harsh conditions found in the environments these applications are often found.

This is just a basic overview of the different types of couplings that Acorn can provide, alongside custom solutions, we can help you to find the exact coupling your machine needs. Our specialised Couplings & Drives department are on hand to answer all of your coupling questions and queries, so get in touch with them today.