What Mechanical Couplings? Types of mechanical couplings and their uses
If you are looking for more details, kindly visit Flexible Coupling Types.
Overview of Mechanical Couplings
Mechanical coupling plays a crucial role in connecting two shafts that belong to distinct machines, such as the motor and wheel shafts. Essentially, it facilitates the linkage between the driving and driven shafts. There are instances where a shaft longer than 7 or 8 meters is needed. In such cases, coupling two shafts together allows us to achieve the desired length while minimizing the impact of shocks. The primary purpose of coupling is to join dissimilar shafts, but it's important to note that different coupling types are required due to varying conditions. Today, we will explore the various types of couplings.
The Importance of Coupling:
- Connecting two different machines.
- Transmitting power from the drive shaft to the driven shaft.
- Reducing the impact of shocks on the equipment.
- Eliminating overload problems in equipment.
Types of Mechanical Coupling:
1. Muff or Sleeve Coupling:
This is the simplest type of coupling, comprising a hollow cylindrical part called a muff or sleeve. The muff's diameter is manufactured to match the shaft's diameter. The driver and driven shafts are fitted on either side of the sleeve, secured in place by threaded holes and bolts to prevent longitudinal motion. A key and keyway arrangement ensures a slip-free connection between the muff and the shaft. This type of coupling is suitable for transmitting low to medium torque. All components must be adequately strong for proper functioning.
Advantages:
- Cost-effective compared to other couplings.
- Simple construction.
- Consists of only two parts: the sleeve and key.
- Disadvantages:
Unsuitable for misaligned shafts.
- Difficult to assemble and dismantle.
- Limited ability to absorb shocks and vibrations due to its rigid design.
2. Split-Muff Coupling:
In this type of coupling, the muff or sleeve is not a single piece but rather made up of two semi-cylindrical parts constructed from cast iron. One part is fitted from above the shaft, while the other is fitted from below. These two parts are joined together using bolts or studs, with two, four, or six holes provided to secure the muff.
Advantages:
- The main advantage is the ability to assemble and dismantle without changing the shaft position.
3. Flanged Coupling:
In flanged couplings, two flanges are brought together and fitted. Both flanges feature the same number of threaded holes, which are used to fasten them using nuts and bolts. A gasket is employed to prevent leakage. Flanged couplings find widespread use and are suitable for medium to heavy-duty applications. To ensure a secure connection with no slippage, a tapered key is utilized.
4. Flexible Coupling:
Similar to flanged couplings, flexible couplings incorporate rubber bushings along with nuts and bolts. The rubber bushing, designed with appropriately sized holes, provides enhanced strength to absorb shocks and vibrations more effectively than flanged couplings. Additionally, it accommodates slight misalignments between the shafts. Flexible couplings are commonly employed in medium-duty applications.
5. Oldham Coupling:
Oldham couplings consist of two flanges connected by a middle plate. They are used when two shafts are misaligned and have a gap between them. The middle plate is joined to the flanges through a tongue and groove arrangement, with the grooves positioned perpendicular to each other. The key advantage of Oldham couplings is their ability to accommodate high parallel misalignment.
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.
6. Universal Coupling:
Universal couplings are employed when two shafts are at an angle. Although the angle may remain constant, it can change during operation. The primary application of universal couplings is in heavy vehicles
7. Gear Coupling:
Gear coupling is a specific type of coupling that falls under the category of flange couplings. It differs from standard flange couplings as it comprises separate parts, namely the flange and the hub. It finds application in heavy-duty scenarios where robustness is essential. Two shafts are connected through fixed holes and secured by a third spindle. Gear couplings are particularly suitable when there is an angular displacement of 4 to 5 degrees in the shafts. Generally, they have a 1:1 gear ratio between the internal and external gears.
8. Fluid Coupling:
Fluid coupling involves connecting one shaft to the power supply and the other to the power generator shaft. It consists of a pump connected to one shaft and a turbine connected to the second shaft. Over time, the speed of the pump impeller and the turbine equalize, resulting in power transmission.
Applications:
- Utilized in marine propulsion systems.
- Widely employed in various industries for efficient power transmission.
Beam couplings are one of the most popular and versatile types of motion control couplings.
Choosing the most appropriate beam coupling to use in motion control applications can be confusing. This article examines the design differences and how to select the proper beam coupling.
In the design of motion control equipment, typically the coupling is left as one of the last components to be specified. In fact, couplings are often overlooked or taken for granted rather than treated as a critical part of the performance of the system. Selection of the proper coupling ensures the equipment will meet the requirements for performance and have a long, trouble free life. Conversely, poor coupling selection can leave designers and end users of equipment frustrated with imprecise positioning and frequent maintenance requirements.
Many types of couplings are available for motion control applications, each with their own pros and cons. One of the most popular and versatile types of couplings is the beam coupling. Beam couplings are an excellent starting point for designers because they do many things well: they have good misalignment capabilities, torsional stiffness for accuracy, and strength for carrying torque loads that allow them to be used in many applications. However, there are several different design categories for beam couplings that allow users to optimize characteristics to meet their needs, including material differences and beam pattern designs.
Before discussing the different varieties of beam couplings available in the market, there are some basic criteria that designers should gather and understand about their application before specification of a coupling can take place:
Beam couplings are flexible and can handle a fair amount of angular misalignment.
Two basic designs of beam couplings exist: single and multiple beam designs, both of which are machined from a single piece of material. Single beam designs consist of one long continuous beam that generally is several complete rotations in length. The long beam yields excellent angular and axial flexibility, however it is not nearly as effective with parallel misalignment. To effectively handle parallel offset, the single beam is forced to simultaneously bend in two different directions. This results in a large stress within the beam that can rapidly cause fatigue and subsequent failure of the coupling. The long single beam also suffers in torsional stiffness capabilities. Its benefit of flexibility under misalignment derived forces is a weakness in the degree of positional accuracy it can deliver. Under torque loads, especially during high rates of acceleration or deceleration such as starts and stops, the coupling &#;winds-up&#; like a spring causing an angular displacement from one end of the coupling to the other negatively affecting the accuracy of the driven end of the system. This windup results in a positioning lag between the driving and driven side of the assembly while in motion. Applications that require precise positioning throughout the entire path of motion may not be suitable for single beam couplings. Torsional stiffness is also a factor when motion comes to a stop. The angular lag of the coupling can force the servomotor to &#;seek&#; its position, causing an oscillation back and forth until the coupling can reach its original free length and the system comes to rest. Long settling times can negatively affect the speed and accuracy of the system.
Multiple beam couplings take a slightly different design approach to improve performance when compared to single beam couplings. They use a single or double set of overlapping beams as opposed to a continuous single beam resulting in beams that are shorter in length increasing torsional stiffness and positioning accuracy. The shorter the length of the beam, the stiffer and stronger it is under torsional loads. However, shorter beams are also stiffer under misalignment loading which reduces the overall ability of the coupling to compensate for manufacturing tolerances in application. The idea of nesting multiple short beams together into a single set of beams improves the ability of the coupling to accommodate misalignment. It still is not as flexible as continuous single beam coupling, but has enough flexibility to be able to be used effectively in almost all applications. The set of beams also creates greater strength due to having the beams work in parallel with each other to achieve higher torque capabilities. This configuration still suffers from issues with parallel misalignment and is even more susceptible to rapid fatigue do to the shorter length and stiffer beams.
Four Beam Coupling, Aluminum
Six Beam Coupling, Stainless
A further enhancement to the multiple beam design is incorporating multiple sets of multiple beams into a single coupling. Multiple sets of cuts adds an extra dimension to the performance of beam couplings &#; the ability to handle parallel misalignment conditions. A beam coupling with a single set of cuts compared to one with two sets of cuts can best be compared to a single cardan universal joint vs. a double cardan universal joint. A single joint easily handles angular misalignment but not parallel while a double joint handles both types of misalignment easily. Unlike universal joints, whether a single or multiple beam coupling, all designs offer the benefit of constant velocity without the phasing associated with universal joints.
There are designs that use two sets of long, continuous single beams, but most designs feature multiple beams in each set. Two sets of multiple beams provide the best overall performance in beam couplings. Ruland offers two different varieties of this design to meet the needs of many different applications. All Ruland beam couplings feature balanced designs making them suitable for high speed applications up to rpm.
The first design - MWC/MWS, PCR/PSR - utilizes two sets of two beams and are available in inch, metric and inch-metric shaft sizes as standard items. The couplings have a compact design that allows for easy interchange with many single beam couplings and fits easily into small areas. These are designed as lighter duty couplings with greater flexibility that are best utilized in low torque application such as encoders, tachometers, and other instrumentation. The length of the beams is kept relatively long - although much shorter than single beam couplings (~1.5 rotations vs. 3 or more) to maintain excellent flexibility in the coupling and has the additional benefit of dampening vibration in the system as well as shock loads. Flexibility allows for greater tolerance in installation and manufacture of the system without causing premature failure of the coupling and also protects expensive components from excessive bearing loads created by reactionary forces due to misalignment of shafts. At the same time, by keeping the beams shorter than single beam couplings and grouping multiple beams together, these couplings are able to achieve higher torque capabilities and torsional stiffness in a coupling that fits in the same overall envelope.
The second design involves two sets of three beams (FCR/FSR) which are also available from stock in inch, metric and inch-metric shaft sizes. The use of three beams in each set further allows for shortening the beams. This series utilizes beams that are only one full rotation in length, resulting in even higher torsional stiffness and torque capabilities as well as raises the natural frequency of the coupling giving the designer opportunity to tune the system to higher performance levels. The stronger beams are combined with larger body sizes to result in a coupling that is best suited for light duty power transmission applications such as connecting a servo motor to a ball screw. Bearing loads are higher than the two beam design so these are best utilized in applications with components such as servo motors and linear stages that tend to have more durable bearing support. This series also features Nypatch anti-vibration treatment on clamp screws to prevent screws from loosening in use.
Aluminum anodizing enhances the finish, durability, and corrosion resistance of aluminum couplings.
Material is a factor that should be considered early in the specification of a beam coupling. Because the coupling is machined from a single solid piece, the specified material determines a vast majority of the performance characteristics of the coupling. Typically, beam couplings are machined from either aluminum or stainless steel but are also available in plastics such as Delrin, titanium, and other engineering grade materials.
Aluminum is the most common choice for material because it has the best mix of attributes for the most common beam coupling applications. Aluminum is lightweight and has an excellent strength to weight ratio which makes it ideal for motion control applications. The light weight allows the couplings to be designed with low inertia to allow for a high level of responsiveness in the system without having the coupling diminish this performance characteristic. Aluminum&#;s strength and fatigue resistance allows for long, service free life, even in demanding applications. Aluminum can be treated with an electrolytic passivation process called anodizing to enhance the finish, durability, and corrosion resistance.
Stainless steel is the next most common choice for beam couplings. Most frequently, stainless steel is chosen to give increased strength to coupling. Stainless steel couplings are typically about twice as strong as an aluminum coupling of the same design and have much higher torsional stiffness as well. However, stainless steel has its tradeoff as well &#; inertia. Stainless steel has a mass almost 3 times that of aluminum which creates a coupling with relatively high inertia which can diminish the responsiveness of the system. For this reason, designers should be cautious of installing stainless steel couplings in motion control systems. The best applications for stainless steel are ones that encounter environmental issues such as weather, temperature extremes, chemicals or exposure to vacuum.
Other materials, such as titanium and Delrin, are far less commonly used. Typically, these are specialty applications and require special designs. For titanium, the costs and difficulty of machining keep this from being a viable option except absolutely necessary to the application - typically aerospace. Delrin has some advantages in that it has less mass and inertia than even aluminum and has the additional benefit of electrical isolation which can be important for applications with components that can be damaged or suffer interference from stray currents passing thru the coupling. However, Delrin has very low strength and can only be suitably used in applications with extremely low torque requirements. A better option for applications requiring isolation is to use aluminum couplings with insulating inserts. This has the added benefit of isolation without sacrificing coupling strength making the combination well suited for many applications.
Couplings are an integral piece of a motion control systems performance. Beam couplings are a versatile coupling that can provide excellent characteristics if applied correctly. Many factors must be considered in the selection of the right coupling for an application. Understanding these factors can lead to reduced coupling failure and better system performance.
Want more information on High Speed Grid Couplings? Feel free to contact us.