How to Choose the Chain Specification of the Chain Coupling?

When it comes to power transmission systems, selecting an appropriate coupling is critical to system efficiency. While there are different coupling styles available, the roller chain coupling remains a flexible and durable solution in the industry. 

Chain couplings are common in agricultural conveyors, textile machinery, and other sectors. However, selecting the wrong type and size can lead to damage. In this article, we’ll walk you through how to select the chain specification of the chain coupling. 

What is a Chain Coupling?

Chain coupling refers to a flexible coupling that is used to join two shafts to transmit power effectively. It is a simple mechanical device that consists of three main components:

1. Two sprockets: The sprockets are attached to the ends of the driving and driven shafts.

2. Double roller chain: The length of the double roller chain is a specific width that connects the two sprockets. 

3. A cover: The cover is a casting that holds lubricant and protects the coupling from dirt and debris. While this is optional, it is highly recommended. 

The chain coupling works by engaging the chain with the sprocket teeth, thus allowing torque to transfer between shafts. The chain provides flexibility, cushioning your bearings and shafts against the forces of the minor misalignment and shock demands.

Why Choosing the Correct Chain Specification Matters

Before we dive into the selection guide, it’s imperative to consider why choosing the correct chain specification matters. Here are a few reasons:

• Easy maintenance: A properly selected chain specification requires less frequent lubrication, maintenance, and replacement. 

• High torque density: Chain couplings transmit a high amount of torque. Therefore, selecting the right chain specification will make them suitable for heavy-duty applications.

• Prevents premature failure: The use of a wrong chain size may lead to overstress. In turn, this will lead to chain elongation, sprocket wear, and failure. However, choosing the correct specification will prevent these problems. 

• Reduce vibration and noise: Selecting an inappropriate specification can lead to an imbalance, uneven distribution, and vibration, and these will be transmitted throughout the entire system. Choosing the right one will reduce vibration and noise. 

• Efficient power transmission: The appropriate chain specification of chain coupling will minimize power loss and enhance system efficiency.

Key Factors to Consider When Choosing Chain Specification of the Chain Coupling

1. Transmitted Torque and Power Requirements

The transmitted torque and power requirements are the most critical factor in selecting a chain coupling. There is a standard calculation formula to follow:

Torque = 9550 Pn

Where:

T = Torque (Nm)

P = Power (kW)

n = Speed (RPM)

Use a service factoring of 1.2 -2.5, which varies depending on circumstances, including shock loads, start-stop cycles and different loads.  Always select a coupling with a rated torque that is higher than the calculated torque. 

2. Shaft Diameter and Bore Size

Chain coupling should be of exactly the same size as the shaft and bore. The size of the bore should correspond to the size of the shaft. An incorrect choice of bore size may lead to a slipping effect and vibration.

The dimensions of the keyway should meet the regulatory standards. Tolerance fit shouldn’t be ignored, as it ensures proper installation. 

3. Chain Pitch and Chain Size

The chain pitch is the same as the distance between the centers of adjacent pins. This is what determines the size of the chain. Popular chain lengths or sizes are ANSI #40, ANSI #50, ANSI #60, ANSI #80, and ANSI #100. 

The larger the pitch, the higher the load capacity. The smaller the pitch, the smoother the operation at higher speeds. Make sure there is compatibility when replacing or sourcing components. 

4. Speed (RPM) Requirements

Another factor to consider is the speed requirements of the chain coupling. The chain couplings are suitable for low-medium speeds. High speed accelerates centrifugal force whereas excessive speed can lead to lubrication problems. When the chain runs at a higher speed than usual, it will wear out. 

5. Working Environment

Another factor to consider is the working environment. Coupling performance may be greatly influenced by the environmental conditions, including temperature, dust, moisture, and corrosion. High temperature may degrade lubrication, while dust and debris can increase wear. 

To solve this, use stainless steel chains for corrosive environments, as they are highly corrosion-resistant. Apply protective coatings and use sealed covers. 

6. Misalignment Compensation

Misalignment compensation is a crucial factor that affects chain coupling. Chain couplings can only accommodate limited misalignment. There are different types of misalignment:

• Angular misalignment: This type of misalignment happens when the centerlines of the two shafts intersect at an angle. That is to say, the sprocket faces are not perfectly parallel. Chain couplings can tolerate a small amount of angular misalignment, around 0.5 to 1 degree.

• Parallel misalignment: Parallel or radial misalignment occurs when the shafts are in parallel positions. However, their centerlines are offset from each other; that is, one shaft is higher or lower than the other. Chain couplings can only accommodate a slight amount of parallel misalignment between 0.015 and 0.05 inches, depending on the size. 

• Axial misalignment: Axial misalignment happens when the distance between the coupling hubs changes along the longitudinal axis of the shaft. In this type of misalignment, the sprockets are either too far apart or too close together. While chain couplings can accommodate a certain amount of axial misalignment, excessive misalignment can cause stress on the bearings of the chain. This can reduce the lifespan of the chain coupling and increases wear. 

7. Safety Factor and Application Type

Different industrial applications require different safety margins. Always include safety factors based on the application type. There are several types of application categories. 

• Light-duty: In light-duty applications, chain couplings are used in fans and small conveyors. 

• Medium-duty: In medium-duty applications, chain couplings are used in pumps and compressors. 

• Heavy-duty: In this type of application, chain copuplings are used in mining and crushers. 

How to Select Chain Specification of Chain Coupling

1. Determine the Bore Size

Determining the bore size is the first step to selecting the chain specification of the chain coupling. You should know the diameter of the driving shaft (for example, the electric motor) and the driven shaft (for example, the gearbox or pump).  

Chain couplings often come in two bore styles:

• Finished bore: The finished bore has a sprocket with a specific hole size, keyway, and set screws, and these are ready to mount. 

• Taper-Lock or QD bushings: In bore style, the sprocket has a large, tapered hole. It is advised to buy a separate bushing that compresses onto the shaft in order to provide a firm grip and prevent corrosion on the shaft. 

Note, however, that it is common for the two shafts to have different diameters. If that’s the situation, you can easily mix and match sprocket bores. For example, you can use a 1-inch bore on the driver and a 1.5-inch bore on the driven shaft. But make sure they are for the same chain pitch. 

2. Calculate the Design Torque

Selecting a chain coupling based on horsepower (HP) alone can affect the efficiency of your power transmission system. You must calculate the torque because this is the actual twisting force the chain must withstand. 

You can use two formulas:

Torque = 9550 Pn

Where:

T = Torque (Nm)

P = Power (kW)

n = Speed (RPM)

You can also use

Torque (in-lbs) = (HP × 63,025) / RPM

Where:

HP = Horsepower

RPM = the speed at which the coupling will rotate

63,025 = a constant used for inch-pound calculations

Real-case scenario: a 10 HP motor running at 1750 RPM produces about 360 inch-pounds of torque. 

3. Apply the Service Factor

Applying the service factor (SF) is a step most people forget. Although the design torque has a perfectly smooth load, the machines in the real world vibrate, shock, and start/stop randomly. Therefore, applying a service factor helps to accommodate the stress. 

Multiply your calculated design torque by the service factor that is suitable for your application. 

• Uniform load: In uniform loads found in fans and centrifugal pumps, use a service factor of 1.0 - 1.2.

• Moderate shock: For moderate shocks in woodworking machinery and compressors, use a service factor of 1.3 - 1.5.

• Heavy shock: Heavy shocks in rock crushers and metal presses should be given a service factor of 1.5 -2.0 or more.

• Engine drives: If you are using an internal combustion engine, add approximately 0.5 - 1.0 to the service factor because of the pulsating torque. 

In other words, selection torque = calculated torque × service factor.

4. Verify Speed Limits

Every chain coupling has a maximum speed rating. Generally, they are not designed for extremely high speeds. 

• Without a cover: Couplings without a cover are limited to lower speeds, which are usually under 500-800 RPM depending on the size. 

• With a cover: The cover retains the grease, causing higher speeds that are often up to 2500 - 4000 RPM for smaller sizes. 

If your application runs at 3600 RPM, please ensure you check the manufacturer’s guidelines to ensure the coupling size you selected is rated for that speed. And do not forget to use a cover.

Conclusion

Choosing the right chain specification of the chain coupling balances key factors such as torque calculation, environmental conditions, and others. Applying the steps mentioned here will ensure you have a connection that is robust and reliable. 

If you want professional guidance on chain couplings, shafts, and other related matters, contact HANGZHOU PERPETUAL MACHINERY & EQUIPMENT CO., LTD.  Our expert team will give you a prompt reply.

FAQs

Can I customize chain couplings for special machinery?

Yes, you can customize chain couplings to meet specific requirements of unique machinery. Material, size, and design can be modified to suit high-torque or high-temperature environments. 

When should I replace a chain coupling?

You should replace a chain coupling when you notice visible chain elongation of over 3% or significant slack. Replace a chain coupling when you notice excessive noise, high vibration, worn sprocket teeth, or damage. 

What is the difference between ANSI and ISO chain standards?

ANSI and ISO chain standards are different in measurement systems and dimensions. ANSI chains are largely used in America. The chains use inch-based measurements and are robust. ISO chains are millimeter-based measurements and are used in European and British markets. 

What chain pitch should I choose for heavy-duty applications?

For heavy-duty applications, use a large chain pitch for superior fatigue resistance and durability. The pitch range should be between #80 and #240, with #80 (1-inch pitch) being the common starting point. 

How do I calculate the correct chain coupling size?

In order to calculate the appropriate chain coupling size, find out the design torque and accommodate the shaft diameters. Next, select the right model according to the category of the application.