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Have you ever wondered why a professional roller chain manufacturer applies a certain amount of tension to a new chain before it is shipped?
The chain has never been used.
It is brand new.
So why does it need to be loaded before delivery?
The answer is preloading.
Preloading is an important manufacturing and quality-control process for industrial roller chains.
It helps stabilize the chain assembly, reduce initial dimensional changes, and provide a more consistent basis for subsequent chain-length inspection.
According to ISO 606:2015, chains manufactured in accordance with the standard shall be preloaded by applying a minimum tensile force equivalent to 30% of the minimum tensile strength specified for the applicable chain.
In this video, we will explain what roller chain preloading means, how it is performed, why it is important, and how it differs from tensile testing.
Let’s start with the basic concept.
Preloading means applying a controlled tensile force to a new chain before final dimensional inspection and shipment.
The purpose is not to break the chain.
The purpose is not to determine the ultimate tensile strength.
Instead, the chain is subjected to a controlled load within the specified manufacturing process.
This allows the components and joints of the chain to settle into a more stable assembled condition.
A roller chain contains many individual components:
· Inner plates
· Outer plates
· Pins
· Bushes
· Rollers
· Connecting links
These components are assembled together to create a flexible transmission chain.
When a new chain is first loaded, small dimensional adjustments can occur within the assembled system.
Preloading helps stabilize this condition before the final chain length is measured.
A new roller chain is manufactured from many individual precision components.
Even when every component is produced within its specified tolerance, there can still be very small clearances and seating conditions between:
· Pins and plates
· Pins and bushes
· Bushes and inner plates
· Rollers and bushes
· Connecting components
When the chain is subjected to its first controlled tensile load, these components can settle into their operating positions.
This is one reason preloading is used before final length validation.
The objective is to make the chain’s dimensional condition more stable and repeatable.
This is one of the most important points.
Preloading and tensile testing are two completely different processes.
Preloading
The chain is subjected to a specified controlled tensile force.
The purpose is to stabilize the chain and prepare it for dimensional validation.
Tensile Testing
The chain is loaded until failure.
The purpose is to determine the chain’s destructive tensile performance.
A tensile test is a destructive test.
Preloading is not intended to destroy the chain.
ISO 606:2015 separately defines preloading and tensile testing as different performance requirements.
For chains manufactured in accordance with ISO 606:2015, the standard specifies a minimum preloading force equivalent to:
30% of the minimum tensile strength
specified for the applicable chain.
For example, if a particular chain specification has a minimum tensile strength of 50 kN, the corresponding minimum preloading force under this requirement would be:
50 kN × 30% = 15 kN
This example is for illustrating the calculation only.
The actual preload value must always be determined from the applicable chain specification and its specified minimum tensile strength.
It is important not to confuse this preload value with the chain’s working load.
No.
This is another important distinction.
The 30% value is a preloading requirement under ISO 606:2015, not a recommended operating load.
It should not be interpreted as:
“30% of tensile strength is the allowable working load.”
The working load of a chain depends on the actual application.
Engineers need to consider:
· Transmitted power
· Chain speed
· Sprocket size
· Shock loading
· Start-stop frequency
· Lubrication
· Operating temperature
· Alignment
· Working environment
· Required service life
The test and preload requirements in ISO 606 are not intended to be treated as working loads.
Let’s look at what happens when the chain is placed on a preloading machine.
First, the chain is installed in the test equipment.
The machine applies a controlled tensile force.
As the force increases, the chain becomes tensioned.
The individual components are pulled into their working positions.
Small internal clearances and seating conditions are stabilized.
The chain then reaches the specified preload condition.
After the preload process, the chain can proceed to dimensional inspection.
This is an important step because chain length measurement is performed after preloading and before lubrication according to ISO 606:2015.
Chain length is one of the most important dimensions of a roller chain.
If the chain is too long or has excessive variation, it can affect:
· Sprocket engagement
· Chain tension
· Transmission accuracy
· Vibration
· Noise
· Parallel-chain matching
· Overall transmission performance
However, measuring the chain before preloading may not provide the final stabilized dimensional condition.
Therefore, the standard specifies that chain length measurement takes place after preloading but before lubrication.
This creates a more consistent reference condition for dimensional inspection.
When people talk about chain length, they often use the term:
Chain elongation
But there is an important distinction.
A new chain that has undergone preloading is not the same as a worn chain that has operated for thousands of hours.
During service, chain elongation is primarily associated with wear in the pin-and-bush articulation areas.
Over time, wear increases the effective pitch of the chain.
This is different from the controlled dimensional stabilization achieved through manufacturing preloading.
Therefore:
Manufacturing preloading ≠ service wear elongation
This distinction is very important when explaining chain quality to customers.
One of the key benefits of preloading is that it helps establish a stable reference condition for final inspection.
Imagine two new chains.
Both are assembled from components that meet their individual dimensional tolerances.
Before preloading, their assembled dimensions may not be exactly the same.
After controlled preloading, the components are seated more consistently.
The manufacturer can then measure the chain length under the specified measuring conditions.
This helps improve consistency from one production batch to another.
After preloading, the chain can be measured using a specified measuring force.
ISO 606:2015 specifies minimum standard measurement lengths depending on the chain size.
For example, for certain smaller chain sizes, the standard measurement length is at least 610 mm, while larger applicable chain sizes use a minimum standard length of 1,220 mm.
The chain is supported along its length and the specified measuring force is applied.
The measured length is then compared with the applicable nominal length and tolerance.
This process helps verify dimensional conformity.
Chain pitch is one of the most important dimensions of a roller chain.
For a standard roller chain, pitch is the distance between corresponding points of adjacent chain joints.
The chain pitch must match the sprocket.
If the pitch is incorrect, the chain cannot properly engage with the sprocket.
This can lead to:
· Poor engagement
· Increased vibration
· Abnormal noise
· Accelerated wear
· Reduced transmission efficiency
Therefore, controlling chain length and pitch-related dimensions is essential.
Preloading and subsequent dimensional validation contribute to this manufacturing control process.
A roller chain and its sprocket should always be considered as a matched transmission system.
The chain pitch must correspond to the sprocket pitch.
The roller diameter, inner width, and other dimensions must also be compatible.
When the chain has stable dimensions, it can engage with the sprocket more consistently.
This is particularly important in applications involving:
· High speed
· Long center distances
· Multiple strands
· Continuous operation
· Precision transmission
· Automated machinery
For duplex and triplex chains, dimensional consistency becomes even more important because multiple strands must work together.
Roller chains can be supplied as:
Simplex
One row of rollers.
Duplex
Two rows.
Triplex
Three rows.
As the number of strands increases, dimensional matching becomes increasingly important.
If multiple strands do not have sufficiently consistent dimensions, load distribution may become uneven.
This can lead to one strand carrying more load than another.
Therefore, manufacturing control becomes especially important for multi-strand chains.
ISO 606 also provides requirements for chain dimensions and length validation for these types of chains.
Preloading should not be viewed as an isolated production operation.
It is part of a broader quality-control system.
A professional chain manufacturing process may include:
Raw Material Inspection
↓
Stamping / Forming
↓
Heat Treatment
↓
Component Machining
↓
Dimensional Inspection
↓
Chain Assembly
↓
Preloading
↓
Length Validation
↓
Lubrication
↓
Final Inspection
↓
Packaging
Each stage contributes to the final product quality.
The exact effect depends on the chain design and manufacturing process.
However, without an appropriate controlled preloading process, the chain may have a less stabilized assembled condition when final dimensional measurements are made.
This can make dimensional consistency more difficult to control.
For high-volume industrial production, repeatability is extremely important.
Customers may purchase thousands of meters of chain.
The chain must maintain consistent dimensions from one batch to another.
Therefore, manufacturing processes such as preloading and length validation are important parts of quality assurance.
This point deserves repeating.
A manufacturer should not say:
“We preloaded the chain, so we know its tensile strength.”
That is incorrect.
Preloading and tensile testing have different purposes.
Preloading:
Controlled loading for manufacturing stabilization and dimensional validation.
Tensile testing:
Destructive loading to determine tensile strength.
Dynamic testing:
Evaluation of chain performance under specified cyclic loading conditions.
ISO 606:2015 separately identifies these performance requirements.
A professional chain quality-control system may therefore use multiple types of inspection and testing.
There is a direct relationship between the two in the ISO 606 requirement.
The preload is specified as a percentage of the chain’s minimum tensile strength.
This means that when the chain size or specification changes, the corresponding preload requirement can also change.
For example:
Chain A
Minimum tensile strength = 30 kN
Minimum preload = 9 kN
Chain B
Minimum tensile strength = 60 kN
Minimum preload = 18 kN
Again, these are simplified examples to demonstrate the relationship.
Actual values must be taken from the applicable chain specification.
When purchasing industrial roller chains, buyers often ask:
“What is the tensile strength?”
That is a good question.
But for a more complete technical evaluation, buyers can also ask:
· Is the chain preloaded?
· What standard is used?
· How is the preload controlled?
· Is chain length measured after preloading?
· What measuring force is used?
· What are the dimensional tolerances?
· Are inspection records available?
· Is the chain suitable for continuous industrial operation?
These questions help distinguish a professional transmission-chain supplier from a simple trading supplier.
Tianjin Haorongshengye Electrical Equipment Co., Ltd. focuses on industrial transmission components including:
· Roller Chain
· Sprocket
· Gear
· Gear Rack
· Timing Belt
· Timing Pulley
· CNC Machined Components
According to the company’s official website, HaoRong was founded in Tianjin in 2008 and has extensive production and export experience. The company states that it operates with its own source factory, accepts standard and OEM products, and provides customized solutions according to customer drawings and technical requirements. Its website also highlights CE and ISO 9001 quality assurance and CNC manufacturing equipment.
For industrial chain customers, the important point is not simply whether a supplier can provide a chain.
The important question is whether the supplier understands the relationship between:
Chain Design → Manufacturing → Preloading → Dimensional Validation → Testing → Application
A reliable roller chain requires more than one test.
A complete quality-control approach can include:
Material Control
Verify material grade and consistency.
Dimensional Control
Check pitch, plate thickness, roller diameter, inner width and other critical dimensions.
Heat-Treatment Control
Ensure appropriate mechanical properties.
Assembly Control
Ensure correct assembly of pins, bushes, rollers and plates.
Preloading
Apply controlled tensile force to stabilize the assembled chain.
Length Validation
Measure chain length after preloading under specified conditions.
Tensile Testing
Verify destructive tensile performance when required.
Dynamic Testing
Evaluate dynamic strength according to the applicable test requirements.
This is how a chain moves from a collection of individual components to a controlled industrial transmission product.
Let’s summarize these three concepts.
| Item | Purpose | Chain Destroyed? |
| Preloading | Stabilize chain and support dimensional validation | No |
| Tensile Testing | Determine destructive tensile strength | Yes |
| Working Load | Actual operating load in machinery | No |
This table is extremely important for engineers and purchasing teams.
Do not use tensile strength as the working load.
Do not use preload as the working load.
The operating load must be determined according to the actual chain application and appropriate engineering data.
So, why does a new roller chain need to be preloaded?
Because professional chain manufacturing is not simply about assembling steel plates, pins, bushes, and rollers.
The chain needs to achieve stable and repeatable mechanical dimensions.
Preloading helps establish a controlled condition before final chain-length validation.
According to ISO 606:2015, compliant chains are preloaded using a minimum tensile force equivalent to 30% of the specified minimum tensile strength, and chain measurement is performed after preloading and before lubrication.
But remember:
Preloading is not tensile testing.
Preloading is not breaking-force testing.
Preloading is not allowable working load.
It is one important part of a professional roller-chain manufacturing and quality-control process.
A reliable chain starts with good materials.
Good materials require controlled manufacturing.
Controlled manufacturing requires accurate assembly.
And accurate assembly requires professional inspection and testing.
At Tianjin Haorongshengye, we focus on industrial transmission components and OEM solutions for customers worldwide.
If you are looking for industrial roller chains, sprockets, or customized transmission components, contact HaoRong for technical consultation and OEM solutions.
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