3 Proven Methods of Verifying Torque Specifications

3 Proven Methods of Verifying Torque Specifications

Last Updated on February 12, 2024 by Ossian Muscad

Bolts play an essential role in securing products together. They are often used in critical applications where failure is not an option. That’s why ensuring that the torque values applied to bolts are accurate is important. Torque is a critical factor in product assembly. It is the force that keeps bolts and screws in place, ensuring that your product is safe and reliable. That’s why verifying torque specifications is essential before you begin assembly. 

This blog post will discuss three methods of verifying torque specifications. Each method has advantages and disadvantages, so choose the one that best suits your needs. Let’s get started!

 

What are Torque Specifications?

Before we discuss how to verify torque specifications, it’s important to understand what they are. Torque specifications are the values that indicate how much force should be applied to a bolt. These values are usually given in Newton meters (Nm) or foot-pounds (ft-lbs). 

Torque specifications are essential because they ensure that bolts are tightened to the correct level. If too much torque is applied, it can cause damage to the bolt or the product. Conversely, the bolt may come loose and cause problems if too little torque is applied. 

 

Why is Verifying Torque Specifications Important?

Verifying torque specifications is essential for several reasons directly relating to the integrity of the assembly and the safety of the final product. Here are some key reasons why verification is necessary:

  1. Preventing Mechanical Failure: Proper torque prevents joints from loosening under dynamic loads, which could lead to catastrophic mechanical failures, particularly in applications such as automotive or structural engineering, where reliability is critical.
  2. Ensuring Safety: Over-torquing can compromise the integrity of the bolted joint, potentially leading to breakage and the release of energy, which may cause injury or damage to machinery. Similarly, under-torquing might result in bolts coming loose, posing safety risks.
  3. Maintaining Product Warranty: Many manufacturers demand adherence to specified torque values to keep warranty claims valid. Failure to comply can void warranties, leaving businesses or consumers responsible for repair costs.
  4. Achieving Consistency: Replicating the exact torque specifications in mass production ensures that every unit performs as expected, maintaining the reputation for quality and consistency of the product.
  5. Complying with Regulations: Certain industries are governed by strict regulatory standards that require torque specifications to be met and verified for safety and environmental considerations.

 

Methods of Verifying Torque Specifications

Traditionally, there are three main test methods for verifying torque specifications. These include the first movement in the fastening direction, the first in the loosening direction, and determining the rotation angle by marking the fastener. Let’s discuss these methods in detail below:

First Movement Torque Test

The First Movement Torque Test, often called the “Loosening Test,” is performed by slowly applying force to the fastener in the direction that would loosen it until a slight movement is detected. This initial movement indicates that the preload or initial tension in the fastened joint matches the applied torque. The measured torque at the point of movement is then compared to the original specifications. If the values are within the acceptable range of the specified torque, the applied torque is accurate.

This method is particularly reliable for detecting under-torque occurrences, making it a suitable check for safety-critical components. However, there are some drawbacks to this approach. For example, testing can slightly loosen the fastener, potentially compromising the integrity of the joint if not properly retorqued after testing. Additionally, this technique assumes that the original torque applied was correct and that the fastener hasn’t been affected by external factors that could change the relationship between torque and tension.

Loosening Torque Test

The Loosening Torque Test, or “Back-off Torque Test,” measures the minimum torque required to initiate the rotation of the fastener in the loosening direction after it has been tightened. This test is useful for assessing the effectiveness of locking elements, such as thread lockers or nylon insert nuts, designed to prevent self-loosening.

To perform this test, a torque wrench is applied to the fastened assembly, and force is gently increased in the reverse direction of the tightening until the bolt starts to rotate. The torque value at the point just before the fastener turns is recorded as the loosening torque. This value should be lower than the tightening torque if the locking features are functioning correctly.

Comparing the loosening torque with the initial tightening torque helps understand the margin between the two and provides insight into the potential for self-loosening under vibration or changing loads. Although this method does not confirm the absolute value of the initial tightening torque, it is an excellent indicator of the joint’s remaining locking performance after assembly, which is vital for maintaining long-term reliability.

Marking Torque Test

The Marking Torque Test is a straightforward method to verify torque specifications that involve marking a point on the bolt head or nut and a corresponding point on the assembly before the tightening process. After applying the specified torque, the fastener should not move past the alignment of these marks during normal operation.

To perform this test, once the bolt has been tightened to the specified torque, a mark is made on the head of the bolt and extended onto the surrounding material. The alignment of these marks is then observed over a period of use or after a certain number of operational cycles. If the marks remain aligned, the joint has maintained its torque. Any misalignment would indicate that the bolt has moved, implying a potential torque loss or joint failure due to vibrations or other operational stresses.

This method is particularly useful for spot-checks during maintenance or inspections where testers can visually confirm the integrity of the joint without applying any additional force that could alter the assembly. Despite its simplicity, this is a non-destructive method that does not affect the joint’s integrity, making it a popular choice for routine checks and for users who do not have access to specialized torque testing equipment.

 

Frequently Asked Questions (FAQs)

Q1: How often should torque specifications be verified on assembled joints?

Torque specifications should be verified according to the manufacturer’s recommendations or industry standards. Typically, it’s also advised to check the torque after any maintenance or if the assembly is subjected to severe conditions that could affect the fastening integrity.

Q2: Can weather conditions affect the torque value of a fastened joint?

Yes, extremes in temperature and humidity can affect the material properties of the components in a fastened joint. They can lead to expansion or contraction that changes the preload, thus affecting the torque value.

Q3: Is it necessary to use a calibrated torque tool for verification?

Yes, using a calibrated torque tool is essential for accurate verification. Such tools should be regularly checked and maintained according to the manufacturer’s or standards’ calibration schedule.

Q4: What’s the difference between torque and tension in bolted joints?

Torque refers to the rotational force applied to the fastener, while tension refers to the stretch or clamping force that results from the applied torque. The correct torque ensures the necessary tension to keep the joint secure.

Q5: How do lubrication or surface treatments affect torque values?

Lubrication and surface treatments can significantly reduce friction and alter the torque-tension relationship. Considering these factors when determining the correct torque specifications and during verification is important.

Q6: What is the risk of using an impact wrench to verify torque specifications?

Using an impact wrench can lead to inaccurate torque verification due to the tool’s hammering action, which can cause the fastener to tighten further or loosen in a way that is not uniform or controlled. Therefore, verification is preferable for a manual torque wrench or a precise torque measuring tool.

 

Measure Torque with DATAMYTE

DATAMYTE, a recognized industry leader in providing robust data collection and low-code quality management solutions, offers a range of torque products designed to enhance accuracy and efficiency in various manufacturing environments.

LightStar Torque Wrench

This precise torque-measuring instrument is designed to eliminate false readings that are difficult to detect. The LightStar Torque Wrench series technology sensor ensures that the operator can pull at any point on the wrench and will receive an accurate measurement.

DataMyte Torque Solution

This solution provides real-time reporting and torque data collection to improve and monitor torque continuously. It’s a comprehensive system for managing all aspects of torque control, from data collection to analysis and reporting.

New Generation of Digital Torque Wrenches

DATAMYTE has introduced a new generation of their LightStar™ Carbon Fiber Torque Wrench. These digital torque wrenches offer improved performance and accuracy, making them ideal for demanding industrial applications.

These products are part of DATAMYTE’s commitment to providing quality management solutions that enhance actionable results based on collected production data. They are designed to ensure consistent, reliable torque application, improving the quality and reliability of assembled products. Book a demo with us now to see how we can help you achieve your torque accuracy goals.

 

Conclusion

The importance of accurate torque application and verification in assembled joints cannot be overstated. Ensuring the correct torque ensures the integrity and reliability of mechanical assemblies in many industries. Various methods and practices can be utilized to maintain the required specifications, from the Marking Torque Test to regular maintenance checks.

As technology and materials evolve, so does the need for precision and vigilance in torque application to mitigate risks associated with fastening failures. It’s imperative that technicians, engineers, and quality control personnel stay informed and equipped with the correct tools and knowledge to uphold these standards for the safety and longevity of mechanical systems.

 

 

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