The Crushing Reality of Impact Loads
At Interface, we understand the incredible range of how load cells are utilized across industry applications, from precision weighing to force measurement in demanding industrial environments.
While our load cells are engineered for durability and high accuracy, there is a silent threat that can compromise their performance and even lead to catastrophic failure: impact loads. Our engineers highlight this in our Load Cell Field Guide, its destructive potential, and the crucial steps you can take to protect your investment in Interface load cells.
Beyond Static: The Dynamic Challenge of Impact
We often think of load cells in the context of static loads – a constant weight or force. But what happens when a force is applied suddenly, as in a dropped object or a sudden jolt? This is where the concept of impact load comes into play and why it is a game-changer.
Unlike static loads, impact loads introduce a dynamic element that significantly amplifies the force experienced by the load cell. The key difference is the rate of force application. A static load increases gradually, giving the load cell time to react. An impact load applies force instantaneously, concentrating the energy and potentially exceeding the load cell’s capacity, even if the weight involved seems small.
Understanding the Impact
Let’s illustrate with a straightforward example. Picture a steel ball dropped onto an Interface load cell. As the ball falls, its potential energy transforms into kinetic energy. Upon impact, this kinetic energy must be dissipated. The load cell ideally measures the force of the impact. However, the ball’s rapid deceleration generates a much higher force than the ball’s weight alone would indicate.
Here is a closer look at the physics at play:
- Impulse and Momentum: Impact is linked to impulse, the change in an object’s momentum (mass x velocity). The impulse-momentum theorem tells us that the impulse equals the change in momentum. In our ball example, the momentum changes from ‘mv’ to zero very quickly, resulting in a large force.
- Force and Time: The average force during impact is related to impulse by the equation: Impulse = Force x Time. Because the impact time is so short, the force becomes large to deliver the same impulse.
- Energy Dissipation: The kinetic energy of the impacting object must go somewhere. Ideally, it is measured by the load cell. However, a large part can be transferred to the load cell’s structure as stress waves, potentially causing damage even far from the impact point if it is overloaded beyond its capacity.
- Stiffness: A stiffer load cell will experience a higher peak force during an impact than a less stiff one, even with the same impact energy. The stiffer cell resists deformation more, leading to faster deceleration and a higher force. READ: https://www.interfaceforce.com/load-cell-stiffness-101/
Six Cautions and Preventative Measures
Protecting your Interface load cells is paramount, given the destructive potential of impact loads. Here are some key precautions:
#1—Analyze your application for potential impact scenarios, including dropped objects, sudden starts and stops, and vibration. For example, using load cells in conveyor systems for quality control and safety may encounter abrupt changes in motion that can generate significant impact forces. Even seemingly gentle actions, like placing heavy items onto a platform scale, can create impact loads if not done carefully. Also, external factors like wind gusts, seismic activity, or accidental collisions might induce impacts.
#2—Evaluate sensor features that include overload protection. Interface has various overload protection load cells and torque transducers in different capacities and configurations. These have mechanisms built into the sensor’s design to absorb overloads that may result from impact. For example, our SMT Overload Protected S-Type Load Cell has internal mechanical stops, preventing overloads up to 10 times the rated capacity. Our MRTP Miniature Overload Protected Flange Style Reaction Torque Transducer features 7X safe overload in a 0.2 Nm (1.77 lbf-in) capacity. The flange design makes it easy to mount. This product has low deflection and high torsional stiffness, which makes it an excellent choice for reciprocating measurements. READ: How Does Load Cell Overload Detection Work?
#3—Consider Interface load cells with significantly higher capacity than required for static loads, providing a safety margin. If your test requirement has a maximum capacity range, ensure that the force measurement device has a higher capacity to absorb potential overload risks. Identify the margin and plan by reviewing capacities for the selected model. Consider a load cell with a capacity higher than the expected maximum impact force. This is particularly important if your testing projects vary.
TIP: Our application engineers can help you determine the appropriate capacity for your specific needs, considering factors like the mass and velocity of the impacting object, the system’s stiffness, and the desired safety factor.
#4—Secure your Interface load cell mounting to a rigid base. A flexible mounting can amplify impacts. Use sturdy mounting hardware and ensure it is properly tightened. For torque transducers, couplings designed for the sensor are valuable accessories. Our load pins have keeper and mounting plate options. Learn more about this by reviewing Load Cell Mounting 101. Interface provides a series of videos that highlight installation and mounting tips.
#5—Examine the distance, as short impacts can be damaging. The change in momentum and resulting force count, not just impact length. Dropping an object from a short distance can still cause damage if the object is heavy or moving quickly.
#6—Inspect the impact-prone environments for signs of damage, such as cracks, deformation, or calibration changes. Every test should start with a visual inspection. If you detect any damage, contact Interface to schedule a repair evaluation.
Package Drop Testing Impact
Simulating the jostling and impacts during shipping is crucial for identifying weak points. By integrating load cells into the drop test set-up, product and test engineers can measure the exact force a package experiences upon impact. This precise data allows them to refine the packaging design for optimal protection, demonstrating the practical application of load cells. Read the application notes here.
Interface is committed to providing high-quality load cells and the knowledge and resources to ensure equipment longevity. You can safeguard your force measurement devices by understanding the physics of impact loads and implementing the preventative measures outlined above.
Interface load cells and maintain the accuracy and reliability of your measurement systems. Contact us today to discuss your application needs and how we can help you mitigate impact risks.
ADDITIONAL RESOURCES
Safeguarding Products and Packaging Integrity Using Load Cells
Understanding and Preventing Load Cell Overload
WMCP Overload Protected Stainless Steel Miniature Load Cell with Male Threads
MRTP Miniature Overload Protected Flange Style Reaction Torque Transducer
MRT2P Miniature Overload Protected Flange Style Reaction Torque Transducer
MBP Overload Protected Miniature Beam Load Cell
