What is a dynamometer?

Complete guide to quality control equipment for packaging

Introduction

A dynamometer is a measuring instrument designed to evaluate the mechanical strength of materials, containers, and products. This equipment applies compressive or tensile forces and quantifies the resistance the material offers before deforming or failing. Dynamometers are essential tools in quality control laboratories, particularly in the packaging, beverage, and manufacturing industries.

The dynamometer operates using a load cell, which is a transducer capable of converting mechanical forces into measurable electrical signals. This technology allows manufacturers to ensure their products meet precise resistance standards.

How does a dynamometer work?

Compression and tensile testing equipment operates using a dynamometer and a motor. The motor applies the tensile or compressive force to the container being tested, while the dynamometer measures this force, allowing the detection of the deformation produced by the applied force.

• Compression: measures the force a material can withstand before it deforms or crushes (e.g., crushing a bottle).

• Tensile strength: measures the resistance to the separation of components (e.g., removing a cap from a bottle).

The load cell is the key component of the dynamometer. It acts as a transducer, converting the cell's mechanical deformation into voltage or electrical current. This signal is processed by an electronic controller, which displays both the complete resistance curve and the maximum (peak) force the material could withstand.

Main applications

Dynamometers are used in many sectors to guarantee quality:

• Beverage industry: compression resistance tests on glass and plastic (PET) bottles.

• Caps and corks: measurement of the force required to remove caps or corks from bottles.

• Toothpaste tubes: evaluation of thermal welds and laminate strength.

• Cables and cords: tensile tests to determine the strength of solid or braided materials.

• Metal containers: such as aluminum cans for soft drinks or metal boxes for preserved foods.

Key concepts: precision and resolution

It is essential to understand the difference between two terms that customers often confuse:

Accuracy: the ability of an instrument to provide repeatable measurements. A dynamometer is accurate if it measures the same value multiple times under the same conditions.

Resolution: the ability to distinguish between very close values. A higher measurement range generally implies lower resolution.

This inverse relationship is essential: a 500 kg dynamometer cannot detect variations less than 1 kg, just as a 30 cm ruler cannot easily measure below one millimeter.

The elastic phase of materials

All materials possess an elastic phase: this is the period during which they can deform and return to their original shape when the force is removed. Once this elastic limit is exceeded, the material undergoes permanent deformation or breaks.

For example, an elastic band can stretch and then return to its original shape, but if it is stretched too far, it breaks. Concrete has a nearly imperceptible elastic phase, while plastic has a more pronounced one. The dynamometer precisely measures the force required to overcome this elastic phase and cause rupture.

Dynamometer calibration

The calibration of a dynamometer is carried out using another dynamometer as a reference standard. The process, called "calibration by direct comparison," consists of:

• Place a reference load cell (of known value) in contact with that of the equipment to be calibrated.

• Apply progressive forces and compare the measurements of the two cells.

• Record errors and uncertainties in order to generate a calibration certificate.

When a dynamometer exhibits an error exceeding the acceptable limit, the cell is not immediately replaced: the conversion factor is first adjusted in the control software. However, if the error exceeds certain limits even after adjustment, the cell must be replaced.

Types of dynamometers and customization

Specialist manufacturers like AT2E offer dynamometers with different capacity ranges:

• Standard models: designed for 3-liter bottles, but adaptable to different sizes thanks to interchangeable bases.

• High capacity models (Dyna 4000): for compressions of 500 kg or more, including metal cans and large water containers.

• Universal models (TCT): versatile for pulling and compressing, with multiple accessories (pliers, corkscrews, etc.).

The operation is semi-automatic: the operator positions the sample and starts the test using manual or automatic controls. The machine performs the movement and records the deformation or breaking strength data.

Conclusion

The dynamometer is an essential tool for ensuring the quality and safety of packaged products. By understanding its operation, the concepts of accuracy and resolution, and the importance of regular calibration, companies can make informed decisions regarding their testing equipment. Choosing the right dynamometer based on the required capacity range and resolution ensures reliable and consistent results in quality control.