In the current situation in the wake of worldwide corona pandemic, German company Mahlo GmbH + Co KG is providing manufacturers of nonwovens with means to measure production processes. By controlling basis weight and material thickness, its new Gravimat DFI sensor helps to ensure quality of respiratory masks and medical protective clothing. 

The Gravimat DFI sensor is part of the modular Qualiscan QMS quality measurement system and measures weight and material thickness using isotope radiation. The measurement is based on the attenuation of radioactive radiation by the substrate in the measuring gap. This weakening of the intensity is a measure of the basis weight of the goods. Mahlo works with different isotope variants in order to do justice to different material properties. Krypton-85 is used for goods with a weight between 10 and 1400 g/m² strontium-90 is used for 100 to 6000 g/m².

The transmitter in the traversing sensor beams onto the running web. Due to its mass, the radiation reaches the receiver in a damped manner. The values of the transmitted and received radiation are calculated to obtain the weight per unit area. Mahlo uses a multi-channel receiver in which the incoming measuring radiation is distributed to different areas of the fabric surface. In this way precise values are obtained, no matter what position the fabric is currently in.

This method also solves one of the biggest problems faced by manufacturers of web-shaped goods such as hygiene fleece: measurement inaccuracies due to fabric flutter. Its sensor technology makes the Gravimat DFI immune to changes in the center of gravity. It measures precisely and unaffected by any changes in degree of dryness, density or thickness.

The Gravimat DFI does not require strong absorbers or highly radioactive sources. Nevertheless, the highest precision, speed and resolution are guaranteed. The sensor can be used for practically all nonwoven applications.

For nonwoven fabric used for face masks, air permeability is of particular importance. After all, the wearer must be able to breathe easily. In this case, Mahlo combines basis weight measurement with an air permeability sensor, which can also measure on the running web with a light touch.

Manufacturers of medical goods are currently under pressure to deliver their goods as quickly as possible, but still with high quality. With process control systems from Mahlo, this balancing act is not only easier to master - production costs are also further reduced. The automatic basis weight control significantly limits the spread of the basis weight and thus guarantees a more uniform end product. Suitable set point settings with minimum tolerance ranges, in addition to ensuring product quality, save considerable material and energy costs. In addition, a safety margin is eliminated, which otherwise means loss of goods and time.