by Msc. Dieter O. Gräf, Milling and Engineering, Vibronet-Gräf GmbH &Co. KG, Germany

The cereal processing industry and, particularly, flour and feed mills are considered to be highly fire-prone due to the occurrence of fine grain and flour dust. In these challenging environmental conditions, it is important to identify potential ignition sources such as the overheating of machines at a very early stage.

Explosion protection is an essential aspect of product safety and one of the main tasks of those responsible for safety and health within a company. Explosions or fires are often severe or fatal. Many are preventable if safety hazards are identified early enough to take protective measures. Many older operations, however, have not yet implemented comprehensive explosion and fire prevention measures. This is why it is necessary to install easy retrofit security surveillance in order to protect both human life as well as to retain the production site. These safety devices should control, alarm and immediately stop the production.

The following measures are absolutely necessary for a safe cereal processing production because they have long proven to be remarkably effective:

  • Decibels (dB) monitoring in every room and on every floor
  • Smoke detectors in every room and on every floor
  • Dust detectors in every room and on every floor
  • Temperature monitoring on gears and motors
  • dB detection through vibration absorbers
  • Temperature control inside the pneumatic filter
  • Dust detection inside the filter
  • Dust concentration monitoring at the pneumatic filter output
  • Temperature monitoring of every roller or sliding bearing
  • Surface temperature monitoring of the corrugated and smooth roller
  • Decibel (dB) monitoring of the roller mill frame

Temperature (°C) is one of the most frequently measured physical quantities. The temperature, or the temperature difference, is an important indicator of the machine condition, both in production and in preventive maintenance.

Amongst all machines in grain processing, roller mills are the most important grinding units. During the grinding process, large steel or cast surfaces meet high contact pressure and high grinding energy. This multiplies the risk of overheating. If, for example, the grinding gap is not correctly set, the rollers are worn or the contact pressure is too high, steel surfaces run on steel or cast surfaces run directly on cast. This leads to an increased temperature and the formation of sparks. Brushes are attached underneath the rollers. If these are not cleaned regularly, caking material can heat up and thus represents an additional dangerous ignition source.

It is, therefore, very important to continuously monitor the condition of the roller mills by measuring the temperature of the roll and the bearing surfaces.

More than 15 years ago, on April 2004, MSc. Dieter Otto Gräf had already been granted the patent for the VIB-TM© 'Infrared Temperature Measurement on Rollers'. VIB-TM© retrofit kits for roller mills of all types and ages are now available with EX approval (explosion-proof) in order to provide an easy-to-install and safe solution for monitoring also older existing roller mills and their bearings.

These retrofit kits monitor temperature differences and give an immediate alarm if the preset values are exceeded, initiating an immediate production stop. They can be retrofitted without much effort, prevent production downtimes and form the basis of a safety concept for comprehensive protection against fires or explosions.

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