Dusts are small solid particles that are present in a settled state at rest, and their settling time is determined by the particle size distribution. By knowing the table below and the particle size distribution of the given powder sample, the settling time can be estimated.

KÉPET ILLESZTENI !

Dust settled in technological systems or in their environment is a source of danger. The thick layer of dust adversely affects the heat transport processes of electrical equipment, it can cause unexpected wear and tear when it gets into mechanical equipment. As a result, electrical and non-electrical equipment may heat up excessively, and a layer of dust deposited on their surface may cause fire nests. The ignition tendency of the deposited dust layer is characterized by its minimum ignition temperature.

The minimum ignition temperature of the dust layer - Layer Ignition Temperatures (LIT) is the lowest surface temperature that can ignite the dust sample in its settled state. Regarding the design of the device used during the measurement, it is a heatable plate, in the middle of which there is a support ring for placing the sample. Thermocouples are used to measure the temperature of the heating plate and the sample.

KÉPET ILLESZTENI !

During the measurement, we observe the powder placed in the support ring on the test surface heated to the desired temperature. The result of the test depends on whether one of the conditions corresponding to the definition of inflammation occurs:

 the sample ignites or starts to burn with flame,  its internal temperature exceeds 450°C,  its internal temperature is 250°C hotter than the surface temperature of the heating plate.

 the sample ignites or starts to burn with flame,

 its internal temperature exceeds 450°C,

 its internal temperature is 250°C hotter than the surface temperature of the heating plate.

If the sample does not ignite after 30 minutes, the test temperature should be increased. In the event of ignition, the maximum temperature of the test is 400°C, if there is no ignition even then, this is recorded.

The standard defines the test for a 5 mm thick sample, but the ignition temperature can be measured with different powder layer thicknesses. The point is that in dusty technology, the surface thickness of the deposited dust layer must be defined and the cleaning schedule must be organized in such a way that a deposited dust layer larger than the defined value cannot form. In general, this is defined by the operation as 5 mm. Typically, by increasing the thickness of the dust layer, the minimum ignition temperature decreases, since the increased insulating capacity of the higher dust layer hinders the heat transport process between the sample and its environment. The relationship between the typical ignition temperature and the thickness of the dust layer is illustrated in the figure below.

KÉPET ILLESZTENI !