Exothermic reaction in an air stream

(Grewer oven)

This test is designed to determine the relative auto ignition temperature of a product in a hot air-stream. It is applied to products which are subjected to elevated temperatures in an air-stream for a short period of time (e.g. spray drier, circulating air tray drier etc.). With this test, the permissible inlet temperature of the drier can be derived.

The auto ignition of the product tested occurs by reaction with the oxygen in the air and/or by exothermic decomposition. The same test may be done in a nitrogen-stream instead of an air-stream. If both results are compared, the influence of the oxygen in the air can be clearly distinguished.

The milled and dried test substance and a same quantity of graphite powder as reference substance are heated up in a fine wire mesh container at a linear rate of 1°C/min, while a hot air stream is blown through them. The temperatures of the samples are recorded.

The test set consists of:

Test Equipment, as per Grewer: Electrically heated stainless steel block with 6 holes to receive 1 reference and 5 test samples. The lower hollow section contains a packing of small cuttings of copper tube through which an air stream in passed. The heated air passes through the holes in the upper part of the block, and flows around and through the test substance contained in a fine wire mesh container.

Temperature controller and data acquisition system: Sipcon

Metal-sheathed iron-constantan thermocouples, inserted in thin glass tubes to protect against corrosion.

Swiss Institute for the Promotion of Safety and Security

Adrien Bisel, Phone +41 (0)61 696 55 99, Fax +41 (0)61 696 70 72

Petra Meier, Phone +41 (0)61 696 57 24, Fax +41 (0)61 696 70 72