Wheels - Definition of the extraordinary thermomechanical stresses on wheels due to composite brake blocks

In view of the replacement of the cast-iron brake blocks with composite blocks in the framework of the EU directive on the reduction of noise emissions by railway vehicles, the working of the UIC has developed a test rig trial for the approval of the brake blocks that is representative of a brake malfunction, plus the associated approval criteria.

The objective was to make sure, before the composite brake blocks were used, that wheels approved for use with composite brake blocks, in accordance with the construction directive, withstand a brake malfunction without impairing the safe running or economic viability of railway operation.

Various brake block products and wheels were tested in the test rig trials. Some of the brake blocks gave rise to such high temperatures or to high temperatures acting upon the wheel for such long periods that the subsequent materials tests found negative effects upon the mechanical and metallurgical properties. To avoid the negative effects and additional monitoring measures for the wheels in operation, criteria were developed for a test rig trial representative of the brake malfunction, plus the acceptance criteria for this trial, taking into consideration the tasks listed above.

It is possible to use such wheels after brake malfunctions without additional special measures, provided that the stated requirements for composite brake blocks are adhered to.

If the requirements are not fulfilled, the brake block should either be withdrawn or specific maintenance measures are required before it can be used.