say from an aluminum alloy a particularly advantageous material 28 is an aluminum silicon alloy in particular with 12 u00b1 1 silicon the silicon means that the coefficient of thermal expansion is around 21 u00d7 10 u2212 6 k u00b1 2 u00d7 10 u2212 6 k and thus in the vicinity of that of stainless steel which is around 18 u00d7 10 u2212 6 k this means that thermal stressing between the base material and the different material 28 is kept to a low level even in the event of pronounced fluctuations in temperature as may occur for example in the case of rubbing this counteracts breakage of the front part of a sealing ring 18 or of a labyrinth tip it is likewise advantageous for the strength of the sealing rings 18 if the boundary surface between the different material 28 and the base material is narrow that is to say is small even with different coefficients of expansion the level of stressing between the materials remains low even in the event of pronounced fluctuations in temperature the different material 28 comprises two material zones of differing materials the front part which is oriented in the direction of the gap 4 and thus in the direction of the sealing region is the aluminum alloy and the rear part is an intermediate layer 30 which promotes adhesion between the base material and the different material 28 in this exemplary embodiment between the steel and the aluminum alloy a particularly suitable intermediate layer 30 is a zinc layer which can be applied to the steel by hot galvanization of the steel likewise suitable is a nickel layer which can be electroplated onto the steel in.