Process for operating a mixing kneader

A process for operating a mixing kneader, comprising one or more shafts on whose surfaces are disposed kneading bars and which are surrounded by a casing, comprising the following steps:

• (a) supplying reactants at an addition site in the mixing kneader,
• (b) converting the reactants in an exothermic reaction, the reaction at first forming a coherent kneadable intermediate,
• (c) tearing and dividing the coherent kneadable intermediate to form a product, the exothermic reaction optionally continuing during the tearing and division,
• (d) withdrawing the product at a withdrawal site in the mixing kneader,
• wherein at least one of the shafts and/or the casing is heated to a temperature above 20° C. during the operation of the mixing kneader and the temperature is maintained using a temperature control medium, and wherein a bending of the at least one shaft is measured and an inlet temperature of the temperature control medium is regulated as a function of the bending.