a sealing device is provided for the cyclical opening and closing of the injection mould and for applying the sealing force on a mould sealing unit on an injection moulding machine for the working of plastics . the sealing device is supported on a support . a high resolution surface deflection sensor is provided as sensor means for recording the tool securing force and the sealing force , which is arranged on the support for the sealing device . a simple , economic and reliable measuring system is thus achieved , which can record the forces throughout the whole cycle .