Apparatus for determining gel time

An apparatus for determining the gel time of an uncured resin fibre specimen (38) contains a heated measuring head arrangement (12) comprising a stationary measuring head part (22) and a measuring head part (26) which is driven in an oscillating manner. The measuring head parts (22, 26) are provided at the end faces with contact surfaces (32, 34) for the specimen which are pressed against one another. In order to achieve a high gel time measurement precision despite a simple and inexpensive construction, heat transfer surfaces (32, 34) which enclose the sample contact surface over a large area and are adjacent to one another with a narrow spacing are provided, according to the invention, in each case on the stationary and the rotatable measuring head part. Only the stationary measuring head part (22) is directly heated, the rotatable measuring head part (26) being heated, on the other hand, exclusively via the heat transfer surfaces. At the same time, the stationary measuring head part has a very high heat capacity compared with the specimen, as a result of which the temperature control at the specimen is made considerably more uniform and a separate, active heating system for the rotatable measuring head part (26) can be dispensed with.