Locating steel cord.

This company's sensor is utilized in a process used to locate steel cords in tire belt material when the cords are completely concealed by a rubber coating. The excess rubber material extending beyond the last steel cord must be trimmed. It is important not to cut into the actual cord with the trimming knife. Downstream production efficiencies can be negatively impacted if too much rubber extends past the trimmed edge, or if the steel cord is cut.

A compromise solution to this problem has been to use a contact guide that follows the most recently cut edge. Extra rubber is left in place to avoid cord contact with the rotary knife, and most are said to be reasonably satisfied with the results. But the contact method is not foolproof and is certainly not trouble-free. Until now, the only non-destructive way to ensure proper cord position has been to use a radiation source such as x-ray to look through the rubber coating and detect the cord edge. This method is used in a few select applications, but is often too expensive for a common solution.

The company's device uses three matched air-coupled transformers to measure the magnetic density of a sample area of the steel cord/rubber material. Transformer A is completely covered by the cord material and establishes a density reference. Transformer B is positioned several inches away from the cord material and left completely uncovered. A reference voltage is established halfway between the covered and uncovered transformer outputs. Transformer C is placed physically between the other two units. When the edge of the cord material is centered in the field of the middle transformer, the output signal C will equal the average of the output voltages from the other two transformers. The reference transformer voltages depend on the same drive signal as the measurement transformer voltage.

Harris Instrument

Circle 8 on card