Detecting spacing faults at the body ply and breaker liner cutter.

In the steel cord reinforced radial tire industry, spacing faults are the most common detects occurring in the production of steel cord reinforced ply.

The steel cord inspection system (SIS) of Roland Industrial Electronics, L.P., has been designed to find these faults at the cutting and splicing operation, be it body ply or breaker liner. The most common spacing irregularities are depicted in figure 1.

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Fault 1: If a wire breaks during ply production, it will show up as a missing wire in the steel cord web.

Fault 2: When splicing two steel cord webs together, the splices can result in smaller or larger gaps between the wires and may not be acceptable to quality control.

Fault 3: When transporting the web in the splicing machine, the steel cord web may be stretched, resulting in bigger gaps between wires than desired.

Fault 4: A broken wire can lay diagonally on otherwise properly processed steelcord webs. (This is actually the most difficult fault to detect because of the numerous angles in which a broken wire can be laying on the web and thereby generating a large variety of signal types and amplitudes.)

If a wire breaks during ply production, be it calendering or extrusion, it will show up as a spacing fault later in the process. Poor splices at the cutter also typically show up as a missing wire fault. Irregularities can have a variety of fault sources. This same also applies to the position change. A loose wire is most often traced back to the calendering process.

Of course, in addition to these main fault manifestations, there can be many other spacing configurations that can be classified as faults, depending on the quality criteria of the manufacturer. For example, some tire manufacturers work with overlapped splices, whereas others accept butt splices only.

One method of detecting these faults is x-ray technology. However, at the cutting and splicing station, this is seldom done because of the high cost of the equipment, regulatory restrictions and environmental considerations. Visual inspection by operators can also eliminate some faults. However, this requires the presence of and the attention of a person.

The SIS steelcord inspection system, which functions according to the magnetic leaking flux principle, makes it possible to detect the above faults without the precautions required for the use of x-ray or the presence of a person.

This system enables the elimination of faulty material early in the production process and thereby saves the cost of the succeeding processing steps, as well as the material cost of a faulty tire being scrapped at final inspection.

Therefore, the magnetic sensor system has proved to be extremely cost-effective with a very short payback period of only a few months in many cases.

Cutting and splicing station

Due to its compact design, the sensor is easily retrofitted into existing machinery. The sensor signals are transmitted in analog form to the measuring system as the front-end of a computer system. In order to ensure a high degree of web coverage, it is recommended to use several sensors across the steel cord web. It is possible to connect up to eight sensors to the measuring system.

The prerequisite for the proper detection of spacing faults is an appropriate mechanical arrangement, in the tire industry, a great number of different transportation facilities is found in the cutting area. However, not all are equally well-suited for the installation of a spacing detector. For good performance, it is necessary that the web travel smoothly across the sensor face without vibration or bulging. This is best accomplished by a conveyor belt designed with the specifics of the spacing detector in mind. Figure 2 shows an appropriate conveyor belt and some details of the sensor installation.

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First of all, the conveyor belt itself must be made of fiber or textile fabric containing no metallic objects, specifically no magnetic steel. This belt should travel over a non-magnetic stainless steel sheet that serves as an assembly plate for the sensors (figure 3).

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As the sensors are magnetic, they pull the steelcord firmly onto the traveling conveyor belt that transports the steelcord. This stainless steel sheet should be reinforced to avoid vibration. Any spacing faults present in the steelcord are therefore reliably detected as faults. In order to ensure good coverage of the steelcord widths, up to eight sensors can be spaced across the web.

The Roland spacing detector for steel cord is based on the simple principle of sensor signal generation by moving the web across the sensor. The sensor emits a strong permanent magnetic field. The steel wires within the web generate electrical signals in the sensor according to the law of induction. Any irregularity in the web, described above as faults, generates a signal that is measurably different from the regular signal pattern given by evenly spaced wires.

Detected faults are displayed visually on the monitor. The system also sends an output signal, which can be used in various ways. It can activate flashing lights, audio signals or actually stop the machine via the machine controls. Figure 4 shows the typical appearance of the sensor signals. In this particular case, one of eight sensors, displayed by the red LED, has detected a fault, because the signal level exceeds a pre-set threshold.

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This system has the highest sensitivity if the cord travels at a 90[degrees] angle over the sensor. However, the detection capability is not limited to 90[degrees] angle steel cord. In order to accommodate variable angle steel cord, the sensors are placed in a pivotable mechanical support. Some details are given in figure 5. It is, however, necessary to adjust the sensors in such a way that the 90[degrees] angle between the steel cord and the sensor face is maintained.

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This steelcord inspection system is also more than a spacing detector or more than a simple fault finder. The greatest benefits are achieved by using this system as a tool to optimize the production process upstream. By running statistics on the actual faults detected, it is easily determined which are the major causes of faulty steelcord. From there, it is often only a small step to eliminate the causes. Customers who have been using this method for fault detection and optimizing the production process have realized substantial savings in manufacturing cost, and as a result eliminated substantial sources of scrap. In that manner, this tool is not only of economic, but also of ecological significance.