EoW January 2013

News Technology

Materials savings from Zumbach

To compete in today’s markets, it is necessary to reduce operating costs. But, cutting costs cannot mean sacrificing a high quality standard, and an in-line measurement and control system incorporated on an extrusion line can reduce material usage. In-line measurements are a requirement for many extrusion lines. The objectives of such measurement systems vary from a simple quality control tool to a completely integrated closed-loop control system. There are different measurement technologies that can be used in the wire and cable industry, and the implementation of such systems can result in significant material and scrap savings. • Laser and infrared technologies suitable for all applications • Ultrasonics for jacketing lines (cable, fibre, etc), insulating lines and multi-layer applications • Inductance for primary lines and insulating lines • X-ray for CV lines Once the method of measurement is established, the system’s processor can be configured to perform closed-loop control. Using the example of a line running 75m/ min and a measurement point location of 2ft from the cross head. In this case, the delay time is dramatically improved (2ft divided by 75m/min equals 0.5 seconds). Although the short-term variation has been significantly improved, the issue of shrinkage must still be considered. An offset can be effectively used, but changes due to such variables as material, cooling, tension, etc, have to be considered. In most applications, these variables are enough to warrant a second loop to the controller. This is called a dual loop system. In a dual loop system, both the “hot end” measurement point and “cold end” measurement point are used. The system takes the readings from the hot end and constantly compares them to the readings at the cold end to establish an accurate offset. These values are shifted to ensure “same spot”comparison. This dual loop (DLP) control strategy can be taken a step further for jacketing applications. To realise the highest potential savings, the desired controlled parameter is the minimumwall. This minimumwall value can be established using a combination of ultrasonics and laser. These technologies include:

▲ ▲ Reducing costs but keeping a high quality standard

cold values in the same way the dual loop controller does. With any controller, not only is establishing the correct control strategy important, but setting up the controller properly can make all the difference. A controller can be set up to be as aggressive as the process can tolerate. The more the process is statistically “in control”, the better a controller can perform. To account for unexpected events in a process, a controller can utilise statistics to tune it. Once accurate measurement has been established, and the controller strategy has been optimised, yet another function can be utilised to improve material savings. Since a product’s key characteristic has a tolerance and a nominal, the typical controller would be set to tolerate the nominal as the controller’s set point. Most likely, these nominal and tolerance values were established based on the line’s performance with the lower tolerance in mind. At one point, someone established the set point with the logic that this is where the operator needs to target to play it safe to ensure the lower tolerance is not violated. It is assumed these parameters were established with a statistical study of some sort. In the real world, these nominals are rarely adjusted. The results are parameters that are padded unnecessarily. By enabling statistics to determine the correct nominal, all factors can be taken into consideration in real time. Zumbach Electronic uses a CPK Pilot lot to perform this function. By entering the desired CPK level, the controller can determine the capabilities of the line. Once this is known, the controller will adjust the nominal value as low as possible, maintaining the desired CPK level.

Zumbach Electronic AG – Switzerland Website : www.zumbach.com

Zumbach’s “DIACAL” technology is used to calibrate the ultrasonics based on the

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January 2013