Inline calculation tool for the determination of the changeover time for color and material changes in polymer processing

Abstract

A change of extruded plastic products into a different material or color is connected to a wasteful process, regarding the loss of material, energy and system availability. Because of this, plastic processing companies want to reduce the required time between the basic and the target product. In the extrusion processes there are two possibilities to change from one material to another. The first option is the manual cleaning of the extruder and extrusion die, which leads to with a production stop and a high personnel effort. The second option is to perform a direct material or color change. The disadvantage of this method are the produced rejects during the change. Further, it is difficult to detect the end of the changing process, based on the product color, without expert knowledge.The LabVIEW inline calculation tool allows to detect the progress of the material change dynamically and to predict the needed time to reach the end of the changing process. Therefore an inline color measurement system ACS 7000 by μEpsilon is used to analyze the continuous change of color of the extrudate. The color information is converted into the numerical L*a*b* -color system and is compared to reference data, which are stored in a material database for different target materials and/or colors. The result of this comparison can be expressed as so-called color distance ΔE, which is necessary to determine the end of the changing process. With increasing changing time, the color distance is decreasing. After reaching a specified color distance ΔE a difference between the extrudate color and the target color is not detectable for the human eye anymore. The color change is finished. By analyzing the measured color changing progress, the tool is also able to predict the needed changing time.The functional capability of the tool is proved by a color change experiment from blue to natural material on a laboratory extruder