External Appearance, Homogeneity, Skew and Waviness

Homogeneity is supervised within certification testing and third-party control of manufacture where sections are investigated at a 6-fold enlargement in accordance with DIN 16726, Sect. 5.1. The sections must be free of voids, pores or foreign inclusions. If the external appearance gives cartse for doubts, homogeneity shotrld always additionally be tested. 

DIN 16726, Sect. 5.2 describes the test of skew and waviness in detail. The tests are ustrally performed as part of the manufacturer in-house qtral-ity control before each operation start-up. Any re-start of the extrusion line 

It has already been mentioned that the thickness during production can be measured and monitored with a 3 radiation thickness gauge. A radioactive P-ray emitter of known intensity is arranged above the geomembrane. The attenuation of radiation decreases exponentially with the thickness. After a calibration (determination of the coefficient of attenuation) the 

The thickness can also be determined by simple, portable ultrasonic devices. The delay time of the echo of an ultrasonic impulse from the back side of the geomembrane is measured which is sent by an ultrasonic measuring head placed on top of the geomembrane. This method is mainly used for the measurement of the thickness of weld seams (see Sect. 10.2). 

Finally, thickness can also be meastrred optically. A smooth cut edge is observed by a handheld microscope. More expensive optical methods can be used for the determination of the thickness of geomembranes with a textured surface which are more difficult to investigate (see Sect. 6.2). 

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