The line scanner is specially developed with functions only required for this application. The components are according to military specfications with high reliability. The infrared emission from the surface represents a temperature image. A temperature profile is recorded by consecutive scans as the billet passes the scanning line. Extremely high sensitivity of the IR detector elements is required to “see” the signal from a defect 0.2 mm deep hairline crack on a moving billet. The high sensitivity is obtained by IR detectors cooled down to cryogenic temperatures. Further increase in sensitivity is obtained by using several separate MCT IR elements in a TDI configuration. The cooling is done by JT-coolers using high pressure air or nitrogen cleaned “def stan clean air quality” standard. Replacing a JT-cooler is done on site and takes 15 minutes.
The infrared emission representing the temperature image across the surface is monitored and recorded by 4 infra-red scanners positioned immediately adjacent to the coil and mounted on movable steel frame. The position of the scanners are such that each scanner sees one face and one corner on square billets and a 90° sector on round bars.
The IR-scanners scan across the surface and record consecutive temperature profiles as the billet passes and creates a temperature image of a passing billet. The recorded temperature profiles are monitored and sent to 4 signal processing units.
The temperature profile is adjusted to correct for the non-linearity in sensitivity of infra-red sensors to obtain equal sensitivity over the surface temperature range of the system. Selectable detection algorithms analyze the image, detect and measure amplitude irregularities in temperature and compare the amplitude with 4 detection thresholds for marking, depth classification and defect categorization. Each defect is identified with length, depth and exact position. This information is recorded and presented in several reports according to customer’s requirement.
The electronic is designed and manufactured by us. This allows us to make modification and improvement with upgrades. The current processor is the fourth generation. A fifth generation is planned with the new scanner.
IRTech has in regular intervals tested new and compared our scanner with the most sophisticated cooled IR-camera to be updated on IR-camera technology. The results of the comparison tests and the 25 years long track record of our line scanner was the deciding factor when we decided to use the same design in our new scanner, instead of commercially available cameras with focal plane array detector. We have designed a new detector unit with increased sensitivity and new electronic.