Measuring the colour of zinc-coated strip materials

HD Lenzen, a specialist in the surface finishing of strip materials, has chosen an inline colour measurement system from Micro-Epsilon to continuously measure the colour of zinc coated strip during production.

In addition to providing 100% quality control during production, the colour measurement system is also helping to reduce waste and customer complaints due to colour variations.

Classic strip material is used to produce punched, bent and deep-drawn components, filters and gaskets, electronic components and packaging components. The raw material, in this case steel or aluminium, is coated for refinement purposes and not only serves to enhance the appearance but also the resistance, while the material becomes easier 

to process.

Consistent product quality

During the surface finishing process at HD Lenzen, steel and aluminium strips are coated with zinc, which is deposited onto the cleaned strip from an electrolyte solution by applying a high electrical current. As well as receiving corrosion- and wear-resistant protection, the strip material also has a defined colour. Reliable testing of this colouring is necessary in order to ensure consistent product quality.

In order to fulfil the high requirements for precision and speed, the colorCONTROL ACS7000 colour measuring system from Micro-Epsilon is used, which recognises colour shades to an accuracy of ∆E < 0.08. Manual, visual inspection is not possible in this area, as a trained human eye can only recognise colour distances up to a maximum of ∆E 0.5.

In addition, the colour measuring system must keep pace with high speed inline measurements. Therefore, the system is installed on a traversing unit that moves over the continuous material, which has a width of 720mm. Influences induced by fluctuating temperatures are minimised by continuous referencing. Via an Ethernet interface, these high precision measurement values are directly transmitted and evaluated by a connected production monitoring PC. Should any deviations occur, the plant operator can rapidly intervene, which means waste is reduced.

The core component of this 100% quality inspection system is the colorCONTROL ACS7000 colour measuring system with an ACS1 sensor head from Micro-Epsilon. The ACS1 sensor is designed with the transmitter and receiver mounted inside one sensor head. The optics are arranged at an angle of 30°/0° to each other, producing a working distance of 50mm from the target.

Plant integration, including software for monitoring and retracing all past production parameters, was designed by TriDiCam, an official system partner of Micro-Epsilon.

Continuous inline colour measurements

The colorCONTROL ACS7000 identifies colours using any of the XYZ; L*a*b*; L*u*v*; RGB and DIN99 measurement definitions (user selectable). The system can be set up to continually monitor a production process and output the colour measurement via Ethernet, EtherCAT or RS422 and can also be taught pass fail/limits and then output out-of-tolerance alarms using digital I/O.

The system is therefore suitable for a wide range of applications where colours and shades must be examined on-the-fly and to very high accuracies. Existing applications include automotive paint inspection, colour measurement of car interiors, coloured glass, transparent film and sheet production, printing, packaging, medical technology, food, cosmetics, pharmaceuticals and in the processing of plastics, food, wood, paper, veneer and textiles.