Thickness profile measurement improves steel strip quality

Based on sites in Stocksbridge and Rotherham, Liberty Speciality Steel is a key division of Liberty Steel, a fully integrated steel manufacturer and distributor within the global metal trading and industrials group, Liberty House Group. Liberty Speciality Steel produces high-value, precision-engineered alloy and stainless steel products for use in demanding sectors such as aerospace, oil and gas, bearings and industrial engineering, as well as bright bar and narrow strip for customers around the world.

Andy Spalding, Works Engineer at Liberty Speciality Steel (Narrow Strip) in Brinsworth comments: "In November 2016, we installed a non-contact inline gauge [thickness] profile measurement system from Micro-Epsilon in our narrow strip slitting line at Brinsworth. The thicknessCONTROL C-frame system has further improved our capability to monitor the strip specifications, allowing us to make improvements to our product quality and consistency."

He continues: "Prior to installing the system, we were manually inspecting strip using micrometers by taking measurements at various points across the strip. We're now using the thicknessCONTROL system to measure not only the thickness profile across the strip, but also three key quality parameters: the crown, the wedge and the edge drop. The system enables us to continuously check that the thickness profile and the key parameters are meeting the customer's specification."

Compensating for oscillating strip

Before selecting the thicknessCONTROL system, Liberty Speciality Steel considered various other thickness measurement systems, including both contact and non-contact systems. As Andy Spalding recalls: "We chose Micro-Epsilon's system primarily due its cost and how technically sound it is. Although most thickness measurement systems can handle the manufacturing tolerances that we work to, the strip does have a tendency to oscillate slightly as it's being processed, which can affect measurement accuracy. We therefore worked closely with Micro-Epsilon to devise a C-frame mounting arrangement that utilises a series of plastic wear plates that help to restrict the movement of the strip to a maximum of 60mm as it's being rolled. This means our measurements are reliable and accurate."

According to Spalding, rolling specialty steels is a very challenging process. The strip materials can quickly wear the rolls, which in turn, affects the profile gauge of the strip. He says: "In order to minimise the effects of roll wear, we used to roll a maximum number of slabs, between 18 and 22 before the rolls would need changing. Now, with the thicknessCONTROL system, we can analyse the measurement data and make a decision whether to extend the number of slabs beyond 22, before the roll wear will start to affect the final quality of the strip produced."

Part of Micro-Epsilon's thicknessCONTROL MTS 8202 family, C-frame systems measure the thickness profile of flexible metal strip. C-frame systems can be installed in hot and cold steel rolling mills, as well as slitting, coating, casting and cutting lines, providing reliable, high-precision measurement results that creates a basis for controlling the production process and product quality.

C-frame systems measure differentially. The measurement system installed at Brinsworth uses two scanCONTROL laser profile sensors that are integrated in the upper and lower arms of the C-frame. The thickness of the strip is derived from the distance between the two sensors and the resulting signals. By combining highly efficient signal processing algorithms and visualisation software, the system is able to achieve accuracies in the single micrometre range.

At Brinsworth, the C-frame is used as a traversing thickness measurement system on linear axes. The control and analysis software is developed in-house by Micro-Epsilon, providing all the required functions in order to continuously record and evaluate production quality. This includes graphical user interfaces and the ability to store multiple product libraries. Also, the software supports and displays Statistical Process Control (SPC) parameters and other "Process Capability' analysis and reporting methods such as Six Sigma PK and PM. Various fieldbus interfaces are available, which enable integration to the customer's production control systems.

Andy Spalding continues: "It's still early days for us in terms of getting the most out of the thicknessCONTROL system. We would like to integrate the system into our overall production process at Brinsworth. Although we can see the measurement data, we would like to give other departments here access to the same information."

"As a supplier, Micro-Epsilon has been great. As well as overseeing the implementation of the measurement system, they've also provided technical support when required. For example, we asked for the software to be modified so that we could measure the three key strip parameters on both a cross-profile view and a profile progression view. Micro-Epsilon made these modifications and delivered a system that does exactly what we want it to do."

As for the measurement system itself, Andy Spalding says: "The capability of the profile measurement gauge to constantly measure our processed strip has enabled us to make changes to our production processes to meet the demands of the customer whilst also increasing productivity. The profile gauge has also enabled us to further strengthen our customer supplier relationships."

Expertise in metal processing

Micro-Epsilon's Systems Group specialises in the development, manufacture and installation of a comprehensive range of non-contact, inline measurement and inspection systems for process monitoring and quality control applications. These include specific measurement systems for metal processing applications, including thickness, length, speed and width measurement of steel (including polished stainless steel) and aluminium strip, coil, sheet and tube.

Glenn Wedgbrow, Sales Manager at Micro-Epsilon UK comments: "Due to ever increasing manufacturing tolerances in metal strip production, the need to find higher accuracy, inline measurement solutions is accelerating. Micro-Epsilon's range of robust, complete turnkey measurement systems offer distinct technical advantages in terms of measurement accuracy, thermal stability and reliability. This is backed up by installation, servicing, maintenance, technical support with guaranteed response times, retrofitting and upgrade services."

For more information on the thicknessCONTROL range, please visit www.micro-epsilon.co.uk.