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How To Ensure Consistent High-Quality Steel Strip Production

Vertical furnaces are used for heat treating strip products in continuous processes such as continuous annealing lines (CAL) which are mostly used for stress relieving cold rolled advanced high strength steel (AHSS) for the automotive industry. 

How To Ensure Consistent High-Quality Steel Strip ProductionOnce annealed the mechanical properties of the strip can be established by temper rolling to give the required yield point and elongation characteristics for further forming into high strength structural or exposed body-in-white parts. 

In most cases the strip is coated in a corrosion resistant zinc alloy which is either applied in an electro-galvanizing line (EGL) or by dipping into a liquid zinc alloy pot referred to as a hot dip galvanizing line (HDGL). 

Most modern HDGL operations can produce between 400,000 to 500,000 tons of fully galvanized strip per year working continuously round the clock for long periods so it is important that key process data is measured and recorded to ensure consistent high-quality strip is produced without defects. 

One of the key pieces of process data is the temperature profile of the strip during the various stages of annealing. 

Non-contact spot temperature readings, using a SPOT Pyrometer, can be taken of the strip continuously whilst inside the furnace and provide accurate monitoring of temperature at one point across the strip width. This is very useful but will not show any variations across the width of the strip which can be influenced by individual heating or cooling elements in the furnace.  Additional line measurements can be taken by further SPOT pyrometers, but the number of lines is limited by dimensions of the pyrometer, width of strip and suitable space within the furnace. 

How To Ensure Consistent High-Quality Steel Strip ProductionFor this application an LSP-HD Infrared Linescanner, which is a scanning spot pyrometer taking 1000 readings across the strip width at up to 150 times a second, gives almost a continuous stream of temperature readings from one measurement device. The output from a linescanner can be displayed as either a 2D or 3D image or as a temperature profile from edge to edge across the width of the strip. A closer look at the 2D or 3D images can also provide valuable information about surface finish or strip shape. 

The SPOT GS pyrometer can then measure the temperature of the highly reflective galvanized surface at the exit of the zinc pot, during galvannealing and in the cooling section.

Accurate temperature measurement reduces production costs and increases yield for steel strip manufacturers.

Read more about Infrared Process Imaging Systems for Vertical Continuous Annealing Lines here


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