Coil building lines – Coil splicing – Seam welders
In a typical manufacturing facility using cold-rolled steel coils, the downtime for coil changes can be significant. In fact, changing the coil and re-winding the thread can result in a 20 to 30% loss in performance. Therefore, it is worth putting a machine in line that will join the end of the steel in one coil to the beginning of the steel in the next coil before machining. If the end of each coil is welded to the beginning of the next coil, then productivity will be maximized without increasing the production rate and taking the risks associated with higher production rates.
There are two main ways of joining coils to build coil lines, with pre-lap seam welding machines and butt welding machines.
Prep seam welders use a joining process that is suitable for several types of coated and uncoated steel. This involves cutting off some of the ends of two pieces of steel and then slightly overlapping the ends before welding them together and then smoothing the resulting joint. A disadvantage of pre-seam welding is that the weld may not be the same thickness as the original material.
Butt welding is an excellent method for connecting coils. The ends of each strip are placed in a copper clamp. Current is passed through the clamps and the strips are pressed together to complete the weld. The only downside is the build up of the flash which needs to be ground. Butt welding is cost effective and has high weld integrity. If a TIG welder is used, an electric arc passes from the electrode to where the strips are joined, melting the material. The arc itself is shielded by an inert gas and the ends of the two strips melt and then solidify instantly. TIG welding coils can be used to weld materials including non-ferrous materials, copper, brass, aluminum, galvanized stainless steel, pre-painted steel and mild steel. As long as the carbon content is in the range of low carbon steel, the build-up of hardness when joining the ends of the coils should not be a problem. For most metals, one welding cycle will take about two minutes.
In production facilities that include a coil welding machine, a coil accumulator is often added so that there is enough steel available to keep the production line running while two coils are connected together. If you have a TIG welder that takes two minutes to connect one coil to another, then you will need a battery that holds steel for at least two minutes.
Consider a stamping facility that uses only an unwinder as input equipment. When the end of the coil is reached, someone must stop the fiber until a new coil is placed and wound into the machine. A typical travel speed of stamping lines is 40 feet per minute. The average downtime for a coil change in the stamping facility is about 10 minutes. The average steel stamping facility will process 5 to 10 coils per day. The larger the steel size, the more coils will be used.
If you know the gain per foot and assume the facility runs 250 days a year, you can easily calculate how much gain is lost due to coil changes. For the steel stamping facility, assume a profit per foot of $0.05.
40 feet/minute x $0.05/foot = $2.00 profit per minute, or $120.00 per hour. If you go from processing 5 coils per day to processing 10 coils per day, the profit can be doubled without having to speed up the processing equipment. A coil build-up line and strip accumulator can be a wise investment that will pay off quickly with increased profits.
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