Coil accumulation lines – Coil bonding – Seam welders
In a typical production facility using cold rolled steel coils, the downtime for coil change can be significant. In fact, bobbin change and threading can result in a 20-30% loss of productivity. Therefore, it is worth inserting an in-line machine that will join the end of the steel in one coil with the beginning of the steel in the next coil before processing. If the end of each coil is welded to the beginning of the next coil, productivity will be maximized without increasing production speed and without taking the risks associated with faster production speeds.
There are two basic ways of joining coils to build coil lines, with prep-lap seam welders and flash butt welders.
Prep-lap joint welders use a joining process that is suitable for various types of coated and uncoated steel. It involves cutting off some of the ends of two pieces of steel and then overlapping the ends slightly before welding, and then planning the resulting joint. One disadvantage of prep-lap seam welding is that the weld may not be the same thickness as the original material.
Butt welding is an excellent method of joining coils. The ends of each strip are placed in a copper clamp. Current passes through the clamps and the strips are pressed together to complete the weld. The only downside is the build-up of lightning, which needs to be rectified. Flash butt welding is cost effective and has high weld integrity. If a TIG welder is used, an electric arc goes from the electrode to where the strips meet, melting the material. The arc itself is protected by inert gas and the ends of both strips melt and then instantly solidify. TIG welded coil assemblers can be used to weld materials including non-ferrous materials, copper, brass, aluminum, galvanized stainless steel, prepainted steel, and mild steel. As long as the carbon content is in the range of low carbon steel, hardness build-up when joining the coil ends should not be a problem. For most metals, a weld cycle will take approximately two minutes.
In production facilities that include a coil accumulation welder, a coil accumulator is also often added so that enough steel is available to keep the production line running while two coils are joined. If you have a TIG welder that takes two minutes to bond one coil to another, then you will need an accumulator that contains at least two minutes of steel.
Consider a stamping facility that only uses an unwinder as input equipment. When the end of a coil is reached, someone has to stop the line while a new coil is placed and threaded into the machine. A typical operating speed for stamping lines is 40 feet per minute. Average downtime to change coils in a stamping facility is approximately 10 minutes. The average steel stamping facility will process 5-10 coils per day. The heavier the gauge of the steel, the more coils will be used.
If you know the profit per foot and you assume the installation runs 250 days a year, you can easily calculate how much profit is lost due to coil change. 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 were to go from processing 5 coils per day to processing 10 coils per day, the profits can be doubled without having to speed up the processing equipment. A coil accumulation line and web accumulator can be a smart investment that will pay off quickly in higher profits.