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Clean Steel, No Oil – Fabricators Love the SCS Surface

Hawkeye Industries, a leading sheet metal fabrication firm was looking for a sheet steel offering a better paint finish for the custom fabricated steel parts this contract fabrication company produces.

Hawkeye's steel buyer engaged his steel suppliers in the search, urging them to find a flat rolled sheet steel with surface finish that might help. One steel supplier brought in sample sheets of a relatively new hot rolled product that had just come to the scene. Its name was SCS, for Smooth Clean Surface - a process that brushes the surface of ordinary hot roll black, leaving it "white glove" clean and rust resistant without the need for any coating or protective oil film.

Hawkeye's painting subcontractor perfomed trials on multiple samples made from sheets of SCS and obtained excellent results - uniform, cosmetically superior surface with good adhesion. With further trials, the painter even found they could use a truncated wash cycle since there was no oil to be removed from SCS.

Mission accomplished. Hawkins was pleased and asked his steel buyer to start replacing some HRPO purchases with SCS. He didn't give this new 'clean steel' much more thought until one of his laser operators said, "Bryan, come out to the shop. You've got to see this."

Hawkins walked out to his TRUMPF 3040 laser cell to see it running a collection of parts. The laser was cutting an SCS steel sheet. The sheet had run nearly 20% faster than their standard for the parts.

Funky Luck? Not with this company that's on the leading edge of laser technology. In addition to running the first TRUMPF 3040 cell in the US, Hawkeye had also installed one of the first TRUMPF TC6000L Punch/Laser Combination cells. Hawkins and his operators are recognized experts on laser technology and efficiency.

They put that expertise to work, adjusting selected laser settings to optimize them for cutting SCS. Hawkins recalls. "New lasers like ours are fast to start with, but SCS sheets give us another 15% to 25% speed advantage over HRPO sheets.

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Steel fabricators became interested in SCS primarily because of its ability to inhibit rusting with no need for protective oil. That not only gives SCS-treated steel a longer 'shelf life', it also may eliminate the need to clean the steel before painting. SCS savings, through eliminating shot blasting or using a leaner paint prep, is what initially attracted manufacturers to SCS.

As the population of SCS users grew, anecdotes about surprising property of SCS began circulating in the industry: SCS-brushed steel sheets or plate laser and plasma cut faster than hot roll black or HRPO sheets of the same thickness and chemistry the same result that Hawkeye Industries had validated.

WHY CLEANER IS FASTER
The TMW team was referred to Precision Laser Manufacturing (PLM) of East Peoria, Illinois. PLM is a contract laser processor offering laser cutting, welding, engraving and heat treating to the con-ag equipment, automotive, medical, food processing and defense industries. Todd Berry, owner of PLM explains, "Laser work is all we do, so we pride ourselves on being especially efficient and able to 'tune' our lasers for different materials. When we were asked by TMW if we could run some side-by-side comparisons of lasering SCS, HRPO and untreated hot roll, I was interested because they were all the same thickness and comparable chemistries. The only difference was the surface preparation."

PLM's laser operator made a few benchmark cuts then started to tune their 4000 watt BALLIU CO2 slab laser for the different materials. Berry reconted, "We alternately varied power, nozzle diameter, focal length and assist gas pressure while we gradually increased travel speed of the laser head. When we got to where the cut quality started to deteriorate, we'd make some adjustments to restore quality, then gradually increase speed again. It was an iterative process, but we found what seemed to be an optimum set of parameters."

"The SCS steel surface definitely cuts faster, especially at the thinner gauges. At 12 and 14 gauge we saw a 25% advantage over our best HRPO speeds, but that advantage will lessen when you go to thicker materials: at 0.250" we see around a 10% advantage. That's completely logical, because what's distinctive about the SCS is its surface. In thinner sheets, that surface effect is magnified relative to thick sheets."

Berry explained his findings, "Lasers work best on the cleanest, smoothest surface. On bare hot rolled, the grit and mill scale makes that surface too irregular. On HRPO, you get oil splash, nearly always get an oil vapor which fogs the laser lens, and that same oil is like a magnet for dirt and debris which can diffract the beam. The SCS surface, being as smooth and clean as it is, kinda looks to a laser like a long, straight stretch of interstate looks to a guy in a Corvette."

TMW took the approach Berry and his team followed to optimize laser settings to arrive at a set of instructions for setting up a laser to take advantage of the cleaner surface offered by SCS steel . But it didn't always work too well. "The variability in laser systems, resonators, assist gas and other factors is too great to come up with a single instruction," states Alan Mueth, TMW's Vice President of Technology and leader of the early SCS laser cutting studies. "We concluded that more general guidelines or 'Best Practices' for adjusting laser settings would be more useful, so we approached those who could best speak to the topic . . . the people who build the laser machines themselves."

SCS sheets of various thicknesses were shipped to TRUMPF and Bystronics. They conducted SCS speed optimization studies using their own methods and experience for what works best. In all cases, the trials supported PLM's findings of repeatable cutting speed increases for SCS in lighter gauges and single digit percent speed increases as thickness exceeded 0.250".

TRUMPF's Laser Application Engineer comments, "I was taken aback by how the SCS-treated material performed as well as it did, since it doesn't look like anything special. HRPO and cold rolled have a fairly uniform color and appearance, while the SCS sheets show the staining, blue edge and darker color typical of hot rolled black. I understand why that is - the SCS retains a very thin, polished layer of the mill scale - but still, it can be deceiving. It's when you really get right down on the sheet and study it that you see how smooth and remarkably clean the surface is. That's why it will perform better."

Based on the laser machine OEM trials, TMW rewrote the SCS laser set up instructions into a set of best practices and more general 'guidelines' for finding that sweet spot. | }

Another contract fabricator searching for a solution to steel surface quality issues decided to try SCS. The difference in this case was the material was in the form of tubular steel, not flat sheets.

Industrial Laser Solutions (ILS), a wholly-owned subsidiary of Tie Down Engineering of Atlanta operates three advanced laser tube cutting cells, but at times encountered problems with rust developing on the hot roll black and HRPO welded tubular steel they purchased. Those rusted tubes had to be sent out for cleaning - a process that added cost to already high steel prices and also added cycle time. ILS did not want to be in the secondary steel recovery business any longer.

Nancy Shadrix, the steel purchasing manager for Tie Down Engineering, proposed trialing SCS-treated hot roll tubular steel, after seeing how SCS tube samples she'd been experimenting with for six months seemed impervious to rust. The trial was a success and Tie Down converted over its tubular steel orders to SCS, which not only eliminated the rust problem, but allowed Tie Down to consolidate hot rolled black and HRPO purchases into a single SCS order.

Chuck MacKarvich, founder and President of Tie Down Engineering, next wanted to replace all his hot rolled sheet steel with SCS steel for the price savings, but needed to be sure it would not create problems in other areas, as Tie Down /ILS also performs several other fabrication operations in addition to lasering. Sloan MacKarvich, Chuck's son and a leader of the ILS enterprise, marshaled SCS material through all of those fabrication processes and was pleased to see it perform well across the board.

"We run four flat bed lasers and, yes, we saw speed increases with the SCS-treated material. But we also get a more precise cut, even at extremely tight tolerances, and we are more confident that our 'lights out' laser operations will run smoothly with the SCS steel sheets."

Sloan adds, "There's another bonus. With the cleanliness of the SCS surface finish we found our weld quality improved and our welding cells became more efficient. What's more, our paint finish looks better on the SCS parts, so next we want to see if we can lean out our paint prep."

"This experience has been pretty novel," concludes MacKarvich. "Too often when you make a material change to address a problem in one area, it creates a different problem or limitation in another area, so you go on searching. This time, we not only solved the original problem, but found benefits in other steel fabrication areas that we had not anticipated. It's kinda like reaching down to pick up a crumpled dollar bill and finding a five dollar bill folded inside it - a nice little bonus for your trouble."

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