STRIPPING NOT ALLOWED

Orange County Ironworks LLC (OCI; Newburg, NY), a service-centric fabricator and erector of a broad scope of structural steel products ranging from stair railings to 1,000 ton building structures, knows this all too well, so they have honed their sawing to a science.

?It?s all about service in our business,? booms railing supervisor Paul Perrone over the din in his shop, where tubular railing sections are busily being transported, sawn, welded and finished. ?Our customers are racing to complete their construction projects, facing hurdles that range from finicky weather to late completion penalties. So our operation must run like a fine-tuned clock, with everything meshing right. In our work, it all starts with sawing tube. If sawing is down, then we?re out.?

SAWING EVERY ANGLE
OCI is not your everyday fabricator. They perform an expanded set of services, from material specification and acquisition to design, fabrication and, in some cases, even erecting their manufactured product in the field. Finished products include stairs, railings, a variety of structural features used in the building and construction industry, and also entire building skeleton structures.

OCI has two plants, 40 employees and a full complement of equipment with process capabilities that include a plasma/CNC plate machine, a beam line for hole punching, and a robotic coper. Although most of their material is Schedule 40 pipe, they also saw solid sections and, occasionally, stainless or aluminum.

On jobs where every operation has a unique angle, the tube is locked in place on an Ellis miter saw to keep it straight while the saw head rotates to the specified angle to make the cut. ?We do a ton of variable and degree cutting to make a whole host of parts, from as short as ¾ in up to 10 ft or 20 ft long. ?Every part is a little different, and they must all fit together perfectly,? notes Perrone.

All of this sawing consumes a steady stock of blades ? to the tune of 100 to 125 per year. But judging by the recent improvement in sawing performance when using a new bi-metal unique® blade from Starrett (Athol, MA), that number is likely to drop. Perrone says, ?We were experiencing tooth strippage when (Starrett representative) Kent Moreau studied our operation and provided a 1 in x .035 in 6-10 variable pitch bi-metal unique test blade to address the problem.?

TUBE SAWING MARATHON
?We immediately noticed a significant difference. Cutting was much smoother, the edges of finished parts were nice and clean, and noise was reduced,? continues Perrone. ?However, above all, shift after shift, the test blade kept running in prime condition. Initially I thought that the blade, which was cutting a variety of materials in addition to our staple Schedule 40 pipe, would hold up a week or two. But it just kept sawing, week in and out. We were even thinking of starting a pool in the shop to guess how long it would last.?

Of course nothing is forever, so after nearly two months the standout blade made its last slice. ?We were totally amazed that this new blade lasted a full seven weeks, making about 19,000 cuts,? explains Perrone. It is also worth noting that the new blade was put fully through the paces. ?One day I heard an operator sawing much too fast from across the shop,? recalls Perrone. ?I thought for sure the blade would strip, but it just ripped right through the pipe, teeth intact.?

There is still another ?unique? aspect of OCI?s sawing operation (although perhaps this shouldn?t be tried in other shops): sawing without coolant. Perrone claims it?s cleaner and less involved without coolant, and there are no ill effects on blades or parts.

When asked about the verdict of the blade test, Perrone sings its praises: ?I can?t imagine any way this blade can be improved. It is a phenomenal blade that has improved our sawing dramatically.?

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

TECHNICAL INSIGHTS: SUCCESSFUL TUBE SAWING
By Kent Moreau

Band sawing applications for tubing create challenges for fabricators because tubular materials can be much more difficult to saw than solid bars and plates.

One challenge occurs when sawing cross-sections of a tube or pipe. This interrupted-cutting method (where the blade enters, exits, then re-enters the hollow shape) produces increased force and stress on each saw tooth. As a result, when one tooth leaves contact with the cut and the next tooth enters the cut, the force is so tremendous that tooth breakage can occur. Once a single tooth chips or strips, it puts more stress on the other teeth, and can eventually lead to premature blade failure.

Many conventional bi-metal blades also produce a heat-affected zone: a stressed area that cannot be avoided when sawing, which can cause the teeth to tear away from the blade.

Another challenge fabricators face when sawing tube involves blade pitch, defined as the number of teeth per inch. The number of teeth that come in contact with the work piece can affect both blade performance and durability. Too few teeth in contact with the work can lead to early tooth strippage. Contrastingly, too many teeth can greatly reduce cutting rates and ultimately make the material impossible to cut. At lower cutting rates there is less penetration per tooth. This causes more rubbing than cutting, which can result in substantial work hardening of the material.

A constant pitch blade (uniform distance from one tooth tip to the next tip) can increase harmonic vibrations. Harmonic vibrations can lead to excessive noise, undesirable saw or saw blade vibrations and, in severe cases, bad cuts. When considering the tooth pitch for the blade, variable-pitch blades can greatly reduce harmonic vibrations. By varying the tooth spacing, sawing rhythms are interrupted, chip evacuation is improved and vibration is reduced, resulting in less noise and a better overall cut.

Cutting tubular material also presents challenges for coolant usage. Due to the shape of the work piece, coolant can be diverted from the cut, leading to inaccurate cutting and causing frictional heat buildup. Both of these problems will prematurely destroy the tooth edge.

NEW BLADE TECHNOLOGY BENEFITS TUBE SAWING
Technologies are available to address tube sawing challenges. For example, a new process has been developed for manufacturing bi-metal blades that eliminates the heat-affected zone and helps reduce tooth-stripping problems. This proprietary saw blade technology from The L.S. Starrett Company, named bi-metal unique®, joins two strips of high speed steel wires to a backing steel in a solid phase, using the principle of solid-state diffusion bonding. The solid-state process uses only 10 percent to 20 percent of the amount of heat rise that is found in a welding manufacturing process.

This solid-state diffusion process generates 170 percent more weld contact area when compared to most bi-metal high speed steels. The result is significantly reduced fracture and breakage at the high speed steel/backing material interface.

During the diffusion bonding process, the high speed steel wires are bonded to the sides of the strip and the fusion zone is parallel to the teeth, creating a grooved-tooth geometry. This grooved-tooth geometry produces two cutting surfaces separated by the blade. Soon after the initial use of bi-metal unique blades, the teeth develop a U-shaped groove which is 0.001 in to 0.002 in deep between the two high speed steel edges, altering the blade area engaged in the cut. The groove remains at a constant depth and wears at the same rate as the teeth.

The cutting action of the grooved-tooth geometry produces dual chips that are more easily removed from the cut. Starrett refers to this as the ?Split-Chip Advantage®? that provides a significant benefit by reducing chips that can bond to the saw teeth. The split chips are less apt to cling to the teeth because they typically curl and fall away as strings instead of thicker, tighter chips.

The groove also permits increased coolant flow to the cutting surface. Proper coolant flow will not only cool and lubricate the blade; it will also flush out chips that are caught in the spaces inside the tubes.

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

Kent Moreau is the technical service engineer and OEM coordinator for the Saw Division of The L.S. Starrett Company, 121 Crescent Street, Athol, MA 01331, 978-249-3551, Fax: 978-249-8495, www.starrett.com.