Band Saw Blade Fills Gap Between M42 and Carbide

The Primalloy band saw blades are also suitable for cutting metals that show adhesive characteristics, such as PH series stainless steels and INCONEL®. For these types of sawing applications, a rich coolant or straight oil is necessary to prevent a built-up edge—chips adhering to the blade—when cutting.

The nature of a metal fabricating shop is one of unpredictability. The shop floor just doesn’t really know what the day’s schedule holds.

When it comes to sawing, fabricators traditionally have relied on bimetal band saw blades with high-speed-steel teeth tips for most jobs. The blades were cost-effective, resistant to wear, reliable, and flexible enough to survive the thousands of revolutions the band saw made. They made sense for the majority of jobs fabricators encountered on a daily basis. With the increased use of specialty steels in product design, however, fabricators now may wind up working with materials that rarely were found on a shop floor only a decade ago.

The emergence of specialty steels, such as precipitation-hardening stainless steels, high-alloy tool steels, and nickel alloys, has added to the unpredictability of fab shop jobs.

“Industry is always coming out with purpose-specific materials to improve upon areas such as heat resistance for aerospace and aircraft applications and corrosion resistance for the petrochemical applications,” said Gene Ramsdell, The L.S. Starrett Co. manager, saw R&D for North America. “With that comes more alloying of metals, leading to different problems in separating the metal or cutting it.”

Until recently metal fabricators had to rely on carbide-tipped blades for these heavy-duty sawing applications.

The shops that cut large volumes of specialty steels didn’t mind the added expense of carbide-tipped blades because the blades lasted longer and kept the band saws going. However, shops that didn’t cut as much of the specialty material more than likely stuck with the traditional bimetal blades, even if they had to replace the blades much more frequently than if they were cutting plain carbon steel.

For these shops, L.S. Starrett Co. introduced its Primalloy™ band saw blades for heavy-duty cutting applications.

“What this does is act as a bridge between M42 and carbide,” Ramsdell said. “This Primalloy has inherently better wear resistance than M42. And it also has 10 percent cobalt versus 8 percent on an M42 blade. That imparts better heat resistance. So those two will aid in giving the traditional user maybe a little bit more of a financial advantage by not having to go into the carbide arena. Carbide-tipped blades are generally three times the cost of bimetal blades.”

The wear resistance is provided by a vanadium content in the blade that is three times that found in M42 blades. The resulting carbide hardness is HRC 84.

That heat and wear resistance are important traits when sawing metals with abrasive characteristics, such as tool steels, mold steels, and heat-treated alloy steels such as 4340 and 4150. These difficult-to-cut steels tend to eat up M42 edge blades quite quickly.

The new heavy-duty blades are also more adaptable to the band saws that most fabricators have on their shop floors, according to Ramsdell. Generally, carbide-tipped blades require a band saw with a very sturdy build because the blades tend to fracture when subjected to shocks or vibrations. The Primalloy blade is more forgiving, according to Ramsdell, and can run on machines designed for traditional bimetal band saw blades.

The blade also has a new tooth design. The teeth have a 12-degree positive rake form that penetrates the workpiece easier than previous tooth designs. The company said the tooth tip chemistry contributes to longer blade life and increased cutting accuracy. The typical tooth hardness is HRC 69, compared to HRC 67/68 for M42.

“This is a different high-speed edge for us,” Ramsdell said. “Due to the high alloy content of this edge, we precision-grind all of the teeth. Also, it requires a much tighter heat-treating tolerance as far as temperatures and soak times go.”

Starrett puts the alloy steel backing material for the blades through a proprietary treatment to help extend its working life. The process occurs as the material is exposed to controlled blast peening. The combination of activities is said to add more residual stress into the surface of the blade, which helps to reduce fatigue cracks that originate along microscopic grain boundaries. Company officials said the benefits of this treatment have been proven with X-ray diffraction and extensive mechanical fatigue tests.

“There is a constant evolution of materials in the marketplace for different applications. When it comes down to separating those new materials, the question for some people is, Can we do the job economically with bimetal, or do we have to look at perhaps buying a more expensive band saw machine to utilize carbide-tipped blades?” Ramsdell said. “With this new product, we can have them try these blades before they have to look at the carbide product.”

The Primalloy blades come in blades widths from 1 to 2.625 in.