Backing strip made of steel for hardening and tempering for bi-metal hole saws and band saws

Bi-metal band saws and hole saws are used in industrial manufacturing as well as in the DIY market for cutting or drilling holes in steel, copper, brass, aluminum, and similar materials. The foundation for these heavy-duty saws is known as backing strip, which Waelzholz manufactures from specially alloyed steel for hardening and tempering with constant properties. In this article, our materials experts reveal which material properties are precisely adjusted with high repeat accuracy and why they play an essential role in the manufacture of high-performance bi-metal saws.

As the name suggests, bi-metal saws consist of two metals: a backing strip made of alloyed steel for hardening and tempering and saw teeth made of high-performance high-speed steel (HSS). The two materials are welded together, resulting in an extremely powerful saw band.

Bi-metal band saws and hole saws have to withstand extreme loads when cutting through tremendously hard materials such as steels and non-ferrous metals, as well as composites that are difficult to cut. In this context, the most important factors are a clean cut and the durability of the saw bands. To achieve both of these, backing strip made of alloyed steel for hardening and tempering with extremely precise properties is used in the manufacture of the saws. The quality of the cold rolled steel strip for the backing strip plays a critical role in the production of these saw blades.

With decades of experience in the development of backing strip, Waelzholz optimally adapts the metallurgy and geometry of its materials to customer requirements and the subsequent sawing application.

As André Sereno, CEO of Waelzholz North America and project manager for saw band steels at the site, explains: “Saw band steels are demanding materials because their production requires consideration of a large number of parameters that are relevant to their subsequent further processing and properties.” These special parameters, which Waelzholz can achieve with its alloyed steels for hardening and tempering for bi-metal saws, include:

• Customized tensile strength values within the tightest tolerances
• Excellent weldability
• Perfect straightness without any curving of the strip
• Edges precisely treated according to specific customer requirements
• High ductility and zero warping
• Highly uniform material properties over the entire strip length
• A wide variety of different analyses

Fully implementing such complex requirements with a high degree of repeat accuracy is one of Waelzholz’s key areas of expertise. The high-performance cold rolled steel strip for these demanding sawing applications is manufactured at the company’s worldwide locations and supplied to customers around the globe. In addition, Waelzholz Brasmetal specializes in skiving cut edges.

For the manufacture of bi-metal band saws and hole saws, Waelzholz offers alloyed steels for hardening and tempering with a specially developed composition of the elements chromium, nickel, and molybdenum which pass through a customized routing of cold rolling and annealing processes. This results in saw band steels with high tensile strength – that are simultaneously extremely ductile and exhibit zero warping.

“We tailor the materials to our customers’ specific requirements. In doing so, we take the subsequent properties as well as the behavior of the material in the customer’s production process into account,” explains Thomas Wittmers, expert for sawing applications from Waelzholz’s Sales Department in Hagen, Germany.

One notable aspect of the saw blade production process is that the metallurgical composition of the backing strip is selected specifically so that the material exhibits a high degree of weldability for the subsequent joining operations. As Wittmers explains, “we are able to keep the material properties constant within the tightest tolerances, even over many delivery batches, so that our customers’ machining processes – such as welding on the saw teeth – can always be carried out under uniform conditions.”

In addition to excellent weldability, perfect edges are required for attaching the saw teeth. For this reason, the material’s edge are is skived at Waelzholz Brasmetal in a separate operation at the customer’s request. This results in highly precise, right-angled edges that have a clearly defined face (see Figure 1). The edge-treated steel strip enables customers to optimally weld the saw teeth to the longitudinal seam – at exactly the desired angle and in a perfectly straight line.

But it isn’t just the joining edge that is relevant, as Thomas Frank from Materials Technology in Brazil explains: “The back edge of the backing strip for bi-metal band saws is also machined to right angles at our facility, but in this case it is then rounded off.” The advantage is that this creates a crack-free, smooth edge that prevents the formation of cracks. This significantly increases the durability and safety of the saw blade in use and ensures that the band saw can be easily guided.

Another notable feature of the material from Waelzholz is its perfect strip shape – with zero curving and zero warping. “The level of straightness isn’t only relevant to the precise positioning of the saw teeth, but also to the saw blade moving perfectly straight during final use. All in all, this means our backing strip ensures that saw bands have exceptional cutting accuracy, optimum endurance properties, and a long service life,” sums up Frank.

During the bi-metal hole saw manufacturing process, the saw teeth are first welded to Waelzholz’s alloyed steel for hardening and tempering. The saw band is then formed into a tube and the ends are welded together (see Figure 2). “To achieve the excellent bendability required for this purpose, Waelzholz tailors the properties of the material so that it exhibits a uniformly high degree of ductility,” André Sereno explains. Despite the material’s high tensile strength thanks to specific rolling processes, this ductility ensures that the material can be bent evenly – without tearing.

Saw manufacturers traditionally request the backing strip for bi-metal band saws and hole saws with thicknesses of 1 – 2 millimeters (0.039 – 0.079 inch) and widths of 19 – 80 millimeters (0.748 – 3.149 inch) with skived edges. When it comes to strip with cut edges, it is possible to produce the material at widths of up to approx. 600 millimeters (23.6 inch). Waelzholz manufactures the strip exactly to the customer’s specifications, maintaining the agreed upon standard of quality to the tightest tolerances over many delivery batches. “Repeat accuracy, even at large quantities, is an important factor for our customers. The constantly high quality and homogeneously defined material properties prevent malfunctions during operation. This means that our customers receive primary materials that make reliable and cost-effective production possible, and which contribute to maximum cutting performance and durability in the final product,” says Thomas Wittmers.

In addition to the highly uniform properties of the steels for hardening and tempering for bi-metal saws, customers around the world also benefit from a wide choice of materials. “We offer our customers a wide variety of analyses so that they can select the best possible chemical composition for the material with respect to further processing and the final application,” Wittmers explains.

Like many other materials from the Waelzholz product range, the specially manufactured steel strip for bi-metal saws is a cross-site project involving materials and sales experts from different locations. Thanks to the internal exchange of expertise, individual material supply routes, and investments in machinery and equipment, Waelzholz is well prepared to meet the diverse requirements of markets worldwide. In this context, the group’s network enables it to serve all of its customers’ needs across all locations.