As the name suggests, a hollowbar is a bar of metal with a central bore running along the entirety of its length. These bars are produced in the same way as seamless tubes, being extruded from a forged bar and then cut into the preferred shape.
This gives the bar a set of excellent mechanical properties, often with an improvement in consistency and impact toughness when compared with rolled or forged components. In addition, the uniformity of shape and dimensional tolerances in this type of material is normally very good.
As we’ve previously mentioned, stainless steel is an alloy of common steel, in much the same way as carbon steel and carbon steel are. Specifically, stainless steel is a mixture of steel and chromium — with roughly 10.5% of the total bar being added chromium.
This infusion of chromium into the new material means that chromium oxide forms on the surface of the bar on contact with oxygen or water. This layer of chromium oxide creates a protective coating for the bar — one that can even repair itself if damaged. This property makes Stainless Steel an excellent construction material.
The only real difference between a stainless steel hollow bar and a seamless tube is the wall thickness. A tube is designed and manufactured for the transport of fluids. As such, any machining is limited to the end only (to form couplings or connectors). In contrast, a hollow bar will typically have a much greater wall thickness in order to allow the machining of various finished components.
Using hollow bars instead of solid bars can be seen to achieve direct savings in material and tooling costs, reduced machining time, and increased productivity. By starting with a near-net-shaped hollow bar, less metal is lost as low-value swarf and obviously less tooling is consumed too. Therefore, there can be immediate input cost savings when using this more sophisticated product form.
More significantly, reducing machining time or totally eliminating machining steps can dramatically improve manufacturing productivity. This can either be valued as reduced machining time or cost for a given part, or also as higher throughput when machines are fully loaded. In addition, replacing solid bars with stainless steel hollow bars eliminates the need for trepanning when producing components with a central bore, which causes the material to work hard and is detrimental to subsequent machining operations.
Hollow bars are produced in a wide range of sizes, typically with 3-5 different internal diameters (ID) for each given outside diameter (OD).
Langley Alloys stocks more than 80 different sizes of stainless steel hollow bar in Sanmac 316L (UNS S31603, 1.4404) and Sanmac 2205 (UNS S32205, 1.4462). Sanmac is a proprietary family of steels produced by Sandvik with ‘enhanced machinability as standard’. Their improved machinability strengthens the argument for using hollow bars in place of solid bars to quickly and efficiently produce components with a central bore.
For more information about our range of Stainless Steel Hollowbars or to make an inquiry about any of our products, please contact Langley Alloys Today.