Roll Bonding Process
Through a combination of art and science, Spur has been delivering high quality clad metal parts to our customers for over 40 years. We have well developed standard processes that make clad metals easy and specialize in the bonding of aluminum alloys. We also take pride in solving new customer problems and expanding our capabilities.
1. Materials
Choices and sizes
At Spur, we roll bond bars that come from plates and extrusions. The base material is the strongest material and the clad is rolled on top of the base. The length and width of the bars is chosen to maximize material yields and nesting of the final parts.
Typical bars are between 6 to 20 inches in width. The length of the bar is optimized for maximizing the yield of the source plate, with ranges from 24 inches up to 96+ inches.
Intense rolling pressure creates the metallurgical bond. Deformation, or "rolling reduction", causes final material thickness to be 30% to 70% of the combined starting thickness.
Materials
2. Surface Preparation
Optimal processing
The key to a perfect bond is surface preparation. At Spur, we have been optimizing our surfacing processes for over 40 years, allowing us to create very uniform bonds and to bond metals in ways others can't.
After mechanical surfacing to remove oxides, Spur optionally applies a very thin layer of inert chromium metal to the bonding surface. This proprietary surface not only increase bondability, but also increases the temperature resistance of the bond. At very high temperatures, standard "Bi-Metal" metallic bonds can be weakened by the formation of intermetallics. Spur's standard process provides the temperature resistance of "Tri-Metal" bonded clads, for much less cost.
3. Preheating
Hot, cold and mixed temperatures
In the case of aluminum being the clad, the material may be slightly above the annealing temperature for a brief amount of time, resulting in some softening. Depending upon the temperature and alloy, rolling will create some work hardening and strengthening. Post roll material testing ensures the final product will meet or exceed the needs of your application.
The hard base metal will likely experience small amounts of work hardening.
Some material combinations can be achieved by rolling a hot clad bar to a cold base.
4. Rolling
High strength metallurgical bonding
Rolling is what breaks up oxide layers causing fresh materials of the clad and base materials to share electrons. The process only happens with intense pressure and results in a bond that usually stronger than the clad material.
The rolling process deforms the materials resulting in an overall thickness reduction. How much reduction is a function of the material combination and rolling temperatures. The ratio of the clad material strength to the base material strength will drive the final thickness of each layer. Although some flexibility can be achieved during the rolling process, target thicknesses can be achieved by pre and post processing. Leveraging Spur's experience in the product design phase can result in standard off the shelf material thicknesses and reduced cost.
5. Flattening
Standard and machined options
The post rolled pack will have lengthwise bends caused by rolling induced stresses. Presses return the material to a flatness of plus or minus 1/16 inches over 12 inches. Applications requiring tighter flatness can be supported through additional flattening and machining.
6. Testing
The bond is stronger than the clad material
Qualification and in process testing ensures the final product meets your application. Tensile and shear testing ensures material properties. In process 90 Degree bend testing and S-Bend testing prove the metallurgical bond of the layers is stronger than the weaker material. The uniformity of Spur's bond far exceeds other bonding technologies, but ultra sound testing is always available.
Bend
Tensile
Shear
S-Bend
7. Cutting
Water jet & saws
The tested bar is cut into finish parts and/or machining blanks by removing the tip, tail and edges of each rolled pack.
Spur has a wide range of horizontal band saws for rough cutting bars. Complex shapes and rings are cut heat free with a water jet.
8. Part Fabrication
Experienced in co-bonded and clad metals
Spur's goal is to help you create Bi-Metals parts that work for your application, whether that means supplying you material or fabricating parts to your specifications. Leverage our expertise in machining, water jet cutting and turning bonded metal parts. From large form CNC machining of entire bars, to precision turning of complex pipe fittings and flanges, you can count on Spur.
