Hydraulic assistance is a technique which involves placing the wheel on a rack which centers the wheel so it can be read out with a dial gauge, then heated. Hydraulic rams located at various points on the rack allow a skilled operator to use the rams as mechanical assistance to press out bends in the heated metal. This has several advantages over other forms of straightening.
- The operator can affect the wheel both radially and laterally, so this technology is capable of straightening bends that others cannot.
- Heating the wheel in the spot to be repaired softens the metal and makes it much less likely that the alloy will crack under the pressure required to straighten the bend.
- The operator is controlling the process rather than watching an automated process work. A good straightener will have a feel for the metal, and can usually tell if the alloy is soft or brittle, and if the wheel is about to crack under pressure.
- Aluminum alloy has a crystalline inner structure at the molecular level. When the alloy is bent, this crystalline structure can be broken up, negating the strength of the metal at that point. The alloy must be heat-treated, or annealed, in order to make it strong again.
- If the crystalline structure of the wheel is not annealed, the fractured structure makes the wheel weaker at the point where the bend was, and subsequent impacts can more easily cause the metal to return to it's previous bent position, or “snap back.” We say of this condition that the metal has “retained a memory” of it's previous state, which is why erasing that memory by annealing the inner structure of the metal is such an important part of the process.
Cold roller technology involves placing a powered roller against the wheel and pressing the bend out as the wheel spins on a lathe. As this process is performed without heat, it
carries an elevated risk of cracking the wheel, and no actual metallurgy or annealing is performed. Cold roller technology is also generally restricted to radial bends as most machines cannot affect the wheel laterally. There are also a number of straightening techniques based on using a lathe in some form, but most are proprietary and secret in some manner.
In addition, there are certain gadgets available on the market that claim to help straighten wheels.
Usually these gadgets involve two crescent shaped metal blocks with a hydraulic ram between them. Supposedly, one places the crescent blocks inside the curve of the wheel and uses a foot pump to spread the blocks until the bend is removed. I frankly can't imagine a better way to destroy a wheel.
