Increasing demands for higher product quality combined with pressure for cost reductions require new solutions, especially for suppliers of engine and transmission components, as well as companies active in propulsion technology and energy production. One such solution is the worldwide patented REM Isotropic Superfinish (ISF) technology.

REM Chemicals and Roesler Oberflaechentechnik have been cooperating for two years, with Roesler developing special finishing equipment and ceramic finishing media in conjunction with REM for the ISF process. By smoothing the parts’ surface down to Ra 0.02µm and Rz 0.2µm, operating characteristics with regard to friction, wear and operating temperatures are significantly improved with a substantial increase in fatigue life. Moreover, the ISF technology allows implementation of product ideas previously impossible due to constraints in the surface finish.

A special relationship

Scientific studies are underway to establish a relationship between the surface roughness of a gear and the life of the bearings in a transmission. However, in industries like automotive, aerospace, bearing, medical, textile equipment, as well as large gears and motor sports it is considered proven that surface smoothness influences the quality and life of the part significantly.

The explanation is that surface treatment methods frequently create a more-or-less rough surface with many ‘peaks’. These peaks can interrupt the oil film – usually 0.2µm - 0.5µm thick – that is required for reliable lubrication of high performance parts. This can create grey staining and micro pitting on the critical parts surfaces such as the teeth of a gear. In addition, the friction can break off the peaks creating debris particles. These particles then pass through the component as small chips and can cause damage.

Removing peaks

The metal removal process takes place very gently, preventing damage to parts

ISF technology removes the peaks on many parts made from carbon steel, high alloy steel, stainless steel and titanium. This process usually takes place in vibratory mass finishing systems specially designed by Roesler with dedicated high-density, non-abrasive ceramic media and special REM active chemical compounds; these compounds create a thin oxide film with a pH value of 1.6 - 5.5.

Via the vibratory action in the work bowl, the ceramic media wipes off this oxide film, and over time removes the peaks. The valleys remain intact and serve as a reservoir for the lubricant. The process continues, with the constant addition of fresh compound, until the required surface finish of Ra 0.02µm or Rz 0.2µm is achieved. The actual ISF refinement process is followed by a rinsing/burnishing process in the same machine by dosing a burnishing compound with water into the machine. The rinse/burnish process removes the remaining oxide film from the parts and creates a mat or high gloss finish.

The machine settings of the vibratory mass finishing machine ensure optimum and gentle movement of parts and media in the work bowl. The metal removal takes place very gently, preventing any damage to the parts. While the ISF process may produce a slight edge break, it does not produce excessive radiusing (round edges), because the media used are non-abrasive.

The ISF process takes place at room temperature and does not affect the material properties of the metal component. Furthermore, long-term experience has shown that there is no danger of hydrogen embrittlement. The required process time and compound usage for achieving a certain surface finish usually is determined by sample component processing trials. This allows exact planning of the ISF process within the overall parts manufacturing process. The result is usually a much better surface finish at lower cost.

Advantages that save money

After the ISF process, parts usually have an extremely fine surface finish. Depending on the initial surface roughness, this increases the contact area significantly – sometimes up to 100 per cent (measured at a depth of 0.4µm). Performance and efficiency of the components are significantly improved, which allows to make gear parts smaller or use higher input power motors at a significantly improved fatigue life.

For example, the life of gears processed with ISF technology could be increased 4 to 5 fold. Moreover, the ISF system creates an isotropic structure on the parts surface, which substantially improves lubrication, reduces friction and wear, reduces operating noise and reduces operating temperatures. This allows the operator to extend the time interval between preventive maintenance work. These quality improvements also lead to energy savings; and the ISF technology also allows the design of parts that previously would not have been possible.

The ISF process produces a small amount of effluent, treatable by standard systems

The ISF process can be applied for parts as small as the head of a match with a weight of less than one gram, up to gears with a weight of 5,000kg. This requires specially engineered equipment to achieve cost effective finishing results.

Roesler offers a wide range of equipment such as double curved wall rotary vibrators. Such rotary vibrators induce an even parts/media rotation in the work bowl allowing a 50 per cent higher fill rate of parts and media compared to straight wall vibrators. At the same time double curved wall vibrators produce a much better surface finish.

The ISF technology produces a relatively small amount of effluent, which can be treated with conventional waste water treatment systems. Due to its low wear rate the high density ceramic media used for the ISF process can be used for a long time before replacement.

www.rosler.com