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Vol. 5
January Issue
Year 2004
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Articles


in Vol. 5 - January Issue - Year 2004
Super-Polishing of Small Compressor Blades „made easy“



Trowal TT90-SM Machine


Media/Paste Roll in TT90 Machine


Super-Polished Compressor Blades

High performance jet engines require a high quality surface finish of engine blades and vanes. Therefore, an increasing demand for airfoil surfaces to be finished to qualities of Ra 0.25µm (RMS 8-10) or better exists.

To achieve this quality special finishing techniques had to be developed on blades and vanes after a shot or glass bead peening process since the average surface quality provided after the peening process is typically Ra 1.0 – 1.2µm (RMS 40-48).
Typically, the improvement of the airfoils to Ra 0.25 requires relatively long cycle times in conventional vibratory finishing machines using fine cutting and polishing media and abrasive Pastes. The metal removal allowance from the surface, leading and trailing edges is limited, particularly in the overhaul stage and this demands non- aggressive, low efficiency processes with minor metal removal.
However, Walther Trowal has developed an efficient super-polishing process in high energy machines as an alternative to the conventional surface finish technology. The principle makes use of the high pressure and the sliding finishing action available in high energy machines and the resultant process cycles can be reduced to a 10th of the common vibratory finishing process.

The process is based upon the use of low cut polishing media which is blended with an abrasive powder paste. This acts against the airfoils and removes the peaks from the metal surface. The fine abrasive cutting grains incorporated in the powder paste break down into very small particles during the process and this procedure then allows cutting and polishing in a one step process.

What makes it so different from conventional vibratory super-polishing?
Firstly, the super-polishing process in Trowal centrifugal force machines is an easy, clean and process to conduct.

The advantages are:
-No waiting time for paste distribution into the polishing media when using powder paste.
-No splashing of paste foam during the process.
-Fast rinsing of slurry.
-Component separation by way of full discharge of media and parts onto a separate, independent screening device.
-No component mixing. Total batch integrity.
-10 times faster process when compared with standard vibratory finishing.
-High flexibility and efficiency in production. 

Trowal centrifugal force machines of the models TT-SM are available in 2 sizes with work bowls of 90 and 140 litres gross volume capacity (3.2 – 5 cuft). These relatively small work-bowls are capable of processing blade sizes of approx. 60 - 80mm in length (2.3 – 3.1“). Larger work-bowl sizes of 280 litres (10 cuft) and 520 litres (18.5 cuft) can also be offered for longer blades where masking of the blade roots is recommended.

The new Walther Trowal high-energy ‘super-polishing’ technique provides enormous flexibility in production, manpower and cost saving, automation and high quality components.




Author: Rolf-J. Picard
For Information: 
Walther Trowal GmbH&Co.KG
Rheinische Str. 35 - 37
42781 Haan, Germany
Tel: +49-2129-571-0
Fax:  +49-2129-571-225
E-Mail: info@walther-trowal.de