An investigation into the materials used for the encapsulation of turbine blades

Abstract

Turbine blades account for the major part of the cost of the aero-gas turbine engine. Many thousands of blades are used in each engine. All are made of sophisticated materials machined to very fine limits. A high technology industry manufacturing turbine blades has grown up in the last 30 years. A relatively new technique of blade manufacture has been developed during the past 15 years. This is blade encapsulation and is used in conjunction with precision forging and precision casting of blades. Encapsulation involves casting a block of low melting point alloy around the precision formed blade, such that the aerofoil is in the correct position relative to the three datum faces of the encapsulation block. The blade is then machined with resultant higher production rates, less scrap and the use of a lower grade of labour. Automation is possible with a blade production line using encapsulating techniques. A survey of current blade encapsulation practices was undertaken on a worldwide basis and the results indicate widely differing methods. Research has been undertaken into three commonly used encapsulating materials. The effects of varying the parameters of the encapsulating process on the physical properties of the encapsulation material were investigated. The parameters were die temperature, alloy pouring temperature and elapsed time after casting. The physical properties under test were hardness, dimensional stability and the blade holding capability. The results of the experiments were statistically analysed using factorial analysis. This is a powerful technique which enabled the significance of the main effects and the interaction between the main effects to be established. There were nine 3 x 3 factorial experiments in the research programme. Not all the experiments gave definite results. The blade holding force tests gave inconclusive results. The research programme enabled firm conclusions to be drawn regarding encapsulating materials and effects of changing the parameters of the process. It is intended that these conclusions will assist blade manufacturers in optimizing their blade encapsulating process.

Date of Award	1978
Original language	English
Awarding Institution	Coventry University
Supervisor	W. Brady (Supervisor)