Silicon nitride has b een much studied as a material for engineering components. However, important problems remain in respect to its use. These problems are mainly concerned with component reliability and component cost. It is now recognized that solutions to these problems are most likely to be found in the form of highly developed powders and methods for shaping these powders to form components of accurate dimension. The basis of the present programme is to link sophisticated powder manufacture with a forming method considered to be most promising in respect to low cost shaping, namely injection moulding. The aim of the work is to develop a powder manufacturing route and a component forming route which are capable of providing low cost shaping, namely injection moulding. The innovation in the work lies in the clear ambition to match the character of the powder to a particular forming route. The economic benefits are seen in that injection moulding offers the best avenue for the preparation of closely shaped low cost components.
The aim of this work was to develop a silicon nitride (Si3N4) powder manufacturing route, namely carbothermal nitridation, and a compound forming route, injection moulding, which are capable of providing low cost shaping. A diesel engine precombustion chamber was selected as a demonstrative part.
A carbothermal nitridation process has been chosen which gives excellent control of morphology and particle size distribution of silicon nitride powders. Silicon nitride powder PyrofineR grade S 1-3 was chosen after several interchanges between partners.
After numerical optimisation of the mould design, prechambers were infected, pyrolysed and sintered. ATOCHEM Pyrofine S 1-3 and Starck LC12 silicon nitride powders were used for comparison. The time available to optimise the injection moulding conditions of the prechamber was too short. It has therefore not been possible to produce uncracked sintered prechambers starting from Pyrofine S 1-3 or Starck LC12. Nevertheless we believe that better quality prechambers could be produced if a mouldable mix with a powder loading of around 60% (maximum of 53.8% today), or more, could be used. Pyrofine S 1-3 seems to be too fine and to have too narrow a particle size distribution for an ideal silicon nitride injection moulding powder. It did, however, have superior pyrolysis characteristics to the Starck blend of silicon nitride powders used in this work.
SILICON NITRIDE HAS BEEN MUCH STUDIED AS A MATERIAL FOR ENGINEERING COMPONENTS. HOWEVER IMPORTANT PROBLEMS REMAIN IN RESPECT TO ITS USE. THESE PROBLEMS ARE MAINLY CONCERNED WITH COMPONENT RELIABILITY AND COMPONENT COST. IT IS NOW RECOGNISED THAT SOLUTIONS TO THESE PROBLEMS ARE MOST LIKELY TO BE FOUND IN THE FORM OF HIGHLY DEVELOPED POWDERS AND METHODS FOR SHAPING THESE POWDERS TO FORM COMPONENTS OF ACCURATE DIMENSION.
THE BASIS OF THE PRESENT PROGRAMME IS TO LINK SOPHISTICATED POWDER MANUFACTURE WITH A FORMING METHOD CONSIDERED TO BE MOST PROMISING IN RESPECT TO LOW COST SHAPING, NAMELY INJECTION MOULDING.
Funding SchemeCSC - Cost-sharing contracts
ST15 0PU Stafford
LS2 9JT Leeds