solid powder of flux cannot be transfor ned wholly into liquid without the appe- arence of liqiid cuteetic micture or additives,because the melting point of every kind of raw materials is higher than the melting temperature determined by the ingredient of flux although the temperature of flux exceeds its melting point. Furthermore,temperature is a necessary condition for the melting of flux,and the fusion rate of simply mixed powder flux is controlled by the formation of eute- ctic mixture and the dissolution of solid powder.The rate of solid dissolution that depends upon the chemical compositions and physical properties (including particle size,ect.)of raw materials,the type and amount of additives,contacts naturally with the diffusion rate of the dissolution of solid substance,the relation between them can be shown as follows: -dw dt.V=K.A.(C,-C)/V where,V-volume of liquid (cm3) W-mass of solid powder (g) K-mass transfer coefficient (cm/s) 4-area of solid-liquid interface (cm2) C。一saturate concentration(g/cm3) C-concentration at time of (g/cm3) From this equation,it is known that the fusion rate of solid powder in liquid 车 flux is related to the mass transfer coefficient,area of the solid-liquid interface (i.e.,the particle size)and the saturate dissoluability (ie.,the difference of concentrations). In the case of prefused powder flux,this fusion process described above has already completed in pretreatment process of flux.The fusion rate is written as: △m/△t=(T2-T1)q8 herc,m-weight of fused flux (g) t一fusing time(s) A-heat conductivity of flux (J/s cmC) T2-temperature of liquid metal (C) Ti-temperature of flux (C) q-latent heat of flux (J/g) 8-thickness of "saturation"liquid flux layer surrounding a solid particle. This equation shows that the fusion rate of prefused flux is in direct propo- rtion to the heat conductivity of flux and superheat,and is in inverse proportion to the latent heat of flux and the thickness of layer of saturate liquid flux su- rrounding a solid particle.Generally,the values of A,g and 6 of flux are 523、 、 〕 〕 〕 卫 。 ， 几 以 。 呈、 住 ， ， 〕 五 · ， 扭 ， 爪 ， 。 ， ， ， 一 牙 · 犷 · · 。 一 犷 阅，卜 ， “ 牙一 一 一 一 。 一 “ 一 “ ， 从 一 ， 一 乓 ， 一 · ， 。 ， · △ 。 △ 凡 一 ， · 占 ‘ 、 ， 一 一 几一 “ 一 爪 。 一 “ 叮一 一 “ · 五 ， 五 又 ， 久 ， 占