Buletinul Institutului Politehnic din Iaşi - Seria Nouă, 1970 (Anul 16, nr. 1-4)
1970 / nr. 1-2
BULETINUL INSTITUTULUI POLITEHNIC DIN IAȘI 374 Secția II 3. Discussion of Results The separation of the fines fraction was performed in a crill separator, model STFI,equipped with a screen of 60 mesh/cm and a rotor of 450 rot/min. The crill content was determined by oxidizing its suspension with a chromic mixture and determining the iodine, educed from potassium iodide, by means of titration with sodium thiosulphate in the presence of starch as indicator. Beating in the PFI mill gives at the same stock wetness a higher breaking length (Fig. 2) but lower tear resistance (Fig. 3) than treating in Ultra-Turrax. From the common strength point of view, a better eharac-teristic of the effects of particular methods of pulp treatment can be obtained by comparing the dependence between braking length and tear resistance. From Fig. 4 one can see, that this dependence comes better when the pulp is treated by high frequency, till the freeness of the stock reaches 40°SR, what corresponds to a breaking length of about 7 500 m and to a tear resistance about 107 G. Further treatement of the pulp in Ultra- Turrax gives dependences less advantageous than beating in PFI mill. Pig. 4. — Comparison of the dependence between breaking length and tear resistance of sheets produced from pulp treated ultrasonically, beaten conventionally and by compound method.