The invention provides a preparation method of insulating flat paper for a
high voltage grade, which belongs to the technical field of insulating product production and comprises the following steps: removing iron from
slurry with the
mass percentage concentration of 3-4%, adding the
slurry into
hydrochloric acid, stirring, washing until the
mass percentage concentration is 3-4%, adding
magnesium bicarbonate, stirring, and
drying to obtain the insulating flat paper for the
high voltage grade. The preparation method comprises the following steps: stirring, washing, deslagging, pulping and deironing, diluting to the
mass percentage concentration of 0.3%-0.8%, purifying, carrying out jet molding at the linear
velocity ratio of (1.1-1.7): 1 to obtain wet paper, controlling the
gram weight of the wet paper to be 50-200
gsm, carrying out vacuum suction
dehydration and squeezing,
drying to the
dryness of 55-65% to form semi-wet paper, and squeezing and
drying again to form the finished product flat paper. The use amount of
hydrochloric acid is 0.5%-1.5% of the
mass fraction of the
slurry, and the addition amount of
magnesium bicarbonate is 2%-2.5% of the
mass fraction of the slurry, so that the technical problems that pure slurry is easily polluted and the phenomenon of breakdown caused by insufficient
electric strength still occurs under
high voltage in the existing flat paper preparation method are solved.