US1536988A - Process for freeing paper pulp from impurities - Google Patents

Description

May 5, 1925.

H. THOMASSEN PROCESS FOR FREEING PAPER PULP FROM IMPURITIES FIG.2.

In van for Henn ant/5 omassen.

Patented May 5, 1925.

UNITED STATES names 'rHoMA ssEN, or HEELSUM, NETHERLANDS.

PROCESS FOR FREEING- PAI'ER PULP FROM IMPURITIES.

Application filed February 16, 1924. Serial No. 693,270.

To all whom it may concern:

Be it known that I, HERMANUS THOMAS- SEN, a subject of the Queen of the Netherlands, residing at Heelsum, the Netherlands, have invented certain new and useful Improvements in Processes for Freeing Paper Pulp from Impurities, of which the following is a specification.

In order to free paper pulp or other fibrous material from impurities such as sand or grit before it flows to the paper machine, it is generally run through a sand trap or grit retainer which may consist of a trough in which are arranged one behind the other oblique cross bars. The paper pulp having to flow up over each of these bars and then descend, the heavier components such as sand are separated out in the trough. In order to retain as far as possible any knots or improperly divided portions of paper fibre a strainer is also used in the form of a very fine meshed sieve.

The sand trap is, however, a not altogether satisfactory arrangement because it does not keep back all the heavy impurities and the lighter impurities it allows to pass. Moreover the paper pulp is liable to clog in the sand trap and then to free itself in. comparatively lar e masses which block up the strainer. In fins respect the sand trap has hitherto constituted an unavoidable evil.

The present invention makes the usual sand trap and even the strainer quite unnecessary. The invention consists in a process where y the heavier and the lighter impurities are all removed and then the knotted and tangled fibres are separated out of the pulp without the disadvantages of the known types of sand trap being experienced. Instead of these disadvantages the process presents certain essential advantages.

According to the invention the paper pulp is not led through a sand trap but into a rotating drum with unperforated sides. It has been found possible by this means to throw out the heavier particles from the paper pulp, without the paper fibres, which themselves possess a higher specific. gravity than water, being thrown out. It is only necessary to rotate the drum at a suitable and not too high speed. The speed of rotation of the drum can be so selected that the knots are thrown out from the paper pulp but not the loose fibres. In this case the strainer is made unnecessary and paper can be produced which contains no impurities. The lighter particles can be retained in the drum by means of a ring, the distance of which from the side. of the drum is less than the thickness of the layer of paper pulp, which in turn is determined by the width of the inwardly directed upper edge of the drum.

In the accompanying drawing is illustrated an apparatus for carrying out the invention, Fig. 1 being a sectional elevation and Fig. 2 a plan view.

The hollow shaft 1 carries the bottom 2 of the rotating drum the side 3 of which is let into the bottom. The drum during operation is rapidly rotated by means of a pulley 4 and gear wheels 5 and 6. The paper pulp which is to be freed from impurities is fed in through the centre tube 7 which is provided with a wide flange 8. The vanes 9 cause the paper pulp on the bottom 2 of the drum 10 to rotate rapidly and a cylindrical layer of paper pulp is formed which lies against the side 3 of the drum, the layer being of a thickness determined by the width of the flange or inturned upper edge 10 of the drum.

In proportion as the paper pulp is fed into the drum through the tube 7, pulp is thrown out of the drum over the edge 10.'

Particles havinga greater specific gravity such as sand, metal particles and also the fibre knots remain at the side 3 of the drum, whilst the lighter particles are held back by the ring 11, which at its outer edge is of greater diameter than the ring 10 at its inner edge, so that the cleansed paper pulp is caught in the stationary receiver 12 from which it is taken to. the paper making machine.

The hollow shaft 1 during operation is closed at its upper end. This shaft is made hollow in order to simplify cleaning of the drum 2, 3, for which operation the shaft is opened at the top.

The advantages of the new process are the following 1. The lighter impurities are removed,

2. The paper fibres which easily become felted during preparatory treatment are completely separated from one another, so

that the paper pulp flows to the paper ma- 3. The loose fibres are less likely to 010 the strainer if one is used than the felte fibres which occur with the hitherto known processes.

4. The thickness of the paper can be instantaneously adjusted by altering the admission fiow of the paper pulp into the centrifugal machine; previously the whole of the contents of the sand trap had to be allowed to flow through the machine.

5. Filling materials such as kaolin, heavy spar or the like can'be rapidly and quite uniformly mixed with the paper pulp in the centrifugal machine.

6. Colouring matters can be added imme- V diately before the paper machine is reached substantially cylindrical layer, collecting the heavier impurities at the outside of the layer, collecting the lighter impurities at the inner I surface of said layer and discharging the purified pulp from between the said impurities.

2. In a process for removing impurities and knots or the like from paper pulp and other fibrous material, supplying the pulp continuously to a centrifugal separator, r0- tating the separator at a speed sufiicient to cause the pulp to accumulate in a cylindrical layer and to cause the knots or the like and the heavy impurities to accumulate at the outer surface of the layer, retaining the said knots and impurities in the separator, I

retaining the lighter'impurities at the internal surface of the layer of plup, and discharging from between the outer and inner surfaces of the said layer purified pulp free from impurities and knots or the like.

3. Apparatus for use in freeing paper pulp or other fibrous material from impurities, comprising a centrifugal separator, a rotary separator drum, means for supplying the pulp to the center of the drum, vanes in the drum for rotating the pulp, means in the drum for retaining therein the heavier and i also the li hter impurities and means for receiving tIie purified pulp discharged by centrifugal force from between the lighter and the heavier impurities in the drum.

In testimony whereof I afiix my signature.

HERMANUS THOMASSEN.

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