The present invention is concerned with a method and a grinder for the manufacture of pulp from ligno- cellulosic material , such as wood chips or the l ike, the fibres being detached from the material by means of grinding tools or members.

Mechanical pulp is manufactured since long ago from round timber in grinders and from wood chips in disc¬ crushers, so-called refiners. Dur ng the last decade the refiner method has been developed so that it now s possible to manufacture a stronger pulp than that which is obtained, in conventional grinding mills. However, the refiner method requires about 50 % more energy than the grinding mill method. Due to the in¬ creased energy costs, the interest has anew become directed towards the grinding mill method. Thus, in the Swedish patent application 7900988-2 there is de¬ scribed a grinding mill which -is operated under pressure whereby a pulp is obtained which is equally strong as refiner pulp, but with an energy consumption as in con- ventional grinding mills. However, grinding mills operated under pressure are expensive to be made and require high-priced round timber. A method to use wood chips as starting material in grinding mills is taugt -γe,t- in the Swedish patent application 7810749-7. To all methods now in use applies that the produced grist requires extensive subsequent treatment such as screenin and milling, which operations are expensive both with regard to investment costs and energy consumption. Known grinders are imperfect in their most important portion, the grinding zone, due to insufficient control possibil ities i a regarding maintenance of the tempera¬ ture in the grinding zone, supply of liquid to the

grinding zone, the pressure in the grinding zone, removal of released fibres, formation of sticks and shives, and orientation of the wood. Regarding the orientation of the wood it has been established both by experiments and practical experience that the consumption of power for manufacture of mechanical wood pulp is at its minimum when the wood is orientated in the plane of the grinding tool and with the grain trans¬ verse to the direction of movement of the surface. The main object of the invention is to reduce the drawbacks inherent to today's grinding apparatus and refiners and relating to the possibility in the grinding zone to control temperature, pressure, liquid supply and liquid removal. In addition, the invention renders possible optimal orientation of the wood in the grinding zone, elimination of formation of sticks and shives, reduction of wear of the grinding members, reduction of energy consumption and _. mprovement of the bright¬ ness and bonding properties of the ground pulp. This and other objects of the invention are achieved thereby that it has been imparted with the character¬ istic features set forth in the subsequent claims.

The invention will hereinafter be described in more detail in conjunction with embodiments illustrated in the attached drawings.

. Figure 1 shows a longitudinal section through a grinde for implementation of the method of the invention.

Figure 2 shows a section along the line 11-II in Figur 1. Figure 3 shows a section along the line 111-111 in Figure 1.

Figure 4 shows a top view from a section following the line IV-IV in Figure 5 of another embodiment of a grinder according to the invention.

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Figure 5 shows a section along the line V-V in Figure

Figures 6 and 6a show sections along the l ine VI-VI - in the Figures 4 and 5, respecti vel y , of two different ^• embodiments.

In the embodiment shown in Figure 1 of a grinder for implementation of the method according to the invention, wood chips are fed into the grinder by means of a slotte si&ve plate 1 , which is used for orientating the wood chips into a predetermined direction. It is advan¬ tageous to use relatively long chips. The chip bits orientated in this way enter now a space or chamber 2 which is formed between a core 4 stationarily mounted in the grinder and an outer tube or casing 7. The orien- tated and loosely packed chip bits in- the chamber are thereafter fed by means of a reciprocating piston device 3 to the right in Figure 1 towards a tapered portion of the chamber 2, within which portion the wood chips are compressed against the stationary core 4 and form a continuous cylindrical or tubul ar ^' body of chips on the stationary core 4. Annexed to the right end, according the figure, of the core 4 is a rotatable grinding member 6, the diameter of which increases conically in the direction towards the right-hand end or the casing 7. in this way, a converging grinding zone 5 is formed, which zone is confined by the inner wall surface, of the casing 7 and the outer circumference of the grinding ~ ^F member 5. Obviously, the converging grinding zone 5 can be formed also by the walls of the casing 7 having decreasing inner diameter and the grinding member 6 being cylindrical , or by both the casing 7 and the grinding member 6 having conical surfaces.

The casing 7 must have a length permitting formation of a plug having sufficient extent for not becoming

forced back by the steam pressure generated within the grinding zone. The plug is retained in the grinding zone 5 by fricti on a ^' gainst the wall of the casing 7. The grinding member 6 may be manuf ctured as a tubular body and its grinding surface may be formed out on the member proper or be procured by means of grinding ^' segments rigidly secured onto the grinding member.

The body or plug ^' of chips which is compressed addi¬ tionally during the continued advancement in the grinding zone 5 along the surface of the rotating grinding member 6 constitutes in the grinding zone 5 a compressed plug which ^' is stationary and from which the fibres are de¬ tached by the grinding member δ. This plug is forced into contact with the grinding member by the pressure from the piston device 3. The grinding member 6 ha-s a surface with projections, preferably in a pattern which produces pressure impacts causing the plug of chips to be worked internally during its advance within the con¬ verging grinding zone 5. The pattern on the surface may be coherant or consist of separate punctiform "burls". In both cases the pattern may have spiral shape with positive or negative course, i e to the left or to the right in the figure, even in a sine-shaped spiral form, but it may also extend in parallel to the axis. The pro- jections of the pattern may also have a recess or "cavity at the top. In a punctiform pattern the projections shoul overlap each other seen in the direction of movement of the grinding member. The pattern may also have pro¬ jections resembling sawteeth, at least one of the edges being curved or rounded and the pattern being arranged so that the rounded edge is turned into the direction of movement (direction of rotation) of the grinding member. The projections should have a height up to 1.2 mm, preferably between 0.03 and 1.0 mm.

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The grinding member may be of a material which has pores in the surface, i e is permeable to water, which permits penetration downwards into the surface of the - grinding member, so that a thin layer of water is formed adjacent said surface. This layer of water creates a hydraulic pressure which results in that the grinding member does not come into direct contact with the fibrou material _„ but the thin water layer transfers the pulsations ' from the- surface pattern to the fibrous material . The thin water layer also contributes to keep the sur¬ face of the grinding memfrer free from material which otherwise could stick fast on the surface. The grinding member or its grinding segments are preferably made of cemented pulverulent material of steel , hard metal or the like o r granules of ceramic material which are com¬ pressed and joined together in. a manner known in this specific art.

Through channels 9 in the grinding member 6 liquid, such as water, but also chemicals, alkali or the like, is supplied at desired places distributed o v e the grinding zone 5. The released fibres are carried away by the added liquid via one or several channels 8 in the grinding member 6. Said grinding member 6, which in the embodiment illustrated in Figure 1 is conical , has a greatest diameter which comes near the inner diameter of casing 7 at the right-hand discharge end thereof. There¬ by, the wood residues form a seal towards the grinding zone 5, when they pass through the gap existing between said casing and the grinding member 6. These wood resi- dues can be taken care of and returned to the incoming chips material . The grinding operation in the grinding zone 5 can also be performed under pressure above atmos¬ pheric (steam pressure) which is built up by generating a counter-pressure in the outlet channel 8, the body of chips precompressed in the chamber 2 forming a plug which seals against the inlet ! for the chips from the

feeding device 1. Obviously, a sluicing device can be used also for feeding the chips into the chamber 2 and/ or discharging the grist from the outlet channel 8. In this latter case the grist passes from the channel 8 into a vessel 10, wherein the grist and the steam are separated from each other and in pressure-tight manner led away from the vessel .

In the embodiment shown in Figures 4 to 6 of the grinder according to the invention, corresponding details of the grinder have been given the same refer¬ ence numerals-as in the embodiment of Figure 1 with the number 1 additionally ahead of said reference numeral. Thus, the grinding member shown in Figures 4 to 6a of th consists of a disc 16 which rotates towards the feed chamber 12 in the casing or housing 1-7. The chips are fed from the slotted sieve plate 11 by means of a piston device 13 into the chips chamber 12. The. chips bits are orientated with the grain radially in the plane of the disc 16 so that the grinding surface of the grinding member or grinding disc 16 in the same manner ^' as pre¬ viously is moved transversally to the fibre grain. The converging grinding zone is formed by the bottom of the chips . chamber 12 having upward slope in the direction of feed, whereby ^' the chips are forced by the piston device 13 into contact with the -grinding disc 16. Water is added to the grinding zone through water inlets 19 pro¬ vided either in the disc 16, see Figure 6, the water then suitably being supplied through a bore in the shaft or, as an alternative, in the casing 17, as illustrated n Figure 6a. Released fibres and water are drawn off through grooves 18 in the disc 16 adjacent the outer wal 1 of the casi ng 17.

The grinding operation may be effected under super- atmospheric pressure by the whole grinding mill being enclosed in a pressurized housing. The wood chips are sluiced into the housing by the piston device 13 whereby

they become compressed to a continuous, seal ing plug of chips. In order to attain uniform load around the grinding disc 16, the chips suitably are fed in at sev- - era! places into the chips chamber 12, e g at three places as is shown in the embodiment of Figure 4.

Obviously, the shown embodiments can be varied within the scope of the invention. Thus, the feeding devices, for example, may in known manner be devised as continuous one, such as screw feeders. The invention may also be applied to the grinding of round timber, in which case the core 4 in the centre is dispensed with and the grinding member 6 is formed as a cone.

Realized experiments show that the invention can be utilized for manufacturing a brighter pulp having im- proved bonding properties over pulp manufactured by known methods and, additionally , with low energy consump¬ tion. The probable- explanation is that the wood in the grinding zone by the rotating member is compressed both axially and radially and forced into contact with the casing. The member produces vibrations which by the thin layer of water are transferred to the wood, whereby fibres are released.

Owing to the defined processing in the grinding zone, a pulp can be manufactured with very low coarse fraction. which is important for the printability of paper made from said pulp.

The invention has the following advantages over pre¬ viously known grinders and refiners:

1. The grinding zone is stuffed with compressed and orientated wood. Therefore, energy can be trans¬ ferred from the grinding member to the wood with¬ out appreciable shock losses, without air ad- , mission and without excess of water.

2. Each wood element is subjected to a defined pro- cessing, i e every surface element of the wood in the grinding zone receives at a definite

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grinding pressure a predetermined number of pressure shocks from the grinding member, which has a settled pattern and is homogenuous, whereb a pulp practical ly free from shives is obtained. Usual i nhomogeneous grindstones with their grains of various sizes mixed at random produce in the s manner as refiner discs varying frequencies whic suppress each other. In known grinders and re¬ finers, the wood is subjected to highly varying

10 surface loading in contrast to the present in¬ vention.

The pattern, of the grinding member transfers vi¬ brations to the wood material via a thin layer o water, for which reason the friction is low and,

15 therefore, the wear of the member slight. In known refiners the wear is great because of the direct contact between grinding disc and wood. The costs for replacement of grinding discs is a great item of expenditure for refiners.

20 The grinding is effected' almost perpendicularly to the grain, which results in the smallest ener consumption. In known refiners the treatment is at random with respect to the grain and, therefo unfavourable .

25. 5 Detached fibres leave the grinding zone quickly via a channel in the grinding member due to the fact that the grinding zone is relatively small . In known grinders and refiners, the fibres have to pass through a larger grinding zone and are

30 subjected there to an uncontrolled treatment. •

6. The grinding operation is effected in the ab¬ sence of air, which prevents the pulp from oxi¬ dization.

The grinding is made in a sealed room where the

35 grinding pressure can be adjusted, whereby the pulp quality can be acted upon.

The term "grinding" in the preceding description is primarily understood to define all kinds of treatment of the fibrous material where the fibres are torn off from the material by means of pressure shocks from the pat¬ terned surface of the grinding member.

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