The present invention relates to a method for treating wood chips prior to their impregnation, in accordance with the preamble of Claim 1.

It is known, inter alia, from CA Patent Specification 773 835 that impregnation of wood chips prior to the manufacture of pulp from said chips, either chemically or semi-chemically, or prior to producing pulp mechani¬ cally from said chips, for instance in a disc refiner, can be made easier and improved by compressing the chips between rotating rollers. The wood chips will preferably contain 40-55 percent by weight water and are compressed to a thickness of from 1/5 - 1/10 of their original thickness in the roll nip defined bet¬ ween a pair of rollers which act on the mutually op¬ posite flat sides of the chips, therewith to loosen the bonds between the fibres of the chips and to render the chips more porous, said chips returning almost to their original shape subsequent to said compression. Thicker chips are compressed more powerfully between the rolls than thinner chips, resulting in an increase in the porosity of the thicker chips, so as to render the entire cross-section of the chips accessible to impreg¬ nating liquid and to achieve comparatively uniform impregnation of the chips. Infeed of the chips into the roll nip can be made easier, by knurling or otherwise' roughening the roll surfaces.

With the intention of improving uniformity during the impregnating process, it is known from WO 89/02951 to produce, by sawing, mutually identical wood pieces having a length of, e.g., 100 mm in the fibre direction and a size of 40 x 10 mm transversely to the fibre

direction, and to compress the wood pieces at right angles to the fibre direction prior to impreg¬ nating said pieces with water or chemicals. For instan¬ ce, the wood pieces can be compressed between rollers or press plates which act on the mutually opposite flat sides of said wood pieces. When rollers are used, the rollers may be shallowly serrated or fluted, so as to facilitate dogging of the wood pieces into the roll nip.

The object of the present invention is to provide a novel and advantageous method for treating wood chips prior to impregnating the chips with water or with aqueous solutions of chemicals typical in the manufac- ture of pulp, and a method which will impart greater porosity and liquid-absorption properties to the chips.

To this end, it is proposed in accordance with the invention that when carrying out a method of the afore¬ said kind, the wood chips are given a curved or undulating configuration in at least one direction in conjunction with compressing said chips, so as to produce a wave¬ shape such that when the chips are seen in section perpendicular to the waves, the top and the bottom sides of the wave crests will both be located on one side of a central plane which extends through respective chips between the bottom side of the wave crests and the top side of the wave troughs, and the top and bottom sides of the wave troughs will both be located on the other side of said central plane. As a result of this method step, as the chip pieces are compressed they are subjected to treatment which further loosens the bonds between the fibres and therewith greatly

increases the liquid absorbency of the chips.

The invention also relates to the use of apparatus which comprises two mutually coacting compression devi- ces, preferably in the form of compression rolls, which present surfaces that are so undulated or wave-shaped in at least one direction that in a chip-compressing position the wave crests of each compression device will protrude into or mesh with the wave troughs defin- ed between mutually adjacent wave crests on the oppos¬ ing compression device,, for carrying out the novel method of treating wood chips prior to impregnating the same.

Further characteristic features of the invention and other advantages afforded thereby will be evident from the depending claims and from the following description of an exemplifying embodiment of the inventive appara¬ tus illustrated in the accompanying drawings.

Figure 1 is a side view, partly in section, of a sche¬ matically illustrated apparatus for use when carrying out the inventive method.

Figure 2 is a fragmentary, sectional view in larger scale which shows mutually coacting parts of two com¬ pression devices for use when treating wood chips in accordance with the invention.

Figure 3 is a diagram which shows the results obtained when impregnating non-treated chips and chips which had been compressed in various ways prior to being impreg¬ nated.

In Figure 1, the reference numeral 1 identifies a con¬ ventional wood-chip hopper, from which chips 2 are fed onto the upper part of an endless conveyor belt 4 extending around guide rollers 3. The belt 4 is per- meable to air. Mounted beneath the upper part or run of the belt 4 is a subpressure source (not shown) , for instance a suction box 5 which is connected to the suction side of a fan, by means of which the chips are held firmly to the upper run of the belt 4 by suction, said upper run being caused to move from right to left in Figure 1 by means of a drive motor (not shown), as indicated by the arrows 6. Mounted immediately above the upper run of the conveyor belt is a brush roller 8 which rotates in an anticlockwise direction, as shown by the arrow 7. The brush roller 8 functions to ensure that only a single layer of chips, lying on one flat side thereof, will.be transported over the suction box 5, so as to be introduced into the nip between two mutually coacting compression devices, in the form of rolls 9, located at the delivery end of the conveyor belt 3, 4. The rolls 9 are rotated in the direction of the arrows 10, in mutually opposite direc¬ tions, by means of a drive device (not shown), and feed the chips 2 falling into the nip defined between said rolls downwardly, e.g., into a storage hopper

(not shown) or an impregnating vessel (not shown) be¬ neath said nip. Arranged between the delivery end of the conveyor belt 3, 4 and the roll nip is a guide means which is indicated by curved guide plates 11, 12 and which ensures that prior to entering the roll nip, the chips 2 will be oriented such that the rolls 9 will act on mutually opposing flat sides of the chips 2.

The surfaces of the rolls or compression devices intended to act upon the flat sides of the chips are undulated in a pattern such that the wave crests 13 of each compression device 9 in a compressing position intended for the treatment of said chips will protrude into the wave troughs 13 defined between mutually adjacent wave crests on the opposing compression device, as clearly shown in Figure 1.

In the case of the Figure 1 embodiment, the surfaces of the rollers 9 have been made undulating by forming grooves therein in substantially the longitudinal dire¬ ction of the rolls. Alternatively, the grooves may be extended at any desired angle relative to said long¬ itudinal direction. For instance, the grooves can ex- tend peripherally, in which case the rolls 9 may be driven at mutually different rotational speeds. The rolls 9 may also be provided with gro.oves which extend in two directions at angles to one another. These angl¬ es are preferably from 45 to 90 . The waves forming said wave pattern are preferably distributed uniformly with a pitch of 5-13 mm, suitably a pitch of 6-11 mm, and preferably 7-9 mm. The wave height should be at least one quarter and preferably at least substantially equal to half the pitch.

Although the compression devices illustrated and des¬ cribed with reference to the accompanying drawing have the form of rolls 9, it will be understood that the compression devices may have any desired configuration within the scope of the protection claimed, for instan¬ ce said devices may have the form of mutually opposing press plates provided with mutually coacting groove patterns.

Figure 2 illustrates parts of two compression devices 9 located in a compressing state. Located in a wave- shaped gap between the devices 9 is a chip 2 which has been compressed in accordance with the pre- sent invention and which is shown in section taken at right angles to the waves. In conjunction with a com¬ pressing operation, in which the devices 9 move towards one another and are caused to act on mutually opposite flat sides of the chip 2, the chip is clamped between the crests of the wave patterns or undulations on mutually opposite devices 9 and is curved or undulated by said crests while, at the same time, being stretched to a corresponding wave-shape such that, when seen in said section at right angles to the waves, the top and bottom sides 15, 16 of the wave crests formed on the chip will both be located on one and the same side of a central plane 19 which passes through the centre of the chip between the bottom surfaces 16 of the wave crests and the top surfaces 17 of the wave troughs, whereas the top and bottom surfaces 17, 18 of the wave troughs are located on the other side of said plane. In addition to being compressed, the degree of chip- compression being adjusted by suitable adjustment of the final gap width and/or the final compressing pressure, the chip 2 is also considerably stretched, which increases its ability to absorb liquid in a subsequent impregnating stage. The final gap width or the final compressing pressure is selected so as not to damage the fibres of the chips, e.g. so that the gap width will be about 1/5 to 1/15 of the average thickness of the chips, measured between the flat sides of said chips, and so that the final compressing pressure will not exceed 30 MPa. The chip pieces 2 are assumed to have conventional dimensions, for instance a thickness of between

3 and 7 mm, and a conventional shape such as that des¬ cribed in many passages of the literature relating to cellulose techniques.

The chips 2 treated in the ^' aforedescribed manner will return to their original shape, at least to a certain extent, as shown at 2" in Figure i. The compres¬ sed chips, however, will have a markedly improved li¬ quid absorbency in comparison both with non-treated chips and chips which have been compressed in some other way.

Example 1

Figure 3 illustrates the result of impregnating with water non-treated chips and chips subjected to a com¬ pression force of 10 MPa. The results constitute the average of batches of eight tests with a chip-impreg¬ nating time of 10 seconds. The percentages recited below are percentages by weight. The chips had an aver- age weight of 25 g in all cases, of which water was responsible for about 50%. It will be seen from Figure 3 that the non-treated chips absorbed about 6 g of impregnating liquid, i.e. their dry content was reduced from about 50%. to about 40%. The chips treated between flat press surfaces absorbed about 9 g of impregnating liquid, i.e. the dry content of the chips was reduced from about 50% to about 37%, whereas the chips which were pressed between rolls which had been serrated or knurled to facilitate introduction of the chips into the roll nip absorbed about 11 g of the impregnating liquid, i.e. the dry content of the chips was reduced from about 50% to about 35%. The wave-profiled rolls used in the impregnating test were both wave-profiled in two mutually perpendicular directions at a wave pitch of about 8 mm and a wave height of about 4 mm.

The chips absorbed about 29 g of impregnating liquid, i.e. the dry content of the chips was reduced to only about 23%.

Example 2

A second test was carried out in which the rolls used were grooved in only one direction (the waves extended substantial- ly parallel with the axes of the rolls, as shown in

Figure 1), with a wave pitch of about 7.8 mm and a wave height of of about 3.9 mm and a pressure of about 10 MPa. Chips having a dry content of about 50% were rolled in mutually different directions and the follow- ing results were obtained when submersing the rolled chips in water for a period of 10 seconds.

Chips that were rolled at right angles to the fibre direction absorbed about 100 % water, i.e. their dry content fell from about 50% to about 25%.

Chips that were rolled parallel with the fibre direc¬ tion absorbed about 76% water, i.e. their dry content fell from about 50% to about 28%.

Chips that were rolled at an angle of about 45° to the fibre direction absorbed about 86% water, i.e. their dry content fell from about 50% to about 27%.

Continued impregnation of the chips for a further 10 seconds resulted in only a marginal increase in the amount of water absorbed.

It is evident from the above results that a good i - pregnating result is obtained even with rolls that are

grooved solely in one direction. It will be understood that correspondingly good results are obtained when impregnating wood chips in conventional pulping solu¬ tions.

If it is desired to undulate the chips in two directions which form an angle with one another, the chips can be passed twice through a roll pair with rolls grooved in one direction, or the chips may be passed through two sequential pairs of rolls grooved in one direction.

It will be understood that the invention is not res¬ tricted to the described and illustrated exemplifying embodiments thereof, and that the invention can be realized in any desired manner within the scope of the inventive concept defined in the following claims.