FI63269C - EFFECTIVE RELEASE FOER THERMOMECHANICAL MASS I HOEG TEMPERATURE AND LAOG CONSISTENCY SAMT EN FOER GENOMFOERANDE AV FOERFARANDET AVSEDD RAFFINATOR - Google Patents

Description

ΓΒ1 mv ANNOUNCEMENT / 7Λ / λ JESTa l J (11) UTLÄCGNINGSSKRIFT ooZoy C (45) Patent granted 10 05 1903 l ^ Siry Patent meddelat 'V (51) K ».ik.3 / fn * .ci.3 D 21 D 1 / 20 FINLAND — FINLAND (ii) ρημ (ιιι «^ - ρμιιμι6ι ^ T8i682 (22) Htk« mi «pUv · —AiNfllaiifl | a4ag 26.05 * 78 (FI) (22) Alkupllvt — Glklf hatadif 26.05 * 78 (41) Tulkit JulklMkal - SlMc affmtlig 09.12.78

Patents Registered by Nihttvlki.p * ™ f. MoonLHk ^ un p * m._

Patent- och regitterttyreiMn 'Ammua utl »* d och utUkrtfun puMkmd 31.01.83 (32) (33) (31) Pyydetty« uoikMa-Iuglrd priortm 0θ. θ6.77 USA 80U518 (71) Beloit Corporation, Beloit, Wisconsin 53511, USA (72) John B. Matthew, Pittsfield, Massachusetts, USA (7 * 0 Munsterhielm Ky Kh (5 * 0 The present invention relates to at temperature and low intensity levels to reduce the specific volume of the fibers and to reduce the amount of fiber breakage in the refiner.

The hot grinding method has been widely adopted in the paper industry for the production of mechanical pulp from wood chips. It has largely replaced the purely mechanical method of sanding wood with abrasive stones and chemical methods involving the use of sulphates or sulphites. Pulps made by the hot grinding method have substantially higher strength values than grinds made by the stone grinding method. Although chemical pulping methods produce higher quality pulp, they require large capital investments in high pressure treatment vessels and the like.

One difficulty with hot mills is the higher specific volume (lower density) of papers made from them. This high specific volume causes problems in the printing and processing steps and can be a problem in itself if the thickness of the final sheet 2 63269 at a given basis weight is critical. In addition, it is usually possible to obtain stronger sheets from a given pulp if the specific volume is reduced, for example by using higher compression pressures.

The treatment of sludges of mechanical pulps with conventional "post-milling processes" in a disc mill with a low consistency of about 3 to 5% has not proved to be completely satisfactory, since the fibers tend to cut during grinding. Although the specific volume can be reduced somewhat in this way, the shortening of the fiber length caused by the rupture of the fibers leads to an excessive increase in the degree of grinding and possibly to a deterioration of the strength properties of the sheet.

According to the present invention, the reduction in fiber length normally associated with post-milling of mechanical pulps is reduced by raising the milling temperature to a range of 95 ° C to 150 ° C, at which temperature the fibers are much more flexible and less prone to cross-section in the mill. In addition to the even higher temperature, the grinding is carried out under as low intensity conditions as is practically possible. Specifically, the grinder is run at an intensity of less than 6.18 x 10 ”** horsepower per centimeter of contact per minute. With conventional size refiners, this knows that the refiner operates at a circumferential speed higher than 1830 m / min. In addition, the stator and rotor plates facing each other use a fairly fine rail pattern, so that high-speed operation when the plates have this type of rail pattern results in as many levels of minute centimeter contacts as are generally possible in practice.

In one embodiment of the post-refiner for carrying out the method according to the invention, the stator plates consist of a synthetic resin such as one of the polysulphone resins, and the rotor plates consist of steel. The widths of the alternating rails and grooves on the surface of both the rotor and the stator must not exceed 3.18 mm.

Other objects, features and advantages of the invention will become apparent from the following description of some preferred embodiments of the invention in connection with the accompanying drawings, although changes and modifications may be made without departing from the spirit and scope of the inventive idea. In the drawing:

Fig. 1 is a partial block diagram illustrating some of the steps that may precede the post-milling operation to which the present invention is directed *, 3 63269

Fig. 2 is a fragmentary view, with parts broken away, illustrating the interior of a disc refiner suitable for use in carrying out the invention;

Figure 3 is a much larger sectional sectional view of opposing rotor and stator plates implementing a preferred embodiment of the invention.

Figure 1 of the drawing shows a flow chart of a typical series of work steps, which may include a post-milling step according to the present invention. Specifically, the fibrous slurry may be treated in one or more plate mills 10 and then passed to one or more mixing types 11, where suitable additives such as kaolin or the like may be added along line 12. The pulp thus treated is then fed to one or more machine types 13 and finally to a post-refiner 11 *, the details of which will be explained below. The pulp entering the post-grinder 1 * + is a slurry with a consistency of 3 ·· * 5 The hot mill is characterized by the presence of softened lignin and a substantial absence of chemical residues. In the post-grinding step, the pulp is treated at a temperature of 95 to 150 ° C and the grinder operates at an intensity of less than 6.18 10 horsepower per minute per cm of contact. Preferably, the intensity is less than 2.32 x 10_l + horsepower per cm of contact per minute.

Conventional disc grinders all act on the fibers by rubbing. There are different types of disc grinders, but most of them use rail-type metal abrasives. Grinding intensity is defined as the net grinding power divided by the number of rail crossings per unit time. Since the grinding effect on the fibers occurs at the leading edge of the abrasive member, the number of cm contacts per minute can be calculated as follows: cm contacts / minute = total length of rotor rails x total length of stator rails x refiner speed / rain.

A typical disc grinder that can be used for the purposes of the present invention is shown in Figure 2 of the drawing. It includes a base 15 on which a shaft 16 is rotatably mounted supported by a bearing 17. The shaft is rotated via a clutch 18 by a suitable motor (not shown). The pulp is fed to a feed port 19 and then flows into a grinding cavity 20, after which the flow of pulp branches through two routed rotor members 21 and 22 attached to a rotating end 23. Such rotor members are described in detail in U.S. Pat. No. 3,338,586.

The rotor members 21 and 22 are in opposite positions with the stator plates 2 * f and 25 on opposite sides of the rotor head. The clearances between the rotor plates and the stator plates can be adjusted by means of a helical gear 26 which cooperates with a positioning screw 27, which in turn is connected to the helical motor 28.

A more detailed view of the grinder plates is shown in Figure 3 of the drawing. · As shown in this figure, the rotor plate 22 is provided with a series of alternating rails 29 and grooves 30 with rail and groove widths not exceeding 3.18 mm. Similarly, the stator 25 is provided with rails 31 and grooves 32, the widths of the rails and grooves of which do not exceed 3.18 mm. In a preferred embodiment of the present invention, the rotor plate 22 consists of stainless steel and the stator plate 25 consists of a synthetic resin such as a polysulfone resin. Further details of these rotor and stator shapes can be found in the present U.S. Patent Application 712,533 and are incorporated herein by reference.

The reduction in fiber length in normal low density "post-milling" of mechanical pulps can be attributed to the relatively high stiffness of the fiber. At normal grinding temperatures of * + 5 · ..60 ° C, brittle fibers break when the contact edges of the grinder strike them. According to the present invention, the refining is run at a higher temperature close to or above the softening temperature of lignin. At these higher temperatures, the fibers are much bent moss and do not tend to become cross-sectioned in the grinder.

To further reduce fiber damage, this High Temperature treatment is performed at as low a grinding intensity as is practically possible. To reduce the intensity, the refiner is run at relatively high circumferential speeds, above about 1830 m / min. This high speed, together with the very fine pattern of the stator and rotor rails, results in the highest practicable levels of cm contact per minute. As a result, when a relatively low power is applied to the refiner, the intensity will be at the lowest practically possible level.

Because the grinder operates at a relatively high speed, it exhibits a considerable rotating load of hydraulic losses. This load can be significantly reduced by reducing the tonnage of the rotor plates, and this reduction in capacity is due to the fact that

Claims (6)

63269 that the wear rate of the steel rotor is lower when used in conjunction with a stator of synthetic resin. This reduction in load therefore contributes to energy savings. To illustrate the difference between the use of the refiner according to the present invention and conventional practice, when a normal 107 cm diameter refiner is normally run, it uses rails and grooves with a width of 4.76 mm, a speed of 514 rpm and a net power of 600 hp. In the grinding operation of the present invention, the width of the rails and grooves is only 3.18 mm or less, the speed is at least 600 rpm and the net operating power is 300 hp or less. A process for the post-milling of hot-milled fibrous slurry, the fibers of which are characterized by the presence of softened lignin and the substantial absence of chemical residues, characterized in that this slurry is treated at a consistency of 3 to 5% and a temperature of 95 to 150 ° C. in a trailed refiner with an intensity of less than 6.18 x 10 4 horsepower / cm contact / minute, the term "cm contact / minute" being understood as the result of the total length of the rails of the rotor surfaces, the total length of the rails of the stator surfaces and the speed of the refiner / min. Method according to Claim 1, characterized in that the post-grinder (14) is operated at an intensity of less than 2.32 x 10 ** horsepower / cm - contact / minute. Method according to Claim 1, characterized in that the post-grinder (14) is operated at 1830 m / min. at a circumferential speed exceeding. Post-grinder for carrying out the method according to claim 1, characterized in that the width of the alternating rails (29, 31) and grooves (30, 32) in the opposite rotor and stator surfaces (22, 25) does not exceed 3.18 mm. Post-refiner according to Claim 4, characterized in that the rotor surfaces (22) are made of steel and the stator surfaces (25) are made of synthetic resin. Post-refiner according to Claim 4 and / or 5, characterized in that the refiner is a disc refiner.