US 2676884 A
Description (OCR text may contain errors)
AF LL 1 April 27, 1954 HAMBURG 2,676,884
MANUFACTURE OF ARTICLES SUCH AS BOARDS AND SHEETS FROM FIBROUS VEGETABLE MATERIALS Filed Dec. 22. 1948 v 2 Sheets-Sheet l Attorney v April 27, 1954 H. HAMBURG 2,676,884
MANUFACTURE OF ARTICLES SUCH AS BOARDS AND SHEETS FRQM FIBROUS VEGETABLE MATERIALS Filed Dec. 22, 1948 2 Sheets-Sheet 2 In venlor HE/UMM HA MjuR 6- Attorney Patented Apr. 27, 1954 TUNlTED STATES PATENT orncr.
Herman Hamburg, Richmond, England, assignor to Syntics Limited, London, England, a British company Application December 22, .1948, Serial No. 66,784
Claims priority, application Great Britain September 19, 1946 a 3 Claims. 1
This is a continuation-in-part of patent application Serial No. 772,903, filed September 8,
i947, now abandoned, and relating to "The Manufacture of Boards, Sheets and Similar Articles from Fibrous Organic Materials.
The present invention relates to the manufacture of articles such as boards and sheets resembling hardwood from vegetable fibrous materials. and. especially from waste fibrous mate- 'rials such as sawdust, woodshavings, straw, and
It has already been proposed to make boards and sheets from vegetable fibrous waste material by mixing the ,waste material with a sufiicient quantity, of resinous binders and shaping the mixture under heat and pressure into boards or sheets. Such boards and sheets, however, are liable to be affected by atmospheric conditions unless a high proportion of synthetic resin,
which is expensive, has been incorporated therein. Moreover, it is diificult to shape the mixture into homogeneous boards or sheets of uniform 7 density and strength.
It is an object of the invention to avoid these drawbacks.
It is another object of theinvention to provide hard wearing homogeneous boards, sheets and other articles of substantially grainless structure and great mechanical strength, which are waterrepellent and moisture resistant, and which have the characteristics of a synthetic hardwood.
It is a further object of the invention to enable vegetable .fibrous waste materials to be utilised for manufacturing boards, sheets and other articles, without grading the waste materials inany way or drying them prior to the manufacturing process. For example, hardwood sawdust may be mixed with softwood sawdust, and the water content of the mixture is immaterial.
It is still another object of the invention, in-
the manufacture of boards, sheets and other articles, to treat vegetable fibrous waste material such a manner that it will not require the addition of any resin or other binding agent to impart the desired mechanical strength and mois-' and substantially grainless structure.
In accordance with the present invention,
' boards, sheets and. other articles aremade from a predigested pulpJike mass 'of vegetable fibrous raw material by impregnating the vegetable fibrous raw material, after the water content of the predigested mass has been reduced by at least one-third, with one or more inorganic salts in solution which will allow the subsequent precipitation of insoluble inorganic compounds within the mass by the subsequent addition of suitable chemical reagents; from the suspension or slurry obtained after such precipitation has been efiected, boards or other desired articles'are formed in known manner, and the articles obtained are subjected to an additional heat treatment. It will be noted that the material is in a comparatively dry state while it is impregnated with the inorganic salt or salts.
It has been found that the finely divided precipitate of an insoluble inorganic compound or compounds confers, even in comparatively small quantities by weight (for example 3 to 4 per cent in the final article), valuable properties upon the fibrous suspension from which the boards 0 other articles are subsequently formed.
In carrying out the process, the predigestion of the vegetable fibrous raw material may be effected either by adding weak alkaline solutions to the raw material or by subjecting it merely to a treatment with steam at an elevated pressure.. The pressure may, for example, be between 20 and 50 lbs. per square inch. Thereby a fibrous 7 preferred method of the invention;
Fig. 2 is a somewhat diagrammatic front view; and
Fig. 3 is a somewhat diagrammatic section along the line III-III of Fig. 2 of a detail of the arrangement of Fig. 1.
Referring first to Fig. 1, in the preferred method illustrated vegetable fibrous waste material is fed to a vessel I and is pre-digested therein for about one to four hours with a weak solution (0.5 to 5%) of caustic alkali or calcium hydroxide at a temperature of about to C. The fibrous mass so obtained is washed and trans- .tween ,pairs of rollers.
3 ferred to a pressure device 2, where it is subjected to heavy mechanical pressure between pairs of suitable rolls 2| of cast iron or stone. The pressure to which the material is subjected may vary according to the type of the raw material and may range from 50 to 1000 lbs. per linear inch in the nip between the rolls 2i. As more clearly shown in Figs. 2 and 3, the pressure device-2 comprises 4 rollers 2i driven from any suitable drive (not shown) and geared together by toothed wheels generally indicated by reference numeral 29 so as to rotate as indicated by arrows in Fig. 3. The pre-digested material passes from an inlet 22 to and between a first pair of rollers 2| formed by the uppermost andthe second of the said rollers. Baffies 23, one of which also acts to scrape the material from the uppermost roller, divert the material so as now to pass between a second pair of rollers 2| formed by the second and third of said rollers; scrapers 24, one of which also acts to scrape the material from the second roller, divert the material so as now to pass between a third pair of rollers 2| formed .by. the third and lowermost of said rollers. Battles 25, one of which acts to scrape the material from the third roller, divert the material to an outlet diagrammatically indicated at 26. The rollers 2| are fixed on shafts 27 rotatably mounted in the side walls 28 of the device, the front wall being omitted in Fig. 2, to render visible the interior of the device. It will be appreciated that with .the pressure device of Figs. 2 and 3 the material is three times passed between pairs of rollers, the second roller being common to the first and second pairs of rollers, and the third roller being common to the second and third pairs of rollers. Instead of passing the material three times between pairs of rollers, it may be passed only once or twice or more often than three times be- By the rolling treatment it is achieved, first that the water content of the pre-digested materialis reduced by at least one third and, second, that the fibres are flattened and the material is converted into a substantially uniform mass of a somewhat pulp-like nature.
The rolled mass is then transferred from the pressure device 2'.to animpregnating vessel 3 (see Fig. 1) in which the mass is intimately impregnated with a solution of an inorganic salt or salts. A wide choice of inorganic salts is available for the impregnation as well as are reagents for the precipitation. For example,
-soluble or partly soluble calcium salts, such as calcium hypochlorite, calcium chloride and calcium hydroxide, and barium salts may be used for the impregnation, and insoluble sulphates may be precipitated within the mass by adding .sulphuric acid or acid salts such as aluminium sulphate.
To facilitate impregnation, the vessel 3 may be provided with any suitable means 3|,
which may for example comprise a screw-mixer,
for intimately mixing the mass with the impregnating material.
From the impregnating vessel 3, the impregnated mass is transferred to a dilution and precipitation tank 1'5, provided with stirring means 1!. Before thepreclpitation iscarried out in this soluble sulphate, are precipitated within the slurry. As another example, insoluble carbonates may be precipitated by the addition of ammonium carbonate or sodium carbonate or by bubbling carbon dioxide through the .slurry. If the fibrous raw material has been pre-digested with calcium hydroxide, barium hydroxide or any other hydroxide of an alkaline earth, the impregnating step may be omitted, and calcium carbonate may vbe-precipitated by the introduction of gaseous carbonic acid-or ammonium carbonate into the slurry obtained by subjecting the pre-digested mass to the rolling treatment and by subsequent dilution. Particularly hard boards have been obtained from fibrous materials treated in this manner.
It will be apparent that the quantity of precipitate may be accurately varied whereby a wide range of difierent types of boards or the like may be obtained.
After the precipitation has been effected, various colouring agents or pigments maybe added tothe acidified pulp if it is desired to produce coloured boards or other articles. If desired, an inorganic filler, such as china clay, may be added to the vegetable fibrous material before or after pre-digesting it.
Boards, sheets, or other articles may be formed in any known manner from the slurry, which may now contain approximately 5 to 10 per cent by weight of solids. The forming of the boards or the like is performed in a forming device 5, to which the material is now transferred. For example, the forming device 5 may be a mould of any desired dimensions and any desired suitable 1 shape, theslurry being poured into such mould.
The mould may be perforated at its bottom so that a large quantity of water is extracted from the pulp through the perforations of the mould, first by gravity and subsequently by the application of a vacuum. A further amount of Water may'be removed by applyin a pressure of up to to a travelling endless wire mesh of the forming device 5, which mesh is similar to those used in Fourdrinier machines for the paper manufacture,
thus forming wet matson such wire meshes.
- Again,a large quantity of water is extracted from the slurry through the wire mesh and a further amount of water is removed by applying vacuum and pressure. From the forming device 5 the article formed is either transferred to a hydraulic press 5, where a hot pressing is applied at a pressure of up to 500 lbs. per square inch, or the article is transferred to a drying oven 1, where it is dried by the application of heat without pressure. The density of the article will depend on the pressure applied; if no pressure or a very low pressure is applied, the article will have a comparatively low density.
The mould, ifused, may have a shape suitable for the production of boards or sheets. It will, however, be appreciated that the mould may have a difierent shape so as to permit other shapedarticles to be produced.
According to a further essential feature of the invention, the moisture resistance of the dried transferred from the hydraulic press 6, or from the drying oven l (as the case may be) to a similar' chamber 8 or 80 respectively in which the additional heat treatment is performed. The
finished articles leaving the chamber 80 are made of a material of low density, while those leavin the chamber 8 are made of a material of higher density.
In a specific example, sawdust is predigested by mixing it with ten time its weight of a 1.5 per cent caustic soda solution and treated for three hours at a steam pressure of 40 lbs. per square inch in any suitable pressure vessel 1 (Fig. 1). After completion of this Dre-digestion the material is washed to remove the excess of caustic soda and is then discharged. It will be found that its water content is about twice the weight of the dry fibres. The pro-digested material is now subjected to pressure by passing it through the nip of a pair of heavy cast iron rollers 2| of the pressure device 2, the gap between the rollers 2| having been adjusted to 0.01. This operation is repeated twice and it will be found that the Water content of the pulp-like mass is now 50% by weight or less. Thereafter, the mass is impregnated by means of a screw-mixer 3| of the impregnating vessel 3 with a previously prepared 5% solution of calcium hypochlorite, the quantity of hypochlorite used being equivalent to of the weight of the dry fibres.
After the impregnating process has been completed the resulting pulp-like mass is diluted with water in the tank 4 until the concentration of the solids in the slurry so obtained amounts to 7%. Under continuous stirring by the stirrin means 4|, a solution of aluminum sulphate is added in a quantity sufficient to reduce th pH value to 4.5, whereby insoluble sulphates are precipitated.
The slurry is now ready to be shaped in the forming device 5 in accordance with standard practice. Some water may be extracted and the material is then subjected to a drying process in the dryin oven 1, or is dried under pressure between heated platens of a hydraulic press 6. Subsequently, the dry boards, sheets, or other articles so obtained are additionally subjected for 20 hours to a temperature of about 125 C. in the chamber 80 or 8 respectively.
Boards and the like produced in the manner described may be treated in a variety of ways in order to make them adaptable to a number of different uses. They may, for instance, be faced with wood veneers. Alternatively, they may be faced with resinous enamels or with resin-impregnated and coloured sheets of paper before or after hot pressing, whereby sheets with highly glossed surfaces may be obtained which may be used as tiles.
Owing to the high resistance to wear, boards or the like may also be used as flooring material.
The boards or the like may be worked in a manner similar to that in which hard wood is worked.
1. The manufacture of a water-repellent, rigid,
product of great dry and wet strength from 11- brous vegetable material, which comprises the steps of mixing the fibrous vegetable material with substantially ten times its weight of a 1.5 per cent caustic soda solution and subjecting the mixture for about three hours to a steam pressure of substantially pounds per square inch to form a pulp, washing the pulp to remove an excess of caustic soda, reducing the water content to about per cent, mixing a 5 per cent solution of calcium hydroxide to the pulp in a quantity of the hydroxide equivalent to about 10 per cent of the dry fibrous material, diluting the pulp with water to form a slurry, stirrin the slurry, adding to the slurry While being stirred a solution of ammonium carbonate in a quantity sufi'icient to precipitate substantially all the calcium of the calcium hydroxide as calcium carbonate, subsequently forming the articles, thereafter drying the articles, and then subjecting the dried articles to an additional heat treatment at a temperature between and including and C. for about 6 to 24 hours.
2. The manufacture defined in claim 1, wherein as fibrous vegetable material sawdust is employed.
3. The manufacture defined in claim 1, wherein as fibrous vegetable material straw is employed.
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