FI75798B - FOERFARANDE FOER FRAMSTAELLNING AV CEMENTBUNDNA TRAEFIBERFORMSTYCKEN. - Google Patents

Description

75798

Method for making cementitious wood fiber moldings

The invention relates to a method for producing cement-bonded wood fiber moldings by forming a mixture comprising Portland cement, silica, wood chips, water and optionally conventional additives and curing the resulting moist mass in a mold under pressure and optionally by heating.

In the known processes according to this technique, in which the binder is formed, in addition to the usual additives such as CatOH® MgCl2, CaCl2 and / or Al2 <SO4> g, only Portland cement, only wood which is insoluble in water or in all cases only very well can be used. small amounts of soluble substances such as sugar and / or phenolic compounds, as these strongly slow down or even completely prevent the hydraulic binding of the binder. Therefore, such methods are essentially limited to conifers; the use of domestic hardwoods is not economically sensible or even impossible.

DE-PS-852 366 discloses a process in which 0.5 to 1 part by volume of diatomaceous earth-aluminum silicate mixture and 1 to 3 parts by volume of sawdust are used per unit volume of cement, the volume ratio of diatomaceous earth to cement being less than 0.2: 1. In this way, however, poplar chips can be pressed into stones with bauxite cement and also quartz sand, brick powder, lava, blast furnace slag, etc. However, even after 8 hours of moisture curing at an atmospheric pressure of 12 atmospheres, such stones reach a flexural strength of only 40 to 53 kg / cm, measured after 28 days. This method is not suitable for the production of cementitious wood panels.

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EP-A1-68742 further discloses a process for the preparation of asbestos-free moldings in which a Hatschekoneone is formed into a sheet of the desired thickness from an aqueous slurry formed of a mixture containing 50 to 90% by weight of cement, 5 to 40% by volume * of highly reactive pozzolanic acid. and only 5-15 volume * cellulosic fibers. In this case, wood cellulose feedstocks with a degree of freedom of between 1Θ and 35 SR are used as cellulose fibers. Thus, the 2-5 mm wide wood chips commonly used in the manufacture of particle board are not used for this purpose. The moldings thus prepared have a weight ratio of binder to cellulose fibers of more than 5: 1.

The object of the present invention is to provide a method as mentioned above, which, even when using hardwood fibers, makes it possible to produce sawdust-shaped pieces which are plate-like, cement-bonded and have very good bending strength.

In order to solve this task, the method according to the invention is given the features set forth in claim 1.

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In the process according to the invention, it is possible to use hardwoods (such as, for example, beechwood), although these release larger amounts of soluble substances, in particular sugar and phenolic compounds, into the mixture. The compression times and pressures are not prolonged compared to known methods, nor are the heating temperatures possibly designed. The binder of the shaped bodies is substantially less alkaline compared to the known methods, so that in particular the base-soluble substances are less soluble and, moreover, the chemical decomposition of the wood fibers is slowed down and clearly reduced compared to the known methods. Subsequent carbonization of the surface of the shaped bodies due to the absorption of atmospheric CCl 4 is also reduced due to a reduction in the alkalinity of the binder, which slows down the embrittlement of the fibrous material. The method is used to obtain shaped bodies whose mechanical properties do not lag behind those already known. After removal from the press, the remaining moisture is lower compared to known methods, so that the time and energy consumption outside the press during drying is reduced. The amorphous silica contained in the binder precipitates in a suitable particle size, for example in the dust of the melting furnaces, and can be advantageously drawn off.

Other preferred embodiments of the invention are set out in claims 2-5.

The invention also relates to a cement-bonded wood fiber shaped body, the features of which are set out in claim 6. A further development of this shaped body is defined in claim 7.

In the following, the preferred embodiments of the method are illustrated by experiments.

Test 1; 2400 g of Portland cement PZ 45 F (70% by weight of binder) was mixed dry with 1030 g of amorphous silica (30% by weight of binder) thoroughly. The specific surface area of the amorphous silica was about 20 m 2 / g and it contained more than 90% of particles with a particle size of less than 10 μm. 1400 g of beech chips with a moisture content of 5% were mixed with 1350 ml of water in which 34 g of Al 2 O 3 had been dissolved. Beech chips were 20 mm long and 2 mm to 5 mm wide and 0.2 to 0.3 mm thick. In a forced agitator, beech chips and water supplemented with 41 g of CaiOH were mixed very thoroughly with a dry, premixed binder consisting of Portland cement and amorphous silica. The weight ratio between the water content, which was not absorbed into the fibrous material, and the binder content in the mixture was about 0.3.

From the mixture of beech chips, water, additives and binder, two plate blanks measuring 44 x 44 cm were formed and thus cured in a heated press at a specific pressure of about 1.5 N / mm 2 and at a temperature of 40 ° C for 8 h until the shape remained unchanged. The plates were adjusted to a nominal thickness of 12 mm by means of corresponding spacers and had a residual moisture of about 20%. After complete drying, their crude density 3 was 1.1 g / cm; their flexural strength was 2.5 N / mm after three days and 7 N / mm after 28 days.

Otherwise, under the same experimental conditions except that pure Portland cement was used as a binder, test panels were made from the same beech chips. Since even after 28 days no change in shape had been achieved through the corresponding binder curing, no comparable strength values could be determined.

Although in this first embodiment of the method the cement and the amorphous silica can be mixed together dry and then added to the fibrous material to which water has been added, it may be advantageous to combine the wood chips or chips first with a mixture of amorphous wood, especially when hardwood solutes are used. silica and a portion of water, and then combines them into a mixture of cement and residual water. Through this, 5 75798 fibrous material becomes surrounded by a chemically inactive silica coating, which prevents, on the one hand, the chemical etching of the alkaline cement adhesive and, on the other hand, the very strong dissolution of the base-soluble substances.

Test 2;

In a colloid mill, 1170 g of Portland cement PZ 35 F (70% by weight of binder) were ground with 410 ml of water and then mixed thoroughly. In a forced mixer, 670 g of dried larch chips (residual moisture 5%) were mixed with a slurry of 500 g of amorphous silica in 300 ml of water and then mixed with a binder-water mixture. The weight ratio of non-absorbable water to binder content was about 0.33.

The mixture was formed into a sheet blank having a size of 44 x 44 cm and then pressed in a press at 40 ° C at a specific pressure of about 1.5 N / mm for 8 h. The residual moisture of the cured sheet was about 22% and reached a flexural strength of 2 4 about 4 N / mm after 3 days and a flexural strength of about 8 N / mm after 28 days.

Otherwise, conventional larch chipboard sheets made under similar experimental conditions with Portland cement as the sole binder reached a flexural strength of 0.4 N / ram after three days and a bending strength of 1.2 N / mm after 28 days.

For this second preferred embodiment of the method, higher requirements are set for the binder properties of the cement adhesive than in the first embodiment. Therefore, before mixing with the amorphous silica and the fibrous material, the cement is pre-ground in the presence of water in a suitable high-cycle mill and then mixed thoroughly with the corresponding part of the water and made into a suspension.

The comminution of the cement clinker achieved in this way into smaller 6 75798 particles simultaneously results in a thorough hydration of the binder.

If it is also desired to take advantage of this advantage in the first embodiment of the process, the cement and amorphous silica can be comminuted and mixed together dry in a ball mill before being mixed with the fibrous material.

The following experiments prove the usefulness of domestic hardwood species in the method according to the invention.

Experiment 3:

In a laboratory cement mill for the production of standard mortar in accordance with DIN 1164, 3 cm of Portland cement 3 PZ 35 F tap water was added 200 cm and a crumbly mass was obtained after grinding. In a forced mixer, 670 g of dried birch chips (sugar content 0.5%, residual moisture 4%) were mixed homogeneously with 770 ml of tap water homogeneously, then 516 g of amorphous silica were added and mixed thoroughly again. The weight ratio between the non-absorbable water content and the binder content was about 0.35. The mixture was formed into a 44 x 44 cm plate blank and then pressed in a heated press at 40 ° C at a specific pressure of about 2 1.5 N / mm for 8 h. The residual moisture of the cured sheet was about 19% and reached a crude density of 1.1 g / cm and a flexural strength of 4.7 N / mm after three days, and 8.7 N / mm after 28 days after drying.

Otherwise, conventional birch chipboards made under similar experimental conditions with Portland cement as the sole binder could not be removed from the press undamaged and could therefore not be examined.

Test 4;

With a laboratory mixer, 1206 g of Portland-3 7 75798 cement PZ 35 F was mixed with 200 cm of tap water to a crumbly mass. In a forced agitator, 670 g of dried poplar chips (sugar content 0.4% and residual moisture 4%) were mixed with 770 cm of tap water, as well as thoroughly homogeneously with each other. 516 g of amorphous silica were added and stirred once more thoroughly. The weight ratio of non-absorbable water content to binder to binder content was about 0.35. The mixture was formed into a plate blank measuring 44 x 44 cm and then pressed in a heated press at 40 ° C at a specific pressure of 1.5 N / mm for 8 h. The residual moisture of the cured sheet was about 18% and reached a crude density of 1.1 g / cm 2, a flexural strength of about 4 N / mm and about 9 N / mm, respectively, after 3 days and 9 days, respectively.

Otherwise, conventional poplar particle boards made under similar experimental conditions with Portland cement as the sole binder had a flexural strength of about 1 N / mm or 3 N / mm after 3 days and 28 days, respectively.

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Experiment 5:

In a forced agitator, 1360 g of larch chips (moisture content 6% relative to Atro wood chips) were mixed with 1520 ml of water, and a further 1720 g of amorphous silica (silica dust) of the species defined in Experiment 1 was added. After thorough mixing, 1720 g of Portland cement (PZ 35 F) was added and mixed again. The cemented wood chips thus obtained were manually applied to 44 cm x 44 cm molds to form slabs and, after weak pre-compression, were pressed between three oiled stainless steel sheets in a hydraulic o 2 press for 7 hours at 40 ° C and 2.0 N / mm, the thickness of the plates was determined to be 12 mm by means of spacers. After removal from the mold, the shape-resistant plates were stored for two days in a moisture box and then cut into 18 test pieces measuring 25 cm x 5 cm, which were left in the moisture box until the tests. Three to six specimens were weighed and tested for flexural strength on the third, tenth, and twenty-eighth days. The following results were obtained: 3 days 10 days 28 days 2 2

Bending strength 4.8 N / mm 6.3 N / mm 10.3

Raw thickness 1.03 1.06 1.07 (Atro or dry)

Similarly made wood-based panels without the addition of silica decomposed after removal from the mold due to the fact that the binder did not harden.

Claims (7)

9 75798 A method of making cement-bonded wood chip moldings by forming a mixture of Portland cement, silica, wood chips, water and optionally conventional additives and curing the resulting moist mass in a mold under pressure and optionally by heating, characterized in that a) amorphous silica is used; having a specific gravity of 2 2 15 to 25 m / g, preferably 18 to 22 m / g, and more than 90% of the particles having a size of less than 10, b) in the mixture the weight ratio of Portland cement to silica is 70:30 to 40:60, c) in the mixture, the weight ratio of Portland cement and silica binder to wood chips is 2.45: 1 to 2.8: 1, and d) the weight ratio of non-absorbable water content to binder content in the mixture is 0.25: 1 to 0.35: 1. 2 J 2 4 3 10 75798 A method according to claim 1, characterized in that the wood chips are first mixed with water and silica and then Portland cement, optionally moistened with a small amount of water, is mixed. Process according to Claim 1 or 2, characterized in that the Portland cement is comminuted in the mill to a crumbly mass before mixing with wood chips and silica. Method according to one of Claims 1 to 3, characterized in that hardwood and / or hardwood chips, in particular beech chips, are used. Process according to one of Claims 1 to 4, characterized in that a further 0.2 to 3% by weight of Ca (OH) and / or Al (SO) is added to the mixture. 6. Cement-bonded wood chip moldings with a hydraulically bound binder consisting of Portland cement and silica, and optionally conventional additives, characterized in that a) the binder contains 40 to 70% by weight of Portland cement and 60 to 30% by weight amorphous silica with more than 90 particles of less than 10 μm in size and b) the weight ratio of binder chips is between 2.45: 1 and 2.8: 1. Cement-bonded wood chip moldings according to Claim 6, characterized in that the wood chips are essentially hardwood and / or hardwood chips, in particular beech wood chips.