RU2784123C1 - Method for extrusion of fiber cement materials using nano- and micro-additives - Google Patents

Abstract

FIELD: building materials.

SUBSTANCE: inventions is intended for the industrial production of building materials and the technology of three-dimensional construction printing. The raw material composition for fiber cement extrusion consists of cement, organic and artificial fibers, a lightweight filler and a plasticizer, while a nanomaterial is used as a plasticizer - a colloidal solution of IG GSM grade graphene. The composition additionally includes dispersants, a water-repellent additive, fly ash and micromaterials with a high specific surface area - metakaolin, microsilica. A method for the production of products from fiber cement, including the extrusion of the specified raw material composition. At the same time, the components of the composition are pre-dosed, mixed in a mixer with the addition of water to a water-cement ratio of 0.48 - 0.56. The semi-dry mixture is supplied by means of a dispenser 8A with nozzles built into it, made with the possibility of final additional moistening of the mixture with water, into the extruder 8B with an upper pair of screws rotating in the same direction, with the help of which the mixture is plasticized. Then, the resulting plasticized mass is unloaded into the vacuum chamber 8C and evacuated. The mass is subsequently molded using two counter-rotating screws of the lower group of the extruder 8D, a transitional die and a press head 8E. Then, cutting and straightening, hardening to stripping strength in a closed chamber without ventilation and drying in a drying chamber are carried out.

EFFECT: improving the physical and mechanical properties of the material and the performance of the resulting fiber cement.

2 cl, 1 dwg

Description

1. Technical field to which the invention belongs

The invention relates to OT3.9 Building materials and technologies and OT3.12 Nano- and hybrid functional materials, nanotechnology and can be used in the production of wall, roofing, cladding and finishing materials, 3D printing of buildings and structures, and the creation of small architectural forms.

2. State of the art

The process of molding fiber cement materials by extrusion has been known since the 1930s. In 1965, the first copyright certificate was issued for the method of manufacturing asbestos-cement pipes by extrusion in a continuous installation (A.S. 177315. SSR, class 80a 34/01 IPC B 28). In the 1970-80s, the theoretical foundations of the technology were developed, separate units and production lines were designed and put into operation for the production of wall panels, beams, window sills and floor slabs (Extruded asbestos cement, Volchek I.Z., Valyukov E.A., Moscow , Stroyizdat, 1989). In the extrusion technology developed in the USSR, the issues of the continuity of the production cycle, the preparation and introduction of plasticizers, and the design of forming units were resolved. The technology was developed for asbestos fibers capable of retaining moisture, so it was allowed to use typical low-efficiency concrete mixers. However, today the use of asbestos in building materials is limited due to some properties of the fiber (strong but brittle, unstable to high temperatures) and a number of open issues related to labor protection and the environment. The use of new types of fibers in such a line leads to an overconsumption of methylcellulose, and as a result, a high cost. The technology does not make it possible to produce high-quality decorative panels with internal cavities or less than 16 mm thick.

With the advent of prohibitions and restrictions on the use of asbestos in Europe, the USA, Japan, Australia, vacuum extrusion technology has been further developed using reinforcing fibers of both organic and mineral origin (US 5047086 (HAYAKAWA and others) September 10, 1991, US 5658624 (ANDERSON et al.) Aug. 19, 1997, US 6309570 (FELLABAUM) Oct. 30, 2001, US 5891374 (SHAH et al.) April 6, 1999, EUR 0340765 B1 (SHIN-ETSU CHEMICAL CO) March 31, 1993 Cement composition for extrusion). The disadvantage of the proposed technologies is also the use of concrete mixers for the preparation of extruded paste. This equipment does not allow efficient distribution of additives by weight, which leads to an increase in the cost of the material.

Further development of technology is associated with the use of intensive type mixers for semi-dry mixing and kneading machine for plasticizing (US 029772A1 (GUERRINI and others) December 3, 2009, CN 100357217C (XAN XIUZHI and others) December 26, 2007, (CHANG-GEUN Cho et al Flexural Behavior of Extruded DFRCC Panel and Reinforced Concrete Composite Advances in Materials Science and Engineering Volume 2012, Article ID 460541, 8 pages) (HASEOG KIM et al. Characteristics of an Extrusion Panel Made by Applying a Modified Curing Method MDPI 7 May 2016) (BIN SHEN et al., Functionally-graded fiber-reinforced cement composite. Cement & Concrete Composites 30 (2008) p. 663-673) The proposed technological solution significantly increases the efficiency of mixture preparation and additive distribution. Since the addition of water, the cement reacts with the release of heat.At a temperature of 70-75 ° C, gelatinization of cellulose ethers occurs and, as a result, the formation is lost. mass identity. When added to the chemical heat, the physical effects of the mixing and extruding units increase the temperature rapidly, making it difficult to maintain balance in continuous production.

The closest to the invention in terms of technical essence is (WO01/43931 A1 (CHEN et al.) June 21, 2001) an extruder with two counter-rotating screws of a special design (US 3883122 A (WERNER), May 13, 1975) for plasticizing the mixture. An extruder with self-cleaning screws has a smaller working volume, but a higher speed and intensity of mixing, which reduces mixing time and, as a result, 1) reduces the consumption of plasticizer; 2) use additives for accelerated hardening; 3) use short fibers. A significant drawback of the technology is the absence of component moisture control algorithms. This leads to a change in the water-cement ratio of the extruded paste during the production process, and, as a result, obtaining a material that is unstable in terms of properties.

In the technology of vacuuming cement-containing paste, given in (US 6309570 (FELLABAUM) October 30, 2001), it is proposed to automatically add water to the upper mixing screws, focusing on an indirect indicator - the value of the current (load) on the drive motor. The disadvantage of this technology is that with the wear of the working group of the extruder, the gaps between the walls of the cylinder and the screw will increase, reducing the resistance to rotation, which will indirectly lead to incorrect dosing of water.

A significant limitation of the development of extrusion technology for the production of fiber cement and other composites remains the high cost of cellulose ethers used as the main additive to improve rheological properties.

The composition of high-strength concrete based on a functional additive of modified graphene is known (CN 104058676 A (TSAI SHAN JEN et al.) September 9, 2015. The patent (CN 113003995 A (VAN SHIRONG et al.) June 22, 2021) describes the technology for the preparation of concrete reinforced with polypropylene fibers with the addition of graphene It is noted (RAGHUCHARAN et al. How to Make Concrete More Ductile, International Journal of Engineering and Technical Research (IJETR) ISSN: 2321-0869, Volume-3, Issue-5, May 2015) that hydromodifiers containing graphene can significantly increase the plasticity of solutions and improve the quality of concrete.

It is known (TAYLOR H F W. Cement Chemistry. London: Thomas Telford Publishing. 1997) that most of the properties of cement are associated with particles smaller than 100 nm. From the point of view of nanotechnology, hardened cement is a nanomaterial consisting of particles ranging in size from 1 nm to several mm. Increasing the specific surface area of concrete components, in practice, makes it possible to design materials with new properties (SOBOLEV K et al. How nanotechnology can change the concrete world: Part 1. American Ceramic Society Bulletin, 84 (10), p. 14-17).

In studies (MOSTAFA JALAL et al. Mechanical, rheological, durability and microstructural properties of high performance self-compacting concrete containing SiO ₂ micro and nanoparticles. Materials and Design 34 (2012) p. 389-400, THALLAPAKA VISHNU et al. Study and performance of high strength concrete using with nano silica and silica fume, International Journal of Civil Engineering and Technology (IJCIET) Volume 6, Issue 11, Nov 2015, pp. 184-196, Article ID: IJCIET_06_11_019, ZHIBIN LIN et al. engineered cements with improved early strength NICOM 4: 4th International Symposium on Nanotechnology in Construction, GENDA CHEN et al Concrete Surface with Nano-Particle Additives for Improved Wearing Resistance to Increasing Truck Traffic 2012 Mid-America Transportation center Report#MATC-MST :441, SINGH LP et al, Quantification and characterization of CSH in silica nanoparticles incorporated cementitious system, Cement and Concrete Composites 79 (2017), pp. 106-116, LIBYA AHMED SBIA et al. Evaluation of modified-graphite nanomaterials in concrete nanocomposite based on packing density principles. Construction and Building Materials 76 (2015). p.413-422) shows the effect of using micro- and nano-particles to modify concrete:

- nanoparticles activate the mixture and make it possible to replace cement with additives, which reduces the cost of the material and makes it possible to use secondary raw materials to a large extent;

- due to the small particle size, the internal density increases - strength, bending improve, water absorption decreases (LI G. Properties of high-volume fly ash concrete incorporating nano-SiO 2. Cement and Concrete Research, 34 (6), p. 1043 -1049);

- characterized by rapid hardening and strength gain in the early stages, which makes it possible to obtain a durable material without losing shape immediately after exiting the extruder, thereby reducing the fleet of molding equipment;

- nano titanium dioxide gives the surface a self-cleaning effect (MURATA et al. Air purifying pavement: Development of photo-catalytic concrete blocks. Journal of Advanced Oxidative Technologies, 4 (2), 227-230);

- nanoparticles are not only a filler, but also act as an activator of the pozzolanic reaction. Despite these advantages, it is noted (BARBHUIYA S et al. Effects of nano-Al 2 O3 on early-age microstructural properties of cement paste. Handbook of Nanotechnology: Construction and Building Materials, 2014. Springer. p. 189-193) (MATUS EP Influence of nanoadditives on the physical and mechanical properties of dispersed-reinforced concrete Modern construction and architecture No. 1 (09) February) that one of the urgent technological problems is the dispersion of nanomaterials in a cement mixture. These works find commercial application in concretes for various purposes, however, the technology of using nanomaterials to improve the properties of extruded fiber cement has not been described. The technological cycle and equipment proposed in this patent makes it possible to effectively mix additives with a graphene content of 0.5% or more, which makes it possible to apply well-known theoretical and practical developments in the production of fiber cement.

Extruded fiber cement must have the following properties: high heat and frost resistance; significant moisture resistance; ease; strength and flexibility; incombustibility; no emission of harmful substances into the environment; good nailability; reduced content of cement, as an expensive and environmentally dirty material.

3. Disclosure of the invention

The invention is based on a technological problem, which consists in the development of a new process for the continuous extrusion of fiber cement, which can reduce the cost of the material and obtain both improved and new consumer properties. To obtain the desired result, a two-stage preparation of the components is used. At the first stage, a semi-dry type of mixing is used in an intensive type mixer. For stable loading of the extruder and reducing the storage time of the mass, 2 or more mixers are alternately used. At the second stage, the mass is plasticized by a twin screw extruder, cut and fed into a vacuum chamber, and the mass is pressed by the lower screws through the dies of the desired shape. The proposed scheme of the production line makes it possible to exclude a kneading machine for plasticizing and a box feeder. This approach reduces the mass preparation time by 5-10 minutes, which makes it possible to avoid an abrupt increase in the temperature of the hardening concrete and the associated loss of mass fluidity. The extruder has a modular design that allows you to quickly replace the worn parts of the screws, housing, adapter head. A reinforcing composition is applied to the working surfaces of the screws and the jacket.

To obtain improved physical and mechanical properties of the material, the proposed method uses: additional grinding of cement; introduction of micro- and nanoadditives; replacement of cellulose ethers with graphene plasticizer; the introduction of dispersants for a better distribution of graphene by weight. The inclusion of micro-nanoparticles in the structural lattice of the fiber-cement composite makes it possible to more effectively use additives to reduce the weight and increase the fire resistance of the material - silica fume, metakaolin, perlite, vermicullite, and also to fix reinforcing fibers (basalt, carbon, organic) more firmly. The dense packing of the composite with small particles does not require increased pressure in the extruder. The proposed composition of the mixture is characterized by a high set of strength in the early stages of hardening and, unlike known methods, does not require subsequent heat-moisture or autoclave treatment, which significantly reduces energy costs. The operation of the equipment at low pressures reduces the wear rate of the working surfaces. To create the necessary texture on the surface of the fiber cement, a calender roller or a hydraulic press with a set of three-dimensional templates is used. Coloring in the mass is carried out through the addition of a pigment of the desired color at the first stage of mixing. To increase frost resistance, a hydrophobic composition is added to the mass.

4. Brief description of the drawings

In FIG. 1 shows the proposed technological scheme for the production of fiber cement materials using nano- and micro-additives by extrusion. In the drawing, the numbers indicate: areas for storage and dosage of cement (1), pozzolanic additives (2), functional micro- and nano-additives (3), dosing system for water (4) and graphene (5), area for preparing cellulose and secondary fibrous raw materials (6 ), intensive mixers (7), extruder with feed hopper (8a), twin screw mechanism (8b) for plasticizing and feeding into the vacuum chamber (8c), twin screw forming group (8d), adapter die and press head (8e), robotic complex cutting and straightening (9), pre-hardening chamber (10), drying chamber (11), final cutting (12), painting (13), packaging (14) and shipping (15) areas.

5. Implementation of the invention

The description below provides a detailed description of the process steps, equipment operation modes, main control characteristics, requirements for raw materials and final quality control of the material. The formation of a composite material containing cement and fibers - fiber cement takes place in a vacuum extruder. The technological process is divided into the following blocks: dosing, mixing, plasticizing, vacuuming, shaping, cutting and straightening, hardening, drying, final cutting, painting, packaging and shipping.

A. Mixing. Mixing of components is carried out on an intensive action mixer with a high-speed mode, for example, Tyazhstankogidropress model CM1500 or Eirch of the R or RV series. In the case of using pulp or waste paper, the required amount of non-fluff fiber is introduced into the mixer at the first stage. For fluff pulp, the addition of 10% water and processing at a speed of 800-1200 rpm for 5 minutes is necessary. Next, dispersants and inert components (metakaolin, microsilica, nanoparticles, pigments) and reinforcing fibers (carbon or basalt, PP, PVA, wollastonite, nanotubes) are introduced and mixed for 3 minutes at a speed of 300-1420, preferably 500 rpm. Then cement, water-repellent additive, graphene plasticizer and water are added to the W / C ratio of 0.48 - 0.56 and mixed at 500 -1300, preferably 600 rpm for 5 minutes. At the final mixing stage, lightweight additives - perlite or vermiculite - are introduced and mixed for 2 minutes at 100-300, preferably 150 rpm.

B. Plasticizing. The semi-dry mixture is fed into the press chamber by a screw feeder. The screw dispenser has nozzles for water supply. When dosing the mixture into the extruder, its final moistening is carried out. The upper pair of screws of the extruder rotates co-directionally and has a modular design with specially shaped successive modules for loading, transporting, plasticizing and unloading into a vacuum chamber through a perforated (D20-30 mm) die. The top augers have a lower conveying capacity and are designed for more shear energy per mass, so the rotation speed of the augers of the upper group is higher than the lower one. The ends of the screws are equipped with knives for cutting the extrudate for uniform loading of the vacuum chamber.

G. Vacuuming. To remove excess water and air from the mixture before molding, the plasticized mass is fed into a vacuum chamber. Vacuuming results in a compaction of the mixture, improving the properties of the finished material. The described technology uses a vacuum level of 0.5 to 4.5 Pa. With the help of vacuum, within certain limits, it is possible to control the density of the composite. To obtain materials with high density, a vacuum of 1.5 - 3.0 Pa is used, with medium and low - 0.5-1.5 Pa.

D. Molding. The lower group of the extruder is equipped with two counter-rotating screws that transport the mass in the direction of the die. To equalize the spasmodic movement of the mass in the direction of the exit, the pitch of the turns of the screws decreases towards the exit. When it is necessary to form materials with high density, cone screws are used. The press mouthpiece is designed taking into account the need to equalize the mass flow rates across the width and provides a transition from the extruder section to the section of the molded product. Ultrasonic generators are used to reduce friction. When molding hollow products, cores of the required section are inserted into the mouthpiece. Molding is carried out at a speed of at least 2m/min. Increasing the rotation speed of the lower augers allows you to create a denser material. To obtain parts of complex shape and surface texturing, a calender roll or a short-stroke hydraulic press with a force of up to 7000 tons with appropriate punches is used.

E. Cutting and straightening. The proposed technology uses a robotic complex for cutting, lengthening and stacking the material into baskets. The complex is equipped with vacuum boxes, a circular cutting knife with a feed rate of 100 mm / s and a right and left installation of the desired length with a pneumatic drive. After exiting the extruder, the material enters the conveyor, where it is cut and straightened. With the help of a vacuum box, the material is transferred to the hardening baskets. The robot-based layout eliminates gantry stackers and additional conveyors from the process equipment.

G. Hardening. The use of nano- and micro-sized components and graphene-based additives in the proposed technology makes it possible to exclude the stage of heat-moisture treatment or autoclaving. Hardening to stripping strength occurs within 9 hours at a temperature not lower than 20°C in a closed chamber without ventilation. Experience shows that at the specified water-cement ratio, there is enough water in the material to hydrate the cement.

Z. Drying. The proposed technology makes it possible to produce material with high decorative properties. To carry out high-quality painting, it is necessary to dry the panels to a moisture content of no more than 8-12%, preferably 9%. For this, a drying chamber with control and removal of moisture is used. Drying of the composite occurs within 12-15 hours. The drying process is carried out not earlier than on the 28th day after the molding of the material.

I. Final cutting. After drying, the material stabilizes, so a final cut is necessary to achieve dimensional accuracy within the tolerances required by the standards. This operation is carried out with gang saws (eg model K34 from Paul Mashinenfabrik) or with the help of cutting centers (eg model Gabbiani GT2 from SCM). Diamond circular knives are used (for example, by Leitz) with a rotation speed of 1100-2050 rpm, a feed rate of 35-85 mm/s. Also, for the production of panels with clamp fastening, milling equipment is required (for example, the Celaschi P40 model from SCM). The equipment must be equipped with an exhaust system of the required power with bag filters. Collected dust from knives can be reused in the material in an amount up to 5% by weight.

K. Painting. The painting of the material is carried out on automatic lines with spray, roller, bulk or vacuum application. The process uses acrylic, epoxy, fluorocarbon, paints and primers. For multi-color images on the surface of fiber cement, digital UV printing is used. To create protective surfaces with self-cleaning and anti-graffiti properties, special UV curing varnishes are used.

L. Packaging. The material is placed on transport pallets with spacers between the front sides of the panels, pulled together with polypropylene tapes and packed in a film.

The proposed technology uses Portland cement without additives, for example, grade PC 500 D0-N (for example, Heidelberg Cement, Magnitogorsk Refractory and Cement Plant). For decorative purposes, it is acceptable to use white cement, such as DecoCem 500 (Holcim) or CEM I 52.5 R (Adana Cimento). The use of cement with additives greatly complicates the process control, due to the fact that in continuous production it is impossible to determine the exact amount and composition of additives in each batch.

The proposed technology makes it possible to replace cellulose ethers, which are currently widely used in practice, with a graphene plasticizer, for example, a colloidal solution of graphene of the IG GSM brand (Graphene Institute). An important technological effect of introducing graphene into the mass is an increase in its fluidity. At the same time, when the temperature rises to 150–200°C, this property of the modified mixture does not disappear. The graphene plasticizer makes it possible to increase the strength of the composite up to 50%, reduce the hardening time, reduce water permeability, and increase frost resistance.

Also in the proposed technology, the use (up to 25%, 7% by weight is recommended) of commercially available fillers with a high specific surface area - metakaolin and microsilica, which increase the positive effect of the use of graphene plasticizer. Microsilica is a lightweight additive that improves the physical and mechanical properties of the material. The proposed technology uses microsilica grades MK and MKU, produced, for example, by the Chelyabinsk Electrometallurgical Plant.

To create a reinforcing mesh, fibers are introduced into the composition of the composite (from 5 to 20% by weight). The composition and quantity of fibers are selected based on the purpose of the material, cost and commercial availability. Pulp is used (for example, unbleached pulp of the FC grade of the Arkhangelsk Pulp and Paper Mill), recycled pulp obtained after processing waste from cellulose-containing packaging such as Tetra Pack, polyvinyl acetate (PVA) fibers (for example, Kuralon KII fiber from Kurarai), polypropylene (PP) fibers (for example, Procon-F from Nycon), carbon fibers (eg UMT from Umatex), wollastonite (eg Nyad G or Nyad MG from Imerys), basalt fibers (eg CX grade fibers from Concrete Exchange). To obtain composites with fire-retardant and heat-resistant properties, it is necessary to use only high-temperature-resistant fibers, such as carbon or basalt.

The proposed technology involves the use of a number of inert functional additives to reduce the weight of the material and make it resistant to high temperatures. The introduction of fly ash with a specific surface area of at least 200 m ² /kg (eg Reftinskaya GRES) in the composite is possible in an amount (up to 60% by weight, preferably up to 20%). Replacing cement with fly ash reduces the cost of the composite by reducing the amount of cement required. At the same time, recycling of secondary raw materials (ash) occurs through the replacement of cement, which is one of the sources of CO ₂ emissions into the atmosphere. It is necessary to choose fly ash with a lower value of specific effective activity. To reduce the weight of the material and increase heat resistance and fire resistance, expanded perlite grades VPM, M75 or M100 (for example, Promperlit) or vermiculite (for example, Uralvermiculite) are used, the latter having better resistance to humid environments and heat resistance up to 1200 ° C. It is possible to introduce into the material up to 15% by weight of these additives, preferably 7-10%.

6. Industrial applicability

The proposed method for the manufacture of composites is used in the production of board materials for various purposes, roofs, sandwich panels, the manufacture of shaped parts, window sills, landscape design elements, for prefabricated housing construction, in agriculture, in the construction of commercial and industrial buildings. The mixture preparation method and the proposed raw material composition are used in 3D printers for construction printing of buildings, structures and their parts.

Claims (2)

1. A raw material composition for fiber cement extrusion, consisting of cement, organic and artificial fibers, a lightweight filler and a plasticizer, characterized in that a nanomaterial is used as a plasticizer - a colloidal solution of graphene of the IG GSM brand, the composition additionally includes dispersants, a hydrophobizing additive, fly ash and micromaterials with a high specific surface – metakaolin, microsilica. 2. A method for the production of products from fiber cement according to claim 1, including extrusion, characterized in that the components of the composition are pre-dosed, mixed in a mixer with the addition of water to a water-cement ratio of 0.48 - 0.56, the supply of a semi-dry mixture using a dispenser 8A with nozzles built into it, made with the possibility of final re-moistening of the mixture with water, into the extruder 8B with the upper pair of screws rotating in parallel, with the help of which the mixture is plasticized, then the resulting plasticized mass is unloaded into the 8C vacuum chamber and evacuated, followed by mass molding using two screws counter-rotation of the lower group of the extruder 8D, the transitional mouthpiece and the head of the press 8E, then cutting and straightening, hardening to stripping strength in a closed chamber without ventilation and drying in a drying chamber.

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