Today, the technology of formless formation of reinforced concrete products has become quite widespread. It has been known for a long time - since the late 1970s, when large-scale all-Union construction of panel houses was carried out. But under pressure from certain circles, the technology became of little use, and in the 90s it practically ceased to be used in Russia.
Until recently, the main suppliers of equipment for the production of concrete products using formless forming technology were three foreign companies that supplied brick-making presses, extruders and splitformers.
Features of lines for formless formation of reinforced concrete products
BOF lines are a specialized set of equipment that allows the formation of beams, piles, road lintels and hollow slabs, as well as other reinforced concrete products for wide use in various fields of construction. At the same time, the use of BF is not always economically feasible - this is due to the technical features of the equipment, which wears out quite quickly, after which it requires service or expensive overhaul.
The design of the splitformer used in the formation of concrete products using formless technology involves the installation of vibrators, which form the main equipment of the forming machine. The disadvantage of this design is the need for lengthy, high-precision adjustment; further maintenance also takes a lot of time.
The operating mechanism of a classic brick making press is much simpler than a splitformer; first of all, it consists in gradually compacting the mixture before the forming equipment. At the same time, BOV equipment places very high demands on the quality composition of the concrete mixture. If the quality of the mixture is insufficient or if unintended fractions, bolts and even small stones get into the mixture, the equipment may produce defective products or even fail.
The high quality of the concrete mixture and the absence of impurities in it is not the only requirement for production using the technology of formless concrete formation. Particular attention should be paid to systematic maintenance of equipment. After each stage of production, it must undergo high-quality cleaning in compliance with routine maintenance.
The key disadvantage is the high price
The cost of the BOF production line is significantly higher (on average about 55-65 million rubles) than the organization of production using “classical” production lines (a set of equipment), which Intek Plant offers on a turnkey basis. It is also worth noting the high cost of components for formless molding lines, in addition, all this can be aggravated by lengthy delivery times for the necessary components.
Investments in the production of reinforced concrete products using formless molding technology can be justified only at large enterprises that are provided with a constant flow of orders, for example, many years of implementation of large infrastructure projects of regional or national importance, where all regulations for the technical operation of this equipment are strictly observed.
Among the minuses, it is also worth noting the difficulty of modernizing the BOF line. The production of different types of reinforced concrete products on such lines is possible with the help of special removable molding equipment, but it is simply not possible to reconfigure the BOF line for another type of production without huge investments. In addition, there are difficulties in the procedure for replacing equipment on a splitformer, and the cost of equipment for the production of one product is at least 1 million rubles.
The use of steel reinforcement in concrete structures leads to the fact that during tension the concrete does not collapse, but it does receive some damage in the form of cracks. This can be avoided if the structure is given a stressed state at the manufacturing stage. The stress in the concrete will be opposite to the stress that arises during use. Formless molding lines allow the production of similar products. These lines are used to produce a wide range of products.
Formless molding lines can be installed in existing buildings of factories for the production of reinforced concrete structures, after the necessary reconstruction. Our experience shows that reconstruction can take up to nine months.
General operating principles
Formless molding lines manufactured by different manufacturers generally operate on the same technological principles.
- At the first stage, the stands are prepared; they need to be cleaned and lubricated.
- At the second stage, with the assistance of hydraulic equipment, the steel reinforcement is tensioned. It is noteworthy that, instead of rods, steel cables can be used.
- At the third stage, the slabs themselves are formed. An extruder or slipformer can be used for this operation. These two methods are somewhat different from each other, in particular, an extruder is used to make hollow-core floor slabs, and a slipformer has more possibilities.
The formed slabs are covered with an awning. This is necessary to minimize water loss. The slabs should gain 70 - 80% of the design strength. To speed up this process, heating is organized using a hot water circulation system.
After the heat treatment is completed and the appropriate strength has been achieved, the slabs are cut to the required size. Cutting is done with a circular saw. Its use allows you to trim the slab at almost any angle.
Economic feasibility
The line for formless molding of hollow-core floor slabs, when properly operated, consumes less resources than traditional methods for producing such slabs. For example:
- The number of staff is only 10 people. An aggregate production line with similar productivity employs 20 to 25 people per shift;
- Energy consumption is 2 - 2.5 times lower than that of lines of traditional production methods.
Lbf used in the domestic construction industry allow increasing production volumes. It can produce up to 50 slabs of standard size per day at a cost lower than that of an aggregate production line. At the same time, the quality of such slabs is higher!
Lines from Canada, Switzerland and other countries are represented on the Russian market.
Increasingly, management of large concrete factories and house-building plants are using formless molding lines for concrete products in their production. This technology was known back in the 70s in the USSR, but due to the decisions of “state criminals” in the 90s, the industry of its application was completely destroyed. Now the tasks of officials have not changed much, so only foreign BF equipment is presented on the market. These are: extruders (Elematic), splitformers (Weiler, Echo), brick presses (Tensyland, Technospan).
BOF lines make it possible to produce: hollow core slabs, piles, beams, road slabs, fence structures, wall and interior partitions, trays, lintels and other reinforced concrete products in large quantities and of high quality. However, production using BF may not always be economically justified and imported equipment is not always the best. At its core, all this equipment works according to the same principle: “loaded concrete - received concrete products at the output,” however, extruders, splitformers and brick-making presses have different designs and associated features.
The extruder supplies concrete to the forming element of the machine using a screw. Considering the constant contact of the working mechanisms of the machine with the hard mixture, they wear out quickly, but the finished products are of very high quality.
The design of the splitformer provides for the installation of vibrators on the forming equipment of the machine. Replacing equipment or other maintenance of a splitformer takes a lot of time.
The mechanism of operation of a vibropress is much simpler and consists in compacting the mixture in front of the forming equipment. However, this type of BOF machines places very high demands on concrete and any violation of the technology for preparing the concrete mixture leads to production defects and equipment breakdown.
Lack of “foolproofing”. BOF lines presented in Russia are completely imported equipment manufactured in Spain, Finland and other countries. Imported equipment does not have guaranteed protection against various production accidents that often occur in Russia. Equipment of all types of lines (regardless of their features) requires the use of high quality concrete and does not allow filler fractions larger than a given size to enter the mechanisms. Any “stray” bolt, nut or large stone can damage the molding machine. In real Russian conditions, ensuring high quality of the concrete mixture supplied to the plant can be very problematic. The quality of the mixture is not the only requirement. Cleaning the machine from concrete residues upon completion of molding and other mandatory procedures require additional equipment and special compliance with production regulations. It was precisely because of the lack of highly qualified specialists in the workshops of reinforced concrete factories in the 70s of the last century that the BF technology did not find its application.
Cost of formless molding lines for precast concrete products
The cost, as well as the productivity of BF lines, is several times higher compared to the implementation of the technology using classic metal molds in the production of reinforced concrete products. Investments in such production can be advisable only if there is a constant high demand for reinforced concrete products (not just high, but very high demand - taking into account the enormous productivity of these lines).
The average cost of a turnkey set of BF equipment is about 60 million rubles! Conventional spare parts for BOF lines are also high in cost, which is actually aggravated by long delivery times for the necessary spare parts.
Difficulties in modernizing lines. The production of various types of reinforced concrete products on BF lines has become possible thanks to removable forming equipment, however, it is simply impossible to convert such a line for another type of production without capital investments. It is also necessary to remember the difficulties of replacing equipment on a splitformer and, again, take into account the average cost of equipment for one product - about 1 million rubles.
The problem of coordinating working drawings. Despite the high declared number of products that, from a technical point of view, can be manufactured on BOF lines, the number of albums of approved working drawings is much less. And it is simply impossible to use uncoordinated products during multi-story construction.
In practice, the introduction of such “capricious” formless molding lines is justified only if wide sales of products are guaranteed (for several years in advance) and compliance with the highest requirements for production organization.
Moscow 1981
Published by decision of the section of factory technology of concrete and reinforced concrete NTS NIIZHB of the USSR State Construction Committee dated March 6, 1981.
The technology for the production of pre-stressed reinforced concrete structures using the formless method at all stages (preparation of concrete mixture, preparation of steel stands, laying and tensioning of reinforcement, molding, heat treatment, cutting strips of hardened concrete into products and their transportation) is described. The requirements for the quality of finished products are given.
PREFACE
In recent years, the USSR has seen the development of formless production of reinforced concrete structures on linear stands, on which, using the method of continuous molding, it is possible to produce products of a constant cross-section along the length of the stand: hollow-core floor panels, flat and trough-shaped slabs, single-layer and three-layer wall panels, etc.
These Recommendations are intended for practical use in prefabricated reinforced concrete factories, where formless production of reinforced concrete structures will be introduced on linear stands equipped with self-propelled forming units and other equipment purchased from Max Roth (Germany) or reproduced in the USSR under a license from this company, and also describe the order of the technological process.
The formless production method using self-propelled forming units provides for special requirements for the quality of concrete mixtures, their transportation to the forming units, control of a continuously moving forming unit, laying and tensioning of reinforcement, heat treatment, stripping and transportation of products.
The recommendations were drawn up on the basis of a practical verification of the provisions of the technical documentation of Max Roth equipment under production conditions at the Seversky reinforced concrete plant of the Glavsreduralstroy Ministry of Heavy Construction of the USSR.
The recommendations were developed by the Research Institute of Reinforced Concrete Construction of the USSR State Construction Committee (candidates of technical sciences S.P. Radoshevich, E.Z. Akselrod, M.V. Mladova, V.N. Yarmakovsky, N.N. Kupriyanov) with the participation of the Glavsreduralstroy of the USSR Ministry of Heavy Construction (engineers E.P. . Varnavsky, S.N. Poish, V.N. Khlybov) and UralpromstroyNIIproekt of the USSR State Construction Committee (candidates of technical sciences A.Ya. Epp, R.V. Sakaev, T.V. Kuzina, I.V. Filippova, Yu. N. Karnet, engineer V.V.
Directorate of NIIZhB
GENERAL PROVISIONS
1.1. These Recommendations apply to the production of prestressed reinforced concrete products with a width of up to 1.5 m and a height of up to 30 cm (hollow-core floor panels and wall panels) from heavy and lightweight concrete using the formless method.
1.3. Features of formless production under license from Max Roth are:
multi-stage continuous molding of products from rigid concrete mixtures;
implementation of vibration impact on the concrete mixture by working parts through contact only with the mixture (surface layer-by-layer compaction);
continuous movement of the compacting elements of the machine relative to the concrete mixture being laid.
The technological line for the formless production of prestressed reinforced concrete products must have the following set of equipment:
steel stands size 150´ 4 m with oil heating registers underneath (process lines with equipment reproduced in the USSR may have smaller stands);
hydraulic tensioning devices for group tensioning of reinforcement and compensation of tension losses when heating the stand and reinforcement during heat treatment (group hydraulic jacks);
"Paul" type hydraulic jack for single tensioning of reinforcement (single hydraulic jack);
self-propelled rebar spreader with deflecting and cutting devices;
coil holders for wire or strand reinforcement;
self-propelled forming unit with dosing hoppers;
trolleys with a thermal insulating blanket to cover the freshly formed concrete strip during heat treatment;
vibrating knife for cutting solid raw concrete;
saws with a diamond blade for cutting hardened concrete;
a self-propelled lifting and transport machine with pneumatic suction cups for removing finished products from the stand and transporting them;
stand cleaning machine;
installation for heating oil (coolant) type MT-3000 (Heinz) or HE-2500 (Kärcher).
In addition, the production line must have a special post for washing the molding unit.
1.4. The peculiarity of molding is that the forming unit, made in the form of a portal on which dispensing hoppers, three stages of compacting vibration elements, movable void formers, form-building and separating movable elements, a lubrication and plasticization system of the stand and controls are mounted, moves smoothly using adjustable rope-tensioning hydraulic device. In this case, the forming unit, using an automatic device, places and presses the transverse upper rod reinforcement and smoothes the open surface of the product.
1.5. The forming unit allows, through appropriate readjustment, to produce products of different widths and thicknesses. In this case, the total width of the molded products does not exceed 3.6 m, and the height does not exceed 30 cm.
1.6. For the manufacture of products, concrete mixtures with a hardness of 20 - 40 s (GOST 10181 -81) can be used.
2. TECHNOLOGY FOR MANUFACTURING REINFORCED CONCRETE STRUCTURES USING FORMLESS METHOD
Requirements for concrete mixture
2.1. Molding of hollow-core panels and solid slabs is carried out from a concrete mixture on a dense aggregate with a design grade of concrete for compressive strength of 300 - 500.
2.2. For molding hollow-core panels and solid slabs, concrete mixtures with a hardness of (25 ± 5) s in accordance with GOST 10181-81 can be used at a molding speed (1.0± 0.2) m/min.
2.3. To prepare concrete, you should use cement with a normal density of cement paste (NGCT) of no more than 27%. The use of cements with a higher NGCT can lead to a violation of the ratio between sand and cement and, consequently, to poor formability of the mixture.
2.4. Sand must meet the requirements of GOST 10268-70. The presence of grains larger than 10 mm in sand is not allowed.
The strength of the aggregate must be at least 2 times the strength of concrete.
2.6. In order to meet the requirements for the rigidity of the concrete mixture and the strength of concrete for calculating and adjusting the composition of the concrete mixture, it is necessary to determine the following characteristics of raw materials:
for cement
activity R c , MPa - in each batch;
NGNT,% - 1 time per shift;
density ρ, g/cm 3 - for each type of cement;
for sand
bulk density g , kg/m 3 - 1 time per shift;
standard (standard deviation) of grains larger than 5 mm per shift, % - in each batch;
size module Mcr - 1 time per shift;
contamination (elutriation), % - once per shift;
natural humidity, % - once per shift;
for crushed stone
density ρ, g/cm 3 - for each quarry;
bulk density g , kg/m 3 - 1 time per shift;
standard of grains larger than 5 mm per shift, % - in each batch;
contamination, % - once per shift;
strength (crudibility), MPa - in each batch;
natural humidity, % - once per shift.
Based on the obtained characteristics, the factory laboratory calculates the composition of the concrete mixture, guided by the provisions set out in paragraphs. - these Recommendations.
Ш = Шр - 0.01Ш р · (к + f), (2)
where to and f- standards for grains larger than 5 mm per shift, respectively, in crushed stone and sand, %;
Шр - estimated amount of crushed stone, kg.
In this case, the consumption of mixed sand P cm and mixed crushed stone Sh cm is determined by the formulas
(3)
where with and d- respectively, the amount of sand in crushed stone and crushed stone in sand,%;
Ш cm = Ш + П - П cm. (4)
2.10. Adjusting the consumption of materials depending on the moisture content of the aggregates W, the presence of sand in crushed stone and crushed stone in sand, and the activity of cement R ts , NGCT, crushed stone voids a carried out if the value newly obtained during testing differs from the previously used one as follows:
W - by ± 0.2%; R - by ± 2.5 MPa; NGCT - by ± 0.5%;
a - by ± 1.0; M cr - by ± 0.1.
2.11. The strength of concrete is determined by the results of testing cube samples molded from a control sample of concrete with a weight whose specific pressure is 4 × 10 -3 MPa. The volumetric mass of freshly molded samples must be equal to the theoretical (calculated) volumetric mass with a tolerance± 2%. Control cubes are steamed along with the product on the stand.
Testing of samples to determine strength is carried out in a hot state (3 samples per stand).
2.12. The molding of wall panels and blocks is made from concrete mixtures on porous aggregate, and the following concretes are used: structural - grades M150 - M200, structural and thermal insulation - grades M50 - M100 and thermal insulation - grades M15 - M25.
2.13. When producing structural and thermal insulating lightweight concrete of grades M50 - M100, a mixture of expanded clay gravel of a 5 - 10 mm fraction of a grade with a bulk density of no higher than 500 and a fraction of 10 - 20 mm of a grade with a bulk density of no higher than 400 should be used, expanded clay sand of a grade with a bulk density of no higher 800, meeting the requirements of GOST 9759-76.
For the manufacture of a thermal insulation layer from large-porous concrete M15 - M25, it is recommended to use expanded clay gravel of fraction 10 - 20 grades with a bulk density of no more than 350.
When producing structural expanded clay concrete grades M150 - M200, it is necessary to use expanded clay gravel of a fraction of 5 - 10 mm of a grade no lower in strength H125.
2.14. The workability of the concrete mixture for structural expanded clay concrete should be characterized by a hardness in the range of 20 - 40 s according to GOST 10181-81.
2.15. The working dosage of materials for mixing is issued by the factory laboratory at least once per shift, with a mandatory check of the hardness of the concrete mixture of the first batches.
2.16. Dosing of cement, water and aggregates must be carried out in accordance with GOST 7473-76.
Dosing of expanded clay gravel and porous sand should be done by volumetric-weight method with adjustment of the mixture composition based on monitoring the bulk density of coarse porous aggregate and sand in a weighing dispenser.
2.17. It is recommended to prepare the concrete mixture for heavy structural and structural-thermal-insulating lightweight concrete in forced-action mixers.
The preparation of the concrete mixture for the heat-insulating layer of large-porous concrete should be done in gravity-driven concrete mixers.
2.18. The duration of mixing of a concrete mixture of a given hardness is established by the factory laboratory in accordance with GOST 7473-76 and is observed with precision± 0.5 min.
2.19. The mixing mode is monitored at least twice per shift.
2.20. The hardness of the concrete mixture coming from each concrete mixer is checked at least three times during the formation of one stand.
Preparation of stands
2.21. After removing the finished products, the stand is cleaned by moving a cleaning machine along it, installed on the stand using a crane.
2.22. The cleaning machine can operate in two modes:
“normal cleaning” - when cleaning the stand without dried concrete;
“full brush mode” - if there are remains of dried concrete on the stand.
2.23. To clean large amounts of raw concrete residue, a special scraper in the form of a bucket with side walls is hung on the cleaning machine. To clean hardened concrete that has strong adhesion to the stand, a scraper beam suspended from the machine is used. The speed of the machine is selected in such a way that the stand is cleaned in one pass of the machine.
2.24. A stand with a small amount of small remains of concrete crumbs is cleaned with a stream of water supplied from a hose under pressure.
Laying and tensioning reinforcement
2.25. The fittings are laid after cleaning the stand. Wire (strands) are drawn using a self-propelled reinforcement spreader consisting of three or six coil holders located behind the stands on the side of the group hydraulic jacks.
The self-propelled reinforcement spreader must move along the stand at a speed of 30 m/min.
The reinforcement is secured to the stops at the ends of the stand manually.
2.26. A batch of wires (strands) fixed to the stand is tightened with a single hydraulic jack at the passive end of the stand until the installation tension of the reinforcement is equal to 90% of the specified force.
The operation is repeated until the installation tension of all reinforcing elements is reached.
2.27. After tensioning the reinforcement, protective brackets must be installed on the stand in case of breakage of the reinforcement elements during its final tension.
2.28. The tension of the entire reinforcement package to 100% of the specified force is carried out using a group hydraulic jack at the active end of the stand after installing a self-propelled forming unit on it and preparing for operation.
The entire process must be carried out in accordance with Max Roth instructions.
Molding
2.29. The forming unit is installed with a crane on the passive end of the stand; Receiving hoppers are installed on the unit, and the power supply cable and cable of the rope-tensioning system are delivered to the active end of the stand using a reinforcement trolley and attached, respectively, to the electrical connector and the special stop bracket located behind the group hydraulic jacks.
2.30. Adjustment and adjustment of the forming unit is carried out on the basis of the instructions for servicing the forming unit included in the set of technical documentation for the equipment supplied by the manufacturer, as well as in accordance with these Recommendations.
2.31. The void formers must be installed in such a way that the distance from the stand surface to the lower edge of the rear part of the void formers corresponds to the design in the product, and in the front part it is 2 mm higher. The back of the sides and partitions should be installed 1 mm above the stand, and the front - 2 mm.
2.32. Vibration compactors of the 1st stage are installed in accordance with the thickness of the base of the panels being manufactured. The front part of the bars supported by rubber shock absorbers should be installed 5 mm higher than the rear part. In this case, the rear part of the 1st stage vibration compactors should be lowered 5 mm from the bottom surface of the void formers following them.
2.33. The 2nd stage vibration compactors are installed so that their rear part is at a distance of 5 mm above the void formers.
The angle of inclination of the vibratory compactors is selected depending on the thickness of the panel and the consistency of the concrete mixture.
2.34. A mechanical tamping device for embedding transverse reinforcement must be installed in the lower position 10 mm above the top mark of the molded product. The control mark in this case is the rear part of the 3rd stage vibration compactors or the surface of the steel sheet of the stands.
2.35. The plates on which the 3rd stage vibration compactors are attached must be installed horizontally and supported by rubber shock absorbers. In this case, the working compacting slab in contact with the concrete mixture will take on the designed inclined position.
2.36. A block of bunkers with a total capacity of 10 m 3 with an automatic device for loading concrete mixture and feeding the mixture into dosing bunkers is installed using an overhead crane on the portal of the molding machine and secured with bolts.
2.37. Before starting forming, the operation of all three stages of vibration compaction, void formers, sides and dividing partitions, and the mechanism for automatically feeding the concrete mixture must be checked at idle speed.
2.38. The rotation of the vibrators of all three stages of compaction should be carried out towards the movement of the molding machine. If the direction of rotation does not match, the phases must be changed.
2.39. When adjusting the position of the sides and dividing partitions that form the side edges of the products, it is necessary to exclude the possibility of the sides coming into contact with the stand during the molding process. The installation of sides and dividing partitions is carried out at the highest point of all stands, to determine which the forming unit moves sequentially along all stands after their installation before trial molding.
2.40. The gap between the 2nd stage vibration compactors and the tensioned upper reinforcement should be (20± 5) mm.
2.41. Before molding begins, the unit is installed in its original position at the beginning of the passive end of the stand; The hoppers of the automatic loading mechanism are filled with concrete mixture supplied from a bucket using an overhead crane.
2.42. Before molding begins, a device is installed to support and fix the stressed reinforcement. Its installation is carried out in such a position of the forming unit when the distance between the dispensing hopper of the 1st compaction stage and the reinforcement spacers is 100 - 150 mm. The direction of the wires (strands) must coincide with the direction of the stand axis; if necessary, adjust the position of the guide bars.
2.43. During the molding process, the concrete mixture must be supplied to the supply hoppers of all three stages of compaction in an amount equal to 1/3 of the hopper volume, which provides a constant pressure necessary for uniform supply of the mixture under the compacting elements of the machine. In the absence of mixture back-up in the supply bins, the mixture is supplied under the compacting elements in insufficient quantities, which leads to under-compaction of concrete in the products.
2.44. Dosing of the mixture from the supply bins is carried out using gates located on the rear wall of the bins using slider levers.
The reciprocating movement of the 2nd and 3rd stage dosing hoppers should be adjusted to 20 - 30 counts/min. In this case, the 3rd stage of compaction must be supplied with such an amount of concrete mixture that would form a small roller in front of the vibratory compactors. This requirement is met by dosing the mixture from the 3rd stage hopper, as well as by rearranging the mechanical compaction device in height.
2.45. Forming of products must be carried out continuously throughout the entire stand without stopping the forming unit. The molding speed, depending on the rigidity of the mixture and the height of the molded product, should be selected experimentally and can be taken equal to 0.5 - 2.0 m/min.
When forming hollow-core panels from concrete mixtures with hardness (25± 5) with recommended speed (1.0± 0.2) m/min. When forming three-layer wall panels with a thickness of 250 - 300 mm from concrete mixtures with a hardness of 20 - 40 s, a speed of 1.0 - 1.5 m/min is recommended.
The total duration of molding a stand strip 150 m long should not exceed 3 hours, and the strength of cube samples molded at the beginning of concreting before heat treatment should not exceed 0.5 MPa.
2.46. When forming multilayer expanded clay concrete panels, the rear part of the 1st stage vibration compactors is installed according to the product drawing above the stand surface at a distance equal to the thickness of the lower structural layer of the product; The gate of the metering hopper should be installed 100 - 120 mm above the lower structural layer.
2.47. The rear part of the 2nd stage vibration compactors is installed above the specified thermal insulation layer by 10 mm, and the gate of the dosing hopper is installed by 50 - 60 mm.
In this case, the vibrators of the 2nd compaction stage must be turned off.
2.48. The rear part of the 3rd stage vibration compactors is installed above the surface of the stand at a distance equal to the thickness of the product, and the gate of the dosing hopper is 100 - 120 mm above the surface of the product.
2.49. Treatment of the stand with OE-2 lubricant and plasticization of the lower layer of the concrete mixture with water is carried out using special devices installed in the front part of the forming unit.
2.50. Before completing the molding, 2 m before the edge of the stand, it is necessary to remove the strips of the guide devices of the reinforcement. The concrete mixture must be fed into the hoppers of the loading device and the supply hoppers evenly so that by the end of molding it is completely consumed.
2.51. After molding is completed, the unit is moved close to the tension rope rotating device, its movement stops and all functional components of the unit are turned off.
2.52. Upon completion of molding at each stand, the forming unit is washed with a high-pressure water jet at a specially equipped washing station.
After the work shift, the forming unit is thoroughly washed. Before this, it is advisable to dismantle the 2nd and 3rd stages of the seal. Mechanical impact (tapping) is prohibited. All mechanisms and motors must be covered before washing.
Forming defects and their elimination
2.53. Broken wire (strand). Check to see if any of the three seal stages are in contact with the wire. Otherwise, the wire may become caught and break in the compacted concrete.
2.54. Loss of adhesion of the strand to concrete or deviation from the design position. It is necessary to check whether the wire (strands) and the 2nd stage vibration compactors are in contact and whether aggregate of a fraction of more than 10 mm gets into the concrete mixture.
2.55. Roughness of the upper surface of panels and transverse cracks. It is recommended to check the consistency of the concrete mixture with the required one, as well as the compliance of the required speeds of forming and dosing of the concrete mixture for the 3rd stage of compaction.
2.56. Cracks on the bottom surface of the panels. It is necessary to check the angle of inclination when installing the 1st stage vibration compactors. In the case of a large inclination angle, the horizontal component during the movement of the working element increases and can lead to discontinuities (exceeds the adhesion force of the concrete mixture to the stand).
The position of the 1st stage vibration compactors in relation to the void formers should be checked. If they are installed incorrectly, void formers will destroy the already compacted base of the panels.
2.57. Formation of cracks on the side edges of panels. It is recommended to check the speed of movement of the sides and separating elements and, if necessary, adjust it.
You should check whether the sides and separating elements are in contact with the stand.
2.58. Insufficient compaction of walls between voids. You should check the dosage of the concrete mixture in the 2nd stage of compaction. It is recommended to check the angle of inclination of the 2nd stage vibration compactors and their operation.
2.59. When checking the operation of vibration compactors, you must make sure that all vibrators are in working order.
The vibration amplitude of the seals should be:
for the 1st stage - 0.9 - 1.0 mm;
for the 2nd stage - 0.7 - 0.8 mm;
for the 3rd stage - 0.3 - 0.35 mm.
Heat treatment
2.60. During the molding period, oil heated in an oil heating unit to 100 °C and circulating in the registers of the stand ensures the temperature of the steel sheets of the stand is at least 20 °C.
2.61. Upon completion of molding and coating of freshly molded concrete with a heat-insulating blanket, the oil temperature is raised to 170 - 200 °C for 7 hours, which ensures a stand temperature of about 90 °C, and the concrete is heated to 65 - 70 °C.
The concrete temperature during the heat treatment period is controlled according to graphs of the relationship between the oil temperature in the system and the concrete temperature based on the oil temperature readings on the control panel of the oil heating unit.
2.62. Isothermal heating is carried out for 7 hours, during which the oil temperature gradually decreases to 100 °C.
2.63. Cooling of products before stress is transferred to the concrete is not allowed [see. “Guide to the heat treatment of concrete and reinforced concrete products” (Moscow, 1974)]. It is recommended to transfer compression forces to concrete no later than 0.5 hours after the end of isotherm and testing of control samples. In this case, the temperature of the concrete should be reduced by no more than 15 - 20 °C relative to the temperature of the concrete during isothermal heating.
2.64. During heat treatment, the stand and reinforcement are tightened when they are lengthened by an automatic device mounted on group hydraulic jacks, due to the activation of a limit switch and an automatic device for maintaining the tension force of the reinforcement. It is recommended to set the operation time of the machine using a time relay to 3 minutes.
Cutting products and transporting them
2.65. The tension is released using a group hydraulic jack at the active end of the stand, followed by cutting off the reinforcement at the passive end of the stand.
2.66. The concrete strip is cut into products of a given length using a saw with a diamond blade, starting from the passive end of the stand. It is possible to use abrasive discs. The time for one transverse cut of a concrete mass 3.6 m wide is 5 minutes.
2.67. Products are removed from the stand and stored at the free end of the stand or its extension using a self-propelled lifting and transport machine with pneumatic suction cups.
2.68. Further transportation of products to a removal cart or vehicle is carried out by an overhead crane using a special beamless lifting beam.
Quality control of finished products
2.69. Quality control of finished products is carried out by the technical control department of the plant on the basis of current regulatory documents (specifications, working drawings) and these Recommendations.
2.70. The deviation of the dimensions of hollow-core panels should not exceed:
in length and width -± 5 mm;
thickness - ± 3 mm.
2.71. The thickness of the protective layer of concrete up to the working reinforcement must be at least 20 mm.
2.72. Panels must have straight edges. In individual panels, curvature of the bottom or side surface is allowed no more than 3 mm over a length of 2 m and no more than 8 mm along the entire length of the panel.
2.73. There should be no sinks on the bottom (ceiling) surface of the panels. Separate small sinks with a diameter of no more than 10 mm and a depth of up to 5 mm are allowed on the top and side surfaces of the panels.
2.74. Collapses in the panels, as well as filling void channels with concrete, are not allowed.
2.75. The panels are produced without reinforced ends.
2.76. The appearance of the panels must meet the following requirements:
the lower (ceiling) surface must be smooth, prepared for painting without additional finishing;
Local sagging, grease and rust stains and open air pores with a diameter and depth of more than 2 mm are not allowed on the lower (ceiling) surface of the panels;
chips and sagging along the longitudinal lower edges of the panels are not allowed;
concrete chips are not allowed along the horizontal edges of the ends of panels with a depth of more than 10 mm and a length of 50 mm per 1 m panel;
cracks are not allowed, with the exception of shrinkage surface cracks with a width of no more than 0.1 mm;
Slippage of stressed reinforcement is unacceptable.
2.77. Deviations from the design dimensions of wall panels should not exceed:
along the length
for panels up to 9 m long - +5, -10 mm;
for panels longer than 9 m - ± 10 mm;
in height and thickness - ± 5 mm.
2.78. The difference in panel diagonals should not exceed:
for panels up to 9 m long - 10 mm;
for panels longer than 9 m - 12 mm.
2.79. The non-flatness of the panels, which is characterized by the largest deviation of one of the corners of the panel from the plane passing through three corners, should not exceed:
for panels longer than 9 m - 10 mm.
2.80. Panels must have straight edges. The deviation from the straight line of the actual surface profile and panel edges should not exceed 3 mm over a length of 2 m.
Over the entire length of the panel, the deviation should not exceed:
for panels up to 9 m long - 6 mm;
for panels longer than 9 and - 10 mm.
2.81. Sinkholes, air pores, local sagging and depressions on the surface of the panel intended for painting should not exceed:
in diameter - 3 mm;
in depth - 2 mm.
2.82. Grease and rust stains on the surface of products are not allowed.
2.83. Concrete ribs with a depth of more than 5 mm on the front surfaces and 8 mm on non-face surfaces, with a total length of more than 50 mm per 1 m of the panel, are not allowed.
2.84. Cracks in panels are not allowed, with the exception of local single surface shrinkage cracks no more than 0.2 mm wide.
2.85. The moisture content of concrete in panels (in % by weight) should not exceed 15% for concrete on porous gravel and 20% for concrete on porous crushed stone.
The moisture content of the concrete in the panels is checked by the manufacturer at least once a month.
Finishing wall panels
2.86. The texture of wall panels is obtained using special equipment. Applying a cement-sand finishing mortar to the surface of a concrete strip and obtaining a smooth front surface of the products is carried out using a finishing unit attached to the forming unit and consisting of a mortar hopper and smoothing bars.
2.87. When decoratively finishing products with cement-sand mortars, you must follow the “Instructions for finishing the facade surfaces of panels for external walls” (VSN 66-89-76).
3. SAFETY
3.1. At the plant, where the production of prefabricated reinforced concrete structures is organized using the formless method on linear stands, all work is carried out in accordance with the “Rules of safety and industrial sanitation at factories and factory sites for reinforced concrete products” (M., 1979), as well as Chapter SNiP III-16-80 "Prefabricated concrete and reinforced concrete structures."
3.2. Special safety rules when carrying out individual technological operations (heating oil, laying and tensioning reinforcement on a stand, cutting finished products, etc.) are set out in special instructions for carrying out these works, contained in the technical documentation for the equipment and supplied with the equipment by the factory - the manufacturer.
3.3. Special safety rules must be duplicated on posters in the workshop.
3.4. Personnel entering the plant must undergo a special training course on the technology of carrying out work at the stand, pass a test and undergo quarterly instruction.
3.5. When working on an installation for heating oil, it is necessary to take into account “Recommendations for reducing the fire hazard of installations using aromatized coolant oil AMT-300” (M., 1967).
