In the 1990s, researchers from the National Aeronautics and Space Administration (NASA) of the United States developed and adopted a new type of space thermal insulation and reflective ceramic layer (Therma-Cover) to solve the heat transfer control problem of the space shuttle. This material is composed of some tiny ceramic particles suspended in inert latex. It has high reflectivity, high emissivity, low thermal conductivity, low thermal storage coefficient and other thermal properties, and has excellent heat insulation and reflection functions. This high-tech material has been widely used in civil engineering, construction and industrial facilities abroad, and exported to some large industrial facilities in China. However, the fly in the ointment is that the high price of this material of $20/kg really makes many domestic industries look down on things and find it unbearable. As a result, a new upsurge of research and development of thermal insulation materials has quietly set off in China, and a new type of space reflection thermal insulation coating with high efficiency, thin layer, thermal insulation, energy saving and decorative waterproofing has been successfully developed among domestic peers. The coating takes silicone-acrylic emulsion and waterborne fluorocarbon emulsion with excellent heat resistance, weather resistance, corrosion resistance and waterproof properties as film-forming substances, takes ultrafine hollow ceramic particles called space age materials as fillers, and the coating film made of hollow ceramsite is composed of various combinations. Visible light and solar heat in the near infrared region are highly reflected in the range of 400~ 1800nm, and an air microporous layer with very low thermal conductivity is introduced into the coating film to isolate the transmission of thermal energy. In this way, by strengthening the obvious impedance of reflecting solar heat and convection transfer, radiation heat transfer and convection heat transfer can be effectively reduced, thus reducing the thermal balance temperature on the surface of the object, which can reduce the roof temperature by 20℃ at most and the indoor temperature by 5~ 10℃. The thermal insulation grade of the product reaches R-33.3, the thermal reflectivity is 89%, and the thermal conductivity is 0.030 W/m k. ..
Development trend: Building thermal insulation is an important aspect of saving energy, improving living environment and using functions. Building energy consumption accounts for 30-40% of the total human energy consumption, most of which is heating and air conditioning energy consumption, so building energy conservation is of great significance. Moreover, because the thermal insulation coating uses water as the dilution medium and does not contain volatile organic solvents, it has no harm to human body and environment; Its production cost is only about 1/5 of similar products abroad, and as a new type of thermal insulation coating, it has attracted more and more attention and favor because of its good economic benefits, energy saving and environmental protection, thermal insulation effect and simple construction. This kind of space thermal insulation reflective coating is undergoing the transformation from industrial thermal insulation to building thermal insulation, and from thick thermal insulation to thin thermal insulation, which is also one of the main development directions of thermal insulation materials in the future. Space reflective thermal insulation coating uses the vacuum cavity layer formed by ceramic spherical hollow particles in the coating to build an effective thermal barrier, which not only has high thermal resistance and low thermal conductivity, but also has high thermal reflectivity, which reduces the absorption of solar radiation heat by buildings and reduces the temperature of the coating surface and internal space, so it is unanimously recognized by experts as one of the high-efficiency energy-saving materials with development prospects.
Nowadays, the global thermal insulation materials are developing towards the integration of high efficiency, energy saving, thin layer, thermal insulation and waterproof external protection. While developing new thermal insulation materials and structural thermal insulation and energy-saving technologies, we should pay more attention to the targeted use of thermal insulation materials, design and construct according to standards and specifications, and strive to improve thermal insulation efficiency and reduce costs. Research on thin-layer thermal insulation coatings has been carried out at home and abroad, and many companies in the United States have produced such thermal insulation coatings, such as SPM Thermo-Shield of the United States, Ceramic-Cover of thermal protection system, Therma-Cover of J.H.International and other products. This kind of space insulation porcelain layer is developed according to the working principle of NASA to control the heat conduction of the space shuttle. Suitable for high-pressure spraying, pollution-free, with good thermal radiation resistance, thin-layer heat insulation, waterproof and corrosion resistance. Previously, this material has turned to general industrial and civil insulation. Many domestic enterprises are developing such materials, such as thin-layer heat-insulating reflective coatings, solar heat-reflecting thermal insulation coatings, water-based reflective thermal insulation coatings, sun-insulating coatings and ceramic thermal insulation coatings. It mainly adopts film-forming materials with good weather resistance, strong water resistance, strong aging resistance, strong adhesion and elasticity, and good compatibility with thermal insulation fillers and reflective fillers, and selects fillers with light weight, high temperature resistance, high heat resistance, good reflectivity and radiation. Ultra-fine powder has high refractive index, high surface finish, high thermal reflectivity and radiation, which is suitable as a reflective filler and forms a low radiation heat transfer layer with film-forming substrate, which can effectively insulate heat. This thin-layer heat insulation reflective coating can be used in buildings, vehicles, ships, petrochemical oil tank equipment, grain depots, cold storage, containers, pipelines and other different places. Broadly speaking, the application field and scope of plate insulation materials are very wide, which can be used for both external wall insulation engineering and internal wall insulation engineering. The insulation body of the board insulation material can be different materials such as foamed polystyrene board, extruded polystyrene board, rock wool board, glass wool board, VIVA wood wool cement board, FOREX Meiyan cement board, etc. Board insulation materials can be divided into single insulation materials and system insulation materials, and the following problems should be paid attention to in the application process:
(a) a single thermal insulation material is the main body of thermal insulation engineering application, and it needs the cooperation of other materials in the process of use. Such as: foamed polystyrene board, extruded polystyrene board, rock wool board, glass wool board, etc. , the following test contents should be tested before use:
1, thermal conductivity (W/m? K): This technical index is the key index related to the thermal insulation effect of the project. Generally speaking, the laboratory test is carried out when the plate is dried to a constant weight, and the application of the material is used under the condition that the air contains a certain humidity, so it should be multiplied by a certain coefficient; Or, directly adjust the material to the use environment for testing.
2. Apparent density (Kg/m3): The apparent density of a material affects its thermal conductivity to a certain extent. Unqualified apparent density will directly lead to the decline of its physical properties, such as strength and dimensional stability.
3. Compressive strength (MPa): refers to the compressive stress of the sample under 10% deformation. It is related to the durability and impact resistance of the surface system.
4. Size change rate (mm): The material with large size change rate will cause the surface layer of the system to crack.
5, water vapor permeability coefficient [ng/ (Pa? m？ S)]: This property determines the permeability to water vapor, and also determines whether the wall is dewy to some extent.
6. Oxygen index: flame retardant type is required, otherwise the fire protection cannot meet the standard. System insulation material refers to a system composed of a single insulation material and other auxiliary materials, which is called system insulation material. The insulation materials of the existing system are as follows:
1. External wall insulation system: foamed polystyrene board (or extruded polystyrene board)+alkali-resistant glass fiber net+polymer mortar containing glue, such as Tewitt external wall insulation system, Beijing Zhongjianyuan external wall insulation system and Prewitt insulation system.
Test items of external thermal insulation system:
A, heat transfer coefficient:
The thermal insulation effect of composite system thermal insulation material and main structure is affected by construction quality and environmental temperature and humidity, and it needs field test to master its actual effect. According to the Code for Thermal Design of Civil Buildings (JGJ 26-95) and local rules, it shall not be lower than its limit;
B, waterproof, freeze-thaw, weather resistance, impact resistance, wind pressure resistance: as the external insulation of the external wall, its facing must resist the attack of unfavorable factors such as rain, freeze-thaw, impact and strong wind.
The tensile strength of alkali-resistant glass fiber grid cloth matched with external thermal insulation system of external wall should be greater than 200N/cm, and the residual tensile strength after alkali resistance should be not less than150 ≥ N/cm; The 7-day tensile bond strength of the adhesive should be greater than 65438±0 Mpa, and the tensile bond strength after water resistance and freeze-thaw resistance should be greater than 0.9Mpa.
2. Internal thermal insulation system: foamed polystyrene board (or extruded polystyrene board)+gypsum board; GRC insulation board (sintered polystyrene board and cement mortar composite); Rock wool sandwich insulation board; Reinforced cement polystyrene insulation board, etc. Slurry thermal insulation materials are mainly used for internal thermal insulation of external walls, and can also be used for insulation of partition walls and household walls, and can also be used for external thermal insulation of external walls when performance permits. There are two kinds of slurry, one is the solidified type based on cementitious materials, and the other is the dry type based on water evaporation. Its main component is a light thermal insulation material composed of sepiolite (polystyrene particles), mineral fiber and silicate, which is compounded by a certain production process. Its products are powder and paste (paste), but they are all applied to the foundation when used. Pay attention to the following test data when using:
(1) Used for internal insulation and partition wall: thermal conductivity, apparent density, volume shrinkage, bonding strength, softening coefficient, asbestos content, water vapor permeability coefficient, water absorption, oxygen index, etc.
(2) Thermal conductivity, apparent density, volume shrinkage, bond strength, hydrophobicity, asbestos content, softening coefficient, water absorption, fire resistance, etc. The materials used for external thermal insulation should be tested, and the thermal insulation of the system should also be tested.
Both plate insulation materials and slurry insulation materials have their own characteristics. As long as we adapt to their characteristics, we can give full play to their advantages and play a multiplier role in building energy conservation. Fire protection: tested by the National Fire-resistant Building Materials Quality Supervision and Inspection Center, it is flame-retardant (B 1 grade), which meets the national standard GB8624- 1997.
Shockproof: PEVA high foaming material is used as the material, and the insulation board and pipe are soft and elastic, achieving good shockproof effect.
Thermal insulation: it has fine independent bubble structure, no air convection and thermal conductivity < 0. 0325 W/MK. 。
Sound insulation: it has an independent fine air chamber with strong sound insulation and can be used in projects that need noise reduction.
Temperature: In the environment of +89℃ and -60℃, the material will not change, which is suitable for cold preservation of various refrigeration projects.
Waterproof: the material is PEVA rubber-plastic sealed bubble structure, and each air chamber is in a closed state.
Anticorrosion: This substance is a high molecular polymer, which can completely prevent the corrosion of acid, alkali and salt.
Processing: easy to cut, easy to bond, soft and elastic, especially easy to install and apply. Rock wool thermal insulation felt is made of basalt and other natural minerals as the main raw materials, which are melted into fibers at high temperature and added with appropriate amount of binder. This product is suitable for the insulation of storage tanks, containers and large-diameter pipelines.
Rock wool thermal insulation felt has excellent thermal insulation performance, convenient construction and installation, remarkable energy-saving effect and high cost performance.
Rock wool thermal insulation felt is a kind of high-quality thermal insulation material with low thermal conductivity. Suitable for large and medium-sized pipelines; Small and medium-sized storage tanks, curved or irregular surface equipment with small surface curvature radius, heat preservation and dew prevention of air conditioning pipes in buildings, sound absorption and heat preservation of walls.
In the design and construction, attention should be paid to the fixation and support of thermal insulation materials. If the insulation layer is more than 80 mm, it is recommended to use double insulation to reduce the heat loss at the joints. Because of the high thermal conductivity of water, the thermal conductivity of water will increase greatly after it enters rock wool products. Therefore, it is necessary to prevent moisture from entering rock wool products in design and construction.