Fund project: Key research project of Shanghai Municipal Education Commission (No. 04FA01) Vacuum insulation board (Vacuum super insulation material. Because of its low thermal conductivity, so when the same thermal insulation technology requirements, with insulation thickness thin, volume The advantages of small size and light weight are applicable to occasions with high requirements for energy saving and requiring small volume and light weight of insulation materials, which are of great technical and economical significance.At present, the thermal conductivity of general insulation materials is about 0.03W/mK, and the thermal conductivity of VIP is about It is about 0.004W/mK and its thickness is about 20mm. With the advent of the energy crisis, the development of the chemical industry and the advancement of vacuum insulation technology, the application scope of VIP has become wider and wider, and it has been applied to refrigerators, cold storage, refrigerated containers, Medical incubators and other fields such as aerospace, transportation, food industry, and various incubators, etc. Therefore, if we can seize the opportunity and successfully develop a super-thermal resistance VIP, it is of great significance to open up the domestic market of thermal insulation industry. The appearance of the VIP is as shown.
2 Production of vacuum insulation panels 2.1 Production process The production of vacuum insulation panels mainly includes the following procedures: production of heat-insulating core plates, including getters, heat-resisting materials, etc.; production of outer metal plates; placement of the core plates on two metal plates The metal plate edge is welded to form a closed chamber, a metal plate has a suction hole; the closed cavity is evacuated through the suction hole, and a heat insulation material is attached to one side or both sides of the sealing suction insulation plate; A plurality of such heat insulation panels are connected to form a cabinet.
2.2 Selection of main technical parameters and production materials Selection of core materials and additives. VIP is mainly composed of three parts: Insulating material, gas getter, and closed barrier.
The insulation of the core is generally a porous material such as powdered silica, aerogels and open-cell foams. Its role is to support firstly, to avoid shrinkage and collapse of the external closed film under vacuum conditions; secondly, to prevent thermal radiation; thirdly, it is a multi-voided material with a small contact surface and low heat conduction.
The role of adsorbent is extremely important. The insulation of VIP is due to its high degree of vacuum. However, during the production process, a small amount of air enters the VIP when it is sealed after evacuation; during the use of the VIP, a small amount of the body enters the VIP through the gas barrier structure; the core material in the VIP is in use. It also releases some gas. These gases include nitrogen, oxygen, water vapor, hydrogen, carbon dioxide, and the like.
Special adsorbents must be used to adsorb these gases in order to maintain a high degree of vacuum within the VIP.
The gas barrier structure is used to seal the core material and create a high vacuum space after evacuation. This structure not only maintains the low thermal conductivity of the vacuum, but also solves the problems of thermal radiation and atmospheric pressure experienced by the core material. Some gas-barrier structures use thin steel plates, some use metal-containing films, and some use multi-layer polyester-based films.
The design parameters and material selection requirements of some core structures are briefly described as follows: 8 is a glass fiber layer, which is formed by pressing multiple layers of glass fibers. Gas substances can penetrate and solid substances cannot pass through and have a certain strength. Although glass fiber has a good thermal resistance, it mainly plays a supporting role in the core layer. The intermediate layer 9 is a heat-insulating layer, and mainly functions as a heat-resisting layer. Generally, it is made of activated carbon, carbon black, silica gel, or a mixture of activated carbon and silica gel particles, and a getter or the like is generally added thereto. If the material of the thermal resistance layer is carbon black or activated carbon, the diameter of the particles is generally selected as 0.41.0 micron, and the density after compression is 1625 pounds per cubic foot; if the material of the core layer is silica gel, the particle diameter is selected as 1.010 At .0 micron, the density after compression is 612 pounds per cubic foot. Silica gel has better adsorption, and the thermal resistance effect of activated carbon is also better, so a mixture of two substances can be used as the core material, and mixed in a certain proportion. The density after compression is 12 to 18 pounds per cubic foot. . The thickness of the intermediate heat-insulating layer is generally selected to be 1/5 to 1/50 of the total thickness of the core layer. Although the thickness of the intermediate layer is thicker, the heat insulation effect is better.
However, too thick will affect the structural strength of the insulation board.
Sectional view of the VIP core section The outer sheet metal material can be cast iron or stainless steel. Usually two metal plates can be made into a disk-shaped structure; it is also possible to make one piece of flat, one piece of plate-shaped, as shown. Vent holes are made on a flat metal plate. The thickness of the metal plate is generally 0.002 inches and 0.013 inches. After a large number of foreign countries) itself is a multi-void material, the contact area is small, and the heat transfer coefficient is low, and the manufacturing principle thereof is as shown in the figure.* The device can be made into the required size and shape, and there is a device 14 below. A vacuum hole 11. In the production, put a layer of glass fiber paper above the hole 11. General device 14 is made of rectangular shape (of course, can also be made of other shapes as needed), size ratio than outside The layer metal plate is slightly smaller. The particulate material 12 to be compressed (the desired mass of a mixture of silica gel and activated carbon, the mass of the mixture depending on the size and density of the selected core layer) is placed therein. A vacuum is then drawn through the hole 11 in order to create a certain negative pressure in the chamber and aid in the compression of the particles. The plate 13 is pressed down (heavier weight above, also piston) to provide some downward pressure until the particles are compressed to the desired size and density.
In order to control the manufacturing accuracy of the VIP, the device 14 suggests the use of numerical control.
2.3.3 Fabrication of Metal Sheets Most manufacturers of VIPs currently use a flat plate and a disk-shaped structure. The shape of the metal plate is generally stamped, leaving a suction hole in the center of one side of the flat metal plate.
In the process of manufacturing the VIP, an air extraction hole 15 is externally connected to the air extraction pipe 16. In order to improve the sealing performance during the air extraction, the extraction pipe is often welded to the metal plate. The material of the exhaust pipe is usually copper or copper-zinc alloy.
The overall production process of the 3VIP VIP is as follows (see ). The glass fiber layer 8, the intermediate heat insulating layer 9, and the glass fiber layer 7 are placed in the disk-shaped metal plate 3. Care must be taken during placement to prevent particles from remaining on the edge of the metal plate 3, especially where soldering is required. Because the presence of these fine particles will affect the welding effect of the metal plates 3, 4, it will also affect the vacuum degree of the VIP, deteriorate the insulation effect of the VIP, and shorten the service life.
The dimensions of the glass fiber layers 7 and 8 are slightly larger than the dimensions of the intermediate insulating layer 9, this design avoids direct contact of the insulating layer with the metal wall surface, reduces heat transfer, and increases the thermal resistance of the VIP.
After all the material of the core layer is placed in the metal plate 3, the metal plate 4 with the suction hole and the exhaust pipe welded is placed on the metal plate 3.
In order to avoid the subsequent evacuation process, the particles are sucked into the air extraction duct 16 , resulting in clogging of the air extraction duct. Therefore, some protective barriers must be provided at the suction hole. See, 19 is a layer of mesh structure of the barrier, it needs to have a certain strength, good air permeability, mesh size should be smaller than the diameter of the particles, the best choice of metal mesh; 18 is a layer of glass fiber, the role and 19 are the same; 17 A layer of silicate, clinging to the side of 18, is used to fix this layer of glass fiber. Even under high temperature conditions, the silicate does not release gas and deteriorate the operating conditions of the VIP. The core material of VIP should try to avoid those materials that may release gas during high temperature or vacuum. Because in spite of adding the getter in the VIP, once the gas material is released, the vacuum degree of the VIP is difficult to protect, which affects its service life.
Solder the edge of the metal plate. There is no special requirement for the welding process, as long as the edge of the plate is welded well, and the sealing effect can be guaranteed. Since the metal is relatively thin, the welding process may deform the metal plate. Therefore, it is recommended that the edges be welded together. The welding method may be resistance seam welding, laser welding, and the like.
Vacuum. After the metal plate is welded, the VIP is heated to 650*F~750*F, and after the plate is kept at this temperature for two hours, the vacuum is drawn and the pressure in the plate is pumped below l3torr. After pumping off the vacuum, the way to seal the suction tube 16 can be varied, or it can be stuffed or pinched or bent, as long as the sealing effect is ensured. Then let the VIP cool naturally.
VIP has at least one side of additional thermal insulation material, ie, Medium 5, which is generally selected as polyurethane foam. The thermal insulation material is attached to the thermal insulation board by means of foaming. Three types are described here.
(a) is better, goes through, and (a) is the profile of VIP.
(b) Snap together two vacuum insulation panels and bond them with adhesive. In order to enhance the thermal resistance, VIP has filling material 5 (polyurethane foam material) on both sides. When connecting multiple pieces of VIP, it can be made into a required insulation wall surface and can be further used to make a box wall surface.
VIP connection method (2) 5 temperature rise comparative test Composite panel refrigerated container body of VIP board and polyurethane foam board Compared with refrigerated container body of polyurethane foam board, 9.3 tons of frozen chicken is loaded for 12 hours, two kinds of cabinets are lost. The difference in heat is 9300kJ. The temperature rise in both cases is compared with 0. Time/h 0 The initial freezing rate of chicken is 0% Comparison of the effect of polyurethane plate and VIP composite plate on the temperature rise in the cabinet 6 Conclusion Consider the economics and practicability of the production of VIP In the production of VIP, we should strive to achieve low overall thermal conductivity, long life, simple manufacturing process and good economy.
VIP board is 5.2 times higher than the traditional polyurethane board insulation performance, suitable for the production of ship refrigerated container box and so on. VIP has a broad market prospect.
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