Views: 11 Author: Site Editor Publish Time: 2019-06-30 Origin: Site
With the continuous improvement of railway bus technology, we have pay more and more attention to passenger comfort. And the people-oriented philosophy has been fully reflected in all aspects of the design.
China is vast in size, and the trains usually move in trans-regional distance; What is more, the temperature difference between north and south is large. When passenger cars run in the north in winter, the Windows will be covered with thick ice, the melting water will affect the safe use of the electric heater and cause the floor cloth bulge, which will bring inconvenience to passengers. Therefore, we need to develop a new type of window, which help take effective insulation measures to reduce the heat conduction and save energy.
1. Heat insulation
Heat insulation refers to the resistance of the car window to heat transfer from the high temperature side to the low temperature side when there exists air temperature difference on both sides of the car window. The heat transfer coefficient (K value) is used to measure the thermal insulation performance of Windows.
Bus windows account for about 8.4% ~ 12.1% of the whole vehicle surface product. Improving the thermal insulation performance of the Windows and reducing the K value of the Windows can greatly improve the K value of the vehicle. Therefore, it is very necessary to adopt the thermal insulation measures of the vehicle windows. At present, the section diagram of the moving window of 25K car is shown in figure 1.
At present, 25B and 25k Windows of railway passenger cars are made of insulating glass inlaid with rubber strips inside the aluminum frame. Therefore, to solve the problem of window insulation, it is best to start with aluminum products.
2. Thermal insulation materials for building doors and windows
Existing building doors and Windows with heat insulation profile has 2 kinds: PU resin insulation aluminum profile and strip insulation aluminum profile.
2.1 PU resin insulation aluminum profile
PU resin heat insulation aluminum profile has been formed by cleverly combining the high strength of aluminum alloy with the low thermal conductivity of PU resin. The thermal conductivity of PU resin of the perfusion heat insulation material was 0105 W/ (m2·K); The tensile strength and shear strength of insulated aluminum profiles are 70MN/ m2 and 100mn/m2 respectively. Doors and Windows made of wind pressure resistance, water tightness, air tightness can reach level 1; The thermal conductivity was 219 W/ (m2·K) ~ 312 W/ (m2·K). Sound insulation performance is 30 dB ~ 40 dB. Therefore, its various performance indexes can meet the requirements of heat insulation aluminum alloy profile standard.
2.2 Strip insulation aluminum profile
Strip-through heat-insulating aluminum profiles are used to connect two pieces of aluminum profiles through heat-insulating strip-through by means of mechanical processing. The connected heat-insulating strips play the role of cutting off the thermal bridge. At present, the main materials of heat insulation strip are nylon (PA66+ GF) and PVC. See table 1 for the performance comparison of the two insulation strips.
From the comparison of the performance of insulation strips of two different materials, the physical and mechanical properties of nylon strips are much higher than those of PVC strips. Nylon (PA66 + GF) thermal insulation strip material is basically used in the production of high strength thermal insulation aluminum window products at home and abroad. The physical and mechanical properties of the strip-through-insulated aluminum profiles are as follows: tensile strength is not less than 12 MN/ m2, and shear strength is not less than 24 MN/ m2. The doors and Windows can withstand wind pressure up to level 1. Water tightness and air tightness can reach grade 2; The thermal conductivity is 3W/ (m2·K) ~ 315w/(m2·K). Sound insulation performance 30 dB ~ 35 dB. Therefore, its various performance indexes can meet the standard requirements of heat insulation aluminum alloy profiles.
3. Difficulties in the application of thermal insulation profiles in railway passenger car Windows
(1) Heat insulation profiles have been widely used in buildings, most of them are right-angle butt joint or large arc connection, but they are blank in the manufacture of passenger car Windows. The profile of window frame of passenger car shall be simmered into arc below R118 mm. In recent years, attempts have been made to make the outer frame of passenger car Windows with strip of aluminum extrusions (see figure 2). Due to the difference in physical properties between the heat insulation strip and aluminum extrusions, the heat insulation layer broke at the rounded corner after bending, and the test was not successful.
figure 2 the outer frame of passenger car Windows with strip of aluminum extrusions
(2) The position of slot drilling in heat insulation profile is limited by the position of heat insulation layer.
(3) It is difficult to weld the window frame with heat insulation profile. The heat insulation layer will be destroyed in the welding process. Only butt structure can be used.
(4) The processing technology of PU resin insulated aluminum profiles and strip insulated aluminum profiles is complex, difficult, and requires high dimensional accuracy and high manufacturing cost.
If the heat insulation profile is used in the manufacture of railway passenger car Windows, the material of the heat insulation layer should be further improved to make its physical and mechanical properties meet the requirements of the manufacture of passenger car Windows. In addition, the overall structure of the Windows needs to be improved and redesigned in combination with the insulation profile.
4. Some Suggestions on improving the thermal insulation performance of railway passenger car Windows
(1) Heat insulation material is added between the profiles inside and outside the passenger car window. In order to reduce heat transfer, the thickness of heat insulation pad can be increased. The material with low thermal conductivity is selected to reduce the number of self-tapping screws.
(2) The aluminum frame of the car window is in the thickness of the side wall of the car body. The exposed profile surface is sprayed with anti-corrosion and heat insulation damping slurry with a thickness of 2 mm, which can not only play a role in heat insulation, but also prevent the radiation of external noise.
(3) Soft engineering plastic is used to cover the exposed profile in the passenger room to avoid frost on the aluminum frame of the passenger window.
(4) The surface of the aluminum frame of the car window is treated by spraying, and the coating thickness reaches more than 60 microns, which can also play a certain role in heat insulation.
The above methods are effective ways to improve the thermal insulation of passenger car Windows, but the following measures are needed to solve the thermal insulation problem of passenger car Windows fundamentally:
(1)Cars running in the north add heat tracing devices.
(2)Combined with the heat insulation profiles for building, the heat insulation profiles suitable for the manufacture of railway passenger car Windows are developed.
(3)To develop a plastic profile with a thickness of about 2 mm on the surface of aluminum profile, as long as there are no cracks, wrinkles and other defects after bending, and the exposed surface is smooth and continuous, this material will be able to replace the existing aluminum profile for the manufacturing of car Windows.
To sum up, from the perspective of economy and energy saving, it is very feasible to develop thermal insulation profile and plastic composite aluminum profile.