Ptfe has a cold flow. That is, the plastic deformation (creep) of material products under continuous load for a long time, which brings some limitations to its application. For example, when PTFE is used as a gasket, the bolts are screwed so tightly that they exceed the specified compression stress, causing the gasket to cool (creep) and be flattened. These shortcomings can be overcome by adding appropriate packing and improving the structure of parts. PTFE has outstanding non-viscosity, which limits its industrial application. It is an excellent anti-adhesion material, which makes it very difficult to adhere to the surface of other objects. PTFE's linear expansion coefficient is 10~20 times that of steel, which is larger than most plastics. PTFE's linear expansion coefficient changes irregularly with the change of temperature.
When applying PTFE, it's easy to lose out if you don't pay enough attention to this aspect of performance. The longitudinal axis of teflon t-beam should coincide with the center line of the support. The longitudinal axes of the plate beam and box beam should be parallel to the center line of the support. To fall beam accurate, in the frame the first span plate beam or box beam, can be in the beam bottom row of the cross position center line of two supports, parallel, level off to make it all stick closely with the rubber support below, avoid bias, empty, the occurrence of uneven support.
The construction sequence is as follows:
1. First according to cast-in-situ beam 1 treatment of support pad stone.
2. The bottom plane of the prefabricated beam in contact with the support shall be horizontal and flat. If there is a honeycomb or inclination should be pre - ramming cement mortar, leveling.
3. Correct placement of rubber bearings. According to cast-in-place beam 2 will be the rubber support on the pad stone according to the design center position. Mark the center line of two supports on the elevation of beam end. Fall beam when be identical with the position Central Line photograph on pier. After the number of spans can be based on the first span beam fall beam.
4. The beam shall be stable when falling, to prevent eccentric bearing compression or initial shear deformation.
5. When placing T beam supports, if the supports are wider than beam ribs, a reinforced concrete pad or thick steel plate slightly larger than the supports should be added between the supports and the bottom of the beam for transition, so as to avoid partial overload and stress concentration of rubber supports. The reinforced concrete pad or steel plate shall be bonded to the beam bottom with epoxy resin mortar.
6. In general, the top surface of the rubber bearing should be kept level after the installation of falling beam. Prestressed simply supported beams, the top surface of which can be slightly tilted backward; The top surface of the support of a non-prestressed simply supported beam may lean forward slightly, but the inclination Angle shall not exceed 5 'when the rubber support is installed.
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