Pre-stressing is through certain technical means, in order to offset the stress received by the structure during service and improve the load bearing capacity of the structure, a reverse stress is applied and maintained for a long time before the structure is put into service. Typical application examples include prefabricated PC bridges, PC floor slabs, sleepers, electric poles, PCCP pipes, curtain walls with cables, pre-stressed steel beams, nuclear containment, rock and soil anchoring, etc. The traditional Chinese barrel hoop is actually one The application of a kind of prestressing technology.
Here PC is the meaning of prestressed concrete, and the abbreviation for non-prestressed concrete is RC.
When the material maintains the tensile stress for a long time, the phenomenon that the stress gradually decreases is called stress relaxation. The ratio of this loss to the initial stress is the stress relaxation rate. Special processing can improve this characteristic and achieve a lower relaxation rate. This is the basic meaning of the concept of low relaxation.
For prestressed steel strands, the standard stress relaxation test condition is 20 degrees, the initial stress is 70% of the nominal maximum force (60% and 80% are rarely used), and the low relaxation level must meet the 1000 hour stress relaxation rate not greater than 2.5 % Requirements, this indicator of ordinary relaxation is 8%, in fact, the long-term relaxation difference is greater than this.
Aluminum Clad Steel Wire
Aluminum clad steel wire is a kind of composite metal wire produced by warm extrusion. The clean steel core during extrusion is preheated and then heated to the extrusion die cavity. The clean aluminum rod with higher purity is extruded into the die cavity, and the hot steel core is wrapped in a high-pressure manner to form a firm bond. The aluminum thickness of the aluminum clad steel wire produced by this process can vary widely, from 5% to 25% of the radius, which is not possible with the traditional hot-dip process.
OPGW is the abbreviation of Optical Ground Wire in English, which means optical fiber composite overhead ground wire. It is a cable product that combines the functions of ground wire and optical cable for power transmission systems. The metal wire of this product is generally made of aluminum-clad steel wire, which plays the role of bearing tension and short-circuit current. The optical fiber cable for communication is generally in a stainless steel tube or an aluminum tube.
The lead quenching process is a heat treatment technology commonly used in the global steel wire industry for the production of high-quality steel wires. The process is to quench the austenitized steel wire in a lead liquid of about 500 degrees, using the high heat capacity and thermal shock characteristics of lead. Close to the process of isothermal transformation, a fine pearlite structure suitable for deep drawing and ensuring the performance of the final product is produced.
This fine pearlite structure is also called sorbite. The structure is a bit like a waffle. Cementite sheets and ferrite sheets are superimposed on each other, forming a large number of fibrous structures during the deep drawing process, and the direction tends to Same as the axis of the steel wire, the microstructure size can reach nanometer level.
The steel wire produced by this process has better fatigue resistance than the steel wire drawn directly with the wire rod, and the processing performance and the toughness of the final product are better.
Although the lead quenching production line can be designed and maintained well to ensure that the working environment meets the specified requirements, there are still companies working hard to develop cleaner technologies, and there are a few applications.