GPW (Gas pressure welding of rebar) process technology was invented and developed in 1952 with the aim of being used in the rail transport industry. With the expansion of construction and the growth of cities and high-rise buildings, attention to the issue of retrofitting and strength of structures in order to preserve the lives and capital of residents became important, and this process due to the high safety factor and reducing costs entered the field of construction.
Structure Test Steel Engineering Company (STS), GPW welder as the first company in the field of GPW of rebar head, run GPW of rebar and welding services, using experts with experience in the field of civil engineering, Metallurgy, welding and with tact and knowledge of the problems and difficulties in the housing construction industry since 2009 has been working in the field of importing new technologies in the world, including the process of GPW of rebar and connecting the rebar by GPW with the goal was to localize this useful technology in the country and also to increase the strength of the construction industry in the country.
At present, Structure Test Steel Engineering (STS) Company, with 27 executive representatives all over the country and holding courses and seminars and the first GPW conference in Iran, has been able as a specialized and pioneering parent company in the field of import, production and scientific and practical welding training.
List of contents for the gas pressure welding of rebar
· History of GPW (Gas pressure welding) and method of GPW
· What is GPW?
· Introduction video of GPW and process
· Important tips on using GWP of rebar and tips video
· Some of projects done by GPW
History of GPW (Gas pressure welding) and method of GPW
GWP of rebar first developed in the 1930s in the United States and Japan as a subset of the oxytocylene gas welding process called gas pressure welding (GWP). Since then, the rebar head welding method has been widely used, first for welding rails and pipes and then for welding steel rebars.
Further research on this method was conducted in Germany, Russia and Japan. In Japan, most steel rebars are joined and welded by GPW method, which is due to the advantages of GPW method compared to other connection methods in execution. Also in Japan, the GPW Association is established and is led by about 200 contractors and craftsmen related to this industry.
Gas pressure welding of rebar is considered as a solid phase method in which the connection is made without complete melting of the base metal. Due to the lack of an intermediate element for connecting two pieces in this method, this type of welding has good advantages over conventional methods.
In the gas pressure welding method, the end of the rebars is heated by an oxyacetylene burner, which causes the two ends of the rebars to become plastic, at the same time pressing on the two rebars, which are facing each other and inside a retaining clamp is restrained, applied and welded.
In the GPW process, when the temperature reaches 1200-1300 ° C (pastry area), the rebar molecules obtain sufficient activation energy and then the rebar molecules penetrate into the joint season area and combine with each other. A state of molecular bonding is established and recrystallization occurs, which is done by welding the two ends of the rebars.
In this method, the heating time and the amount of pressure applied depend on the diameter of the welded rebars.
It is very important in this method that the end surfaces of the rebars are free of oxide layer, so that the presence of oxide impurities in the weld joint causes the instability of this type of connection. The use of cutting and edging equipment made by cargo of this welding method is mandatory.
What is GPW?
Gas pressure welding (GPW) and gas pressure weld process is a welding process from the sub-branches of oxyacetylene welding, which heat from gas fuel with hydraulic pressure causes intermolecular bonding in the rebar and creates a very strong and secure connection. The strength of this method in terms of metallurgy and welding engineering is the absence of intermediate material such as electrode or welding wire or welding powder and the two pieces are welded to each other without another material, which reduces the effective parameters and ease of welding.
Other strengths are the lack of electricity and the effect of voltage and amps in this process, which makes the gas pressure welding a convenient process. It should be noted that due to the convenience and ease of this welding process, the need for a valid certificate of proficiency in this work is very important. For operators of the gas welding method, there are three levels of training. At the beginning and at the beginning of the work, the rebar welding operator, after passing practical and theoretical trainings in the GPW school and passing the exam, receives 3th grade
With this GPW certificate,Forge Welder s allowed to weld rebars up to size 22, and after at least 3 months of operation and submitting work documents, pictures and videos of his projects, he has participated in the 2th grade test and is also allowed to weld rebars of size 25 and 28. Turns. Finally, after 6 months from the beginning of the work and with the final test, a GPW welder can receive a certificate and certification and also weld size 32 rebars.
In any project, the employer or his representative or the supervising engineer must request a certificate appropriate to the size of the rebars in the project from the forging work and check its validity date. Note that the operator who has the certificate must personally operate perform rebar welding.
Grading table of GWP operators
Certificate rating (grade)
Size of permitted welding rebars
It should be noted that the technology of gas pressure welding of rebar in other countries has also flourished.
Important tips on using GWP of rebar and GWP tips video
Introduction video of GPW and GPW process
Important tips on using GWP of rebar and GWP tips video
Some of projects done by GPW
View all GPW
Rafsanjan Kerman project – welding rebars of columns
Majd Mashhad, residential complex – welding shear walls
Shokre-elahi, Vard Avard project – welding short rebars of shear wall
Shahid Rajai Hospital, Tehran – welding head rebars of columns