Bar gas pressure welding
1 scope
This technology is applicable for
industrial and civil reinforced concrete structure ⅰ of 14~40mm
diameter grade ⅲ steel bar in a vertical position, horizontal or inclined position
of the docking connection. When the two steel bar diameter is not the same as
pressure welding can also be used, but the difference between two diameter not
greater than 7mm.
2 construction preparation
2.1 materials and equipment;
2.1.1 steel: steel grade, diameter must
conform to the design requirements, certificate and retest report of the
factory. Import steel chemical retest should also form, its chemical
composition requirements should be met, and solderability testing.
2.1.2 oxygen (O2): gas pressure welding
using oxygen purity above 99.5% and quality GB3863 of class ⅰ and class ⅱ level in
technical requirements.
2.1.3 acetylene (C2H2): best to use bottled
dissolved acetylene, shall comply with the quality requirements of GB6819. Its
purity must be above 98%, phosphine concentration not greater than 0. 6%,
hydrogen sulfide content shall not be greater than 0. L%, moisture content of
not greater than 1L/m3, acetone content should be not more than 45g/M3. When
used directly in the production of acetylene acetylene generator, using calcium
carbide must conform to the provisions of the relevant standards of quality
premium grade or grade requirements.
2.1.4 main equipment:
2.1.4.1 supplying unit: includes dissolved
oxygen cylinder, acetylene cylinder (or pressure acetylene generator), tempered
to prevent dry, regulator and hose. Dissolved acetylene oxygen tanks and gas
cylinders used shall comply with the relevant provisions of the State.
Cylinders for dissolved acetylene gas supply must meet the requirements of
maximum diameter of reinforcing bar welding supply, if it is no longer enough,
multiple parallel use of the bottle.
2.1. more than 4.2 mouth pipe heaters:
oxy-acetylene mixing chamber of gas heater gas consumption needs should be met,
talkative ring tube heaters shall be equipped with a variety of specifications
of the heating coil in order to meet the needs of different diameter bars
welded, multiple flame should burn evenly, easy to adjust the flame.
2.1.4.3 pressure: the pressure capacity
needed to achieve maximum diameter welded axial pressure.
2.1.4.4 welding fixture: should ensure that
the clamping bar, and when the steel under axial pressure, no relative slip
between the bars and chucks; should be accessible to the location and
installation of the steel, and to maintain sufficient rigidity in the welding
process; Chuck and Chuck should be concentric, and when welding of different
diameter bars, and should remain one.
2.2 operating conditions:
2.2.1 the welder qualification test of
welders must hold a valid certificate.
2.2.2 equipment and gas supply should meet
the requirements.
2.2.3 when steel pressure welding in the
field, when the wind speed exceeds 5.4m/s, measures should be taken from the
wind; in construction at negative temperature, insulation freezing on gas
source device shall take appropriate measures when the air temperature is
below-15 c, should develop a preheating and heat insulation joints, slow
cooling measures.
2.2.4 site safety measures, formulation and
implementation of safety measures, strengthen the welder's protection to
prevent the occurrence of accidents such as burns, fire, explosion and damage.
2.2.5 Note header location, pay attention
to the same percentage of the sector in the joint area of steel, not in line
with the concrete structure construction and acceptance specification of the
relevant provisions of the regulations, to resize the header location before
welding.
3 operational processes
3.1 process:
Check equipment, gas bar end preparation
source →
→ → welding
fixture for installation of concrete and steel welding test, specimens →
Welding → → remove fixture
quality checks
3.2 checking equipment, air supply, to
ensure that in the normal state.
3.3 bar end preparation: end should be
tangent, and with bars perpendicular to the axis; in the end part twice times
the diameter range, if any attachments such as cement, should be removed. Reinforced
edge burrs and end face of rust, greasy dirt and oxide film should be cleaned
and polished, its exposed metal luster, no oxidation.
3.4 installation of welding fixtures and
steel: when you install the welding fixtures and steel, two bars, one clamp should
be, and the two axis of the bar on the same line. Steel installation pressure
after pushing, local gap between the two bars must not be greater than 3mm.
3.5 welding test, specimen: project for the
official prior to welding, gas pressure welding technology of steel bar test
under the field conditions. To verify that the pressure welder's skill, confirm
the solderability of reinforcement on site, and select the best welding
technology. Test of steel captured from in the entry bar. Each batch of welded steel
6 joints, after passing the Visual inspection, 3 tensile tests, bending
experiment of 3. After passing the test, press OK for gas pressure welding
technology.
3.6 bar gas pressure welding, should be
selected according to specific conditions such as diameter and welding
equipment such as pressure, secondary compression or pressure method of welding
process times. In two reinforced slot key and upsetting, axial pressure of
reinforcement, steel cross sectional area, should be 30~40MPa. Axial pressure in
order to ensure the reinforcement value should be under pressure type, by
diameter size, converted to oil pressure gauge reading in advance and written
signs for accurate control.
Gas pressure welding of steel bar 3.7 start
flame carbide should be adopted, at the two reinforced seams of heating, and
inner flame around the gap, preventing end surface oxidation.
After the confirmation of two reinforced
the gap completely closed instead you neutral flame, to the welding surface is
the Center, on each side 1 time times the bar diameter length range wide heated
back and forth.
End the proper temperature should be
1150~1250℃; upsetting district heating temperature on the surface of bars
should be slightly higher than the temperature and temperature gradient with the
diameter size difference may be.
3.8 in the steel bar gas pressure welding,
by the end of the heat and pressure, should make the appropriate shape of the
upsetting forming of joint provisions; then stops heating, slightly delayed,
remove pressure remove welding fixture.
3.9 in the heating process, if in the
reinforced end of the gap is completely closed before the fire break,
reinforcement should be removing back grinding, Setup, and then weld the
kindling of a flame. If at the end after the gap completely closed, continue
heating, welding job has completed.
3.10 quality checks; in production of
welding the welder should be carefully checked, if eccentric, bending,
upsetting the diameter and the length is not enough, the bonding surface
offset, circumferential crack, steel bars was seriously burned, joint burning
metal, no quality defect such as weld, excision of joint welds, and find out
why a timely elimination.
4 quality criteria
4.1 project:
4.1.1 steel variety and quality must comply
with the design requirements and the provisions of the relevant standard.
Note: imported rebar should first undergo
chemical testing, welding, comply with the relevant requirements before they
can weld.
Inspection method: check the factory
certificate and test report.
4.1.2 of welded joints of steel
specifications, location, within the same section of a joint bar area
percentage, you must meet the requirements of specification for design and
construction.
Inspection method: observation or standard
checks.
4.1.3 mechanical properties of gas pressure
welded joint of testing must be qualified.
Mechanical property testing and cut
randomly from each connector 3 connector test. According to project needs, can
also cut the 3 connectors for bending test.
4.1.3.1 the general structure, 200
connectors for a group.
4.1.3.2 in situ reinforced concrete in
structures of houses, 200 connectors in the same floor as a group of; still
less than 200 joint as a batch.
Inspection method: check the weld sample
test report.
4.2 Basic project:
Steel bar gas pressure welding should be
carried out by a Visual inspection result shall conform to the following
requirements:
4.2.1 eccentric weight shall not be greater
than 0.15 times times the bar diameter, and may not be larger than 4mm when
different diameter steel welding, calculated according to the smaller diameter,
when the limit is exceeded, removal of welding.
4.2.22 steel axis bending angle not greater
than 4 °. When the limit is exceeded, it should be reheated to correct.
4.2.3 upsetting diameter should be not less
than 1.4 times the diameter of steel, if smaller than this limit, should be
heated again upsetting.
4.2.4 upsetting length should not be less
than 1.2 times times the bar diameter, and the raised portion should be gently
rounded. If smaller than this limit, should be reheated long heading.
4.2.5 welding surface deviation shall not
be greater than 0.2 times times the bar diameter.
4.2.6 joints without transverse cracking,
if found to have this crack, removal of welding.
4.2.7 upsetting surface must not have
serious burns.
Inspection method: Visual observation or
measurement.
5 finished product protection
Welded, must be a little pause before you
can remove the fixture to avoid joint bent.
6 quality problems to be noticed
6.1 in the production of steel bar gas
pressure welding, should be attached to any part of the welding process.
Reinforced face to cut the flat and perpendicular to the axis; polished gloss,
free oxidation; steel installation unity, clamp fastening to prevent shaking;
heat to moderate, and pressure should be appropriate. If abnormal, should refer
to the table 4-19 to find reasons to eliminate.
6.2 gas pressure welding can be carried out
at the negative temperature conditions, but when the ambient temperature is
below-20 c. Not suitable for welding.
On rainy days, snowy days should not be a
weld, when you have to weld, effectively shielding measures should be taken.
Not cooling after welding joints, encountered snow and ice should be avoided.
7 quality records
This standard shall meet the following
quality records:
Steel quality certificate or test report
7.1.
7.2 mechanical properties of reinforced
reexamination report.
Bars gas pressure weld welding defects and
prevention measures in table 4-19
Welding defects prevention
Axis offset
(Eccentric)
1. welding jigs two Chuck not properly
aligned
2. the surface joining the bar tilt
3. steel bar do not clamp for welding
4. welding jigs demolition early 1.
Checking fixture, repaired or replaced
2. the tangent end surface
3. the clamping bar again
4. remove half a minute after removal
fixture
2
Bend
1. welding jigs two Chuck not properly
aligned
2. the surface joining the bar tilt
3. welding jigs demolition early 1.
Checking fixture, repaired or replaced
2. the tangent end
3. turn off half a minute after removal
fixture
1. effective stroke welding fixture Chuck
enough
2. top cylinder enough effective stroke
3. heating temperature is not enough
4. insufficient pressure
1. heat range is not wide enough
2. too much pressure too fast 1. Increased
heating range
2. Pressure should be stable
Welding surface offset
Steel head heating on both ends is
inappropriate
1. diameter bars heated on both ends should
be symmetrical
2. different diameter bars heated, large
diameter steel
Bar heating time slightly longer
1. heating temperature too high
2. steel bar, carbon and other elements too
high 1. Lower heating temperature
2. check the chemical composition of steel
1. fire power is too high
2. the heating time is too long
3. uneven heater oscillating
1. insufficient heating or heat
distribution does not apply
2. pressure is too small
3. the joint face dirty
4. surface oxide
5. improper midway without fire or flame
Reasonable selection of welding parameters,
master operation
7.3 import steel chemical composition and
solderability test report the test report. Made in steel in the process of
brittle fault, poor weldability and mechanical properties significantly
abnormal, chemical composition inspection report.
7.4 tensile test for steel joint report.
7.5 If the project needs, bending test for
reinforced joint report.
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