Steel flash butt welding
1 scope
This technology is applicable to industrial
and civil buildings of hot-rolled steel continuous Flash welding, preheating
flash butt welding, Flash a preheating flash butt welding.
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 major equipment: welding of welding
machines and related platforms, protective dark glasses, welding gloves, and
insulated footwear, steel bar cutting machines, air compressors, water,
descaling machine or wire brushes, drawing straight lines.
Commonly used welding machine technical
data see table 4-20.
Commonly used welding machine technical
data sheet 4-20
Welding machine type UN1-50 UN1-75 UN1-100
UN2-150 UN17-150-1
Clamp drive lever compression spring
(manually operated) motor cam gas-hydraulic
Rated capacity kVA 50 75 100 150 150
Load rate of 25 20 20 20 50
Power supply voltage v 220/380 220/380 380
380 380
Secondary voltage range v 2.9~5.0 3.52~7.04
4.5~7.6 4.05~8.10 3.8~7.6
Secondary voltage regulator series 6 8 8 16
16
Continuous Flash welding of large-diameter
mm 10~12 steel 12~16 16~20 20~25 20~25
Preheating flash butt welding steel bar
diameter 20~22 32~36 40 40 40
Maximum number of Weldments of 50 75 per
hour 20~30 80 120
Cooling water consumption, l/h 200 200 200
200 600
Compressed air pressure MPa 0.55 0.6
Compressed air consumption m3/h 15 5
2.2 operating conditions:
2.2.1 the welder must have a valid test
certificate.
2.2.2 welding machines and related
equipment, cooling water, compressed air, shall conform to the requirements.
2.2.3 power supply should meet the
requirements when the supply voltage drops greater than 5% is less than 8%, and
shall take appropriate measures to improve the welding transformer series; is
larger than 8%, no welding.
2.2.4 site have safety protection facilities,
fire protection and ventilation measures necessary to prevent the occurrence of
accidents such as burns, electric shock and fire.
2.2.5 familiar material, determine joint
position, technical clarification.
3 operational processes
Process flow:
Welding and inspection equipment → parameters → welding
test, sent simulated specimens → test →
Determining parameters of welding → welding ¡ú quality
inspection
3.1.1 continuous Flash welding process:
→ Flash closed circuit (two minor contact bar end) →
Continuous Flash heated to nearly the
melting point (two steel end slowly moving contact) charged upset → no → electric
upsetting
3.1.2 preheating flash butt welding
process:
→ Closed circuit intermittent flashes Preheat (two steel end
alternate contact and separate) →
Continuous Flash heated to nearly the
melting point (two steel end slowly moving contact) charged upset → no → electric
upsetting
3.1.3 Flash a preheating flash butt welding
process:
→ Flash Flash end faces closed circuit (two minor contact slowly end)
→
Continuous Flash preheater (two steel end
alternate contact and separate) →
Secondary continuous Flash heated to nearly
the melting point (two steel end slowly moving contact) charged upset → no → electric
upsetting
3.2 welding method: when the diameter is
small, less steel, continuous Flash welding can be used. Continuous Flash
welding and the welding of the maximum diameter should meet the requirements of
table 4-21. When the diameter is larger, end-a flat, preheating flash butt
welding should be used when surface is not flat enough, you should use Flash a
preheating flash butt welding.
Continuous Flash welding steel cap diameter
table 4-21
Welding machine capacity (kVA) steel-level
bar diameter (mm)
Class I 25
150-ⅱ level 22
Grade 20
Level 20
100 grade 18
Grade 16
Level 16
75 grade 14
Grade 12
ⅳ steel welding, regardless of size, should take the preheating flash
butt welding or Flash a preheating flash butt welding process.
3.3 welding parameters selection: Flash
butt welding, the rational selection of variable elongation, which amount,
upsetting and welding parameters such as transformers series. Connecting Flash
welding see 4-33 Flash-preheating flash butt welding, see 4-34.
3.4 check power supply, welding machines
and welding platform, the underground placement of insulating rubber pad, such
as cooling water, compressed air, everything must be in a secure and reliable
State.
Figure 4-33 steel continuous Flash welding
,-Adjustable extended length; +-which is
variable; +-upsetting; +-upsetting; +-without electric upsetting
4-34 steel--preheating flash butt welding
,-Adjustable extended length; +-which is
variable; +-the quadratic which is variable; +-preheating allowance;
+-Upset; +-upsetting; +-without electric
upsetting
3.5 prior to welding, the class try in each
class before any welding, should be selecting the welding parameters 6
specimens, of which 3 tensile test, 3 cold bending test. After passing the
test, can determine the mass production of welding parameters.
3.6 the welding operation:
3.6.1 continuous Flash welding: power Hou,
should take rib operation Rod makes two steel end surface minor contact, makes
its produced resistance hot, and makes steel end surface of protruding part
each other melting, and will melting of metal particles to outside Jet formed
fire Flash, again slowly constantly to mobile steel formed continuous Flash,
stay scheduled of which left volume disappeared Hou, to appropriate pressure
quickly for top forged, that completed whole continuous Flash welding.
3.6.2 preheating flash butt welding: power,
should enable the two end alternate contact and separate, intermittent flashes
between steel surface, form which the preheating process. When the preheating
process is complete, should be immediately transferred to the sequence and
upsetting.
3.6.3--preheating flash butt welding: the
power, the Flash should be first, when end when formed, shall immediately
proceed to preheat, Flash and forging process.
3.6.4 guarantee the weld joint location and
operation requirements:
3.6.4.1 before welding and the welding
process, check and adjust the electrode position, tighten the clamp screw.
Rebar on the electrode must be clamped, jaw deformation of electrodes should be
replaced and repaired immediately.
3.6.4.2 reinforced ends such as bending or
"Horseshoe" shape shall not be welded must be simmered or removal.
3.6.4.3 bar ends 120mm range of rust,
grease, must be completely removed.
3.6.4.4 during welding, sticking to the
iron oxide on the electrodes must always be clean.
3.6.4.5 close section there should be
proper even upsetting deformation of welded joints, end face should not be
oxidized.
3.6.4.6 welded after slightly cooled in
order to release the electrode tongs, remove the steel must be smooth to avoid
joint bent.
3.7 quality checks: in the production of
steel welding, welders should be carefully performing a self-test, if
eccentric, bend, Burns, cracks and other defects, excision of joint welds and
find out why, to eliminate.
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 the percentage of joint, you
must meet the requirements of specification for design and construction.
Inspection method: observation or standard
checks.
4.1.3 for the mechanical properties of
welded joints testing must be qualified.
Mechanical properties Testing, from each
batch of random cut 6 specimens in the joints, 3 tensile test, bending test of
3.
In the same class, by the same welder complete
with 300 levels, with diameters of welded joints. If fewer welded joints within
the same class, can be accumulated in a week. If the total is still less than
300 joints, shall be calculated according to the number of.
Inspection method: check the weld sample
test report.
4.2 Basic project:
Steel flash butt welded joint inspection
result shall conform to the following requirements:
There shall be no transverse crack in 4.2.1
joint.
4.2.2 electrode contact surface of steel
without obvious Burns ⅳ steel welding shall not be burnt.
Inspection method: Visual check.
4.3 allowable deviation:
4.3.1 joint bending angle of not greater
than 4 °.
4.3.2 the joint axis offset wood than 0.l
times the bar diameter and not more than 2mm.
Inspection method: Visual observation or
measurement.
5 finished product protection
After welding cooling to release the
electrode tongs, remove the steel must be smooth to avoid joint bent.
6 quality problems to be noticed
6.1 in the production of steel welding,
should be attached to any part of the welding process to ensure the welding
quality if there are anomalies, should refer to the table 4-22 to find reasons
to eliminate.
Steel weld anomalies, defects and
prevention measures table 4-22
Anomalies and types of defects prevention
Which is excessively violent, and have a
strong
Explosion 1. Reducing the transformer
series
2. slow burn speed
2
Unstable Flash 1. Clear the level of bottom
and surface oxide
2. transformer series
3. speed up the burn speed
3
Joints in the oxide film, lack of
penetration or slag
1. increasing the preheat level
2. accelerate the pace of which is closer
to the upset
3. ensure that the electric upsetting
process
4. accelerating upsetting rate
5. increased forging
4
Joint shrinkage
1. reduce transformer series
2. avoid burn process too strong
3. appropriate top and increase the amount
of upset forging
5
Burning or heat-affected zone of the weld
metal is overheating
1. reduce the extent warm-up
2. speed up the burning speed, shorter
welding time
3. avoid too much electric upsetting
Continued
Anomalies and types of defects prevention
1. for survey of reinforced carbon, sulfur,
and phosphorus content; if it does not meet the requirements, you should
replace the steel
2. low-frequency Preheat method increasing
the preheat level
1. clean steel by clamping parts of the
rust and oil
2. clean electrode surface of oxides
3. improvement of electrode notch shape,
increasing the contact area
4. clamping bars
8
Joint bending or axial-inclination
1. properly adjust the electrode position
2. trim deformation of electrode jaws or
replace the electrode
3. removal or straightening steel elbows
6.2 cold drawn steel bar welding should be
carried out prior to the drawing. Cold-drawing process, when the connection
breaks, in the removal of heat-affected zone (away from the center of about 0.7
times times the bar diameter) after welding pull, but not more than twice.
Meanwhile, the cold-drawing process and requirements should be consistent with
the code for construction and acceptance of concrete structures (GB50204-92)
requirements.
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.
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 splices in tensile and bending test
report the test report.
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