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A No Skill,
Nil Visibility Welding System
Speciality Enterprises (T/A weldcraftpro) has developed solutions to the long-standing problems associated with underwater wet welding and in particular the skills required to produce high quality welds in poor and/or nil visibility. The new system, which has been named HammerheacFM in keeping with the companies 'fish' brands, addresses problems in obtaining high quality wet welds in nil visibility, without the need for experienced (skilled) welder-divers.
Wet-Spot welding System:
By removing the individual welding skills from the operation theres no need for the diver to control parameters that affect quality, such as travel speed, electrode angle, arc length, arc deposition, etc. Because the operator no longer needs to control these parameters, its not essential to have good visability. So, even in nil visibility conditions, high quality repeatable welds can be produced time after time.
How the system works:
In removing the skills necessary to carry out underÂwater wet welding, we have modified the fundamental approach to how 'stick' welding is carried out. Our system allows the operator a far more simplified role.
How is all this achieved?
In simple terms, by creating a spot/plug weld rather than having to deposit a fillet weld within a specified joint. By removing the need for a fillet weld deposit we have also simplified the joint configuration (simple lap joint) and all the preparation that goes with it, while also removing the need for extensive cleaning of the joint area, chipping off meters of slag prior to additional passes, etc. In fact there's no need for additional passes as the process is designed as a 'one-shot' approach, i.e. one electrode produces one spot/ plug weld.
Other than the control system all other equipment is exactly the same as conventional stick welding equipment. The control unit is connected to the welding power source via the remote control facility and is powered by 110v supply. All welding leads pass through our 400 amps safety switch before going to the diver.
The role of the control unit:
The control system manages and manipulates the following:
1: A timer
2: First peak/ high current setting
3: Second background/ low current setting
The first high current setting allows the electrode to pierce through the materials, thereby, creating a hole through which both materials are joined toÂgether. The role of the timer is to limit the depth of this penetration, so as to avoid bursting through the base (back) material. After the first weld cycle is completed and depth of penetration achieved, the second, lower current is automatically initiated and it's this current that fills the hole, creating a spot/ plug weld that has penetrated both sections of material, creating a weld nugget. During the operation the diver or indeed robot need only apply sufficient pressure to the electrode to push it through the material while welding.
The guidelines shown below provide basic benchmark settings for selecting current and timer. The operator can then make any minor adjustments as are seen necessary to ensure adequate weld quality. Presently only one size of electrode is available, namely 3.2mm (1 / 8").
3.2mm/1/8" Electrode Timer High Current Low Current
8-8mm (16mm) 5/8 inch 4-6 Sec 250-260 150-160
10 Â10 mm (20 mm) 3/4 inch 5 -8 Sec 260 -270 150 -170
12 Â12 mm (24 mm) 1 inch 7-9 Sec 270-280 160-180
Weld strength properties:
The size of a given weld and therefore the number of welds required is based on the following principle. (Area of a circle with'd' as the diameter of the weld).
pi d squared /4. Therefore, a single spot weld can offer the followÂing theoretical strength properties.
Max load = --x shear strength. (eglecting any bending moment).
Typically the shear strength for plain carbon steel is generally assumed to be 4/5 the ultimate tensile strength. The Hammerhead electrode offers a tensile strength of 650/mm2 (94ksi) and therefore, will offer a shear strength of approx. 520/mm2 (75ksi). Therefore, a 10.0mm (3/8") diameter weld nugget will produce a max load capability of 40.840 k (9,181lb/f) per spot. Using the following principle to calculate the overall stress acting on weld (G2.2), (see report 5402460) i.e.
Stress = force/area = 606/Nmm2 Therefore, = 39.8kN/65.62mm2
We see the spot weld shown took 40kN to fracture and had a total area of 65mm2. The UTS was 606/mm2. Compare this to a defect free multipass fillet weld (D2.2) fracturing at 259kN, but having a total area of 746mm2 with a UTS of 347N/ mm2. We see the spot weld offers nearly twice the UTS capability for a fraction of the deposited weld metal. So when you consider the time saved in deposited weld metal, cleaning, preparation and ease of use, as well being able to weld in nil visibility, the benefits are considerable. The weld offers strength improvements over normal ferritic steel electrodes and generally the heat affected zone (HAZ) hardness is improved. The specially formulated electrodes, which have a 27.5Cr and 14.45 Ni equivalent, thereby, allowing for high percentage dilutions, of up to 50%.
Petromin NOVEMBER 2005