Before welding wear parts onto mobile or fixed plant machinery it is critical to have key information that will enable the best possible weld quality.
It is best to slow the heating and cooling rates of the weld metal and weld heat-affected zone (HAZ) by using suitable preheat temperature, interpass temperature and post-weld heat treatment as these reduce the risk of cracking and permanent deformation.
In addition, the use of low-hydrogen welding consumables, appropriate welding procedures, and weld designs are all key elements that will enable a high-quality weld.
Before Welding – OHS:
Prior to commencing any welding work, a risk assessment should be carried out to identify any hazards, assess the risks associated with them, and implement risk control measures using the hierarchy of control.
Appropriate approved personal protective equipment (PPE) must be worn such as appropriate clothing, hearing protection, hard hat, safety boots, safety glasses and gloves. All work areas should be clean of any trip hazards and be sufficiently ventilated. The item being welded should also be removed from machinery and safely secured.
Other factors to consider before welding wear parts:
All welding surfaces must be free from dirt, scale, grease, water, and paint to ensure a good surface for welding and reduce the chances of weld cracking. Weld preparation can be in the form of grinding, sanding, sand blasting and shot blasting.
The importance of pre-heating:
To deliver a quality weld, it is critical to pre-heat your wear part and the material it is being welded to or you will likely see cracking and premature failure.
By uniformly pre-heating your materials to a minimum temperature of 200°C (Refer to AS 1988.1 regarding minimum preheat temperature calculations), it reduces the thermal gradient between the molten weld metal and cooler base metal by lowering the cooling rate.
In addition, pre-heating provides more time for hydrogen to diffuse from the weld zone and helps reduce moisture content in the base materials which is a source of hydrogen absorption into the weld. Hydrogen content must be controlled to prevent hydrogen embrittlement and associated risks of cracking and porosity.
The area preheated should be monitored at a distance of 4 x ”t” (where “t” is the thickness of plate that the GET is being welded to) away from the longitudinal edge of the weld groove or repair cavity, for “t” <50mm or at a minimum distance of 100mm from the joint preparation for “t” >50mm and on the reverse side of the plate to the heat source.
Digital contact thermometers or infrared heat guns are the best tools to accurately provide welding pre-heat temperatures quickly. However, thermal crayons/chalk – which melt when they reach a certain temperature – are still commonly used thanks to being cost effective.
Welding Consumable Guide
|Welding Type||AWS Standard||AS/NZS Standard (Classification)|
|MMAW (Stick)||AWS A5.1 – E7018||AS/NZS 4855-B (E4918 A U H5)
|FCAW (Flux Cored Wire)||AWS A5.20-79, Class E70T-1C-H16||AS/NZS ISO 17632-B (T49 3 T1-1 CA-K-U H10)
|MIG (Solid Wire)||AWS A5.18 – ER70S-4||AS/NZS 2717.1 (ES4-GM/C W503AH)
- The use of smaller electrodes and corresponding lower amperage is recommended where possible.
- The use of a E81T-1 wire is recommended for larger sections when using FCAW, such as Lincoln Outershield 81Ni1-H.
The use of the stringer bead welding technique is recommended. Any slag should be removed from the weld deposit between each pass, by chipping, peening, or wire-brushing. After each pass, check for undercut, slag and porosity, and grind out as required.
Detailed Guide to Wear Parts Welding Procedures
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