Welding Materials Essentials: Key Requirements

Basic Requirements for Welding Rods

The basic requirements for welding rods are as follows to ensure welding quality:

1.The weld metal should have good mechanical or other physical properties. For instance, structural steel, stainless steel, heat-resistant steel welding rods all require the weld metal to have specified mechanical properties such as tensile strength, as well as physical properties like corrosion resistance and heat resistance.

2.The deposited metal of the welding rod should have specified chemical composition to ensure its performance meets the requirements.

3.The welding rod should exhibit good process performance, such as stable arc, minimal spattering, good slag removal, well-formed weld bead, high production efficiency, and low dust and toxicity.

4.The welding rod should have good resistance to porosity and cracking.

5.The welding rod should have good surface (coating) quality. The flux coating should evenly and smoothly cover the weld core. The eccentricity should meet the specified standards. The coating should be free from defects like cracking, peeling, or bubbles. The tip and tail should be rounded, with dimensions meeting the requirements.

The weld core should be free from rust marks, and the coating and core should have a certain bonding strength and moisture resistance.

6.To protect the environment and ensure the safety and health of welders, the dust emission and toxic gases from the welding rod should comply with relevant standards.

Basic Requirements for Welding Wire

1.The welding wire should have specified chemical composition.

2.The welding wire should have a smooth surface, without adverse effects on welding characteristics, welding equipment operation, or weld metal performance, as well as without cracks, pits, scratches, oxide skin, wrinkles, folds, or foreign matter.

3.Each continuous length of the welding wire should consist of material from a heat number or a batch number. When there are joints, they should be properly treated so that the welding wire can be fed uniformly and continuously without affecting its use on automatic and semi-automatic welding equipment.

4.Unless otherwise specified, the welding wire may be coated with a suitable protective layer, such as copper.

5.The winding of the welding wire should be free from entanglement, kinks, sharp bends, overlaps, and embedding, allowing the wire to unwind freely without constraint. The outer end of the welding wire (the start of welding) should be marked for easy identification and securely fixed to prevent loosening.

6.The bounce and spiral of non-straight welding wire should allow uninterrupted feeding in automatic or semi-automatic welding equipment. The bounce and spiral of non-straight welding wire for gas shielded welding should comply with relevant regulations.

Bounce refers to cutting several coils of welding wire from the package, placing them unconstrained on a flat surface, and observing the diameter of the resulting ring. Spiral refers to the maximum distance from any point on the welding wire ring to the flat surface during the bounce test.

7.The packaging of welding wire should comply with relevant regulations. The packaging forms include straight, spooled, coiled, and drummed.

Basic Requirements for Flux

(1) Flux should have good metallurgical properties.

When used with suitable welding wire and reasonable welding parameters, the weld metal should have appropriate chemical composition and good mechanical properties to meet the design requirements of the product. Additionally, the flux should have strong resistance to porosity and cracking.

(2) Flux should have good welding process performance.

Under specified parameters, the welding process should ensure stable arc burning, good fusion, smooth transition, well-formed weld seams, and easy slag removal.

(3) Flux should have low moisture content and good moisture resistance.

The mass fraction of water in the flux at the time of production should not exceed 0.20%. When placed in an environment with a temperature of 25°C and a relative humidity of 70% for 24 hours, the moisture absorption rate should not exceed 0.15%.

(4) Control of mechanical impurities in the flux.

The mass fraction of carbon particles, iron filings, raw material particles, and other impurities in the flux should not exceed 0.30%, with the mass fraction of carbon particles and iron alloy beads not exceeding 0.20%.

(5) Flux should have low sulfur and phosphorus content.

The mass fraction of sulfur and phosphorus in the flux is generally: S ≤ 0.06%, P ≤ 0.08%.

(6) Flux should have a certain particle size distribution.

The particle size of flux is generally divided into two categories: regular particles range from 2.5 to 0.45 mm (8 to 40 mesh); fine particles range from 1.18 to 0.28 mm (14 to 60 mesh). The content of fine powder smaller than the specified particle size is generally greater than 5%, and the content of coarse powder larger than the specified particle size is generally not more than 2%.

(7) Flux for Submerged Arc Welding.

In order to ensure stable submerged arc welding and obtain good weld joints, the flux for submerged arc welding, in addition to meeting the general requirements for flux, should also have the following special requirements:

①The electrical conductivity of the slag should be within an appropriate range.

If the electrical conductivity of the slag is too low, it will hinder the welding process; if it is too high, it may ignite the arc between the welding wire and the slag, disrupting the electroslag welding process.

②The viscosity of the slag should be appropriate.

If the viscosity of the slag is too low, leading to excessive flow, it can result in the loss of slag and metal, causing interruptions in the welding process. Conversely, if the viscosity is too high, it can lead to defects such as undercut and slag entrapment.

③Controlling the evaporation temperature of the flux is crucial.

The composition and boiling points of fluxes vary according to their specific applications. The temperature at which the slag begins to evaporate is determined by its most volatile component. Compounds with low boiling points, such as fluorides, can reduce the starting temperature of slag evaporation, increasing the likelihood of arc generation, thus reducing the stability of the electroslag welding process and leading to spattering.

Additionally, the flux should possess good slag removal properties, resistance to hot cracking, and the ability to resist porosity.

An increase in the SiO2 content in the flux results in decreased electrical conductivity and increased viscosity. Conversely, an increase in fluorides and TiO2 leads to increased electrical conductivity and decreased viscosity.

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