TIG Welding

Tungsten Inert Gas (TIG) Welding

TIG Welding is also a slang term commonly used. Tungsten inert gas welding (TIG welding) is a gas shielded welding process and is one of the fusion welding processes. TIG welding’s proper name is Gas Tungsten Arc Welding or “GTAW". This is the name the American Welding Society and other welding organizations refer to this process on their welding procedures. TIG welding also goes by the term HeliArc welding.

When TIG welding was introduced around the 1940’s Helium gas was the primary shielding gas used in process. The term Heliarc welding was the common phrase used back in the day Most old timers and veteran welders refer to TIG welding as Heliarc welding.

Since the name includes the term “Tungsten" and tungsten is what makes TIG welding possible, it is good to know what tungsten is! Tungsten is a very hard, slightly radioactive, and brittle metal. At 3380 degrees Celsius, tungsten has the highest melting point of all pure metals in the periodic system. This means that the electrode does not melt when it emits an arc that heats and liquefies the material. In TIG welding the tungsten is made into a non-consumable electrode that is used to create the arc for TIG welding.

THIS IS HOW A TIG WELDING SYSTEM IS STRUCTURED:

(1) Mains connection

(2) Power source

(3) Hose pack

(4) Grounding cable

(5) Welding torch

(6) Ground terminal

(7) Workpiece

(8) Filler metal

(9) Shielding gas

TIG welding requires three things, heat, shielding, and filler metal. The heat is produced by electricity passing through the tungsten electrode by creating an arc to the metal. The shielding comes from a compressed gas cylinder that flows to the weld area to protect it from air. The filler metal is just a wire that is dipped by hand into the arc and melted.

TIG Welding is a manual welding process that requires the welder to use their both hands to weld. When TIG Welding one hand is used for holding the TIG torch that produces the arc and the other hand is to add the filler metal to the weld joint.

Shielding gas is selected according to the material being welded. Argon - the most commonly-used shielding gas. Helium and helium/argon mixtures - adding helium to argon will raise the temperature of the arc. This promotes higher welding speeds and deeper weld penetration.

In the TIG welding process the arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium. TIG welding must be operated with a drooping, constant current power source - either DC or AC.

ADVANTAGES OF TIG WELDING

No formation of welding spatter

Particularly high optical quality of weld seams

All welding positions are possible

Very high weld seam quality

DISADVANTAGES OF TIG WELDING

Requires high degree of skill

Low welding speeds

Rust must be removed without fail when preparing the weld seam

Not suitable for thick workpieces

Dry film thickness

Dear Readers,

Over the past several decades, industrial painting has changed, owing to the use of new, more durable finishes. Coating is the most critical component in an anticorrosive coating system. The main function of coating is to provide corrosion protection by adhesion to the substrate. A coating thickness gauge (also referred to as a paint meter) is used to measure dry film thickness.

Dry film thickness (DFT) is the thickness of a coating as measured above the substrate. This can consist of a single layer or multiple layers. DFT is measured for cured coatings (after the coating dries). Thickness of a coating depends on the application and type of process employed. DFT is a parameter that is considered during quality control or inspection processes.

Dry film thickness (DFT) can be measured using two methods: destructive thickness measurement, where the coating is cut to the substrate using a cutter; and non-destructive coating thickness measurement, using techniques which do not damage the coating

Dry film thickness can be measured on either magnetic steel surfaces or non-magnetic metal surfaces such as stainless steel or aluminium using a digital coating thickness gauge. The principle of electromagnetic induction is used for non-magnetic coatings on magnetic substrates such as steel. The eddy current principle is used for non-conductive coatings on non-ferrous metals substrates.

Types of DFT gauges include:

Magnetic pull-off (Type I)

Constant pressure probe (Type II)

Electronic magnetic flux

Eddy current gauge

Standards concerning DFT measurements include:

ISO 2808

BS 3900 Part C5

BS 5494

ASTM D1005

D1400

D2691

SIS 184160

Hot Weather Concreting

The intention of this article is to provide knowledge to general users with simple actionable works. To understand requirements, without going in to details of theoretical concepts, scientific and engineering analysis.

Concreting continuous throughout the year in construction industry but doing concreting in any extreme weather is a biggest challenge. Doing concreting in cold weather we don’t have much problem since concrete hardening being an exothermic reaction during cold weather.

To protect concrete from heat, common understanding of using chilled water is there or alternate is to do concreting in night shift. But with higher temperature in most part of the day, such strategy does not work for a durable concrete. General understanding in which concrete evaporates more than 1Kg/Sqm/Hr water.  It is perfect time to have a deep look in understanding hot weather concreting during summer.

Care during Designing

Care during Concrete Production

Care during Transportation

Care during Pouring

Care during Finishing surface and

Care during Curing

Care During Designing

Summer Concrete Shall be deigned with low heat of hydration materials.

PPC or Slag Cement, Low heat cement will help in many ways to have a good concrete with lower rate of reaction

Good quality Admixtures especially Polycarboxylic ether (PC) based can help to maintain good workability for relatively longer time and can also slowdown evaporation of water from concrete

Concrete shall be designed for the atmosphere in which the concreting is going to happen. (Maximum permissible fresh Pour Concrete is 35 Degree)

Care during Concrete Production

Care shall be taken to keep the fresh concrete temperature as lower as feasible. It is easier to care for fresh concrete rather than placed concrete

Mixing system shall not induce more heat and preferably insulation of mixing system shall be done

Cement (Bags) shall be stored in shaded area for sufficient time

Coarse aggregates shall be sprinkled with cold water

For Fine aggregates sprinkling of water if done shall be stopped couple of hour early to reduce moisture variation

For Higher temperature reduction, ice flakes shall be used

If ice flakes used shall be mixed with weighment to maintain the water cement ratio in line with design mix

Use of Liquid nitrogen is an option (Not Cost Effective and not feasible due to practical reasons)

Care during Transportation

Transportation time shall be kept minimum as much as possible (Batching location should be very nearer)

Transit Mixer drum shall be insulated to reduce the heat gain during transportation

Hessian cloth shall be used as an insulation material

Care during Pouring

During Pouring of concrete, pump pipe lines should be insulated to reduce temperature gain.

Dense Hessian cloth with sponge layer wrapping followed with wetting chilled water shall be done

Temporary shed shall be used for direct exposure to sun and wind. If shed is not feasible at least covering with thick plastic sheet shall be covered for shuttering and reinforcement before and during the concreting

Concrete pour area shall be water sprinkled (If Feasible) to cool shuttering and reinforcement. Care shall be taken that there is no standing water anywhere.

Care during Finishing surface

Late finishing shall be done before concrete starts being in semi plastic state

Evaporation reducing admixtures shall be used

Fogging of Concrete surface can be done during concrete green stage

Care during Curing. (Post Initial Set, Hardening of Concrete)

Once concrete can take a person’s weight, it is understood that concrete has initial set

Mist sprinkling of water can be done with a cover of hessian cloth

Water curing can continue either by ponding or intermittent watering surface

Time of form removal and start of curing is an important factor. Curing shall start with in 45 minutes of form removal

In short, Mass concreting during summer requires a detailed analysis, review and action plans for concrete care.