Electrode made of tungsten
Tungsten electrodes relate to a group of non-consumable material. They possess perfect mechanical properties: hardness, wearing resistance, immunity to strong heating, minimal coefficient of thermal expansion in comparison to other metals, good heat conductivity, unique resistance to thermal creep, very high module of elasticity. Demand for them increases annually.
Tungsten is very rare element of lithosphere. It is very hard, heavy and insufficiently malleable in standard conditions. Difficulty of its obtaining in pure state and heavy treatment increase cost of final product.
Workable plasticity of tungsten is minimal. But with temperature raise, it increases. That is why mill-products made out of them can be obtained by hot working under pressure. Firstly, there are manufactured blanks (billets) with a help of powder metallurgy method. After heating up, they must be hammered out on forging machine. As a result, there are obtained bars with a diameter of 2−3 mm. After drawing in hot state, there is obtained wire with a diameter of 0.2−0.3 mm.
Tungsten welding electrode is thin core with special covering or without it. Between it and detail appears an arc — electrical stable discharge in ionized atmosphere with such temperature that can melt the metal. Simultaneously there must be additionally given filler material — welding wire. Electrode covering gives a possibility to stabilize arc burning, to protect molten material from air effect ant to give additional qualities to seams. Used coverings: sour, basic, cellulose, rutile. Components included into composition: fluxing, sponging, alloying, stabilizing, oxidizing.
Optimization of welding process
EWP grade is badly kindled. In order to improve it and to stabilize the arc, there is used zirconium additive. Thorium additive can also simplify kindling ability (WT-20) and increase duration of operational use. Yttrium additive to grade WY-20 allows jointing of details at permanent or alternate current. Welding arc current supply can be single-phase or three-phase at alternate current.
There are used electrodes with zirconium additive for joint of details out of non-iron metals. Welding seam has become very consistent even between details of various chemical composition. Argon-arc welding even more allows strengthening seam, to protect working area from gaseous atmospheric mixture (oxygen, nitrogen, carbon dioxide). At that, it increases seam quality and inhibit electrode burning.
Characteristics of domestic electrodes
Tungsten electrode WL-20 (EWLa2) is multi-operated for any working currents DC/AC and alloy grades. Application of grades WL, WP, WC gives operational reliability and high thermal stability to seam. Tungsten electrode can be made of different parameters according to customer’s drawing. Tungsten electrode, alloyed with La2 O3, possesses very easy initial start-up, repeated arc kindling, resistant arc, low propensity for burn-through. Lanthanum oxide additive (not more than 2%) increases peak current half as much and loading capacity. Grades, which contain lanthanum, are more durable than thoric, ceric. They become slower fretted from an electrode tip. These electrodes bring a smaller quantity of tungsten to welding seam. Equilibrium distribution of lanthanum oxide allows keeping initial electrode sharpening much longer. Grades WL-20, EWP (according to TC48−19−527−91) are used in electric arc cutting, deposit welding, spattering in inert gaseous environment.
Tungsten WY-20 electrode can perfectly perform welding of constructions made out of copper, titanium alloys, stainless low-alloyed steels with direct-current straight polarity. Among all existing tungsten electrodes, the most resistant is yttrium tungsten electrode. Yttrium oxide (not more than 2,2%) can stabilize cathode spot by making resistant an arc independently from operational current.
|Electrode grade||Percentage composition|
|Lanthanum oxide||Tungsten||Additives of Al, Fe, Ca, Si|
|WL-20||1.6 — 2||more than 99.9||0.1|
|EWP||-||97.9 — 98.3|
|Electrode grade||Limit||Diameter, mm||Limit||Length, mm|
|WL-20||±0.1||1, 1.6, 2, 2.5, 3, 4||±2.0||75; 150; 200|
|EWP||±0.1||1, 1.6, 2, 2.5, 3, 4|
|±0.2||5, 6, 8|
Standard tungsten electrode has a length of 1000 mm and diameter of 1.6; 2; 3; 4 mm. Surface is grinding, flat, without cracks, lubricant, fins, shearing distortions, lubricant spots. Surface of bar with a diameter of 1; 2; 2.5; 1.6 mm must be etched. There is allowed a presence of flaws, forging folds, heat tint according to limit of tolerance. Electrodes must be cut from striking ends. There are allowed shearing distortions but not bigger than 1 mm. Bar straightness can have divergences — not more than 0.25% of whole length. WL-20 electrodes are marked by oil-base black paint.
Characteristics of foreign electrodes
Tungsten electrode of grades WP, WL-20, WC-20, WT-20, WZ8, WY-20 is widely used in arc welding in atmosphere of inert gas. There are used WIG, GTA electrodes for Tungsten Insert Gas (TIG-welding). It can be semi-automatic, automatic, or arc manual in protective atmosphere. There are used inert argon, helium, active oxygen, hydrogen, carbon dioxide, nitrogen and their mixtures (Не+ Аr, О2+ Аr, СО2+ Аr).
Electrodes in containers are used for argon-arc welding:
|Color code||Quantity (1kg)||Additions||Diameter, mm||Note|
|Grey (WC-20)||151||1.8−2.2% (cerium dioxide)||1.6||Stainless, heat resistant, acid-resistant metals and stells (niobium, molybdenum, nickel, titanium, tantalum, and their alloys bronze, copper, silicon bronze).|
|Blue (WL-20)||151||1.8−2.2% (lanthanum dioxide)||1.6||Joint of high-alloyed steel; thin sheets; weld deposit of valves, forms; cutting of aluminium, copper, bronze, high-alloyed steels.|
|Red (WT-20)||151||1.8−2.2% (Thorium dioxide)||1.6||Direct current for welding. Facile arc sparking. Shape stability at heavy currents. Cutting angle can be changed. Durable.|
|White (WZ8)||151||0.8% (zirconium dioxide)||1.6||Identical to pure tungsten. Arc stability and facile sparking. Welding of responsible joints with alternate current.|
|Green (WP)||96||Pure tungsten without alloying additives||2||Welding of aluminium, manganese alloys with alternate current. Durable operational use. Good kindling ability of arc.|
|Navy blue (WY-20)||151||1.8−2.2% (yttrium oxide)||1.6||Welding of responsible joints with direct current. Durable operational use, facile arc sparking.|
WL-20 tungsten electrode (contains lanthanum oxide additive up to 2,2%) has facile arc sparking, facile repeated kindling, very stable arc, off-chance burn-through. Loading capacity of electrode and maximum voltage increases half as much while working with alternate current. In comparison to grades WT-20, WC-20 (with thorium and cerium additives), lanthanum grades are more durable. They have smaller wearing problem of tips and contamination of welding seam. Lanthanum oxide can keep initial grinding at equilibrium distribution in electrode.
There is needed spherical grinding of working electrode tip for sinusoidal alternate current. Ceric oxide in WC-20 (up to 2,2%) simplifies initial start of arc, increases peak welding current, improves emission. This grade is intended to be used while working with alternate or direct current of normal polarity. WC-20 grade possesses high arc stability (even at low current indexes). Such electrodes are used while welding pipelines, thin-sheet steel, pipe orbital welding. There is a demerit: while working with high voltage ceric oxide starts to concentrate at working electrode tip.
Optimal current value at argon-arc welding for tungsten electrode.
|Electrode diameter, mm||Direct current||Alternate current|
|Reverse polarity||Direct polarity||Negative half-wave is bigger than positive||Negative and positive half-waves are equal|
|4||40 — 55||400 — 500||300 — 400||200 — 320|
|3,2||25 — 40||250 — 400||225 — 325||160 — 250|
|3||20 — 35||220 — 350||200 — 300||140 — 230|
|2,4||15 — 30||150 — 250||140 — 235||100 — 180|
|2||12 — 25||100 — 200||80 — 160||70 — 130|
|1.6||10 — 20||70 — 150||70 — 150||60 — 120|
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