Maine Welding Company Get the finest quality TIG Welding in Maine. Sat, 24 Dec 2016 15:06:46 -0500 Sat, 24 Dec 2016 15:06:46 -0500 Tig Welding Stainless Steel <h2 id="span-styletext-decoration-underlinestrongemimg-classalignright-size-medium-wp-image-4643-srchttpmeweldingcomwp-contentuploads201204tigweldingstainlesssteel-300x225jpg-alttig-welding-stainless-steel-width300-height225-tig-welding-stainless-steelemstrongspan"><span style="text-decoration: underline;"><strong><em><img class="alignright size-medium wp-image-4643" src="" alt="TIG Welding Stainless Steel" width="300" height="225" />TIG Welding Stainless Steel</em></strong></span></h2> <p>Known as 300 series, austenitic stainless steels are the most commonly welded. These chrome nickel steels, in contrast to lower cost stainless have more alloys and are 鈥渘on magnetic鈥?(Exception, types 310 鈥?330).</p> <p>Austenitic grades of stainless steel typically contain a minimum of 16-26% chromium and 6-22% nickel.</p> <p>308 Grade stainless steel, for example, is also referred to as 18-8 stainless steel and contains about 18% chromium and 8% nickel.</p> <p>Austenitic stainless steels can be hardened by cold working, but not by heat treatment. In the annealed condition, all are nonmagnetic, although some may become slightly magnetic by cold working. At room temperature the 300 Series stainless steels retain an austenitic micro-structure. While resistance to corrosion is their principal attribute, they are also selected for their excellent strength properties at high or extremely low temperatures. They are considered to be the most weldable of the high-alloy steels. Comparatively little trouble is experienced in making satisfactory welded joints if their inherent physical characteristics and mechanical properties are given proper consideration.</p> <p>The principal criteria for selecting stainless steel is usually resistance to corrosion, and while most consideration is given to the corrosion resistance of the base metal, additional consideration should be given to the filler material and to the base metal immediately adjacent to the weld zone. Welding naturally produces a temperature gradient in the metal being welded, ranging from the melting temperature of the fused weld metal to ambient temperature at some distance from the weld.</p> <p>Because of the long-term cost effectiveness and inherent corrosion resistance of stainless steel, it has become a staple material across many industries. <strong><em>TIG welding stainless steel</em></strong> poses a number of distinct challenges, the greatest of which are carbide precipitation and distortion. The key to preventing these issues is good heat control, correct travel speeds and adequate <a href="" title="TIG Welding Stainless Steel : Gas Coverage">gas coverage</a>.</p> <h2 id="section">#</h2> Mon, 16 Mar 2015 00:00:00 -0400 Tig Welding Stainless Steel Stainless Steel TIG Welding Welding Techniques TIG Welding Stainless Steel Basics <p><img class="alignright size-medium wp-image-4641" src="" alt="TIG Welding Stainless Steel" width="300" height="169" /></p> <h3 id="tig-welding-stainless-steel-basics">TIG Welding Stainless Steel Basics</h3> <p>In comparison with the welding of mild steel, for example, the austenitic stainless steels have several characteristics that require some revision of welding procedures that are considered standard for mild steel. The melting point of the austenitic grades stainless steels is lower, so less heat is required to produce fusion. 300 Series stainless steels electrical resistance is higher than that of mild steel so less electrical current (lower heat settings) is required for welding. These stainless steels also have a lower coefficient of thermal conductivity, which causes a tendency for heat to concentrate in a small zone adjacent to the weld. The austenitic stainless steels also have coefficients of thermal expansion approximately 50% greater than mild steel, which calls for more attention to the control of warpage and distortion in the heat affected zone.</p> <p>During the <strong><em>TIG welding of stainless steels</em></strong>, the temperatures of the base metal adjacent to the weld reach levels at which micro-structural transformations occur. The degree to which these changes occur, and their effect on the finished weldment in terms of resistance to corrosion and mechanical properties, depends upon alloy content, thickness, filler metal, joint design, weld method, and welder skill. Regardless of the changes that take place, the primary objective in TIG welding stainless steels is to provide a sound joint with qualities equal to or better than those of the base metal.</p> <blockquote> <p>To ensure success when TIG welding stainless steel, it is important to have good heat control, gas coverage and travel speeds.&lt;/p&gt; Typically, TIG welding stainless steel requires a DC power source and pointed tungsten (any type except pure). Like aluminum or any metal to be welded for that matter, it should be free of oil, paint and/or dirt prior to welding to achieve optimal results. Stainless steel should be wire brushed between welding passes with a dedicated stainless steel wire brush that has not had contact with mild steel to help remove potential inter-pass oxides.</p> </blockquote> <p>Filler rod is recommended on applications with a base material thicker than gauge 18 and will be contingent upon joint design. For example, outside corners may not require filler rod, but an inside joint will. Most TIG applications require overmatching of the filler rod. That is, a filler rod with higher strength properties should be used. For example, on 304 series austenitic stainless steel, an ER308 rod should be used. Typically, austenitic stainless steel filler rods are available in diameters ranging from .035 to 5/32 (.9-to 4.0-mm) and chosen according to the joint design, welding parameters and applications.</p> <h3 id="tig-welding-stainless-steel--filler-rod-selection">TIG Welding Stainless Steel : Filler Rod Selection</h3> <table border="1" width="555" cellspacing="3" cellpadding="2"> <tr> <td valign="top"> <strong><em>Stainless Steel</em></strong> </td> <td valign="top"> <strong><em>Filler Rod </em></strong> </td> <td valign="top"> </td> <td valign="top"> <strong><em>Stainless Steel</em></strong> </td> <td valign="top"> <strong><em>Filler Rod </em></strong> </td> </tr> <tr> <td valign="top"> 301 </td> <td valign="top"> 308 </td> <td valign="top"> </td> <td valign="top"> 310S </td> <td valign="top"> 310 </td> </tr> <tr> <td valign="top"> 302 </td> <td valign="top"> 308 </td> <td valign="top"> </td> <td valign="top"> 314 </td> <td valign="top"> 310, 312 </td> </tr> <tr> <td valign="top"> 302S </td> <td valign="top"> 308 </td> <td valign="top"> </td> <td valign="top"> 316 </td> <td valign="top"> 316 </td> </tr> <tr> <td valign="top"> 304 </td> <td valign="top"> 308 </td> <td valign="top"> </td> <td valign="top"> 316L </td> <td valign="top"> 316 </td> </tr> <tr> <td valign="top"> 304L </td> <td valign="top"> 308 </td> <td valign="top"> </td> <td valign="top"> 317 </td> <td valign="top"> 347 </td> </tr> <tr> <td valign="top"> 305 </td> <td valign="top"> 308, 310 </td> <td valign="top"> </td> <td valign="top"> 321 </td> <td valign="top"> 347 </td> </tr> <tr> <td valign="top"> 308 </td> <td valign="top"> 308 </td> <td valign="top"> </td> <td valign="top"> 330 </td> <td valign="top"> 347 </td> </tr> <tr> <td valign="top"> 309 </td> <td valign="top"> 309 </td> <td valign="top"> </td> <td valign="top"> 347 </td> <td valign="top"> 347 </td> </tr> <tr> <td valign="top"> 309S </td> <td valign="top"> 309 </td> <td valign="top"> </td> <td valign="top"> 348 </td> <td valign="top"> 347, 348 </td> </tr> <tr> <td valign="top"> 310 </td> <td valign="top"> 310 </td> <td valign="top"> </td> <td valign="top"> </td> <td valign="top"> </td> </tr> </table> Mon, 16 Mar 2015 00:00:00 -0400 Tig Welding Stainless Steel tig welding Stainless Steel TIG Welding Tungsten Electrodes <p><img class="alignright size-full wp-image-4321" src="" alt="tungsten electrodes" width="265" height="283" /></p> <h3 id="tungsten-electrodes"><strong><em>Tungsten Electrodes</em></strong></h3> <p><a title="fig5_32" name="fig5_32"></a>Non-consumable <strong><em>tungsten electrodes</em></strong> for GTAW (Gas Tungsten Arc Welding) 聽or TIG (Tungsten Inert Gas) welding, generally are of several聽types.</p> <p><a title="fig5_32" name="fig5_32"></a>聽<strong>Tungsten electrodes types and their typical application can be identified by color coded end marks as follows.</strong></p> <ul> <li>Pure Tungsten : 聽Green</li> <li>2% Ceriated : 聽Gray</li> <li>2% Thoriated : Red</li> <li>2% Zirconiated : Brown</li> <li>1.5% Lanthanated : Gold</li> <li>2% Lanthanated : Blue</li> </ul> <p><a title="fig5_32" name="fig5_32"></a>聽<span style="text-decoration: underline;"><strong>Pure tungsten electrodes</strong></span> are generally used on less critical welding operations than the tungsten electrodes that are alloyed. This type of electrode is used for AC welding, has a relatively low current carrying capacity and a low resistance to contamination.<a title="fig5_32" name="fig5_32"></a></p> <p><span style="text-decoration: underline;"><strong>Thoriated tungsten electrodes</strong></span> (1 or 2 percent thorium) are superior to pure tungsten electrodes because of their higher electron output, better arc-starting and arc stability, high current-carrying capacity, longer life, and greater resistance to contamination. 2% thoriated tungsten electrodes can be used for AC welding, but they excel in DC electrode negative (straight polarity) GTAW on carbon and stainless steel, nickel, and titanium. 聽Welding operators should note that 2% thoriated tungsten electrodes contain low levels of radioactivity. Therefore, they must always follow manufacturer鈥檚 warnings, instructions, and the MSDS聽(Material Safety Data Sheet) for their use.</p> <p><span style="text-decoration: underline;"><strong>Lanthanated tungsten electrodes</strong></span>聽contain a minimum of 97.80 percent tungsten and 1.30 percent to 1.70 percent lanthanum, or lanthana, both 1.5 and 2% lanthanated tungsten electrodes offer excellent arc starting at low amperages, provide long electrode life and stability, and have a low burn-off rate. They also resist tip wear. The聽2% lanthanated tungsten electrodes are considered to have superior characteristics. 2% lanthanated tungsten electrodes are often used in critical applications, such as in the aviation industry, and can be used to replace 2% thoriated tungsten electrodes. Both electrodes are well suited to welding carbon steel, stainless steel, nickel alloys, titanium, and aluminum. They work well on AC or DC electrode negative with a pointed end, or they can be balled for use with AC sine wave power sources. 聽Unlike thoriated tungsten, lanthanated electrodes are suitable for AC welding and, like ceriated electrodes, allow the arc to be started and maintained at lower voltages. Compared with pure tungsten, the addition of 1.5 percent lanthana increases the maximum current-carrying capacity by approximately 50 percent for a given electrode size.</p> <p><span style="text-decoration: underline;"><strong>Ceriated tungsten electrodes</strong></span>聽contains a min of 97.3 % tungsten, with 1.8 to 2.2 % cerium, 聽is used for low current settings and has a low-amp arc.聽These electrodes perform best in DC welding at low current settings but can be used proficiently in AC processes.</p> <p><a title="fig5_32" name="fig5_32"></a><span style="text-decoration: underline;"><strong>Zirconium tungsten electrodes</strong></span> contain 0.7鈥?.9% zirconium and are known for their ability to ball up easily in AC applications. 聽Zirconium electrodes generally fall between pure tungsten electrodes and thoriated tungsten electrodes in terms of performance. There is, however, some indication of better performance in certain types of welding using ac power.</p> <p><a title="fig5_32" name="fig5_32"></a>Finer arc control can be obtained if the tungsten alloyed electrode is ground to a point (<a href="#fig5_33">fig. 5-33</a>). When electrodes are not ground, they must be operated at maximum current density to obtain reasonable arc stability. Tungsten electrode points are difficult to maintain if standard direct current equipment is used as a power source and touch-starting of the arc is standard practice. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can best be accomplished by superimposing a high-frequency current on the regular welding current. Tungsten electrodes alloyed with thorium and zirconium retain their shape longer when touch-starting is used.</p> <p><a title="fig5_33" name="fig5_33"></a><img class=" aligncenter" src="/images/fig5-33.gif" alt="Tungsten arc welding electrodes : Correct electrode taper" width="350" height="136" /></p> <p><strong>The angle of taper on a tungsten electrode has a direct affect on arc stability and bead profile.聽</strong><img class="aligncenter wp-image-4325 size-large" src="" alt="TIG welding tungsten grind angle taper" width="735" height="99" /></p> <p>To properly grind tungsten electrodes, use a grinding wheel specially designated for tungsten grinding (to avoid contamination). Note: if you are grinding thoriated tungsten, make sure you control and collect the dust, have an adequate ventilation system at the grinding station and that you follow manufacture鈥檚 warnings, instructions and MSDS sheets.</p> <p>聽</p> <p><img class=" size-full wp-image-4332 alignright" src="" alt="tungsten electrodes preparation" width="155" height="273" /></p> <p>Grind the tungsten electrode straight on the grinding wheel rather than at a 90-degree angle to ensure that the grind marks run the length of the electrode. Doing so reduces the presence of ridges on the tungsten that could create arc wandering or melt into the weld puddle, causing contamination.</p> <p>Generally, you will want to grind the taper on the tungsten to a distance of no more than 2.5 times the electrode diameter (for example, with a 1/8-in. electrode you would grind a surface 1/4 to 5/16-in. long). Grinding the tungsten to a taper eases the transition of arc starting and creates a more focused arc for better welding performance.</p> <p><a title="fig5_33" name="fig5_33"></a>The tungsten electrode extension beyond the gas cup is determined by the type of joint being welded as well as the amount of shielding gas coverage provided. For example, an extension beyond the gas cup of 1/8 in. (3.2 mm) might be used for butt joints in light gauge material, while an extension of approximately 1/4 to 1/2 in. (6.4 to 12.7 mm) might be necessary on some fillet welds. The tungsten electrode of torch should be inclined slightly and the filler metal added carefully to avoid contact with the tungsten. This will prevent contamination of the electrode. If contamination does occur, the electrode must be removed, reground, and replaced in the torch.</p> Sun, 15 Mar 2015 00:00:00 -0400 tungsten electrodes tig welding Electrodes and Filler Metals TIG Welding TIG Welding <p><img class="wp-image-1288 alignright" title="TIG Welding Advantages" src="" alt="TIG Welding Advantages" width="238" height="177" /></p> <h2 id="tig-welding-advantages">TIG Welding Advantages</h2> <p>One of the greatest advantages of聽the <span style="text-decoration: underline;"><em><strong>TIG (Tungsten Inert Gas) welding</strong></em></span> or Gas Tungsten Arc welding (GTAW) process is that it will weld more kinds of metals and metal alloys than any other arc welding process.</p> <p>TIG welding can be used to weld most metals, including聽 aluminum, magnesium, copper, brass, bronze, stainless steel, nickel alloys like titanium, and even gold.</p> <p>Utilizing the <strong>TIG Welding</strong> process you can also weld dissimilar metals to each other, like copper to brass and stainless steel to mild steel.</p> <h3 id="tig-welding-produces-a-concentrated-welding-arc">TIG welding produces a concentrated welding arc</h3> <p>The <strong><em>TIG welding</em></strong> arc is concentrated, which enables pin point accuracy and complete control of heat input to the work piece, resulting in a much smaller heat-affected zone.</p> <p>The high concentration of heat is an advantage when welding metals with high heat conductivity such as aluminum and copper, which readily disperse the heat applied to the base metal.</p> <p>A smaller heat-affected zone is an advantage when TIG welding, because it prevents the base metal from undergoing changes due to the super heating and fast cooling of the welding arc.聽</p> <p>The heat-affected zone is where a welded joint is weakest and is the area along the edge of a properly made weld bead that is most likely to break during destructive testing.</p> <p>The enhanced articulation of the TIG welding electrode enables finer control of the welding puddle.</p> <h3 id="tig-welding--no-slag">TIG Welding聽 = No Slag</h3> <p>With the TIG welding process there is no requirement for flux. Therefore, there is no slag to obscure the welder鈥檚 vision of the molten weld pool. The finished weld will not have slag to remove between passes. Entrapment of slag in multiple pass welds is rarely seen.</p> <h3 id="tig-welding--no-sparks-or-spatter">TIG Welding聽 = No Sparks or Spatter</h3> <p>In the TIG Welding聽 process there is no transfer of metal across the arc. There are no molten globules of spatter to聽 contend with and no sparks produced if the material being welded is free of contaminants. Also under normal conditions the TIG welding arc is quiet without the usual cracks, pops, and buzzing of Shielded Metal Arc Welding (SMAW or Stick) and Gas Metal Arc Welding (GMAW or MIG). Generally, the only time noise will be a factor is when a pulsed arc, or AC welding mode is being used.</p> <h3 id="tig-welding--no-smoke-or-fumes">TIG Welding = No Smoke or Fumes</h3> <p>The TIG welding process itself does not produce smoke or injurious fumes. If the base metal contains coatings or聽elements such as lead, zinc, nickel or copper that produce fumes, these must be dealt with, just as in any fusion welding process on these metals. If the base metal contains oil, grease, paint or other contaminants, smoke and fumes will definitely be produced as the heat of the arc burns them away. The base material should be cleaned to make the conditions most desirable.</p> <h3 id="tig-welding-disadvantages">TIG Welding Disadvantages</h3> <p>The main disadvantage of the TIG welding process is the low filler metal deposition rate, as filler rod is manually fed into the weld puddle.</p> <p>Another disadvantage of TIG welding is that the hand-eye coordination necessary to accomplish the weld is more difficult to master, and requires a great deal of practice to become proficient in.</p> <p>The arc rays produced by the TIG welding process tend to be brighter than those produced by Shielded Metal Arc welding (SMAW ) and MIG welding or Gas Metal Arc Welding (GMAW). This is mostly due to the absence of visible fumes and smoke.</p> <p>The increased amounts of ultraviolet rays from the welding arc also cause the formation of ozone and nitrous oxides.</p> <p>Care should be taken to protect your skin with the proper clothing and protect your eyes with the correct shade lens in your welding helmet.</p> <p>When welding in confined areas, concentrations of shielding gas, like Argon may build up and being heavier than air will displace oxygen. Make sure that these areas are ventilated properly.</p> <h3 id="tig-welding-process-summary">TIG welding Process Summary</h3> <p>TIG Welding is a clean process. TIG Welding is desirable because of the advantages outlined.</p> <p>When TIG welding, the welder must maintain excellent welding conditions by properly cleaning material, using clean filler metal and clean welding gloves, and by keeping oil, dirt and other contaminants away from the area to be welded.</p> <p>Cleanliness when welding cannot be overemphasized, especially when welding aluminum or magnesium. These metals are more susceptible to contaminants than are ferrous metals.</p> <p>Porosity in aluminum welds have been shown to be caused by hydrogen. For this reason, it is very important to eliminate all sources of hydrogen contamination such as moisture and hydrocarbons in the form of oils and paint.</p> Sun, 15 Mar 2015 00:00:00 -0400 tig tig welding welding process TIG Welding The Art of TIG Welding Stainless Steel <p><img class=" wp-image-3932 size-medium alignright" src="" alt="tig welding stainless steel" width="300" height="159" /></p> <h3 id="the-art-of-tig-welding-stainless-steel">The Art of TIG Welding Stainless Steel</h3> <p>When <strong><em>TIG welding stainless steel</em></strong> there are a few points to keep in mind to achieve a cosmetically appealing and sound weld. Because stainless steel does not adequately dissipate heat, maintaining proper heat input when welding is critical. Too much heat can lead to warping, embrittlement or rust. As little as five amps too much can damage stainless steel鈥檚 properties. There are, however, several ways to control heat input:</p> <p><strong>Good fit-up:</strong> Adding filler metal to fill gaps puts more heat into the part, so good fit-up is important. It鈥檚 impossible to add a lot of filler metal and keep energy out of the part.</p> <p><strong>The correct filler metal:</strong> The filler metal diameter should be thinner than the base metal. If it鈥檚 thicker than the base metal, too much heat is needed to melt the filler metal. The filler metal should also match the base metal alloys in order to maintain consistent mechanical and corrosion properties.</p> <p><strong>Choose the right tungsten size:</strong> You can鈥檛 weld precisely on 1/16-in. material with a 1/8-in. tungsten. Use the right tungsten diameter based on your amperage.</p> <p><strong>Use the correct tungsten geometry:</strong> The tungsten鈥檚 shape plays a role in the weld鈥檚 width and penetration. In <strong><em>TIG welding stainless steel</em></strong>, the sharper the tungsten, the wider and less penetrating the bead will be. On a sharper point, (ground to a taper length that is more than 2陸 times the electrode diameter), the arc tends to fan out, creating a wider heat affected zone. With a blunter point (less than 2.5 times the electrode diameter), the arc comes straight down with less flaring for a deeper, thinner bead and thinner heat affected zone.</p> <p><strong>Use a fingertip or foot control:</strong> You need to be able to start the arc and adjust the amperage from the beginning to the end of the weld. Set the welder to the desired amperage, which should be just a bit more power than you鈥檒l need. If your welder is fairly accurate, you鈥檒l only need to adjust the fingertip or foot control a little bit to adjust welding output.</p> <p><strong>Start with low amperage and allow the puddle to form:</strong> Then back off two or three amps and add filler.</p> <p><strong>Maintain the correct puddle size:</strong> The weld puddle should be the thickness of the base metal. If the puddle grows too large, turn down the heat. Eliminate craters by easing down the current at the end of the weld and adding filler metal until the puddle solidifies. Use your torch鈥檚 fingertip or foot pedal control or your welder鈥檚 sequencer. Keep the gas flowing and directed at the puddle until the orange color fades. The post flow also cools the puddle and the tungsten. Moving the torch too fast can blow gas away from the tungsten, turn it black and make it more difficult to start next time.</p> <p><strong>Use pulsing:聽</strong>To control heat input, use a welder with DC pulsing capabilities. In pulsing, the current transitions between a high peak amperage and a low background amperage that maintains the arc but allows the puddle to cool. The peak current provides good penetration, but the background current allows the weld puddle to cool slightly, preventing warping, embrittlement and carbide precipitation. <strong>Pulses per Second (PPS):</strong> Is simply how many times the machine will complete one pulsing cycle in a time span of one second. Increasing the number of pulses per second produces a smoother ripple effect in the weld bead, narrows the weld bead. Reducing the number of pulses per second widens the weld bead. Pulsing also helps agitate the puddle and release any porosity or gas trapped in the weld.聽For** TIG welding stainless steel**, use a聽pulse聽rate of 100 to 500 PPS. Start at 100 and work upward. Higher pulsing (generally above 100 pulses per second) increases puddle agitation, which in turn produces a better grain molecular structure within the weld. High speed pulsing also constricts and focuses the arc. This increases arc stability, penetration and travel speeds, and it produces a smaller heat-affected zone.</p> <h3 id="tig-welding-stainless-steel--finish-the-weld">TIG Welding Stainless Steel : Finish the Weld</h3> <p>Stainless steels, in particular, 304 and similar materials, are widely used in food, dairy, drug and processing equipment. To prevent bacterial growth, all fractures, cracks and crevices in the weld should be removed, and exposed surfaces be ground and polished to match the parent metal. If welds are made in pre-finished stainless steel, the weld beads should be held to a minimum size to avoid excessive and expensive finishing costs. The chrome-nickel grades are more difficult to grind than the straight chromium grades, so weld metal deposits should be as flat as possible. Heat from grinding should be held to a minimum also to avoid distortion of thin gauge materials. If the grinding wheels or belts were used previously on carbon steel, chemical cleaning should follow to remove any iron particles that might have become embedded in the stainless steel surface.</p> <p>A technique of butt-welding polished sheets from the reverse or unpolished side has been successful. Sheets are first sheared from the back side so that any 鈥渟hear drag鈥?is on the polished side. Full penetration of the joint is achieved with a minimum of welding alloy penetrating the polished side. Relatively light grinding can then be used to prepare the weld on the polished side for final polishing and blending with the surrounding area.</p> <h3 id="how-to-tig-weld-stainless-steel-video">How to TIG Weld Stainless Steel Video</h3> <p><strong>TIG welding stainless steel</strong>聽provided by a good <strong><a href="" title="TIG Welding Service">TIG Welding Service</a>聽</strong>produces a smooth uniform beads that are easy to grind, polish or finish.</p> Sun, 15 Mar 2015 00:00:00 -0400 Tig Welding Stainless Steel tig welding Stainless Steel TIG Welding Welding Carbon Steel <h3 id="img-classalignright-size-medium-wp-image-4702-srchttpmeweldingcomwp-contentuploads201503welding-carbon-steel-300x242jpg-altwelding-carbon-steel-width300-height242-welding-carbon-steel"><img class="alignright size-medium wp-image-4702" src="" alt="Welding carbon steel" width="300" height="242" />Welding Carbon Steel</h3> <h4 id="weldinglow-carbon-steel">Welding聽Low Carbon Steel</h4> <p>For welding low carbon steel with the metal-arc welding process, the bare, thin coated, or heavy coated shielded arc types of electrodes may be used. These electrodes are of low carbon type (0.10 to 0.14 percent). Low carbon sheet or plate materials that have been exposed to low temperatures should be preheated slightly to room temperature before welding. In welding sheet metal up to 1/8 in. (3.2 mm) in thickness, the plain square butt joint type of edge preparation may be used. When long seams are to be welded on this material, the edges should be spaced to allow for shrinkage because the deposited metal tends to pull the plates together. This shrinkage is less severe in arc welding than in gas welding. Spacing of approximately 1/8 in. (3.2 mm) per foot of seam will suffice. The backstep or skip welding technique should be used for short seams that are fixed to prevent warpage or distortion and minimize residual stresses. Heavy plates should be beveled to provide an included angle up to 60 degrees, depending on the thickness. The parts should be tack welded in place at short intervals along the seam. The first or root bead should be made with an electrode small enough in diameter to obtain good penetration and fusion at the base of the joint. A 1/8 or 5/32 in. (3.2 to 4.0 mm) electrode is suitable for this purpose. This first bead should be thoroughly cleaned by chipping and wire brushing before additional layers of weld metal are deposited. The additional passes of filler metal should be made with a 5/32 or 3/16 in. (4.0 to 4.8 mm) electrode. For overhead welding, best results are obtained by using string beads throughout the weld. When welding heavy sections that have been beveled from both sides, the weave beads should be deposited alternately on one side and then the other. This will reduce the amount of distortion in the welded structure. Each bead should be cleaned thoroughly to remove all scale, oxides, and slag before additional metal is deposited. The motion of the electrode should be controlled to make the bead uniform in thickness and to prevent undercutting and overlap at the edges of the weld.</p> <p><strong>Carbon-arc Welding.</strong> Low carbon sheet and plate up to 3/4 in. (19.1 mm) in thickness can be satisfactorily welded by the carbon-arc welding process. The arc is struck against the plate edges, which are prepared in a manner similar to that required for metal-arc welding. A flux should be used on the joint and filler metal added as in oxyacetylene welding. A gaseous shield should be provided around the molten base and filler metal, by means of a flux coated welding rod. The welding should be done without overheating the molten metal. If these precautions are not taken, the weld metal will absorb an excessive amount of carbon from the electrode and oxygen and nitrogen from the air. This will cause brittleness in the welded joint.</p> <h4 id="welding-medium-carbon-steel">Welding Medium Carbon Steel</h4> <p>When welding medium carbon steel, the plates should be prepared for welding in a manner similar to that used for low carbon steels. When welding with low carbon steel electrodes, the welding heat should be carefully controlled to avoid overheating of the weld metal and excessive penetration into the side walls of the joint. This control is accomplished by directing the electrode more toward the previously deposited filler metal adjacent to the side walls than toward the side walls directly. By using this procedure, the weld metal is caused to wash up against the side of the joint and fuse with it without deep or excessive penetration. High welding heats will cause large areas of the base metal in the fusion zone adjacent to the welds to become hard and brittle. The area of these hard zones in the base metal can be kept to a minimum by making the weld with a series of small string or weave beads, which will limit the heat input. Each bead or layer of weld metal will refine the grain in the weld immediately beneath it. This will anneal and lessen the hardness produced in the base metal by the previous bead. When possible, the finished joint should be heat treated after welding. Stress relieving is normally used when joining mild steel. High carbon alloys should be annealed. When welding medium carbon steels with stainless steel electrodes, the metal should be deposited in string beads. This will prevent cracking of the weld metal in the fusion zone. When depositing weld metal in the upper layers of welds made on heavy sections, the weaving motion of the electrode should under no circumstances exceed three electrode diameters. Each successive bead of weld should be chipped, brushed, and cleaned prior to the laying of another bead.</p> <h4 id="welding-high-carbon-steel">Welding High Carbon Steel</h4> <p>When welding high carbon steels, the welding heat should be adjusted to provide good fusion at the side walls and root of the joint without excessive penetration. Control of the welding heat can be accomplished by depositing the weld metal in small string beads. Excessive puddling of the metal should be avoided because this will cause carbon to be picked up from the base which, in turn, will make the weld metal hard and brittle. Fusion between the filler metal and the side walls should be confined to a narrow zone. Use the surface fusion procedure prescribed for medium carbon steels. The same procedure for edge preparation, cleaning of the welds, and sequence of welding beads as prescribed for low and medium carbon steels applies to high carbon steels. Small high carbon steel parts are sometimes repaired by building up worn surfaces. When this is done, the piece should be annealed or softened by heating to a red heat and cooling slowly. Then the piece should be welded or built up with medium carbon or high strength electrodes and heat treated after welding to restore its original properties.</p> Fri, 13 Mar 2015 00:00:00 -0400 Welding Carbon Steel Arc Welding - SMAW Welding Techniques How to Solve Issues with Welding Over Paint <h4 id="img-class-size-medium-wp-image-4344-alignright-srchttpmeweldingcomwp-contentuploads201502welding-over-painted-surfaces-300x199jpg-altwelding-over-paint-width300-height199-"><img class=" size-medium wp-image-4344 alignright" src="" alt="Welding over paint" width="300" height="199" /></h4> <p>There are a couple of聽welding problems that require some explanation and solutions. <strong><em>These are welding over paint and painting of welds.</em></strong></p> <p><strong><em>Welding over paint</em></strong> is discouraged. In every code or specification, it is specifically stated that welding should be done on clean metal. In some industries, however welds are made over paint, and in other flame cutting is done on painted base metal.</p> <p><strong>CAUTION</strong>: Cutting painted surfaces with arc or flame processes should be done with caution. Demolition of old structural steel work that had been painted many times with flame-cutting or arc-cutting techniques can create health problems. Cutting through many layers of lead paint will cause an abnormally high lead concentration in the immediate area and will require special precautions such as extra ventilation or personnel protection.</p> <p>In the welding, metalworking and several other industries, steel, when it is received from the steel mill, is shot blasted, given a coating of prime paint, and then stored outdoors. Painting is done to preserve the steel during storage, and to identify it. In sane shipyards a different color paint is used for different classes of steel. When this practice is used, every effort should be made to obtain a prime paint that is compatible with welding.</p> <p><em>There are at least three factors involved with the success of the weld when welding over paint: the compatibility of the paint with welding; the dryness of the paint; and the paint film thickness.</em></p> <p>Paint compatibility varies according to the composition of the paint. Certain paints contain large amounts of aluminum or titanium dioxide, which are usually compatible with welding. Other paints may contain zinc, lead, vinyls, and other hydrocarbons, and are not compatible with welding. The paint manufacturer or supplier should be consulted. Anything that contributes to deoxidizing the weld such as aluminum, silicon, or titanium will generally be compatible. Anything that is a harmful ingredient such as lead, zinc, and hydrocarbons will be detrimental. The fillet break test can be used to determine compatibility. The surfaces should be painted with the paint under consideration. The normal paint film thickness should be used, and the paint must be dry.</p> <p>The fillet break test should be run using the proposed welding procedure over the painted surface. It should be broken and the weld examined. If the weld breaks at the interface of the plate with the paint it is obvious that the paint is not compatible with the weld.</p> <p>The dryness of the paint should be considered. Many paints employ an oil base which is a hydrocarbon. These paints dry slowly, since it takes a considerable length of time for the hydrocarbons to evaporate. If welding is done before the paint is dry, hydrogen will be in the arc atmosphere and can contribute to underbead cracking. The paint will also cause porosity if there is sufficient oil present. Water based paints should also be dry prior to welding.</p> <p>The thickness of the paint film is another important factor. Some paints may be compatible if the thickness of the film is a maximum of 3 to 4 mm. If the paint film thicknesses are double that amount, such as occurs at an overlap area, there is the possibility of weld porosity. Paint films that are to be welded over should be of the minimum thickness possible.</p> <p>Tests should be run with the dry maximum film thickness to be used with the various types of paints to determine which paint has the least harmful effects on the weld deposit.</p> <p><strong><em>Painting over welds</em></strong> is also a problem. The success of any paint film depends on its adherence to the base metal and the weld, which is influenced by surface deposits left on the weld and adjacent to it. The metallurgical factors of the weld bead and the smoothness of the weld are of minor importance with regard to the success of the paint. Paint failure occurs when the weld and the immediate area are not properly cleaned prior to painting. Deterioration of the paint over the weld also seems to be dependent upon the amount of spatter present. Spatter on or adjacent to the weld leads to rusting of the base material under the paint. It seems that the paint does not completely adhere to spatter and some spatter does fall off in time, leaving bare metal spots in the paint coating.</p> <p>CAUTION</p> <blockquote> <p>Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners having a pH above 10, as they may react chemically. Other nonferrous metals should be investigated for reactivity prior to cleaning.</p> </blockquote> <p>The success of the paint job can be insured by observing both pre-weld and post-weld treatment. Preweld treatment found most effective is to use antispatter compounds, as well as cleaning the weld area, before welding. The antispatter compound extends the paint life because of the reduction of spatter. The anti-spatter compound must be compatible with the paint to be used.</p> <p>Post-weld treatment for insuring paint film success consists of mechanical and chemical cleaning. Mechanical cleaning methods can consist of hand chipping and wire brushing, power wire brushing, or sand or grit blasting. Sand or grit blasting is the most effective mechanical cleaning method. If the weldment is furnace stress relieved and then grit blasted, it is prepared for painting. When sand or grit blasting cannot be used, power wire brushing is the next most effective method. In addition to mechanical cleaning, chemical bath washing is also recommended. Slag coverings on weld deposits must be thoroughly removed from the surface of the weld and from the adjacent base metal. Different types of coatings create more or less problems in their removal and also with respect to paint adherence. Weld slag of many electrodes is alkaline in nature and for this reason must be neutralized to avoid chemical reactions with the paint, which will cause the paint to loosen and deteriorate. For this reason, the weld should be scrubbed with water, which will usually remove the residual coating slag and smoke film from the weld. If a small amount of phosphoric acid up to a 5% solution is used, it will be more effective in neutralizing and removing the slag. It must be followed by a water rinse. If water only is used, it is advisable to add small amounts of phosphate or chromate inhibitors to the water to avoid rusting, which might otherwise occur.</p> <p>It has been found that the method of applying paint is not an important factor in determining the life of the paint over welds. The type of paint employed must be suitable for coating metals and for the service intended.</p> <p>Successful paint jobs over welds can be obtained by observing the following: minimize weld spatter using a compatible anti-spatter compound; mechanically clean the weld and adjacent area; and wash the weld area with a neutralizing bath and rinse.</p> Sat, 28 Feb 2015 00:00:00 -0500 welding over paint Welding Problems and Solutions Alloy Steel <h3 id="img-classalignright-size-medium-wp-image-4065-srchttpmeweldingcomwp-contentuploads201502alloysteel-300x300jpg-altalloysteel-width300-height300-span-styletext-decoration-underlinealloy-steelspan"><strong>聽<img class="alignright size-medium wp-image-4065" src="" alt="alloy_steel" width="300" height="300" /><span style="text-decoration: underline;">Alloy Steel</span></strong></h3> <dir> <strong><em>聽Alloy steel </em></strong>is frequently recognizable by its use. There are many varieties of alloy steel used in the manufacture of equipment. They have greater strength and durability than carbon steel, and a given strength is secured with less material weight. Manganese steel is a special alloy steel that is always used in the cast condition. Basic carbon steels are alloyed with other elements, such as chromium and nickel, to increase certain physical properties of the metal. </dir> <p>聽Nickel, chromium, vanadium, tungsten, molybdenum, and silicon are the most common elements used in alloy steel.</p> <ol> <li>Chromium is used as an alloying element to increase hardenability, corrosion resistance, and shock resistance. It imparts high strength with little loss in ductility.</li> <li>Nickel increases the toughness, strength, and ductility of steels, and lowers the hardening temperatures so than an oil quench, rather than a water quench, is used for hardening.</li> <li>Manganese is used to produce greater toughness, wear resistance, easier hot rolling, and forging. An increase in manganese content decreases the weldability of steel.</li> <li>Molybdenum increases hardenability, which is the depth of hardening possible through heat treatment. The impact fatigue property of the steel is improved with up to 0.60 percent molybdenum. Above 0.60 percent molybdenum, the impact fatigue property is impaired. Wear resistance is improved with molybdenum content above 0.75 percent. Molybdenum is sometimes combined with chromium, tungsten, or vanadium to obtain desired properties.</li> <li>Titanium and columbium (niobium) are used as additional alloying agents in low-carbon content, corrosion resistant steels. They support resistance to intergranular corrosion after the metal is subjected to high temperatures for a prolonged time period.</li> <li>Tungsten, as an alloying element in tool steel, produces a fine, dense grain when used in small quantities. When used in larger quantities, from 17 to 20 percent, and in combination with other alloys, it produces a steel that retains its hardness at high temperatures.</li> <li>Vanadium is used to help control grain size. It tends to increase hardenability and causes marked secondary hardness, yet resists tempering. It is also added during manufacture to remove oxygen.</li> <li>Silicon is added to obtain greater hardenability and corrosion resistance, and is often used with manganese to obtain a strong, tough steel.</li> </ol> <p>High speed tool steels are usually special alloy compositions designed for cutting tools. The carbon content ranges from 0.70 to 0.80 percent. They are difficult to weld except by the furnace induction method.</p> <p>High yield strength, low alloy structural steels (often referred to as constructional alloy steels) are special low carbon steels containing specific small amounts of alloying elements. These steels are quenched and tempered to obtain a yield strength of 90,000 to 100,000 psi (620,550 to 689,500 kPa) and a tensile strength of 100,000 to 140,000 psi (689,500 to 965,300 kPa), depending upon size and shape. Structural members fabricated of these high strength steels may have smaller cross sectional areas than common structural steels, and still have equal strength. In addition, these steels are more corrosion and abrasion resistant. In a spark test, this alloy appears very similar to the low carbon steels.</p> <p align="center"> NOTE </p> <blockquote> <p><em>Alloy聽steel is much tougher than low carbon steels, and shearing machines must have twice the capacity required for low carbon steels.</em></p> </blockquote> <p>聽</p> <p><strong><span style="text-decoration: underline;">Alloy Appearance test</span></strong></p> <dir> 聽Alloy steel appears the same as drop-forged steel. </dir> <p><strong><span style="text-decoration: underline;">Alloy Fracture test</span></strong></p> <dir> 聽Alloy steel is usually very close grained; at times the fracture appears velvety. </dir> <p><strong><span style="text-decoration: underline;">Alloy Spark test</span></strong></p> <dir> Alloy steel produces characteristic sparks both in color and shape. Some of the more common alloys used in steel and their effects on the spark stream are as follows: </dir> <p><strong><span style="text-decoration: underline;">Chromium</span></strong></p> <dir> 聽Alloys containing 1 to 2 percent chromium have no outstanding features in the spark test. Chromium in large amounts shortens the spark stream length to one-half that of the same steel without chromium, but does not appreciably affect the stream鈥檚 brightness. Other elements shorten the stream to the same extent and also make it duller. An 18 percent chromium, 8 percent nickel stainless steel produces a spark similar to that of wrought iron, but only half as long. Steel containing 14 percent chromium and no nickel produces a shorter version of the low-carbon spark. An 18 percent chromium, 2 percent carbon steel (chromium die steel) produces a spark similar to that of carbon tool steel, but one-third as long. </dir> <p><strong><span style="text-decoration: underline;">Nickel</span></strong></p> <dir> 聽The nickel spark has a short, sharply defined dash of brilliant light just before the fork. In the amounts found in S. A. E. steels, nickel can be recognized only when the carbon content is so low that the bursts are not too noticeable. </dir> <dir> </dir> <dir> </dir> <dir> </dir> <dir> 聽The sparks given off during a spark test are straw colored near the grinding wheel and white near the end of the streak. There is a medium volume of streaks having a moderate number of forked bursts. </dir> <p><strong><span style="text-decoration: underline;">Manganese</span></strong></p> <dir> Alloys containing Manganese produces a spark similar to a carbon steel spark. A moderate increase in manganese increases the volume of the spark stream and the force of the bursts. Steel containing more than the normal amount of manganese will spark in a manner similar to high-carbon steel with low manganese content. </dir> <p><strong><span style="text-decoration: underline;">Molybdenum</span></strong></p> <dir> 聽Alloys聽containing Molybdenum produces a characteristic spark with a detached arrowhead similar to that of wrought iron. It can be seen even in fairly strong carbon bursts. Molybdenum alloy steel contains nickel, chromium, or both. </dir> <p><strong><span style="text-decoration: underline;">Molybdenum with other elements</span></strong></p> <dir> 聽When molybdenum and other elements are substituted for some of the tungsten in high-speed steel, the spark stream turns orange. Although other elements give off a red spark, there is enough difference in their color to tell them from a tungsten spark. </dir> <p><strong><span style="text-decoration: underline;">Tungsten</span></strong></p> <dir> 聽Tungsten will impart a dull red color to the spark stream near the wheel. It also shortens the spark stream, decreases the size, or completely eliminates the carbon burst. Alloys聽containing 10 percent tungsten causes short, curved, orange spear points at the end of the carrier lines. Still lower tungsten content causes small white bursts to appear at the end of the spear point. Carrier lines may be anything from dull red to orange in color, depending on the other elements present, if the tungsten content is not too high.. </dir> <p><strong><span style="text-decoration: underline;">Vanadium</span></strong></p> <p>Alloys containing vanadium produce sparks with a detached arrowhead at the end of the carrier line similar to those arising from molybdenum steels. The spark test is not positive for vanadium steels.</p> Fri, 20 Feb 2015 00:00:00 -0500 alloy steel Metals Identification TIG Welding Stainless Steel : Gas Coverage <p><img class="alignright size-full wp-image-4647" src="" alt="tig welding gas coverage" width="228" height="240" /></p> <h3 id="tig-welding-stainless-steel--gas-coverage">TIG Welding Stainless Steel : Gas Coverage</h3> <p>Using the appropriate type and amount of shielding gas is another important way to prevent carbide precipitation when TIG welding stainless steel. Typically, pure argon provides the best results when welding thinner austenitic stainless steel, but the addition of small percentages of helium is not uncommon when better penetration and faster travel speeds are desired, especially on thicker pieces. The average flow rate required is between 15 to 20 psi, anything greater will cause turbulence in the gas flow and weld puddle and result in a poor weld. The use of a gas lens is highly recommended when TIG welding stainless steel. A <strong>gas lens</strong> is a copper and brass component with layered stainless steel mesh screens that replaces the collet body in a standard TIG torch. The gas lens helps distribute gas more evenly around the tungsten, arc and weld puddle and provides good cooling action. Full penetration welds require back purging. Covering the back of the weld with shielding gas ensures that the underside of the weld is protected from atmospheric elements and can be done with commercial apparatuses or individually manufactured methods.</p> <p><strong>The use of Chill Bars</strong>聽The successful welding of stainless steel by various welding methods depends to a large extent on the type of back-up bar or plate used. Experience has indicated that pure copper is the most satisfactory material for backing up a weld. The high heat conductivity of such a back-up bar or plate will prevent its sticking to the weld metal, while its chill-mold effect will assure a clean smooth weld metal surface. Copper back-up bars can be made by cutting pieces from copper plate or sheet. Chill bars serve the best purpose by controlling distortion on light gauge material, and also help to prevent excessive burn-through or melting of the base metal.</p> <p>Finally, remember to maintain adequate post-flow. The best practice is to maintain one second of post-flow for every 10 amps of welding current used during welding.</p> <h3 id="avoiding-distortion-and-cracking-when-tig-welding-stainless-steel">Avoiding Distortion and Cracking when TIG Welding Stainless Steel</h3> <p>Because stainless steel is prone to greater thermal expansion than other materials it tends to distort easily. Too high of a current setting and/or too slow of travel speeds contribute to this problem. Thermal expansion occurs because the HAZ (heat affected zone) on austenitic stainless steel is more localized than with other materials. When the weld cools, there is slow thermal transfer to the surrounding material that can lead to buckling. By clamping, using a fixture or adequately spaced tack welds, especially on thin gauge material, you can reduce the chances of buckling. Along with distortion comes the potential for cracking, By using a joint design consisting of a V-grove, modified V-grove, U-grove of a J-grove that limits the number of weld passes and the amount of heat applied the chance of cracking will be reduced. Cracking will also occur in the weld initiation and crater area. One way to prevent cracking in this area is to use run-on/run-off tabs. These tabs need to match the base material for the best results. The tabs provide an area to 鈥榬un-on鈥?or 鈥榬un-off鈥?the weld thus eliminating arc starting and craters on the actual weld joint and can be easily ground or cut off-after the weld cools.</p> <p><strong>Remember:</strong> even with the right type and amount of gas, good heat input and proper travel speeds, training and practice is still the best defense against the pitfalls of TIG welding stainless steel.</p> Sun, 15 Feb 2015 00:00:00 -0500 Tig Welding Stainless Steel tig welding Stainless Steel How to TIG Weld Stainless Steel Effectively : Preventing Carbide Precipitation <p><img class="alignright wp-image-4058 size-medium" src="" alt="tig weld stainless steel" width="300" height="225" /></p> <p>In order to effectively <strong><em>TIG weld stainless steel</em></strong>, it important to consider carbide precipitation.</p> <h3 id="tig-weld-stainless-steel--carbide-precipitation">TIG Weld Stainless Steel : Carbide Precipitation</h3> <p><strong>What is Carbide Precipitation</strong>? Carbide precipitation occurs when the chrome and carbon in 300 series stainless steel is drawn out of the material and reacts to the atmosphere. It occurs around between 800 to 1650 degrees Fahrenheit (426 to 899 degrees Celsius), so care should be taken to keep the weld zone below that range or in an inert atmosphere (via argon shielding gas).</p> <p>A characteristic of an annealed austenitic stainless steels such as 304, is its susceptibility to an important micro-structural change if it is exposed to temperatures within an approximate range of 800-1650F. Within this range, chromium and carbon form chromium carbides, and these precipitate out of the solid solution at the boundaries between the grains. The rapidity of carbide development depends on a number of factors. The actual metal temperature between the range of 800-1650F is one factor. Chromium carbides form most rapidly at about 1200F, and the formation falls off to nil at the upper and lower limits. Another factor is the amount of carbon originally present in the material, the higher the carbon content the more pronounced the action. Time at temperature is a third factor.</p> <p>The effect of carbide precipitation on corrosion resistance is to reduce the chromium available to provide corrosion resistance. Because low-carbon content reduces the extent to which carbide precipitation occurs, the low-carbon austenitic grades may be preferred for weldments to be used in highly corrosive service. 304 with a maximum carbon content of 0.08% is widely used. Also available are low-carbon 304L, 316L, and 317L with 0.03% carbon.</p> <p><strong>Heat and Travel Speed</strong></p> <p>Generally speaking, there are three causes of carbide precipitation: heat, travel speed and gas. Specifically, too hot of a TIG weld, too slow of travel speed and/or inadequate shielding gas coverage can individually, or in combination, cause the problem.</p> <h3 id="some-methods-of-preventing-carbide-precipitation-when-tig-welding-stainless-steel"><strong>Some methods of preventing carbide precipitation when TIG Welding Stainless Steel</strong>:</h3> <ol> <li>Stainless steel requires 1/3rd less amps for every thousandths of an inch of material thickness compared to mild steel.</li> <li>Maintaining an appropriate travel speed helps prevent an excess amount of heat from entering the TIG weld.</li> <li>Choose the correct tungsten and filler rod diameter.</li> </ol> Sun, 15 Feb 2015 00:00:00 -0500 Tig Welding Stainless Steel tig welding Stainless Steel TIG Welding 国内精品久久久久影院_强壮的公么征服我完整版韩国_欧美zooz人禽交