Preperation for welding
A weld of quality can be achieved by fine preparation.
Preparation for welding includes;
o design of structures
o deciding where the welds should be placed
o type of joint design that should be used for each weld
o the sequence that should be followed in making the welds.
Welding that has been used in many industries for assembling metal for over a century increased in efficiency. This was done by using different techniques and materials.
The stages before the welding process remain the most important. It has been found that welders often neglect and do not pay the attention needed to this step in which inappropriate techniques are used which can result with unsatisfactory and negative outcomes. Pure welds start with weld preparation. In shops, grime and dirt accumulate quickly which contaminates the weld. Cleaning the material beforehand becomes a priority as it helps to ensure a pure weld is succeded.
Importance of Preperation
All different types of metals are welded for various different types of use. However, for welding processes to be fine, accurate and effective the first time around the parent material have to be properly prepared.
Material preparation is so important that often it is documented to ensure consistency in the process, regardless of the material. Removing coatings such as oils, greases,paint and rust makes certain that the area to be welded is in a good possible condition.
When working with carbon steels it is important to remove impurities such as mill scale and rust. Oil-based coatings must be removed before welding happens. Removing chromium oxide produces a decorative finish on stainless steel alloys which is often achieved in a more direct process.
In stainless steel the cleaning of welded areas to remove surface oxide allows for the formation of protective layers that is important in the stabilization of steel alloys. The stabilization is known as passivation.
Nonferrous materials have their challenges in the weld preparation process. With metals such as titanium and aluminium, there is a time between the surface cleaning and welding, as oxidations form rather quickly. Cleaning areas too early before welding leads to the necessity for rework.
For a good overall performance of a product used to prepare a surface weld, it’good to calculate and control both the friction applied to the surface and speed. Your best bet is to study the manufacturer’s recommendations for the highest RPM for safe use of material and disc size.
Maintaining Corrosion Resistance
Preparation of the weld zone
The arrangement of the weld zone is critical for a protected and fruitful watertight material detail. The weld zone is 300mm min and must be spotless of refuse, sand and cement. All cutting of sheets must be finished by a saw not a processor, and all burrs expelled. Sheets inside the weld zone must be completely upheld by a non combustible, inflexible, thick protection. Duorock is typically utilized. For security all combustible material must be evacuated or secured preceding the welding works beginning. To guarantee welding is conceivable, a greatest hole of 5mm between the aluminum sheets is reasonable. The weld light will pursue the readied line. Along these lines, in the event that you need a straight weld, you deliver a straight sliced through the aluminum sheets. Painted surfaces notwithstanding the abovementioned, where painted/covered sheets are utilized, all paint must be expelled, at least 25mm either side of weld line, including the underside of the sheet. This ought to be finished utilizing a wire wheel/brush. The utilization of grating circles will lessen the thickness of the sheet and store incorporations into the sheet.
What to avoid when preparing a surface for welding
Avoid removing much of the parent materials or creating scratches around the area of weld area. Removing too much material which is also known as undercutting result in inclusions during the weld process. This is a serious concern if one is working with stock that has been worked with torch cutting or plasma. This leaves deep marks in the work piece and drive the surface impurities deep into the material to be welded with the chance of increasing the likelihood of weld porosity or poor coating adhesion at a later stage in the fabrication process.
Also avoid cross-contamination by using a new abrasive product. Contamination can occur both directly and indirectly. Direct contamination as when using a steel wire brush on aluminium is preventable as long as one keep consumables for nonferrous and ferrous materials separated and organized.
Prevention from indirect contamination is important. This can be caused by airborne dust from other manufacturing processes. The use abrasive product will create dust which can spread throughout the space. An efficient solution is storing new abrasive products in plastic bags to keep them protected from dust.
Contamination risk is lowered when a cleaning regimen is established on the working area which includes lamp tops, toolboxes, and cabinets.
Factors which influence choice of edge preparation;
o Welding process
o Extent of penetration required
o Welding distortion
Impurities / contaminations that can affect a weld
Porosity in welding is a contamination which is in the form of trapped gas. Shielding gases are a result of the torch being applied to the treated metal which are absorbed into the molten metal, also release of solidification happens. In other circumstances, the shielding gas does not reach the atmospheric air and the weld pool and so it affects the weld bead.
Welding Porosity is the cause of a contaminated surface. Any oil, moisture content or grease on a surface can contribute to the contaminations.
During the steel welding, oxidation occurs in the weld seam if oxygen reaches this area. When a metal is contaminated with this impurity, it is no longer corrosion resistant and more treatment is necessary. Oxygen monitor can prevent oxidation from happening.
Though there are other concerns when it comes to producing a pure weld, a proper preperation will improve the final weld quality.
Proper preparation of the weld joint is considered as a critical part of welding. A variety of mechanical methods are exist for initial weld joint preparation. The plasma arc cutting process is normally used to cut alloy plate into different shapes and prepare the weld angles. Edge preparation can be performed using both grinding and machining techniques applicable to Co- and Ni-base alloys.
It is necessary to make all cut edges’ condition bright and shiny metal prior to welding. In addition to weld angle which is generally 25 mm wide band on the surface of the weld zone should be conditioned to bright metal with an 80 grit flapper disk. It is especially important that the surface oxides be removed before welding. Melting temperatures of the surface oxides are much higher than the base metals being welded so the probability is that they stay solid during welding and become trapped in the weld pool which form incomplete fusion defects.
Beveling or grooving
Beveling or grooving is particularly alluring for butt joints thicker than 5/8 in.. In situated tee joint or comer joint filet welding where finish root infiltration is wanted, the adjoining part is for the most part angled if the profundity of combination wanted for each weld surpasses 3/8-in.
End with Bevel
Tidiness is viewed as a critical part of Ni-/Co-base weld joint readiness. Preceding any welding task, the welding surface and adjoining locales ought to be completely cleaned with a suitable dissolvable, for example, CH3)2CO, or a fitting basic more clean. All oils, cutting oils, pastel imprints, machining arrangements, erosion items, paints, scale, color penetrant arrangements, and other outside issue ought to be totally evacuated. Any cleaning buildup ought to likewise be evacuated preceding welding. Tainting of the weld area by lead, sulfur, phosphorus, and other low-dissolving point components can prompt extreme embrittlement or splitting. For Co-and Fe-base composites, surface contact with copper or copper-bearing materials in the weld district ought to be maintained a strategic distance from. Indeed, even follow measures of copper at first glance can result in copper sullying breaking, a type of fluid metal embrittlement, in the warmth influenced zone of the weld.
Surface iron sullying coming about because of contact with carbon steel can result in rust recoloring, however it isn’t viewed as a significant issue and, in this manner, it is commonly not important to evacuate such rust stains preceding administration. What’s more, liquefying of little measures of such surface iron sullying into the weld pool isn’t relied upon to altogether influence weld-metal consumption obstruction. While such pollution isn’t viewed as a difficult issue, if sensible consideration is practiced to dodge the issue, no specific remedial measures ought to be essential preceding administration.
Treated steel wire brushing is regularly adequate for bury pass cleaning of weldments. The wire brushes that are utilized amid welding ought to be saved for use on Ni-and Co-base compounds just, and ought not be utilized for carbon steel. The pounding of begins and stops is prescribed for all curve welding forms. In the event that oxygen-or carbon dioxide-bearing protecting gases are utilized, light pounding is vital between goes before wire brushing. Slag expulsion amid SMAW will require chipping and pounding pursued by wire brushing.