Complete program from pre-welding to post-welding weld grinding
Pre-treatment before welding:
Since the processes involved and surface finishes required will often vary and are often driven by the type of material you have and its inherent surface finish requirements, this article will look at both carbon and stainless steel.
Before even making a weld, especially with carbon steel, the workpiece should be cleaned to remove any oxidized skin formed during the hot roll manufacturing process – oxidized skin affects the quality of the weld.
Therefore, it is necessary to Peeling Wheel Pre-treatment of the material surface to remove rust and impurities
| carbon steel | stainless steels |
| Metal Inert Gas Welding | Tungsten Inert Gas Welding |
| Gas Metal Arc Welding (GMAW) is a low-cost, high-productivity welding method for all common metals and alloys.
The process uses an inert shielding gas and a semi-automatic wire feeding device, which acts as a filler material. Metal inert gas welding is generally considered to be the best choice for heavier or thicker workpieces, but produces thicker welds. We recommend metal inert gas welding on carbon steel. |
What can be called gas tungsten arc welding is a more precise arc welding process that utilizes a tungsten electrode to form the weld.
It is generally recognized that tungsten inert gas welding is a more difficult skill to master and is much slower than metal inert gas welding. The weld is neater and smaller and is the most commonly used weld on stainless steel. |
Welding type
Difference between carbon and stainless steel:
| carbon steel | stainless steels |
| The decision as to which finish to achieve is closely related to the application of the finished product and the base material itself (carbon steel is almost always painted).
It should be noted that although this article focuses on removing welds, not all welds need to be removed for the metal to work. This is especially true of carbon steel for applications where the seam is not visible. For example, in subsea pipelines or when the metal is structurally important and hidden behind panels. After all, unfinished welds are inherently stronger than finished welds due to the material removal involved in grinding. With carbon steel, finishing a weld is a fairly simple process. In most cases, the steel only needs to be prepared to the extent that paint can be applied. A rough and well-scratched surface actually provides better adhesion than when fully polished. In fact, in cases where powder coating is to be used to color the metal, a two-step weld removal of coarse particles may be sufficient. |
Stainless steel is inherently stronger than its carbon steel counterparts and is often used in much thinner gauges.
This feature has implications for grinding and will be discussed when we make the initial cut. Stainless steel has a large number of commercial applications and the chosen weld finish is intrinsically linked to this application. For example, a highly finished finish can be used for aesthetic reasons (which this article will help you achieve), whereas an elevator ledge or handrail must have a specialty stainless steel finish to hide the visibility of fingerprints and scratches. This results in a more practical finish. |
It should be noted that if you are using both materials at the same time, they should be stored separately in the finishing section of the shop to avoid cross-contamination. Especially when going from carbon steel to stainless steel.
The last thing you will want to do is add some carbon steel blanks to your stainless steel workpiece. Make sure to also store all abrasives to be used separately as well.
Initial weld grinding
| The first stage of weld finishing is the same; removing excess stock from the weld itself. The objective here is to grind the joint to the same level and continuous surface as the rest of the base metal.
To achieve this initial cut, the metalworker may choose to use a simple grinding wheel with an angle grinder if surface finish is not essential. Using grinding wheels on weld seams Although grinding wheels can be used to remove blanks on both materials, a high degree of skill and experience is required to obtain acceptable results on stainless steel. Pits such as air planes and undercuts may be encountered, so care must be taken to ensure that the correct angle is used when grinding. |
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| carbon steel | stainless steels |
| Grinding wheels should be the choice for carbon steel; they will remove welds quickly and are well suited to this operation as the appearance of scratches is not an issue compared to stainless steel.
Grinding wheels have self-sharpening ceramic particles that bite and lightly cut the blank. As previously mentioned, the use of grinding wheels on stainless steel requires a high level of skill and experience to achieve a suitable finish. Instead, many people opt for fiber optic discs or flap discs at this stage (we will cover them). |
If you use a grinding wheel, you must use a suitable stainless steel product; round sheet blotters identify it as non-ferrous (no iron)
Use a medium grit on the rough option for the following reasons.1. The resulting scratches will be difficult to blend in at a later stage, especially if you are creating delicate finishes.2. Stainless steel gauges are thin and you run the risk of forming noticeable flat spots. Especially on tubular parts. |
There are many potential options when choosing a grinding wheel. As always, grain size, grain type and adhesive will determine the performance and feel of the product, so make sure you are clear on what is needed before proceeding!
VIDEO: Steel Pipe Detail Joints Clean Welds with Soft Resin Grinding Wheel
Use of baffles on welded seams
Flap discs are the most popular choice for welding finishes on stainless steel and carbon steel, and it’s not hard to see why, as they offer key advantages over standard grinding wheels.
Flap discs are ideal for their long service life, comfort and operator control (often providing the user with a greater margin for error), lower noise generation and quality of surface finish, all of which are important reasons for choosing these abrasives.
| carbon steel | stainless steels |
| Selecting P40 grit in the valve disc will immediately eliminate the carbon steel weld and prepare the workpiece for further conditioning (if required) prior to final painting. | Metalworkers often choose baffle discs when a higher quality, finer surface finish is required, as such baffle discs (or fiber discs) are the best of stainless steel. Our abrasives are suitable for the first stage of stock removal. |
Regulating and mixing welded joints
| carbon steel | stainless steels |
| If you are powder coating carbon steel, the grinding process is almost over. The nylon grinding wheel only needs one more stage of mixing.
Powder coating is thick enough to mask the appearance of residual scratches from rough abrasives and adheres easily to the scratched carbon steel surface. If the coating layer is thinner than the powder coating, then you may need to refine the scratches further so that they don’t show up in the final layer. |
Here, we recommend using a medium grit conditioning pad to quickly mix the medium. Whether you are looking for a highly finished finish or a professional stainless steel finish, stainless steel will definitely need further conditioning and blending.
On stainless steel surfaces, where initial scratches look unsightly, to mix well, a nylon wheel performs best in the 5000-6000 RPM range, a non-woven abrasive that provides a consistent, stain-free coated finish to the metal. If that’s still not good enough, a polishing wheel is required. The soft material combined with fine silicon carbide particles provide a smooth, glossy finish. |
At this stage, the weld between the pieces of molten metal should almost disappear. For carbon steel, this surface is now ready for painting or use.
In the case of stainless steel, further steps are required to achieve a finer finish, so the information below relates to stainless steel only.
The decision as to which finish to choose for a stainless steel workpiece depends entirely on the purpose of the end product.
A bright, uniform finish can be obtained relatively easily and quickly.
To blend surface defects and scratches left on the stainless steel from previous processes, we recommend the use of a nylon grinding wheel. High quality silicon carbide will give the metal a truly impressive bright appearance.
It is necessary to use the movement slowly over the metal at an angle of 10-15°, using only the weight of the angle grinder.
For best results and to avoid burning at 6000 to 7000 RPM.
This finish should leave the seamless glossy surface you want, but if you want a more lustrous shine, felt discs are perfect.
Professional stainless steel finish
For railings or handrails, a specialty stainless steel finish may be specified. Professional Stainless Steel Finish is a common but specialized stainless steel finish that cannot be achieved by rotating an abrasive such as a disc.
Its linear appearance can only be achieved with a belt or wheel. In this case, the previous steps would be replaced by using a grit sanding belt, then an intermediate non-woven belt, and finally a very fine non-woven belt to buff it out.
The goal here is to remove only a small amount of surface metal without significantly affecting the total thickness. It is important to ensure that sanding is done in one direction only if a linear effect is desired.
It should be noted that on flat surfaces we need a machine with belts or staggered grinding wheels on the pump bushing and, for tubes, sanding belts on a tube finishing machine.
To go beyond the stage of specialized stainless steel processing to produce a clean, smooth and seamless shine on welds requires finer grade abrasives with very low cut rates.
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