How to efficiently sanitize different types of weld joints

Welding has been and will continue to be the most efficient and reliable method of joining metal parts while ensuring quality. There are many types of welding processes, depending on the materials and requirements. In the field of boilermaking, when a strong and durable bond is needed, methods that add material are used to strengthen the resulting bond. This always generates an excess or bulge that, in some cases, regulations prohibit reducing so as not to weaken the joint. In most cases, adjustment or correction is needed. In this article we will try to clarify how and why the most suitable weld seams and abrasives must be cleaned to carry out this process with guarantees.

Pre-Weld Preparation

One of the crucial factors when joining two pieces is the condition of the surface on which the joint will be made. It is essential to ensure that this surface is clean and free of impurities and oxidations that could reduce the resistance of the weld. Whether it’s beveling or preparing a specific weld area, it’s critical to properly condition the surface before welding to prevent contaminants from getting trapped in the weld, which could cause structural failure or breakage later on. To ensure effective bonding, the area should be cleaned with gentle mechanical sanding using a coarse-grained flexible abrasive, between 40 and 80, verifying that there are no impurities or thermal discolorations that indicate oxidation. If beveling is required, a 36-grit ceramic abrasive is suitable for roughing and creating surface roughness suitable for direct welding, without the need for additional refining.

Types of Sanitizing Processes

There are several types of weld joints, which implies different ways to carry out a correct cleaning of the weld:

• Weld Finish

In metal welds with filler material, a bead is formed that has a wavy protrusion due to the excess material necessary to ensure that the bath covers the entire joining area, avoiding narrower and weaker sections than the pieces to be joined.

An appropriate surface finish of the bonding area is crucial for its strength and durability, as well as the aesthetic appearance. A good welding procedure can lose effectiveness if the final finish is not taken care of. Depending on the skill of the welder or the use of manual or automatic processes, the bead can vary in appearance. The decision whether or not to reduce this lump can depend on several factors.

• Simple sanitation without grinding

There are welding procedures with instructions that prohibit the grinding of the bead, especially in heavy boilermaking and carbon steels. This may be because the welded joint is in an area that is not visible, has no aesthetic purposes, or to avoid weakening the joint with excessive grinding, especially in butt joints. In these cases, simple mechanical sanitization can be performed using a non-aggressive and adaptable abrasive, such as an abrasive fleece disc, to remove surface impurities without disturbing the bead. This provides a slight roughness sufficient for good adhesion of the coating. In the case of stainless steel, where the joint is not usually painted or coated (since it is a material that is usually chosen precisely because it does not require protection), there are several cases where it is chosen not to grind the bead, since a good welding seam can be more attractive and attractive than a rectified and polished surface. thus fulfilling an aesthetic function as well as saving time. Stainless steel constructions are usually much thinner than carbon steel, which implies a greater risk of weakening due to accidental over-grinding.

• Weld recess, calibration, or grinding

There are several reasons for lowering a weld, since in many cases, this action not only does not weaken the joint, but can make it more effective, as long as the thickness of the material is not compromised. A proper recess process in a weld seam can improve several aspects of the final product, including aesthetics, strength and durability. A cord or seam is always an additional or “artificial” element in a welded assembly. As mentioned, a well-made weld on stainless steel can be very attractive and visually pleasing. The overall appearance of the set tends to be cleaner and suggest higher quality when no seams are observed. In addition, smoothing the transitions of this bead or “bump” can also reduce surface tensions, minimizing the risk of cracks, especially in welds that present irregularities. In materials with low thermal conductivity, such as stainless steels, a welding process will also generate a ZAT or Thermal Affectation Zone that will be more critical on the surface, where the high temperature in contact with oxygen will cause discoloration in response to surface oxidation. With a slight surface grinding, this discolored or “oxidized” area will be eliminated, favoring the generation of a passivating layer, which will protect the piece effectively. And finally, correct recess and grinding will also provide a better fit in the event that the welded parts need to be fixed to other parts.

Abrasives for working a weld seam

There are several formats of abrasives for weld remediation, but it is important to find out which one is optimal according to your sanitation process.

• Grinding discs: They are intended for manual work. It is an economical product, but on the contrary very noisy and with very poor finishes. It usually generates very slow process times and very high vibrations, although it has a special advantage as it allows work at the tip and that is that it can reach bends where other formats cannot.

• Flap discs: Its use is focused on manual applications. They can be made of corundum, zirconium or ceramic grain. Although it is a very versatile and easy to use tool to perform various tasks, it is not the fastest or most effective abrasive in massive or repetitive processes.

• Fibre discs: They are the most effective alternative to speed up process times. Their cutting capacity is the highest of all those analysed in this section, and they can be combined with a harder or more flexible support plate according to the need and comfort of the operator.

• Velour discs: They are a very versatile tool for use in refining processes where it is only intended to remove very low input beads or to perform fine finishing and polishing steps. Like fibre discs, they can be combined with a harder or more flexible support plate depending on the operator’s need and comfort.

• Sanding belts: If there is the possibility of using a sanding head with a belt, the advantages of the fibre disc can be added to a much higher performance due to the large surface area and grain load available. They are the most cost-effective solution in automated processes.

The effectiveness of a welded joint can be seriously compromised by poor preparation or poor sanitation, therefore, it is important to know the right abrasives for the process, in addition to the different sanitation processes that can be carried out. If you are interested in learning more about abrasives, I suggest you contact VSM Abrasives. They are true specialists in the manufacture of flexible abrasives and have in-depth knowledge of their applications. Do not hesitate to explore their experience to find solutions suitable for your needs.