Why Weld Seams Need Grinding?

In many welding sites, it is common to see workers or weld seam grinders repeatedly grinding the completed weld seams of workpieces. With sparks flying and harsh noises, the originally protruding and rough weld seams are processed to be smooth and flat. Many people may wonder: since the weld seams are already firmly welded, why bother with this extra step of grinding? Actually, weld seam grinding is by no means a "cosmetic project" but a crucial process related to safety, performance and service life.

        During the welding process, the high-temperature molten metal will shrink when cooling down. Moreover, due to the uneven structure during molten pool crystallization, a large amount of "internal stress" will be generated in the weld seam and its surrounding areas. More importantly, the untreated weld seams often have obvious defects such as protrusions, undercuts and weld beads. These areas are like "weak links" in the structure, which will cause internal stress to concentrate here—just like a dead knot tied on a rope, which is most likely to break at the knot under tension.

        One of the core functions of grinding is to trim the shape of the weld seam, grinding sharp edges and protruding weld beads into smoothly transitional curves, so that the stress can be evenly distributed in the entire connection area.

        Metal corrosion is an "invisible killer" of engineering structures, and weld seams are precisely the high-risk areas for corrosion. During welding, the high temperature will form a layer of oxide scale on the surface of the weld seam. This oxide scale has a loose structure, which not only cannot block the intrusion of moisture and corrosive media, but also accelerates the rusting of the internal metal. In addition, corrosion sources such as salt and oil stains will remain in the slag, spatter and microcracks on the weld surface, becoming a "hotbed" for corrosion.

        Grinding can completely eliminate these surface hazards: on the one hand, it removes oxide scale, slag and spatter through physical grinding, exposing a fresh and clean metal matrix; on the other hand, the smooth surface after grinding enables better adhesion of anti-corrosion coatings (such as paint and galvanized layers), avoiding problems such as blistering and peeling of the coating. Take the welding of electric water heater inner tanks as an example. The inner tank is in an environment of alternating water and high temperature for a long time. If oxide scale or slag remains on the weld seam, local corrosion will easily occur, and in severe cases, it will cause water leakage of the inner tank. After fine grinding, the weld seam of the inner tank can be evenly covered with an anti-corrosion coating, forming a complete protective barrier. This extends the service life from 3-5 years (for ordinary untreated products without grinding) to 8-10 years, greatly improving product reliability.

        In some scenarios, weld seams not only need to be "firmly welded" but also "well connected", and grinding is precisely the key to improving connection quality. For example, after the welding of the water heater inner tank is completed, there may be tiny unevenness or gaps at the weld seam. These subtle defects are likely to become leakage hazards under water pressure and also increase the risk of scale accumulation. Through refined processing of the weld seam with special grinding tools, these tiny defects can be accurately eliminated, making the inner wall of the inner tank form a continuous and smooth curved surface. This not only eliminates the risk of leakage but also reduces the attachment points of scale, making the inner tank easier to clean. At the same time, the smooth weld seam also makes the product appearance more in line with industrial design standards and improves the user experience.

In addition, in some high-precision welding scenarios, grinding can also cooperate with non-destructive testing to timely detect and handle tiny welding defects, ensuring the reliability of the connection.

        Smooth and flat weld seams can not only improve the aesthetics of the product but also avoid problems such as scratches and dirt accumulation caused by rough surfaces.

        It is worth mentioning that weld seam grinding is not "the smoother the better", but the grinding degree should be controlled according to specific scenarios—excessive grinding may reduce the effective cross-sectional area of the weld seam, thereby reducing its strength. Professional grinding will formulate precise grinding processes based on factors such as welding materials and structural applications to achieve the best effect under the premise of ensuring performance.

        Our water heater inner tank welding production line is equipped with special weld seam grinding equipment, which adopts an automatic grinding system. It can accurately adjust the grinding force and grinding path according to different positions of the inner tank weld seam and welding process parameters. The equipment is equipped with pressure sensing technology that can monitor the grinding pressure in real time, avoiding the decrease of weld seam strength caused by excessive grinding, and at the same time ensuring that the grinding effect of the weld seam of each inner tank remains highly consistent. This standardized grinding process not only abandons the disadvantages of traditional manual grinding that relies on experience and has large quality fluctuations but also ensures the uniformity of the products from the production line through process solidification, significantly improving the stability of product quality and building a solid line of defense for users' safety in use from the source of production.