How is the hip annealed for varus foot deformity?

Elimination of internal stresses so that they do not affect the joints and the entire structure is most effectively achieved by annealing. The product is placed in an oven, chamber or induction heat source and brought to a temperature of 550-680°C. For thick-walled products, a certain annealing time (from a few minutes to a few hours) is provided in order to sufficiently heat the structure. The product is then allowed to cool slowly in the oven.

Deformations and stresses during welding: basic principles

The welder must not only pay attention to the correct shape of the weld, but also anticipate the effects of welding on the future structure. Since the metal is heated locally to a temperature of 3,000-5,000 ⁰C during electric welding or when working with a gas burner and the rest of the metal remains cold, internal stresses arise that deform the product. Such physical phenomena not only spoil the appearance of the product, but also lead to failure of connections subjected to additional stress. Let's take a closer look at how internal tension arises, what types of tension there are and what can be done to prevent or eliminate them.

Let's start with a definition of these phenomena. Welding tension – is the mechanical action that occurs in the welding area and affects the connection itself and the surrounding structure:

Deformation during welding – is a change in the shape of the structure caused by an internal force (stress) or a change in the structure of the material. Some deformations occur immediately and distort the product parameters, flatness and symmetry. Other deformations occur later in the form of dimensional changes, corrosion and weld failures.

The simplest example of stress and deformation is observed when two thin steel sheets are joined by a continuous one-sided weld. As a result, the product loses its flatness as the panels bend and pull against each other and the structure takes on a V shape. The more seams, transitions and the more complex the product, the greater the likelihood that internal tensions will develop.

The extent of the deformation determines the further usability of the structure. In some cases this becomes impossible or dangerous, so welders must know the causes of these phenomena and, if possible, prevent or correct them.

Why do welding stresses and deformations occur?

The main cause of stress in metal during welding is linear expansion due to heat. If the material in the area of the weld heats up significantly and the rest of the material remains cool or slightly warm, physical stresses occur. As the weld cools, it tightens and pulls the joined sides of the workpiece together, causing deformation.

When welding two different materials, e.g. B. Mild steel and carbon steel or carbon steel and high alloy steel, stresses are inevitable. They have different melting points and therefore different coefficients of thermal expansion. If the two materials are closely connected to each other, one expands into the other.

Structural changes can occur when the heat during welding hardens the material. Its density and volume change, and stresses act on neighboring areas, causing them to break. These are natural consequences of the welding process and we will discuss how to anticipate and prevent them below.

Other causes of tension and stretching include:

Rapid cooling of the workpiece. The welders are in a hurry, but cannot hold the welded workpieces because of the high temperature, so they immerse them in a container of cold water or pour them from above. Incorrect calculations when welding. Consider where the metal will expand when heated and allow for appropriate tolerances. Error during assembly. Failure to comply with the distances indicated in the drawings or welding without edge cutting where necessary will result in excessive stress and deformation of the structure. Short welding distances. If the welds are close together, the surface will inevitably overheat and expand or contract. When designing a structure, it is important to space the welds at the correct distance from neighboring welds. Errors in choosing the welding process. Excessive current, incorrect electrode diameter, incorrect torch holding angle lead to overheating of components and distort the design parameters. Errors in the order of the welds. Experienced welders know that metal stresses can be controlled by aligning the product by alternating welds in different places. Without a strict sequence and change of heating sides, the product will simply leak.