The manufacturing process of pressure vessels includes raw material preparation, scribing, blanking, bending of plates, forming, edge processing, assembly, welding, inspection, etc.
Preparation of raw materials
Before marking the steel, the steel must be pre-treated first. The pretreatment of steel refers to the purification treatment, correction, and protective primer coating of steel plates, pipes and section steels.
Purification treatment is mainly to remove rust, oxide scale, oil stains and welding slag on the surface of steel plates, pipes and sections before scribing, cutting, and welding, and after the steel is cut, beveled, formed, and welded.
Orthopedics is the process of correcting the deformation of steel during transportation, hoisting or storage.
Protective paint is mainly used to improve the corrosion resistance of steel, prevent oxidation, extend the life of parts and equipment, and apply a layer of protective paint on the surface.
Scribing is the first process in the manufacturing process of pressure vessels. It directly determines the dimensional accuracy and geometric accuracy of the parts after forming, and has a great impact on the subsequent assembly and welding processes.
Scribing is to draw the blanking line, processing line, various position lines and inspection lines on the raw material or the preliminary processed blank, and mark (or write) the necessary signs and symbols. The marking process usually includes the unfolding, lofting and marking of parts.
The size of the blank should be determined before scribing.
The size of the blank is composed of the unfolded size of the part and various machining allowances.
There are mainly the following methods to determine the unfolded size of a part:
- Drawing method: refers to the use of geometric drawing method to expand the part into a plane figure.
- Calculation method: refers to the calculation formula derived according to the principle of expansion or the principle of constant area before and after compression (drawing) deformation.
- Test method: It refers to determine the unfolded size of the blank of the more complicated shape part through the test formula. This method is simple and convenient.
- Comprehensive method: For overly complex parts, drawing and calculation methods can be used for different parts to determine the size of the blank. Sometimes it can also be verified by experimental methods.
Parts for manufacturing containers can be divided into two categories:
Expandable parts and non-expandable parts, such as circular cylinders and elliptical heads, are respectively expandable and non-expandable parts.
Cutting sheet metal
Cutting sheet metal is also called blanking, which refers to the process of separating the required blanks from the scribed raw materials.
There are two methods for cutting sheet metal: mechanical cutting and thermal cutting.
Mechanical cutting mainly includes shearing, sawing, milling and punching, etc. Its characteristic is that mechanical force plays a major role in the cutting process.
Shearing is to press the scissors into the workpiece to make the shear stress exceed the shear strength of the material to achieve the purpose of shearing. This method has high efficiency and high cutting precision. It can be used as long as the material hardness and size are appropriate, but the metal 2~3mm away from the cut has obvious hardening. According to the plane shape to be cut, it can be divided into straight-line shearing and curve-cutting.
There are two types of shearing machines that use straight long shear blades to cut, namely, flat-cut shears and oblique-cut shears.
In flat shears, the two straight cutting edges are parallel, and the cutting process is carried out simultaneously along the length of the cutting edge, so the shearing force is large and the impact is strong, and it is suitable for cutting thick and narrow strips.
In the oblique shear, the two straight cutting edges are obliquely intersected at a certain angle, and the cutting process is gradually carried out along the length of the cutting edge. Therefore, the shear force is smaller than that of the flat shear when cutting workpieces of the same thickness, and the impact is reduced. It is suitable for shearing. Thin and wide sheets.
In equipment manufacturing, gantry shears are often used to cut linear workpieces. The shearing machine is easy to use, simple to feed, fast in cutting speed and high in precision.
Sawing is a cutting process, and the equipment used includes grinding wheel saws, circular saws, etc. Sawing is generally used for cutting pipes and profiles.
Oxygen cutting is abbreviated as gas cutting, or flame cutting. Oxygen cutting is thermal cutting. A preheating flame is required for cutting, but the flame alone cannot achieve cutting. The key is to have a high-speed pure oxygen flow.
Plasma is a state of matter in which all matter is ionized into positive and negative ions. Plasma cutting uses high-temperature, high-speed plasma flame flow to fuse materials to form incisions. It belongs to high-temperature melting and cutting in thermal cutting.
It is not restricted by physical properties. It can cut metals and non-metals, but it is mainly used to cut stainless steel, aluminum, copper, nickel and their alloys.
Forming of the cylinder
The cylinder body is composed of a number of cylinder sections welded by circumferential welds, and the cylinder sections are welded by plate rolling and longitudinal welds.
Bending of plates
The principle of the rounding of the barrel section: The rounding of the barrel section is also called bending of plates (plate bending) or plate rolling, which is the basic manufacturing method of the barrel section.
The principle of bending of plates is to use a plate bending machine to apply continuous and uniform plastic bending to the steel plate to obtain a cylindrical surface.
Forming of the head
There are three main methods of forming the head: stamping method, spinning method and explosive forming method.
At present, the commonly used methods are stamping method and spinning method.
Welding is a process in which the weldment achieves interatomic bonding by heating or pressurizing, or both, and forming a permanent joint.
The welding process is involved in 50% of the world’s annual steel consumption.
Welding can be divided into three categories: fusion welding, pressure welding and brazing.
A processing method in which the workpiece to be welded is locally heated to melt, and then condensed to form a weld to connect the components together.
Including arc welding, gas welding, electroslag welding, electron beam welding, laser welding, etc.
Fusion welding is a widely used welding method. Most low-carbon steels and alloy steels are welded by fusion welding. Special fusion welding can also weld non-metals such as ceramics and glass.
Pressure must be applied during the welding process, which may or may not be heated to complete the welding. The main purpose of the heating is to soften the metal, and the metal is plasticized by applying pressure, so that the atoms are close to the distance of mutual attraction. This is essentially different from the heating during fusion welding.
Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold pressure welding, explosive welding, diffusion welding, and magnetic welding.
Its characteristics are small welding deformation, less cracks, and easy automation.
A soldering method in which the solder with a lower melting point than the base material is heated to melt, but the heating temperature is lower than the melting point of the base material, and the molten solder fills the weld, wets the base material, and diffuses with the base material to form an integrated welding method.
Brazing is divided into two categories: hard brazing and soft soldering.
The heating temperature of brazing is greater than 450°C, and the tensile strength is greater than 200MPa. Silver-based or copper-based solder is often used. It is suitable for occasions with high working stress and high ambient temperature, such as the welding of cemented carbide turning tools and geological drills.
The heating temperature of soft soldering is less than 450℃, and the tensile strength is less than 70MPa. It is suitable for environments with low stress and low working temperature, such as tin-based soldering of circuits.