The manufacturing process of pressure vessels includes raw material preparation, scribing, blanking, bending, forming, edge processing, assembly, welding, inspection, etc.
Preparation of raw materials
Before scribing the steel, the steel must first be pretreated.
- Pretreatment of steel: refers to the purification treatment, orthopedic and protective primer of materials such as steel plates, pipes, and profiles.
- Purification treatment: It is mainly to remove rust, oxide scale, oil stains, and welding slag on the surface of steel plates, pipes, and profiles before scribing, cutting, and welding, and after cutting, and beveling, forming, and welding.
- Correcting: The process of correcting the deformation of steel during transportation, hoisting, or storage.
- Applying protective paint: mainly to improve the corrosion resistance of steel, prevent oxidation, prolong the life of parts and equipment, and apply a layer of protective paint on the surface.
Scribing: The first procedure in the pressure vessel manufacturing process directly determines the dimensional accuracy and geometric shape accuracy of the parts after forming and has a great impact on the subsequent assembly and welding procedures.
Scribing is to mark the blanking line, processing line, various position lines, and inspection lines on the raw material or the pre-processed blank, and mark (or write) the necessary signs and symbols. The scribing process usually includes the development, lofting, and marking of parts.
The size of the blank should be determined before scribing. The blank size consists of the unfolded size of the part and various machining allowances.
There are mainly the following methods for determining the unfolded size of a part:
- Drawing method: refers to the use of the geometric drawing method to expand the part into a plane figure.
- Calculation method: refers to the calculation formula derived from the principle of unfolding or the principle of the constant area before and after compression (tension) deformation.
- Test method: refers to determining the size of the blank of the more complex parts by the test formula. This method is simple and convenient.
- Comprehensive method: For overly complex parts, the drawing method and calculation method can be used for different parts to determine the size of the blank, and sometimes the test method can be used for verification.
The parts for manufacturing containers can be divided into two categories: expandable parts and non-expandable parts, such as circular cylinders and oval heads, which belong expandable and non-expandable parts respectively.
Cutting, also known as blanking, refers to the process of separating the required blanks from the raw materials that have been crossed. There are two cutting methods: mechanical cutting and thermal cutting.
Mechanical cutting mainly includes shearing, sawing, milling, 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 so that the shear stress exceeds the shear strength of the material to achieve the purpose of shearing. This method has high efficiency and high incision precision. As long as the material’s hardness and size are suitable, it can be used, but the metal 2~3mm away from the incision has an obvious hardening phenomenon. The plane shape to be cut can be divided into straight line cutting and curve cutting.
There are two types of shears that use straight long shearing edges shearing, namely flat shears and oblique shears.
- In flat shears, the two straight cutting edges are parallel, and the shearing process is carried out simultaneously along the length of the cutting edges, so the shearing force is large and the impact is strong, and it is suitable for cutting thick and narrow strips.
- For oblique shears, the two straight cutting edges intersect at a certain angle, and the shearing process proceeds gradually along the length of the cutting edge, so the shearing force is smaller than that of the flat shears when cutting workpieces of the same thickness, and the impact is reduced, which 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 in feeding, fast in cutting speed, and high in precision.
Sawing is a cutting process, and the equipment used is grinding wheel saws, circular saws, etc. Sawing is generally used for cutting pipes and profiles.
Oxygen cutting is referred to as gas cutting, also known as flame cutting. Oxygen cutting is thermal cutting. A preheating flame is required for cutting, but only a flame cannot achieve cutting. The key is to have high-speed pure oxygen flow.
Plasma is a state of matter in which matter is fully ionized into positive and negative ions. Plasma cutting is the use of high-temperature, high-speed plasma flame flow to fuse materials to form incisions, which belongs to high-temperature melting and cutting in thermal cutting. It is not limited by physical properties, it can cut metal and non-metal, but it is mainly used for cutting stainless steel, aluminum, copper, nickel, and its alloys.
The forming cylinder of the cylinder is composed of a number of cylinder sections welded by circumferential welds, and the cylinder sections are welded by metal plate rolling and longitudinal welding. The rolling principle of the barrel section the roll bending of the barrel section, also known as plate roll bending or plate rolling, is the basic manufacturing method of the barrel section.
The principle of roll bending is to use a plate rolling machine to apply continuous and uniform plastic bending to the steel plate to obtain a cylindrical surface. Head forming There are three main methods for forming the head: stamping method, spinning method, and explosion forming method. At present, the commonly used methods are the stamping method and spinning method.
Welding is a process in which the weldment achieves atomic bonding and forms a permanent joint by heating or pressing, or both.
Welding processes account for 50% of the world’s annual steel consumption.
Three welding methods
A processing method in which the workpieces to be welded is locally heated to melt and then condensed to form welds 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, and 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.
Welding can be accomplished with pressure, which may or may not be done with heat. The main purpose of its heating is to soften the metal, by applying pressure to plastically deform the metal so that the atoms are close to the distance of mutual attraction, which is essentially different from the heating during fusion welding. Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold pressure welding, explosion welding, diffusion welding, and magnetic force welding. It is characterized by small welding deformation, fewer cracks, and easy automation.
A welding method in which the solder with a lower melting point than the base metal is heated to melt, but the heating temperature is lower than the melting point of the base metal, and the molten solder fills the weld, wets the base metal, and diffuses with the base metal to form an integral welding method. There are two main types of brazing: brazing and soldering. The heating temperature of brazing is greater than 450 ℃, and the tensile strength is greater than 200 MPa. Silver-based and copper-based brazing filler metals are often used, which are suitable for occasions with high working stress and high ambient temperatures, such as the welding of carbide turning tools and geological drills. The heating temperature of soldering is less than 450°C, and the tensile strength is less than 70MPa, which is suitable for environments with small stress and low working temperature, such as tin-based soldering of circuits.