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. The pretreatment of steel refers to the purification, orthopedic and protective primer of steel plates, pipes and profiles.
Purification treatment is mainly to remove rust, oxide scale, oil stain and welding slag on the surface of steel plate, pipe and section steel before scribing, cutting and welding and after cutting, beveling, forming and welding.
Orthopedics is the process of correcting the deformation of steel during transportation, hoisting or storage.
The main purpose of applying protective paint is to apply a layer of protective paint on the surface to improve the corrosion resistance of steel, prevent oxidation, and prolong the life of parts and equipment.
Scribing is the first procedure in the manufacturing process of the pressure vessel, which directly determines the dimensional accuracy and geometric 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:
1) Drawing method: refers to the use of geometric drawing method to expand the parts into plane graphics.
2) Calculation method: refers to the calculation formula derived from the principle of unfolding or the principle of constant area before and after compression (drawing) deformation.
3) Test method: refers to determining the size of the blank of the more complex shape parts through the test formula, this method is simple and convenient.
4) 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 cylinder and oval head, which belong to 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.
1. Mechanical 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, 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 hardness and size are suitable, it can be used, but the metal 2~3mm away from the incision has obvious hardening phenomenon. According to the plane shape to be cut, it can be divided into straight line cutting and curve cutting.
1) Straight cut
There are two types of shears that use straight long shearing edges for shearing, namely flat shears and oblique shears.
In the 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.
In the oblique shears, the two straight cutting edges intersect at a certain angle, and the shearing process proceeds gradually along the length of the cutting edges, 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 are grinding wheel saws, circular saws, etc. Sawing is generally used for cutting pipes and profiles.
2. Oxygen cutting
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 flame cannot achieve cutting. The key is to have high-speed pure oxygen flow.
3. plasma cutting
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.
Forming of the barrel
The cylinder body is composed of a number of cylinder sections welded by circumferential welds, and the cylinder sections are welded by sheet rolling and longitudinal welds. The rolling principle of the barrel section The rounding of the barrel section, also known as spheronization or coiling, is the basic manufacturing method of the barrel section. The principle of roll bending is to use a rolling 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 head forming: stamping method, spinning method and explosion forming method. At present, the commonly used methods are 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.
Welding can be divided into three main categories: fusion welding, pressure welding and brazing.
(1) Fusion welding
A processing method in which the workpieces to be welded are 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.
(2) Pressure welding
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, less 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 °C, and the tensile strength is greater than 200 MPa. Silver-based and copper-based solders are often used, which are suitable for occasions with high working stress and high ambient temperature, such as the welding of carbide turning tools and geological drills. The heating temperature of soldering is less than 450℃, 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.
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