Pressing process code of head
This specification specifies the technical requirements and operation methods of pressure head stamping. It is also applicable to the heating, pressing and repair of flanging, flat dismantling tubesheet, elliptical head, dished head and arched tubesheet made of carbon steel and low alloy steel.
- Heads for steel pressure vessels (GB/T 25198-2010).
- GB/T 25198-2010 technical conditions for manufacturing pressure parts of shell boiler.
Technical requirements for operators
Operators shall be familiar with drawings, technical requirements and process specifications.
The operator shall be familiar with the performance, structure and necessary maintenance knowledge of the equipment, molds and tools used, and strictly abide by the operating procedures. The operators of heating furnace and press must hold the operation license before they can work.
Operators shall do a good job in site management. Workpieces, molds and tools shall be provided with corresponding station instruments, which shall be placed neatly at the designated place to prevent damage and corrosion.
Equipment and tooling
The performance of various oil press, heating furnace, feeding trolley and other equipment shall comply with the provisions in the equipment manual.
Tooling molds, tools and gauges are provided with forming molds, composite molds, stripping devices, supporting feet, fastening wrenches, hand hammers, sledgehammers, pneumatic grinding wheels, pneumatic shovels, steel tapes, box rulers, steel ruler, bending ruler, caliper, internal and external calipers, thermometer, etc. the molds can be used only after passing the inspection. Measuring tools and instruments shall pass periodic verification as required.
Manufacture of head blank
Blank size of head (calculation formula) P = (PN)+ δ+ 2h).
When drawing the blanking line, draw the cross center line first, then the blank line and manhole opening line. The long and short axis of the manhole shall coincide with the cross center line, and the long axis must be perpendicular to the rolling direction of the steel plate (the rolling direction is usually the length direction of the steel plate).
During blanking, the outer circle of the head blank can be cut manually, which is easy to use centering cutting. Profiling cutting is recommended.
Splicing of head blank
The head blank shall be made of a whole steel plate as far as possible. If splicing is required, two steel plates are allowed to be spliced according to GB/T 25198-2010 and GB/T 25198-2010 standards and construction drawings.
After welding, the weld reinforcement of the inner surface splicing weld and the outer surface splicing weld affecting the forming quality shall be polished to be flush with the base metal before forming, and the leveling length shall be 300 ~ 350mm from the outer edge of the round billet.
When pressing the perforated head, the small hole in the middle shall be smooth and flat, and the serrated gas cutting edge shall be polished smooth to avoid cracking during hole flanging.
The blank must be transplanted with material marks according to the regulations, and the marks must be clear and correct.
Technical requirements for billet heating
Preparation before heating
The obstacles around the heating furnace must be removed, and the sundries in the heating furnace should be removed. Before charging, the sundries on the blank should be removed.
Check the feeding tools to ensure normal operation and safe charging.
The diameter, thickness and material of the blank must be clearly checked with the drawing, and the temperature rise record must be made.
During loading, ensure that the mark of material transfer is on the lower surface of the blank, so that it can be exposed on the outer surface after stamping.
For blank heating, see table 11-1 for heating specifications.
Heating temperature, ℃
Final pressure temperature, ℃
Stamping normalizing temperature, ℃
Note: normalizing treatment is generally not required after stamping. If necessary, the treatment temperature shall be specified in the heat treatment process card.
Precautions during heating
The billet shall be fed into the furnace when the furnace temperature is less than 600 ℃, and then heated with the furnace. After reaching the heating temperature, the holding time is about 1 min/mm.
Several billets are allowed to be heated at the same time, but attention must be paid to the distance between billets during furnace loading, and the distance between the billets on the bottom and the furnace bottom shall not be less than 150mm.
When several steel plates are heated together, the amount added at one time should not be too much, and it is appropriate to press continuously for half an hour. When one of them is taken out, the rest of the billets will continue to be heated in the furnace, and the same stack of steel plates will be taken out one by one. It is not allowed to add cold billets before taking out, so as to avoid over burning of some billets.
In case of press failure, it is allowed to simmer the furnace charge that has been put into the furnace only when the failure is eliminated in a very short time. However, the furnace temperature shall be reduced to 600 ~ 700 ℃ to prevent oxidation.
After the blank is kept warm for the specified time, it can be taken out with tools (feeding trolley and forklift) and sent to the lower die.
Technical requirements for head stamping
Preparation before stamping
Test run for several minutes before stamping to confirm that the equipment is in good condition for stamping.
Correctly select the mold according to the process specification and avoid wrong use. Measure the thickness of the blank, check whether the specification of the die is appropriate (to prevent the lower die from expanding and cracking), and use it after passing the inspection by the inspector.
After the upper and lower dies of the head are installed on the oil press, check the position of the upper and lower dies. The clearance between the upper and lower molds shall be uniform, and the bolts
Nuts and other fasteners shall be tightened to ensure safety.
Before stamping, the die shall be coated with lubricant. The lubricant is prepared with 40% graphite powder and 60% engine oil, or with graphite powder and water.
Before or during the stamping of the head, if the working surface of the blank holder ring is found to be roughened, it shall be polished in time.
Range of blank holder ring:
(1) Oval head: low carbon steel D0/S≥85; Low alloy steel D0/S≥80.
(2) Flat head: D0/S≥16.
The gap between blank and blank holder ring shall be as small as possible to ensure no bulge.
When pressing the flat head (tube plate), after the upper die passes through the lower die ring, it can continue to the working platform of the press to ensure that the head plane is leveled once.
After demoulding, the head and tubesheet are not allowed to contact with the upper die again or press again to prevent excessive size.
After the stamped flat head is cooled to 550 ℃, it can be carefully taken out from under the lower die and lifted away to prevent deformation. Pay attention not to bump and scratch. For the head with extra large size, measures shall be taken to prevent lifting deformation.
After the head is removed from the press, it shall not be placed at the air outlet. In particular, the flat head shall be placed flat to prevent inconsistent cooling speed and deformation and warpage.
Batch pressing can be carried out only after the first piece passes the inspection.
After continuously pressing 10 ~ 15 heads, measure the overall dimension of the workpiece to avoid the increase of the geometric dimension of the workpiece due to mold overheating.
In case of oversized workpiece due to mold overheating, appropriate cooling measures shall be taken for the mold, and the mold temperature measured by thermometer shall not exceed 250 ℃.
During the stamping process of the die, lubricant shall be added in time.
When installing molds for perforated heads and flanging flat tubesheets, it shall be noted that the gap between manhole flanging punch and mold manhole flanging hole (punch and upper die) shall be uniform.
Spinning of head
Head cold spinning is a feasible and reasonable new head manufacturing process. In order to ensure the quality of head cold spinning, this process code is specially formulated.
The code follows the relevant provisions of GB150-2011 and GB/T 25198-2010.
This code is used together with relevant product drawings, technical conditions, process procedures and safe operation procedures of spinning machine.
Preparation before spinning
Check whether the blank material, mark and specification are consistent with the “process flow inspection card”.
The blank weld and edge shall be strictly polished and flush with the base metal.
Correctly select the mold according to the process specification and avoid wrong use. The flanging machine shall adjust the track curve of the pressure wheel to be consistent with the corresponding forming wheel.
Before spinning, test the machine for several minutes to confirm that the mechanical, cold pressing system and electrical system are intact for spinning.
The drum pressing force should be as small as possible for a given thickness of material, so as to avoid thinning of blank thickness and causing cracks. It is recommended that the pressure of drum should be controlled at 5-15mpa, and the maximum pressure should not exceed 20MPa. The depth of drum should be guaranteed, not shallow, and too deep should be avoided. In addition, pay attention to the smoothness of the surface, and finally use the sample plate for strict acceptance.
Control the arcing point and flanging amount to know well before flanging.
The flanging return time shall be flexibly mastered according to the proficiency level. It is not allowed to be eager for success. It is not allowed to take too long. It is necessary to be bold and careful.
If cracks occur at the edge of the head during flanging, it shall be shut down for repair. If the flanging is continued, the head will be staggered.
Strictly measure the outer circumference and control the range of positive and negative deviation.
In addition to stainless steel, cold formed heads shall be subject to heat treatment after forming. Generally, 20g and 16MnR materials shall be subject to intermediate annealing after bulging. If the user has special requirements, relevant heat treatment shall also be carried out.
The annealing temperature is recommended to be 620-650, holding for 1-2 hours, and discharging air cooling after furnace cooling to 300-400 ℃. Direct air cooling is not allowed.
Inspect the geometric dimension, shape deviation, thickness reduction and other items of the formed head according to relevant technical standards.
Inspection and repair
The quality inspection of the head mainly checks the surface condition, geometry and size of the head. For a small number of minor cracks, the cracks on the cylindrical part of the manhole flange that are more than 5mm from the starting point of the flange arc can be repaired and welded with the consent of the technical inspection department, and the thickness of the steel plate after grinding shall still be within the standard allowable deviation. After repair welding, the next process can be carried out only after the surface NDT is qualified.
For convex and concave scars, when their depth does not exceed 10% of the plate thickness and the maximum is not more than 1mm, they can be polished and transition smoothly; When the depth exceeds, it shall be repaired and polished, and the same strip shall be treated after repair welding.
Individual bulges after pressing the sheet head (D0/S ≥ 150) can be repaired by cold repair or partial heating hammering; When the roundness of the head is out of tolerance, it can be checked with the foreign template and corrected by hammering. However, the hammering correction cannot directly hammer the workpiece. It must be padded with a flat hammer or iron plate or corrected with a wooden hammer. If there are individual hammer marks, they shall be polished.
NDT shall be carried out after repair welding of surface defects.
The geometric shape and dimensional deviation of the head shall meet the requirements in GB/T 25198-2010 and GB/150-2011 and the requirements in the product production drawing.
General manufacturing process of cone
- Scope of application; The CHA cone head made in this standard has provisions, and individual special cases need to be negotiated.
- This process refers to the standard GB/T 25198-2010;
- According to different clamping angles, the vertebral body is divided into CHA (30 °), CHA (45 °), CHA (60 °), blanking and scribing of the cone.
Splitting principle of cone:
- a. Try to reduce the number of segments, that is, the number of starts;
- b. Considering the size of conventional plate rolling and transportation conditions, customized plate shall not be used as far as possible;
- c. Consider the height of the upper die.
Setting out and cutting
a: The template shall be made. The scribing template shall be in the form of a whole single piece, based on the endothelium, and the dimensional error shall not be less than 1mm. The template shall be made of thin iron sheet and linoleum paper.
Before scribing, check whether the material, material and size are consistent with the standard, confirm that the re inspection is qualified, and draw the blanking cutting line and the unfolding dimension line of cone flap endothelium. After marking, check the arc length, diagonal and bus length, and punch and cut after there is no error.
Mold preparation and equipment selection
The upper mold diameter is generally 50mm-80mm bar with R-arc, and the length is generally 1000mm-3000mm.
The lower die adopts two bars with a diameter of 50mm-80mm and a length of 1500mm-3000mm, which are placed in an eight shape. The included angle of the lower die is properly adjusted according to the cone size parameters and the allowable pressing capacity of the equipment.
For the selection of equipment, different presses are selected according to the plate thickness and cone size.
- a. Confirm the drawings, clarify the production tasks of this process, carefully read the drawings, read the technical requirements, and communicate with the technicians in time in case of any doubt.
- b. The super thick and split manufacturing of large cone is different from that of thin-walled cone. The thick plate cone shall be made as a three-dimensional template. The arc length of the template shall not be less than 1/3 of the arc length of a single piece. The template adopts the integration of large and small openings to facilitate the diagonal size in the pressing process.
The pressing method adopts cold spot pressing and forming, alternately pressing from both ends to the center, and the pressing force must be uniform. During the pressing process, the sample plate must be often used for testing and single-chip size inspection. The pressed cone petal shall be tested with the sample plate, and then the arc length, chord length, diagonal and bus length of large and small openings shall be checked. The allowable error of diagonal and bus shall be 3-5mm Scribe (flush) and cut grooves on both sides.
Scribing, scribing with the whole sample plate during blanking, and checking the arc length, chord length, diagonal and bus length. After all dimensions are correct, scribing, punching and cutting. Before cutting, inspectors or technicians shall be present to confirm the confirmation point of each cone flap, select an unsatisfactory cone flap, only make one groove, and reserve for final research and matching.
Simulation group pair
First, place a piece as the standard reference. The requirements are as follows:
- a. The large opening scribed part shall contact the assembly line as much as possible.
- b. The large mouth and small mouth of the cone are adjusted horizontally by using the principle of the connector.
- c. The height difference and included angle of large and small openings shall comply with the drawings. Then, other cone lobes are assembled in this way, the edge angle of the weld is given priority, and all cone lobes are on the same horizontal line.
For the lapping and fitting of the last valve, one end of the last valve shall be well lapping and fitting. Because the vacancy of the last valve is a little different from the calculation and drawings, it shall be scribed, cut, assembled and welded according to the actual situation.
After the grinding and assembly, the defects during cutting shall be added to the detection process according to the regulations. If repair welding is required, PTinspection shall be conducted after welding, and PT/UT inspection shall be conducted after all grooves are polished. Finally, it is welded and formed.
Source: China Head Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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