Author: Cao Hongbiao
Talking about head making process and equipmentAbstract: Head is an indispensable and important part of the pressure vessel equipment in petrochemical industry, atomic energy industry, foodstuff industry, pharmacy industry and so on, and it is the end cover on the pressure vessel, and it is one of the main pressure-bearing parts of the pressure vessel. The quality of head is directly related to the long-term safe and reliable operation of pressure vessel. The article mainly takes boiler head as an example and discusses the processing equipment and processing technology of head.
1?Shape and use of head
Head is an important pressurized component of pressure vessel and boiler, and it can be divided into flat head, disk head, ellipsoidal head and spherical head in terms of shape. High-pressure vessel and boiler head are mostly spherical, oval head is mostly used above medium pressure, and only a small number of low-pressure vessels use disk head.
2?Head processing method
(1)Stamping. Adapt to mass production, press thick-walled small-diameter head, to be more sets of head mold.
(2) Spinning. Some oversized and ultra-thin heads, especially in chemical industry, mostly large and small batch, are especially suitable for spinning. Oval head is very suitable for spinning, while disk head is used less and spherical head is harder to press.
3?Head processing equipment and tools
(1) Heating equipment. Gas furnace, most of the large-scale factories use gas furnace. Now heating using chamber or reflective heating furnace, should be as far as possible to use fuel oil or gas heating, because it is characterized by clean burning, high efficiency, easy to control the temperature, not easy to overcooking, not easy to decarburization. Heating furnace should be equipped with temperature measuring device and temperature recorder.
(2) There are two kinds of head presses: single-acting and double-acting; there are also two kinds of hydraulic presses and oil presses.
Single-action that is, only the stamping cylinder, no crimping cylinder, only small and medium-sized factories and then used. Large factories use double-action, that is, there is a crimping cylinder, a stamping cylinder.
The transmission medium of the hydraulic press is water, cheap, fast action, not smooth, the sealing requirements are not as high as the hydraulic press, the efficiency is lower than the hydraulic press, the guidance requirements are not strict. Hydraulic press transmission medium for oil, change an oil to be more expensive than water, smooth transmission, high sealing requirements, high requirements for guidance, high oil requirements, oil filtration can not be or soon change direction, close the oil circuit will make the system in some of the action of the impact, so that the press action is not smooth, so we must be diligent oil filtration, on time to change the oil, oil change, clean the oil circuit thoroughly, the oil tank.
(3) Use of tooling. Various kinds of head forming upper and lower molds and feet, etc. (must be in accordance with the relevant technical conditions of acceptance, there should be no air holes, shrinkage, dregs, etc., geometric dimensional accuracy. (Curves can be used only after passing inspection).
(4) common tools. Fastening wrenches, sledgehammer, crowbar, steel ruler, tape measure, photoelectric thermometer, inside and outside calipers, handling tools and so on.
4?Calculation of unfolding size of head blank
4.1?Unloading of disc head blank
(1) Perimeter method
Theoretical formula D0=d2+π(r+s/2)+2h+2δ
Empirical formula D0=d2+r+0.5s+2h
(2) Area method
< p>4.2?Ellipsoidal head blank undercutting(1)Perimeter method
D=p+2hk0+?2δ(2)Area method
Diameter of head blankFor the standard ellipsoidal head, d1=4b,ke=1.38
4.3?Spherical head blank undercutting
Also Approximate calculation D0=1.43d+2h, when h＞5%(d-s), h in the formula should be substituted by h+5%.
4.4?Factors affecting the thick wall of head
There are many factors affecting the change of thick wall of head, which are summarized as the following:
(1)Properties of material. For example, the amount of thinning of lead head is much larger than that of carbon head.
(2) Shape of head. Disc-shaped head has the smallest amount of thinning, spherical head has the largest amount of thinning, and oval head is medium.
(3) The larger the radius of the lower die corner, the smaller the amount of thinning.
(4) The larger the clearance between upper and lower dies, the smaller the thinning amount.
(5) Good lubrication, the thinning is small.
(6) The higher the heating temperature, the larger the amount of thinning (to be within the standard, otherwise overcooking).
(7) compression force is large, then the thinning is serious.
5 Selection of cold pressing or hot pressing
The use of hot pressing or cold pressing for head is mainly determined according to the following two aspects:
(1) Performance of material used for head. For the material with better plastic at room temperature cold pressing, for the material with better thermoplasticity hot pressing.
(2) Generally δ4~δ12 plate thickness, the material with better plasticity at room temperature is often cold pressed, and the edge ring is pressed as the case may be, and more than the above plate thickness is often hot pressed.
(3) Size of head blank. When the head is thin, for carbon steel and low alloy steel S/D0x100＜0.5, for stainless steel and alloy steel S/D0x100≥0.5 should be hot pressing; for stainless steel and low alloy steel S/D0x100＜0.7 should be hot pressing.
6 Head production process
6.1 Preparation before head pressing
(1) Before operation of hydraulic press, the worker should understand the design drawings and the corresponding technological requirements, and should check the material of blank, specification size of blank and the mark of steel seal on blank, etc., and find out the corresponding head mold according to the drawings, clear the foreign matter on the mold, test the mold and do the commissioning and lubrication work for hydraulic press at the same time. At the same time, we should do a good job of debugging and lubricating the hydraulic press.
(2) The mold should be installed in the center of the hydraulic press table, and its eccentricity is allowed to be 160mm. the mold should be fastened after installation and debugging to ensure safety. Mold installation should ensure that the upper and lower mold circumferential clearance uniform, installation can be measured and adjusted with a steel plate ruler or a wire with a diameter equal to the value of the deviation, and the permissible deviation of its circumferential clearance is shown in Table 1.
(3) When press head adopts crimping ring, the gap between crimping ring and contact surface of lower die shall be not more than 0.5mm, when press head with hole, it shall be ensured that the lower die is concentric with manhole ejector punch, and its deviation shall be not more than 3mm.
(4) For the blank of spliced head, the height of weld seam shall be not more than 1.5mm in the length of L. For the length of L, the height of the weld seam shall be not more than 1.5mm, and it is more than 1.5mm that shall be planed by arc gas planer or grinded by portable sander. Or use portable sander to grind it flat.
(5) the heating furnace grate and furnace chamber cleaning, and then for ignition preparation, and check whether the photoelectric thermometer is normal.
6.2 Heating of head blank
(1) Head blank shall be placed in such a way that the steel marking side shall be facing downward, so that the material marking shall be exposed on the outer surface of the formed head after stamping.
(2) The head blank shall be heated in a hot furnace, and the temperature of the furnace shall be more than 600°C. Carbon steel can be added to the furnace at any time, and special materials shall be specified separately.
(3) each furnace charging can generally be stacked side by side in the furnace, each piece of refractory bricks should be separated, in order to prevent deformation, the support point should be uniform, the two stacked distance should be not less than 200mm, billet from the bottom of the furnace distance is not less than 150mm, not more than four at a time loading.
(4) When the spliced head blank is heated and loaded in the furnace, its weld should be placed at the higher temperature of the furnace as far as possible.
(5) The door of the furnace shall not be opened arbitrarily when the blank is heated, and the heating situation in the furnace shall be observed through the peephole on the door, and the door shall be closed as soon as possible when it must be opened.
(6) equipment failure, only in the case of ensuring that the fault can be removed within 45min, it is allowed to have been into the furnace billet smothering, but the furnace temperature should be reduced to 600 ~ 700 ℃; otherwise the furnace should be stopped, and open the door to cool down, take out the billet.
(7)When the head blank is heated up to the specified temperature,the time of the blank material from the furnace to pressing should be shortened as much as possible,and it should not be more than 3min.The head blank should be heated up strictly according to the process regulations,the heating specification of the different materials is shown in table 3,and the materials which are not in the table 3 are stipulated separately in the pressing.
6.3?Pressing of head
(1) Before pressing of each head, the oxidized skin on the head blank shall be removed. Before pressing, lubricant should be coated on the die, 40% graphite mixed with 60% water (machine oil) is used for cold pressing, and molybdenum disulfide lubricant can be coated for hot pressing.
(2) When pressing, the head blank should be placed concentric with the mold as much as possible, and the center offset between the blank and the lower mold should be less than 5mm, when pressing the perforated head, attention should be paid to the elliptical opening on the blank and the mold in the same direction of the long and short axes, and in the process of pressing, firstly, the manhole punches will be pushed out against the position of the opening on the blank, and then pushed out to the plane of the lower mold which is a little bit above the plane of the lower mold (about 20mm), and then the upper mold is pressed downward again, and the manhole punches will fall down at the same time, and the manhole punches will be removed from the blank and the blanks will be removed. Then the upper die will be pressed downward and the manhole punch will fall down at the same time to press the head into shape. During pressing, the punching pressure should be increased slowly from small to large, and should not be increased or decreased suddenly.
(3) The hot stamping head can be dragged away from the mold for transportation only when it is cooled down to below 600℃, and it shall not be put in the air outlet, and it shall not be stacked more than two pieces before it is cooled down to room temperature. When continuous stamping, the temperature of the die rises to about 250℃, the stamping should not be continued, and the work can be continued only after the cooling measures are taken to make the temperature of the die drop.
(4) The perforated head shall be shaped as far as possible at one time, and when it cannot be shaped at one time due to the condition limitation, attention shall be paid to the concentricity with the head when stamping manhole and to the uniformity of wall thickness at the flange of manhole.
7 Quality inspection of headIn order to ensure the quality of head, molding head must be inspected carefully. Quality inspection of end socket includes surface condition, geometric shape and geometric size of end socket.
The inspection of surface condition of end socket is mainly to check whether there are wrinkle cracks, indentation, pit, bulge, decarburization and so on on the surface of end socket. After molding, the head shall remove the oxidized skin on the inner and outer surfaces, and the surface shall not be allowed to have the defects such as cracks, heavy skin and so on. Tiny surface cracks and individual bumps with a height of 3mm shall be trimmed. Manhole within the trigger edge of the starting point of the bend is greater than 5mm at the crack can not affect the quality of the premise, and after the inspection department agreed to be able to carry out repair grinding or filler weld, after grinding the thickness of the steel plate should be in the allowable deviation range of steel plate thickness.
Defects such as depressions and scars are handled as follows:
(1) hot water boilers and steam boilers with rated steam pressure less than 9.81MPa, the depth of more than 0.5mm, but not more than 10% of the nominal wall thickness and not more than 3mm of the depressions and scars should be repaired and ground into a rounded transition, and more than that should be patched welded and repaired and ground.
(2) For steam boiler with rated steam pressure not less than 9.81MPa, the depressions and scars shall be repaired and ground into smooth transition if the depth is 3~4mm, and shall be welded and repaired and ground when exceeding 4mm. When the molding head has defects, it is allowed to repair, the larger defects and the defects of low alloy steel head shall be repaired according to the relevant process, and the non-destructive flaw detection shall be carried out after the defects are patched and welded.
Description of symbols
D0-Diameter of head blank;
h-Length of straight side of each type of head;
H-Total height of head;
d1-Inner diameter of elliptical head;
d2-disc head inner diameter;
d-spherical head inner diameter;
δ-mechanical machining allowance of head edge, usually 15~40mm;
r-radius of folding area of disc head;< /p>
s-thickness of various types of head blanks;
p-half circumference of ellipsoidal part of the head;
k0-material tensile coefficient, usually 0.75~0.8;
ke-ellipse coefficient When standard elliptical head d1=4b, ke=1.38;
a-long half-axis of ellipse;
b-short half-axis of ellipse;
D-medium diameter of the head after it is made into shape.
How to draw the head in chemical drawing
With CAD drawing, take the diameter of the head as the long axis, take the height of the head as the short axis to draw the ellipse, and then delete half of it, and then draw the straight side that is.