What is the valve casting process
What is the valve casting process?
Casting valve is the valve made of cast iron, the general casting of the valve pressure level are relatively low (such as PN16, PN25, PN40, but there are also high pressure, can be up to 1500Lb,, 2500Lb), most of the caliber DN50 or more.
Valve casting is an important part of the valve manufacturing process, with a good casting determines a significant proportion of the success of a good valve.
Valve manufacturing materials
Due to the wide variety of valve specifications, such as general-purpose valves, gate valves, globe valves, check valves, ball valves, butterfly valves, hydraulic control valves; industrial valves have solenoid valves, regulating valves, pressure reducing valves, high-temperature and high-pressure valves, low-temperature valves and other special valves, are used in various areas of the national economy, the use of the occasion is very different, such as high temperature and high pressure, low temperature deep cold, flammable and explosive, highly toxic, strong corrosive media and other working conditions. The material of the valve has put forward harsh requirements.
Valve manufacturing materials in addition to cast iron, carbon steel, alloy structural steel, but also a large number of CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, Monel alloy, Inconel alloy, Hastelloy and G0CrW carbide, etc.. The casting, welding and processing properties of these high-alloy materials are very poor, which makes the manufacturing process very difficult. Coupled with the fact that most of these materials are high alloy, high strength, high hardness precious materials, there are many difficulties in the selection, preparation and procurement from the materials. Some materials are difficult to procure and supply due to the small quantity used.
Casting of valve blanks
Most of the valve blanks are thin shell castings with complex structures, which require not only good appearance quality, but also dense internal quality and good metallographic structure, and cannot have defects such as porosity, shrinkage, sand trapping and cracking. Therefore, the casting process is complex and the heat treatment technology is difficult. In the machinery industry, the valve pressure thin shell casting blank casting difficulty is far more complex and more difficult than the castings of other mechanical components.
The following is an introduction to the design of the casting process and several casting process methods commonly used in the valve industry.
The casting process design of the casting
Correct and effective control of casting solidification is the first important condition to obtain high-quality cast steel parts, take the correct process measures such as: pouring system, riser and cold iron, process correction amount, etc., the formation of a reasonable process program. Valve cast steel parts due to its uneven wall thickness, should take the principle of sequential cooling, sequential solidification, in order to reduce the internal stress of the casting, shrinkage and shrinkage and other defects.
Control the process measures for sequential solidification of cast steel parts.
- (1) Design a reasonable parting position, pouring position and pouring system.
- (2) The design of the riser in the last part of the casting solidification, in the role of shrinkage, while delaying the solidification of the steel around the riser, resulting in the conditions of sequential solidification.
- (3) Pouring operation, when the steel rises to the riser height 1/4, change from the top of the riser pouring, its role can increase the steel pressure head, can also improve the riser temperature.
- (4) Cast steel riser size determination: its methods are modulus method (determined by the heat capacity of the casting); volume shrinkage method (determined by the steel solidification shrinkage rate); ratio method (determined by the type of complementary shrinkage of the casting) and the thermal knot circle method (determined by the thermal knot circle of the casting). At present, in order to meet the convenient design requirements in the factory, the hot knotted circle method is commonly used to determine the size of the riser.
- (5) The casting shrinkage rate selected: cast steel parts in the process of solidification and cooling, its volume and size will shrink to reduce the amount of shrinkage from the liquid state solidification for the solid state is generally expressed in terms of the amount of change in length – the line shrinkage rate (%).
Many factors affect the casting shrinkage rate, the casting in the casting solid shrinkage is also affected by external resistance, which will reduce its actual shrinkage, then known as non-free shrinkage, and non-free shrinkage rate is always less than the free shrinkage rate. Factors affecting the shrinkage rate of casting are mainly the type of metal alloy, casting structure and size length, in addition to molding materials, core tightness, etc. also affect the casting to produce non-free shrinkage rate.
Sand casting commonly used in the valve industry, according to the different binder can also be divided into: wet sand, dry sand, water glass sand and furan resin self-hardening sand, etc..
(1) Wet sand is a bentonite binder molding process, it is characterized by: the sand does not need to dry, do not need to go through hardening treatment, sand has a certain wet state strength, sand core, shell recession is better, easy to clean up the castings fall sand. High molding production efficiency, short production cycle, low material cost, easy to organize assembly line production. Its disadvantages are: the casting is easy to produce porosity, sand trapping, sand sticking and other defects, the quality of the casting, especially the internal quality is not ideal.
(2) Dry sand is the clay as the binder of the molding process method, slightly add bentonite can improve its wet strength. Its characteristics are: sand needs to be dried, good permeability, not easy to produce sand punching, sand sticking, porosity and other defects, the intrinsic quality of the casting is better. Its disadvantage is that it needs sand drying equipment and the cycle time of production is long.
(3) Water glass sand is water glass as the binder of the modeling process method, it is characterized by: water glass encountered CO2 has the function of automatic hardening, can have a variety of advantages of air hardening method of modeling and core making, but there are poor shell collapse, casting sand cleaning difficulties and the old sand regeneration, reuse rate is low.
(4) Furan resin self-hardening sand molding is a casting process method with furan resin as the binder, at room temperature due to the chemical reaction of the binder under the action of the curing agent and curing the sand. It is characterized by the sand does not have to be dried, which shortens the production cycle and saves energy. Resin sand is easy to compact, good collapse, the casting sand is easy to clean, the casting size accuracy is high, the surface finish is good, which can greatly improve the quality of the casting. Its disadvantages are: high requirements for the quality of raw sand, slight irritating odor at the production site, and the cost of resin is also higher.
Furan resin self-hardening sand mixing process: resin self-hardening sand is best to use continuous sand mixer, the original sand, resin, curing agent, etc., in turn to join, rapid mixing, ready to mix, ready to use.
When mixing resin sand, the order of adding various raw materials is as follows.
Raw sand + curing agent (aqueous solution of p-toluenesulfonic acid) – (120～180S) – resin + silane – (60～90S) – out of sand
(5) Typical sand casting process card.
(6) Typical sand casting production process.
The traditional method is to obtain casting drawings and then send the drawings to the foundry. This process can be completed in the quotation. Today, more and more customers and foundry manufacturers use computer-aided design instead.
In sand casting molds are made of wood or other metal materials. In this process, we ask our engineers to make the mold size slightly larger than the finished product, where the difference is called shrinkage allowance. The purpose of which is to melt the metal to the mold to ensure that the molten metal solidifies and shrinks, thus preventing voids in the casting process.
3. Core making
Core making is done simply by placing resin sand grains in the mold to form the internal surface of the casting. Thus the gap between the core and the mold eventually becomes a casting.
A mold needs to be prepared in the melting and molding process. Molding usually involves the supporting frame of the mold, pulling out the mold so that it separates during the casting process, melting the previously placed core in the mold and then closing the mold mouth.
The purpose of cleaning is to remove sand, sanding and excess metal from the casting. Welding, sand removal can improve the surface appearance of the casting
The burnt sand and scale are removed to improve the surface appearance of the casting. Excess metal and other risers are cleared. Further steps such as welding and grinding are followed. Finally check its defects and overall quality.
Before shipment, reworking. According to the requirements of different customers we can do heat treatment, surface treatment, additional inspection, etc. for them again.
In recent years, valve manufacturers are paying more and more attention to the appearance quality and dimensional accuracy of castings. Because a good appearance is the basic requirement of the market, but also as a positioning benchmark for the first process of machining.
Valve industry commonly used precision casting is the solution mold casting, is briefly described as follows.
When using wax material as a mold, investment casting is also known as “lost wax casting”. Melt casting usually refers to the fusible material made in the mold sample, the surface of the mold sample covered with several layers of refractory materials made of shell, and then the mold sample melted out of the shell, so as to obtain the cast without parting surface, after high-temperature roasting can be filled with sand casting program. Due to the widespread use of wax materials to manufacture mold samples, so often called fusion casting “lost wax casting”.
(1) Two process methods of melting mold casting.
- ① using low-temperature wax-based mold material (stearic acid + paraffin). low-pressure wax injection, water glass shell, hot water dewaxing, atmospheric melting and casting process, mainly for general quality requirements of carbon steel and low-alloy steel castings, casting size accuracy can reach the national standard CT7 ~ 9 grade.
- ② using medium-temperature resin-based mold material, high-pressure wax injection, silica-sol mold shell, steam dewaxing, rapid atmospheric or vacuum melting and casting process, casting size accuracy up to CT4 ~ 6 precision castings.
(2) Typical process flow of solution mould casting.
1. Take out the wax cylinder from the holding tank and install it on the duplex hydraulic wax mold press injection machine, which should remove the air and hard wax from the wax material before use.
2. Place the mold on the table of the press, check whether all the cores of the mold are correctly positioned, and whether the wax injection port of the mold and the injection nozzle of the press are correct.
3. Check if the mold opens and closes smoothly.
4. Open the mold and spray a thin layer of parting agent.
5. Adjust the time cycle of the injection press according to the technical regulations, including the injection pressure, injection temperature, holding time, cooling time, etc.
6. After each cycle, pull out the core, open the mold, carefully remove the wax mold and put it into the cooling water or storage tray as required.
Note that wax molds with the following defects should be scrapped.
- A. the wax mold with local bulging due to the air involved in the mold material
- B. if the wax mold has any part with missing corner
- C. deformation of the wax mold that cannot be simply repaired.
- D. The size does not meet the requirements.
7. Clear the residual mold material on the mold, note that only bamboo knives can be used, do not use metal blades to remove residual mold material to prevent damage to the mold cavity and parting surface.
8. Close the mold and press the wax mold next time. At the end of each shift or when the mold is finished, use soft cloth or cotton swab to clean the mold and fasten the mold with screws.
9. If the mold is found to be damaged or abnormal, it should be reported to the foreman immediately and handled by the foreman.
Investment casting process operation points.
- 1. Do not spray too much parting agent in the mold cavity.
- 2. Press the molten (wax) mold cycle parameters established, do not easily change. If there is a problem with the quality of the pressed wax mold, you must tell the foreman immediately, and the foreman will handle it.
- 3. The defective wax mold must be scrapped and must not be sent to repair and welding.
- 4. The wax mold should be placed in the storage tray and isolated from each other so as not to touch the damage. If necessary, jigs can be used to avoid deformation of the wax mold.
- 5. The use of new molds, be sure to clarify the melt casting process mold assembly, disassembly order, wax mold removal method, mold in the press injection machine fixed method, and strictly check the initial pressing of the wax mold, such as the failure to obtain quality wax mold, should be timely contact with the technical management.
(3) The characteristics of the solution mold casting.
- ① High dimensional accuracy of castings, surface finish and good appearance quality.
- ② Can cast the structure of complex shapes, difficult to achieve processing parts with other technology methods.
- ③ Casting materials are not limited to a variety of alloy materials such as: carbon steel, stainless steel, alloy steel, aluminum, high-temperature alloys, and precious metals and other materials, especially difficult to use forging, welding and cutting alloy materials.
- ④ Good production flexibility and adaptability. Can be mass production, also suitable for single piece or small batch production.
- ⑤ Solution casting also has certain limitations, such as: cumbersome process, long production cycle. Due to its limited means of casting process can be used for casting pressurized thin-shell valve castings, its pressure-bearing capacity can not be very high.
Analysis of casting defects
Any casting internal is going to have defects, the existence of these defects to the casting of the intrinsic quality brings a great hidden danger, in the production process for the elimination of these defects for welding will also bring a great burden to the production process. Especially for valves as thin-shell castings subjected to pressure and temperature, the denseness of their internal organization is very important. Therefore, the internal defects of the casting becomes a decisive factor affecting the quality of the casting.
Valve castings of internal defects are mainly porosity, slag, shrinkage and cracking.
(1) Pores: pores generated by gas, pore surface is smooth, produced in the casting or near the surface, the shape is more round or oblong.
The main sources of gas generated pores are.
- ① Metal in the dissolved nitrogen, hydrogen in the casting solidification process is included in the metal, the formation of closed round or oval walls with a metallic luster of the pores.
- ② The moisture or volatile material in the modeling material will turn into gas due to heat, forming a dark brown pore with an inner wall.
- ③ Metal in the pouring process, due to instability in the flow, the air will be involved and generate pores.
Prevention methods of porosity defects.
- ① In smelting should be used as little as possible or do not use rusted metal raw materials, tools and steel ladle to bake dry.
- ② Steel pouring to high temperature out of the furnace, low temperature pouring, the steel should be properly sedated to facilitate the floating of gas.
- ③ The process design of the pouring mouth should increase the pressure head of the steel to avoid gas involvement, and set up artificial gas path, reasonable exhaust. ④The modeling material should control the water content, gas generation, increase the air permeability, sand and sand core should be baked dry as far as possible.
(2) Shrinkage (loose): it is produced in the casting internal (especially in the hot section parts) is coherent or incoherent round or irregular cavity (cavity). the inner surface is rough, dark color, metal grains coarse, more dendritic crystallization, gathered in one or more places, hydraulic test is easy to occur leakage.
Produce shrinkage (loose) reasons: metal solidification from the liquid state for solid volume contraction, at this time, such as not enough steel supplement, is bound to produce shrinkage. The shrinkage of cast steel parts is basically caused by improper control of the sequential solidification process, the reason may be incorrect setting of the riser, steel pouring temperature is too high, metal shrinkage, etc..
Prevent shrinkage (pine) generated by the following methods.
- ① Scientific design of casting pouring system, so that the steel to achieve sequential solidification, the first solidified parts should be supplemented by steel.
- ② Correctly and reasonably set the riser, subsidies, internal and external cold iron to ensure sequential solidification.
- ③ In the steel pouring, the last top injection from the riser is conducive to ensure the temperature of the steel and the complementary shrinkage, reducing the generation of shrinkage holes.
- ④ In terms of pouring speed, low speed pouring is better than high speed pouring for sequential solidification.
- ⑤ In the pouring temperature should not be too high, the high temperature of the steel out of the furnace, after calming pouring, is conducive to reducing shrinkage.
(3) Sand trap (slag): sand trap (slag) Commonly known as trachoma, is the appearance of incoherent round or irregular holes in the interior of the casting, the hole is interspersed with sand or steel slag, size is not regular, gathered in one or more places, often more in the upper part of the type.
Causes of sand (slag): Slag is due to the steel in the smelting or pouring process, discrete steel slag with the steel into the casting formed. Sand is due to modeling cavity tightness is not enough, when the steel into the cavity, the sand washed up by the steel into the castings caused by the internal. In addition, improper operation when repairing the mold, closing the box, there are sand drop phenomenon is also the cause of sand trapping.
Prevent sand trapping (slag) generated by the following methods.
- ① Steel smelting to try to exhaust slag thoroughly, the steel out of the furnace in the steel ladle after the sedation, conducive to the steel slag float.
- ② Steel pouring package as far as possible without turning the package, but with a teapot package or bottom injection package, so as to avoid the upper part of the steel slag along the steel into the casting cavity.
- ③ In the steel pouring to take castor slag measures to minimize the steel slag with the steel into the cavity.
- ④ In order to reduce the possibility of sand trapping, in the modeling to ensure the tightness of the sand, repairing the type of attention not to drop sand, before closing the box to blow the cavity clean.
(4) Crack: Most of the cracks in the castings are thermal cracks, which are irregular in shape, with or without penetration, continuous or interrupted, and the metal at the crack is dark or with surface oxidation.
The cause of cracks: there are two aspects, namely high-temperature stress and liquid film deformation.
High-temperature stress is the steel shrinkage deformation at high temperatures and the formation of stress, when the stress exceeds the strength of the metal at that temperature or plastic deformation limit will produce a crack. Liquid film deformation is a liquid film between the grains of steel in the solidification and crystallization process, with the solidification and crystallization, the liquid film deformation, the amount of deformation and deformation rate exceeds a certain limit, it produces a crack. The temperature range of thermal cracking is about 1200 ~ 1450 ℃.
The factors influencing the generation of cracks.
- ① S, P elements in steel is a harmful factor to produce cracks, they and iron eutectics reduce the strength and plasticity of cast steel at high temperatures, resulting in cracks.
- ② Slag and segregation in steel increase the stress concentration, thus increasing the tendency of thermal cracking.
- ③ The larger the linear shrinkage coefficient of the steel grade, the greater the tendency of thermal cracking.
- ④ The greater the thermal conductivity of the steel, the greater the surface tension, the better the high temperature mechanical properties, the less the tendency of thermal cracking.
- ⑤ The structural design of the casting is not well crafted, such as rounded corners are too small, the wall thickness disparity is too large, and the stress concentration is serious, which will produce cracks.
- ⑥ The tightness of sand is too high, and the poor yielding of the core will increase the tendency of cracking by hindering the shrinkage of the casting.
- ⑦ Other such as improper arrangement of the sprue, casting cooling speed is too fast, cutting sprue and heat treatment caused by excessive stress will also affect the generation of cracks.
In view of the above causes and factors of cracking, take corresponding measures to reduce and avoid the generation of cracking defects.
Comprehensive analysis of the causes of the above casting defects, find the existing problems, take corresponding improvement measures, you can find a solution to the casting defects, which is conducive to the improvement of casting quality.
Valve manufacturing process
Step 1: valve body manufacturing
Valve body (casting, sealing surface overlay welding)
Casting procurement (according to the standard) ➱ into the factory inspection (according to the standard) ➱ overlay groove ➱ ultrasonic flaw detection (according to the drawings) ➱ overlay and post-weld heat treatment ➱ finishing ➱ grinding sealing surface ➱Hardness testing of sealing surfaces. Coloring flaw detection.
Step 2: Valve internal parts manufacturing process
A. The internal parts that need to weld the sealing surface such as valve flap. Valve seat, etc.
Raw material procurement (according to the standard) ➱ into the factory inspection (according to the standard) ➱ make the blank (round steel or forgings, according to the drawing process requirements) ➱ rough machining ultrasonic flaw surface (when the drawing requirements) ➱ rough machining surfacing groove ➱ surfacing and after welding Heat treatment ➱ Finishing ministries ➱ Grinding seal faces ➱ Seal face hardness test. Coloring flaw detection.
B. Valve stem
Raw material procurement (according to standard) ➱Incoming inspection (according to standard) ➱Make blank (round steel or forging, according to drawing process requirements) ➱Rough machining of overlay groove ➱Overlay and post-welding heat treatment ➱Finish machining of each ministry Grinding of the outer circle ➱ Surface treatment of the stem (nitriding. Quenching. Chemical plating)➱Final treatment (polishing. Grinding, etc.) ➱ Grinding of sealing surface ➱ Hardness test of sealing surface. Coloring flaw detection.
C. Internal parts that do not require overlay welding of seal faces, etc.
Raw material procurement (according to the standard) ➱ Intake inspection (according to the standard) ➱ Production of blanks (round steel or forgings, according to the drawing process requirements) ➱ Rough machining ultrasonic flaw detection surface (when required by the drawing) ➱ Finishing ministries.
Step 3: Fastener manufacturing
Fastener manufacturing standard DL439-1991.
Raw material procurement (according to the standard) ➱Incoming inspection (according to the standard) ➱Make blanks (round steel or forgings, as required by the drawing process) and take samples for necessary inspection ➱Rough machining ➱Finishing ➱Spectral inspection.
Step 4: General assembly
Pick up parts➱Cleaning. Cleaning➱Rough assembly (as per drawing)➱Hydrostatic test (as per drawing. Process)➱After passing. Disassemble. Wipe clean➱Final assembly➱Commissioning with electrical installation or actuator (for electric valves)➱Painting and packaging➱Shipping.
Valve product production and inspection flow chart
Step 5: Valve product production and inspection process
- 1. The company purchases raw materials of various specifications.
- 2. Material testing of raw materials with spectral analyzer and print out the material testing report of raw materials for backup.
- 3. Cut the raw materials with the machine.
- 4. Inspectors check the cutting diameter and length of raw materials.
- 5. Forging workshop to forge and shape the raw materials. 6.
- 6. The inspectors inspect the various dimensions of the billet for forming.
- 7. The workers are cutting the scrap edge of the billet.
- 8. Sand blasting workers are sand blasting the surface of the blank.
- 9. The inspector carries out the surface treatment inspection after sandblasting.
- 10. Workers are machining the blank.
- 11. valve body sealing thread processing — staff in the processing of self-inspection inspectors to the product after the product for post-processing inspection.
- 12. Valve body connection thread processing.
- 13. Center hole processing.
- 14. The inspector carries out the general inspection.
- 15. Qualified semi-finished products are sent to the semi-finished products warehouse.
- 16. Semi-finished products are plated.
- 17. Plating surface treatment inspection of semi-finished products.
- 18. Various accessories (ball, stem, seal seat) are inspected.
- 19. assembly workshop for product assembly – assembly line inspectors inspect the products.
- 20. The assembled products go to the next process after pressure testing and drying.
- 21. The assembly workshop carries out the product packaging —- packaging line inspectors to inspect the sealing, appearance and torque of the product. Unqualified products are never allowed to be packed.
- 22. Qualified products are bagged and packed and sent to the finished product warehouse. 23.
- 23. All inspection records will be sorted and stored in the computer for reference at any time.
- 24. The qualified products are sent to the domestic and international markets by container.
What is the difference between forged valves and cast valves?
Forged valves are forged and generally used in high grade pipelines with smaller caliber, generally below DN50. But there are some imported valves, forged caliber has a large diameter, such as the United States VTON VTON forged globe valve, caliber from DN15-500. Forged globe valve material is generally divided into A105, forged stainless steel, P91, F91, etc..
Casting valve is the material in the mold as a whole casting molding valve, the general casting of the pressure level of the shut-off valve are relatively low (such as PN16. PN25. PN40, PN64 but there are also high-pressure, can be up to 1500Lb. . 2500Lb), most of the diameter are DN15 or more. For example, the U.S. VTON cast globe valve, cast globe valve materials are mainly cast iron, ductile iron, cast steel, 304, 304L, 316, 316L.
1. Casting: the metal is melted into a liquid that meets certain requirements and poured into the casting mold, after cooling and solidification. After cleaning treatment to get a predetermined shape. Size and performance of the castings (parts or blanks) process. The basic process of modern machinery manufacturing industry.
2. Casting production of blanks at low cost, for complex shapes. Especially with complex internal cavities of the parts, more show its economy; at the same time it is more adaptable, and has a better overall mechanical properties.
3. But the materials required for the production of casting (such as metal. Wood. Fuel. Molding materials, etc.) and equipment (such as metallurgical furnaces. Sand mixing machine. Molding machine. Core making machine. Sand casting machine. Shot blasting machine. (cast iron plate, etc.) more, and will produce dust. Harmful gases and noise and pollution of the environment
4. Casting is an early human mastery of a metal heat processing process, has a history of about 6000 years. 3200 BC, Mesopotamia appeared copper frog castings. Between 13 BC and 10th century BC, China has entered the heyday of bronze castings, the process has reached a high level, such as the Shang Dynasty, weighing 875 kg Simuwu tripod. Warring States of Zeng Houyi Zun plate and the Western Han Dynasty, such as translucent mirror are representative of ancient casting products. Early casting by the influence of pottery, castings mostly for agricultural production. Religion. Life and other aspects of tools or utensils, artistic color is strong. 513 B.C., China cast the world’s earliest written records of cast iron – Jin cast tripod (about 270 kg weight). Around the 8th century A.D., Europe began to produce cast iron parts. 18 century after the Industrial Revolution, castings into a new period of service for large industries. In the 20th century, the development of casting is rapid, has developed ductile iron, malleable iron, ultra-low carbon stainless steel and aluminum-copper. Aluminum silicon. Aluminum-magnesium alloy, titanium-based. Nickel-based alloys and other casting metal materials, and the invention of a new process of breeding treatment of gray cast iron. 50s, the emergence of wet sand high-pressure molding, chemical hardening sand molding and core making. Negative pressure molding and other special casting. Shot blasting cleaning and other new processes. 5.
5. Many types of casting, according to the customary molding method is divided into:
① Ordinary sand casting, including wet sand type. Dry sand type and chemically hardened sand type 3 categories.
② Special casting, according to the modeling materials can be divided into natural mineral sand and gravel as the main modeling materials for special casting (such as investment casting. Clay casting. Foundry shell casting. Negative pressure casting. Solid casting. Ceramic casting, etc.) and metal as the main casting material of special casting (such as metal casting. Pressure casting. Continuous casting. Low-pressure casting. (centrifugal casting, etc.) two categories
6. Casting process usually includes.
① Casting (so that the liquid metal into a solid casting container) preparation, casting according to the material used can be divided into sand. Metal type. Ceramic type. Clay type. Graphite type, etc., according to the number of uses can be divided into one-time type. semi-permanent type and permanent type, casting preparation is the main factor affecting the quality of the casting.
② Casting metal melting and pouring, casting metal (casting alloys) are mainly cast iron. Casting steel and casting non-ferrous alloys.
③ Casting processing and inspection, casting processing, including the removal of the core and casting surface foreign matter. Cutting out the sprue. Shovel grinding burrs and phi seams and other protrusions and heat treatment. Shaping. Anti-rust treatment and rough machining, etc.
1. Forging: is the use of forging machinery to apply pressure to the metal billet, so that it produces plastic deformation to obtain a certain mechanical properties. Certain shapes and sizes of forgings processing method. 2.
2. One of the two major components of forging. By forging can eliminate the cast looseness of the metal, welded holes, forgings are generally better than the mechanical properties of the same material castings. High load in machinery. Working conditions are severe and important parts, in addition to the simpler shape of the available rolled sheet. Profiles or welded parts, more forgings. 3.
3. Forging can be divided into the following according to the forming method.
- ① Open forging (free forging). The use of impact or pressure to make the metal in the upper and lower two against the iron (anvil) between the deformation to obtain the required forgings, mainly manual forging and mechanical forging two.
- ② Closed mode forging. Metal billet in a certain shape of the forging die chamber pressure deformation and obtain forgings, can be divided into die forging. Cold heading. Rotary forging. Extrusion and so on. According to the deformation temperature forging can be divided into hot forging (processing temperature higher than the recrystallization temperature of the billet metal). Warm forging (lower than the recrystallization temperature) and cold forging (room temperature). 4.
4. Forging materials are mainly carbon steel and alloy steel of various compositions, followed by aluminum. Magnesium. Titanium. Copper and its alloys. The original state of the material is bar. Ingot. Metal powder and liquid metal, etc. The ratio between the cross-sectional area of the metal before deformation and the die cross-sectional area after deformation is called forging ratio. The correct choice of forging ratio is very important to improve product quality. Cost reduction is very relevant.
The differences of casting valves and forging valves
Casting is the material in the mold as a whole pouring molding, it is a uniform distribution of stress, no restrictions on the direction of pressure. Forgings are pressed by the same direction of force, it has a directional internal stress, can only withstand the directional pressure.
The same material, the same wall thickness of castings and forgings, in strength and crystal phase structure, forgings are better than castings. For the shut-off valve, the same pounds. The wall thickness of the same material of the castings globe valve is thicker than forgings. Its pressure strength is equal to that of forgings.
Casting requirements for the casting process is higher, the most important feature is that it can make more complex shapes, the body structure of the globe valve and the flow channel are irregular, casting can be a one-time molding, as long as the process is good, you can cast the body of the large diameter globe valve.
Forgings are better dense, but for too complex flow paths and shapes can not be formed at once, often need to be modular, separate forging and then welded together, so the size of forgings are somewhat limited.
Forgings are often not machined to produce complex, streamlined runners. The runners are machined by turning and form many sharp corners inside the transition, which can easily cause uneven stresses and cracking at these sharp corners. At the same time, the modular welded design, forged globe valve seat bore is relatively fixed, in some globe valve size, its bore is small, affecting the flow capacity. This results in increased flow resistance of the globe valve and reduced efficiency of the entire system.
Due to the limitations of the forging process in large size globe valve, and to save costs, many manufacturers usually use the center part of the valve body castings, forgings at both ends of the structure. Whether castings, forgings. In the processing, there are possible product defects. The main defects of castings are in trachoma, bubbles, etc.; the main defects of forgings are in large grains, cold hardening phenomenon, cracks, cracks, etc. In order to obtain qualified product quality, the corresponding castings need heat treatment to eliminate the stress in the casting process, while using X-ray, magnetic particle flaw detection, penetration inspection and other detection means.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.sfutube.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Stainless Steel Valves, 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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