Taking the difference between forging cut-off valve and casting cut-off valve as an example, this paper introduces the difference between casting cut-off valve and forging cut-off valve in detail. If you think the answer is helpful to you, please give a compliment to the American Witton VTON valve.
Casting valve is a kind of valve that casts materials in a mold as a whole. Generally, the pressure grades of casting globe valves are relatively low (such as PN 16, PN25, PN40 and PN64), but some have high pressure, which can reach 1500Lb and 2500Lb, and their diameters are mostly above DN 15. For example, the American Witton VTON casting globe valve is made of cast iron, ductile iron and cast steel, 304, 304L, 365, 438+06, 365 and 438+06L.
Forged globe valves are forged, generally used for high-grade pipelines, with a relatively small diameter, generally below DN50. However, there are also some imported valves, which are forged with large caliber, such as the American Witton VTON forged globe valve, whose caliber ranges from DN 15-500. The materials of forged globe valves are generally divided into A 105, forged stainless steel, P9 1, F9 1 and so on.
I. Casting valves
1. Casting: It is the process of melting metal into a liquid meeting certain requirements, pouring it into a mold, cooling, solidifying and cleaning to obtain a casting (part or blank) with a predetermined shape, size and performance. Basic technology of modern machinery manufacturing industry.
2. The cost of the blank produced by casting is low, which can better reflect the economy of the parts with complex shapes, especially those with complex cavities; At the same time, it has wide adaptability and good comprehensive mechanical properties.
3. However, there are many materials (such as metal, wood, fuel, molding materials, etc. ) and equipment (such as metallurgical furnace, sand mixer, molding machine, core making machine, sanding machine, shot blasting machine, cast iron flat plate, etc.). ) required by foundry production, and will produce dust, harmful gases and noise to pollute the environment?
4. Casting is an early metal hot working process mastered by human beings, with a history of about 6000 years. In 3200 BC, bronze frog castings appeared in Mesopotamia. During the period from BC 13 to BC 10, China entered the heyday of bronze casting, and its technological level reached a fairly high level. For example, Simuwu Fang Ding, weighing 875 kg in Shang Dynasty, Zunpan in Ceng Houyi in Warring States and transparent mirror in Western Han Dynasty are all representative products of ancient casting. Early casting was greatly influenced by pottery, and most of the castings were tools or utensils for agricultural production, religion and life, with strong artistic color. In 5 13 BC, China cast the earliest recorded iron castings in the world-Jin Guoding (about 270kg). Around the 8th century, Europe began to produce iron castings. /kloc-after the industrial revolution in the 0/8th century, castings entered a new era of serving large industries. In the 20th century, casting developed very rapidly. Foundry metal materials such as nodular cast iron, malleable cast iron, ultra-low carbon stainless steel, Al-Cu, Al-Si, Al-Mg alloy, Ti-based alloy and Ni-based alloy have been developed successively, and a new technology of inoculation treatment for gray cast iron has been invented. After 1950s, new technologies such as green sand high pressure molding, chemically hardened sand molding and core making, negative pressure molding, other special casting and shot blasting cleaning appeared.
5. There are many kinds of casting, which are customarily divided into: ① ordinary sand casting, including wet sand mold, dry sand mold and chemically hardened sand mold. ② Special casting, according to the molding materials, can be divided into special casting with natural ore as the main molding material (such as investment casting, clay casting, shell casting in casting workshop, negative pressure casting, full mold casting, ceramic mold casting, etc. ) and special casting with metal as the main mold material (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc. ).
6. The casting process usually includes: ① Preparing molds (containers for making solid castings from liquid metal), which can be divided into sand molds, metal molds, ceramic molds, clay molds, graphite molds, etc. According to the times of use, it can be divided into disposable mold, semi-permanent mold and permanent mold, and the quality of mold making is the main factor affecting the quality of castings. (2) Melting and pouring of casting metals, casting metals (casting alloys) mainly include cast iron, cast steel and casting nonferrous alloys; (3) Casting processing and inspection. Casting treatment includes removing foreign bodies from the core and the surface of the casting, cutting off the riser, shoveling off burrs, overlapping seams and other protrusions, as well as heat treatment, shaping, rust prevention and rough machining.
Second, forging valves.
1. Forging: It is a processing method that uses forging machinery to exert pressure on metal blank to produce plastic deformation, so as to obtain forgings with certain mechanical properties, shapes and sizes.
2. One of the two elements of forging. Forging can eliminate the as-cast porosity and welding holes of metal, and the mechanical properties of forgings are generally better than those of castings of the same material. Forgings are mostly used for important parts with high load and bad working conditions in machinery, except for rolled plates, profiles or weldments with simple shapes.
3. According to the American Witton VTON method, forging can be divided into: ① free forging (free forging). The metal is deformed between the upper and lower supports (anvil) by impact or pressure to obtain the required forgings. There are two main methods: manual forging and mechanical forging. ② Closed forging. Forgings are obtained by pressure deformation of metal blanks in a forging die chamber with a certain shape, which 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 (the processing temperature is higher than the recrystallization temperature of the blank metal), warm forging (lower than the recrystallization temperature) and cold forging (normal temperature).
4. Forging materials are mainly carbon steel and alloy steel with various compositions, followed by aluminum, magnesium, titanium, copper and their alloys. The original state of materials includes rod, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of a metal before deformation to the broken die area after deformation is called forging ratio. The correct selection of forging ratio has a great relationship with improving product quality and reducing cost.
Three, the main difference between casting valve and forging valve
Casting is the integral casting of materials in the mold, and its stress distribution is uniform, and there is no limit to the compression direction. Forgings are stressed in the same direction, so the internal stress is directional and can only bear directional pressure.
Castings and forgings with the same material and wall thickness are superior to castings in strength and crystal structure. For globe valves, the wall thickness of globe valves with the same weight and material is thicker than that of forgings. Its compressive strength is equivalent to that of forgings.
Castings require high casting technology, and the biggest feature is that they can be made into complex shapes. The valve body structure and flow passage of globe valve are irregular, which can be cast and formed at one time. As long as the process passes, the body of large-diameter globe valve can be cast.
For example, American Witton VTON forged globe valve, imported forged ball valve, and the diameter of imported forged globe valve can reach 20 inches.
Forgings have good compactness, but for too complicated runner and shape, they cannot be formed at one time, and often need to be modularized, forged separately and then welded together, so the size of forgings is limited to some extent.
Forgings usually can't process complicated streamlined runner. The runner is machined by turning, and there are many sharp corners in it, which easily leads to uneven stress and cracks. At the same time, the modular welding design makes the valve seat diameter of forging globe valve relatively fixed, and in some globe valves, its diameter is small, which affects the flow capacity. The flow resistance of stop valve increases, and the efficiency of the whole system decreases.
Due to the limitation of forging process of large-diameter globe valves, and in order to save costs, many manufacturers usually adopt the structure that the valve body is cast in the center and forged at both ends. Whether it is a casting or a forging. In the process of processing, product defects are possible. The main defects of castings are sand holes and bubbles. The main defects of forgings are large grains, cold hardening, cracks and cracks. In order to obtain qualified product quality, the corresponding castings need heat treatment to eliminate the stress in the casting process, and X-ray, magnetic particle inspection and penetrant inspection are adopted at the same time. For forgings, this requires strict weld heat treatment and corresponding detection means to ensure. Forgings often need ultrasonic inspection. In addition, it should be mentioned that the welding process is very strict, and the qualification of welding engineer is the key.