What are the differences between forged and cast valves?

The casting is made by pouring the material in the mold as a whole, and its stress distribution is uniform, and there is no restriction on the direction of compression. The forging is pressed by the force in the same direction, and its internal stress has directivity, which can only bear directional pressure.



1、 Casting

1. Casting: it is the process of melting the metal into a liquid that meets certain requirements and pouring it into the mold. After cooling, solidification and cleaning, the casting (part or blank) with predetermined shape, size and performance can be obtained. The basic technology of modern machinery manufacturing industry.

2. The cost of casting blank is low, and it is more economical for the parts with complex shape, especially for the parts with complex cavity; at the same time, it has wide adaptability and better 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, sand dropping machine, shot blasting machine, cast iron plate, etc.) needed for foundry production, which will produce dust, harmful gas and noise and pollute the environment.

4. Casting is a kind of metal hot working technology mastered by human beings earlier, which has a history of about 6000 years. In 3200 BC, copper frog castings appeared in Mesopotamia. From the 13th century BC to the 10th century BC, China has entered the heyday of bronze casting, and the technology has reached a fairly high level. For example, the simuWe square tripod weighing 875 kg in the Shang Dynasty, the zunpan of marquis Zeng Yi in the Warring States period and the transparent mirror of the Western Han Dynasty are representative products of ancient casting. The early casting was greatly influenced by pottery. Most of the castings were tools or utensils for agricultural production, religion, life and other aspects, with strong artistic color. In 513 B.C., China produced the earliest recorded iron casting in the world, the Jin Ding (about 270 kg). Around the 8th century, iron castings were produced in Europe. After the industrial revolution in the 18th century, castings entered a new period of service for large industry. get into

In the 20th century, the development of casting is very fast. Ductile iron, malleable iron, ultra-low carbon stainless steel, aluminum copper, aluminum silicon, aluminum magnesium alloy, titanium base, nickel base alloy and other casting metal materials have been developed, and a new process of inoculation treatment for gray cast iron has been invented. After 1950s, new technologies such as wet sand high pressure molding, chemical hardening sand molding, core making, negative pressure molding and other special casting, shot blasting and cleaning appeared.

5. There are many kinds of casting, which can be divided into: 1) ordinary sand mold casting, including wet sand mold, dry sand mold and chemical hardening sand mold. ② According to the molding materials, the special casting can be divided into the special casting with natural mineral sand and stone as the main molding materials (such as investment casting, clay mold casting, shell mold casting in foundry, negative pressure casting, full mold casting, ceramic mold casting, etc.) and the special casting with metal as the main molding materials (such as metal mold casting, pressure casting, continuous casting, low pressure casting, centrifugal casting, etc.) There are two types.

6. The casting process usually includes: ① preparation of casting mold (making liquid metal the container of solid casting); according to the materials used, the casting mold can be divided into sand mold, metal mold, ceramic mold, clay mold, graphite mold, etc.; according to the times of use, it can be divided into disposable mold, semi permanent mold and permanent mold; the advantages and disadvantages of casting mold preparation are the main factors affecting the casting quality; ② Melting and pouring of casting metal, casting metal (casting alloy) mainly includes cast iron, cast steel and casting non-ferrous alloy; ③ casting treatment and inspection, casting treatment includes removing foreign matters on the core and casting surface, removing casting riser, relieving burr and seam and other protrusions, as well as heat treatment, shaping, anti rust treatment and rough machining.



2、 Forging

1. Forging: is the use of forging machinery to exert pressure on metal billets to produce plastic deformation, in order to obtain a certain mechanical properties, a certain shape and size of forgings processing method.

2. One of the two major components of forging. The casting porosity and welding holes of metal can be eliminated by forging, and the mechanical properties of forgings are generally better than those of castings of the same material. For the important parts with high load and severe working conditions in machinery, forgings are mostly used except for the simple shape of rolled plates, profiles or weldments.

3. Forging can be divided into: ① open forging (free forging). There are mainly two kinds of forging, manual forging and mechanical forging, which are used to deform the metal between the upper and lower anvil blocks by impact force or pressure. ② Closed mode forging. The forging is made of metal billet in a certain shape forging die, which can be divided into die forging, cold heading, rotary forging, extrusion and so on. According to deformation temperature, forging can be divided into hot forging (processing temperature is higher than recrystallization temperature of blank metal), warm forging (lower than recrystallization temperature) and cold forging (normal temperature).

4. The main forging materials are carbon steel and alloy steel, followed by aluminum, magnesium, titanium, copper and their alloys. The original state of materials includes bar, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to that of the die after deformation is called forging ratio. The correct choice of forging ratio has a great relationship with the improvement of product quality and the reduction of cost.



3、 Identification of castings and forgings

1. For the fine density of the surface structure of forgings, the surface of castings should be coarser, while the machined surface of forgings should be brighter.

2. Cast iron section is gray and dark, while forged steel section is silver.

3. Listen to the sound, the forging is compact, the sound is crisp after striking, and the casting is dull.

4. Use a grinder to polish and see the difference between the two sparks (the brightness of forgings) and so on.