Valve forging knowledge
Casting and forging are two different processing processes.
Casting is the transformation of shapeless molten metal into a shapeless solid. Cast valves are valves made by casting.
Forging is mainly formed by extrusion method at high temperatures. It is possible to refine the grains in the part. Forged valves are forged.
Valve forging knowledge
：Types of forging
一. Valve forging knowledge：Classification according to deformation temperature
When the temperature exceeds 300-400 °C (the blue brittle zone of steel) and reaches 700-800 °C, the deformation resistance will be sharply reduced valve forging knowledge, and the deformation energy will also be greatly improved. According to the forging carried out in different temperature areas, according to the different requirements of forging quality and forging process, it can be divided into three forming temperature zones: cold forging, warm forging and hot forging. The starting recrystallization temperature of steel is about 727 °C, but 800 °C is generally used as the dividing line, and above 800 °C is hot forging; Between 300~800 °C is called warm forging or semi-hot forging. Forging without heating at room temperature is called cold forging for more information visit here.
When forged at low temperatures, the size of the forgings changes very little. Forged below 700 °C, less oxide scale formation, and no decarburization phenomenon on the surface. Therefore, as long as the deformation can be within the forming energy range, cold forging is easy to obtain good dimensional accuracy and surface finish. As long as the temperature and lubrication cooling are well controlled, the temperature forging below 700°C can also obtain good accuracy. During hot forging, large forgings with complex shapes can be forged because the deformation energy and deformation resistance are small. To obtain forgings with high dimensional accuracy, they can be hot forged in the temperature range of 900-1000°C. In addition, attention should be paid to improving the working environment of hot forging. The life of the forging die (hot forging 2-5,000, warm forging 1-20,000, cold forging 2-50,000) is shorter than forging in other temperature domains, but it has a large degree of freedom and low cost.
The blank is deformed and work hardened during cold forging, so that the forging die is subjected to high loads, so it is necessary to use high-strength forging dies and hard lubricating film treatment methods to prevent wear and bonding. In addition, in order to prevent billet cracks, intermediate annealing is carried out when necessary to ensure the required deformation capacity. In order to maintain good lubrication, the billet can be phosphated. In the continuous processing with bar stock and wire rods, the cross-section cannot be lubricated at present, and the possibility of using phosphating lubrication method is being studied.
Valve forging knowledge：
Classified according to how the billet is moved
According to the movement mode of the blank, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, closed upsetting forging.
1. Free forging
Definition: A processing method that uses impact force or pressure to free deform metal in all directions between the upper and lower anvil surfaces, and obtain the required shape and size and certain mechanical properties without any restrictions, referred to as free forging.
Features: The tools and equipment used in free forging are simple, good versatility and low cost. Compared with casting blanks, free forging eliminates defects such as shrinkage holes, shrinkage looseness, porosity, etc., so that the blank has higher mechanical properties. The shape of the forgings is simple and the operation is flexible. Therefore, it is of particular importance in the manufacture of heavy machines and important parts.
Classification: There are mainly two types: manual forging and mechanical forging. Manual free forging has low production efficiency and high labor intensity, and is only used for repair or the production of simple, small, and small batch forgings.
In modern industrial production, machine free forging has become the main method of forging production, and in heavy machinery manufacturing, it plays a particularly important role. The shape and size of the resulting forgings are mainly determined by the technical level of the operator.
Basic processes: The basic processes of free forging include upsetting, lengthening, punching, bending, twisting, misshifting, cutting and forging.
Definition: Die forging refers to the forging method of obtaining forgings by using molds to form blanks on special die forging equipment. The forgings produced by this method are accurate in size, with small machining allowance, and the structure is relatively complex and has high productivity.
Features: The process of forging and forming metal blanks with forging dies on die forging hammers or presses. The die forging process has high production efficiency, low labor intensity, accurate size, small processing allowance, and can forge forgings with complex shapes; Suitable for mass production. However, the mold cost is high, and special die forging equipment is required, which is not suitable for single piece or small batch production.
Process and process: The process of die forging is billet making, pre-forging and final forging. The bore of the final forging die is determined according to the size and shape of the forging, plus the allowance and deviation.
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