Guangdong mechanical processing plant casting is a kind of manufacturing process that melts metal into or into a suitable mold cavity and solidifies in it. During or after cooling, the casting is removed from the mold and delivered. Casting technology and casting material technology change from simple to highly complex
It's a big change. The choice of material and process depends on the complexity and function of parts, the quality requirements of products and the level of cost budget. By casting, castings can be made very close to their final dimensions. Looking back to 6000 years of history, all kinds of casting techniques have been developed
Just like the progress of science and technology, it is in a state of continuous improvement and development.
1、 Sand casting
Sand casting is used to make large parts (typically iron, in addition to bronze, brass and aluminum). The molten metal is poured into a mold cavity made of molding sand (natural or artificial). Sand casting process, including mold, gate, runner and design
Considering factors and casting allowance. The cavity in the sand mold is made of molds (approximate copies of real parts), which are usually made of wood and sometimes metal. The entire cavity is contained in an assembly that is placed in a box called a sandbox. The sand core is inserted
A sand mold used to create internal features such as holes or inner channels. The sand core is placed in the cavity to form a hole of the desired shape. The core seat is a specific area added to the mold, core or mold to position and support the core inside the mold.
Riser is an additional space added inside the mold to accommodate excessive molten metal. The purpose is to add molten metal to the cavity when the molten metal solidifies and shrinks, so as to prevent porosity in the main casting. In a typical two box sand mold, the upper part (including the top part of the mold, the sand box and the sand core) is called the upper box, and the lower part is called the lower box. Parting line or parting surface is the line or surface separating the upper and lower boxes. First, the molding sand, sand core seat and sand core are partially filled into the lower mold box, and the gating system is placed near the parting line. Then the upper and lower mold boxes are assembled together, and the molding sand is poured into the upper mold box to cover the mold, sand core and gating system. Molding sand is compacted by vibration and mechanical methods. Then remove the upper box from the lower box and take out the mold carefully.
The purpose of Guangdong machining factory is to take out the mould without destroying the cavity. It is easy to take out the mold by designing the draft angle - the slight angle offset of the vertical intersecting surface of the mold. The minimum draft angle is generally 1.5mm (0.060in.), which can only be larger than this. The thicker the mold surface is
Rough, the draft angle should be larger. Molten metal is injected into the cavity from the pouring cup, which is the part of the gating system that supplies molten metal to the cavity.
The vertical part of the gating system is connected with the pouring cup by the pouring gate. The horizontal part of the gating system is called the runner, and the gate is called the gate which leads the molten metal into the cavity at many points. In addition, there is an extension of the gating system called the vent, which provides a channel for the synthesis gas and replacement air to be discharged to the atmosphere. The cavity is usually larger than required to allow shrinkage as the metal cools to room temperature. This is achieved by making the mold larger than the required size. In order to solve the shrinkage effect, generally speaking, when the mold is larger than the required size, the linear factor must be considered and acted on all directions. Shrinkage allowance is only approximate because the exact allowance is determined by the shape and size of the casting. In addition, different parts of the casting may require different shrinkage allowance. Generally, the surface of sand castings is rough, sometimes with surface impurities and surface variation.
The allowance of machining (the last process) is used for such defects.
Generally speaking, the typical stages of sand casting operation include:
1. Make mould. It is made into a shape for forming a cavity in molding sand.
2. At the same time, sand core should be made. These cores are made of bonded sand and will be broken and taken out after the casting is completed.
3. Molding sand and additives such as bentonite are fully mixed to enhance the connection and overall strength.
4. Molding sand is formed around the mold, and gate, runner, riser, discharge port and pouring cup are placed as required. Compaction is usually required to ensure good coverage and a strong mold.
The sand core is placed to make the concave structure or internal features of the casting. In order to match the mold in the future, we need to use the positioning pin. For high quality castings, it may be necessary to add coolant to make it cool faster.
5. Remove the mold and bake the mold to increase strength.
6. Match the upper and lower molds to prepare for casting metal.
7. The metal is preheated in the furnace or crucible to a suitable range higher than the liquefying temperature (it is not expected that the metal will solidify before casting). The exact temperature should be strictly controlled according to the application.
During this period, exhaust and other treatment steps, such as removing impurities (i.e. slag), are also carried out. A certain amount of scrap from the original metal casting can be added for remelting - 10% is appropriate.
8. Fill the mold slowly and continuously with metal.
9. As the molten metal cools (from a few minutes to a few days), the shrinkage volume of the metal decreases. During this period, molten metal may flow back from the riser to the part to maintain its shape.
10. When the part begins to solidify, a small dendrite of solid metal is formed inside the part. During this period, the metal properties are determined, and the internal stress is also generated. If the part cools slowly enough at a constant rate, the final part will be relatively homogeneous and internal stress released.
11. Once the part is completely solidified below the eutectoid point, it can be removed without considering the final properties of the metal. At this time, it is easy to break the sand mold and take out the parts, but there will be a lot of sand adhering on the surface of the parts, and there is a solid sand core inside.
12. A large amount of residual molding sand and sand core should be removed by mechanical percussion. Other options include vibration table, sandblasting / shot peening machine, manual operation, etc.
13. Finally, the runner gate system should be cut off by cutting tools, spray guns, etc. so that the final shape is close to the final shape. Then the grinding operation is used to remove the redundant part.
14. Cutting parts to final shape by machining. Cleaning operations may also be used to remove oxides, etc.
2、 Investment casting
Investment casting is also called lost wax processing. It's one of the oldest manufacturing processes. Egyptians used it to make gold ornaments (hence the name investment) during the reign of the Pharaohs about 5000 years ago.
Complex shapes can be made with high precision. In addition, more difficult to machine or make metal can use this process. It can also be used to produce parts that cannot be produced by general manufacturing technology, such as turbine blades with complex shapes or aircraft parts that must withstand high temperature.
The mould made by Guangdong Machinery processing factory is made of paraffin or other materials that can be melted away. The wax mold is immersed in a heat-resistant slurry, allowed to cover the mold and form a shell, and then allowed to dry. Repeat the soaking and drying process until sufficient thickness is obtained.
When finished, melt the wax in the oven. This makes a mold that can be filled with molten metal. Because this kind of mold is formed around the whole mold (it does not need to draw the mold like the traditional sand casting process), it can make very complex parts and relief.
The paraffin mould itself can be reproduced by stereo plate making or similar models - this can be made by computer stereo model original.
For lower melting temperature, the material used for heat-resistant slurry is a mixture of gypsum as binder and powdered silica as heat-resistant material. For higher melting temperature, sillimanite or alumina silicate is used as temperature resistant material and anhydrous silicic acid as binder.
Sillimanite and ethanyl silicate can also be used according to the final required finish. The resulting mold can be used directly for thin-walled castings or reinforced by placing it in a larger container with more heat-resistant slurry.
Before casting, the mould was preheated to about 1000 ℃ (1832 ℃) to remove the remaining paraffin and harden the adhesive. Casting in the preheated mould can also ensure that the mould is fully filled.
Casting can be done by gravity, pressure or vacuum. When pressure is used, attention must be paid to permeability so that air can escape while casting.
General tolerances may be as low as 0.5% of length and as low as 0.15% for small dimensions. Although the weight of castings with normal size ranges from 200g to about 8kg (7oz to 15lb), it can actually range from a few grams to 35kg (0.1oz to 80LB). For alloys that are easy to cast, usually
The types of materials that can be used for casting are: aluminum alloy, bronze, tool steel, stainless steel, tungsten chromium cobalt alloy, nickel base alloy and precious metal. Investment casting parts often do not need further processing, because investment casting can achieve precise tolerances.
3、 Centrifugal casting
As a kind of casting, centrifugal casting includes centrifugal casting, semi centrifugal casting and centrifugal casting. In centrifugal casting, the permanent mold rotates around its axis at a high speed (300 to 3000 rpm) during molten metal casting.
Under the action of centrifugal force, the molten metal is thrown to the inner wall of the mold, where it cools and solidifies. This kind of casting is usually a fine grain casting with very fine grains at the outer diameter, which can resist atmospheric corrosion, and the typical case is the pipe. There are more impurities and inclusions in the inner diameter, but there is no significant difference
It can be removed by machining.
Only cylinders can be produced by this process. The size is limited to 3 m (10 feet) in diameter and 15 m (50 feet) in length. The wall thickness is 2.5mm to 125mm (0.1-5.0in.). The outer diameter tolerance shall be kept within 2.5mm (0.1in.) and the inner diameter tolerance shall be kept within 2.5mm (0.1in.)
Typical materials that can be cast by this process are: iron, steel, stainless steel and alloys of aluminum, copper and nickel. By adding a second material in the production process, two kinds of materials can be cast. Typical parts manufactured by this process are: tubes, boilers, pressure vessels
Vessels, flywheels, cylinder liners and other axisymmetric parts.
1. Semi centrifugal casting: the mold can be permanent or expendable, and can be superimposed as needed. Its rotational speed is lower than that of centrifugal casting.
There are defects and pores near the central axis of the part, so it is only applicable to the parts that can be removed by machining. This process is used to make wheels, nozzles and similar parts that can be subsequently machined to remove the central shaft portion.
2. Centrifugal casting: centrifugal casting is used to force metal from the central axis of the equipment into a separate cavity distributed on the circumference. It provides a way to increase the filling pressure for each cavity and allows complex details to be reproduced. This method is often used in investment casting
Type
3. solid mold casting is a technology similar to that of investment casting, but the consumption material used for making moulds is polystyrene foam instead of paraffin wax. Foam mold is covered with refractory material. The mold is put into the integral sand mold. When the metal is poured in, the foam material evaporates and the metal takes.
Instead of its position. It can produce complex shape castings without draft angle and seam ridge. However, due to the consumption characteristics of the mold, the mold cost may be higher. The minimum wall thickness is 2.5mm and the tolerance can be kept within 0.3% of the size. Effective value of surface roughness (root mean square)
It can be maintained at 2.5 μ M to 25 μ m(0.1 μ In. To 1.0 μ In.).
The weight limit is from 400g (1lb) to several tons. No draft allowance is required. Typical materials used in this process are aluminum, iron, steel, nickel alloy and copper alloy. The types of parts that can be manufactured by these processes are pump housing, multiple joints and automatic brake components.
Ruinuohong Precision Machinery Technology Co., Ltd. has rich experience in processing castings and advanced processing technology