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Centrifugal Casting is a technique and method that injects liquid metal into a high-speed rotating mold, so that the liquid metal is centrifugal motion to fill the mold and form a casting.
Machining of Centrifugal Castings
Due to the centrifugal movement, the liquid metal can fill the mold well in the radial direction and form the free surface of the casting; the cylindrical inner hole can be obtained without the core; it helps to eliminate the gas and inclusions in the liquid metal; it affects the metal The crystallization process improves the mechanical and physical properties of the casting.
Technology Classification
According to the spatial position of the rotation axis of the mold, common centrifugal casting can be divided into horizontal centrifugal casting and vertical centrifugal casting.
Centrifugal casting when the rotation axis of the mold is in a horizontal state or when the angle with the horizontal line is small (4°) is called horizontal centrifugal casting.
Centrifugal casting when the rotation axis of the mold is in a vertical state is called vertical centrifugal casting. Centrifugal casting in which the rotation axis of the mold has a large angle with the horizontal and vertical lines is called inclined axis centrifugal casting, but it is rarely used.
Application field
Castings with significant production benefits include:
Bimetal cast iron roll; Heat-resistant steel roller table of heating furnace bottom;
Special steel seamless steel pipe; Brake drum, piston ring blank, copper alloy worm wheel;
Special-shaped castings such as impellers, metal dentures, gold and silver mesons,
small valves and cast aluminum motor rotors.
Centrifugal casting was first used to produce cast pipes, and then this process has been developed rapidly. At home and abroad, centrifugal casting is used in metallurgy, mining, transportation, irrigation and drainage machinery, aviation, national defense, automobile and other industries to produce steel, iron and non-ferrous carbon alloy castings.
Among them, the production of castings such as centrifugal cast iron pipes, internal combustion engine cylinder liners and shaft sleeves is the most common. For some forming tools and gear castings, centrifugal force pouring can also be used for the molten mold shell, which can not only improve the accuracy of the casting, but also improve the mechanical properties of the casting
Castings with large production output include:
Iron pipe: Nearly 1/2 of the total annual output of ductile iron in the world is iron pipe produced by centrifugal casting
Cylinder liners of diesel engines and gasoline engines
Various types of steel sleeves and steel pipes
Bimetallic steel back copper sleeve, bearing bush of various alloys
Paper machine drum
Technical characteristics
Advantage:
There is almost no metal consumption in the gating system and the riser system, which improves the process yield;
The core is not used in the production of hollow castings, so the metal filling ability can be greatly improved when the long tubular castings are produced,
the ratio of the wall thickness of the castings to the length or the diameter can be reduced, and the production process of sleeves and pipe castings can be simplified;
The casting has high density, few defects such as pores and slag inclusion, and high mechanical properties;
It is convenient to manufacture barrel and sleeve composite metal castings, such as steel-backed copper sleeves, bimetallic rolls, etc.; when forming castings,
centrifugal movement can be used to increase the metal filling ability, so thin-walled castings can be produced.
Disadvantages:
There are certain limitations when used in the production of special-shaped castings.
The diameter of the inner hole of the casting is not accurate,
the surface of the inner hole is relatively rough, the quality is poor, and the machining allowance is large;
Castings are prone to segregation of specific gravity,
so they are not suitable for castings that are prone to segregation of specific gravity of alloys
(such as lead bronze), and are especially not suitable for casting alloys with impurities that are larger than molten metal.
Craftsmanship
Metal filtration, pouring temperature, casting speed, solidification under slag, coating use, casting de-molding, pouring system, pouring quantitative, etc. are process problems that must be determined or resolved in centrifugal casting production,
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because they directly affect the quality and quality of castings. Productivity.
Metal filtration
There are more difficult to remove slag in some alloy liquids, and various filters can be placed in the pouring system to remove the slag, such as foam ceramic filters, glass wire filters, etc.
Pouring temperature
Centrifugal castings are mostly tubular, sleeve-shaped, and ring-shaped parts. The resistance encountered when molten metal is filled is small, and centrifugal pressure or centrifugal force strengthens the filling capacity of molten metal, so the pouring temperature during centrifugal casting can be higher than that of gravity pouring It is 5~10°C lower.
Mold speed
It is an important process factor in centrifugal casting. Different castings and different casting processes have different mold speeds when castings are formed.
Too low casting speed will cause poor metal liquid filling during vertical centrifugal casting, and liquid metal rain during horizontal centrifugal casting, which will also cause looseness, slag inclusion, and unevenness on the inner surface of the casting;
The mold speed is too high, and defects such as cracks and segregation are easy to appear on the casting. The outer surface of the sand centrifugal casting will form defects such as expansion box, and it will also cause the machine to experience large vibration, aggravation of wear, and excessive power consumption.
Therefore, the principle of selecting the casting speed should be to select the smallest value on the premise of ensuring the quality of the casting
Slag utilization
In order to overcome the defects of subcutaneous shrinkage caused by two-way solidification of thick-walled centrifugal castings, slag-forming agent and molten metal can be poured into the mold during pouring.
The molten slag covers the inner surface of the casting to prevent the heat dissipation of the inner surface. Sequential coagulation conditions from outside to inside eliminate subcutaneous shrinkage.
At the same time, the slagging agent can also play a role in refining molten metal.
The method of pouring slagging agent is: sprinkle powdery slagging agent in the casting trough during pouring; pour molten slag and molten metal into the mold together.
Paint use
The composition of the coating for centrifugal metal molds is similar to that of gravity metal mold casting.
When pouring slender centrifugal castings, because it is difficult to remove the residual paint on the working surface of the mold, the residual strength of the binder in the paint composition after high temperature work should be as low as possible to facilitate removal.
Deformation of castings
In order to improve production efficiency, under the premise of ensuring quality, the casting should be removed as soon as possible.
Sometimes in order to prevent the cracking of the casting, the casting after de-molding should be immediately put into a holding furnace or buried in a sand pile to cool down.
For some castings that are not easy to release and require slow cooling to prevent cracking, the mold with castings can be removed from the centrifugal casting machine immediately after the mold stops rotating, and buried in the sand pile to cool down slowly. type.
Gating system
The pouring system in centrifugal casting mainly refers to the pouring cup that accepts the metal and the pouring trough connected to it, and sometimes also includes the runner in the mold. When designing the gating system, the following principles should be noted:
When pouring long-length and large-diameter castings, the pouring system should enable the molten metal to spread quickly and evenly on the inner surface of the mold;
When pouring easy-to-oxidize molten metal or using centrifugal sand molds, the casting trough should enable the molten metal to fill the mold in a balanced manner to minimize splashing of the molten metal and reduce the erosion of the sand mold;
When pouring forming castings, the runner in the mold should enable the molten metal to flow into the cavity smoothly;
After pouring is finished, there should be no metal and slag left in the pouring cup and pouring trough. If there is residual metal and slag, it should be easy to remove.
Quantitative pouring
The inner diameter of centrifugal castings is often determined by the amount of molten metal poured, so during centrifugal casting, the amount of molten metal poured in the mold must be controlled to ensure the size of the inner diameter.
The installation of pressure sensors on the pouring ladle racks for centrifugal pouring and automatic quantitative pouring of the induction furnace electromagnetic pump has also been applied in production.
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T5.13 Forest without borders: National Forest Inventory Networks and their potential for large scale monitoring and reporting Jenny Wong Lai Ping1 1 United Nations Climate Change Secretariat, Bonn, Germany The Framework Convention on Climate Change (UNFCCC) recognizes the critical role of forests as terrestrial carbon sinks for combatting climate change and calls for transparency of climate actions, including those in the forest sector. The Paris Agreement continues to uphold the principle of transparency. It established the Enhanced Transparency Framework (ETF) with the aim to build mutual trust and confidence among countries in their monitoring and reporting of climate actions and to track progress of such mitigation actions. Forests play a key role in all aspects of the implementation of the Paris Agreement. Numerous countries, both developed and developing, have identified forest and land use-related mitigation and adaptation measures and actions as part of their climate targets in their nationally determined contributions to fulfill the goal of the Paris Agreement. The world is now in an era where transparency of data and information and actions are indispensable for ensuring coordination among relevant ministries and agencies and effective decision-making at all levels. Transparent, robust and comprehensive data and information on greenhouse gas emissions and climate actions are essential for informing national policies, plans and strategies and helping countries meet their international commitments on climate change. The same applies to forest data and information and its reporting to multilateral environmental agreements. Additionally, robust institutional arrangements, including for national forest inventories (NFI) as part of national forest monitoring systems and GHG management systems, form the basis for ensuring transparent data and information from these processes and systems and for meeting the requirements for reporting under the ETF. The aim of this review analysis is to highlight the importance of transparency in monitoring and reporting and for building trust in climate actions. The analysis will provide an overview of the requirements and necessary elements for monitoring and reporting on the forest and land use sector in the ETF and the challenges faced. This background will serve as a basis for stimulating discussions and exploring potential collaborative solutions offered by strong institutional arrangements and collaborative networks (such as NFI networks) and to facilitate identification of effective capacity-building needs of developing countries.
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