Centrifugal Casting Process

Introduction to Centrifugal Casting Process

In this section, we learn about the centrifugal casting process and its development by A. Eckhardt in England in 1809. We explore how centrifugal forces are utilized to distribute molten metal into mold cavities, resulting in the desired geometry of the casting.

Centrifugal Casting Process

• Centrifugal casting process utilizes centrifugal forces caused by rotation to distribute molten metal into mold cavities.

• The molten metal sticks to the walls of the rotating mold due to centrifugal force, resulting in the required geometry of the casting.

Types of Centrifugal Casting Processes

This section discusses different types of centrifugal casting processes, including horizontal true centrifugal casting, vertical true centrifugal casting, semi-centrifugal casting, and centrifusing.

Horizontal True Centrifugal Casting

• Horizontal true centrifugal casting is used for producing cylindrical hollow parts.

• The mold is rotated about a horizontal or vertical axis, holding the molten metal against the walls until it solidifies.

• Cylindrical metallic molds are supported by top and bottom rollers during rotation.

• After solidification, the rotation stops, and a finished hollow cylindrical casting is obtained.

Vertical True Centrifugal Casting

• Vertical true centrifugal casting is suitable for heavy parts where diameter is more important than length.

• Similar to horizontal true centrifugal casting, a cylindrical mold rotates while molten metal is poured inside.

• The rotation continues until solidification occurs within the metallic mold.

Conclusion

The transcript provides an introduction to the centrifugal casting process and explores its various types. It explains how rotational forces are used to distribute molten metal into molds and obtain desired castings.

Centrifugal Casting Process Overview

This section provides an overview of the centrifugal casting process, including the steps involved and its advantages and disadvantages.

Steps in Centrifugal Casting Process

• The metallic mold is coated with a ceramic slurry to prevent molten metal from sticking.

• The mold rotates at a predetermined speed (300 to 3000 RPM), and molten metal is poured into it without the need for a gating system.

• After solidification, the mold stops rotating, and the casting is extracted from it.

• The final step involves removing impurities through machining, grinding, or sand blasting.

Advantages of Centrifugal Casting Process

• Flexibility in casting composition allows for a wide range of product metallurgical characteristics.

• Central core is not required for making holes or pipes in castings.

• Hollow cast components can be produced without using cores.

• No gating system is required, resulting in close to 100% casting yield.

• Relatively light impurities move towards the center and can be easily removed.

Disadvantages of Centrifugal Casting Process

• Suitable only for axial symmetrical components and hollow components.

• More segregation of alloy components during pouring under rotation forces.

Casting Yield Definition and Calculation

This section explains the concept of casting yield and how it is calculated.

Definition of Casting Yield

Casting yield refers to the ratio of weight of the casting to weight of the poured metal multiplied by 100. It represents the efficiency of metal utilization in the casting process.

Calculation of Casting Yield

• Weight of the casting is not equal to the weight of the poured metal.

• Casting yield should be maximum for industry benefit.

• Green sand casting typically has a yield between 70% to 80%, while centrifugal casting can achieve close to 100% yield.

Impurity Removal and Fettling in Centrifugal Casting

This section discusses impurity removal and fettling in the centrifugal casting process.

Impurity Removal

• Impurities are subjected to lesser centrifugal force and collect at the center during rotation.

• Impurities can be removed by machining, brushing, or chipping.

Fettling Cost Reduction

• Fettling costs are reduced as there is no gating system to remove.

Conclusion

The centrifugal casting process offers advantages such as flexibility in composition, wide range of product characteristics, and high casting yield. However, it is suitable only for axial symmetrical components and hollow components. Impurities can be easily removed, and fettling costs are reduced.

Centrifugal Casting Process: Disadvantages and Applications

This section discusses the disadvantages and applications of the centrifugal casting process.

Disadvantages of Centrifugal Casting Process

• Inaccurate internal diameter due to impurities collected on the inner surface of the casting.

• High investment required for setup, making it a costly process.

• Skilled labor is needed to operate the setup effectively.

• Long lead time may occur.

Applications of Centrifugal Casting Process

• Manufacture of pipes, bushings, nozzles, bearings, and inner liners for IC engines.

• Production of bimetal steel bronze bearings.

Materials Used in Centrifugal Casting Process

This section provides an overview of the materials used in centrifugal casting.

Materials Cast

• Alloy steel, carbon steel, cast iron, stainless steel, aluminum, copper, nickel.

Size Range

• Part size varies from 0.25 meters to 3 meters in diameter and up to 15 meters in length with a weight up to 5 tons.

Components Produced by Centrifugal Casting Process

This section showcases various components produced using centrifugal casting.

Hollow Components

• Tubes and other hollow components are produced using centrifugal casting process.

Bimetallic Pipes

• Bimetallic pipes can be produced using centrifugal casting process with different combinations such as outer layer: 5% chromium steel and inner layer: stainless steel. Other combinations include outer layer: stainless steel and inner layer: mild steel, outer layer: mild steel and inner layer: copper, outer layer: copper and inner layer: gray cast iron, outer layer: stainless steel and inner layer: gray cast iron, outer layer: mild steel and inner layer: nickel hard steel.

Solidification Time Calculation in Centrifugal Casting

This section explains the calculation of solidification time in centrifugal casting.

• The time lapse between solidification of the first metal and pouring of the second metal is calculated using the formula d = k * sqrt(t), where d is the thickness solidified, k is the solidification constant, and t is the time.

Semi Centrifugal Casting Process

This section introduces the semi centrifugal casting process as a variation of true centrifugal casting.

Difference from True Centrifugal Casting

• In semi centrifugal casting process, the mold is filled completely with molten metal supplied through a central sprue. Unlike true centrifugal casting, hollow components are not obtained in this process.

Mold Filling

• The force generated by rotation ensures uniform distribution of molten material into the mold. A revolving table is used for rotation in this process.

Timestamps may vary slightly due to differences in video versions or edits made to the transcript.

New Section

This section discusses the advantages of the semi centrifugal casting process and showcases a component produced using this method.

Advantages of Semi Centrifugal Casting Process

• The semi centrifugal casting process allows for the production of components with intricate features, including narrow ribs that may not be possible with ordinary sand casting.

• The centrifugal force in this process ensures successful flow of molten metal even in areas with potential discontinuities.

• Multiple molds can be stacked together and fed by a common central sprue, enabling the production of more than one casting at a time.

• Similar to true centrifugal casting, the semi centrifugal casting process ensures purity and forms a poorer structure at the center of the casting, which can be machined off.

New Section

This section highlights some applications of the semi centrifugal casting process, such as wheels and pulleys.

Applications of Semi Centrifugal Casting Process

• Wheels and pulleys are commonly manufactured using the semi centrifugal casting process.

New Section

This section introduces the third classification of centrifugal casting: the centrifuging process. It explains how multiple castings can be manufactured within a single mold using this method.

Centrifuging Process

• In the centrifuging process, multiple molds are arranged around a central sprue to produce several castings simultaneously.

• The molds contain all necessary geometry for the cast parts as well as gating systems that allow for increased filling pressure within each mold.

• Centrifuging is often used in conjunction with investment casting when manufacturing castings with intricate shapes or tiny features that are difficult for molten metal to penetrate.

• Spin casting is a variation of centrifuging where molds made from silicon rubber are used, and it is commonly employed for casting materials such as zinc-base alloys, lead-base alloys, tin-base alloys, aluminum, and plastics.

New Section

This section compares the centrifuging process with the semi centrifugal casting process and explains the difference between them.

Centrifuging Process vs. Semi Centrifugal Casting Process

• In the centrifuging process, multiple components are manufactured within a single mold by connecting several mold cavities along the circumference.

• Each cavity is meant for one casting, and after solidification, the castings are cut apart to obtain individual components.

• The centrifuging setup involves a central sprue connected to multiple castings.

• Unlike in the semi centrifugal casting process where only one component is manufactured using one mold.

New Section

This section provides further details on the centrifuging process and its setup.

Centrifuging Process Setup

• The centrifuging process involves pouring molten metal into a central sprue while the mold rotates due to centrifugal force.

• Multiple castings connected to the central sprue are produced simultaneously.

• The setup includes a central sprue and several individual castings joined together along its circumference.

Centrifugal Casting Process and Economical Benefits

This section discusses the economical benefits of the centrifugal casting process on a large scale.

Economical Benefits of Centrifugal Casting

• The centrifuging process allows for multiple castings to be made with one sprue, resulting in high yield and cost-effectiveness.

• The use of a single central sprue reduces the amount of molten metal consumed for the gating system, leading to higher casting yield.

• Castings generated through centrifugal casting have excellent filling properties due to the application of centrifugal force on the molten metal.

• Cleaning and fettling costs can be reduced for centrifugal castings. Additionally, these castings have physical properties similar to forged products, resulting in low rejection rates.

• Centrifugal casting provides an easy way to achieve directional solidification.

Requirements and Defects in Centrifugal Casting

This section covers the requirements and common defects associated with centrifugal casting.

Requirements of a Centrifugal Casting Machine

• The machine must be able to accelerate, maintain smooth spinning, and decelerate the mold within a reasonable time frame. It should also provide provisions for heating and coating the mold before pouring molten metal to prevent sticking.

• There must be means for safely pouring molten metal into the rotating mold at a controlled rate, position, and orientation. Additionally, there should be provisions for adding inoculants or fluxes if required.

• A proper solidification and cooling rate must be established in the mold to obtain desired casting microstructure.

• The machine should allow for quick extraction of solidified castings from the mold at elevated temperatures without deformation.

Common Mould Materials and Defects

Common Mould Materials

• Metallic permanent molds are widely used due to their reusability, accurate casting geometry, and high productivity. Refractory lined metal molds, sand-lined metallic molds, and graphite molds are also used.

Defects in Centrifugal Casting Molds

• Segregation banding: Annular segregated zones of low melting constituents can occur in true centrifugal casting, especially with wide solidification ranges. Adjustments to rotational speed, pouring rate, and mold temperature can reduce or eliminate this defect.

• Raining: This phenomenon occurs in horizontal centrifugal casting when the mold rotates at too low a speed or if the metal is poured too fast, causing the molten metal to rain or fall from the top to the bottom of the mold. Proper process control can eliminate this defect.

• Vibration defects: Not mentioned in the transcript.

The transcript does not mention any further defects or information regarding vibration defects.

Summary

The centrifugal casting process offers economical benefits on a large scale by allowing multiple castings to be made with one sprue and generating high yield. It provides excellent filling properties and reduces cleaning and fettling costs while producing castings with physical properties similar to forged products. Additionally, it enables easy achievement of directional solidification.

To meet requirements for centrifugal casting, machines must be capable of accelerating, maintaining smooth spinning, decelerating molds within a reasonable time frame, heating and coating molds before pouring molten metal, safely pouring molten metal into rotating molds at controlled rates and positions, establishing proper solidification and cooling rates, and allowing for quick extraction of solidified castings without deformation.

Common mold materials include metallic permanent molds, refractory lined metal molds, sand-lined metallic molds, and graphite molds. Defects in centrifugal casting molds can include segregation banding and raining, which can be mitigated through adjustments to process variables.

Please note that the transcript does not mention any further defects or information regarding vibration defects.

Combustion Synthesis in Centrifugal Casting Process

This section discusses the use of combustion synthesis in the centrifugal casting process to fabricate intermetallic and ceramic layered components.

Combustion Synthesis Process

• The process involves a reactor, sample container, and igniter.

• The reactant mixture undergoes combustion inside the chamber.

• Intermetallic components with metal and ceramic layered components can be fabricated using this process.

Electrical Heating Variation

• An alternative to combustion is electrical heating.

• The process involves a green compact, mold part, alumina container, heating coil, thermocouple, inner steel container, outer steel container, electric source, graphite brush, and slip ring.

• By heating the green compact using electricity, bimetallic parts with metal and ceramic layers can be obtained.

Summary of Centrifugal Casting Processes

This section provides an overview of the three broad classifications of centrifugal casting processes: true centrifugal casting process, semi-centrifugal casting process, and centrifuging process.

True Centrifugal Casting Process

• Involves horizontal or vertical rotating molds.

• Molten metal enters the molds to produce hollow components or castings with holes inside.

Semi-Centrifugal Casting Process

• A variation of true centrifugal casting where molds always rotate about a vertical axis.

• Molten metal completely fills the mold without any hollow cavity.

Centrifuging Process

• Molds rotate about a vertical axis in both semi-centrifugal casting and centrifuging processes.

• In semi-centrifugal casting, only one cast component can be produced per mold.

• In centrifuging process multiple castings can be made using a single mold. Cast components may not have symmetrical geometry.

Conclusion

This lecture covered the principles and classifications of centrifugal casting processes, including the use of combustion synthesis and electrical heating. The true centrifugal casting process produces hollow components, while the semi-centrifugal casting process does not have a hollow cavity. The centrifuging process allows for multiple castings using a single mold.