Centrifugal Casting

CENTRIFUGAL CASTING

1. INTRODUCTION

Centrifugal casting is the manufacturing process used to cast symmetrical objects having axis of revolution such as pipes, tubes gear blank etc. The centrifug centrifugal al casting casting process process uses uses rotati rotating ng molds molds to feed feed molten molten metal metal uniformly into the mold cavity. The centrifugal force of the rotating mold forces the molten against cavities of the mold under constant pressure until the molten metal has solidified. There are essentially two basic types of centrifugal casting machines the horizontal type, which rotates about horizontal axis and vertical type, which rotates about horizontal axis and vertical type, which rotates about a vertical axis. Differ Different ent types types of molds molds are used used in centri centrifug fugal al casting casting process. process. old old is designed according to various design considerations. Tubular casting produced in  permanent molds by centrifugal casting usually have higher yields and higher  mechanical properties.

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CENTRIFUGAL CASTING

2. CLASSIFICATION

Centrifugal casting process is classified as, True centrifugal casting: -

"t is used to produce cylindrical or tubular castings by spinning the mold about its own axis castings produced by this method will always have a true cylindrical bore of inside diameter regardless of shape or configuration. Castings produced in metal molds by this method have true directional cooling or solidification from the outside of the casting or solidification from the outside of the casting toward the axis of  rotati rotation. on. This This direct direction ional al solidi solidifica ficatio tion n results results in the produc productio tion n of high high #uality #uality edfect$free casting without shrinkage.

Semicentrifugal Semicentrifugal casting: -

"t is used to produce castings with configurations determined entirely by the shape of the mold on all sides inside and out, by spinning the casting and mold about is own own axis. axis. Cores Cores may may be nece necessa ssary ry if the the casti casting ng is to have have hall hallow ow secti section ons. s. Directional solidification is obtained by proper gating. Casting that are difficult to  produce statically can often produced by this method, because centrifugal force feeds the molten metal under pressure higher than static casting. casting. Thinner castings sections can be produced with this method than with static casting. Typical castings of this type include great blanks pulley sheaves, wheels, impellers and electric motor rotors.

Centrifuge Centrifugal Casting: -

"t has the widest field of application. "n this method the casting cavities are arranged arranged about the center axis of rotation rotation like the spokes spokes of a wheel, thus permitting permitting the production of multiple castings. Centrifugal force provides the necessary pressure on the molten metal in the same manner as in semicentrifugal casting. This casting method is typically used to produce valve bodies and bonnets, plugs, yokes, brackets and a wide variety of various industrial castings. College Of Engineering Pandharpur 

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CENTRIFUGAL CASTING

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CENTRIFUGAL CASTING

. !ORI"ONTAL C#NTRIFU$AL CASTIN$

%rinci&le: -

'orizontal centrifugal casting is used to cast pieces having an axis of  revolution. The techni#ue was the centrifugal force generated by a rotating cylindrical mold to throw the molten metal against the mold wall and from the desired shape. #'ui&ment: -

( horizontal centrifugal machine has following importing important parts. !)

old

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*oller track  

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+nd plate

)

-pinning pot

)

Cooling track  

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-pout

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'ousing

%r(cess Details: -

olten metal can be introduced into the mold at one end, at both ends, or  through channel of variable length. 1ouring rate widely according to the size of the casting being produced and the metal being used. 2or example, a pouring rate of !.! t %.% tons3min. has been used to cast/ alloy steel tubes of $$mm in outside diameter  with $mm thick walls. 1ouring rates that are too slow can result in gas porosity while high rates slow solidification are one of the main causes of longitudinal cracking.

Cast tem&eratures: -

The degree of superheat re#uired to produce a casting is a function of the metal or alloy being poured. The following empirical formula has been suggested as general guideline to determine the degree of super heat. 4 5 %.  T 6 !!$

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CENTRIFUGAL CASTING

7here the length of spiral fluidity 8in mm) and

 T

is the degree of superheat

8in degrees centigrade) old Temperatures 9 "nitial mold temperatures vary over a wide range according to the metal being cast, the mold thickness, and the wall thickness of tube being cast. "nitial mold temperature does not affect the structure of  the resultant casting as greatly as the process parameters discussed above do.

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CENTRIFUGAL CASTING

S&ee) (f r(tati(n: -

:enerally the mold is rotated at a speed that creates a centrifugal force ranging from 0 to !%$g speed of rotation is varied during the casting process. The cycle can be divided into three parts; < (t the time of pouring, the mold " rotating at a speed sufficient to throw the molten metal against the mold wall. (s the metal reaches the opposite end of the mold, the speed of rotation is increased. -peed of rotation is held constant for a time after pouring the time at constant aped varies with mold type, metal being cast, and re#uired wall thickness. The ideal speed of rotation causes rapid adhesion of the molten metal to the mold wall with minimal vibration. -uch conditions tend to result in a casting with a uniform structure. (s the molten metal enters the mold a pressure gradient is established across the tube thickness by centrifugal acceleration. Too low a speed of rotation can cause sliding and result in poor surface finish. Too high speed of rotation can generate vibrations, which can result in circumferential segregation.

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CENTRIFUGAL CASTING

*. +#RTICAL C#NTRIFU$AL CASTIN$

%rinci&le: -

"n vertical centrifugal casting uses the centrifugal force generated by a cylindrical mold about vertical axis throw the molten metal against the mold wall and form the desired shape. #'ui&ment: -

( vertical centrifugal casting machines have following important parts. !)

old

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(dapter table

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2unnel

)

-pinner machine

%r(cess )etails: Casting Insi)e Diameters: -

7hen making castings on a vertical centrifugal casting machine, the inside diameter 8bore) of the casting will be tapered in accordance with the following formula.

n 5%/

h r!% 9 r%%

7here n is speed of rotation, r! is the inside radius at the top of the casting, r% is the inside radius at the bottom of the casting and h is casting height.

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CENTRIFUGAL CASTING

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CENTRIFUGAL CASTING

S&ee) (f r(tati(n: -

To establish a temperature gradient of the molten metal from the outside diameter towards the centre of rotation. "t is usually necessary for the mold to be spinning when the metal is poured. "n some cases, in order to eliminate defects such as erosion and dirt in sand molds, it is desirable to pour at a slow speed of rotation. 'owever, true centrifugal castings having a wall section of !%.0mm or less must be  poured at spinning speed because the metal in this thin section.  >omographs are available for determining the proper speed of rotation for centrifugal casting. +#uation used to calculate spinning speed. : 5 $,$$$$!%Dn 7here g is the centrifugal force, D is the inside diameters of the casting, and n is the speed of ration.

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CENTRIFUGAL CASTING

,. %OURIN$ T#C!NIU#S

%(uring Tecni'ues In Centrifugal Casting

2or permanent molds, the metal is generally poured about $ $ C higher than the temperature used for the same casting if poured statically in a sand mold. This is  because of the more rapid chilling effect of permanent molds. The pouring rates re#uired for successful permanent mold centrifugal casting are #uite high compared to those for static casting in sand molds. "t is particularly important that the initial rate of pour at the beginning be very high to prevent cold laps and cold laps and cold shuts. 2or most types of centrifugal castings weighing less than  kg, a pour rate of about ? kg3s, is recommended. 2or castings weighing up to $ kg, an initial pour rate of g to %& kg3s is recommended. 7hen pouring into spinning mold, it is recommended. 2or castings weighing more than $kg, pour rate of  to ?$ kgs are recommended. 7hen pouring into spinning mold, it is important to introduce the molten metal into the mould in such a way as to prevent or minimize turbulence of the molten metal, which can cause splashing, spraying, of droplets and can result in undesirable defects. (lthough many vertical centrifugal castings can be poured directly into the mold from the ladle to produce a #uality centrifugal casting it is more often desirable to use a pouring funnel. 7ith a pouring funnel, the nozzle can be lined to the re#uired diameter so that, with a certain raises height of molten metal in the funnel, a controlled pour rate can be obtained for a particular casting weight. "n addition, with a  pouring funnel, the entry of molten metal into the mold can be made to impinge upon the body of the mold with initial metal floe in the direction of mold rotation. This type of pouring will provide superior casting #uality by minimizing or eliminating any upsetting turbulence in the flow of molten metal that might cause defects. #/tracti(n (f castings: -

Commercially available casting pulling tongs 82ig. 0) are recommended for  extracting vertical centrifugally cast castings. These pullers engage onto the inside diameter of the casting and are used to lift the casting from the mold. College Of Engineering Pandharpur 

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CENTRIFUGAL CASTING

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CENTRIFUGAL CASTING

0. SOLID#FICATION

"n centrifugal casting, heat is removed from the solidifying casting only through the water:-

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(T+*"(4-

A4 ! %. @4(CE (>D E-'+*

(>D 1*C+--+- "> 2:. &. '(F*( C'GD'(*"

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+4++>T- 2 7*E-'1 T+C'>4:H A4 !; anufacturing.

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