CA1045335A - Method for the centrifugal casting of metallic blanks - Google Patents

Abstract

ABSTRACT
Introduced into a mould spinning about its longitudinal axis is a metal, the means of introducing being the trough of a pouring contrivance. Introduced into the mould directly during the process of pouring metal is a flux-forming composi-tion with metal refining properties whose melting point is by 100 to 600°C below that of the metal. The metal with flux are kept in the mould for a period required for the process of the solidification and cooling of the metal to take place.
By virtue of the present invention it is possible to produce bulky quality blanks in metal and reduce the reject to between 2-3 times of that commonly encountered with the known methods of centrifugal casting. The method disclosed enables the production of bulky castings from alloys contain-ing readily oxidizable elements, such as aluminium, c?omium, titanium.

Description

~ :

The present invention relates to casting blanks in iron, steel and non-ferrous metals, and more specifically to ~ methods for the centrifugal casting o~ metallic blanks.
-~ The method will enjoy wide-spread use in chemical, !: , .
agxicultural and transport engineering. It will also be applied ;; in the manufacture of pipes for water mains, bulky blanks of ', paper-mill rolls, cylinder liners of internal combustion engines ' and other parts where high structural and chemical homogeneity, good mechanical properties, resistance to corrosion and low friction are the essential requirements to be met by the metal.
~, The surface of said parts must be free from any imperfections originating from the interaction with slag or gas.
There is known a method for the centrifugal casting of ~ metallic b~anks which consists of introducing a pre-refined metal ;~ into a spinnins mould and keeping the metal cast in the mould ; for a period required for the process of solidification and cool-; ~ ing. Yet, blanks produced by the known method suffer all from `
an inherent defect which is the formation of what may be called ~-~ the "defective" zone in castings. It is a concentration of non- ' ` 20 metallic inclusions, harmful admixtures and gases beginning at r ` the inner surface of blank and extending outwards within a dis-;i~ tance which is sometimes 1/3 of the blank wall thickness. The `~
'' defective zone is commonly removed during , '~! r ,,.,.' , . ,1 .`, .
~ l .. ..

.: i ,~i. .

,~ j ... ..
... ;1 .. i, . .
,....................................................................... ... .

''.'', ''.: .
~ ,.. -, ,~ , ..

,i;. i ~ ~

~ ` ~

~ 533~ ~
, the process of machining blanks which is thus a labour and ,; power-consuming one. If the thickness of defective zone exceeds .
~; the stock allowed for the machining, the blank is beyond repair. ,, '~ The defective zone is formed due to the action of the '~ centrifugal forces coming into play during the process of casting , ,~ and causing the non-metallic inclusions, harmful admixtures and `',, gases always present in the metal to move towards the inner sur- ;
i'~ face of blank. During the cooling down of the blank obtained the i'~. ;,:
, front of crystallization develops at the inner and outer surfaces ,- 10 and the solidified inner surface prevents said inclusions, mix-~- tures and gases from escaping from the blank.
~, It is known nowadays that the quality of blanks can be , , substantially improved if the process of casting is carried out ,;,'~ in the presence of a liquid flux or any other refractory mater-~ ial. To that end poured into a spinning mould is a pre-refined ,;~' metal and then is introduced a liquid flux or refractive mater-,' ial at a temperature by far exceeding the temperature of the , ~ .
i;, metal cast.
,', Serving as a kind of heat insulation applied to,the ',, 20 inner surface of blank, the liquid flux or refractory material ~
,', slows down the rate at which the front o-f crystallization propa- ,, , . i I , .
~'', gates at the inner surface, reducing thereby the thickness of the ';;
,, t.~
~, '.. ~ .
,i .
,'1 .,: 1 , -~., , ,.
. -, ,:

.. , :
,;, ~.

, . ,:
.,j .
.,, ~ ` ~

:`
33~

~ defective zone. But the known methods of centrifugal casting ,~, --` are based on sophisticated technique, call for the use of addi- , .~,.
~i~ tional equipment such as special furnaces and casting ladles : ., required to obtain and handle the liquid flu~. If bulk refrac-:~.. .
, tory material is used, this needs preliminary heating to a high ~. ~
.,: temperature, entailing high power requirements.
The main disadvantage of the known methods for the cen-trifugal casting of metallic blanks under a flux is that said . .
method fails to provide for a reliable protection of the metal poured from secondary oxidation which impairs the quality of blanks and their mechanical properties. Furthermore in spite of the fact that the metal is pre-refined the degree of the ~, refining preparatory to casting is, as practical experience goes ~ -to show, not adequately high with the result that poured into .; .
; 1 the mould is a metal containing unwanted admixtures in consider~
,: ~
" able amounts.
.... . .. .
It is an object of the present invention to eliminate said disadvantages.
; Another object of the present invention is to provide .i j .
, 20 a method for the centrifugal casting of metallic blanks which will improve the macro- and micro-structure of the blank and expand , .. . .
its mechanical properties. '`' ~'l A further object of the present invention is to pro- `
vids a method for the centrifugal casting which will simplify the ;, ~
. ,' :.
;
I'' . .
. . '~ .

..
',''' ', `': `
:,, , ., " ' ' .
, ., .:
'0'~ .
. .

,. ~ ::

..a~ S335 technique of producing metallic blanks.
, According to the invention there is provided a ,' method for the centrifugal casting of metallic blanks under , a flux comprising pouring a molten metal into a spinning mould by means of a trough of a pouring device, introducing ~-~ a flux-forming composition with metal-refining properties into the molten metal during the pouring, maintaining the metal with flux in said mould for a period sufficient for solidification and cooling.
~;: 10 By virtue of the method disclosed it is feasible ~-,i to produce high-quality metallic blanks and reduce the reject to between 2-3 tlmes that encountered with the known methods. The method disclosed also paves the way to produc-ing bulky blanks in castable alloys containing readily , oxidable elements such as aluminium, chromium and titanium. ;
,~ In an embodiment of the present invention, the flux-forming composition is an exothermic flux-forming composition with metal-refining properties. The use of an exothermic flux-forming composition during the centri-' 20 fugal casting by the method disclosed not only improves the~ I .
quality of blanks but reduces the number of operations in the mouldlng cycle, rendering redundant the pre-,, . j , .
~ ' ,.
" . ~ - .

,,,i,~,, ', ",j ~,,. :~
.:
,~ ,i .;. . ' .:;I .
.,: .

c: , , .~ .:
B
.j, . .
.....
,............................................................ . ....

n~ 1 09~335i melting of the flux-forming composition employed, ~;, ~ It is expedient to introduce the flux-forming co~posi-: tion into the mould directly during the process of pouring metal i:
in an amount between 0.5 and 5 wt. %. The use of the flux-form-ing composition in said amount assures deep refining of the metal '~ in the mould and protects the metal from oxidation.
It is also expedient to introduce the flux-forming com-position into the pouring contrivance directly during the pro ~; cess of pouring metal. In an embodiment of the invention, the flux-forming composition is introduced into the trough of the ~ pouring contrivance. ' " According to the present invention, the flux-forming '~ composition can be introduced into the metal contained in the ~,~ mould during the process of its pouring. Said technique of in-troducing the flux-forming composition into the mould provides for the refining of the metal in the most efficient way so as to ,i obtain quality metallic blanks irrespective of the layout of the , ~ i .,.
' pouring contrivance.
~; Further objects and advantages of the present invention ~" 20 will be best understood from the following description of a method '' for the centrifugal casting of metallic blanks.
The ingredients of flux-forming composition, pre-dried ,, at a temperature between 120 and 150C to remove all traces of ,, moisture, are reduced to dust, passed through a sieve with a mesh , size of 0.5 mm, intermixed in the requisite proportion and placed ~' in a metering hopper of an outfit for the centrifugal casting ,, `j~ of metallic blanks.
`~ According to the present invention, use can be made of ~ either low-melting flux-forming compositions containing cryolite, ''l 30 fluorspar, table salt and having a melting point which is by lO0 , to 650C lower than that of the metal cast or exothermic flux-forming compositions.
, 1 '.

, ~:

Si335 . .
~, It is advisable to give preference to said low-melting ~~
compositions in all those cases when bulky blanks weighing between ; 1 and 40 tons are being cast centrifugally in stainless steels and non-ferrous alloys because there will be practically no drop .
in the temperature due to the melting of the composition at the `~, metal interfa~e.
I, ! , The recourse of an exothermic flux-forming composition . with metal-reflnillg properties iS preferred in producing metallic ;~- blanks of a weight which, as a rule, is inside the limits of 5 to -~

-' 10 20 kg.
;, , ~ The process of exothermic combustion and melting of said ~-:., .
~ composition takes place due to the reactions between the ingredients .. ...
~ of the composition which, in accordance with the invention, com-. : .
~ prises combustible ingredients (aluminium, calcium, silicon, mag- ~
t ;~;
nesium), oxidizing agents (sodium nitrate, manganese ore, cinder) and flux-forming ingredients (fluorspar, sodium silicate, blast-~ :i furnace or cupola slag). The interaction of the combustible com-, ponents with the oxidizing agent yields compounds which make the refining of the metal possible.
, . ~ .
~: 20 The refining of the metal is also accomplished due to , ;; the processes of physical and chemical nature taking place due to the intermixing of the alloy with fluxes with the result that the flux absorbs the non-metallic inclusions (oxides of compounds ! ~ .
whose composition varies with the grade of alloy) and harmful ad-:.
mixtures (sulphur and phosphorus).

ii Another possible way of refining is due to the inter-`;! . -, actlon of non-metallic inclusions with flux ingredients. This is '~ exemplified by the refining of aluminium bronze with the aid of a cryolite-based flux containing also fluorspar and table salt.

~`` 30 The aluminium oxide present in the bronze is decomposed due to the reaction:-. ., ~ - 6 -,.. :; .
~."

.:

335i

2 3 ~

which is accompanied by the liheration of heat and gases in con-siderable amounts and the products of decomposition being dis-j posed of into the flux.
`i According to the invention it is proposed to introduce ~ one of the above-said flux-forming compositions with metal-refin-.: ~
; ing properties from said metering hopper into a mould during the ` process of pouring the metal while the mould is being rotated about its longitudinal axis.
As it has been discovered, the amount of the composition `
;~ used varies over the range between 0.5 and 5 wt. %. The actual amount to be taken depends on the chemical composition of the ., ~ .
metal cast, the presence of non-metallic inclusions, harmful ad-,~~ mixtures and gases as well as on the overall dimensions o the part to be cast. Thus, if the casting is in a copper-based non-ferrous alloy or cast iron with a weight between S and 1000 kg, the amount of the flux-forming composition is between 0.5 and 2 ' wt. %. Carbon-steel castings require 2 or 3 wt /O of the flux-forming composition and in the case of stainless steel blanks this amount is between 3 and 5 % by weight of the metal. l'he introduction of the flux-forming composition in an amount ex-ceeding the upper recommended limit may lead to an ill-effect i'~ which consists in the presence of traces of the composition in ' the casting.
It has been found that the introduction of the flux-forming composition exactly during the process of pouring the `1 metal into the mould is the factor which assures the production ~`~
; :., of metallic blanks displayihg good mechanlcal properties. The ;~

~`~ explanation is that the techni~ue disclosed practically elimin- -~

ates the secondary oxidation of metal and the presence of non-` metallic incluslons, harmful admixtures and gases in the metal :., ~
'`,, , ~'. :

:

;.~; which influence to a considerable extent the mechanical properties ~ of the product made therefrom.
: ~he efficiency of the refining of metal by means of a . . . .
'~ flux substantially varies with the area of the contact between the metal and flux, other things being equal. I-f the flux form-ing composition is being introduced during the operation of pour-.'~ `; .:
;~ ing metal, the intensity of the interaction between the ingredients~
;~, of the composition and the metal is at its maximum because said ingredients are emulsified by the metal. If the flux is intro-"~ 10 duced before or after the pouring of metal, the area of the inter-action between the metal and flux is only a fraction of that ob-tained in the course of introducing the flux during the opera-tion of pouring the metal.
The use of a low-melting mixture whose melting point is . .
below that of the metal or of an exothermic mixture has shortened and simplified the cycle of casting metallic blanks due to the , ` elimination of some operations connec-ted with the pre-heating of the flux.
; When introduced into a mould spinning about its longi-; 20 tudinal axis, liquid flux intermixes with the meta~, assuring its efficient refining and the removal of non-metallic inclusions, harmful admixtures and gases. After that the flux is carried .... . .. .
~ due to the action of centrifugal forces towards the inner surface 1~,; . .
of the blank where it provides a reliable protection against the ~1 secondary oxidation of metal and serves as a heat insulation with ;~ the result that the non-metallic inclusions, harmful admixtures ' ~ and gases which have been left over in the metal after the refin-. , , ing are removed from same at an acceptable degree of completeness.
In accordance with the invention, the exothermic or ;~ 30 low-melting flux~forming composition with metal-refining proper-`` ties is introduced either into the pouring contrivance directly, for example, into the trough of said contrivance during the ; - 8 -. ... .
' ' :. ... , . . ... - ... . - ~ . . . ..

~` .

33~ -operation of pouring the metal into a mould, or the mixture is introduced onto the metal in the mould during the operation of pouring. This depends on the design of the pouring contrivance .. ..
~"~r available.
...... .
; ~he mixture is introduced into the pouring contrivance when use is made of centrifugal casting machines with short troughs ,..... ... , . :
; commonly employed in the manufacture of pipes. On machines with a long trough such as those used in the piece production of bulky casting, the mixture is introduced onto the trough. The intro-. ..... ... ... ~ .
duction of the mixture directly onto the metal in the mould is practiced on cantilever-type machines used in the mass-production ~- of small castings.
Above,said ways of introducing the mixture provide ; for the versatility o the technique disclosed which is thus adaptable to centrifugal casting machines of various kind.
i~ ' ' ' ~ 1 ,' ~ ' ,........................................................................ ..
In the manufacture of bulky blanks in aluminium bronze, such as those for rolls of extra-wide paper mills, use was made ,~ of a low~melting composition comprising cryolite, fluorspar and ;
table salt. Preparatory to the use, the ingredients were dried at 120 to 150C so as to remove all moisture, reduced to dust, .,", ~ .
` intermixed in the requisite proportion and loaded into the meter- -~.:: ; -~ ing hopper of a centrifugal casting machine. The composition com-",' prised 75 wt. % of cryolite, 5 wt. % of fluorspar and 20 wt. % of .: :, .:, .
'il table salt.

, While pouring the metal into a mould at ambient tem-,, . . j .
perature, sald flux was introduced onto the trough of the pour- -, ing contrivance or directly into the pouring contrivance of the ~ centrifugal casting machine in metered amounts varying between ,; 30 0.5 and 2% by weight of the metal. On contacting the stream of metal, the composition had melted due to the heat liberated by ~' the metal and had formed a liquid flux which entered the mould '-' _ g _ .
.; , ~.

:;
33~
! with the metal, mixed with same and refined the metal, removing !, non-metallic inclusions, harmful admixtures and gases from i-t.
During the process of shaping the casting, the liquid flux was carried by the centrifugal forces to the inner surface of cast-ing, protecting the liquid metal from oxidation, During the process of cooling of the blan~, the liquid flux concentrating at it,s inner surface had cracked and dropped down the bore of blanX.
~;,; Owing to the use of flux in the centrifugal casting of bulky ~
: blanks in aluminium bronze, the reject of castings due to mould ~-; 10 splashes, wrinkles and checks had been eliminated.

Example 2 During the centrifugal casting of cylinder liners for internal combustion engines used on tractors, use was made of an exothermic flux-forming composition comprising the follow-~ ing combustible ingredients, oxidizing agents and flux-forming ;i components:
.;, .
aluminium powder, 12 wt. %

: ! calcium silicon (ground), 8 wt. %, . ,." ~
~ sodium nitrate, 14 wt. %, , fluorspar, 26 wt. %, ', sodium silicate (ground), 20 wt. %, ;;~

cinder, 20 wt. %.

Preparatory to the use, the ingredients of the exo-.,.;~ .
thermic composition were dried at 120 to 150C so as to remove ~" all moisture, reduced to dust, intermixed in the requisite pro portion and loaded into the metering hopper of a centrifugal casting machine.
: ,.
!''J.' While pouring the metal into a mould, the composi-tion was introduced onto the trough of a pouring contrivance in metered amounts of I to 2 % by weight o~ the casting. Upon con-~ -- 10 --~ .
. ,.

; . . :: . ; . ; . . .

:~; i .. ,., .. :
` tacting the metal, the composition had ignited, melted and over- ~
heated due to the heat of the exothermic reactions between the ~ ;
combustible ingredients and oxidizing agents. The liquid flux ~ so obtained had entered the mould, intermixing there with the r' ' : metal and refining same from non-metallic inclusions, harmful ,~ admixtures and gases. During the process of shaping the casting, -~; the centrifugal forces compelled the liquid flux to move to the ; inner surface of casting so as to serve as a heat insulation and provide for directional solidification. The flux was removed from the casting during the process of machining. The use of flux ~ during the centrifugal casting of cylinder liners for internal :~ combustion engines had reduced -the rèjec~ of castings from 10 -~ 12% to 3-5%. -,. . .
. :-:,~ :. , .:
.: ~ . .
,,,~ ,~ , .
.

''.' ::

.~,'' ' , ~,.: ~ .
.;,~, ~
~., ~ . .
'`'`'': ,, .
1., '' ' .
; `` ' :, .. :

.: i ;, ~ ,i.:, ; ` ':
': ,.
~: .' '' .: ' "
i',` - 11 - .. "
,; ~ , , ~, .

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A method for the centrifugal casting of metallic blanks under a flux comprising pouring a molten metal into a spinning mould by means of a trough of a pouring device, introducing a flux-forming composition with metal-refining properties into the molten metal during the pouring, maintaining the metal with flux in said mould for a period sufficient for solidification and cooling.

2. A method for the centrifugal casting of metallic blanks according to claim 1, wherein said flux-forming com-position has a melting point lower than that of the metal by 100 to 650°C.

3. A method for the centrifugal casting of metallic blanks according to claim 1, wherein said flux-forming com-position is an exothermic flux-forming composition.

4. A method for the centrifugal casting of metallic blanks according to claim 1, wherein said flux-forming com-position is introduced directly in an amount between 0.5 wt%
and 5 wt%.

5. A method for the centrifugal casting of metallic blanks according to claim 1, 2 or 4, wherein the flux-forming composition is introduced directly into the pouring device during the pouring.

6. A method for the centrifugal casting of metallic blanks as claimed in claim 1, 2 or 4, wherein the flux-forming composition is introduced directly into the trough of the pouring device during the pouring.

7. A method for the centrifugal casting of metallic blanks as claimed in claim 1, 2 or 4, wherein the flux-forming composition is introduced directly into the metal in the mould during the pouring.