CA1060630A - Process for applying a coating to a centrifugal casting mold - Google Patents

Process for applying a coating to a centrifugal casting mold

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Publication number
CA1060630A
CA1060630A CA257,952A CA257952A CA1060630A CA 1060630 A CA1060630 A CA 1060630A CA 257952 A CA257952 A CA 257952A CA 1060630 A CA1060630 A CA 1060630A
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CA
Canada
Prior art keywords
mold
suspension
casting
internal surface
introducing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA257,952A
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French (fr)
Inventor
Gottfried Brugger
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Individual
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Individual
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Priority to CA257,952A priority Critical patent/CA1060630A/en
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Publication of CA1060630A publication Critical patent/CA1060630A/en
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Abstract

Abstract of the disclosure:

A process for applying a coating to a centrifugal casting mold for casting copper or alloys thereof in which prior to introducing the molten metal into the mold, an ??quous suspension of powdery material is introduced into the mold and applied on the internal surface thereof in form of a thin layer. wherein the constituent components of the suspension are zir??? oxide (ZrO2) and an inorganic binder material, preferably non-sintered alumina (Al2O3), so that a heat-conductive and gas-permeable layer is formed on the surface of the mold.

Description

3~

'~he present invention refers to a process for applying a coating to a centrifugal casting mold for casting copper or alloys thereof, wherein, prior to introducing the molten metal into ~he mold, a suspension of powdery material is being introduced in form of a thin layer.
~ ubular bodies produced by a centrifugal casting process and consisting of copper or alloys thereof, particularl~ of bronze, and being used as a raw material for the production of bushings, rings and other shaped ~odies suffer from the ~0 draw-back that the outer zone and the inner ysne are different in structure from the remaining zone of the castin~. ~he outer zone has gas inclusions over a considerable thickness to such an extent that this outer zone is unsuitable and must be removed on a lathe. ~he inner layer is porous and contains oxides and the thickness of the inner layer primaril~ depends on the cooling speed of the meit and the rapidit~, reæpectivel~, of transition from the liquid state into the solid ~tate. Up till now, in centrifugal oasting processe~ for copper and copper alloys, particularl~ bro~ze, the centrifugal casting mold additionally had to be relatively slowly fill~a and ~ome-time~ also ~on-uniforml~ filled for the purpose of avoiding so-callea pin-holes, but this has as a consequence inexact dimensions at the inner side of the casting and non-uniform temperature stress of the mold. A further consequence is increased material consumption and a rapid mold wear. Further-more, the structure and the techni¢al properties of the casting fre~uently are strongl~ different, what in most cases cannot be tolerated. Furthermore, the mold must be kept at a relatively high temperature for limiting gas evolution at the area of the ~0 inner wall of the mold. -It is an object of the invention to avoid the mentioned draw-backs. It is a further object of the invention to improve a process of ~he kind described above such that the casting opera-tion can be accelerated with low expenditure. It is another object of the in~ention to substantially improve the quality of the tubular bodies obtained. It is still another object of the invention that the mold used has an ex*ended lifetime.
In a process of the kind described above, these objects of the inve~tion are essentially achieved by using, for the purpose of providing a heat-conductive and a gas-permeable la~er, as powdery materials for the suspension the constitutin~
components zirconium oxide (ZrO2) and an inorganic binder material. ~he inorganic binder material preferably consists of non-sintered aluminium-oxide (Al203). ~his layer forms a protective layer which does, even under the heat influence of the molten metal, not produce gases in a substantial amount but which is capable of venting the gases in longitudinal direction of the mold wall, which are set ~ree on cooling down the melt, and which i8 ~ in view of its good heat conductivity, capable to rapidly cool the melt for attaining a fine structure of the casting~ It has been found that such rapid heat removal provides the advantage that during the castin~ operation a solid metal layer, restricting any gas evolution at the outer zone of the casting, is rapidly formed. On further cooling of the casting, any evolved gases are thus prevented from escaping through the metal in inward direction and from disturbing the formation of a uniform structure o~ the casting, so that the so-called pin-holes can be avoided in an efficient manner.
In view of the ~uality of the casting being substantially 3o improved when working accordin~ to the inventive process, par-3l~fciV~ticularly in view of achieving a substantially uniform structure of the casting, the oversize of the casting required for machining the cas-ting can be reduced to a minimum, for example to only 1 mm at the outer side of the casting. In view of the ~entioned rapid heat removal from the melt, the cooling time for centrifugal castings having a wall thickness below 30 mm is reduced to such an extent that, in contrast to processes known up till now, no substantial oxide formation can take place a-t the inner surface of the casting. ~his allows to restrict the oversize needed for machining purposes at the inner surface of the casting to 1 mm for castings having a wall thickness up to 15 mm and to 2 to 3 mm for castings having a wall thickness up to 30 mm. In view of the small oversizes required at the outer surface and at the inner surface it is now possible to produce in an economic manner and with a high dimensional accuracy raw centrifugal castings with a wall thickness of ~t least 9 mm. ~his outstanding dimensional accuracy of the raw centrifugal castings, which in the inventive process is + 0.2 mm at the outer surface and + 0.5 mm at the inner surface, results, based on work on lathes as well as on waste in the form of - turnin~s, in a much more simple and thus also much cheaper production of final proaucts.
Also the technical properties o~ the raw castings are sub-stantially improved over those of raw castings produced according to known processes. By using a suspension of zirconium oxide as a dressing for the mold, the temperature o~ the mold can be kept relatively low in view of the properties o~ the suspension.
Because there are no dif~iculties whatsoever to intensely cool the mold during and after the casting operation b~ mea~s of water, also the temperature of the inner surface of the mold can be _ 4 _ 3~

kept relatively lo~. Under consideration o~ the low heat insulating effect o~ the mold dressing formed of the zirconium oxide layex, this results in a particularly rapid solidification of the melt, and, as a conse~uence o~ these parametres, the technological properties o~ the raw castings, above all the tensile strength, the elongation on rupture and the Brinell hardness, are increased, noting that the improvement 9~ these properties amounts up to 20 % over the presently valid prescrip`
tions for centri~ugal castings (DIN ~705, DIN 1709).
A fu~ther substantial advantage of the procèss according to the invention resides in a substantial increase of the life-time of the centrifugal mold. ~his statement particularly applies if the suspension is applied to the preheated mold and if, according to the invention, the melt is, a~ter application f the suspension, introduced into the mold over its whole length simultaneously. ~his mode of operation does not onl~
allow to more rapidly fill the mold but also allows to uni~ormly ~ill the mod, so that the heat influence is essentially uniform over the whole length of the mold and, therewith, heat tensions and thus also premature ageing and damaging of the mola can be avoided.
It is known (DT 0~ 2 343 174) to use ~or containers for molten metal, refractory materials whose chemical constituents consist of SiO2, A1203, ZrO2 and sedium silicate, noting that the content in sodium ~ilicate i~ kept within the range of approximately 3 and approximately 10 percent by weight.
~hereby it is intended to obtain thix~tropic properties, noting that the refractory material is brought into a liquid state under the influance o~ vibrations in spite o~ the low water 3o co~tent o~ the refractory material. Irrespective of the diffi-3~
culties which are encountered if one tries to apply such a material in form of a layer to the wall of a container, a heat insulating layer shall be obtained because it is intended to keep hot the melt within the container. The low water ¢ontent and the relativel~ great particle ~ize of the material used make it impoQsible to produce a suspension within the spirit of the present invention, particularly when considering that the material used according to this known process immediately solidifies if it is not subjected to vibrations.
It is also known (FR PS ~ 027 534) to clad a re~ractory centrifugal casting mold used for casting iron or steel, with metal oxides, ~or example with A120~, which are mixed with non-metallic constituents. However, there are considerable dif~er-ences between centrifugal casting of cast iron or steel and centri~ugal casting of copper and allo~s thereof. ~xperience has shown that mold claddings known for casting cast iron and steel fail in processes for casting copper and copper al~oys, particularly bronze, which might be attributable to the require-ments mentioned above. ~hus, it is not possible to derive from the above-mentioned known claddings, irrespective of such claddings serving as transport containers or for centrifu~al casting molds for casting cast iron or steel, anything which might be suitable for centrifugal casting of copper and copper alloys.
Aocording to a pre~erred embodiment of the invention, the ; mold is, during introducing the suspension 9 rotated around its axis with a lower speed of revolution than during introducing the melt. ~he reason there~or being that the suspension can be most easi~ly distributed over the inner surface o~ the mold at a relatively low speed o~ revolution of the mold, whereas it is i3~
desirable to work in the m~dium range of speeds o~ revolution when charging the mold ~ tn the mol-ten metal. Vntil the moment of complete dis-tribution of ~the melt within the mold, a non-uniform distribution of centrifugal ~orces can be observed ~rrhich can be kep~ within a tolerable range at medium speeds of revolu-tion.
As alread~ mentioned, the heat conductivity of the 1ayer used in a process according to the inven~ion can be further increased by selecting the thickness of this layer correspondingly small, particularly within the range between approximately 0.1 and 0.3 mm, which is substantially smaller than in known pro-cesses. It is convenient to aim at a thicl~ess of the layer within quite narrow limits. For this reason it is no~ to re-commend to apply the layer to the mold by means o~ a brush, as is frequentl~ the case in known processes, but it is to recommend to rotate the mold during the introduction of the suspension as has been describea above.
The suspension used is preferrably an aequous suspension, and the preferred inorganic binder material used is extremely finely elutriated alumina (Al203)~
Example~.
~ his example illustrates the production of a raw casting in a centrifugal casting process having an outer diameter of 162 mm ~nd an inner diameter o~ 138 mm and a length of 660 mm and from which a friction bearing is to be produced which has an outer diameter of 160 mm and an inner diameter o~ 140 mm.
~he bronze used meets the standards according to DIN 1705, melt composition Gz-Rg 7. ~he steel mold, which is supported in horizontal position, is preheated to approximately 150G and 3~ covered at its inner surface~ while being slowly rotated with i3~
300 revolutions er minu-te, by means of an aequous suspension containing zirconium oxide and extremely ~inel~ elutriated alumina as a binder, until a la~er o~ a thick~ess of approxim-ately 0.2 mm is obtained. After closing the mold, the means for introducing the molten metal is being centrally applied.
1`he spout of the casting funnel is dimensioned in correspondence with the composition o~ the molten metal and has a diameter of 28 mm. A casting channel extending within the mold over t~o thirds of the length of the mold in an approximately horizontal position is connected to the casting funnel. With this means for introducing the molten metal, a kno~m weight of the molten metal heated to a temperature above 1150C iS9 with acceleration of the circumferential speed of the inner surface of the mold to 7 m/sec, introduced such that the casting funnel remains filled with molten metal up to a level of approximately 200 mm, whereby a constant flow of the molten metal and an even distri-bution of the molten metal within the mold by means of the casting channel can be reliably obtained. ~he cas~ing time lasts only about 4 seconds. ~ubsequently, the means for casting molten metal is being removed and the mold is being coo1ed with water, whereupon, after solidi~ication of the raw casting, the raw casting is being removed from the mold.
In view of the sm~ll oversize of only 1 mm of the raw casting at its outer side and as well at its inner side, the friction bearing can be finished in one sin~le turning operation.
~ he following table illustrates the improvement of the technical-properties as compared with the properties required according to DIN.

.. ...

i~ccordin~ According to to DIN 1705 the inventive ior Gz-~g 7 process tensile strength (kp/mm2) 30 32 elongation on rupture (~) 20 25 Brinell hardness (kp/mm2) ~5 95 ~ he invention is particularly applicable for ca~ting in molds, i.e. repeatedly useable molds and permanent molds, respectively, copper and such copper-containing alloys in which copper is a substantial constituen-t and maaor constituent, respectively.

_ 9 _

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for applying a coating to a centrifugal casting mold for casting copper or alloys thereof, said mold having an internal surface, comprising the step that prior to introducing the molten metal into the mold a suspension of powdery material is introduced into the mold and applied to said internal surface thereof in form of a thin layer, wherein the constituent compo-nents of said suspension are zirconium oxide (ZrO2) and an inorganic binder material, so that a heat-conductive and gas-gas-permeable layer is provided on said internal surface.
2. A process as claimed in claim 1, wherein said inorganic binder material used is non-sintered Al2O3.
3. A process as claimed in claim 1, wherein an aequous sus-pension of finely grained zirconium oxide (ZrO2) and extremely finely elutriated alumina (Al2O3) is applied in said internal surface of the mold.
4. A process as claimed in claim 1, wherein said suspension is applied to said internal surface of the mold in a uniform thickness.
5. A process as claimed in claim 1, wherein said suspension is applied to said internal surface of the mold with a thickness of 0.1 to 0.3 mm.
6. A process as claimed in claim 1, wherein, during intro-ducing the suspension, said mold is rotated around its axis with a lower speed of revolution than the speed of revolution maintained while introducing the melt into the mold.
7. A process as claimed in claim 1, wherein said suspension is introduced into the preheated mold.
8. A process as claimed in claim 7, wherein said mold is heated to about 150°C.
CA257,952A 1976-07-28 1976-07-28 Process for applying a coating to a centrifugal casting mold Expired CA1060630A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CA257,952A CA1060630A (en) 1976-07-28 1976-07-28 Process for applying a coating to a centrifugal casting mold

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA257,952A CA1060630A (en) 1976-07-28 1976-07-28 Process for applying a coating to a centrifugal casting mold

Publications (1)

Publication Number Publication Date
CA1060630A true CA1060630A (en) 1979-08-21

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
CA257,952A Expired CA1060630A (en) 1976-07-28 1976-07-28 Process for applying a coating to a centrifugal casting mold

Country Status (1)

Country Link
CA (1) CA1060630A (en)

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