WO1992003238A1

WO1992003238A1 - Die casting from dies having coated expendable cores

Info

Publication number: WO1992003238A1
Application number: PCT/US1991/005725
Authority: WO
Inventors: Robert E. Downing
Original assignee: Doehler-Jarvis Limited Partnership
Priority date: 1990-08-13
Filing date: 1991-08-12
Publication date: 1992-03-05
Also published as: EP0495969A1; KR920702262A; JPH07112594B2; EP0495969A4; JPH05500478A

Abstract

A high pressure die casting with an undercut region having a smooth and lustrous surface of an average profilometer reading of less than about 4.0 microns and preferably less than 2.0 microns, produced by forming an expendable coated core of specific composition, placing it in the die in a die casting machine, injecting molten metal into the die to form the casting and separating the casting from the die and the core from the casting. The composition of the expendable coated core comprises a base sand core held together by a resin binder; a first, bottom, hard refractory coating comprising fused silica and a refractory binder; and a second, top, soft, or release coating containing a release material selected from the group consisting of anhydrous powdered aluminum, graphite, talc, titanium dioxide and zircon, and a resinous binder; each coating also containing at least two different surface-active agents.

Description

TITLE: DIE CASTING FROM DIES HAVING COATED EXPENDABLE CORES

RELATED PATENT AND PATENT APPLICATION

This application is to describe more specifically the properties of the original die cast products, namely the smooth and lustrous surface of the undercut regions of the die cast products. These properties have been claimed and are produced by the coated cores and processes disclosed in the following related patent applications and patents :

This application is a continuation of copending appli¬ cation Serial No. 07/374,649 filed June 30, 1989, which is a continuation of U.S. Patent No. 4,867,225 issued September 19, 1989, which in turn is a continuation of application Serial No. 07/173,558 filed March 23, 1988, now abandoned. All of these continuing applications contained claims to the die casting per se produced by the process and coated cores described in all these applications and patent.

This application is also an improvement in the castings produced with the die casting sand cores and core coatings disclosed in applicant's assignee's U.S. Patents to Enno H. Page

No. 4,766,943 issued August 30, 1988 and No. 4,413,666 issued

November 8, 1983, and to Dybala and Maczko No. 4,529,028 issued July lo, 1985.

^!TE BACKGROUND OF THE INVENTION

There are many patents on expendable cores that produce undercut regions in die castings . Generally, the surface of such undercut regions are relatively rough , the best previously known having a profilometer reading of greater than about 4.0 microns . The undercut surfaces are produced by the coatings on the expendable cores of which there are various compositions and which must withstand hot metals poured or injected into the dies until the metals are solidified . Even the above mentioned related patents have coated expend¬ able sand cores that have good shake-out properties , good wash-out resistance , good resistance to surface penetration , good shelf-life , and high core strength to withstand pressures in excess of 1000 psi .

Nevertheless , still higher pressures in die casting processes are often desired and therefore it is essential to increase the strength of the expendable cores used therein and the smoothnesses of the surfaces on the undercut regions of the castings formed with such cores . Applicant , after considerable experimenting and testing , has unexpectedly discovered new compositions and additives for the coatings of such expendable sand cores for die casting dies , which coated cores have improved physical properties over what has been known before ; namely to withstand greater pressures and hotter metal melts , and to produce smoother and more lustrous surfaces on the undercut portions in die castings .

SUBSTITUTE SHEET OBJECTS AND ADVANTAGES

Accordingly , it is an object of this invention to produce a smooth and lustrous surface on the undercut regions in a high pressure die casting , which surface has an average profilometer reading of less than about 4.0 microns and preferably less than about 2.0 microns .

Another object is to produce such a smooth undercut surface on a die casting with a specially coated expendable sand core such as disclosed in applicant's Patent No. 4 , 867 , 225 issued September 19 , 1989 .

SHEET SUMMARY OF THE INVENTION

The die casting products produced by this invention have undercut regions with smooth and lustrous surfaces of an average profilometer reading of less than about 4.0 microns and preferably less than about 2.0 microns . In order to produce such surfaces with an expendable sand core , two improved coatings have been made : a first , base , hard refractory coating and a second, top , soft release coating. This coated core is then placed into a die casting die . Next , molten metal is injected under high pressure into the die to produce a casting with an undercut region formed by the coated core . When the metal has solidified and the resulting casting, usually of aluminum and its related metals and alloys , is removed from the die casting die, the core is then easily removed from the casting forming a smooth undercut region therein .

The expendable core is preferably formed of silica sand placed in a mold so that each sand grain is in contact with an adjacent sand grain , and the sand grains are bound together by a resin oxidized in the mold .

This sand core is then dipped or sprayed with an aqueous suspension comprising the first , base , hard refractory coating for the core , which aqueous suspension contains finely ground fused silica as its primary and major refractory material, but which may also contain a minor amount of other refractory oxides . These refractory materials have particle sizes less than about 100 microns and an average particle size of less than about

50 microns so as to be easily suspended in an aqueous solution . This first coating aqueous suspension also includes less than about 15% by weight of a binder for these particles which is a refractory material and comprises colloidal silica . Particles of the refractory and binder are maintained in this aqueous suspension by the addition of less than 1.5% and usually less than about 1% by weight

SUBSTITUTE SHEET of the aqueous suspension of two different compounds or additives selected from the groups of additives consisting of 1 ) a suspension agent , 2) a dispersant , 3) a wetting agent , and 4) an anti-skinning agent . These four additives may act , respectively , also as a 5 thickening agent , a deflocculent, to reduce surface tension, and to reduce water evaporation . These agents not only improve the shelf life of the aqueous suspension , but also unexpectedly improve the quality of the coating, and as a result thereof, an improved surface on the undercut region in the final die cast product . In 10 this composition the amount of water in this first coating aqueous suspension is critical for the proper effect of the additives , that is the water content is at least 12% and not more than 30% by weight of the whole mixture suspension .

15 After the first , base , or refractory coating is dried on the sand core , the second , top , soft release coating is applied by either dipping or spraying, which second coating liquid suspension comprises primarily solid particles of a release material selected from a group consisting of powdered aluminum , graphite, talc , 0 titanium dioxide , and zircon , suspended in a non-aqueous solvent , such as for example isopropyl alcohol . The particle size of the release material solids are less than about 100 microns and preferably having an average particle size of less than about 40 microns . This solvent or liquid comprises at least 30% and up 5 to 90% by weight of this second coating liquid suspension. In order to insure a uniform suspension of the particles of release material in this organic solvent , there is added less than about 10% by veight of a resinous binder, preferably a thermoplastic resin , and less than about 15% of at least two different compounds - " or additives selected from the groups of additives consisting of:

1) a suspension agent of an aluminum silicate compound (similar to the suspension agent employed in the first coating aqueous suspension) , 2) a dispersant, and 3) an anti-settling agent .

5 When this second or release coating has dried, the coated core is then ready for placement into the die casting die for production of a casting with an undercut region formed by this coated core .

SUBSTITUTE SHEET BRIEF DESCRIPTION OF THE VIEWS

The above mentioned and other features , objects and advantages and a manner of attaining them are described more specifically below by reference to an embodiment of this invention shown in the accompanying figures , wherein :

FIG . 1 is a photograph of the undercut regions of three samples of aluminum die cast castings , Samples

No . 1 and 2 being of longitudinally sectioned portions of die cast automobile water pumps , Sample 1 at the top showing a rougher undercut surface produced by a coated core according to the prior art of the above mentioned Dybala et al patent; Sample 2 in the center (still having the mounting flanges and conducting duct uncut therefrom) showing a lustrous and smoother surface produced by a coated core according to the present invention previously mentioned in applicant's above copending applications ; and Sample 3 is cut from a die cast engine block showing the inside surface of water cooling cavity formed by an expendable core having coatings according to applicant's present invention ;

FIGS . 2 , 3 and 4 are micro photographs of the surfaces magnified 25 times of Samples 1 , 2 and 3 , respectively , in which is is readily seen that there are many rough particles on the surface of the prior art Sample 1 which do not appear as large or UP f roHfic on the surfaces of th<_ Spmples 2 and 3 in Figs. 3 and 4 produced according to the present invention.

SUBSTITUTE SHET DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

1. The Casting Per Se

In order to point out better and more specifically the improved smooth and lustrous surface on the undercut regions of castings produced by the process and with the coated core described in applicant's original U . S . Patent Application Serial No. 07/ 173 ,558 filed March 23 , 1988 , samples of a die cast water pump for an internal combustion engine for automobiles was found produced with a prior art coated core (Sample 1) and with applicant's coated core (Sample 2) . The Sample 1 had an under¬ cut region cast with a core according to that described in the above mentioned Dybala et al No. 4 ,529 , 028. Sample 2 in Fig. 1 of the drawings still has the mounting flanges and connecting end attached thereto which have been cut from Sample 1. Also there is disclosed a Sample 3 in. Fig. 1 which is cut from the water jacket undercut portion of a die cast aluminum engine block, the smooth and lustrous surface of which can readily be seen in the photograph in Fig . 1 .

Approximately the same areas on the surfaces of the undercut regions of the water pump Samples 1 and 2 were gauged by a profilometer using a stroke of .8 millimeters and making ten readings of each area , plus a same-sized area on Sample 3 , viz :

SUBSTITUTE SHEET Sam le 3

Average 5.0 1.7 1.5

SUBSTITUTE SHEET Thus it can readily be physically detected , as well as visually seen , that the prior art sample averages 5.0 microns with the lowest being 4.3 microns so that much rougher undercut surfaces existed in the prior art , with an undercut region made with a coated core according to the Dybala et al patent producing a smoother surface than any other known by applicant in the prior art. In comparison , Sample 2 produced by a core coated with applicant's invented composition averaged 1.7 microns for its profilometer reading, which is almost a third less than Sample 1. Furthermore, a more recent surface has been obtained on the inside of an engine block with a core coated according to applicant's invention had an average profilometer reading of 1.5 microns and even obtaining a smoothness as low as .9 microns in one spot .

Figs . 2 , 3 and 4 are micro structure photographs of 25x magnification of .the same portions of the surfaces of Samples 1 and 2 shown in Figs. 2 and 3 , respectively, and also of the surface of the engine block water jacket duct in Fig. 4. It can readily be seen from these photographs that the number and size of particles in the surface of Sample 1 shown in Fig. 2 are greater and more profuse than are the particles seen on the surface of Sample 2 in Fig. 3 and further less in Sample 3 in Fig. 4.

Accordingly , applicant's original claiming of improved surface smoothness and luster in the undercut regions of the dies produced according to applicant's original and now abandoned application , of which this is a continuation , are physically illustrated and detectable by the profilometer readings and micro structure photographs .

SUBSTITUTE SHEET II . The Expendable Core

A . Sand Base Core

The composition of the sand base core may be a white silica washed spherical grain sand having a low acid value and a neutral pH , that is between 6 and 8. These sand particles are blown into a mold and bound together by a binder which comprises between about .7 and 5% by weight of the sand. If this binder is a furan resin it may range between about .75 and 2.5% by weight of the sand , and preferably between about 1 and 2% , and more preferably between about 1.3 and 1.7% by weight of the sand. This furan resin is cured in situ in the mold with sulfur dioxide gas. The binder also may contain between about 2 and 20% by weight of the binder of silane , preferably between about 3.5 and

15% and more preferably between about 5 and 10% by weight of the furan resin . This furan resin also contains methyl ethyl ketone peroxide in an amount between about 40 and 70% by weight of the binder , and preferably between about 50 and 60% , and more preferably about 55% by weight of the binder . Thus , this base sand core is similar in composition to that disclosed in the above mentioned related patents and patent application assigned to applicant's assignee .

B . The First , Base Hard Refractory Coating

The composition of the aqueous suspension which forms the first , base hard refractory coating on the sand core comprises primarily fused silica ground so that all the particle sizes are less than 100 microns , with an average particle size of less than about 50 microns . This refractory comprises between about 40 and 85% and preferably between about 65 and 85% by weight of the aqueous coating, and of this refractory the fused silica ranges between about 40 and 80% by weight of the aqueous suspension. In the grinding of this fused silica there is obtained less than about 15% of colloidal silica and usually less than about 10% , that is of less than about 1 micron in size , which colloidal silica acts as a binder for the particles in the final coating and more colloidal silica may be added, if desired. However, a minor percentage of the solids in the final coating may comprise similar micron sized particles of other refractory oxides , such as alumina, zirconia and kaolin , which may range from 0% up to less than about 50% by weight of the aqueous suspension , and correspondingly a minor percentage of these other refractory particles in the coating. However , coatings without any other refractory oxides than fused silica therein have been found to be very satisfactory.

To this aqueous suspension of refractory and binder particles there are added less than about 1.5% by weight of aqueous suspension of at least two different compounds or additives from the following four groups of additives or agents , namely:

1) The first additive , namely a suspension agent , in this instance acts more as a thickener or thickening agent and comprises a clay derivative or aluminum silicate compound , such as for example "Bentone" which is an aminated bentonite , semectite, or hectorite . The percentages of this suspension agent ranges up to about 1% by weight of the aqueous suspension .

SUBSTITUTE SHEET 2 ) The dispersant which acts as a deflocculent or a dispersing agent is added in an amount less than about 1 .5% and preferably less than about .8% by weight of the aqueous suspension . This agent may comprise an alkali phosphate and/or poly acrylate , including a poly methacrylate , which promotes and maintains the separation of the individually extremely fine particles of solids of refractory in the suspension and prevents their flocculation .

3) The wetting surfactant agent improves the dispersing of the particles in the liquid by reducing the surface tension when dissolved in water , such as causing the water to penetrate more easily into or to be spread over the surface of the particles in the suspension . An effective wetting agent includes compounds having acid and hydroxyl radicals such as a tertiary acetylene diol . The percentage of the wetting agent is less than about 0.5% and preferably less than 0.1% by weight of the aqueous suspension .

) The anti-skinning agent prevents evaporation of water from the composition and may comprise a higher aliphatic alcohol of 8 or more carbon atoms . The percentage of anti- skinning agent is less than about 0.1% by weight of the aqueous suspension .

After the core has been coated with this aqueous suspension of the first coating and dried , this hard coating lias a thickness of between about 25 and 2000 microns , and preferably between about 100 and 750 microns ( .004 and .030 inches) and more preferably between about 150 and 500 microns (micrometers) ( .006 and .020 inches) .

S EET C . The Second , Top , Soft Release Coating

The core with its dried first coating is then coated with the liquid suspension of the second soft coating which comprises primarily solid particles of one or more release materials selected from the group consisting of anhydrous aluminum powder, graphite, talc, titanium dioxide, and zircon, which materials are suspended in an organic solvent , such as isopropyl alcohol. These solid particles of release materials have a particle size of less than about 100 microns and an average particle size of less than about 40 microns . The percentage of these release material particles in the suspension ranges between about 5% and 60% by weight of the whole suspension for the heavier particles like titanium dioxide and zircon, and only up to about 40% by weight of the lighter particles like anhydrous aluminum , graphite and talc .

In order to bind together the particles of the release material in the final coating, there is added to the second liquid suspension a resinous binder, such as a dark brittle high melting point alaphatic hydrocarbon insoluble thermoplastic resin or a phenolic resin , in an amount between about .2 and 10% and prefer¬ ably between about 1% and 5% by weight of the liquid suspension .

In addition to the release materials and binder in this outer or top coating, there are also added less than about 15% by weight of the liquid suspension of at least two different compounds or additives from the groups of additives consisting of 1) a suspension agent, 2) a dispersant, and 3) an anti- settling agent. The suspension agent may be similar to that employed in the first coating, namely a clay derivative composition or aluminum silicate compound, including clays , "Bentone" , bentonite , kaolin, and the like . The amount of the suspension agent is less than about 10% by weight of the liquid suspension . The dispersant may be a phosphate , polycarbonate or sulfonate and added in an amount up to about 4% by weight

SUBSTITUTE SHEET of the liquid suspension . The anti-settling agent may be a methoxy propylamine and may be added up to an amount of about 3% by weight of the liquid suspension .

In the second or release coating, the non-aqueous or organic liquid is generally a major portion of the suspension composition, namely ranging between about 30 and 90% by weight of the liquid suspension including the solids therein .

When the second and soft coating is dried on the first coating on the core, the thickness of this second coating is usually less than that of the first coating and ranges between about 15 and 2000 microns and preferably between about 25 and 750 microns ( .001 and .030 inches) and more preferably between about 50 and 200 microns ( .002 and .008 inches) .

Since this top coating is softer than the first coating, it can be compressed by the pressure of the hot metal flowing against it , and accordingly can be made thicker than the hard base coating, if desired.

D . Specific Examples

The following Table I is of six different compositions of the aqueous first , base , hard refractory coating that have been used on sand cores of the specific composition mentioned above , which coatings have produced successful cores and die castings with undercut portions :

SUBSTITUTE SHEET TABLE I FIRST COATING SUSPENSION COMPOSITION

Ingredients in Percentage by Weight Example 1 Example 2 Example 3 Example 4 Example 5 Example 5

Refractories 40-85%

50.67 73.00 69.30 60.17 60.57 65.34 15.11 14.76

25.5

10.9

5.63 8.09 7.70 9.01 9.03 9.16

1) Suspension Agent 0-1%

A ine-treated Bentonite ("Bentone") 0.20 0.20 0.50 0.20

2) Dispersant 0-1.5%

Alkali Polyacrylate 0.10 0.20 0.20 Alkali Phosphate 0.30 0.10

3) Anti-skinning Agent 0-.l%

More than 8 carbon atom alcohol 0.05 0.01

4) Wetting Agent 0-.5%

Tertiary Acetylene Diol 0.05

Water 12-30% 17.7 18.60 22.40 15.60 15.24 14.40

The second , top , soft release coatings were produced according to the five examples in the following Table II and were applied to the first coatings in the Examples 1 through 6 in Table I above , and successful results were obtained therefor both in the production of the coated cores and in the final castings with smooth undercut regions .

SUBSTITUTE SHEET TABLE II SECOND COATING SUSPENSION COMPOSITIO

Ingredients in Percentages by Weight Example 1 Example 2 Example 3 Example 4 Exam

Release Materials 5-60%

Anhydrous Powdered Aluminum 0-30% 12.7

Graphite 0-40% 28.5 28.5

Talc 0-4ff% 13.1 O Titanium Dioxide 0-40% Ϊ5. c_σ

GO Zircon 0-60% 9 .1

Binder .2-10%

Phenolic Resin 0-5% 1.5

CO Thermoplastic Resin 0-5% 1 .7 1 .

Additives .05-15%

1 ) Suspension Agent 1-10%

"Bentone" 4.3 2 .6 4 .3 2.7 4.

2) Dispersant .05-4%

Phosphate Ester/ Sulfonate 0.5 0.5 0. Polycarbonate . 1 .1

3 ) Anti-settling Agent 0-3%

Methoxy Propylamine 1.2 1 .2 1 .

Solvent 30-90% Isopropyl Alcohol 64.0 70.3 63.5 73.6 67.

While there is described above the principles of this invention in connection with specific apparatus and compositions , it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of this invention .

SUBSTITUTE SHEET

Claims

THE CLAIMS :

1 . A die casting having an undercut region , which region

' has a smooth and lustrous surface having an average profilometer reading of less than about 4.0 microns formed by an expendable coated sand core having: a) good shake-out properties ; b) good wash-out resistance; c) freedom from surface penetration; d) good shelf life ; and e) high core strength to withstand pressures in excess of 1000 psi; said core consisting essentially of :

A) a base of sand having grains that touch each other with the spaces between the grains being at least partially filled with a resin binder; B) a first refractory coating on said base; and

C) a second release coating on said refractory coating, whereby said expendable core is placed in a die casting die and said casting is formed by injecting molten metal into said die around said core , and after the metal has solidified and the core has disintegrated , the core and casting are removed from the die, and the disintegrated core is shaken out of the casting.

2. A die casting according to claim 1 wherein said average profilometer reading on the surface of said undercut regions is less than about 2.0 microns .

3 . A die casting having an undercut region , which region has a smooth and lustrous surface having an average profilometer reading of less than about 4 .0 microns formed by an expendable coated sand core having : a) good shake-out properties ; b) good wash-out resistance ; c) freedom from surface penetration ; d) good shelf life ; and e) high core strength to withstand pressures in excess of 1000 psi ; said core consisting essentially of :

A ) a base of sand having grains that touch each other with the spaces between the grains being at least partially filled with a resin binder ; B ) a first aqueous coating on said base consisting essentially of :

1 ) at least about 40% by weight of said first coating of a refractory comprising fused silica having a particle size of less than about 100 microns and an average particle size of less than about 50 microns ;

2 ) at least 1% and less than about 15% by weight of the first aqueous coating of a binder ; and 3) at least .1% and less than about 1.5% by weight of said first aqueous coating of at least two different additives selected from the groups of additives consisting of : suspension agents , dispersants , wetting agents , and anti-skinning agents ; and C) a second liquid release coating; whereby said expendable core is placed in a die casting die and said casting is formed by injecting molten metal into said die around said core , and after the metal has solidified and the core has disintegrated , the core and casting are removed from the die , and the disintegrated core is shaken out of the casting .

EET - 23 -

4. A die casting according to claim 3 wherein said average profilometer reading on the surface of said undercut region is less than about 2 .0 microns .

-

5 . A die casting having an undercut region , which region has a smooth and lustrous surface having an average profilometer reading of less than about 4.0 microns formed by an expendable coated sand core having: a) good shake-out properties ; b) good wash-out resistance ; c) freedom from surface penetration ; d) good shelf life ; and e) high core strength to withstand pressures in excess of 1000 psi ; said core consisting essentially of :

A) a base of sand having grains that touch each other with the spaces between the grains being at least partially filled with a resin binder ; B ) a first aqueous refractory coating on said base ; and C ) a second liquid release coating on said first refractory coating consisting essentially of : 1 ) solid release particles having a particle size less than 100 microns and an average particle size of less than about 40 microns selected from the group consisting of: anhydrous powdered aluminum , graphite , talc , titanium dioxide and zircon ; 2) between about .2 and 10% by weight of said second liquid coating of a resinous binder;

3 ) between about .05 and 15% by weight of said second liquid coating of at least two different additives selected from the groups of additives consisting of a suspension agent , an anti- settling agent and a dispersant ; and

4) at least about 30% by weight of an organic solvent ; whereby said expendable core is placed in a die casting die and said casting is formed by injecting molten metal into said die around said core , and after the metal has solidified and the core

UTE SHEET has disintegrated , the core and casting are removed from the die , and the disintegrated core is shaken out of the casting.

6. A die casting according to claim 5 wherein said average profilometer reading on the surface of said undercut region is less than about 2.0 microns .

7. A die casting having an undercut region , which region has a smooth and lustrous surface having an average profilometer reading of less than about 4.0 microns formed by an expendable coated sand core having: a) good shake-out properties; b) good wash-out resistance; c) freedom from surface penetration; d) good shelf life ; and e) high core strength to withstand pressures in excess of 1000 psi ; said core consisting essentially of:

A) a base of sand having grains that touch each other with the spaces between the grains being at least partially filled with a resin binder; B ) a first aqueous coating on said base consisting essentially of :

1) at least about 40% by weight of said first coating of a refractory material comprising fused silica having a particle size of less than about 100 microns and an average particle size of less than about 50 microns ;

2) at least 1% and less than about 15% by weight of the first aqueous coating of a binder; and

3) at least .1% and less than about 1.5% by weight of said first aqueous coating of at least two additives selected from the groups of additives consisting of: a suspension agent , a dispersant , a wetting agent , and C) a second liquid release coating on said first refractory coating consisting essentially of:

1) solid release particles having a particle size less than 100 microns and an average particle size less than about 40 microns selected from the group consisting of: anhydrous powdered aluminum , graphite , talc , titanium dioxide and zircon; 2) between about .2 and 10% by weight of said second liquid coating of a resinous binder;

3) between about .05 and 15% by weight of said release coating of at least two additives selected from the groups of additives consisting of a suspension agent , an anti- settling agent, and a dispersant , and

4) at least about 30% by weight of an organic solvent; whereby said expendable core is placed in a die casting die and sai casting is formed by injecting molten metal into said die around said core, and after the metal has solidified and the core has disintegrat the core and casting are removed from the die , and the disintegrate core is shaken out of the casting.

8. A die casting according to claim 7 wherein said average profilometer reading on the surface of said undercut region is less than about 2 .0 microns .