AU427017B2 - Oxygen flushing pressure die casting method - Google Patents

Description

3.119-7171 This invention relates to oxygen flushing pressure die casting method and more particularly to an improved oxygen flushing pressure die casting methodto produce sound die casting product which does not have almost any troubles in the strength by causing the shrinkage pores to be gathered in the unimportant portions of the casting product, the portions of which being removable after casting or requi.r- ing no substantial strength during use of the product. The pressure die casting method is a very effective casting method for mass producing efficiently casting pro- ducts having beautiful casting surface and high dimensional accuracy. According to the conventional pressure die cast- ing methods, however, air entrapped in the molten metal during injection thereof into the die cavity is left as the blow holes in the casting product. Therefore, thus obtained casting product is of less mechanical strength and undesirable to be used for the machinery parts, struct- ural members or the likes which require high strength re- liability, In the oxygen flushing pressure die casting method, injection casting of molten metal is carried out by intro- ducing oxygen gas into the die casting apparatus to dis- place air present beforehand in the die cavity.akd injec- tion passageway of molten metal such as injection sleeve and runner. According to this method, oxygen gas entrapped in the molten metal which was injected into the die cavity immediately reacts with the molten metal to become fine ~Metal oxide particles in the casting product, therby metal casting product which is almost free from blow holes can -be obtained.

2 427017,

31.197/71. However, the casting product obtained the above oxygen

flushing pressure die casting method is provided with such

the defect that very large shrinkage pores are apt to be

formed in the product, as compared with the product obtain-

ed by the conventional die casting method. Therefore, the

above mentioned excellent effect derived from the oxygen

flushing pressure die casting method can not be displayed

by such the defect. The molten metal injected into the die

cavity according to the die casting method is shrunk when

solidifying it and tends to form the shrinkage pores in the

portion of the casting product where the splidification

retards. According to the conventional die casting method,

however, air entrapped in the injected molten metal is dis-

persed and retained in the form of numerous compressed air

bubbles throughout the molten metal filled in the die cav-

ity and these air bubbles expand to a some extent when

solidifying and shrinkage the molten metal, thereby the

formation of the shrinkage pores is prevented by the ex-

tent of expansion of the bubbles. According to the oxygen

flushing pressure die casting method, on the other hand,

due to very few amount of the air bubbles contained in the

molten metal it is assumed that the shrinkage pores caused

by the solidification and shrinkage of the-molten:metal are

gathered in the portion of the casting product where the

solidification retards.

The present invention is based on the above mentioned

principle that in the casting product obtained by the oxy-

gen flushing pressure die casting method the large shrink-

age pores appear concentrically in the portion of the

product where the solidification relatively retards and

3

31.197/71 directed to the above oxygen flushing pressure die cast-

ing method characterized by using a die assembly consist-

ing of a fixed die and a movable die, each of which pro-

vided with the heat-insulated zones in the die wall por-

tion which is to be in contact with an unimportant part of a casting product to be formed in the die cavity, said unimportant part being t-bo. removed by a mechanical means after completion of the casting or not required to maintain

the strength during use of the product. According to the present invention the molten metal injected into the die

cavity retards in its solidification at each portion which

contacts with each insulated zone as compared with the

solidification in other portions of the molten metal,

whereby most of the shrinkage pores are gathered in the

unimportant parts of the casting product, while preventing

the shrinkage pore from being formed in other important parts of the casting product which are required to main-

tain the strength.

The heat-insulated zones can be formed in the portion

of the die wall by providing the recessed parts in the die

wall and fitting in each of said recessed parts an insert

element made of ceramic material and having a shape cor-

responding to said recessed part or a metallic insert

element having such,a bobbin-like shape in the cross-

section as to provide the gaps between the die wall and

in the insert element after completion of the fitting.

The above heat-insulated zone may be modified by provid-

-ing heating wires embedded in and passing through the

heat-insulated zone and the die wall so as to more ef-

fectively carry out the method of the present invention.

4- 427017.

31,197 Therefore, an object of the present invention is to

provide an improved oxygen flushing pressure die casting

method for producing the casting products, wherein the

shrinkage pores are gathered in the unimportant parts, where no strength is required, of the casting product.

Another object of the present invention is to provide

the improved oxygen flushing pressure die casting method

for producing the sound casting products, wherein any

strength trouble caused by the shrinkage poies and blow

holes can be eliminated during use of the product.

Still another object of the present invention is to

provide the improved oxygen flushing pressure die casting

method for producing the casting products which can be

used as the machinery parts and structural members.

The present invention shall be explained with refer-

ence to the accompanying drawings in the followings.

In the drawings;

Figure 1 is a longitudinally sectional view showing the principal part of a die casting apparatus for carrying

out the die casting method according to the present inven-

tion to cast a side-cover of a housing for small electric

motor.

Figure 2 is a sectional view of the die-casting ap- paratus along the line A-A in Figure 1.

Figure 3 is a longitudinally sectional view of a product made according to the die casting apparatus shown

in Figure 1 and showing the state of the product which was

taken out immediately after completion of the casting.

Figure 4 is a longitudinally sectional view of the

same product as shown in Figure 3, but showing the state

427017

A

31,197/71 thereof after finishing was made.

Figure 5 is a sectional view showing a heat-insulated

zone formed in the die wall.

Figure 6 is a sectional view showing a modification

of the heat-insulated zone shown in Figure

Figure 7 is a sectional view showing a still another

embodiment of the heat-insulated zone shown in Figure

Referring to Figures 1 and 2, the die casting apparatus

comprises a die plate 1, a fixed die 11 attached to the die

plate 1 and a movable die 12 which is to be in close con-

tact with the fixed die 11 by operation of a die clamping

piston 3, so that when the fixed die 11 is bodily contacted

with the movable die 12, a split-die may be formed, in which a die cavity 4 of a desired shape and a runner 5 having a

narrow cross-section are provided. A molten metal inject- ing sleeve 6 extends passing through the die plate 1 and severs to eject a molten metal M poured therein into the die cavity 4 through a runner 5 by operation of a plunger 7 which reciprocates along the inside wall of the sleeve. The sleeve 6 is provided on its upper side with a molten metal inlet 8. An oxygen feeding nozzle 9 is to be insert- ed in the molten metal inlet 8. Formed in the portions of the die wall are heat- insulated zones 10 which correspond to the parts forming. bolt-holes 10' or rotor holes 10" of the product, as shown in Figure 4, the parts of which being removed after com- pletion of the casting. Figures 5, 6 and 7 show respectively an embodiment of the heat-insulated zone formed in the die wall. In Figure 5, the heat-insulated zone is formed with

6 L an inserting element 13 ma~'o ceramic material (such as fire brick, porcelain, castable refactory material, etc.) which is fitted into a recessed part 14 provided in advance in the die wall.

In Figure 6 showing a modification of the heat-insul-

ated zone, an inserting element 15 is made of metallic

material and of such a bobbin-like shape in the cross-section

as to provide gaps 16 between the die wall 14 and the

element 15 when the element 15 is fitted in the recessed

part of the die wall.

In Figure 7 showing a still another modification of the heat-insulated zone, an inserting element 17 is provided

with heating wires 18 embedded therein. The heating wires serve to heat the heat-insulated zones 10, thereby retard-

ing effectively solidification of the portions of molten

metal which are in contact with the heat-insulated zones

According to the method of the present invention, air

present in the sleeve 6, runner 5 and die cavity 4 is dis-

placed in advance with oxygen gas fed into the sleeve 6

through the nozzle 9, then the molten metal is poured into

the sleeve 6 from the molten metal inlet 8 and the plunger

7 isoperated to eject the molten metal within the, sleeve

into the die cavity 4 through the runner 5, wherein most

of oxygen gas entrapped in the molten metal at the time of

ejection thereof reacts immediately with the molten metal

to produce fine metal oxide particles dispersed in the

molten metal, thereby considerably reducing the number of

7

31,197171 the pores in the casting product.

Furthermore, in the method of the present invention

the portions of the molten metal which are in contact wit!

the insulated zones 10 solidifys at very slower velocity E

compared with solidification of the other portions of the

molten metal, therefore, as shown in Figure 3,-the shrink-

age pores are gathered in the portions of the molten meta

(the portion indicated by the dotted lines in Figure 3) which are in contact with the insulated zones 10, the mol

*metal portions of which being removed by a mechanical mesa after completion of the casting, so that the sound produc

having a fed blow holes and fed shrinkage pores can be ob- tained.

The foregoing description of the present invention ii

directed to the embodiment of the method for casting the

product having the portions to be removed after completioz

of the casting. However, the method of the present inven-

tion can also be applied to the casting of the product hai

no portion to be removed. That is, when casting the prodi

having the portion where no particular strength is requir(

during its use, the die provided on its wall with the heal

insulated zones can be employed in the same manner as in I

foregoing embodiment so that the shrinkage pores may be gathered in the portion of the product where no particula3

strength is required, thereby the product having a high reliability in the strength can be obtained.

As can be seen from the foregoings, the products mad,

according to the method of the present invention can be

used with a high reliability in the strength as the machii

ery parts or the structural members, hence the blow holes snd shrinkage pores are not provided in the portion of th

product where the strength is required.

8 442701

Claims (3)

31.197/71 The claims defining the invention are as follows:-

1. A die casting method for carrying out the injection-

casting of molten metal under the condition wherein air

present in a die cavity is displaced in advance with oxy-

gen gas, said method comprising the step of using a die

assembly consisting of a fixed die and a movable die, each

of which being provided with heat-insulated zones in a

portion of the die wall which is to be in contact with an

unimportant part of a cooling product to be Cormed in the

die cavity, said unimportant part being removed by a

mechanical means after casting or being not required to

maintain strength, whereby most of the shrinkage pores are

gathered in the portions of the casting product, whereto

said heat-insulated zones were contacted.

2. A die casting method according to claim 1 wherein

said shrinkage pores are gathered in the portions of the

casting product, said portions being removed by a mechanical

means after completion of the casting.

3. A die casting method according to claim 1 wherein

said shrinkage pores are gathered in the portions of the

casting product, said portions being not required a par-

ticularly high strength in use of the product.

4. A die casting method according to claim 1 wherein each of said heat-insulated zones is formed with an inserting element made of ceramic material fitted in a recessed part provided in advance in hBe die wall. A die casting method according to claim 1 wherein each of said heat-insulated zones is formed with an inserting element made of metallic material fitted in a recessed part

9 427017

31.197171 provided in the die wall, said inserting element being of

such a bobbin-like shape in the cross-section as to provide

the gaps between the die wall and the inserting element.

6. A die casting method according to claim 1 wherein each

3 1,19 7 PA of said heat-insulated zones is provided with a heating means embedded therein. 7. A die casting method substantially as described with reference to the drawings.

-DATED this 12th day of July, 1971.

NIPPON LIGHT MJETAL COMAPANY IMITED By their Patent Attorneys, ARTHUR S. CAVE CO.

31.19 771

I ll-u--i

FI G. 2

F I G.3 FIG.4

3 119 7/71

FIG.

FI G.6

FI G.7 -14