KR930002837B1 - Process for the lost-foam casting under pressure of metal articles - Google Patents

Abstract

The invention relates to a lost foam pressure casting process for metal pieces. This process consists, after having filled the mould with metal in the liquid state and before the solidified fraction of metal exceeds 40% by weight, in applying an isostatic gaseous pressure over the entire mould/metal, of which the value is between 1.5 and 10 mPa. The invention applies to the production of pieces, particularly made from aluminium alloys, having improved mechanical characteristics and, in particular, better resistance to fatigue. <IMAGE>

Description

Pressurized Lost-Form Casting of Metal Products

1 is a micrograph of an A-S7G03 alloy casting according to the present invention under a pressure of 7 MPa after heat treatment.

FIELD OF THE INVENTION The present invention relates to a pressurized roast-foam casting process for metal products, in particular aluminum and aluminum alloy products.

US Pat. No. 3,157,924 is known to those of ordinary skill in the art that polystyrene foam molds enclosed in molds formed from dry yarns that do not contain a binder can be used for casting. .

In this method, the metal that is to be pre-dissolved first flows through a channel through the dry sand, contacts with the polystyrene foam, and burns the mold to deform into steam which escapes between the particles of sand. The metal to be made is filled in place of the mold and gradually replaced.

This method densifies and coagulates the powder refractory materials, thereby avoiding the inconvenience of preforming rigid molds connected in a fairly complex structure through the channels to the cores, simplifying the recovery of castings, and facilitating the casting material. As it can be recycled, it attracts attention as a method that can be used on an industrial scale.

However, this method is flawed by two factors:

The relative gentleness of the coagulation, which promotes the formation of pin-holes caused by the gas,

-Relative fragility of thermal gradients that can cause microshrinkage if the contours of each part complicate the supply.

For the purpose of resolving these deficiencies, the applicants have developed a lost-foam casting method which forms the subject of French Patent Application Publication No. 2,606,688.

The application states that after filling the mold with molten metal, i.e., when the mold becomes completely obsolete by the molten metal and the vapor released by the foam escapes, the equilibrium gas pressure is preferably before the molten metal begins to solidify. The manner in which the combination of is described is described.

At this time, the gas pressure is applied to a value that is increased for the entire time to avoid metal penetration, and the maximum value is obtained in 15 seconds or less.

Under these circumstances, the resulting casting increases in density, resulting in improvements in mechanical properties, in particular in strength.

However, the present applicants preferred that the maximum pressure in the present application be 0.5 to 1.5 MPa, and it is unnecessary to exceed 1.5 MPa.

Indeed, further studies have shown that as pressure rises further, fatigue resistance (F) is improved as well as mechanical properties such as breaking strength (Rm), yield stress (LE) and elongation (A). Got to know.

The present invention therefore relates to a method for pressurizing roast-foam casting of metallic materials, in particular aluminum and aluminum alloys, in which the organic foam form of the product to be cast is contained in walls formed by a dry sand bath containing no adhesive of the mold. The mold is filled with molten metal that is crushed, replaced with foam and gradually solidified, and the rising equilibrium gas pressure is simultaneously applied before the molten metal is filled into the mold and molten metal, with a gas pressure of 1.5-10 MPa. Will be.

Therefore, the present invention is designed to use a gas pressure of 1.5-10 MPa, preferably 5-10 MPa.

As described in French Patent No. 2,606,688, the pressure can be exerted by a sealed box in which the mold is placed, suitably distributed over the mold walls and installed with a plurality of nozzles connected to the gas source under pressure. have.

In the selected pressure range, the present applications have found that the phenomena that occur during the application of pressure differ significantly from the prior art.

In fact, under pressures of 0.5-1.5 MPa, this pressure stops the effect mainly when the solid network reaches a certain stage of progression, and serves to accelerate the flow of molten metal between the dendrite crystals of the solidified metal.

In particular, this is how at low pressures an agitator can effectively prevent shrinkage due to shrinkage of the metal to be solidified.

On the other hand, the flow effect of the molten metal predominantly at the beginning of solidification is gradually replaced by the heat deformation effect of the existing solidified metal network under pressure of 1.5 MPa or more, especially 5 MPa or more, and this phenomenon becomes remarkable, and the solidification rate is alloyed. It is excluded if the value of 50-70% is reached, depending on the type of casting.

Thus, the application of high pressure will give shape after an equilibrium heat treatment affecting the entire surface of the casting.

The attached Figure 1 is a micrograph of the A-S7G03 alloy casting according to the present invention with the effect of filling pores under 7 MPa pressure, showing the plastic deformation state using a dendritic network, the metal being applied by the method Loss is good for the forging effect.

Under these circumstances, the products find that the mechanical properties are remarkably improved, in particular the fatigue resistance is improved.

Only pressure values of 10 MPa or more do not result in much improvement.

This new pressure range is preferably applied before the amount of solidified metal reaches 40% to act as a liquid flow.

It is also desirable to obtain the maximum pressure applied before the amount of solidified metal to exceed 90% to be useful by the deformation effect.

As described in French Patent No. 2,606,688, metals in particular coagulate in order to prevent "metal penetration", a phenomenon resulting from the instantaneous imbalance between the pressure applied directly to the metal and the pressure applied to the metal by the dry sand. It is desirable to allow the pressure to gradually increase and be applied at the beginning of the process.

Indeed, the dry sand bath causes relatively large filling losses in the transition of pressure to push the metal through the sand particles at this pressure in the metal part that comes into contact with the sand and to deform the casting.

The present invention will be described in the following specific embodiments: The conventional method and the present invention provide a hollow-cylindrical cylinder consisting of ribs adjacent to bosses having an outer diameter of 45 mm and a wall thickness of 4 mm and 20 × 20 × 80 mm. Casting is performed by the method according to the above.

That is, an equilibrium gas pressure corresponding to atmospheric pressure and corresponding to 1 MPa and 10 MPa is applied to the inside of the chamber containing the mold just before solidification starts, respectively.

The cylinders are then made in the form of two alloys with high mechanical properties.

Composition ratio per weight -100%, Fe 0.20: Si 6.5-7.5; Cu 0.10: Zn 0.10: Mg 0.25-0.40: Mn 0.10: Ni 0.05: Pb 0.05: Sn 0.05: Ti 0.05-0.20: A-S7G03 forms the remainder of Al composition.

-Fe 0.35: Si 0.20: Cu 4.20-5.00: Zn 0.10: Mg 0.15-0.35: Mn 0.10: Ni 0.05: Pb 0.05: Sn 0.05: Ti 0.05-0.30: A-U5GR which forms the composition of Al

As a result of the mechanical test on both cylinders after the standard Y23 heat treatment for A-S7G03 and Y24 heat treatment for A-U5GT, the following characteristics were measured.

For A-S7G03, the quality indicator (Q) is expressed as Q = R + 150 logA in MPa, where R is the strength in MPa and A is the elongation in% in both thick and thin parts of the product. to be.

For -A-U5GT, yield stress is expressed as "LE" in MPa, strength as "R" in MPa, and elongation is expressed as "A" in% in both thick and thin portions of the product.

In addition, the fatigue resistance (F) is measured in units of MPa from the respective pressures and respective alloys applied from the torsion test on the sample machined in stepwise 107 cycles.

Fatigue resistance (F) is applied to both thick and thin portions because it is not dependent on the rate of solidification but on the porosity, ie the pressure applied.

Each measurement result is shown in the following table.

[table]

Improvements in all measured properties are observed, in particular improvements in elevated fatigue resistance.

Claims (4)

The organic foam form of the product to be constructed consists of walls formed as a bath of dry sand containing no adhesive and is contained in a mold filled with molten metal that removes the foam and slowly solidifies, Equilibrium gas is applied to the mold and molten metal at the same time, just before filling, and the pressure of the applied balance gas rises to a value between 1.5-10 MPa. Pressurized roast-foam casting of products. The method of claim 1 wherein the applied pressure rises to a value between 5-10 MPa. The method of claim 1 wherein pressure is applied when the amount of solidified metal is 40% by weight to the maximum. 2. A method according to claim 1, wherein the maximum pressure value is obtained before the solidified metal is 90% by weight in weight.

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