CN1017784B - Process for 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.

Description

Process for lost-foam casting, under pressure, of metal articles

The present invention relates to metallic article, particularly the compression casting method that defoams of aluminium and Al-alloy products.

The person skilled in the art knows (particularly from USPNO.3157924 as can be known), can adopt the polystyrene foam model is embedded in the casting mold of being made by dry sand that does not contain binding agent and cast.In this process, metal molten that earlier will be to be cast, by means of the passage that crosses molding sand liquid metal is poured into casting mold then and contact with model, and combustion model little by little, make foam be transformed into vapour from loss between sand grains, like this, the metal that pours into has then replaced model gradually.

Because this method has avoided carrying out the refractory material of compacting and agglomerated powder powder and with quite complicated mode with the casting mold of rigidity through passage this initial manufacture process that links to each other with core, and can reclaim foundry goods simply, easily carry out the recirculation of Modeling Material, therefore, this method is proved to be in large-scale production that are attractive.

But this method has two adverse factors:

-slow relatively process of setting can impel the formation of sucking-off pin hole;

If the profile of-parts makes feeding become complicated, may cause micro-contraction a little less than the relative thin of thermal gradient.

In order to overcome these defectives, a kind of casting method that defoams has been developed in application, and it has constituted the theme of French publication number 2606688 patent applications.

This application is disclosed to be, after the deposite metal is full of casting mold, also promptly destroy by motlten metal fully when model, and during by vapour emptying that foam produced, the air pressure of equilibrium is applied on casting mold and the metal, preferably before metal begins to solidify, applies.This applied pressure increased along with the time, and to avoid the phenomenon of osmosis of metal, its maximum reaches in less than 15 seconds time.

Under these conditions, the density of foundry goods is improved, mechanical performance improves, particularly intensity.

Yet the applicant thinks, preferably uses the maximum pressure between 0.5 to 1.5MPa in this application, and does not exceed the latter's the limit.

In fact, we notice after having passed through the repeatedly research of exploration: if pressure further increases, be not only mechanical performance, as fracture strength R _mYield stress LE and percentage elongation A can improve, and anti-fatigue performance also can improve.

Therefore, the invention provides the compression casting method that a kind of aluminium and Al-alloy products defoam, in the method, the organic foam model for the treatment of cast product is imbedded in the casting mold, the wall of this casting mold is limited by the flat sand pond that does not contain binder material, in casting mold, pour into melt metal to replace foam, metal solidifies gradually, air pressure in the equilibrium that increases finishes after-applied on casting mold and metal in cast, applied before the amount of metal that has solidified reaches 40% according to the pressure that the present invention executed, and institute's applied pressure is increased to a numerical value between 1.5～10MPa.

Therefore, the present invention includes the pressure that applies 1.5-10MPa, preferably apply the pressure between 5～10MPa.

Can apply by means of a seal box with regard to french patent application NO.2606688, pressure, casting mold is put into the sealing case.Said seal box has the one or more nozzles that are distributed on the tank wall, and they are connected on the pneumatic supply.

The applicant has been found that in selected pressure limit, compares with the effect that produces according to prior art institute applied pressure according to the application institute applied pressure, and be significantly different.

In fact, be mainly used in when solid desmachyme at the pressure between the 0.5-1.5MPa and reached certain development during the stage, quicken just in the skeleton of frozen metal and the molten metal flow between the outward appearance cut-off region (effectstops), Here it is, and low pressure energy makes rising head prevent that effectively the contraction owing to the metal that is solidifying from producing the reason of shrinkage phenomenon.

On the other hand, the thermomechanical effect of the metal net shaped tissue that molten metal flow effect (motlten metal is what to be in the great majority when solidifying beginning) has been solidified gradually replaces, when pressure is higher than 1.5MP, when particularly pressure is higher than 5MP, this phenomenon becomes main phenomenon, afterwards, (it depends on the type of casting alloy) then it is exclusive phenomenon when solidification rate reaches about 50-70%.Therefore, use high pressure to produce a kind of isobaric forging, it influences the whole surface of foundry goods.

Accompanying drawing 1 is to carry out the microphoto that the casting of A-S7G03 alloy is heat-treated then according to the present invention under the pressure of 7MPa, this photo has shown and has acted on the netted structural plastic deformation of dendroid (this distortion has the effect of filling pore), and shown the forging effect that metal is stood well in this process.

We have found that under these conditions, the mechanical performance of metallic article, particularly anti-fatigue performance have substantial change, the pressure that is higher than 10MPa can only produce immaterial variation.

This new pressure limit is preferably in the amount of metal that has solidified and reaches and apply before 40%, so that this pressure can act on the metal liquid stream.

The amount that the pressure of executing is preferably in the frozen metal reaches maximum before surpassing 90%, so as can be from distortion obtain on whole benefits.

With regard to french patent application NO.2606688, institute's applied pressure preferably increases gradually, particularly solidifying at first, preventing " metal penetration " (penetration) phenomenon, this phenomenon results from and is applied directly to pressure on the metal and dry sand pond and is applied to imbalance between the pressure on the metal. In fact, with the contacted metallic region of sand, promote the pressure that metal passes sand grains and make foundry goods produce deformation tendency and make it to produce considerable damage in transmittance process medium sand pond.

The present invention can be illustrated by the following example.

Be that 45mm, thickness are 4mm with external diameter and comprise connection rib and the original technology of hollow cylinder body and function of 20 * 20 * 80mm boss is cast, and then cast with method of the present invention, that is to say, the balanced air pressure that is equivalent to equal atmospheric pressure, 1MPa, 5MPa and 10MPa is being solidified the inside that the chamber of casting mold is arranged in being applied to respectively before just beginning.

These housings (hollow cylinder) are made by two kinds of alloys with high-mechanical property:

-A-S7G03, its composition (percentage composition) is: iron 0.20; Silicon 6.5-7.5; Copper 0.10; Zinc 0.10; Magnesium 0.25-0.40; Manganese 0.10; Nickel 0.05; Plumbous 0.05; Tin 0.05; Titanium 0.05-0.20; All the other are aluminium;

-A-U5GT, composition are (%): iron 0.35; Silicon 0.20; Copper 4.20-5.00; Zinc 0.10; Magnesium 0.15-0.35; Manganese 0.10; Nickel 0.05; Plumbous 0.05; Tin 0.05; Titanium 0.05-0.30; All the other are aluminium.

Described housing carries out (carry out Y23 heat treatment for A-S7G03, A-U5GT is carried out Y24 heat treatment) after the conventional heat treatment, carries out Mechanics Performance Testing again, and following mechanical performance can be used as the effect of exerting pressure.

-for A-S7G03, quality refers to that (being) number Q is unit with MPa, and corresponding expression is Q=R+150logA, and wherein, R is an intensity, is unit with MPa, and A is the thick and thin regional percentage elongation of goods, represents with %.

-for A-U5GT, yield stress LE is unit with MPa, and intensity R is unit with MPa, and A is a percentage elongation thick, thin zone, represents with %.

In addition, to every kind of metal and each institute's applied pressure, the torsion test measurement fatigue resistance F(that carried out for 10 weeks with staircase method (staircase method) on the sample of processing is unit with MPa).The mensuration of F should be in thin zone also will be in thick zone because it does not depend on the speed of solidifying, but depend on porosity (shrinkage porosite) thus and depend on institute's applied pressure.

Result of the test is provided by following table.

Claims (3)

1, the compression casting method that defoams of a kind of aluminium and Al-alloy products, in the method, an organic foam model treating cast product is imbedded in the casting mold, the wall of this casting mold is limited by the dry sand pond that does not contain binding agent, with the described casting mold of liquid metal filling, metal replaces foam (model) and solidifies gradually, the air pressure of an equilibrium that is increasing finishes after-applied on casting mold and metal in cast, it is characterized in that, described pressure applies before the amount of solidifying (weight fraction) of metal reaches 40%, and institute's applied pressure is elevated to a value between 1.5 to 10MPa.

2, in accordance with the method for claim 1, it is characterized in that institute's applied pressure is raised to a value between 5 to 10MPa.

According to the method for claim 1, it is characterized in that 3, institute's applied pressure surpasses the 90%(weight fraction at the amount of metal that solidifies) reach maximum before.