AU2004235962A1

AU2004235962A1 - Moulding material, moulding part and method for the production of a casting mould

Info

Publication number: AU2004235962A1
Application number: AU2004235962A
Authority: AU
Inventors: Thomas Steinhauser
Original assignee: Hydro Aluminium Deutschland GmbH
Current assignee: Hydro Aluminium Deutschland GmbH
Priority date: 2003-05-09
Filing date: 2004-05-08
Publication date: 2004-11-18
Also published as: DE502004000846D1; EP1620216A1; WO2004098811A1; ES2267068T3; ATE330733T1; DE10321106A1; PL1620216T3; MXPA05011996A; EP1620216B1

Abstract

The invention relatest to a moulding material for moulding parts of casting moulds used to cast metal melts, especially light metal melts such as aluminium casting melts. Said moulding material makes it possible to produce non-sand-adherent cast moulding parts which are, especially casting cores, in an economical manner by virtue of the fact that it is produced using a basic mould material which is based on quartz-free sand, especially olivin sand, and an inorganic binder based on waterglass mixed with the basic mould material. The invention also relates to moulding parts which can be produced in an economical manner and a method enabling said moulding parts to be produced.

Description

TRANSLATOR'S CERTIFICATE 1, the undersigned, being familiar both with the German and English language, certify that the at tached English translation is a true and exact translation of all the parts of the PCT/EP2004/004936. P. M6nkemeyer DOsseldorf, November 15, 2005 SI/cs 021320 WO 7 May 2004 Moulding material, moulding part and method for the production of moulding parts for a casting mould The invention relates to a moulding material for the production of moulding parts for casting moulds used to cast metal melts, especially light metal melts, such as aluminium casting melts. Furthermore the invention relates to moulding parts produced from such a basic mould material. Finally the invention provides a method by which moulding parts can be produced from of moulding materials according to the invention. Usually quartz sand is used as the basic material of moulding materials, from which moulding parts, such as casting cores are produced for casting moulds. To start with this sand is put into a mixer and mixed with a binder therein. The moulding material obtained from this mixture is then injected into the cavity of a moulding tool determining the shape of the moulding part to be produced. Subsequently the moulding part solidifies in the moulding tool. If an organic, for example synthetic resin-based binder, is used in addition a chemical reaction is caused in the moulding material injected into the moulding tool. On the other hand if an inorganic, for example waterglass-based binder is used, as a rule heat is applied to the moulding material contained in the moulding tool, in order by evaporation of the water contained in the moulding material to cause solidification of the moulding part being produced. However it is also possible to chemically harden the moulding material containing waterglass by aerating with CO 2 gas. The use of quartz sand as the basic material for the production of casting mould parts has proved of value particularly in the field of casting light metal materials in several respects. Thus such quartz sand can be procured economically and is characterized by easy workability and good quality for reproducing the moulding elements of the casting mould part to be produced in each case.

2 With the use of a moulding material with quartz sand as the basic material, which contains a binder based on waterglass, however the disadvantage that adherent sand remains on the casting surfaces reproduced by the moulding parts, detracts from these advantages. This adherent sand can only be removed, by blasting the castings in a separate processing stage, for example with a blasting material or by cleaning with pressurized water. The complexity of production and the accompanying costs of producing castings rise due to the necessity for rework. The expense linked with the rework is especially high, if the moulding parts are used as casting cores, which reproduce the interior areas of the casting. Attempts have been made to reduce the expense linked with cleaning castings by using moulding materials the basic mould material of which contains high quantities of synthetic mullite. Moulding materials of this kind possess the property of automatic disintegration in the course of solidification in the casting so that they can be simply removed after final solidification of the casting. However the quantities of mullite, necessary for this, lead to high costs of the basic mould material. The object of the invention therefore consisted in designating a moulding material which permits the economical production of casting mould parts, in particular casting cores. Furthermore economically producable moulding parts and a method enabling said moulding parts to be produced were to be indicated. Regarding the moulding material for moulding parts of casting moulds used to cast metal melts, especially light metal melts, such as aluminium casting melts, this object is achieved due to the fact that such a moulding material is produced from a basic mould material made on the basis of quartz-free sand and an inorganic binder mixed with the basic mould material which binder's made on the basis of waterglass. Olivine, which concerns a widespread mineral and is economically available in large quantities, is particularly suitable as quartz-free sand.

3 Surprisingly it has been shown that moulding materials, which are produced according to the invention on the basis of a basic material entirely consisting of quartz-free sand or where at least by far the predominant part is quartz-free sand are also perfectly released from the finished casting, even if they are bound with a waterglass binder. In this case, the adherent sand remaining on the casting is reduced to a minimum. In this way also when using moulding parts, which are produced from moulding materials, containing a waterglass binder according to the invention, it is possible to guarantee that non-sand-adherent cast parts are obtained. The moulding material according to the invention, produced on the basis of quartz free sand, in particular olivine, creates the pre-condition for economical production of castings. Thus when using moulding materials according to the invention the expense of removing the sand is reduced in relation to the expense, which results from cleaning castings, which have been cast using moulding parts produced from conventional, quartz-containing moulding materials. In principle the basic mould material used according to the invention can consist entirely of quartz-free sand. However in order to ensure apart from the non-adherence also particularly easy release of the moulding parts from the finally solidified casting, it is possible in accordance with an advantageous embodiment of the invention to add a quantity of synthetic mullite to the basic mould material. This quantity of mullite mixed with the principal component of quartz-free sand, in particular olivine, assists the automatic disintegration of the moulding parts produced on the basis of the basic mould material according to the invention in the course of the solidification of the cast component. This is proven to be particularly favourable if the moulding parts concern casting cores, which reproduce cavities in the finished casting. The positive effects achieved by the use of moulding materials according to the invention materialize with all usual waterglasses. This applies in particular to such waterglasses, which have a module of 3.3 - 2.

4 A composition of moulding material in particular fully meeting the practical requirements is characterized in that it contains 1.5 - 3.0 wt.-% waterglass in each case. In order to improve the lifetime of the sand the moulding material according to the invention can contain 0.3 - 0.5 wt.-% of soda lye. Regarding the moulding part the object specified above is achieved by the fact that a moulding part according to the invention for casting moulds, which in particular concerns a casting core is made of a moulding material according to the invention. In principle the advantageous effects achieved by using a moulding material system based on mixing quartz-free sand and an inorganic waterglass binder for casting light metal melts, materialize irrespective of what process has been used to produce the particular moulding parts, in particular casting cores. It has however been shown that the so-called "inorganic warmbox process" is particularly suitable for this purpose. According to the invention the object specified above as regards the method for producing a moulding part for casting moulds, in particular for producing casting cores is achieved accordingly by carrying out the following work stages: - Production of a moulding material according to the invention, - Filling the moulding material into a cavity of a tempered moulding box, said cavity reproducing the moulding part, - Solidification of the moulding material in two phases - wherein in the first phase of solidification the moulding material is kept in the tempered moulding box until an abrasion-resistant outer shell of the moulding part is formed, and - wherein the moulding part is subsequently taken out of the moulding box and under the effect of microwave heating is finish hardened.

5 Using this method moulding parts which not only possess particularly high strength and true reproducibility but furthermore have the property of disintegration without adhesion during the production of the castings can be reliably made from moulding materials, which are produced by mixing quartz-free sand according to the invention, in particular olivin sand basic materials, with an inorganic binder. Disintegration promoting additives are no longer necessary in the binder system. Therefore whenever the invention is applied pollution of the environment and danger to the operatives through escaping gases, the evolution and inadvertent spreading of which can only be minimized in conventional production methods with large technical complexity, are prevented. The formation of the permanent outer shell permitting onward transfer into the microwave oven can be assisted by holding the moulding material under negative pressure during the first phase of solidification. In this first phase of solidification the moulding material hardens to such an extent that a firm layer, which ensures sufficient inherent stability of the moulding material during the next production stage, develops in its boundary region bordering the mould walls. Depending on the complexity of the shape of the particular moulding part being produced the temperature of the moulding box in the first phase of solidification should be 1500 C - 2000 C. By maintaining this temperature range during the formation of the firm boundary region of the moulding parts such casting cores, which exhibit greatly varying diameter gradients or very irregular mass distributions can also be reliably produced. It has been shown that if a suitable temperature is selected, an outer shell of the moulding part, which is sufficiently stable for subsequent processing, materializes, even if the first phase of solidification only lasts 10 - 50 seconds. Finally the complete hardening of the moulding part reliably materializes, if the reaction time of the microwave heating in the second phase of solidification is 2 - 5 minutes. Within this time span the particular reaction period, under consideration of the complexity of the shape, can be adjusted in such a way that an ultimate strength 6 and dryness of the moulding part sufficient for the casting process are ensured at the end of the microwave treatment. The invention is described below in detail on the basis of an exemplary embodiment. In order to produce a casting core intended for casting a cylinder head from an aluminium casting alloy, firstly a basic mould material, which consisted entirely of olivine sands, was produced. From this basic mould material a moulding material was subsequently produced, wherein the basic mould material was blended with a waterglass binder. Additionally a quantity of soda lye was added to the basic mould material in order to improve its durability. The basic mould material composed in such a way contained 2.5 % of waterglass binder, 0.3 % of soda lye and the remainder as the basic mould material with the composition detailed above. This moulding material was injected into the cavity of a preheated moulding box, said cavity reproducing the finished casting core. In this case due to the excellent fluidity of the moulding material small, difficult to shape areas of the cavity were also reliably filled. This reliable mould filling was also assisted by the fact that the moulding box was already subject to negative pressure during the filling process. The negative pressure was 0.3 bar. The temperature of the moulding box when filling the moulding material was 180* C. The moulding material after completion of the filling process was held at this temperature in the moulding box for 30 seconds, still subject to effective negative pressure. During this time a firm outer shell was formed in the vicinity of the regions of the moulding material bordering the inner walls of the moulding box. In this way a moulding part, the strength of which was sufficient in order to be able to transfer it safely into a microwave oven, was obtained at the end of the first phase of solidification completed in the moulding box.

7 In the microwave oven the moulding part was heated for 3 minutes by microwaves, until it reached an ultimate strength sufficient for the casting process. The casting core produced in such a way was then set into a casting mould, in which the melt produced from the aluminium alloy was subsequently cast into the cylinder head to be manufactured. In the course of solidification, due to the temperature influence of the casting heat and the mechanical stress occurring due to the solidification of the casting the casting core automatically disintegrated into numerous small fragments, which could be easily removed after complete solidification of the casting. After removing the fragments of the casting core it was shown that sand no longer adhered to the walls of the casting, which had come into direct contact with the casting core. Subsequent cleaning of the channels reproduced by the casting core and cavities of the cylinder head was no longer necessary.

Claims

1. Moulding material for moulding parts of casting moulds used to cast metal melts, especially light metal melts, such as aluminium casting melts, produced from a basic mould material made on the basis of quartz-free sand and an inorganic binder mixed with the basic mould material which binder is made on the basis of waterglass.

2. Moulding material according to Claim 1, characterized in that the quartz-free sand is olivine.

3. Moulding material according to any one of the above claims, characterized in that the basic mould material contains a quantity of synthetic mullite.

4. Moulding material according to any one of the above claims, characterized in that the waterglass has a module of 3.3 - 2.

5. Moulding material according to any one of the above claims, characterized in that it contains 1.5 - 3.0 wt.-% of waterglass.

6. Moulding material according to any one of the above claims, characterized in that it contains 0.3 - 0.5 wt.-% of soda lye.

7. Moulding part for casting moulds, in particular casting cores, made of a moulding material composed in accordance with any one of the above claims. 9

8. Method for producing a moulding part for casting moulds, in particular for the production of casting cores, which comprises the following work stages: - Production of a moulding material composed in accordance with any one of Claims 1 to 7, - Filling the moulding material into a cavity of a tempered moulding box said cavity reproducing the moulding part, - Solidification of the moulding material in two phases - wherein in the first phase of solidification the moulding material is kept in the tempered moulding box until an abrasion-resistant outer shell of the moulding part is formed, and - wherein the moulding part is subsequently taken out of the moulding box and under the effect of microwave heating is finish hardened.

9. Method according to Claim 8, characterized in that the moulding material is held under negative pressure during the first phase of solidification.

10. Method according to either of Claims 8 or 9, characterized in that the temperature of the moulding box is 150 - 2000 C during the first phase of solidification.

11. Method according to any one of Claims 8 to 10, characterized in that the first phase of solidification lasts 10 - 50 seconds.

12. Method according to any one of Claims 8 to 11, characterized in that the reaction period of the microwave heating in the second phase of solidification is 2 - 5 minutes.