WO1994026438A1

WO1994026438A1 - Method and manufacturing of moulding sand, such moulding sand and application thereof

Info

Publication number: WO1994026438A1
Application number: PCT/DK1993/000163
Authority: WO
Inventors: Palle Norup JØRGENSEN
Original assignee: Pv Sand Fredericia AS
Current assignee: Pv Sand Fredericia AS
Priority date: 1993-05-14
Filing date: 1993-05-14
Publication date: 1994-11-24
Anticipated expiration: 1995-11-14
Also published as: AU4308693A

Abstract

A moudling sand, produced from free and mainly pure quartz sand particles, mixed with free and mainly pure feldspar particles in the amount of 5 to 20 percent by weight, is well suited for use in the production of iron castings in which blatribs must be avoided. The amount of free feldspar particles creates a buffer which allows the quartz sand particles to perform an expansion without any risk of formations of cracks in the sand. Furthermore, the produced moulding sand will have a good binding so that there is no risk that edges are broken off from cores or moulds at ingates.

Description

METHOD -AND MANUFACTURING OF MOULDING SAND, SUCH MOULDING SAND AND APPLICATION THEREOF

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing moulding sand which contains quartz and feldspar, such moulding sand, and the use of same. The moulding sand according to the invention may be used both as sand for cores and as sand for moulds, but it is used prima- ily as sand for cores.

Moulding sand which contains a mixture of quartz and feldspar is known from natural occurrences. Thus a natural occurence of quartz sand con¬ taining feldspar is known, e.g. from Sweden. In practice, however, the quartz sand containing feldspar has turned out to be connected with several drawbacks. Thus, the adhesive power of the sand is relatively poor. Thus it has turned out that edges on moulds or cores will break off at ingates because of the poor cohesion. However, the moulding sand is advantageous as only few so-called blatribs occur on the mate- rial that is casted when using this sand.

It is generally known that so-called thermal shocks occur in moulding sand based on quartz. Thus quartz will undergo substantially no expan¬ sion during a temperature increase up to 575°C. When that temperature is attained, a drastic and sudden expansion of the quartz will occur, which is known as a thermal shock. During a subsequent temperature increase, the quartz involved may again be heated substantially with¬ out expansion.

In moulding sand the thermal shock means a high risk of formations of cracks in the sand. Hereby the so-called blatribs are formed as liquid material flows into the cracks. It is desirable to use quartz sand because it is resistant to very high temperatures.

Therefore, attempts to avoid the blatribs have been made for many years. Thus, it is wellknown to create a buffer in the sand, e.g. by adding various substances, e.g. wood flour, which will burn so that the necessary buffer for the expansion of quartz is created. A moulding sand is also known in the form of chromite sand. This sand also provides an advantageous buffer because it has a linear expan¬ sion. However, chromite sand is disadvantageous because it has a vo¬ lume weight being approximately three times the volume weight of quartz sand. Chromite sand is further disadvantageous since it is difficult to dispose of the sand waste owing to the chromite contents, which means that it must be deposited under controlled conditions.

Despite the fact that there has been investigated in the manufacture of moulding sand for many years in order to avoid the above-mentioned problems, the attempts have hitherto been unsuccessful.

The inventor, who has been working in this field for many years, got the idea of producing a moulding sand containing quartz and feldspar according to a method which is characteristic in that 80-95 parts by weight of free and mainly pure quartz particles are mixed with 5-20 parts by weight of free and mainly pure feldspar particles.

The sand produced according to this method turned out to have sur- prisingly good properties. Thus when using this sand, there are no occurrences of edges breaking off at ingates such as is known from the naturally occurring quartz sand containing feldspar. In addition, the use of a moulding sand produced by the method according to the inven¬ tion with adequate proportions of feldspar particles and quartz par- tides has demonstrated that mouldings can be made in which the pro¬ blem of blatribs is substantially eliminated.

It has not been possible to give a direct explanation of the favour¬ able results, but it is assumed that the presence of free feldspar particles, mixed with particles of sand, is essential. This condition differs essentially from the naturally available quartz sand contain¬ ing feldspar, in which the feldspar is present in a chemically bound condition. During heating of the prior art quartz sand containing feldspar, it is assumed that feldspar will be broken off and this gives rise to the poorer cohesion of the sand which causes breaking of edges of moulds and cores.

Practical tests which have been performed have shown that the proper¬ ties of the produced moulding sand are affected by the proportion of mixture. It has turned out that favourable results are obtained when the percentage of free feldspar is kept within said 5 to 20 per cent by weight, preferably within 8 to 15 per cent by weight.

Furthermore, it has turned out that any content of bound feldspar in the quartz sand should give rise to a reduced amount of added free feldspar particles. In order to avoid the drawbacks of broken edges, quartz sand should be used which is substantially quite pure and which has a content of quartz of not less than 99 per cent by weight. How- ever, a small proportion of chemically bound feldspar may be con¬ tained.

The properties of the produced moulding sand are also affected by the average grain size, the grain distribution, and the grain shape of the feldspar particles and the quartz particles of the mixture. In order to obtain the best and most homogeneous mixture of feldspar particles and quartz particles, identical average grain sizes, grain distribu¬ tions and grain shapes should be used for the two elements of the mixture.

As mentioned above, the average grain size, the grain distribution, and the grain shape are parameters which influence the quality of the produced moulding sand. Thus, in practice it has turned out that with increasing average grain size a smaller proportion of feldspar should be used, that with increasing grain distribution a larger proportion of feldspar should be used, and that with more round grains a larger proportion of feldspar should be used. However, the amount of feldspar used should be kept within the above-mentioned limits.

The moulding sand according to the invention may be used by itself. In certain instances, however, it may be desirable to use the produced mixture together with prior art moulding sand. Through the use of the moulding sand according to the invention, a considerably easier hand¬ ling of moulds is obtained than through the use of chromite sand a- lone. Furthermore, the consumption of sand will be reduced drastically since the moulding sand according to the invention has a volume per weight unit which is 3 times as big as the volume per weight unit of chromite sand. The moulding sand according to the invention is used primarily as core sand. In a subsequent emptying of moulds containing moulding sand, e.g. quartz sand, the moulding sand according to the invention (the core sand) will be mixed with the sand for the mould. This mixture may be used again as sand for the mould without any negative influence on the sand for the mould.

The moulding sand according to the invention is particularly suitable as moulding sand for casting items in cast iron and non-ferrous metals where no problems will arise due to a lowering of the sintering point, which feldspar will bring about. The moulding sand according to the invention is characteristic in having been produced from mainly pure quartz particles which have been mixed with free and mainly pure feld¬ spar particles. The content of free feldspar particles in the moulding sand is preferably from 5 to 20 per cent by weight, and especially from 8 to 15 per cent by weight. However, it should be noticed that in connection with moulding sand according to the invention it is pos¬ sible to add ferric oxide in order to create a moulding film in a way known per se. This way the moulding sand may be applied at higher temperatures.

As mentioned above, there has been much investigation in binding ma¬ terials in order to obtain a buffer effect in the material which is present anyway around the sand grains in order to bind them together. Although various binding materials have been manufactured, they will be disadvantageous, since they require heating of the mould prior to the casting, i.e. use of the so-called hot-box method. This results in prolonged process times.

In case no heating of the sand moulds is required, the so-called cold-box method, a more rapid cycle is obtainable. The cold-box method may be used together with moulding sand according to the present in¬ vention.

Accordingly, the invention also relates to the use of a mixture con¬ sisting of 80-95 per cent by weight of mainly pure quartz particles and 5-20 per cent by weight of mainly pure feldspar particles as moulding sand, primarily for cores, in castings according to the cold-box method.

Claims

C L A I M S

1. A method of manufacturing moulding sand which contains quartz and feldspar, c h a r a c t e r i z e d in that 80-95 parts by weight of free and mainly pure quartz sand particles are mixed with 5-20 parts by weight of free and mainly pure feldspar particles.

2. A method according to claim 1, c h a r a c t e r i z e d in that 8 to 15 per cent by weight of free feldspar particles is used for the mixture.

3. A method according to claims 1 or 2, c h a r a c t e r i z e d in that the amount of free feldspar particles is relatively reduced cor- responding to any content of bound feldspar in the quartz used.

4. A method according to any of the preceding claims, c h a r a c ¬ t e r i z e d in that quartz sand particles and feldspar particles are used in which the average grain size, grain distribution, and grain shape of the particles have been analysed prior to the mixture, and in that identical average grain sizes, grain distributions, and grain shapes for both the quartz sand particles and the feldspar par¬ ticles are used.

5. A method according to claim 4, c h a r a c t e r i z e d in that with increasing average grain sizes a smaller proportion of feldspar particles is used in the manufactured moulding sand, that with in¬ creasing grain distributions a larger proportion of feldspar particles is used in the manufactured sand, and that with increasingly round grains a larger proportion of feldspar particles is used in the manu¬ factured moulding sand.

6. Moulding sand which contains quartz and feldspar, c h a r a c ¬ t e r i z e d in having been produced from mainly pure quartz sand particles which have been mixed with free and mainly pure feldspar particles, the amount of free and mainly pure feldspar particles in the moulding sand being 5-20 per cent by weight.

7. Moulding sand according to claim 8, c h a r a c t e r i z e d in that the contents of free feldspar particles in the moulding sand is from 8 to 15 per cent by weight, that the quartz sand particles have a contents of not less than 99 per cent by weight of pure quartz, and that the amount of free feldspar particles is reduced relatively cor¬ responding to any content of bound feldspar in the quartz sand par- tides.

8. Use of a mixture consisting of 80-95 per cent by weight of mainly pure quartz sand particles and 5-20 per cent by weight of mainly pure feldspar particles as moulding sand, primarily for cores, in moulding according to the cold-box method.

9. Use of the moulding sand according to claim 6 together with known binding agents chosen from clay and curable binding agents for the production of a curable mixture.

10. Use of the moulding sand according to claim 6 together with known moulding sands for the production of a moulding sand mixture.