IE54891B1 - Use of additives for environmentally harmless foundry mould sands - Google Patents

Abstract

1. The use of a carbon product or of several such products, containing volatile components to a total of 0.5-20% by weight, wherein with naturally occurring products containing mineral materials the content in volatile components is calculated to the natural product without the mineral components.

Description

- 2 - - 2 - 5489 1 The present invention relates to the use of additives to foundry mould bulk sands which not only give improved results in foundry technology, but are substantially better at satisfying the requirements of pollution control in the work-5 place.

It is known to add carbon, containing additives as well as conventional binders e.g. bentonite, to mould sands intended for the manufacture of casting moulds. An example of this is mineral coal dust, which is added for the 10 special purpose of improving the surface quality of the moulded objects (cf DE-A- 1 952 235). Addition of mineral coal dust takes place on the assumption that, during casting, burning of the sand onto the cast object is avoided, giving rise to a smooth clean surface, by reason 15 of the gas formation and the coating of the quartz grains with coal.

It was also found that the use of mineral coal dust in the mould sand contributes to the uniformity of sand expansion and to the avoidance of sand blemishes. Another proposal is 20 that the additive consists of a thermoplastic resin which - 3 - - 3 - 54891 is an unsubstituted polymerised hydrocarbon in non-foamed form, e.g. consists of polymers of styrene, ethylene or propylene (cf likewise DE- A- 1 952 357). This proposal sought to replace the previously used coal dusts and use 05 instead the thermoplastic resins described, mainly on the assumption that lustrous carbon was formed thereby in the casting moulds under the influence of the casting temperature, and that it puts a skin on the grains of the mould sand and coats the quartz grains of the mould body.

Another suggestion is to add, to the foundry sand, resins which are obtained from mineral oil distillation as hydrocarbon polymers in the form of so-called petroleum resins (cf DE-A- 2 064 700). This solution also proceeds from the assumption that under the conditions of hot 15 casting, a partial volatilization of the additives takes place and that lustrous carbon is precipitated from the gas phase and effects the separation between the metal and the material of the mould.

The progress achieved, however, remains highly unsatis-20 factory, both in general and from the viewpoint of pollution control in the work place. The following table 1 lists the products previously used and the components which are volatile at casting temperature, the latter measured according to standardized internationally accepted measuring 25 methods, i.e. DIN 5172. The subsequent table 2 lists the total amounts of volatile components given off from various products between 400 and 700°C in both oxidizing and reducing atmospheres. - 5 -54891 CM Μ 03 < CD U-i C MW pH (D -P-Ι X2 Όw a · u in jj & c ο Φ φ e c C 4J **H 0 <0 T- ft g σ' Φ to 0 c Η Φ υ jq u N Φ 3 φ ·Η Eh JJ ΗΌ Φ η -π m μ 4JKOH Φ o & iH to g Ο Ό -U Φ > C U μ Φ 3 4h *a μ O DO C C VJ Φ V ·Ή Οι μ Ηϋ Φ Φ 3 £ ΉΌ ο >* Φ U μ uh £ Φ Ό •Η μ Φ (0 Φ 0$ Φ Δ 0S α ςη to - γΗ Ο Ό Φ Ε·Η 0 μ χ Ο < ο C •Η 0) σ φ m μ Ό Φ Φ ε μ « 3 Φ Φ J= ι-Η a σ' 0 CO - U 0 Ό μ ε ή Φ μ χ dt < Ο σ' Ό Φ Φ μ μ ο$ (0 φ 3 r τ> α σ to - «Η 0 Ό φ ε ·ή 0 μ Μ υ < ο σ' •σ φ φ μ tc φ C Δ Φ Ο* σ' Β w · 3 Ο Ό μ g ·μ σ' r- «Λ a Ο ο Ρ- 0 Γ— Ο ο «Η Ο ο ο γΗ C Μ ΙΑ Ο γ- «Π 9% ΓΗ ΓΗ Ο ΓΗ ΙΑ ιΛ Γ* Ο a ΓΗ ο Ο C r* ι-Η ο ο pH Ρ- ο ο ιΛ Ον ο ο pH Ο *9 •9 νί Νβ Ο Λ «9 Ο Ον Ν ΓΗ ΓΗ Λ Ο Ό Φ 1— φ « μ ΡΜ φ ω J3 α σ' £ (0 - 0 0 Ό μ £ ·Η •Η μ χ ΡΜ < ο υ -4 ΙΑ <9 9 lit ΙΑ «Ο ι- ΓΗ Ό Ό να *Λ Os Ον Ον Η «9 Η Γ— Γ* 1- Η <9 ο VC Γ ΓΗ ΙΑ ΙΑ ΓΗ ΙΑ ΙΑ Η ν% •9 ΙΑ ΙΑ Ον σν Ον ον VD Γ» Γ— •9 Ηί Ο Ο 0» Ο να ιΛ ΙΑ ιΛ Ον «Η ΓΗ ΙΑ •9 Γ- Ο β ο» Ρ- Ο CD pH Φ Ον •9 νΟ fC •9 Ον Ον μ 3 0 JS φ C ο μ Ο ΜΗ Φ μ 3 •μ Φ μ φ aε φ μ χ: ο φ φ φ Ό ι—I Φ Λ Φ Φ Φ μ Φ * φ £ Φ μ 3μ Φ μ Φa ε (0 φ φ (0 Φ Ζ φ οa * οο Ό φ xs ΕΗ - 6 -s 4 ci y i according to the invention there is provided the use of a carbon product or a mixture of several such products, the additive product containing volatile components to a total of 0.5-20% by weight, wherein in the case of naturally occurring products containing 5 mineral components the content of volatile components is calculated relative to the natural product without mineral corcponents.

According to all processes up to now, the activity of the carbon-containing additives used 153 to new is supposed to be based on the volatilization of hydrocarbon coirpounds which takes place in the 10 temperature conditions of casting, after which, when a reducing atmosphere has been formed, the so-called lustrous carbon precipitates above 650°C. The lustrous carbon formed is said to effect the separation between the molten metal and the mould material, by coating the grains of the mould sand.

Listed below are the decomposition products, and their composition, of a gas coal aid a hydrocarbon resin, arising during thermal reaction in a reducing atmosphere.

A) Yield of gas, benzene and tar fran a gas coal having 33% volatile components 20 100kg of cool = 43.8 N n? gas 3.6kg tar 1.15kg benzene CjH (i.e., the heavy hydrocarbons) together consist of: Average analysis of the gas 25 COg 1.8% CnHm ^‘e·' '(^le heavy hydrocarbons) together CnHra 2.3% consist of: 02 0.2% C2H6 0.82 % CO 4.7% C2H4 1.21 % HZ 64.6% C3H3 0.07 % CH4 24.5% C3H6 0.20 % N2 1.3% C6H6 0.6% 30 · - 7 - 54891 B) Analysis data of the volatile components of tar in the boiling point range 0-170° C 170-230° C 230-270° C 270-350°C pitch benzene - toluene - xylene -phenol - pyridine naphthalene - phenol - cresol - bases creosote - naphthalene - neutral oils anthracene - phenanthrene - corbazole c. 0.5% 3,4-benzopyrene free carbon - phenanthrene - chrysene c. 1.0% 3,4-benzopyrene boiling point of 3,4-benzopyrene about 495.5° C boiling point of 1,2-bcnzopyrene about 492.9° C C) Thermal decomposition of a hydrocarbon resin at 1,000°C, analysis of volatile components arising Hydrocarbons, lower 0.3% cyclopentadiene 0.2% benzene 1.5% toluene 2.7% ethylbenzene +jnj, ο-, £-xylene 2.2% styrene 7.3% cumene 0.2% allylbenzene 0.1% ethyltoluene 0.4% alpha-methylstyrene 1.4% o—, m-, p-vinyltoluene 18.0% beta-methylstyrene 0.3% indene 19.4% dimethylstyrene 8.4% methylindene 18.5% naphthalene 19.1% - 8 - As can be seen, when the previously known additives are used, volatile components are given off, some of which are extremely damaging from a pollution control viewpoint, such as the aromatics benzene, toluene and xylene, which as carcinogens are no longer permitted in other technical fields e.g. as solvents, (cf R.W. Schimberg et al., Belastung von Eisengiessereiarbeitern durch mutagene polycyclische aromatische Kohlenwasserstoffe, Staub-Reinhalt. Luft volume 41 (1981) pp. 421-424). Even the gases arising during the casting process have carbon monoxide contents which are intolerable in the workplace.

Compared with the previously assumed precondition for the effectiveness of the previously used carbon-containing additives to foundry mould sands, the additives used according to the invention comprise carbon products exhibiting a content of volatile components from 0.5-20%, preferably 0.5-10%, based on the amount of the carbon products free from the mineral components present in the natural product, if any. Advantageously they are present in the additives in a particle size smaller than 1mm, preferably smaller than 0.15mm. Products of this kind which are specially suitable are the so-called crystalline carbon products, which in general contain less than 1% volatile components. Since these products are relatively expensive as a rule, organic carbon products can be mixed in, which can themselves form crystalline carbons above 650°C in the reducing atmosphere produced during the casting process, and which have a proportion of volatile components from 1-20%, preferably between 5 and 10%, provided that the total carbon product in accordance with the invention contains volatile components only within the limits given above, and that the maximum content of volatile components, of 20%, preferably 10%, is not exceeded. - 9 - - 9 - >4891 Examples of the crystalline carbon products which can be used in accordance with the invention, and of miscible carbon products are given in table 3, and of the volatile components given off in casting at the temperatures arising 05 in the sand of the foundry moulds are shown in table 4.

The expression "natural graphite" in what follows is to be understood in the sense that the naturally occurring graphite minerals generally contain significant amounts of mineral components, which must be separated therefrom in 10 known flotation or chemical treatment processes, before they can be used as additives to foundry mould sands. The product thus purified, and not occurring in nature in this pure form, is (herein) normally designated "natural graphite". i 54 89 1 11 54891 CQ tO O' --Ϊ CM γ- γο to cM cm n r- in t£> cm Η (N N irt h rt Isο η ή « CM CO VD ON η cm m *n I ζ a a o From this it can be seen that, as a result of the thermal stresses during the casting process, with the mould sands according to the invention, the additives (carbon carriers) according to the invention, and their use as additives to foundry mould sands, the quantity of gas given off is substantially smaller. In general it can be observed that the shooting flames usually encountered in using the conventional additives (e.g. based on gas coal) and which arise from ignition of the evolving volatile components in the mould sand, are no longer encountered when using the mould sands with the carbon carriers of the invention as additives. The quantities of carbon carriers to be added for regenerating the mould sand can be reduced by 25-50% in this way, with the result that pollution in the foundry is reduced to a minimum.

Numerous gas analyses have shown that when carbon carriers with a volatile component content of 8-10% waf are used, the carbon monoxide content in the atmosphere of the casting line and the unpacking station is reduced to about 20ppm, apart from the reduction of hydrocarbon compounds. When carbon carriers with a volatile component content of 40-45% waf are used, the CO value then rises to 80-100ppm, so that the MAK limiting value of 50ppm is clearly exceeded.

Having regard to the previous teaching in the state of the art, it is surprising that the surface of the cast body is actually free from defects* such as band ribs and the like, and the separation between the mould sand and the cast body proceeds faultlessly, in spite of the substantially reduced quantities of volatile components in the additives, and this even though the quantity of additive in the mould sand has been greatly reduced.

The combination of the crystalline carbon products with anthracite coal or lean coal as coal additive product has proved particularly advantageous. Anthracite and lean coal react even at low temperatures, (150-400°C) during the - 13 - casting process, with the atmospheric oxygen present in the mould cavity, and thus create very quickly a reducing atmosphere, which is a precondition for the crystalline carbon products suffering only very small losses during or after the castng process.

The foundry bulk sand additives used according to the invention form an ideal protective layer between the molten metal and the sand mass of the mould, by which reactions between the metallic melt and the mould sand are prevented.

A further advantage of the use of the additives (carbon carriers) in accordance with the invention is the small water demand of the thus produced mould sand according to the invention during the preparation process, since the additives (carbon carriers) used according to the invention have a substantially smaller surface than the conventional carbon compounds.

The flow characteristics and sealing behaviour of the mould sand treated with the additives used according to the invention are likewise improved, since the additives (carbon carriers) used according to the invention substantially reduce the frictional resistance of the quartz grains coated with clay.

Besides the advantages in foundry technology described above, of the additives used according to the invention, pollution in the foundry is substantially reduced. At present, in the Federal Republic of Germany alone, c. 70,000 tons per year of carbon carriers or additives to foundry sand on a basis of carbon with a proportion of 38-40% of components which are volatile at casting temperatures are used, i.e. c. 20,000 tons per year of hydrocarbon compounds are released to the atmosphere. 20,000 tons per year of 14 - hydrocarbon compounds correspond, assuming a c. 40% proportion of volatile components, to 10,612,000 m3 of gas, 85,400kg of tar and 272,000kg of benzene.

Experimental Report The following sand mixtures were prepared for the experiments; Sand mixture: 160 kg of sand 14.4 kg mixture of % carbon carriers 70% bentonite 4.3 kg H2O 8 mixtures were prepared: Mixtures 1-5; carbon carriers = natural graphite with various surfaces Mixture 6 : Carbon carriers = pure bitumen Mixture 7 ; Carbon carriers = mixture of very volatile coals + bitumen Mixture 8 : - Carbon carriers = mixture of low volatility coal + bitumen The sand mixtures have the following sand values: Mixture h2= Compressive Compress- Weight of strength ibility test body 1 2.9 600 55 155 2 2.7 630 60 152 3 2.6 490 55 149 4 2.9 800 63 152 5 2.9 610 61.5 148.5 6 2.7 700 63.0 150.0 7 2.8 660 61.0 149.0 8 3.0 610 62.0 148.0 - 15 - - 15 - 54891 A special model was selected for all experiments so that comparisons were possible.

The sands were used as model sand without sieving.

In the casting of all boxes it was shown that in tests 6, 7 and 8 there was a stronger evolution of flame.

Gas Analysis Samples taken 1 Casting line before casting 2 Casting line during casting 3 Unpacking station during unpacking Sample 1 Sample 2 Sample 3 vol. % vol. % vol .* C02 0.12 0.10 0.28 °2 21.0 21.0 20.8 CO 33 62 118 H2 0.02 0.02 0.02 ch4 0.00 0.00 0.02 n2 78.85 78.83 78.81 02»6 0.00 0.00 0.00 C2H4 0.00 0.02 0.02 02«2 0.00 0.00 0.00 C3H8 0.00 0.00 0.00 C3H6 0.02 0.00 0.02 C4H10 0.00 0.00 0.00 C4H8 0.00 0.00 0.00 c6H6 negligible negligible negligible 99.99 99.98 99.98 Unpacking Characteristics The moulded bodies or samples were unpacked under the same conditions. Samples 1-8 were judged as follows: Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Sample 8 practically no odour evolved very strong odour evolved strong odour evolved η n n Moulded Bodies after Irradiation The general cast surfaces were evaluated first. -Samples 1-8 clean surfaces.

The moulded body has a tendency toward the formation of leaf ribs, and it was ascertained that the higher the volatile components in the carbon carrier are, the more the leaf rib formation rises.

Samples 1-5 showed no leaf ribs, compared with samples 6 and 7 which had a strong tendency toward leaf ribs, and in sample 8 only weak attacks of leaf ribs were recorded.

Claims (9)

54891 - η -

1. Use of a carbon or a mixture of several such products, the additive product containing volatile components to a total of 0.5-20% by weight, wherein in the case of naturally 5 occurring products containing mineral components the content of volatile components is calculated relative to the natural product without mineral components.

2. Use according to Claim 1, wherein the carbon product or products are fine-grain or coarse crystalline carbon product, 10 lampblack, pyrographite, pyrocarbon product, anthracite or non-coking coal.

3. Use according to Claim 1 or 2, wherein the additive product is present in a particle size of less than lmm.

4. Use according to Claim 2 or 3, wherein the carbon 15 product is a crystalline carbon product.

5. Use according to Claim 4, wherein the crystalline carbon product was prepared from hydrocarbon-containing compounds in a reducing atmosphere at a temperature between 650 and 1,000°C.

6. Use according to Claim 4, wherein the crystalline carbon product is a natural graphite.

7. Use according to Claim 6, wherein the natural graphite 2 has a surface area of 0.4-15m .

8. Use according to Claim 4, wherein the crystalline 25 carbon product consists of synthetic graphites.

9. Use according to Claim 1 of a carbon product or a mixture of several such products, substantially as hereinbefore described and exemplified. F. R. KELLY & CO., AGENT FOR THE APPLICANTS.