SE539306C2

SE539306C2 - A carbonacous additive for a moulding material for casting iron

Info

Publication number: SE539306C2
Application number: SE1650208A
Authority: SE
Inventors: Nayström Peter
Original assignee: Swerea Swecast Ab
Priority date: 2016-02-17
Filing date: 2016-02-17
Publication date: 2017-06-27
Also published as: EP3208012A1; SE1650208A1

Abstract

ABSTRACTA carbonaceous additive for a moulding material for casting iron,wherein the carbonaceous additive comprises coke in an amount of 25 % byweight of the carbonaceous material or more, but less than 50 % by weight ofthe carbonaceous material, pit coal in an amount of 45 % by weight of thecarbonaceous material or more, but less than 65 % by weight of thecarbonaceous material, and optionally coal dust replacement in an amount of20 % by weight of the carbonaceous material or less, and in that the amount of pit coal is greater than the amount of coke.

Description

A CARBONACOUS ADDITIVE FOR A MOULDING MATERIAL FORCASTING IRON Technical field The present invention relates to a carbonaceous material additive for amoulding material and a method for casting iron, the carbonaceous materialcomprising pit coal and coke.

More particularly, the present disclosure relates to a carbonaceous materialadditive for reducing emissions during the casting process and sandadherence or sand sticking to the iron work piece.

Backgroundln the casting of iron in green sand moulds, it is known to form a moulding material that contains about 80-90% by weight of sand, about 5-1 1% by weight of binder (usually bentonite), about 3-4% by weight of waterand about 2-6% by weight of carbonaceous material, these are conventionallycalled clay-bonded sand moulds. ln commercially used moulding materials, the carbonaceous material consists mainly of powdered coal, or alternatively a coal dustreplacement. A problem associated with this kind of carbonaceous material isthat it contains a certain amount, usually about 30% by weight, of volatilecompounds (such as VOC - volatile organic compounds), which are set freeas the moulding material is heated, and which cause emissions and problemswith odour from the foundry plant. However, these volatile organiccompounds have a beneficial effect on the casting performance by reducingthe adherence of, for example, the moulding material to the cast object, thusreducing the amount of moulding sand that has to be removed from the castobject in subsequent production stages.

A carbonaceous additive for moulding materials is known fromEP1800771A1. Further experience has shown that this additive works well forsmaller work pieces, such as work pieces having a mass of 10 kg or less, orhaving a maximum wall thickness of 20 mm or less. ln particular, this additiveprovides a very good trade-off between VOC emission and sand adhesion.

However, for larger work pieces, while the VOC emission remains low,the sand adhesion has turned out to be greater than what is desirable. Hence, there is a need for a carbonaceous additive which is suitable for larger workpieces.

Summarylt is an object of the present disclosure, to provide an improved carbonaceous material or additive for a moulding material for casting ironwhich eliminates or alleviates the disadvantages of the prior art foundry sand.

More specific objects include providing a carbonaceous materialor additive for casting iron providing reduced and acceptable level ofemissions of volatile organic compounds (VOC) while still giving anacceptable sand adherence to the work pieces molded in the foundry sand.

The invention is defined by the appended independent claims.Embodiments are set forth in the appended dependent claims and in thefollowing description.

According to a first aspect there is provided a carbonaceous additivefor a moulding material for casting iron, wherein the carbonaceous additivecomprises coke in an amount of 25 % by weight of the carbonaceous materialor more, but less than 50 % by weight of the carbonaceous material, pit coalin an amount of 45 % by weight of the carbonaceous material or more, butless than 65 % by weight of the carbonaceous material, and optionally coaldust replacement in an amount of 20 % by weight of the carbonaceousmaterial or less, and in that the amount of pit coal is greater than the amountofcoke.

This additive has proven to be surprisingly effective and applicable incasting larger work pieces, i.e. pieces having a weight of at least 10 kg, whilestill providing both acceptable VOC emissions and an acceptable sandadherence to the work piece.

The amount of coke may be 35-45 % by weight of the carbonaceousmaterial and the amount of pit coal is 55-65 % by weight of the carbonaceousmaterial.

The amount of coal dust replacement may be less than 10 % by weight,preferably less than 5 % by weight or less than 2 % by weight.

Coal dust replacement may for instance be used to enhance thesurface finish of the product, but does not generally contribute to the loweringof VOC emissions or the sand adherence.

The coal dust replacement may be selected from a group consisting ofcarbon containing material such as pyrolytic or lustrous carbon former in solid or liquid form such as asphalt, gilsonite, petroleum destillates, organicpolymers, dextrin, and starch.According to a second aspect there is provided the use of an additiveaccording tothe first aspect, in a process of casting a part of iron having a mass of 10 kgor more, preferably 20 kg or more, 50 kg or more or 100 kg or more.According to a third aspect there is provided the use of an additiveaccording to thefirst aspect in a process of casting a part of iron having a sma||est wallthickness of 10 mm or more, or preferably 20 mm or more.According to a fourth aspect there is provided a mou|dingmaterial comprising:sand in an amount of 80-95 % by weight of the mou|ding material,binder in an amount of 4-15 % by weight of the mou|ding material, andthe additive according to the first aspect in an amount of 0.5-10 % by weightof the mou|ding material.The additive may be added in an amount providing a carbon content inthe range of 1.5 to 4 % by weight of the mou|ding material.By carbon content is thus meant the measured carbon content inthe mou|ding material, a measurement which is routinely performed in afoundry, usually before every casting cycle to ensure a reproducible result ofthe casting and the quality of the casting. The amount of additive needed inthe mou|ding material will be dependent on factors such as for instance sandto metal ratio. The skilled person would be able to recognize this and knowhow to calculate an appropriate addition of the carbonaceous materialadditive.

Description of Embodiments The carbonaceous material comprises coke in an amount of 25 % by weight of the carbonaceous material or more, but lessthan 50 % by weight of the carbonaceous material, pit coal in an amount of 45% by weight of the carbonaceous material or more, but less than 65 % byweight of the carbonaceous material. The amount of pit coal is thus greaterthan the amount of coke in the carbonaceous material additive. additive according to the invention The amount of coke may be 35-45 % by weight of the carbonaceousmaterial and the amount of pit coal is 55-65 % by weight of the carbonaceousmaterial.

By pit coal is also meant powdered coal, or coal dust. Pit coal inthis respect may also be called sea coal, or be of similar types of coal thatcomprises around 30 % volatile organic compounds. ln EP1800771A1 it was shown that a conventional foundry sand havingmainly pit coal/coal dust replacement as the carbonaceous material gave veryhigh emissions of VOCs, but also exhibited very low sand sticking (seesample 3 of EP1800771A1). ln contrast a foundry sand where thecarbonaceous material consisted of only coke, gave very low VOC emissions,but on the other hand high amount of sand sticking (see sample 1 ofEP1800771A1). ln EP1800771A1 it was further proved that a carbonaceousmaterial comprising powdered pit coal and coke, with coke as the mainconstituent of the carbonaceous material, gave not only reduced VOCemissions, but also an acceptable level of sand sticking or sand adherence.The carbonaceous material additive as disclosed in EP1800771A1 hasshowed to be in particular efficient for smaller work pieces.

The present document discloses an inventive carbonaceous materialadditive that is particularly suitable for larger work pieces. lt may thus be usedin a process of casting a part of iron having a mass of 10 kg or more,preferably 20 kg or more, 50 kg or more or 100 kg or more and in a processof casting a part of iron having a smallest wall thickness of 10 mm or more, orpreferably 20 mm or more.

The carbonaceous material may be added to the foundry sand or material in a rangefrom 0.5 to 10 % by weight of the foundry sand.

The carbonaceous material additive may be added to the foundry sand or materialgiving a measured carbon content in a range from 1.5 to 4 % by weight of thefoundry material or sand. ln this respect the difference between the expressions“carbonaceous material", which is the material that is added to the foundrysand mixture and the “carbon content", which is a measured value of the totalcarbon content in the foundry sand mixture is to be noted.

The carbonaceous material may also comprise coal dust replacement,preferably in an amount of 20 % by weight of the carbonaceous material or less. The amount of coal dust replacement may be less than 10 % by weight,preferably less than 5 % by weight or less than 2 % by weight. The coal dustreplacement may be selected from a group consisting of carbon containingmaterial such as pyrolytic or lustrous carbon former in solid or liquid formsuch as asphalt, gilsonite, petroleum destillates, organic polymers, dextrin,and starch. The organic polymer may be for instance polystyrene.

Trial The carbonaceous additive according to the invention was tested in an actualfoundry for industrial manufacture of cast iron. lron engine blocks, i.e. workpieces having a weight of more than 10 kg, and a minimum wall thickness of10 mm or more, were casted in a trial to test the possible reduction inemissions by using the additive, and how the additive affected the sandsticking or sand adherence to the work piece, i.e. if the additive could be usedin a production effective manner.

The carbonaceous additive was added to the moulding material orfoundry sand to give measured carbon content in the moulding material ofaround 1.5 to 4 % by weight.

The measurement if the carbon content in the moulding material orfoundry sand is well-known to the skilled person and routinely performedbefore each new casting cycle. lf the carbon content is too low morecarbonaceous material will have to be added.

The carbonaceous material added to the foundry sand comprised 40 %by weight of the carbonaceous material coke, and 60 % by weight of thecarbonaceous material pit coal or powdered (pit) coal.

The carbonaceous material was added to the foundry sand in a rangeof from 0.5 to 10 % by weight of the foundry sand. The amount added will bedependent on the desired and/or measured carbon content of the foundrysand, and will vary from foundry to foundry, and be dependent on the type ofwork piece that is to be casted.

A mould was made from the mixture of the carbonaceous material andthe moulding material. The emissions and smoke from the casting processwere led off via a ventilation duct, where the VOC emissions were measured.

The VOC can be measured using different types of measurementmethods known to the skilled person. One such method is by using FlDinstruments (gas chromatography with flame ionization detector) or by using so called Tenax ® tubes followed by analysis with gas chromatography andmass spectrometry (GC-MS). The FlD instruments measures the total VOCemission, including methane. Tenax tubes may further allow for analysis ofthe various hydrocarbons except for the lightest such as methane and can beused as a complement in a measuring process. ln the above described casting process FlD measurements weretaken continually during the entire casting period, i.e. during casting, coolingand shale-out. All of the samples were taken from the ventilation duct.

The values of the VOC emission from the casting process usingthe inventive carbonaceous material was compared to VOC emissions whenusing a conventional carbonaceous material, such as powdered coal, i.e.powdered pit coal.

The trial clearly show that VOC emissions have been reduced for whenusing the additive compared to a conventional pit coal additive, i.e. theinventive carbonaceous material additive yields much lower VOC emissionthan conventional pit or sea coal dust or powdered coal.

When these products and additives are introduced in foundryproduction, it is standard practice to start with a combination of ordinarycarbonaceous material additives and the inventive additive. The usualproportion of the latter is approximately 50%, which is then graduallyincreased. VOC emissions are thereby reduced to a corresponding degree.

The measured VOC emissions in the above described trial wereultimately reduced by up to 50 % by using the inventive carbonaceousmaterial additive, while still giving an acceptable sand adherence and thusgood working efficiency of the foundry sand.

Claims

1. A carbonaceous additive for a moulding material for casting iron, characterized inthat the carbonaceous additive comprises coke in an amount of 25 % by weight of thecarbonaceous material or more, but less than 50 % by weight of thecarbonaceous material, pit coal in an amount of 45 % by weight of thecarbonaceous material or more, but less than 65 % by weight of thecarbonaceous material, and optionally coal dust replacement in an amount of20 % by weight of the carbonaceous material or less, and in that the amountof pit coal is greater than the amount of coke.

2. The additive as claimed in claim 1, wherein the amount of coke is 35-45 % by weightof the carbonaceous material and the amount of pit coal is 55-65 % by weightof the carbonaceous material.

3. The additive as claimed in claim 1 or 2, wherein the amount of coaldustreplacement is less than 10 % by weight, preferably less than 5 % by weightor less than 2 % by weight.

4. The additive as claimed in any one of the preceding claims, whereinthe coal dustreplacement is selected from a group consisting of carbon containing materialsuch as pyrolytic or lustrous carbon former in solid or liquid form such asasphalt, gilsonite, petroleum destillates, organic polymers, dextrin, and starch.

5. Use of an additive as claimed in any one of claims 1 to 4, in aprocess ofcasting a part of iron having a mass of 10 kg or more, preferably 20 kg ormore, 50 kg or more or 100 kg or more.

6. Use of an additive as claimed in any one of claims 1-4, in a processof casting a part of iron having a smallest wall thickness of 10 mm or more, orpreferably 20 mm or more.

7. A moulding material comprising:sand in an amount of 80-95 % by weight of the moulding material,binder in an amount of 4-15 % by weight of the moulding material, and5 the additive as ciaimed in any one of ciaims 1-4 in an amount of 0.5-10% by weight of the moulding material.

8. The moulding material as ciaimed in claim 7, wherein the additive isadded in an amount providing a carbon content in the range of 1.5 to 4 % by10 weight of the moulding material.