industRy CylInDer HeaDTOMORROW’S CYLINDER HEAD PRODUCTIONECOLOGY, ECONOMY AND
MATERIAL ENHANCEMENT BROUGHT IN LINE

BMW presently runs the first emission-free foundry worldwide
in the company’s landshut plant with the production ofshaping sand cores. In tight cooperation with aSK Chemicals,
BMW light-Metal Foundry changed over the core production
from customary organic binders (“the glue for the sand”)
to the environmentally-friendly inorganic binder system Inotec.

48

aUTHOrSdR. techn. emmeRich weissenBekis Project Manager Inorganic
Bonded Sandcores at the BMWlight-Metal Foundry in landshut(Germany).

dR.-ing. thomas kautZ

is Manager Core Shop at the BMW
light-Metal Foundry in landshut(Germany).

diPl.-ing., diPl.-wiRt.-ing.
JÖRg BRotZki

is Head of Corporate application
Technology at the aSK Chemicals
GmbH in Hilden (Germany).

dR. ReR.nat. Jens mÜlleRis Head of Product Management
Inorganic Binder Systems at theaSK Chemicals GmbH in Hilden(Germany).

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intRoduction

Such inorganic binders basically consist ofsilica sand dissolved in water, which meansthat hazardous emissions are next to none.
Apart from the environmental aspect, theinnovative process offers significant
advantages with respect to component
strength which is considered the main
engine feature as well as to quality andcosts. This article both highlights thechemical background of the sand core
manufacture as well as the advantages
for the casting process.
Presently, the inorganic core manufacture is one of the greatest challenges forthe foundry industry. Beside the positive
impact on strength properties, quality andcosts, it is the potentials especially concerning sustainable and environmentallycompatible production that will demand
the change-over from sand core manufacturing to die casting in the next years.
Since BMW Group is playing a pioneering role in implementing both efficient
dynamics with every vehicle as well as
efficient environmental protection (seealso BMW Sustainable Value Report 2010[1]), the casting production with inorganic bonded sand cores represents an important contribution to the strategy of sustainability. BMW Light-Metal Foundry pickedup this relevant issue in 2005 and initiateda development partnership with ASK
Chemicals [2, 3]. The complex development and conversion scenario in full operation, also called “brown field approach”
is completed by now [4,5]. Only inorganic
sand cores are being employed in the current die series production. Until now, approximately 7 million sand cores havebeen blown, and approximately 2 million
casting pieces have been produced – among
which a total of approximately 1 million
cylinder heads, whilst having saved 4000 tof CO2.
Among all engine components, the cylinder head is by far the most crucial one
in respect of properties concerning thefunctional behavior, thus setting extremely
high demands for the casters. The constructional goal is to combine as manyfeatures as possible in the most confined
space while simultaneously maintaining
the basic physical properties such as durability and material strength. The following
casting processes are nowadays popularin foundries:: die casting: lost Foam Process: sand casting: high-pressure die casting.
Almost 90 % of all cylinder heads inEurope are being produced with die casting. During this process, the outer contours of the casting are modeled by permanent molds (so-called dies). The innercontours of a cylinder head, such as waterjacket, gas exchange and oil channels aswell as possibly other integrated functions
or channels are modeled by sand cores.
The sand cores are positioned into the die
immediately prior to pouring – either individually or assembled to a core packet.
Since the construction is becoming increasingly compact with filigreed channels
and a substantially reduced wall thickness
all over the cylinder head, the sand coreproduction is often enough considered themost complex task within the castingprocess.
coRe making

In order to yield absolutely sand-free casting pieces for further processing, duringcore making, especially for cylinder heads,
it must be ensured that both mold material and binder system can provide:: excellent dimensional accuracy: clean and smooth surface: superior thermal stability: good shakeout (binder collapsibility).
The classical binder is generally a phenol
resin which is mixed together with thepoly isocyanate and the mold material(silica sand). The ready mixed sand is thenvirtually “blown” inside the core making
machine under high pressure into the corebox. The curing is done with a tertiaryamine catalyst, which is very powerful
und takes just a couple of seconds. The
whole core making process can be realized in less than a minute. The cores canbe handled immediately after the process,i.e. assembled into core packages andpositioned into the die. Binder amounts
for aluminum casting typically range
about 0.6 weight% per component.
This core making process, however, isknown for the negative aspect of amineemissions, especially during unfavorable
manufacturing conditions. If the chemicalcomponents come into contact with the
hot metal during pouring, BTX emissions,
CO and CO2 are likely to develop during

49

Industry Cylinder Head❶ Description of Inotec core making process sequence

combustion. After pouring, the moldmaterial is reconditioned either mechanically or thermally [6] and re-inserted into
the core making process and recycled.
Requirements for theInotec Process &Chemical BackgroundA large number of system properties havebeen a significant challenge for the development of a novel, environmentally-friendly
binder with the following features::: good flowability of the core sandmixture:: good strength level immediately after
core manufacture:: superior hot strength of the cores:: good storage stability:: productivity comparable to the customary core making processes – if not
improved:: recyclability of the core sand:: odorless during core production andpouring:: no harmful gasses during core production and pouring:: good shake-out after pouring:: no condensate formation on the die.
Inotec is a binder on silicate basis, which
in simple words is nothing but silica sanddissolved in water. It has some affinity to
the waterglasses employed in the sodium
silicate (CO2) process. Contrary to the CO2
process, however, the curing is not entirely
a product of chemical reaction but rather50

a combination of physical drying process
and chemical reaction. This is the reason
why the Inotec process requires heatedtools. The tool temperature (150 to 200 °C)
not only drives the water (solvent for thesilicates) out of the core but also initiates
a chemical reaction which leads to a crosslinking of the silicate molecules. Water isagain formed as a by-product of the crosslinking. Chemically, this process is called
condensation reaction, which means that
two molecules bond, while simultaneously
separating a smaller molecule, i.e. waterin this case. During curing, water is re­­leased from two different sources (solvent+ reaction by-product). Ideally, this che­­mical-physical curing process is favoredby hot purge air (approximately 150 °C)
in order to reduce the cycle times duringcore making and to make sure that themoisture is driven from the core to a 100 %,❶. The residual moisture remains in thecore and becomes visible as water vapor
during pouring.
The curing reaction is in part reversible(balance reaction). This means that energy
and water (i.e. elevated temperatures andhigh ambient moisture) are able to initiate
a reverse reaction which eventually dissolves the cross-link of the silicates. Inconsequence, the cores lose strength andbreak.
This can be avoided by removing thewater component out of this balance, i.e.
by storing the cores in a dry environment.
Since this is not always easy in practicaloperation, additives are used to substantially decelerate this reverse reaction andto allow for a process reliable core handling even following “regular” storage.
Advantages of the Inorganic
Binder System Inotec❷ shows the pouring of a cylinder headmodeled with organic sand cores. Boththe smoke and the typical foundry smell
developing in the process are combustion
products deriving from the incineration oforganic binders contained in the sand❷ Core gas developing during casting a cylinder head made with organically bonded cores

tion residues) on the tools is often thecause, which has to be eliminated regularly by means of CO2 blasting with dryice. The physical strain for the workers
dealing with the hot dies is quite high,not to mention the high degree of noise
pollution in this area. Casting with inorganically bonded cores reduces thisintensely costly and energy-consuming
cleaning procedure by more than 75 %,and the noise, of course, too. Anotheradvantage is the omission of expensive
exhaust air system cleaning, and the useof hazardous materials, e.g. peroxide, in
waste air purification plants is no longer
necessary.
Advantages for
Component Strength and Lightweighting Potential❸ Combustion residues (condensate) during a lab casting test (left: conventional organic binder;
right: new inorganic process)cores. The result of an equivalent test
tube trial, ❸, is shown left for the organic
binder and right for the environmentallyfriendly inorganic binder. Both variants ofbonded sand are each heated up in therespective test tube until reaching pouring
temperature.
The organic smoke (exhaust fume) condenses on the test tube wall, leading to avisible color change. The test tube on theright (with the inorganic binder) does notshow any signs of condensation even after
having been heated up to pouring tempera­
ture. The organic smoke and condensate
formation has a negative impact on manyfactors, such as::: working conditions for the employees:: component strength:: cycle time:: equipment and tool service life as well as:: purification of exhaust air and theresulting consumption of energy.
Advantages for the Employees

The omission of amine catalysts duringcore making and the absence of smoke
during pouring provide for an improved
working environment with substantiallyreduced odor development. When castingtakes place with organically bonded sandcores, condensate precipitation (combus-400

14300

12250

10200

8150

6100

450

200Precedent (organic)

New engine (inorganic)❹ Strength levels in comparison; casting results with conventional organic binder system vs. new cylinder
head for R6 in-line Diesel engine made with inorganic binder systems

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Volume 72

Breaking elongation [%]Strength [MPa]350

16Rp(0.2)
Rm
A5

The combustion byproducts of the corebinders getting in contact with the hot
aluminum in the mold cavity (the die)are not only harmful to the workers
involved, but also to the process as awhole. Similar to moisture precipitations
on windows during winter, reaction
products in the form of condensate areto be found in the tools as well as in theextraction and hall venting systems.
The lower the ambient, i.e. the tool temperature, the higher the condensate pollution. By implementing the inorganiccore manufacture in the Light-Metal
Foundry of BMW Group in Landshut, it
has become possible to realize accelerated solidification speeds (up to – 20 %)with significantly cooler casting tools(< 100 °C instead of > 200 °C), whilst
improving the component strength(reduced dendrite arm spacing) andsimultaneously lowering the cycle times
under the aspect of cost efficiency. ❹shows a comparison between the component strength obtained for the new cylinder head of the BMW six-cylinder in-line
engine [7, 8]. The improved component
strength is of vital importance for the de­­velopment of new fuel efficient and highly
supercharged engines with higher ignitionpressure and higher power density.
Energy Consumption,
CO 2 and Cost Advantages

With reference to a comparative evaluation of inorganic and customary organic

51

industRy CylInDer HeaD

binder systems in foundry operation, it isessential to view the whole process
chain. The higher capital expenditure in
the core shop will be compensated for in
the process chain. As compared to thecurrently used core making methods, themanufacturing costs focus at a comparable level [5, 6], whereas the core box
maintenance costs are getting lower due
to less dirt. This guarantees higher efficiency during casting. The total absenceof organic components also provides two
decisive advantages for the components
during pouring and cooling: significantly
prolonged cleaning intervals and shorter
cycle times.
The main optimization potentials in thecasting process given by the use of inorganically bonded sand cores are:: cycle time: - 15 %: productivity: + 15 %: tool maintenance: - 50 %: tool service life: + 25 %.
Apart from the cost saving potentials, also
the reduced energy consumption plays animportant role. Cleaning requirements are
drastically reduced, and the dry ice demand
shrinks to a minimum. Cost cutting becomes most effective, though, in the areaof the waste air extraction system. Until
recently, the aluminum foundry of BMW
Group in Landshut has been paying a natural gas bill over 400,000 Euros per year
for waste air treatment (thermal afterburners). With the complete conversion
to inorganic core making, this matter of
expense as well as the CO2 equivalent,
have become a thing of the past. ❺ shows
the CO2 equivalents of different core making processes.
PRosPects

The conversion of the core shop to inorganic binder systems has brought aboutcompletely new potentials regarding
component strength, sustainable manufacture, productivity and component

52❺ Comparison of CO2 consumption with various casting and core making processes

quality. Process-inherent cutbacks referring to the die casting layout may now bereconsidered. Especially for high-performance engine key components suchas cylinder heads and crank cases, thecasting technique now provides additional potentials for improved strength
which is a relevant contribution towards
downsizing. Thus, “BMW Clean Production” forms the technical basis for “BMWEfficient Dynamics”. This means a vast
improvement of working conditions
inside the plant and of living conditions
for the residents as well. A new ecologically and economically improved state oftechnology has been already defined. As
far as highly developed countries withstringent environmental regulations areconcerned, this favorable development
also provides competitive advantages
and will be sooner or later part and parcel of environmental legislation.

RefeRences[1] BMW Sustainable Value report 2010[2] Müller, Koch, Frohn, Weicker, Körschgen,
Schreckenberg: Inotec – Das praxisbewährte
anorganische Bindersystem, Gießerei 95 (2008),
no. 1 P. 44 – 48
[3] Weissenbek, Willimayr, Wolf: BMW leichtmetallgießerei setzt auf anorganisch gebundene
Kerne, Gießerei 95 (2008), no. 6, P. 30 – 33
[4] Kautz, Weissenbek, Blümlhuber: anorganischeSandkernfertigung: ein Verfahren mit Geschichte.
Gießerei 95 (2010), no. 8, P. 66 – 69
[5] Weissenbek, Hübner, Kautz, Blümlhuber:
nachhaltiger leichtmetallkokillenguss durch anorganische Sandkernfertigung. aTZ Produktion 3(2010), no. 03/04, P. 62 – 67
[6] Schwickal, Hoffmann, Weissenbek, Blümlhuber:regeneration von anorganisch gebundenen Gießereisanden. Gießerei 96 (2009), no. 9, P. 52 – 56
[7] Weissenbek, Willimayr, Blümlhuber, Stastny:anorganische Kernfertigung für hochbelastete
Zylinderköpfe am Beispiel des neuen BMW Sechszylinder Dieselmotors, Magdeburger Symposium
Gießtechnik um Motorenbau 2009[8] Pabel, Kneißl, Brotzki, Müller: anorganischesBindersystem: einsatz von Inotec-Kernen für deutlich verbesserte mechanische eigenschaften von alGussteilen Giesserei-Praxis 11 (2009), 359 – 366.

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