243 01 Cold Box Process

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N ew Sand Reclaimed Sand

As Gassed 350 310

1 Hour 495 410

24 Hour 550 515

Humidity Resistance 320 260

New Sand Reclaimed Sand

Loss on Ignition 0.15 2.29

Average Grain Size 280 291

Fines Content 0.150 0.25

Dust Content 0.00 0.00

Introduction

Developed over 30 years ago, thePolyurethane Cold Box Process(PUCB) is still the most popularorganic cold box technique forthe automated production ofhigh volume cores in bothferrous and non-ferrousfoundries.

The reason for its popularity isbased upon several factors suchas high out of box strength, highproductivity levels, excellentbreakdown properties and cost.

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FOSECO has recently introduced newtechnologies with the emphasis onadding value for the customer byimp rovin g key areas such as productivity,low er VOC (volatile organic comp ounds)

emissions and by reducing w aste.

The follow ing case studies are goodexamples of these new technologies inaction.

Recent developments in the application of thePolyurethane Cold Box process

PSA Peugeot-Citron Sept-Fons Site. Thedevelopment of a new PUCB binder foruse on mechanically reclaimed sandbased on low VOC solvent technology.Environm ental regulations and laws for

the protection of the external environm entand the internal w ork place are having amajor im pact on foundries using chemicalbinders . Nowadays the foundry in dustrydemands new developm ents in chemicalbinders which wi ll offer excellentperform ance but have little or nodetrimental effect on the environm ent.The present challenge for all major bindersuppliers is to develop and supply bindersystems that offer lower monomercontents and improved environmentalproperti es such as the use of solvents and

other additives that conform to ever morestringent health and safety requirem ents.

PSA Peugeot-Citron Sept-Fons site is one such fo undry that is d rivingbinder suppl iers to take up the challenge.

To pr oduce all these castings, the foundry uses a tremendou s amount ofsand. Due to the stringent legislation appertaining to the dumping ofwaste sand and the ever i ncreasing costs of new sand, the Sept-Fonssite has intro duced a dry attritio n sand reclamation process.

Mechanical and m agnetic treatment of th e sand:The sand coming from the shake out (mix of moulding sand and coresand, burnt or unburnt) is treated:

Magnetically separate green sand Mechanically to elimin ate the resin residuesThe reclaimed sand is used at 100% in the coreshop.

The challenge for the bi nder supplier w as to develop a system thatwou ld gi ve the same strength characteristics as for new sand as well aslowering the emissions of aromatic hydrocarbon solvents, withoutcompromising casting quality.

Using a conventio nal PUCB resin system based on arom atic solvents,revealed that o n reclaimed sand the core strengths w ere 20% lower t hanwith new sand and in addition the bench life of the mixed sand wasmuch short er. Obviously a novel approach to th e chemistry of the bi ndersystem was needed.

Case study 1

Type of Casting Tonnes Produced

Cylinder Blocks 61,163

Brake Discs 44,192

Brake Drums 11,721

Total 117,076

Table 1 Foundry output 2003

Table 2 Sand properties (base sand Silfraco LA32)

Table 3 Strength development comparison

Values are transverse strength N/cm 2 based on a tot al binder content

of 1.2%. Humidity Resistance = 24hours at 20o

C / 95% Humidity.

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Aromatic Solvent System Politec* E2000 / E9000

Benzene 13 ppm 3 ppm

Toluene 10 ppm 2 ppmXylene 15 ppm 1 ppm

Table 5 Comparison of VOC emissions during the casting process

New Sand Reclaimed SandAs Gassed 365 325

1 Hour 310 275

2 Hours 280 200

3 Hours 245 150

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Table 4 Bench life properties

Values are transverse strength N/cm 2 based on a tot al binder contentof 1.2%.

The simple solution to increase strength on reclaimed sand would beto i ncrease the resin additi on, how ever, there are clear disadvantages

associated with this:

Reduced sand flowability requiring higher blowing pressures Higher blow pressures would cause resin wipe off and sticking of

the cores Higher binder levels would result in poor core breakdown and core

shakeout Higher binder levels would also increase the risk of casting defects

associated with lustrous carbon and gas evolution Higher process costs

Clearly an increase in resin content w as not a satisfactory solutio n andas such, alternative solutio ns woul d need to be identif ied.

A new binder was selected based on two novel manufacturingprocesses. Firstly, a route w as identified w hereby w ater could beremov ed in pr ocess mor e efficiently. This resulted in a signif icantchange to the molecular structure of the resin resulting in a much morereactive resin that enabled high er out of box strength s to be achieved.

The second development route was based on the introduction of newlow aromatic solvents. These had a significant im pact on the levels ofVOC emissions particularly d uring the casting stage.

Aromatic Solvent Politec E2000 / E9000System

As Gassed 310 350

1 Hour 420 480

24 Hour 550 600

Humidity Resistance 250 350

Table 6 Strength development comparison: Politec E2000 / E9000 on reclaimed sand

This new development resin system,Politec E2000 / E9000 has now beenestablished at PSA Peugeot-Citro n Sept-Fons Site for use throughout the core shopusing reclaimed sand (figure 1). Thissystem has met the technical requirementsin terms of strength perfor mance andenvironmental improvements withadditional process benefits such as goodbench life, humidity resistance and castingquality being achieved. A further benefithas been a reduction in r esin w ipe offwhich in turn reduces box cleaning thusimproving productivity.

Figure 1 Core assembly at PSA Peugeot-CitronSept-Fons Site

Values are transverse strength N/cm 2 based on a tot al binder content of1.2 %.


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TMA: The application of (TMA)Tri-methylamine using new aminegenerator technologyThe choice of am ine for use as a trigger inthe PUCB process is based upon thefollow ing factors; reactivity, odour, costand the ease at which the ami ne liquidcan be vapourised and injected into asuitable inert carrier gas (usually hot air).This carrier g as penetrates the mou ld orcore mass promoting a reaction between

the resin and MDI (Methl y Di-Isocyanate)components.

Several amines have b een usedsuccessfully, how ever, they all haveprocess limitations, for example TEA(Tri-Ethyl Amine) is not very reactiveresulting in higher am ine demand, it alsohas the highest boiling point making itdifficult to keep in a vapour form, leadingto condensate form ing in the gas supplysystem. DMEA (Di-Methyl Ethyl Amine),is more reactive and has a lower boiling

point but has a greater odour and istraditionally m ore expensive.

FOSECO recently introduced a new aminefor use with the PUCB process based onTMA. This amine is significantly morereactive than DMEA resulting i n extremelylow application rates, which if appliedusing specifically designed am inegenerators gives rise to low levels ofodour in use.

Furtherm ore the in crease in reactivity and

low application rates means that higherprodu ctivity gains are achieved by usingshorter gassing and pur ge cycle times,making t he overall p rocess costs lower.

TMA exists as a gas at room temperature,compared to other traditional amines,wh ich are liquid. Based on this diff erencea new approach had to be found in termsof injecting TMA into the carrier gas

Case study 2stream to ensure that pro cess reproducibilit y could be achieved. Initiallya TMA generator was developed which involved heating the TMA gascylinder above 65 oC to achieve a high p ressure enabling TM A gas to bedrawn off and in jected into the carrier gas. Whilst several generators ofthis type have been buil t and com missioned successfully in severalfound ries a number of technical concerns needed to b e resolved. Themajor concern was that as TMA was drawn out of the gas cylinder thepressure dropped. To m aintain pressure, and thus ensuring consistentflow application rates, more heat had to be put into the cylinder, thisproved difficult especially at low volumes of TMA within the cylinder.In addition, when the TMA was exhausted, a new cylinder had to beheated to the required temperature to achieve working pressureresulting in production down time. A final obvious concern was thehealth and safety issue concerning t he basic principle of heating g ascylinders containing TMA having a low flash point.

Clearly a better design based on the use of cold TMA had to be foun dif the benefits of this new amine technology were to be exploited.Reviewin g a combin ation of existing gas application techniques andlooking at new developm ents in low level metering devices a proto typeTMA generator was built with the co-operation of Omega FoundryMachinery Limited.

TMA GeneratorTMA is now supplied in a dual port syphon cylinder which whenpressurised with a constant nitrogen pressure at ambient temperatureenables liquid TMA to be drawn from the cylinder. As the TMA is at afixed pressure the flow rate from the cylinder remains constant.

The liquid TMA is then atomised at the point of entry into the carrier gasstream using a low level atomiser capable of atom ising 1cc of ami ne percycle. To achieve this level of accuracy a digital pressure control systemprior to the atom iser removes any pressure spikes.

The above process is built in to a generator p ackage which suppli es thecarrier gas at the required tem perature, controls gas and purge cycletim es through an on board PLC system and allow s variations to be madein term s of carrier gas application pressure. As this system allow s theuse of TMA as received, no down tim e is necessary wh en the cylinder isexhausted, bottl e change can be made in l ess than 1 mi nute. A fur therbenefit can be achieved by using a mu ltiple gas cylinder manif old orbulk TMA supply, in that th e operator does not have to handle the amin ecomponent resulting in the elimination of a hazard risk.

This new concept generator (figu re 2), has undergone fi eld applicationstudies and the results observed show t hat this pr ocess has a lot to of ferparticularly in terms of improved productivity and the safe handling andapplication of a very reactive amine.


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Cope/ Drag Assembly Water Jacket Inlet Port Core

Machine Cycle Time : DM EA 56 seconds 43 seconds 42 seconds

Machine Cycle Time : TMA 43 seconds 37 seconds 35 seconds

Cores per Hour : DMEA 64 84 86

Cores per Hour : TMA 84 97 103

Cope/ Drag Assembly Water Jacket Inlet Port Core

Total Binder Content (BOS) 1.3 % 1.4 % 1.1 %

DMEA Addition Rate (BOR) 16.7 % 32.2 % 31.46 %

TMA Addition Rate (BOR) 3.85 % 3.98 % 5.45 %

Cost/ Tonne of Sand : DMEA 21.95 26.68 20.85

Cost/ Tonne of Sand : TMA 20.42 22.04 17.80

Amine cost saving 6.9% 17.4% 16.6%

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Table 8 Comparative productivity rates

Table 9 Foundry case study : Cost in use comparison, TMA vs. DMEA

Figure 2 TMA Amine generator

Table 7 Comparison of Physical Properties of Commercial Amines

TEA DMIA DMEA TMAChemicalFormula (C2H5)3N (CH 3)CHN(CH 3)2 C2H5N(CH 3)2 (CH3)3NMolecular Wtg/mol 101.2 87.1 73.1 59.1Boiling Point 0C 89 65 35 3Vapour Pressurembar (20 0C) 69 170 580 2200

DMIA: Di Methyl Iso Propyl Am ine


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Case study 3Reclaimed Shell Sand for t he production of PUCB cores,the reduction of a waste sand stream.RSM Castings is a repetition iron foundry producingautomotive, hydraulic and general engineeringcomponents in grey and SG Iron using the shell mouldand core process.

Four years ago, RSM Castings invested in 2 corebelters(figure 3), to enable them to produce PUCB cores sothat they could eliminate the sub contract purchase ofcores and convert some shell production to PUCB to

reduce costs.

It soon became apparent, however, that produ ction costswere increasing significantly due to r ising costs inrespect to new sand purchase and also the ever-increasing cost of sand disposal

With assistance from FOSECO, RSM Castings began astudy to investigate the feasibility of using the wastesand stream f rom its shell mould ing pr ocess as areplacement for new silica sand i n it s PUCB process. ThisPUCB process being based upon a 50 AFS grade new

silica sand, bonded w ith FOSECO Poli tec XP1000 / XP1080 PUCB binder system in conjunction with TEAamine. RSM Castings produce approx imately 250 tonnesof waste stream shell sand per month.

Figure 3 Corebelter

Initial chemical examination of this waste stream showedthat the level of bin der residue was very low, typically0.4% due to the low sand to metal ratio associated w iththe shell process resulting in excellent therm alcombustion of the organic component. The mainconcern, how ever, was the increase in alkalinity o f thesand, caused by ox ide residues melting and for min g analkali coating o n the sand gr ain. It is known i n the PUCBprocess that high alkali sands can give technicalproblems such as low out of box strengths and anincrease in amine demand which in turn results inreduced productivity.

Trials were conducted using a pilot dry attrition plant tosee if this increase in alkalinity wo uld be detrimental tothe process prior to embarking on any capital outlay onnew equipment.

Several tonnes of shell sand were processed ready forevaluation o n one of the production corebelters. A sampleof this sand was tested and the results indicated that thealkalinity was even higher t han the init ial w aste streamsample, this high alkalinity being due to the very highdust content of the sand, the pilot plant had no extractionsystem at this tim e. It was decided, however, that thi ssand w ould be evaluated on a trial production basis withbinder levels being increased to compensate for theincrease in AFS and surface area of the sand caused bythe high dust content. The resultant cores produced(figure 4), were surprisingly of excellent quality in t ermsof edge retention and strength, it w as also noted that theamine dosing and purge times did not need adjustment.

Figure 4 Cores (reclaim)

Castings from these cores were produ ced withcomparable results in surface finish to castings m ade innew sand and with the added benefit of a reduction inthe amount of veining defects .


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From these positive results, further qu antities of w astestream sand were treated on the pilot plant, with a dustextraction system fitted, and the pro duction exerciserepeated with standard bi nder addition levels. Onceagain good qu ality cores and castings were prod uced(figure 5).

Figure 5 Castings

RSM Castings were pleased wit h th e observed resultsand a commercial study confirmed that the purchase of a3 tonnes per hour reclamation plant would give a returnon investment within 12 months.

Based on th is a reclamation plant w as purchased andcomm issioned in September 2003.

RSM Castings are now able to satisfy totally theirrequirem ent for PUCB sand fr om their w aste shellstream. Furtherm ore, RSM Castings supplier of shellsand showed an int erest in the w aste shell stream andare now successfully recoating 100 tonnes per mont hwith a moulding grade shell resin.

Sample AFS Loss On Ignition pH Fines% Dust %

New Silica Sand 50 0.27% 7.40 0.45% 0.01%Waste Stream Pilot Plant 70 0.68% 8.10 10.96% 1.41%No Extraction

Waste Stream 64 0.32% 7.38 0.88% 0.32%Production Plant

Table 10 Sand properties

Sand Total Binder 1 Hour 2 Hour 4 Hour 24 Hour

New Silica Sand 1.2 % 290 310 360 375

Waste Stream 1.2 % 220 265 280 295

Waste Stream 1.4 % 285 325 355 39

Table 11 Strength development comparisonStrength values: Transverse N/cm

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Conclusion

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PUCB New Sand PUCB Waste Stream SandNew Silica Sand 24.00 -

Sand Disposal 10.00 -

Waste Stream Sand * - 0.20

Total Binder 1.2 % 17.59 -

Total Binder1.4 % - 20.31

Total Cost 51 .59 20.51

* Energy cost required to pro cess 1 tonne of w aste stream sand .

Table 12 Commercial comparison

The above case studies clearly demonstrate that th e introdu ction of n ew technology toan existing core process can help foundries to im prove their p rocess costs, whether it isby improved productivity, the reclamation of sand or indeed by looking at alternativemethods for eliminating waste streams. Above all, it is important to continue thisprocess of continuous improvement to ensure that foundries remain competitive andmaintain a working environment that meets current and future Health and Safetyrequirements.

Peugeot-Citron Sept-Fons FoundryOmega Foundry Machinery LimitedRSM Castings LimitedDynea UK LimitedMo ulay Bouhanani : Dynea UK LimitedChristoph Genzler : FOSECOBarrie Jones : RSM Castings Limited

References/ acknowledgments

Documents

243 01 Cold Box Process