mold preparation

8/3/2019 Mold Preparation

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Procedures for making the shown productusing sand casting


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Moulding box with patternboard, base removeThe moulding box is placed topdown with the pattern boardsandwiched between drag andcope. The base board is removed.Note the arrows showing theorientation

Looking into the bottom of themoulding boxThe moulding box is now ready toreceive the pattern

Pattern and runner in positionThe pattern is placed on thepattern board along with thewooden plug that will form therunner

Parting powder applicationThe pattern and runner are lightlydusted with limestone flour whichacts as a parting line to easeremoval of the pattern from thesand without damage to themould


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First covering of sandThe first layer of the oil-boundmoulding sand is sieved over thepattern to ensure a smooth finishwithout disturbing the partingpowder

Topping upOnce the first layer of mouldingsand is pressed into the patternby hand, the mould box is thenfilled with sand

RammingThe moulding sand is rammeddown firmly, using an air rivetterwith a fabricated footplate toensure that the sand contains novoids, and that it will bindtogether for subsequent handling

StricklingThe sand is topped up andconsolidated and then broughtback to flat across the bottom ofthe box by strickling the sand off


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Ready to turnAs Showing the whole box readyto turn. You can see the patternboard between the two halves ofthe box

TurnedThe whole box is now inverted.Note the arrows showing theorientation. You can now see thetop side of the pattern board

Top half removedThe top of the moulding box isnow removed

Pattern board removedWhen the pattern board isremoved the back of the oatternand the runner former are visible.You can also see the partingpowder on the sand


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Replace topThe top is now replaced andbolted down firmly

Top in placeWith the top bolted we are nowalmost ready to fill the secondhalf

GatesBut first we need to placegates which will connectrunner to the pattern

PartingMore parting powder so that themould halves will separate cleanlyand we can easily remove thegate pieces

thethe


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Sprue formerI use a short piece of plastic waterpipe about 30mm diameter toform the sprue. lt is placed on thecentre of the runner oiece andheld in position with a handfull ofmoulding sand

UndoUnbolt the top from the bottom -now comes the delicate bit!

Filled upThe toprammedwas.

now filled andthe bottom box

box isjust as

Lift and separateThe top box is now carefully liftedoff leaving the bottom box as itwas previously


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Top boxThe underside of the top box nowcontains the gate pieces

Rapping the top boxThe gate pieces are rapped with abar to slightly loosen them in theirsand bed and then carefullvremoveo

SprueNext the sprue piece is removedwith a careful twisting and pullingmotion

FunnelformingOn the outside face of the topbox, the sprue hole is carefullyenlarged to form a filling funnelaround 80mm diameter and25mm deep


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VentingTo allow trapped gasses to escapea pattern of small holes is formedthrough the sand in the top box tothe outside world

Runner piece removalThe runner piece is now rappedand removed. You can see thesmall wood screws being insertedand used as handles, just as theyare used on the oattern andgates.

Rapping the patternNow the pattern is rapped andremoved. This also requires asteady hand and a careful straightlift to avoid disturbing the sand With the pattern and pieces allremoved we can now give the

mould a last inspection and a verygentle blow out if any loose grainshave been disturbed

Bottom box finished


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stainless steel scraper to removeany surface oxidation andimpurity. lt is then removed fromthe furnace with a large pair oftongs and poured smoothly andsteadily into the mould. Note thegauntlets and leather apron

Close the boxNow the top box is very carefullyreplaced. The cavity for the metalis now completely formed. Thetwo halves of the box are fittedwith line-up pins so that thealignment remains consistentevery time the parts areassembled

Removed from the sandAfter a 2 hour cooling period thecasting is removed from the sand.Notice the shrinkage visible in thefunnel area because there is noriser and funnel acts as a riser

PouringWhen the brass is fully up totemperature (about 1030 degreesC) the crucible is skimmed with a

mold preparation

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