VACUUM MOULDING PLANTS V-PROCESSdpl-foundry.com/wp-content/uploads/2014/03/V-process_EN.pdf · VACUUM MOULDING PLANTS V-PROCESS ... elimination of subsequent machining in ... mould

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VACUUM MOULDING PLANTSV-PROCESS

VACUUM MOULDING PLANTS

The moulding process for high-quality castings

Vakuum-Prospekt_GB_25.03.08:Vakuum-Prospekt_GB 25.03.2008 9:44 Uhr Seite 1

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MODERN VACUUM MOULDING PLANTS

Sample of Vacuum Moulding Plant VFK 7


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Sample of Vacuum Moulding Plant VFK 7


Sample of a Vacuum Moulding Plant VDK 10

M12M12

M12 M12

M12

M10M10

M10M10

M10M10

M20M20

M30

M30 M30M30M30

M30

M30

M30 M30

M30M30

M30

M20M20

M16 M16

M16M16

M20

M12M12 M12

M12M12

M20M20

M30M30

M30M30

M30M30

M30 M30M30

M30

M30M30

M30 M30

M8M8

M30 M30

M30M30

M30M30

M30M30

M30 M30

M30

M30

M30

M30

M30M30 M30

M30 M30M30

M30 M30

M30 M30

M30 M30M30

M30

M30M30 M30

M30M30

M30M30

M30M30

M8M8

M8M8

M8M8

M6

M8M8 M12

M30M30

M30M30

M30M30

M24M24 M24

M24

M24 M24

M24 M24

M12M12

M12 M12

M12

M10M10

M10M10

M10M10

M20M20

M30

M30 M30M30M30

M30

M30

M30 M30

M30M30

M30

M20M20

M16 M16

M16M16

M20

M12M12 M12

M12M12

M20M20

M30M30 M30

M30

M30 M30

M30 M30

M30 M30

M30M30

M30M30

M8 M8

M8 M8M6

M8M8

M12M8 M8

M8 M8

M30 M30

M30 M30

M30 M30

M30

M30 M30

M30

M30

M30

M30

M30

M24

M24 M24

M24

M24 M24

M24 M24

A

FK-J1-KEL

Ø500

Ø250

Einbauraum für

Winkelverschr.

Einbauraum für

Winkelverschr.

Einbauraum für

Winkelverschr.

Einbauraum für

Winkelverschr.

Winkelverschr.Einbauraum für

M10M10

M10 M10

M20

M20

M20 M20

M20 M20

RR 300x200x16

M20 M20

M20

M20

M20 M20

M20M20M20

M20M20M20

M20

M20

M20M20

M20M20

M20

M20

M20 M20

M20 M20

M20

M20

M20M20

M20M20

M20 M20

M20 M20

M20

M20

M20

M20

M20M20

M20M20

220

M30 M30

M30M30

M30 M30

M30M30

M20M20

M20 M20M20 M20

M30 M30

M30M30

M30 M30

M30M30

HvO5

4

MODERN VACUUM MOULDING PLANTS


HV

O 3

P2 P2 P3

P2

P3P3

P1

P2

P2

P2

P3P2

P2

P2

P2

P3

P2

P2

P2

P2

P2

P2

P2

P2

P2

P2 P2

P2

DR220

DR220

DR220

DR220

DR220

M30

M30M30

M30M30M30

M30 M30

M24 M24

M24M24

M30M30M30

M30M30M30

M30 M30 M30

M30 M30 M30

M30M30M30

M30M30M30

M30 M30 M30

M30 M30 M30

M20

M20

M20

M20

M12 M12

M12M12

M20M20

M20 M20

M20

M20

M20

M20

M12M12

M12 M12

M20 M20

M20M20

M12 M12

M12 M12

M30

M30

M30 M30

M30 M30 M30

M30M30

M30

M30

M30M30

M30

M16 M16 M16M16

M20M20

M20 M20

M20M20

M20 M20

M16M16

M16 M16

M16M16

M16 M16

Rillenkugellager 6221-2RS1 SKFAbgedichtetes CARB Toroidal-Rollenlager C4024-2CS5V SKF

Wellenmutter mit Klemmstück KMFE21 SKF

Rillenkugellager6221-2RS1SKF Abgedichtetes CARB Toroidal-RollenlagerC4024-2CS5VSKF

Wellenmutter mit KlemmstückKMFE21SKF

M30

M30M30

M30M30M30

M30 M30

M30

M30M30

M30M30M30

M30 M30

M30

M12 M12

M12 M12

M30

M30

M30 M30

M30

Sand einfüllen

Deckfolie auflegen

M12

M12

M12

M12 M12M12 M12

M12

M12

M12

M12

M12

M12

M12

M12

M16

M16M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

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M16M16

M16M16

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M16

M16

M16

M16

M16

M16

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M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M16

M20

M20M20

M20M20M20M20

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M12

M12

M12

M12

M20

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M20M20

M20

M20M20

M20 M20 M20M20

M20 M20

M20

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M20 M20M20

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M20M20M20

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M20 M2

0M2

0

M20

M20M20M20

M20M20

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M20

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M12

M12

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M12

M20

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M20

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M20

M20

M20

M20

M20

M20

M20

M20

M12

M16

M16

M16

M16M12

M16

M16

M16

M16

M12

M12

M12

M16

M16

M16

M16

M16 M16

M16M16

GTS 25x35x45x25

M12

M12

M12

M12

M12 M12

M12 M12

M16

M16

M16

M16

M16

M16

M16

M16

M12

M12

M20M20M20

M20M20

M20

M20

M20

M20 M2

0M2

0

M20

M12 M12

M20

M20M20 M20

M20

M20

M12

M20

M20

M20

M20

M20

M20

M12

M20 M20

M20 M20 M20M20

M20 M20

M20M20M20

M20M20

M20 M20

M20 M20

M20 M20

M20

M20

M20M20

M20M20

M20 M20M20 M20

M20 M20

M20

M24 M24

M24 M24

M20

M20

M20

M20

M20

M20

M20

M20M20

M20

M20M20M20

M20

M20M20

M20M20

M20 M20 M20M20

M20 M20

M16

M16

M16

M16

M16

M16

M16

M16

M12M12

Deckfolie auflegen

M16

M12

M12

M20M20

M20 M20

M20M20

M20 M20

M12M12

M12M12M20

M20

M20M20

M20M20

M20

M20

M20

M30 M30M30 M30

M20 M20

M20M20

KSR 16.LO.12.10.15.08

KSR 16.LO.12.10.15.08

EPRM 1

00

Sample of a Vacuum Moulding Plant VDK 6

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6

VACUUM MOULDING PLANTS FOR HIGH-QUALITY CASTINGS

A characteristic feature of the process isthe inclusion of dry, binder-free silicasand between two plastic films with a sub-pressure of 0.3 – 0.6 bar. This canbe compared to coffee or peanuts in avacuum packaging, for example.

What sets vacuum-moulded casting -„Vacuum casting“ apart from others is,above all, the high quality of the surfaceand the excellent dimensional accuracy.On certain conditions it can utilized with-out pattern draft which usually is neces-sary. That means reduction or even elimination of subsequent machining inindividual cases.

Further advantages are:

■ no pattern wear

■ low wall thickness are pourable

■ there are no or only small burrs in themould joint

■ the fettling costs are low

■ the process is environmentally-friendlyand ergonomical favourable

■ Picture 3: Part of a vacuum moulding plant with horizontal mould joint (core setting line).

■ Picture 2: Diagram of the process at horizontal mould joint

■ Picture 6: Finished mould part with vertical mould joint. ■ Picture 9: Finished casting – a slide case DN 400/PN 10, made of nodular graphite iron GGG-40

The pattern is mounted on a closed eva-cuating case - the vacuum box. Both areequipped with numerous vents. Above thethermoplastical plastic film – the patternfilm - which is tensed in a frame, theappropriate radiant heating system issituated.

The warmed-up and so to a high degreeworkable plastic film is lowered onto thepattern. The vacuum box is admitted witha sub-pressure of 0.5 – 0.6 bar and sothe film is sucked accurately to the shapeof the pattern. After that a black wash isapplied on the film.

Radiant heating system

Film holding frame

Pattern film

Mould deaeriation

Air suction ventsPattern

Pattern plate

Suction pipeMoulding box

Sprue cupPattern film

Pattern

Pattern bolster pair


After switching off the vacuum in the pattern carrier, the mould part which iscovered with plastic film on both sidesand still is admitted with the vacuum ispicked-up from the pattern device.

The drag mould is produced in the sameway and rotated by 180° afterwards. Necessary cores are set and the twoflasks are put together to a ready-to-pourmould. The vacuum remains switched onduring pouring and solidifying of themelt.

■ Picture 4: Lowering of the warmed-up pattern film.

■ Picture 7: Casting with set core

■ Picture 5: Pattern with film sucked accurately to the shape by vacuum.

■ Picture 8: Pouring of vacuum moulds with vertical mould joint

During the pouring process the film eva-porates and/or burns when filling in thecasting metal. Because of the vacuum theresidues of the film penetrates into themould and they form a thin shell with thesand particles which compacts the mouldin its skin layer. This process is supportedby the applied black wash.

For shaking out the flask the vacuum isswitched off, the sand flows out and thecasting is free for further handling.

The double-walled flask, equipped withsuction tubes and windows on the inside,is lowered onto the pattern device.

The flask is filled with fine-grained, dryand binder-free sand and is precompac-ted by vibration. The mould part is cover-ed by a plastic film. The sand betweenboth films is pressed together through theatmospheric air pressure by switching onthe vacuum.

on pipe Cover film

7


DIMENSIONAL ACCURACYDependent on the special characteristicsof the vacuum moulding process

■ using very fine-grained, graded moulding sands,

■ high and consistent sand compaction,

■ no wear of the pattern equipment,

■ less or no need of draft,

■ possible elimination of vibration tablefor stripping the pattern off the mould,

■ no movement of the mould wall due tohigh mould hardness,

■ no derformation by volatilizing mould-ing sand additives,

the dimensional accuracy and weightconstancy of the castings are excellent.The same applies to large casting dimen-sions, high casting weights and difficultgeometric moulds. The reproducibility ofthe good values at the serial production isexcellent, from batch to batch there areno differences ascertainable.

Approximately ± 0.3% can be indicatedas a reference value for the dimensionalaccuracy. Further information concerningthe reachable tolerances are given in picture 15.

The accuracy to size and repeatability of the vacuum casting offer the workerexcellent starting conditons; especially therequirements of modern machining tech-niques with NC- and CNC- machines aremet, an adjustment is usually not neces-sary.

In general the following influences thedimensional accuracy:

Is it a so called mould bonded or non-mould bonded size, that means is itformed by one single part of the mouldor by several parts of the mould.

An example for this is given with picture10 showing the table of a millingmachine; its outside dimensions are 1250 x 803 x 143 mm (length x width xheight). Table 1 shows the correspondingevaluation of the measuring results of 10 parts compared to the accuracy gradeGTB 15 which is the exacting general tolerance for grey cast iron according toDIN 1686. At the mould bonded lengthdimension of 1250 mm the range is 0.8 mm, this corresponds to 0.06%;comparatively GTB 15 permits for thisbasic dimension a tolerance zone of 4.4 mm as per DIN 1686.

8

■ Picture 10: Table for milling machine; material:GG-25,size: 1250 x 803 x 140mm, Mass: 560 kg;dimensional evaluation of 10 castings, see table 1.

■ Picture 11: Rope drum; material: GGG-40 orGGG-40.3, dimensions: 790 x ø 650 mm, Mass:280 kg; dimensional evaluation of 15 castings seetable 2

Table 1: Mass and dimensions of 10 vacuum mouldedcastings of the table for milling machines according topicture 10

Serial number Mass Length Width Height[kg] [mm] [mm] [mm]

1 561.5 1250.3 805.2 143.32 560.0 1249.7 804.7 144.33 557.5 1250.5 804.3 142.24 561.0 1250.1 804.4 142.35 558.0 1250.3 804.4 142.56 562.5 1249.9 804.4 142.07 557.0 1249.8 804.2 142.28 561.5 1250.0 804.5 142.89 562.0 1250.3 804.5 142.6

10 558.0 1249.8 803.6 142.3

Desired dimension 1250.0 803.0 143.0

maximum value xmax 562.5 1250.5 805.2 144.3smallest value xmin 557.0 1249.7 803.6 142.0average x 559.9 1250.1 804.4 142.7standard deviation s 2.08 0.27 0.40 0.69range R 5.5 0.8 1.6 2.3

=̂ 0.98% =̂ 0.06% =̂ 0.20% =̂ 1.61%

permissible tolerance range according to DIN 1686 GTB 15 4.4 4.0 2.6

Table 2: Dimensions of 15 vacuum moulded castings ofthe rope drum according to picture 11

Serial number Distance Diameter of the grove peaks of the grove peaks

[mm] [mm]

1 789.7 650.52 789.7 651.53 790.5 650.44 789.8 652.05 790.6 651.46 791.0 650.07 790.4 650.28 790.1 650.49 790.7 651.2

10 790.2 651.511 790.3 651.512 790.2 651.013 790.0 651.214 790.1 651.315 789.7 652.0

Desired dimension 790.0 650.0

maximum value xmax 791.0 652.0smallest value xmin 789.7 650.0average x 790.2 651.1standard deviation s 0.39 0.63range R 1.3 2.0

=̂ 0.17% =̂ 0.31%

permissible tolerance range according to DIN 1685 GTB 15 3.8 3.8


at the production of the pattern.But thisdoes not influence the repeatability of thevacuum moulding process, as shown bythe table.

Parallel walls are a typical characteristicof the rope drum, see picture 11. Theyare perpendicular to the grooves and arevacuum poured without conical form.

Now the wear of the rope is much lessthan in the past because of the high sur-face quality. Table 2 shows measured val-ues for the diameter and the mutual dis-tance of the walls. At the tolerance zoneof 3.8 mm each according to GTB 15

this is only 13 mm (=0.17%) at a mouldbonded distance dimension of 790 mm,however, at the non-mould bonded diam-eter of 650 mm it is 2 mm (=0,31%).

Axle bridges of utility vehicles from whicha rigid axle and a steering type axle areshown in picture 12, may have consider-ably bigger dimensions than the compo-nents mentioned so far. According to thedimension they have piece weights ofapproximately 100 to more than 250 kg.The dimensions of 15 vacuum mouldedaxle bridges are shown in table 3. At anaverage linear dimension of approximate-ly 1614 mm, the difference between thelargest and the smallest size is only 2 mmand that corresponds to a tolerance zoneof 0.12 %; according to GTB 15.5 mmare permissible. The comparison of themass with the axle bridge which has beenproduced conventionaly with green sandcasting before, is remarkable because thesame pattern has been used. Because ofits high mould stability and/or mouldhardness respy the vacuum mouldingprocess lead to a (unmachined part) masswhich was approx. 6 % lower.

The segment shown in picture 13 wasproduced for an underground tunnel ringwith an inside width of 5800 mm. Thearc length is approximately 2200 mm,the nominal value for the width „B“ is1104.9 ±1.5 mm. The evaluation of 445 segments shows that with vacuumcasting the standard deviation „s“ with aprobability of 68% has been reduced toonly 0.5 mm, that corresponds to0.045%. Concerning size, geometry andposition, the accuracies reached eliminatethe need to machine the arc-shapedflanges.

The width dimension of 803 mm is alsomould bonded; its range is 1.6 mm (=0.2% , as per GTB 15 possible: 4.0 mm).At a non-mould bonded height of 143 mm– this is formed by drag and cope mould–with 2.3 mm (= 1.6% is possibleaccording to GTB 15: 2.6 mm) the rangeis higher.

At the width dimension, see table no. 1, itis conspicuous that the desired dimensionof 803 mm is outside the tolerance zonereached in the production. The reason isthat not all influencing variables at thecontraction allowance to be calculatedcould have been taken into consideration

■ Picture 12a: Axle bridge for a steering type axle; material: GGG-40 or GGG-40.3

■ Picture 12b: Axle bridge for a rigid axle; material: GGG-40 or GGG-40.3

Table 3: Mass and sizes of 15 vacuum moulded axlebridges of of utility vehicles


1 149.5 1615.0 182.3 386.02 150.0 1614.0 182.3 385.33 150.0 1614.0 182.1 385.64 151.0 1613.5 182.7 385.35 150.0 1614.0 181.5 384.96 152.0 1613.5 181.6 385.47 150.0 1613.0 182.4 385.38 151.5 1614.0 181.6 385.29 150.0 1614.0 181.8 385.3

10 150.0 1614.0 181.7 384.711 1614.0 181.6 385.612 1614.0 182.4 385.613 1613.0 181.7 384.914 1614.0 181.9 384.315 1613.5 181.8 384.9


=̂ 1.66% =̂ 0.12% =̂ 0.66% =̂ 0.44%

permissible tolerance range according toDIN 1685 GTB 15 5.0 2.8 3.2

9


10

DIMENSIONAL ACCURACYWith a maximum size of only 440 mm theworkpiece, shown in picture 14 – closingcylinder for an injection mouldingmachine - is proportionally small for avacuum casting. As you can see from theevaluation of the measuring result intable 4, the range of the dimensionalvariations is within the „usual“ scope; thisapplies to the mould bonded linear andlatitudinal size as well as to the non-mould bonded measure of altitude.

The averages mentioned in the tables 1 –5 as well as in picture 13 to the size tol-erances are compared in picture 15,dependent on the nominal size, to theaccuracy grade GTB 15 which is thesmallest tolerance series for cast iron withnodular graphite (ends at 800 mm nomi-nal size) and is the smallest toleranceseries for grey cast iron according to DIN 1686. It demonstrates that the per-missible tolerances according to GTB 15

are half by using the vacuum mouldingprocess and even the accuracy gradeGTB 12 according to DIN 1680 isreached. The non-mould bonded sizesare an exception because here the toler-ances are a bit higher.

The experience and tables mentioned sofar have been made available by differentfoundries. To find out possible differencesin production dependent on the foundries,five foundries united to a co-operative

■ Picture 13: Segment for a tunnel ring with a clear opening of 5800 mm in a light-weight construction and evaluation of the latitudinal measure B of 445 castings;material: GGG-50, dimensions: 2200 x 1100 mm, thickness of back wall: 8 mm,Mass: 400 kg

■ Picture 14: Closing cylinder for a plastic- injection moulding machine; material:GGG-40, dimensions: 440 x 440 x 400 mm, mass: 148 kg; dimensional evaluation see table 4.

Table 4: Mass and sizes of 10 vacuum moulded closingcylinders for a plastic-injection moulding machineaccording to picture 14


1 147.6 439.0 440.1 399.62 147.6 439.1 440.2 401.53 148.0 439.4 439.5 401.84 147.9 439.3 439.7 401.45 148.0 439.9 440.0 401.76 147.5 439.7 439.8 401.77 147.9 439.7 440.0 401.58 148.3 439.9 439.9 401.59 148.0 440.3 439.7 401.2

10 148.5 440.0 439.7 402.0

Desired dimension 440.0 440.0 400.0


=̂ 0.67% =̂ 0.20% =̂ 0.16% =̂ 0.60%

permissible tolerance range according to DIN 1686 GTB 15 3.4 3.4 3.4

B


The measuring results of the co-operativetest are also written down in picture 15.This shows that they are within the usualscope. Consequently, the dimensionalaccuracy of the vacuum mouldingprocess is determined by the system,company specific influences are not relevant.

Special advantages will be reached withthe vacumm moulding process if the spa-tial bent functional surfaces can be pro-duced so exactly that a machining is nolonger required due to dimensional accu-racy and surface quality.

This applies, for example, to the blade ofthe ventilator (picture 18) at which differ-ences in position, size and weight as wellas a rough surface would have a nega-tive effect on the resting, the conceptionand the efficiency of the plant.

At a production of 152 pieces the masses of the single pieces only differed by 150 g,that corresponds to a tolerance of 0.2%at an average mass of 75 kg. The thick-ness measurements of all wing blades(wall thicknesses of 4.2 to 13.8 mm) aretaken at 18 measuring points; a deviationfrom 0.1 to max. 0.4 mm has been mea-sured.

test and they worked with the same pat-tern equipment. As workpiece they usedthe table of a milling machine (Picture 16)with a mass of 495 kg which could bepoured horizontally as well as vertically andwhich fit in flasks of different sizes due toits dimensions of 810 x 810 x 140 mm.

Table 5 shows the results of the co-opera-tive test. The linear and latitudinal measureare with 1.5 mm (=0.18%) and/or 2 mm(=0.25%) respy within small tolerance limits, with 0.6 mm – this corresponds to0.43% at a nominal size of 138 mm – thenon-mould bonded measure of altitudehas a range which is a bit higher. With arange of less than 1% a high weight constancy has also been found out.

■ Picture 16: Table of a machine-tool; material: GG-25, size: 810 x 810 x 138 mm,mass: 495 kg; dimensional evaluation see table 5

Nominal size range (mm)

Tole

ran

ce (

mm

)

0 200 400 600 800 1000 1200 1400 1600 18000

1

2

3

4

5

6

GTB 15

■ Picture 15: Dimensional tolerances of vacuum casting in mm (left) and % (right)in dependence on nominal size compared to the accuracy grade GTB 15 accor-ding to DIN 1680, DIN 1685 and DIN 1686.

Nominal size range (mm)To

lera

nce

(%

)0 200 400 600 800 1000 1200 1400 1600 1800

0

0,2

0,4

0,6

1,0

1,2

1,4

0,8

1,6

GTB 15

Sizes depending on mould

Sizes non-depending on mould

The measuring points are mostly average values from 10 – 15 single measure-ments.

Table 5: Dimensions of a vacuum moulded and pouredworkpiece according to picture 16 with the same patternequipment at different manufacturers

Manufacturer Length Width Height [mm] [mm] [mm]

1 811.0 809.0 138.52 809.5 807.0 138.43 810.5 808.5 138.94 811.0 809.0 138.45 810.5 807.5 138.3

maximum value xmax 811.0 809.0 138.9smallest value xmin 809.5 807.0 138.3average x 810.5 808.2 138.5standard deviation s 0.61 0.91 0.23range R 1.5 2.0 0.6

=̂ 0.18% =̂ 0.25% =̂ 0.43%

permissible tolerance range according toDIN 1686 GTB 15 4.0 4.0 2.6

11


12

POURING WITHOUT DRAFTSIn contrast to castings produced by con-ventional methods a draft, at least partial,is not necessary. Through reversing thesub pressure during the moulding process,that means at lifting the part off themould from the pattern equipment (picture 2e), there is almost no frictionbetween pattern and film, so that it is alsoeasy to lift the pattern with a draft of 0°.To fully utilize this process-related benefit, an intensive dialoque betweenthe foundry men and the design engi-neers is highly recommended.

The height of the side walls of the case(picture 17) is 130 mm and they are pou-red without any draft. Aside of the majorimprovements, the number of cores canbe reduced, e.g. the bore holes withsmall diameter are already pre-casted. As a result, machining expenditures arealso less.

Another example can be given from thesection of armatures. The case of thewedge gate valve shown in picture 9 ispoured upright, top flange (picture 19)and both flow flanges are not conical, afacing of the sealing surface is sufficient.

The direct contact between metal andmoulding sand during the pouring can beavoided by applying a coating on the filmand so the surface quality of the vacuummoulded casting is almost independent ofthe casting material. Compared to con-ventional technics it is astonishing that forexample workpieces made of cast ironand cast steel have the same fine surface,even if the pouring temperature andaggresivness of the melt are quite differ-ent.

Picture 20 gives an impression of the highoutline accuracy and the surface qualityof vacuum moulded castings ; the pictureshows a part of a machine piece made ofgrey cast iron with a mass of approxi-mately 200 kg. Here, the pattern filmcracked and had been repaired with atransparent scotch tape before coating.The „shape“ of the scotch tape fixedcrosswise on the casting is clearly visible.

While in the past some authors onlymade verbal comparisons between thesurface of vacuum casting and rolledsteel, in the meantime objective measure-ments have been made and it is possibleto quantify values. Picture 22 a showsthat the depth of roughness Rmax ofvacuum casting is only 80 µm. Alsoshown is a profile screed of dry sandcasting (furan resin bonded, picture 22b)and green sand casting (bentonite bon-ded, picture 22 c).

The surface quality of vacuum casting isso high that, for example, the often usedsubsequent shot blasting may even havea negative effect on the surface rough-ness. The indications of table 6 which arecompared to conventionally mouldedcasting show this clearly. Therefore, shotblasting may be considered as an„enemy“ of the vacuum pouring, espe-cially when it is carried out improperly. –It should be pointed out that the informa-tion in line 1 of table 6 – cleaned withwire brush- is the evaluation of the profilescreed in picture 22.

■ Picture 17: Side flask; material: G-AISi8Cu3,dimensions: 650 x 480 x 130 mm, mass: 11 kg

■ Picture 19: Top flange of the case of the wedgegate valve according to picture 9 (DIN 400) whichis poured without conical form such as the two flowflanges

■ Picture 18: Blade for wind tunnel blower; materialGGG-40, length 750 mm, mass: 75 kg

Picture 11 has already shown such asolution. The walls of the rope drum,O.D. of 650 mm, had to be machined onthe inside previously because of the exi-sting draft, guaranteeing perfect entry ofthe rope. By using the vacuum processmachining is no longer required and thefinished product can be offered with lesscosts.

The used moulding material and the spe-cial production cycle at vacuum mouldinglead to an excellent surface quality of theworkpieces. There are several reasons forthis result. By using a dry, binder-freemoulding sand a so called „bridging“between single sand grains and a differ-ent compacting does not occur whilecompacting by vibration and the follow-ing application of the vacuum and there-fore the casting surface is correspondinglysmooth. In addition, very fine-grainedsand is used, as it is not necessary toconsider the usually indispensable perme-ability to gas off the mould.


SURFACE QUALITYThe roughening of the casting surface byshot blasting is also carried out at con-ventional aluminium-permanent mouldcasting. Usually, it has to be used toremove the oxide film but this does notapply for vacuum castings. In picture 21both surfaces are compared and the dif-ferences are obvious.

Vacuum pouring has also remarkablecharacteristics below the surface – in thesurface layer. There is no casting skin inthe usual sense. On the one hand thecomplete coating of the mould preventsreactions between casting metal andmoulding sand and on the other hand thequenching effect of the dry mouldingmaterial is considerably lower comparedto green sand casting. The latter is alsoshown in table 6 when comparing thelines 2 and 3: Annealing at a temperatu-re of 750 °C does not have an influenceon the depth of roughness after shot bla-sting the vacuum casting. The higher skinhardness of green sand castings, can bereduced by two additional process steps(annealing and shot blasting).

The high quality surface of the vacuumcasting enables painting without using aprime coating, thus reducing productioncost (picture 23). A further advantage ofthe surface quality is that the burr which iscreated automatically at the mould jointnormally is smooth and small, so that it isnot necessary to fettle it.

However, if a burr still has to be grinded,an uneven pressing of the grinding wheelwould be enough to get an uncleanmicrograph at the casting, as picture 25shows schematically; due to high require-ments to the surface quality it has to bechamfered.

■ Picture 20: The crack of the pattern film was repai-red with scotch tape – an accurate detail revealedby applying the vacuum process

■ Picture 21: Surface quality of sandblasted alumini-um-permanent mould casting (above) and vacuumcasting (below), where sandblasting is not neces-sary; V = 5:1 (original: 6:1)

a = Vacuum casting

Perthen Mahr Feinprüf

makrograph perthograph milligraph

b = Dry sand casting

Feinprüf Perthen Mahr

milligraph makrograph perthograph

c = Green sand casting

Perthen Mahr Feinprüf

makrograph perthograph milligraph

Table 6: Influence of shot blasting with steel shot on surface quality of differently produced grey cast iron parts

Condition of treatment Moulding process

Vacuum Dry sand Green sandpouring casting moulding

(Furan resin- (Bentonite-bonded) bonded)

Depth of roughness Rmax (mm)

As-cast condition (unannealed),cleaned with wire brush1) 0.08 0.33 0.27

As-cast condition (unannealed), shot blasted with steel shot in shot-blasting wheel- or hose blasting cabin2) 0.09 to 0.13 0.13 to 0.14 0.23 to 0.34

Annealed at 750 °C, shot blasted in shot-blasting wheel cabin2) 0.13 0.15 0.16

1) Measurements of roughness depth see picture 22 2) With different fines grades of steel shot

13


14

MECHANICAL CHARACTERISTICS

This can be avoided in case a chamfer ison the pattern on the level of the mouldjoint which is not grinded and can beclearly be seen as, for example, a circula-ting ring on the workpiece (see picture25). The burr is integrated almost invisi-ble into this chamfer. However, if there isa mould joint burr which has to be grin-ded, the chamfer is grinded in its comple-te height and/or its width respy, themicrograph is even and in a certain cir-cumference an uneven grinding will notbe noticed.

The good surface of vacuum casting hasa decisive importance and/or is animportant argument for a machine andplant builder in case, these high demandsare reflected on the final product: i.e. „ifit is bought with the eyes“. Functionaladvantages are achieved, too. Because ofthe clean surface filter clothes of vacuummoulded chamber filter plates have a lon-ger life time than in the past.

Differing from other moulding- and/orcasting methods respy. a special coolingbehavior of the melt in the mould hasbeen found out at vacuum moulding pro-cess. At the outset the cooling velocity isheigher for a short time as there is noinsulating gas pad: The melt is in directcontact with the mould wall. After that,the cooling velocity is much lower andthis can be explained by the missing moi-sture of moulding material, the low ther-mal conductivity of the sand and the mis-sing of convection in the moulding mate-rial.

Thereby the strength properties are notinfluenced much and the differences areeven getting lower with the rising degreeof saturation (shown in table 7). Thelower hardness has a good influence onthe machinability. The slow cooling has agood influence on the toughness pro-perties, too.

Workpieces made of GGG-40.3 , forexample, – a type with a guaranteednotch impact energy according to DIN1693 – can be produced without anyproblems in the as-cast condition byvacuum moulding process, if a minimumwall thickness of about 12 mm is given;then an additional heat treatment is notnecessary.

Slow and constant cooling of the castingafter pouring reduces the casting strains.In spite of high demands to the stresscondition of a workpiece in general nostress relief by heat treatment is necessary.

The profitability of vacuum mouldedcasting already starts with the pattern.Because of the plastic film lying lies bet-ween the moulding sand and the patternthere is no direct contact with the pattern.The pattern does not wear and expensivemetal-or plastic pattern are not required.„Simple“ wood pattern with a sufficientstability are enough. Even pattern for conventional machine moulding can beused, the necessary air suction bore holescan also be made later without any problems.

■ Picture 23: Side wall for a printing machine; material: GG-25, size: 80 x 1050 x1280 mm, mass: 480 kg

■ Picture 24: Machine case; material: GG-25, mass: 144 kg

Mould partition

Stress marks

Burr

Mould partition

Stress marks

Burr

Chamfer

■ Picture 25: Mould joint burr above: conventional burr, an uneven micrograph is often created when grinding below: an even micrograph is reached by means of a chamfer which takes upthe burr


PROFITABILITY

High surface quality and low dimsensio-nal tolerances reduce the extent of machi-ning and perhaps it is not necessary atall. The latter mainly applies to mouldingwithout drafts.

The vacuum moulding process offersseveral possibilities to save material andto correspond to the requirements of thelightweight construction. The low dimen-sional tolerances enable a correspondingreduction of the wall thickness of weight-bearing cross sections. Furthermore, com-pared to other methods films, the flowabi-lity of the casting metal between the coa-ted films is better by 20 %, dependentamong other things on the air in themould and the mould emission which aresucked off by the vacuum during casting.

A remarkable convincing example forlightweight construction with vacuumcasting is a tunnel ring consisting of 10segments with an inside diameter of5800 mm, picture 13 shows one of them.By reducing the wall thickness it was pos-sible to approve the economic castingtype and to replace the concrete con-struction used so far. In case of outermeasurements of approximately 2200 x1100 mm a back wall thickness of only 8 mm (!) is realized. The two-sided, arc-shaped connecting flanges are vacuum

casted and ready for assembly, withoutthe necessity of machining; with a latitudi-nal dimension of approx. 1100 mm thefigures of picture 13 give an impressionof the high manufacturing accuracy.

Reduction of mass has a special impor-tance in the vehicle industry because lowdead weight reduces the fuel consumpti-on and increases the load capacity. Mea-sures in this direction are mainly effectiveif the components in question areunsprung, as for example axle bridges,(picture 12). Compared with the past, themass is reduced by 5 – 7 % with vacuumcasting due to a higher dimensionalaccuracy.

However, there are also limits regardingthe consistent usage of all possibilitiesoffered by the vacuum moulding proces-ses to reduce the wall thickness – depen-dent on the geometric shape of the work-piece. So the difficulty for the caster toproduce the gear box for the drive of anelectric locomotive (picture 26, the mate-rial is GGG-40; the wall thickness is only8 mm) was not the filling of the mouldduring pouring but the seal feeding ofmany junctions; this was a consequenceof the reduction of the wall thickness,through which the construction wasdispersed in a multitude of feeding areas.The tightness of the highly stressed junc-tions had to be detected by x-ray testing.

The low quenching effect of the water-freemoulding material and its good heatinsulation cause a very slow solidificationof the casting metal and cooling of thecastings.

That leads to constant mechanical cha-racteristics, also at considerable differen-ces at the wall thickness. As also smallwall thicknesses at casting metal have agrey solidification and there is no hardedge, a machining is unproblematic andcan be executed economically.

The high stability of the vacuum mouldsinfluences the profitability as well; becau-se it is a prerequisite for the so-calledriserless pouring of cast iron materials,with which the output – the relation between liquid insert and raw castings –is improved.

In many cases the good characteristics ofvacuum casting lead to economicallyinteresting results. Possible are:

■ Saving of pattern costs

■ renunciation of permanent moulds byusing ligth metal casting,

■ less or no priming before painting

■ less scale of machining,

■ better machinability,

■ ligthweight construction;

■ stress-relieved castings.

A conversation between casting consumerand vacuum caster is always worthwhile,above all, if it concerns cast iron castingswith a mass of approx. 100 kg – 1000kg as well as aluminium castimgs with amass of approx. 10 kg – 50 kg.

■ Picture 26: Gear box for the drive of a electric loco-motive; Material: GGG-40, Mass: 200 kg

Table 7: Some mechanical characteristics of 5 types of grey cast iron, poured in vacuum- and in bentonite bonded green sand moulds

Trial Degree Vacuum mould Gree sand mouldnumber saturation

tensile lateral deflection tensile lateral deflectionstrength power strength power

Sc (N/mm2) (kN) (mm) (N/mm2) (kN) (mm)

1 0.84 346 14.1 11.2 321 12.7 9.62 0.87 303 13.1 11.5 277 12.6 9.03 0.89 274 12.4 10.8 268 11.8 8.74 0.92 236 10.6 9.8 237 10.5 7.85 0.96 216 10.1 7.8 228 10.3 7.0

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16

CONSTRUCTIONAL ADVICES

0,5 H < T < HT < 0,5 H

T H T H

15°

0,5 H < T < H

T H

15°

Fundamentally, the vacuum mouldingprocess offers the designer the same pos-sibilities of modelling like the conventio-nal sand mould methods with mechanicalor chemical bond of the moulding materi-al.

The utilization of cores and inserts (com-posite casting), for example, should bementioned; undercuts can be done at lesscost without cores by using loose parts onthe pattern or by means of pattern partsof foamed material remaining in themould (partial full-mould casting). There-fore, in general the “typical casting“ advices apply to construction of a vacu-um casting.

In addition, there are some specific fea-tures, whose observance has a positiveinfluence on the profitability of the pro-duction of vacuum casting. The usage ofdry, binder-free moulding sands with theirexcellent flowability makes the fabricationof such workpiece contours possible, forwhich additional efforts would be neces-sary by using other methods. On theother hand it should be taken into consi-deration that the expansion of the cover-ing film of the pattern is not unlimited.Concerning these two points the followingexamples are given:

The horizontal surface of tension pocketsand similar recesses can be executedhorizontally up to a depth T of 50 % ofthe height H.

For bigger depths up to T = H, depen-dent on the ratio to each other, an incli-nation angle up to 15° should be inten-ded on the surface which is lying aboveduring the moulding.

The undercut arising here is produced bymeans of a loose or a foamed part.

Oil grooves can be produced withoutcore by means of loose parts or foamedparts.

Their dimensioning ratio (that heightbears to depth) corresponds to those ten-sion pockets which are described above.

Fastening eyes can be fixed to the exter-nal shape as well as to the internalshape; arising undercuts are produced bymeans of loose parts and foamed parts.


The depth T of blind holes, pockets andslots is limited; the maximum depth is125 % of the diameter and/or of the

width B respy.; the length of open andclosed slots can be choosen anyway.

The distance B between two ribs has tobe at least 80 % of the rib height. The riblength can also be choosen anyway.

Narrow distances, for example betweenan eye and a wall can be bridged bymeans of a rib.

Reinforced ribs of components manufac-tured according to other methods areusually conical because of productionreasons. The stretched fiber, on which aheavy strain is put, consequently has thesmallest cross section (on the left); withthe vacuum moulding process a stressadjusted cross section is possible withoutany problems (on the right).

Ø

T

T < 1,25 Ø

B

T

T < 1,25 B B > 0,8 H

H

B

If possible, a smooth surface whichremains on the casting to place the ven-ting or the feeder should be intended onthe highest point of parts with round or

nodular contours; so the fettling costs arereduced. Often a draft is not required.However, if a draft is necessary, at least

partially, vertical walls can be intended,for example for bearing surfaces inmechanical devices.

Connecting rip

Stretching fiber

Bearing surface

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PRODUCT SAMPLES

■ Axle bridge for utility vehicles; material: GJS-400, mass: 190 kg

■ Case; material: G-AISi12, mass: 33 kg, dimensions: 650 x 610 x 470 mm ■ Filter case DN 200 for shipbuilding; material: GL-250, mass: 112 kg


■ Case for roll stand; material: GJS-400-18LT, mass: 420 kg

■ Pallet bogie for moulding machine; material: GJS-500-7, mass: 1070 kg, dimensions: 1800 x 1200 x 160 mm

■ Cooler case with high demands to the gas tightness, material:G-AISi10Mg wa, mass: 10 kg,dimensions: 710 x 300 x 120 mm

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PRODUCT SAMPLES

■ Moulding box for a moulding machine; material: GJS-500-7, mass: 800 kg, dimensions: 1790 x 1400 x 350 mm

■ Half-axle for utility vehicle; material: GJS-400, mass: 79 kg

■ Case DN 400 for water meter;material: grey cast iron or nodulariron, mass: 250 kg

■ Sewage casting; material: GJL-200,mass: approx. 80 kg, Ø 700 mm


■ Plates for filter presses with protection against corrosion, material: GJS-500-7, dimensions: 2000 x 2000 x 80 mm

■ Lining ring for a shaft of ø 4800 mm in potassium mining, consisting of 9 segments with a wall thickness up to 120 mm; material GJS-500-7, segment mass: 3.3 t

■ Side shield for sheet metal shears; material: grey cast iron or nodular iron, mass per piece: 52 kg

■ Tool holder for a injection moulding machine, without drafts, only poured with grinding allowance; material: GJS-500-7, mass: 270 kg, dimensions: 580 x 550 x 400 mm

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PRODUCT SAMPLES

■ Grinding toolmaterial: GS, mass: 1005 kg

■ Axle-case housingmaterial: GJS, mass: 104 kg


23

■ material: GS, mass: 560 kg

■ Devices of a railway chassis-frame

■ material: GS, mass: 430 kg


■ Case of driving gear; material: GJL-250, mass: 495 kg

■ Axle-bearingmaterial: EN-GSmass: 743 kg

■ Axle-bearingmaterial: EN-GSmass: 725 kg

PRODUCT SAMPLES

Heinrich Wagner Sinto Maschinenfabrik GmbHBahnhofstraße 101 · D-57334 Bad Laasphe, Germany, Tel. +49(0)27 52/9 07-0 · Fax +49(0)27 52/9 07-2 80E-mail: [email protected] · Internet: http://www.wagner-sinto.de LM

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