With 20+ years experience in white side of lost foam casting, Castchem developed a new product in 2016 for pattern making in white side- StMMA-FD. To compare with the EPS, what is the advantage of the StMMA-FD? Please read my article.

1. CASTCHEM INC
www.zj-castchem.com Tel:+86-570-3888828 Fax:+86-570-89021292
Use STMMA-FD instead of EPS for pattern
making in lost foam casting process
Author:Technical Dept at Zhejiang Castchem New Material Co.,Ltd
Translation:Wujong,Foreign trading manager at Castchem INC
In order to reduce the cost of production, improving the quality of casting products and
qualified rate is the ambition for every lost foam casting foundry. However,the expandable
resin for foaming plastic pattern is an essential factor restricting the lost foam casting
technique development. All of us are agreed that poor quality in white side means poor quality
in black side.
With more than 20 years research, we find out that many of the lost foam casting foundries are
using the traditional EPS(Expandable polystyrene) for production with low qualification
rate,multi-defects and high labor costs.
Aimed at these shortcomings,we self-developed a new series copolymer resin STMMA-FD.It
can solve the low molecular weight,low intensity and rigidity problem of the EPS,and reduce
the carburization during casting.The STMMA-FD could be mostly used medium-grade or
low-grade foundries such as grey iron and aluminium alloy casting. After practices in
production of many domestic lost foam casting foundries,with same process as using EPS in
the prefoaming(pre-expansion), aging, pattern making(molding-demolding) and coating drying,
the STMMA-FD resin beads greatly improved the stability,intensity and surface smoothness of
the castings.The carburization defects had been also reduced, percent of qualification rate are
increased 6% or more.

2. CASTCHEM INC
www.zj-castchem.com Tel:+86-570-3888828 Fax:+86-570-89021292
1.Analysis of lost foam casting pattern foaming materials
High quality raw material foam of pattern is the first condition for lost foam casting. Look at the
pattern making technique all around the world, there are two kinds of pattern raw material
before the invention of STMMA-FD - EPS and copolymer resin. EPS is the short writing of
Expandable polystyrene, copolymer resin including Castchem’s STMMA and Mitsubishi’s
ClearPor.
As we know, most of the casting EPS raw material are used from packaging or building
expandable polystyrene. The sources of the EPS raw material are complicated,most of the
EPS are also mix with other raw materials, even 95% of them are added flame retardant
because the packaging and building EPS needed fire protection grade. All of these brought us
more cast defects to the foundries, low qualification rate of castings, and also brought us high
production costs.
2.The defects of EPS
Most of the lost foam casting foundries are using the EPS scraps from packaging or building,
the used EPS is monomer polymerized by styrene, its molecular weight is too low to give the
castings enough strength and rigidity, it is actually not suitable for lost foam casting.
As we know, there are a mass of C molecules in the styrene(C8H8) because of the special
benzene ring structures, it comes into being liquefied carbon and black smokes during
burning.In the same reason, EPS contains 100% styrene, it is easy to be carbonized during
thermal decomposition.To solve this problem, we add an amount of methyl
methacrylate(C5H8O2) into the STMMA-FD resin,it will reduce the carbon content and less
carbonized reaction during the casting,reduce the carbonized defects and improve the
qualification rates.
When the mould patterns foamed by EPS beads used in the lost foam casting, the weak
energy bones in the molecule broken first after pouring the metal melt.As the temperature
continue to rise, the strong energy molecular bonds broken too and formed low molecular
weight hydrocarbon compounds. There are C=C double bond or C=C triple bond in the
hydrocarbon compounds, these EPS patterns will finally increase 0.3~0.5% carbonized
content in the surface of steel castings, especially in the ductile iron and gray iron casting, it
appears as wrinkled,cooling scared or lacunose in the surface or slag inclusion inside,such
defects result in weak mechanical properties of the castings.Because of the above-mentioned
reasons, many foundries still don’t dare to try lost foam casting technique, or some of them
have already assembled a lost foam casting production line but still not have quantity
producing capacity.
Especially in the aluminum alloy foundries, the carbon inclusions became the big problem in
the lost foam casting. The carbon inclusion happened when the two kind of melts flowing
together but not yet mixed with each other and then caused ‘cold shut’.If the castings are
heated circularly and cold,the carbon inclusions may cause the metal fatigue to fracture. If a
casting has a defect of carbon inclusion,in general case, this carbon inclusion defect will

3. CASTCHEM INC
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happened in every casting.If the carbon inclusions are happened in the important parts such
as the engine cylinder blocks, the defect will cause seepage inside the castings because the
engine have to bear temperature’s high and low changes, this will finally become a serious
failure.
3.STMMA-FD beads introduction
In order to solve the deficiency of the EPS, we developed the new product STMMA-FD resin
beads to reduce the carbonized defects of the casting. This product also solved the low
molecular weight problem of EPS,to give castings more strength and rigidity.
The STMMA-FD resin beads are compounded by adding methyl methacrylate into styrene, it is
a reformative expandable polystyrene beads.In the meantime, adding organic bromine both
with methyl methacrylate will greatly reduce the carbonized defects. The organic bromine will
generate hydrogen bromine after heated, the hydrogen bromine will react with the C=C double
bond and C=C triple bond, this will break the previous C bonds and make the carbon atoms
percent in the whole molecules going down to reduce the carburetting. In the other side, the
molecule weight of the bromine atoms are more than C atoms,with the adding of methyl
methacrylate, the carbon percent is greatly decreased compare with the EPS.
The STMMA-FD resin beads are mainly used in casting of gray iron and aluminium
alloys.Compare with the expandable polystyrene, it has advantages as below -
1.)Reduced the carbonized defects of casting.
2.)Improved the mould pattern’s strength and stability of shaped size.
3.)Improved the surface smoothness and qualification percent of castings.
4.)Reduced the general costs of foundries.

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STMMA-FD general performance compare with EPS -
Item EPS STMMA-FD
Composition (C8H8)n
Carbon content 92% 82%
Temperature of foaming 80~85 ℃ 85 ℃
Temperature of decomposition 912℃ 900℃
Gas evolution of 900℃ 600ml/g 700ml/g
Casting temperature(for gray iron) 1500~1460℃ 1480~1450℃
Residuum after foamed mold
decomposing
more less
Foamed mold quality
particle size bigger, uneven
density distribution in the mold
beads are
homogeneous,
mold's
consistency is
good
Shrinking percentage of foamed
molds
0.3~0.5% 0.2~0.4%
Rate of finished casting
products(for boxes and motor
housings)
80~92% ≥93%
4.STMMA-FD bead size and expanding rate-
Specifications Diameter of beads
Theoretical
expanded ratio
Actual expanded
ratio by tested
STMMA-FD special 0.9~1.25mm ≧40:1 68~85:1
STMMA-FD1# 0.6~0.9mm ≧40:1 65~83:1
STMMA-FD2# 0.45~0.6mm ≧40:1 64~80:1
STMMA-FD3# 0.35~0.45mm ≧40:1 63~80:1
STMMA-FD4# 0.25~0.35mm ≧40:1 ——

5. CASTCHEM INC
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5.Comparison of carbon content and mould pattern combustion residues in the
lost foam casting-
The tested residues percent of EPS,STMMA and STMMA-FD-
Item
Weight of
pattern
Weight of
residues
Percent of
Residues
Density of
panttern
EPS 3.37g 2.22g 65.90% 21g/L
STMMA-FD 3.37g 1.03g 30.60% 19g/L
STMMA 3.37g 0.15g 4.45% 20g/L
After our STMMA and STMMA-FD produced, hundreds of foundries had been using our
products. All of them feed back us that the resin beads are good for casting, it pleasures us
that these inventions made a small contribution to lost foam casting technique and the
foundries all over the world.
The STMMA-FD resin applied in lost foam casting production-
1.The STMMA-FD beads casting application for some customers of us-
Case ONE.
Jiangsu Yancheng Co.,Ltd used to produce 180kg iron ball gearbox with EPS beads by lost
foam casting, the gross weight of iron gearbox is 180kg, with minimum wall thickness of 12mm,
max wall thickness of 20mm.The carbonized defects and ‘cold shut’ problem were always
happened in the castings, the percent of waste products used to be 15~20%, general cost was
very high.

6. CASTCHEM INC
www.zj-castchem.com Tel:+86-570-3888828 Fax:+86-570-89021292
Firstly we chose the STMMA-FD to foam a pattern with the same size as EPS patterns, the
test as below-
A.)Chose the beads: STMMA-FD 2#(0.45mm~0.6mm)
B.)Pre-foam density:19g/L±0.5g/L
C.)Pre-foam,Pattern-making, drying are all the same as before.
D.)Pattern size shrinking ratio is the same as using EPS, cast workblank in same size.
E.)Pouring process:QT450-10 box, pouring temperature 1500~1450℃.All casting technique
same as before,pouring speed same as using EPS pattern,no back-spraying during the
pouring.
E.)The quality of finished castings:In the same lost foam casting technique process as before,
the castings produced by STMMA-FD patterns have good surface smoothness, almost no
carbonized defect in outside, the quality improved greatly as using EPS patterns.
F.)Mass production compare to EPS: using the STMMA-FD beads to cast 5pcs of gearbox,
4pcs in good quality, 1pc with few carbonized defect in surface but not affect the after-process.
Case TWO.
Hebei Hengshui Co.,Ltd used to produce water-cooling machine bed of air blower by using an
expandable polystyrene bought from domestic market. The gross weight of this machine bed
is 20kg,min wall thickness of 6mm,max wall thickness of 20mm.The finished castings used to
be unsmooth on surface, carbon defects and cold shut problem are always coming out.
Pressure testing caused seepage and waste rate nears to 10~20%.
Because the pattern size must be same as using EPS, we chose STMMA-FD,test as below-
A.)Chose the foaming resin beads:STMMA-FD3#(0.35mm~0.5mm)
B.)Pre-foam density:22g/L±0.5g/L
C.)Pre-foam,Pattern-making, drying are all the same as before.
D.)Pattern size shrinking ratio is the same as using EPS, semi-finished castings in same size
like before.
E.)Pouring process: HT250water-cooling machine bed,pouring temperature 1450℃,all casting
technique same as before,pouring speed same as using EPS pattern,no back-spraying during
the pouring.
F.)The quality of finished castings:In the same lost foam casting technique process as before,
the castings produced by STMMA-FD patterns have good surface smoothness, almost no
carbonized defect in outside, the quality improved greatly as using EPS patterns.
G.)Mass production compare to using EPS: using the STMMA-FD beads to cast 6pcs of
gearbox, 5pcs in perfect quality without seepage problem after pressure testing, 1pc with few
carbonized defect in surface but not affect the after-process.
After the testing, this foundry produced several batches of castings,the qualified rate were
keeping to 95% with 400Ton capacity per month.Because the production quality and qualified
rate are promoted, their cost of castings decreased 200.00Yuan per Ton.
Case THREE

7. CASTCHEM INC
www.zj-castchem.com Tel:+86-570-3888828 Fax:+86-570-89021292
Zhejiang Huzhou Co.,Ltd was using the EPS beads to producing electrical motor housings by
lost foam casting technique, model no 160-355, gross weight 10~300kg, min casting wall
thickness 3mm,max wall thickness 20mm. The finished housings have problems of unsmooth
surface, carbon defects and cold shut, especially the cooling fins in the housings has sawtooth
on the rim, waste products rate over 10%.
Using our Castchem’s new material STMMA-FD beads to replace the EPS, the test as below-
A.) Chose the foaming resin beads:STMMA-FD3#(0.35mm~0.5mm)
B.) Pre-foam density:22~23g/L±0.5g/L
C.) Pre-foam,Pattern-making, drying are all the same as before.
D.) Pattern size shrinking ratio is the same as using EPS, semi-finished castings in same size
like before.
E.)Pouring process: HT200 electrical motor housing,pouring temperature 1500℃,all casting
technique same as before,pouring speed same as using EPS pattern,no back-spraying during
the pouring.
F.)The quality of finished castings:In the same lost foam casting technique process as before,
the castings produced by STMMA-FD patterns have good surface smoothness, almost no
carbonized defect in outside, the quality improved greatly as using EPS patterns.
G.)Mass production compare to using EPS: using the STMMA-FD beads to cast 100pcs of
housing, 99pcs in perfect quality without saw tooth on cooling fins, 1pc scrapped because
sand mixed when casting.
After the testing, they cast several batches of production, the qualified finished-products were
keeping to 97% with 500Ton capacity per month. Finally their cost of production decreased
200~230Yuan per Ton.
2.The economic benefit for lost foam casting foundries after using the
STMMA-FD resin beads-
The price of STMMA-FD is about $3700/T, most of the EPS costs 3400/T, some of the
customized EPS used for aluminium alloy casting may cost $4500/T. Compare with the
cheapest EPS raw material resin, the costs will increase $1.00 if using STMMA-FD to produce
per ton castings.
If the castings to be sold of $1000 per Ton, after using the STMMA-FD resin beads, the
production costs will decrease $10 per Ton when the qualified finished-product rate increased
1%.
Zhejiang Huzhou Co.,Ltd:: After putting the STMMA-FD into their lost foam casting production
line, the qualified products rate increased 6%, in that case, their castings costs per ton
decreased as below-
$10x(6%/1%)-$1=$59.00
If the qualified products rate increase more,the castings costs decrease more.

8. CASTCHEM INC
www.zj-castchem.com Tel:+86-570-3888828 Fax:+86-570-89021292
Tel:+86 15068719527(WhatsApp/Line/Viber/Tango)
Email:info@zj-castchem.com
Website:www.zj-castchem.com
Production base: No10 Weiyi Road,High-Tech Industry Zone,Quzhou,Zhejiang
Province,China 324002