Chapter II White Area 2.2 STMMA Raw Material Model, Characteristics and Scope of Application


2.2.1 Model Specifications

 

Specifications

specification

Particle size range (mm)

particle size range

Volatile (mass fraction,%)

≥ Volatilization (quality score)

Suitable for specific gravity

   Appropriate for proportion

STMMA-1#

0.6-0.9

7

19g/L

STMMA-2#

0.45-0.6

7

19~21g/L

STMMA-3A#

0.4-0.55

7

20~22g/L

STMMA-3#

0.35-0.50

7

21~23g/L

STMMA-4#

0.25-0.35

6

 23~26g/L

 

2.2.2  STMMA与EPScomparison of physical and chemical characteristics

Project    Item

SingleBit  unit

EPS

STMMA

Compositioncomposition

 

[C8H8]n

[(C5H8O2)x(C8H8) and] m

Carbon contentCarbon content

%

92

69.6

Tf

80-90

85-100

       decomposition heat  heat decomposition

j/g

1500-1580

1350-1450

initial gasification temperature Initial Vaporization temperature

275-300

268

Final gasification temperature final vaporization temperature

460-500

400-450

Gas evolution (900 ℃)       Gas evolution amount

ml/g

600

900

Pouring temperature (gray iron, box type) Casting temperature(gray iron, box series)

1500-1580

1350-1450

Decomposition residueModel decomposition residue

 

Many much

Less little

Carbon increase rate     Recarburization  rate

%

0.1-0.3

≤ 0.06

Appearance quality           model quality

 

Easy to form carbon residue defects/carbon adhesion       Easy to form carbon slags defects/much carbon adhesion

Less likely to form carbon defects/less carbon attachment             Not easy to form carbon slags defects/little carbon adhesion

Shrinkage of pattern         model shrinkage rate

%

0.3-0.8

<0.3

Casting finished product rate/(cast iron processing parts.) castings finished product rate

%

Low,low<80

high,high>90

2.2.3 Scope of application and storage of STMMA:

   STMMAIs a special lost foam casting pattern material of the expandable copolymer resin beads,.EPS has more excellent casting performance. Mainly used for productionValves, pipe fittings, auto parts and various construction machinery parts, etc., especially the more complex parts of ductile iron..

STMMA Requirementslow temperature refrigeration≤ 10 ℃), if there is no customer with this condition, please keep it inDry and ventilatedNo direct sunlight, cool place. When it is not used up after opening, remember to tie the bag tightly again and cover the barrel to prevent the loss of pentane. It is best to place the beads in the designated position, and pay attention to fire prevention in the bead storage place.

2.2.4 and EPSCompared to STMMA advantages:

The carbon defects of the casting are reduced.

The surface carburization defects of steel castings are reduced.

Reduced smoke carbon.

The surface roughness value of the casting is reduced.

 

2.2.5The selection principle and matters needing attention of the original material

Introduced above respectivelyEPS and STMMA model, characteristics and scope of application, how to determine the choice of raw materials according to their own situation. Must first understand the production of castings size, wall thickness, surface quality requirements and so on.

First of all, according to the casting material and the quality requirements of the casting to choose varieties, such as non-ferrous metals, gray iron and general carbon steel parts.EPS, and valve housing valves, pipe fittings, auto parts and various construction machinery accessories, etc., especially ductile iron more complex parts choose STMMA.

The size (grain size) of the beads is selected according to the minimum wall thickness of the casting. In advanceThe expansion ratio of 40-50 times increases the bead diameter by about 3 times. In order to obtain a good surface state of the pattern, during secondary foaming (molding), the minimum wall thickness of the pattern should arrange 3 beads in the direction of the minimum wall thickness, so the maximum bead particle size generally allowed is 1/9-1/10 of the minimum wall thickness. For example, if the thickness of the cooling fin of the motor case is generally 3-5mm, then EPS is selected as the H-4S material, while if it is a common carbon steel part with uniform wall thickness, such as anode steel claw model with a thinnest wall thickness of 8-10mm and telegraph pole flange with uniform wall thickness of 10-15mm, we recommend using dragon king H-S. If it is STMMA and for a 7mm thin casting, one tenth is 0.7mm bead, then the STMMA-1#0.60~0.90mm can be selected. if the surface requirement of the casting is high, then one more specification is sufficient. generally, customers are not recommended to use too fine beads, mainly considering the transportation in summer and the storage factors in the customer's factory.

If the company produces castings of different sizes and wall thicknesses, it is recommended to choose a variety of beads according to the wall thickness of different castings. The purchase volume should be based on the company's production tasks to a reasonable plan, generally each purchase volume should not exceedDosage for 3 months.

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