Introduction of special foam beads for lost foam casting (2)

November 08, 2018

a. Vacuum pre-expander operation process parameters:

1 plus resin for 6 seconds

2 preheating see the table below

3 water injection 50-75ml/10 seconds under vacuum

4 atmosphere stable for 5 seconds

5 vacuum stable for 20 seconds

6 discharge 45 seconds

Vacuum preheating process parameters

Feeding amount (g)
Jacket steam pressure (Mpa)
Pre-density (g/l)
Copolymer resin 500
3-5
0.15-0.18 18-20
EPMMA500
5-7
0.18-0.20 22-25
EPS 500
2-3
0.11-0.15 16-22

b. Pressurized pre-expansion machine

EPS pre-exposure temperature is 100-105 ° C;

The prepolymerization temperature of the copolymer resin is 105-115 ° C;

EPMMA resin pre-expansion temperature 115-120 ° C;

The pre-expansion of the beads is generally controlled by the pre-expansion temperature and time.

c. Drying and ripening of pre-expanded beads

The vacuum pre-expander not only has a high pre-expansion of the beads, but the beads have a uniform particle size and the pre-formed beads are dry. If pre-expansion by pre-expansion is used, the moisture content of the pre-expanded beads is high, and it needs to be treated by fluidized bed drying. The drying air temperature is 25-35 ° C, and the moisture content of the beads is reduced to 2% or less.

The pre-emerged beads must be stored for a period of time before they can be used. This period of time is called ripening. The recommended EPS ripening time is:

Bulk density (g/l)
15
20
25
30
Optimal ripening time (hours)
48-72
24-48
10-30
5-25
Minimum ripening time (hours)
10
5
2
0.5

The pre-bead aging time of EPMMA and copolymer resin is shorter than the recommended value of the above EPS aging time.

The optimum ripening time is related to the ambient temperature and air flow, and whether the ripening is completed can be judged by the elasticity of the beads. Note that the curing temperature should not be too high, and the time should not be too long, otherwise the excessive loss of the foaming agent will affect the molding foaming quality. After ripening, the beads are stored in a sealed container and stored at low temperature.

d. Forming foaming

Lost foam foam generally adopts two processes of steam cylinder molding and press molding:

1 When steaming cylinder is used, heating steam pressure (Mpa)

EPS
0.1
Copolymer resin
0.11-0.15
EPMMA
0.15-0.18

The holding time should be determined by experiments according to the size of the model, structural characteristics, and the like.

2 Typical molding conditions (model size 50×200×200) using press molding

Model material density (g / liter) steam time (seconds) jacket steam pressure (Mpa) cooling time

(second)

Minimum maximum normal

Copolymer resin (20) 13 30 13 0.12-0.15 90

EPMMA(26) 10 45 25 0.13-0.15 110

EPS(24) 3 15 9 0.10 130

After the molding foaming, the model is dried and stored (stabilized), and the model is shrunk during drying and storage. The EPS model yield is 0.4-0.8%; the EPMMA copolymer resin model shrinkage is 0.2-0.4%; therefore, the shrinkage rate of the foam model should be considered in the design of the molding die.

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