CORPORATE TRAINING AND PLANNING*TRANSFER MOULDING

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*INTRODUCTIONFor some applications, it is desirable to close the mold first and then introduce the molding compound in its fluid state through a small opening or gate leading to the mold cavity or cavities. This technique is called transfer or plunger molding.

This is variation of compression molding and is particularly valuable when intricate shapes have to be molded. It is also useful when metal inserts have to be incorporated (as in electrical component).

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*PROCESSOPERATIONS:

In transfer moulding, a known amount of moulding powder is placed in a heated chamber (transfer pot), outside of the mould. When liquefaction is completed a piston forces the resin through a connecting channel into the mould. As in compression moulding the mould is kept heated and this completes the chemical reaction which leads to hardening of the moulding. A systematic diagram of Transfer Moulding is shown in fig.1.

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*Fig. 1

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*TRUE TRANSFER OR POT TYPE TRANSFER MOULDING

In true transfer or pot type transfer moulding, the mould is closed and then placed in an open press. The charge of moulding compound is introduced into an open pot at the top of the mould. The plunger is then placed into the pot and the press is closed. As the press closes, it pushes against the plunger, which in turn exerts pressure on the moulding compound, forcing it down through a vertical passage called a sprue and through runners and gates into the cavities. After the curing, the mould is removed from the press, the plunger is withdrawn, the mould is opened, and the parts are ejected. (Fig. 2)

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*Fig. 2

CORPORATE TRAINING AND PLANNING

Plunger Transfer Mold

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*MOULDING SEQUENCEThe mould is closed and material is placed into the hot transfer chamber of fully automatic transfer moulding and plastication.Fig. 3

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*MOULDING SEQUENCEThe plunger descends into the pot, causing material to melt and flow through runners into hot mould cavities.

Curing under the pressure of transfer ram. Fig. 4

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*MOULDING SEQUENCEAfter cure, the press opens, the plunger retracts, and parts are ejected with cull and runners.

Deflashing and mould cleaningFig. 5

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*ADVANTAGESTool maintenance is generally low, although gates and runners are susceptible to normal wear. Because the mold is closed before the process begins, delicate inserts and sections can be molded. Higher tensile strengths are easier to obtain with transfer molding. Automatic de-gating of the mold's tunnel gates provides cosmetic advantages.

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*LIMITATIONSThe cull and runner system of transfer molding leaves waste material, but this scrap can be greatly reduced by injection molding with live sprues Fiber degradation of orientation occurring in the gate and runner system reduces the molded part's impact strength. Compared to compression molding, high molding pressures are required for the transfer process

CORPORATE TRAINING AND PLANNING

CORPORATE TRAINING AND PLANNING*USEFUL DATA

CORPORATE TRAINING AND PLANNING

Recommended temperature range for thermosetting moulding compounds

Material

Temp C

TempF

Phenol-formaldehyde

140-160

290-350

Melamine- formaldehyde

135-160

280-350

Urea- formaldehyde

135-160

275-310

Polyester

80-150

180-300

Diallyl phthalate

120-165

250-325

Epoxy

140-200

290-390

Silicone

150-190

300-370

Recommended moulding pressures for compression moulding thermosets

Type of Filler

Mouding Pressure (PSI)

Type of Filler

Mouding Pressure (PSI)

PHENOLIC

Woodflour

1500 3500

Mica

1500 3000

Cotton flock

1500 4500

Asbestos

2000 4000

Macerated cotton

2000 5000

Mineral

2000 3000

Tire cord

2000 5000

Glass:

Diced Squares

Choppes roving

Bulk

2000 10000

2000 6000

1000 - 6000

Sisal

2000 5000

Rubber

1500 3000

CORPORATE TRAINING AND PLANNING*USEFUL DATA

CORPORATE TRAINING AND PLANNING

Type of Filler

Mouding Pressure (PSI)

Type of Filler

Mouding Pressure (PSI)

UREA

DIALLYL PHTHALATE (DAP)

Alpha cellulose

4000 8000

Synthetic (Nylon, orlon, dacron)

500 2000

Alpha cellulose plus plasticizer

2000 4000

Glass Fibre

500 2000

MELAMINE

Asbestos

500 2000

Alpha cellulose

2000 8000

POLYESTER

Asbestos

2000 8000

Glass fibre (premix)

50 500

Mineral

2000 6000

Sisal

50 500

Glass :

Chopped roving

Bulk

2000 8000

2000 - 6000

Mineral (clay)

50 300

EPOXY

ALKYDS

Mineral

100 1000

Mineral (granular)

1000 - 1500

Glass fibre

100 2000

Glass :

SILICONE

Extruded rope

600 1000

Asbestos

1000 8000

Putty

400 800

Glass fibre

1000 5000

Bulk

1000 2500

Mineral

1000 5000