Figure 1 3: plate; 8: bolt; 11: ejector; 12, 16: plate; 13: ejector pin; 14.1, 15.2: bush; 18: spme bush (Courtesy: Kralhnann GmbH & Co. KG, Hiddenhausen) Single-cavity mold for polycarbonate compact discs

Example 62: Single-Cavity Injection Compression Mold for a Cover Plate Made from Unsaturated Polyester Resin 185 Example 62, Single-Cavity Injection Compression Mold for a Cover Plate

Figure 1

3: plate; 8: bolt; 11: ejector; 12, 16: plate; 13: ejector pin; 14.1, 15.2: bush; 18: spme bush

(Courtesy: Kralhnann GmbH & Co KG, Hiddenhausen)

Single-cavity mold for polycarbonate compact discs

Example 62: Single-Cavity Injection Compression Mold for a Cover Plate Made from Unsaturated Polyester Resin 185

Example 62, Single-Cavity Injection Compression Mold for a Cover

Plate Made from Unsaturated Polyester Resin

When injection molding thermosetting resins,

undesired fiber orientation in the molded part can be

largely reduced by employing injection compres-

sion If side action is also needed to release the

molded part, the drive mechanism for this side

action must take into account the compression

movement

The cover plate (Fig 1) is produced from a free-

flowing thermosetting resin and has a dovetail-

shaped slot that must be released by means of a

slide

Mold (Fig 2)

The cavity is formed between the core insert (1) and

cavity insert (2) The core fits into the cavity recess;

the lateral shear surfaces have a slight taper to

facilitate entry The slide (3), which is attached to

the piston rod (5) of a hydraulic cylinder by means

of the slide retainer (4), is located in the cavity A

lock (6) fits into an opening in the slide retainer (4)

to hold the slide in position The lock fits against the

wear plates (7)

Runner System/Gating

The molding material enters the mold via the

jacketed spme bushing (8) A system of cooling

channels (10) in the spme bushing keeps the

molding compound within at a temperature of 90 to

100°C (194 to 212°F) to prevent curing The insu-

lating gap (9) ensures thermal separation between

the heated mold (approx 180°C (356°F)) and the

spme bushing (8)

Heating

Heating of the mold is accomplished with the aid of

high-capacity cartridge heaters (1 1) that are divided

into 4 heating circuits Each heating circuit is provided with a thermocouple for individual temperature control The power and thermocouple leads are brought to a junction box (16) in accor- dance with the appropriate electrical codes (VDE 0100)

Mold Steels

The mold is constructed of standard mold compo- nents The part-forming components (core, cavity and slide) are made of hardened steel (material no 1.2083) The slide retainer and wear plates are made

of case-hardened steel (material no 1.2764)

Operation

Prior to mold closing, the slide is hydraulically set in the cavity so that the lock (6) enters the opening in the slide retainer (4) before the core (1) enters the cavity (2) The mold is not completely closed during injection of the molding material The exactly metered shot volume initially fills the gap in the runner region and a portion of the cavity During the subsequent closing motion (compression phase), molding compound fills the entire cavity and cures there under the action of heat

During the compression stroke, the lock (6) prevents the slide (3) from being displaced outward by the molding pressure

The molding material in the runner region also cures The boundary between cured and uncured material in the spme bushing is located approxi- mately at the cavity end of the cooling channel (1 0) The spme puller (13) and ejector (14) remove any remaining cured runner material The molded part is ejected by means of four ejectors not described here

186 3 Examples Example 62

-3

Figure 2

1: core insert; 2: cavity insert; 3: slide; 4: slide retainer; 5: piston rod;

6: lock; 7: wear plate; 8: jacketed m e r (cold runner); 9: insulating gap; 10: cooling channel; 11: cartridge heaters; 12: insulating plate;

13: sprue puller; 14: ejector; 15: pushback pin; 16: junction box (Courtesy: Hasco)

Single-cavity injection compression mold

Example 63: Two-Cavity Injection Compression Mold for a Housing Component Made from a Thermosetting Resin 187

Example 63, Two-Cavity Injection Compression Mold for a Housing

Component Made from a Thermosetting Resin

Fiber orientation, deflashing and lost runner material

are problems that result in costs especially in the

area of thermoset processing The mold presented in

this example shows how expenses for the above can

be reduced A device that permits more exact

metering of the molding compound to the two mold

cavities is described

The molding material is injected into the partially

opened two-cavity mold (Fig 2 and 5)

Flow Divider

Distribution of the molding material to the two

cavities is accomplished with the aid of a conical

flow divider (1) with appropriately designed

grooves During injection, the flow divider is

opposite the discharge opening of the spme bushing

(2) After injection, the molding compound lies in

the common pocket (Bakelite system) at the mold

parting line in the form of two approximately equal

masses

Compression Step

With final closing of the mold, the molding

compound is forced into the two cavities (3, 4),

where it cures under the action of the mold

temperature (approx 180°C (356°F)) As a result of

the compression step, fiber orientation in the molded

part is considerably less than would have been the

case with injection into a closed mold

Degating

The flow divider (1) protrudes into the spme bush-

ing (2) during compression and blocks it off from

the parting line

The standardized jacketed spme bushing is provided

with cooling channels (5), as a result of which the

molding compound in the spme bushing is held at a

temperature of 90 to 100°C (194 to 212”F), so that it

does not cure (“cold runner system”) Only the

protruding tip of the flow divider is warmer ~ as a

cures here As a result, material lost in the form of a runner is limited to only the small amount of material in the grooves of the flow divider (1) An insulating gap (1 7) provides thermal separation between the spme bushing and mold

Flash

During the compression step, the molding com- pound flows past the projected area of the mold cavities and forms flash

The mold cavities (3, 4) are provided with flash edges (7, 8) to ensure clean separation of the molded parts from the flash during ejection Figure 3 shows the common pocket (9) with flash edges (7, 8) located on the movable side of the mold parting line Figure 4 shows the two molded parts and the asso- ciated flash

Common Pocket

The shear edge (12) defines the size of the common pocket Details of the shear edge configuration and gap are shown in Fig 5 The different edge radii (0.8/2.4mm) impart increased stiffness to the flash rim (13) and give the numerous ejector pins located behind it a good means for ejecting the flash A slight undercut (1 4) holds the flash on the movable side during mold opening

Mold Steels

The mold is constructed largely of standard mold components The part-forming inserts are made of steel (material no 1.2767, hardened)

Heating

The mold is heated by means of high-capacity cartridge heaters divided into 6 control circuits Six thermocouples control the mold temperature

188 3 Examples Example 63

Figure 1 Housing component

Figure 2 Two-cavity injection compression mold for a housing component

1: flow divider; 2: sprue bushing; 3, 4: mold cavity; 5: cooling channel; 6: cartridge heater; 7, 8: flash edge; 10: ejector; 12: shear edges; 13: flash rim; 15: pressure sensor; 16: insulating plate; 17: insulating gap; 18: support

Figure 3 Common pocket

7, 8: flash edge around cavity; 9 : common pocket; 10: ejector Figure 4 Molded (bottom) parts with separated flash (top)

Figure 5 Shear edge

Example 64: Injection Compression Mold for a Plate Made from Melamine Resin 189

Example 64, Injection Compression Mold for a Plate Made from

Melamine Resin

Plates, cups and a variety of household items are

often made of melamine resin, type 152.7 In addi-

tion to the “classical” compression molding tech-

nique, injection molding machines are employed to

mass-produce such parts by means of the injection

compression technique Figure 1 shows the mold in

the three steps of production: injection (I),

compression (11) and ejection (111)

The plate is molded using a pinpoint gate When

injection molding without subsequent compression

with this type of gating, the melt would be subjected

to severe orientation that could lead to molded-in

stresses in the part and thus warpage or even cracks

which the compression plate c passes through the mold plate b and forms the underside of the plate

The mold operates as follows: the injection molding

machine closes the mold until the two mold plates a and b contact one another and a compression gap z

is formed between mold plate b and compression plate c After injection of the carehlly metered

amount of molding compound, the mold is closed completely, compressing the material in the mold

cavity As the mold opens, the spring washers t initially cause plates b and c to separate by the amount of the compression gap z, which is limited

by the stripper bolts x Since the machine nozzle d is still in contact with the mold at this point in time, a vacuum that holds the molded plate against mold

plate b is formed in the “molding chamber” After

the mold has opened completely, the machine nozzle

d retracts from the mold Because of the undercut h,

the cured spme is pulled out of the spme bushing and ejected from the nozzle with the aid of a pneumatically actuated device With opening of the

gate, the vacuum in the molding chamber f is

released The molded plate is ejected by means of a

ejection, the molded parts are held by the suction cups on a part extractor and subsequently placed on

a: mold plate; 6 : spacer plate; c: compression plate;

nozzle; f : molding chamber; h: undercut on nozzle;

b x i c heater; m: heater band; n: insulating plate; t: spring

x:

Injection compression mold for a plate

d : machine

k : cartridge washers; v:

190 3 Examples Example 64/Example 65

insulating plates n The gate is so designed that upon

retraction of the machine nozzle d only a relatively

small gate vestige remains on the molded part after

the spme breaks away This vestige is removed mechanically in a subsequent finishing operation

Example 65, Five-Cavity Unscrewing Mold for Ball Knobs Made from a

Phenolic Resin

Ball knobs of a thermoset resin, e.g type 3 1, in a compression molding as a means of producing these

1 : gear; 2: threaded spindle; 3: guide bushing; 4:

threaded core; 5 : center plate; 6: stop; 7: ejector rod;

8, 9: cavity inserts; 10: spring bolt; I, 11: parting lines;

x:

Example 66: Four-Cavity Injection Mold for a Thin-Walled Housing Made from a Phenolic Resin 191

mold shown schematically in Figs 1 to 3, it is

possible to produce ball knobs with different

diameters and optionally with or without internal

threads Initially, molds were produced in which a

film gate was located in the parting line on the

periphery of the ball knobs During degating,

however, the molded parts were often damaged and

could not be repaired even in a secondary finishing

operation

With conversion to a three-plate mold with two

parting lines, it was possible to mold the ball knobs

by means of a ring gate on the seating surface Since

the relatively clean gate mark after degating is not on

a visible surface or hnctional area of the molded

parts, subsequent finishing is not required To permit

production of ball knobs with different diameters, all

part-forming components have been designed to be

interchangeable (mold inserts (8, 9)) By replacing

the threaded cores (4) with unthreaded core pins,

ball knobs without internal threads can be produced

If threads with a different pitch are to be molded, the

threaded spindles (2) and guide bushing (3) must

also be replaced The threads of the guide bushing

(3) must always have the same pitch as the threads

on the threaded cores (4) Only in this way is it

possible to release the threads and ensure exact

positioning of the threaded cores prior to injection

The mold is heated by cartridge heaters located in the mold plates and insert retainer plates The heating circuits are closed-loop controlled Insulat- ing plates x are provided to separate the mold from the machine platens and the drive mechanism The mold operates as follows: with the mold closed and the cores in the forward position, the molding compound is injected into the cavities via the ring gates After the molded parts have cured, the threa- ded cores (4) are unscrewed from the ball knobs by a hydraulic motor that is controlled through an inter- face on the machine To prevent the ball knobs from turning, unscrewing takes place while the mold is closed The rotary motion is transmitted to the threaded spindles (2), which are displaced axially

during unscrewing, by the chain a and the gear (1)

Upon mold opening, the spring bolts (10) separate parting line I Following this, plate (5) continues moving until it reaches the stop (6) after parting line I1 has also opened Undercuts hold the runner on the movable half of the mold after the ring gates have

separated from the ball knobs Next, the runner y is

ejected by the ejector rod (7) which is connected to the machine ejector During mold closing, parting lines I1 and I close automatically Following this, the threaded cores (4) are returned to the molding position by the hydraulic motor

Example 66, Four-Cavity Injection Mold for a Thin-Walled Housing

Made from a Phenolic Resin

The housing component shown in Figs 1 to 3 was

produced in a thermosetting resin by means of

injection molding The special features of this part

are the thin wall sections of 0.7 111111, some of which

taper down to 0.3 111111 As a result of the very slight

Fig 2

I

Fig 1

Fig 3

Figures 1 to 3 Thin-walled housing component of a thermoset

shrinkage, there is no guarantee that the molded parts will remain on the core for ejection It was not possible to provide undercuts to hold the molded part on the core This means that ejection poses a particular problem Since there was also no possi- bility to eject the part only by means of ejector pins because of the extremely thin wall sections, a three- plate mold was selected

The four-cavity injection mold shown in Figs 4 to

10 operates as follows: after the housings have been molded via the spme (4) and runner system and the molding compound has cured, the mold opens at parting line I through the action of the spring-loaded inserts (3) This pulls the spme (4) out of the spme bushing, since an undercut is provided in the guide bore for the somewhat recessed center ejector Simultaneously, the slide (5), which forms the holes

in the side of the housing is pulled by the cam pin (6) and held in position by the spring-loaded detent

(7) Parting line I now opens until mold plate (8) is stopped by latch (9), whereupon parting line I1 opens This pulls the core (10) out of the housing

Example 66: Four-Cavity Injection Mold for a Thin-Walled Housing Made from a Phenolic Resin 193

The molded part is supported by the two ejectors

(12) during this motion The ejector plate (13) is

connected to mold plate (8) by stop bolts (14) so that

the ejectors (12) do not change their position with

respect to the molded part during opening of parting

line 11 As the mold opens fiuther, pin (16) releases

latch (9) so that the movable half can now retract

completely Ejector rod (18), which is connected to

the hydraulic machine ejector, now advances the

ejector plates (13) so that the ejector pins (12) eject

the housings from the cavities in plate (8) along with

the runner system Advancing and retracting the

ejector plates several times ensures that the molded

parts do not stick on the ejector pins This pulsating

ejection also clears the ejector guide bores of any slight flash that might impair venting of the cavities and operation of the mold In the present case, the parting line around the core (10) provides a good means for venting After a short guiding surface, plate (8) is relieved (22) In addition to hctioning

as a vent, this relief acts as a discharge for any thin residual flash that could otherwise cause a mallkction The mold is heated by high-capacity cartridge heaters (23); the temperature is controlled with the aid of thermocouples (24) The insulating plates (25) prevent heat transfer to the machine platen, thereby saving energy and ensuring a more accurate temperature in the mold

194 3 Examples Example 67

Example 67, Thermoset Injection Mold for a Bearing Cover Made from

Phenolic Resin

Because of the production quantities expected, a The molded part is ejected via knockout pins In

Figure 1 Thermoset injection molded bearing cover for an electric motor

Molds for processing of thermoset molding

compounds are, in principle, comparable to those

employed for processing of thermoplastics, with the

understanding that there are certain material-specific

considerations Molds must be designed to be very

rigid in order to prevent “breathing” and deforma-

tion, which contribute to the formation of flash To

monitor the injection pressure, which serves as the

basis for mechanical design calculations, the design

incorporates pressure sensors in the stationary and

moving mold halves, for which blind plugs (35) are

inserted as placeholders The mold base utilizes

standard mold components

Steel grade 1.2767 is used for the mold inserts (39,

40), while grade 1.23 12 (heat-treated to a strength of

1080 N/mm2) is employed for mold plates (4, 5) as

well as the ejector plate (9) Steel grade 1.1730 is

used for the remaining plates and rails Thermal

insulating plates (19, 20), which are available in

sizes to match the standard mold plates, serve to

insulate the mold from the machine platens

The molding compound enters the mold via the

jacketed (temperature-controlled) spme bushing

(21) While the mold is heated to a temperature of

about 170°C (338°F) by cartridge heaters (22,23) to

allow the molding compound to cure, the tempera-

ture of the material in the spme bushing is kept

below the cross-linking temperature, allowing it to

be processed hrther Material in close proximity to

the gate cures The interface between cured and

uncured material in the spme bushing is located at

approximately the face of the spme bushing (Fig 2)

A more recent version of this spme bushing contains

a restriction, or narrowing, in this region, which

vent the cavity during filling It is in part for this reason that the knockout pins are located beneath ribs and other deep sections of the part, where entrapped air is to be expected

The mold filling pattern during injection of the molding compound as well as the mechanical and