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10 16-Cavity Hot-Runner Mold for Cover Caps with Segmented Internal Contours Made from Polypropylene (PP) or Polyethylene (PE)

10 16-Cavity Hot-Runner Mold for Cover Caps with Segmented Internal Contours Made from Polypropylene (PP) or Polyethylene (PE)

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Example 10: 16-Cavity Hot-Runner Mold for Cover Caps with



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Figure 2 16-cavity hot-runner mold with needle-shutoff nozzles

1: cavity plate FS, 2: needle-shutoff nozzles, 3: mold insert FS, 4: hot-runner manifold, 5: distributor bush, heated, 6: nozzle heater band, 7:

support disk, 8: thermal insulation sheet, 9: pneumatic cylinder, 10: clamping plate DS, 11: collapsible core, 12: mold insert BS, 13: mounting

elements, 14: core retainer plate, 15: clamping plate BS, 16: internal core retainer plate, 17: stripper plate, 18: latch lock, 19: ejector rod, 20: core

head cooling.

(Courtesy: Hasco, Liidenscheid)



locks (18). This stroke motion is performed via

the ejector rod (19) that is connected to the ejector

system. During this sequence, the V-guided profile

cores and V-ledges (in 11) leave their injection

position and collapse over the inside core taper.

After approx. 15mm stroke, the undercuts have been

demolded. In the second demolding sequence,

the latch locks release the block on both platens so

that the stripper plate can remove the article.



Cooling

The small tolerances permitted for the molded part

and the 10 s cycle time are made possible by very

intense circulation cooling in the mould platens

and the separation of insert cooling into several

circuits. This has been contributed to by dividing

the serial core head cooling of the collapsible cores

into four groups (20).



64



3



Examples



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Example 11



Example 11, Four-Cavity Injection Mold for a Housing Made from

Acrylonitrile-Butadiene-Styrene (ABS)

The four-cavity mold is used to produce two each of

the upper and lower halves of a cosmetic device

housing. The two halves of the housing are joined

together by means of snap fits. These hook-shaped

connections form internal and external undercuts on

both parts that are released by lifters.



Mold

The four cavities are arranged in a rectangle at the

mold parting line (Fig. 3). The mold inserts (1 1, 14)

are made of hardened steel; the lifters (7, 8, 20) are

case-hardened.

The lifters move sideways in the ejector plates (9,

10) and are attached to slide blocks (12) that run in

corresponding guide grooves. The four leader pins

for the two mold halves as well as the guide pins for

the ejector plates are not shown in the drawing.

Mold dimensions are 296mm x 547 mm, with a

mold height of 290mm. The mold weighs approximately 280 kg.



Runner System/Gating

The melt flows from a heated sprue bushing (13)

through an H-shaped runner system to the four

submarine gates feeding into the cavities (Figs. 1, 3).



Mold Temperature Control

The cavity inserts are provided with cooling channels for temperature control, while the cores contain

bubblers in which baffles (19) ensure that the cooling water is directed to the tip of the bubbler well.

The temperature in the cavity inserts is monitored

with the aid of thermocouples (1 6).



Part Release/Ejection

Upon opening of the mold, the molded parts and

runner system are retained on the core half. As soon

as the machine ejector actuates the ejector plates (9,

lo), the runner system and molded parts are released

and pushed off the cores by the lifters (7, 8,20) and

ejectors (17). The submarine gates shear off, while

the lifters release the undercuts formed by them.

Inside the housing halves (H) there is an undercut

boss formed by the end of a core pin (18) and the

surrounding hole in the core insert. The core pin

(18) is fitted into the core insert with a certain play

(V). As the parts are ejected, this pin is carried along

by the molded part until the boss is clear of the hole

in the core insert. The core pin (18) now stops and

the boss is stripped off the end of the core pin by the

remaining ejector motion. Before the mold closes,

the ejectors must be pulled back.



Fig. 2

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Fig. 3



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Figures 1 to 3 Four-cavity injection mold to produce a housing

with integrated snap fits

1: mold plate; 2: bar; 3: mold plate; 4, 5: bars; 6: clamping plate; 7, 8:

lifters; 9, 10: ejector plates; 11: mold insert; 12: sliding block; 13:

heated spme bushing; 14: mold insert; 15: O-ring; 16: thermocouple;

17: ejector; 18: core pin; 19: baffle; 20: lifter



Example 11: Four-Cavity Injection Mold for a Housing Made from Acrylonitrile-Butadiene-Styrene (ABsj







12



Next Page



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Examples example 12



Example 12, Four-Cavity Injection Mold for a Nozzle Housing Made from

Polyamide

The nozzle housing for a windshield washer system

has three interconnected channels and two external

mounting clips. Core pulls and slides are required to

release the molded parts.

The nozzle housing (Fig. 1) is used to distribute the

water coming from the water pump to the two spray

nozzles of an automobile windshield washer

system. The hose from the pump is slipped over the

conical tip on the end of a tubular extension A. The

channel in this extension divides inside the housing

into two channels D that lead to the spray nozzles. A

hook H and a snap spring F are used to attach the

housing. The ribs R serve to stiffen the tubular

extension.



Mold

The mold (Figs. 2 to 4) contains four cavities. To

release the hook and snap springs, four pairs of

slides (12, 13) actuated by cam pins (28) are used.

The cavity surface is formed by the slide inserts

(32). The slides are held in place in the closed mold

by the heel blocks (9) and wear plates (10).

The channels D are formed by core pins that are

attached to a total of eight slides (22). The cam pins

(18) are employed to actuate the slides, while the

pins (26) hold the slide (22) in place when the mold

is closed.

The channel in the tubular extension A is formed by

the core pin (19), the conical tip of the extension by

the bushing (23). The adjacent core pins (19) and

bushings (23) on one side of the mold are attached

to a bridge (15, 16). The base of the cylinder (24) is

also bolted to the center of the bridge between the

two core pins. The rod of cylinder (24) is attached to

the backup plate (4). To pull the core pins (19) the

piston in the cylinder is pressurized and the cylinder,

along with the bridge and core pins, moves away

from the mold. The bushing (23) are held in place by

the pins (25).



The cavity insert (21) is made of through-hardened

steel, while the slide inserts (32) and slides (22)

utilize case-hardened steel.

The drawings were produced on a CAD system;

Figs. 2 to 4 two dimensionally (2D), Fig. 1 three

dimensionally (3D).



Runner System/Gating

The melt flows from the sprue bushing (1 1) into the

mold via an H-shaped runner system through the

cavity insert (21) to a pinpoint gate at the parting

line associated with each pair of slides and enters the

cavity at the hook H of the molded part (Fig. 3).



Mold Temperature Control

Cooling channels in the plates (1, 3 and 4) are

provided for mold temperature control.



Venting

The ejector pin (3 1) is located in the cavity where air

entrapment may occur. It thus also aids in venting.



Part Release/Ej ection

Part release and ejection are accomplished by means

of a latch mechanism (17) and stripper bolt (27) not

described in M h e r detail.

The mold first opens at parting line I, at which point

the gates shear off the molded parts and are pulled

out of the cavity insert (21). The runner system is

held on the sucker pins (30). The cam pins (18)



Figure 1 Nozzle body for an automobile windshield washer system,

diagram

A tubular extension; D: channels; F: snap spring; H: hook; R: rib



Previous Page

Example 12: Four-Cavity Injection Mold for a Nozzle Housing Made from Polyamide



actuate the slides (22), which withdraw the short

core pins from the molded parts.

As the mold opens at parting line 11, the slides (12,

13) on mold plate (4) are spread apart by the cam

pins (28). At the same time, the undercuts on the

hooks and the snap springs are released along with

the pins (25) blocking the hydraulic side cores. so



that the core pins (19) can now be withdrawn. The

parts are now ejected by ejectors (29) and (31).

Finally, the runner stripper plate (2) is actuated by

the stripper bolts (27) (parting line 111) and the

runner system is stripped off the sucker pins (30).

Before the mold closes, the ejectors must first be

retracted and then the hydraulic cores set.



Fig. 4



Fig. 2



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20



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Fig. 3



21



22



26



18



Figures 2 to 4 Four-cavity injection mold for a nozzle housing of

polyamide

1: clamping plate; 2: m n e r stripper plate; 3: mold plate; 4: backup

plate; 5: bar; 6: clamping plate; 7, 8: ejector plates; 9: heel block; 10:

wear plate; 11: sprue bushing; 12, 13: slides; 14: slide guides; 15, 16:

bridge; 17: latch mechanism; 18: cam pin; 19: core pin; 20: runner

plate; 21: cavity insert; 22: slide; 23: bushing; 24: hydraulic cylinder;

25, 26: locking pins; 27: stripper bolt; 28: cam pin; 29: ejector; 30:

sucker pin; 31: ejector pin; 32: slide insert



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Examples example 13



Example 13, Single Split Cavity Mold for a Threaded Plug Made from

Polyacetal (POM)

The threaded plug is a cylindrical body 65mm in

diameter and 23 mm high with a trapezoidal thread

having a pitch of 3.5mm. A split cavity is used to

form the threads. The necessary number of split

cavity segments depends on the thread pitch and its

profile as well as on the material used to mold the

Part.

Figure 1 shows the plan view of a thread with a

trapezoidal profile. If one attempted to form this

thread in a split cavity with two halves, i.e. the

parting line lay in the plane of the figure, the mold

would damage the thread upon opening, because of

the undercuts at the positions H.



H



Mold

The present mold (Figs. 2, 3) has four cavity

segments (1) each of which is actuated by two cam

pins (2). The cavity segments are guided on the

mold plate (3) and when closed are held in position

by means of wear plates (4) attached to the mold

plate (5). The mold is constructed of standard mold

components.



Runner System/Gating

The part is gated centrally via a pneumatic

nozzle (6).

Operation of the nozzle is described in Example 97

The spme (8) in the nozzle tip (7) is attached to the

molded parts via 2 pinpoint gates next to the central

hole.

Before the mold opens, the spme (8) is separated

from the molded part and ejected by actuating the

pneumatic nozzle (6).



Figure 1 Thread with rectangular profile (plan view)



The more pronounced the flanks of the thread profile

are inclined (trapezoidal/triangular thread) and the

smaller the thread pitch and depth, the smaller are

the undercuts. With injection molding, the size of

the undercut is decreased by the shrinkage of the

resin up to the moment of ejection. In addition,

many resins are still elastic enough to withstand

minor deformation without damage. If in spite of all

these factors the undercut is still too large, the

number of segments forming the split cavity must be

increased.

The investigation of the situation with regard to

undercuts and the determination of the necessary

number of cavity segments is best carried out with

the aid of a computer which can be used to search

out the regions endangered by the undercuts on the

basis of the thread geometry.



Part Release/Ej ection

As the mold opens, the four cavity segments (1) are

spread apart by the eight cam pins (2) and the

threads are released. Now the ejectors (9) can strip

the molded part off the core.

Ejection takes place hydraulically via the molding

machine. The molded part is blown off the ejectors

(9) by a blast of air.



Mold Temperature Control

The mold plates (3) and (5) as well as the cavity

segments (1) are provided with cooling channels.

The hollow core (10) contains a cooling insert (1 1)

with grooves to guide the cooling water.



Example 13: Single Split Cavity Mold for a Threaded Plug Made from Polyacetal (POM)



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Fig. 2



Fig. 3



view C



A



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Figure 4



Threaded plug with sprue



Figures 2 and 3 Single split cavity mold for a threaded plug of

POM

1 : cavity segments; 2: cam pin; 3: mold plate; 4: wear plate; 5 : mold

plate; 6: pneumatic nozzle; 7: nozzle tip; 8: spme; 9: ejector; 10:

hollow core; 1 1: cooling insert

(Courtesy: Hasco)



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Examples



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Example 14 / Example 15



Example 14, Demolding a Polyethylene Container with External Undercuts

The twenty-liter container (US Patent 4648834)

shown in the mold drawing (Fig. 1) has several

external rims that normally require side action in the

mold to be released.

Such side action significantly increases the cost of a

mold. This example shows that with clever use of

the shrinkage of the molded part and for moderate

undercut depth mold costs and manufacturing time

can be saved while simplifying mold handling

(weight, volume, mechanics).



Mold

The mold consists of a cavity half (1) and a core half

(2) which are guided by means of leader pins (3) and

aligned with respect to one another by means of a

taper lock (4).

A ring (5) that forms the underside of the rim on the

outside of the container is attached to the cavity half

(1).

Stripper rings (7, 8) that give the shape of the

external undercuts move on guide pins (6) attached

to the core (2) and passing through the tapered

alignment section (4). Stripper ring (7) is actuated

by ejector rods (9), while stripper ring (8) is attached

to stop bolts (10) that limit its motion.



Part Release/Ejection

Part release and ejection are described in Fig. 2 in

four steps.



Step I

The mold has opened. The molded part and core

have separated from the cavity.



Step I1

The stripper ring (7) is pushed forward by the ejector

rod (9). The molded part is pushed off the core,

while the undercuts continue to pull stripper ring (8)

along. The taper of the core now releases the inner

surface of the molded part, the diameter of which

decreases as the result of shrinkage, so that the rim

formed in the ring (8) can now be snapped out of the

recess. The ring (8) now stops.



Step I11

Stripper ring (7) now completely pulls the rim on the

molded part out of the ring (8).



Step IV

Ring (7) comes to a stop. The molded part is ejected

by air.

The air used to eject the part is directed to the inside

through the valve insert (1 1). Before the mold opens,

compressed air is forced under the bottom edge of

the container through the cavity half in order to

facilitate removal from the cavity.



Example 15, Injection Mold with Reduced Opening Stroke for Milk Crates

from Polyethylene

Beverage crates (US Patent 4731014) usually have a

grid-like structure on their exterior surfaces as a

result of the stacking rim, reinforcing ribs and

handles, the release of which requires the injection

mold to have external slides (side action). If the

slides are located in the stationary cavity half of

the mold, the opening stroke required equals twice

the crate height plus the axial stroke of these slides

in order to be able to eject the molded part.

The ejection principle described here needs a shorter

opening stroke. It is thus well suited for especially

deep parts or for stack molds.

The milk crate shown in Fig. 1 has dimensions

of 300mm x 300mm and a height of 280mm. Its

grid-like structure forms external undercuts.



Figures 2 to 4 illustrate the ejection principle along

with the additional possibility of releasing internal

undercuts (on the core).

The mold (Fig. 2) consists of the core (1) with core

lifters (2), cavity bottom plate (3) with spme bushing

(4) and the cavity frame (5) with movable external

slides (6). The cavity frame (5) can be moved in the

direction of mold opening by means of hydraulic

cylinders (7).

During opening (Fig. 3), the cylinders (7) hold the

bottom plate of the cavity (3) and cavity frame (5)

together. The molded part (8) is held in the cavity by

virtue of its external undercuts; the core (1) is

withdrawn. Any undercuts on the inside of the

molded part are released by the displacement of the



71



Example 15: Injection Mold with Reduced Opening Stroke for M i k Crates from Polyethylene

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Figure 2

Figure 1 Mold for a 20-liter container with external undercuts

1: cavity half; 2: core half; 3: leader pin; 4: taper lock; 5 : ring; 6: leader pin; 7:

stripper ring; 8: stripper ring; 9: ejector rod; 10: stripper bolt; 11: valve insert



8



7



Ejection sequence



Example 14



Example 15

Figure 1 Milk crate



7

5



6



2

1



a



Figure 2 Single-cavity mold for a milk crate

1: core; 2: core lifters; 3: bottom plate of cavity; 4: sprue bushing; 5 :

cavity frame; 6: external slides; 7: hydraulic cylinders; 8: molded part



72



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Examples



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Example 15/Example 16



Figures 3 and 4 Single-cavity mold for a milk crate

1 : core; 2: core lifters; 3: bottom plate of cavity; 4: spme bushing; 5 :

cavity frame; 6: external slides; 7: hydraulic cylinders; 8: molded part



core lifters (2) on the core (1). The molded part can

now shrink freely and becomes smaller than the

cross-section of the core. The cylinders (7) then

push the cavity frame (5) toward the core (Fig. 4).

The rim of the molded part which is now smaller

pushes against the core lifters (2) or core (1) in

which case the core lifters (2) if present are

pushed back.

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The external slides (6) located in the cavity frame (5)

do not follow the axial movement of the frame until

they are far enough apart to release the external

contour of the molded part (8). The molded part can

now drop free.

The opening stroke of the mold is thus only somewhat larger than the crate height H plus the distance

B required for the side action.



Example 16, Two-Cavity Injection Mold for Recessed Refrigerator

Handles Made from Polyamide

A two-cavity injection mold had to be made for

injection molding recessed handles for refrigerators

of polyamide reinforced with 35wt.% glass

fibres. The recessed handles (Fig. 1) have a grooved

internal structure, three flat channels from the

outside to the inside, two metal inserts to be

encapsulated, and recesses, into which the case of

the refrigerator door engages when the handle is

mounted.



Construction of the Mold (Figs. 2 to 5)

Because of the hnction of the molded part the main

axis of the handle indentation is set at an angle of

45" to the recesses which engage with the case walls.

Since the recesses and the attached and encapsulated

metal inserts are to demold on opening the mold

(Fig. 2), an ejection motion with an angle of less

than 45" to the handle must release the molding



Figure 1 Recessed refrigerators handles of

polyamide reinforced with 35 wt.% glass

fibers and two metal inserts

top: front; bottom: rear



Example 16: Two-Cavity Injection Mold for Recessed Refrigerator Handles Made from Polyamide



[rum the core (1 1). Further, a mechanical slide (13)

is required for releasing the flat channels and the

beaded edge of the mold.



Ejector Mechanism

The handles must be pushed away from cores (1 1)

without any tilting; thus, hydraulically operated

ejectors are not acceptible since, because of possible

differences in forward motion, they do not guarantee

exactly parallel guidance. It was decided to operate

the ejector by means of rack and pinion mechanisms

(23), which are dnven through pinions (19), shaft

(25), external geai-wheel (21), and racks (24), by the

opening movement of the mold. In order to ensure

the necessary delay in the ejector motion until

release of the molding by the mechanical slide (13),

the block (39) in the top half of the mold, which

encloses the outer racks (24), runs freely along a

distance of 24 mm in the recess in the mold plate on

the nozzle side, until meeting the stop. The loosely

inserted spring (42), which is tensioned by mounting

the mold on the machine, acts as support. Only when

the block (39) is stopped by the spring (42) on the

opposite side does the relative movement of the

outer rack (24) begin, rotating the outer gear wheels

(21), which again operate the internal rack drive.

The block (39), outer racks (24), outer gear wheels

(21), and spring (42) were economically mounted in

milled grooves on the top side of the mold, partially

enclosed by the cover plate (41). The shafts (25)

were mounted in bearings (36) under the outer gear

wheels (21) to maintain a low bending moment in

the spindles. Their exact position is achieved by

bearings, fitting the inner racks (23) to the actual

ejector (32), as well as by mutual displacement of

the outer racks (24) made possible by means of

slotted holes in these. The racks are finally

connected to the block (39) by pins (40). Subsequently, the outer racks are finally calibrated along

their length in order to ensure a precisely defined

ejector position in the case of a closed mold.



73



The slides (13) are made of steel with material no.

1.2541, while the mold components (10, 11, 12)

utilize steel no. 1.2343.



Runner

The spme opens into an S-shaped runner formed in

the cavity block (12). The S-shape provides a central

spme for both cavities, which are displaced because

of the rack and pinion ejector mechanism. An

overlapping gate connects with a central lug of the

respective molded part, which is concealed when the

handle is mounted, so that the mark caused by this is

unobtrusive.



Mold Operation

As the opening motion begins, the mechanical slides

(13) are moved outward by the cam pins (15) and

release the three flat channels. Simultaneously, the

spme begins to be released from the spme bushing

(31). After an opening distance of 24mm the open

recesses of the molded part and the metal inserts are

withdrawn from their cores. Then the motion of the

outer racks (24) begins relative to the ejector-side

mold half. The ejectors (32) are advanced, effecting

a movement of the molded part at an angle of 45" to

the mold axis. The resulting movement vertical to

the mold axis pulls off the overlapping gate. The

axial component of the ejection movement carries

with it the strip (lo), such that after a distance of

14 mm the recesses formed by the strip (10) are also

released. The moldings are now pushed hrther until

they fall from the core (1 1). Finally, the spme, which

in the meantime has also been hlly released, is also

ejected by the machine ejector through the spme

ejector (27).

On closing the mold, the spring (42) ensures that the

ejectors (32) have returned before the mold finally

closes. The return pins (28) for the spme ejector

have the same effect, but in this case synchronously

with the closing action.



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