Figure 2 Two-cavity injection mold for PMMA lighting fixture covers

The lifter 3 releases Gating/Runner System The two cavities are edge-gated and filled via a sprue and runner cut into the mold parting line.. Part Release/Ej ection Because the latch l

1 : slide; 2: cam pin; 3: ejector pin; 4: ejector delay mechanism; 5 ,

6: ejector plates; 7: detail insert; 8: pushback pin

Example 118, Two-Cavity Injection Mold for Polyacetal Hinges

The hinge shown in Fig 1 (dimensions: 86mm x

61 mm x 33 mm) requires a fairly complex release

and eject sequence, because of numerous hc tional

elements

Mold

The two cavities are oriented in the mold symme-

trically (Fig 2) The bore for the hinge pin is

released by means of a core (1) actuated by a cam

pin (2) (Section C-C, Fig 2) The lifter (3) releases

Gating/Runner System

The two cavities are edge-gated and filled via a sprue and runner cut into the mold parting line

Part Release/Ej ection

Because the latch lock (5) (View x) holds parting line I1 closed, the mold opens at parting line I During this motion, the cam pin (2) pulls the core (1) out of the bore for the hinge pin Opening stroke

I is limited by the stop (7) In the meantime, the latch lock (5) has released parting line 11 Next, the tapered surface on pin (8) releases the locking pin (9), which is withdrawn from the side core (4) by spring (lo), thus permitting the short tube on the top

of the hinge to be released Finally, the ejector rod (11) advances the ejector plates (12, 13), and the lifter (3) releases the hook-shaped undercut it contains, while the ejector pins eject the part and runner

Figure 1 Polyacetal hinge

1: core; 2: cam pin; 3: lifter; 4: side core; 5 : latch lock; 7: stop; 8: pin; 9; locking pin; 10: spring; 11: ejector rod; 12, 13: ejector plates

Two-cavity injection mold for polyacetal hinges

Example 119, Eight-Cavity Injection Mold for PE-HD Threaded Caps

The threaded cap shown in Fig 1 (dimensions:

30mm x 30mm) is part of a spray top for a bottle

At the top end, there is an inner ring with a bead that

forms an undercut all the way around

Mold

The mold is constructed from standard mold plates

with dimensions of 296mm x 196mm and has a

shut height of 356mm The eight cavities are

arranged in two groups of four cavities each The

internal threads are formed by two-piece threaded

cores that have the threads for the molded part at one

end (1) and gear teeth at the other end (2) Inside the

threaded cores are inner cores (3), the ends of which

form the inside surface of the inner ring with its

bead and associated undercut Each set of four

threaded cores is driven by a gear (4), which, in turn,

is driven by the main drive gear (5) The main drive

gear (5) is powered by a motor-driven quill (6), the

interior of which houses the ejector rod (7)

Gating/Runner System

The melt reaches mold parting line I via a hot-runner

manifold (8) and two hot-runner nozzles (9) There,

two spider-shaped runners convey the melt to the

submarine gates cut into the sides of the cavity

inserts (1 0) Sprue puller bushings (1 1) with ejector

Figure 1 PE-HD threaded caps

pins (12) for the runners are located opposite the tips

of the hot-runner nozzles (9)

Venting

The sleeve inserts (17, 18) provide venting for the region of the cavity that forms the circular rings at the top of the cap

Temperature Control

The cavity inserts (1 0) are cooled by circular cooling channels, while the mold plates on each side of mold parting line I are cooled by drilled cooling channels The inner cores (3) are hollow and contain a bubbler for water cooling

Part Release/Ej ection

The mold opens first at parting line I The caps are pulled out of the cavities, shearing off the submarine gates The threaded cores start to rotate and unscrew themselves from the caps Under the action of the springs (1 3), the mold opens at parting line I11 by an amount equal to that by which the cores have unscrewed from the caps After a distance H (View z), the latch lock (14) releases mold parting line 11 The inner cores (3) are now pulled out of the threaded cores as well as the inner rings in the molded caps The circular undercut is spread apart and released As soon as the threaded cores are unscrewed completely, the caps are ejected by the remaining ejector stroke available for ejector plate (1 5) Finally, the ejector rod (7) advances the runner ejector pins (12) to eject the two spider-shaped runners

The tension on the springs (13) must be adjusted carehlly to prevent unacceptable loads or even deformation of the ends of the threads as the result

of excessive force having been applied at the end of unscrewing

1 , 2: thrcadcd corcs; 3: inncr corc; 4: gcar; 5 : main d r i w gcar: 6: quill; 7:

ejector I-od; 8: liot-ruizr manifold; 9: hot-1-uuiei- nozzle; 10: cavity inseit;

I I : spiue puller biishing; 12: iiuuiei- ejector pin, 13: spring: 14: latch lock;

IS: ejector plate; 17; I S : .sleeve inserts

(Courtesy: Hasco, L.iidnisclieid Geiiiiaiiy)

Example 120, 4-Cavity Hot-Runner Mold for Connectors Made from

Polystyrene

The part, referred to as “connector”, is a rotationally

symmetrical sleeve with a total length of 134mm

The molded part is divided centrally by a

membrane-like intermediate wall and has a collar

in the same plane Its wall thickness all-round is

1/8mm The demolding incline is 0.2” (Fig 1) The

visible part has a high surface quality, and any gate

mark on the surface is unacceptable The design

specifies demolding in the direction of mold

opening

Figure 1 Connector made from polystyrene, diagram

Mold

This mold design with dimensions of

24mm x 246mm is based on a standardized modular

system The mold half on the nozzle side is designed

as a three-plate “hot half” and screwed together in

blocks (19, 20, 21) The centering and guide

elements (31 to 35) are arranged for easy servicing

The hot-runner mold has a high mounting height,

dictated by the article Both cavity plates (5, 6) are

equipped with mold inserts (23,24) Internal support

is provided by four support pillars (27), (Fig 2)

Gating

The direct gating point is located in the middle of the article intermediate wall It promotes uniform melt flow, thereby producing parts with little warp- ing The air-insulated melt chamber insert and the gate for the long, slim nozzle (18) are located in the contour insert (24a) made from hardened 1.2343 steel The nozzle body is screwed to the cavity plates (3) The nozzle and hot-runner manifold are force-fit connected by a sliding seal face

Thin walls and long flow paths require high injection pressures The externally heated, fourfold standard hot-runner distributor (1 7) with shrink-fitted diverters (17a) is naturally balanced The electric lines from the hot-runner manifold, the nozzle heaters, and thermocouples lead to the connection housing (30) and are connected according to DIN

16765, version B In order to reduce convective heat loss (so-called chimney effect) and to protect against flashing at the machine nozzle, a flat, form-fit GFK seal ring is mounted over the centering bush (16)

Cooling

Using water as coolant, heat is transferred via the outer surfaces of the mold insert (23, 24) and the cores (25) standing on the ejector side in the core retainer plate (1 0) Coolant is supplied to separately controlled, parallel configured circuits Core cooling

is done with long diverting elements via the clamping plate on the ejector side (1 1)

Demolding

The molded articles are demolded by the ejector sleeves guided by the mold core (26) The ejector assembly is set on pillars with fourfold rods (29) and sleeves (28) and connected to the machine ejector via the central ejector rod (1 3) Four return pins (36) move the ejector plates to start position

Figure 2

3, 5, 6: cavity plates, 9a, b: ejector assembly, 10: core retainer plate, 11: clamping plate, 13: ejector rod 16: centering bush, 17: hot-runner manifold block, 17a: diverter, 18:

Open sprue bush with tip, 23, 24: mold inserts, 24a: contour insert, 25: core, 26: ejector sleeve, 27: support rollers, 28: sleeve, 29: rods, 30: ancillaq housing, 31-35: centering sleeve

and guide elements, 36: return pin

(Courtesy: Hasco, Liidenscheid)

Fourfold hot-runner mold for connecters made from polystyrene

Example 121, Single-Cavity Mold for a Polypropylene Cutlery Basket

The basket (dimensions: 287 mm x 157 mm x

140mm; Fig 1) is used to hold cutlery in a dish-

washer It is divided into 16 compartments by three

partitions running lengthwise and crosswise The

outer walls and the bottom have a grid-like structure

In addition, two of the partitions have two openings

each lOmm square The numerous partitions, to-

gether with the high shrinkage of polypropylene,

pointed toward a high ejection force requirement to

strip the molded basket off the mold core Accord-

ingly, special measures were taken in order to ensure

that the part could be ejected without being damaged

in spite of its flexible grid-like structure

Mold

The mold (dimensions: 596 mm x 496 mm x

687 mm; Figs 2 to 6) was constructed largely using standardized mold plates from Strack Norma, Wuppertal, Germany Steel grade 1.2767 (hardened

to HRc 54) was used for the part-forming compo- nents The side walls of the basket are formed by four slides (18, 19) (Fig 2) that move laterally in gibs (33, 34) mounted on the stripper plate (3, Fig 4) The slides are supported by heel blocks (20,

2 1, 29) located in mold plate (2) and, when the mold

is closed, are held by additional support blocks and rails (30 to 32) in the stripper plate (3) When the mold is in the open position, the slides are held by spring-loaded ball detents to prevent any uninten- tional movement The slides are actuated by angled rods (38, 39) set at angles of 15" and 20" An angle

of 20" is used for angled rods (38) for the following reason: support block (30) serves also as a safety stop for the lower slide 18/1 If the angled rod (38) were set at an angle of 15", a collision with stop (30)

Hot runner mold for polypropylene cutlery basket

would have resulted For this reason, an angle of 20"

was specified, with the result that, for the same

stroke as the other slides, the length of the angled

rod could be reduced

Gating and Temperature Control

The part is filled via a hot runner system (23) using

two valve gates located in the bottom of the basket

Eight circuits, comprising cooling channels in the

slides, cavity inserts and cores, provide for mold

cooling

Part Release/Ejection

The part release and ejection sequence is controlled

by latches (A and B in Fig 6)

Step 1

The mold opens at the main parting line (I) or a

distance of 13mm, because parting line (11) is

initially held closed by latch (A) This releases the

part from the bottom of the cavity (12) The slides

(19, Fig 2) that form the short sides of the basket

move outward This releases the core pins (25),

10 mm, thereby bringing the blade ejectors as well as the stripper bar (54) into contact with the basket and supporting the part release operation

Step 3

Latch B locks parting line I1 at the lOmm position and releases parting line I hlly All four slides separate, releasing the molded part completely

Example 121: Single-Cavity Mold for a Polypropylene Cutlery Basket 3 17

The ejector plates (6) are advanced the remaining

distance by the machine's ejector The blade ejectors

(42) and the stripper bars (54) strip the basket

entirely off the mold core The positions of the

ejector plates, and thus of the blade ejectors and

stripper bars, are monitored by proximity switches

To prevent mold damage during set-up or in the

event of a mal hct ion of the ejector mechanism, a

mechanical safety is also incorporated:

~ The ejector plates (6) are not allowed to be

actuated until the mold has opened far enough to

permit the part to be stripped off the core

completely To this end, the ejector plates (6)

have attached to them inhibitor pins (43, Fig 4)

that prevent movement of the ejector system until

View ,A Mold open for 13 mm

the bores S in the slides (1 9) line up with the pins (43) Once the slides, and thus the mold, have opened sufficiently far, the pins (43) can enter the bores S, and the ejectors can advance

In order to prevent the ejectors from damaging the bottom of the cavity and also to avoid jamming the stripper bars into the slides, the mold

is not permitted to close until the ejectors are hlly retracted To this end, the inhibitor pins (43) that have entered the bores S in the slides (1 9) prevent closing of the slides as long as the ejector system

is not retracted As the mold closes, parting line (11) closes before parting line (I) is hlly closed This prevents the core pins (25) from scuffing the contour-forming cores as the slides (18) close completely Return pins (40) ensure that the ejectors are in the hlly back position

Example 122, Two-Cavity Injection Mold for Cover Plates Made

from Polyacetal

The cover plates (dimensions: 25 mm x 30 mm)

feature four mounting studs on one side and, in the

center of the other side, a pushknob that snaps into a

hole (Fig 1)

Instead of using the usual design based on slides to

release the circular undercut formed by the snap-fit

head on the pushknob, this mold uses two standard,

ready-to-install assemblies (Fig 2) Each of these

(supplier: Strack-Norma, Germany) consists of an

outer cylindrical sleeve (1, Fig 3) that holds two

jaws (2) which, when closed, form a truncated

square pyramid and move in dovetail guides in the

bore of the sleeve The jaws are actuated by a

pneumatically powered piston (3) on the rod end of

which the drive washers (4) are attached The jaws

are hardened; the internal shape was produced via

EDM Both the sleeve (1) and the pneumatic

Figure 1 Cover plate

cylinder (5) have circular cooling grooves that are sealed by Viton O-rings (6)

Gating/Runner System

The melt flows through a hot sprue bushing (7) to the runner channel cut into the mold parting line At each end of the runner, a submarine gate leads to one

of the mounting studs on the part

Part Release/Ej ection

As the mold opens, the jaws (2) stay in contact with the face of the moving half of the mold until the undercuts on the molded parts have been released The molded parts and runner remain on this half of the mold as it continues to open At the end of the opening stroke, the ejectors advance, separating the runners from the parts and ejecting both

The collapsible core assemblies are also available as standards with four jaws and ~ depending on the requirements and conditions ~ can be actuated by mechanical means, for instance, ejector systems Elastic ejector pins offer an alternative means of demolding undercuts Because of their elastic spring properties, these ejector pins release the undercut on mold opening A spring travel of up to 3 m m is available

1 : sleeve; 2: jaws; 3: piston; 4: drive washers; 5 : cylinder; 6: O-ring; 7: hot spme bushing

Part release and ejection

Example 123, Single-Cavity Injection Mold for a Joystick Baseplate

In order to satisfy the high functionality demands on

the molded part while keeping mold costs under

control, the baseplate (Fig 1) is produced from

PA 66 in a single cavity injection mold The article

dimensions are 49 x 49 x 3.4mm The molded part

weighs 2.8g with a spme weight of 1.6g

largely prefabricated standardized elements Due to circumstances in the mounting space for the injec- tion molding machine, longitudinally projecting clamping plates were selected that simplify tooling with threads for lifting and threaded bores The cavity plates are produced from prehardened steel and have quadratic pockets for installing the hardened inserts

A central two-stage ejector (6) is located on the closing side of the mold with predefined stroke sequence and variable stroke in order for the spme

to be removed separately upon demolding The hctional connection between the fourfold pillar- guided ejector assemblies (22 and 25) follows the scheme of the two-stage ejector shown in Fig 2 The relatively tall ejector box requires two spacer strips (7) that are connected with centering sleeves (8) Support pillars (9) are included to achieve the required bending strength Precise congruence is provided by three centering units with expansion compensation (1 0) between the nozzle-side cavity plate (2) and the stripper plate (3)

Figure 1 Joystick baseplate made from PA 66, diagram

Gating

Mold

This design (Fig 3) can be characterized as a

stripper plate mold with guide pillars (5) mounted

on the ejector side and a bush-guided stripper plate

(3) The mold is constructed from standardized

platens with dimensions 218mm x 246mm and

A flat machine nozzle is scheduled to feed in the centrally installed standard spme bush with a long spme cone (1 1) The semicircular cross-section of the submnner is incorporated in the mold insert and demolded in the cycle Since the sub runner is incorporated in the spme bush, an anti-twist device (dowel pin, 13) is required The part is injected laterally via a submarine gate Internal mold pres- sure is measured by a pressure transducer (14)