Example 35: Mold for a Polyamide V-Belt Pulley

Example 36: 2 x %Cavity Hot-Runner Stack Mold for Yoghurt Cups Made from Polypropylene 115 Example 36, 2 x %Cavity Hot-Runner Stack Mold for Yoghurt Cups Made from Polypropylene Stac

Example 35: Mold for a Polyamide V-Belt Pulley 113

0 6 5 m m

Figure 2

(Courtesy: Eisenhuth, Osterode)

Configuration of runner and gate

Example 35, Mold for a Polyamide V-Belt Pulley

Internal and external undercuts on injection molded

parts cause the costs for both mold making and mold

maintenance to increase considerably, since slides

and their actuating mechanisms become necessary

Moreover, with increasing use of the mold, the

reliability drops due to wear of precisely these

additional components

The polyamide V-belt pulley shown in Fig 1 is an

example of a practical design showing how slides in

the mold can be avoided If the V-belt pulley were of

a one-piece design, two or three slides per cavity would be required to form the V-belt groove in the pulley Any flash formed in the groove with this mold design could be removed only with a great deal

of effort If the flash were not carehlly removed, there would be a danger of damaging the V-belt By dividing the pulley across the axis of rotation, the mold design shown in Fig 2 becomes possible Furthermore, the snap fit required for assembly may also be achieved without the use of slides Both halves of the pulley were designed to be identical, so that the mold inserts are identical and any two pulley halves may be assembled together

The three-plate mold (Fig 2) operates hlly auto- matically Opening begins at parting line I, since plates (3) and (4) are held together by pin (25) and

latch (24) until the bar (23) releases the latch (24) via the adjustment screw (27) Further opening movement of (3) and (4) is prevented by stop bolts,

so that parting line I1 also opens, and the molded parts may be ejected by the ejector pins (17) After removing the diaphragm gates, the molded parts may be snapped together to form the V-belt pulleys

Figure 1

parts by means of Polyamide V-belt pulley, assembled from a snap connection two identical

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1 14 3 Examples Example 35

25 2L

1, 2: stationay-side clamp plates; 3: upper cooling plates; 4: upper cavity retainer plate; 5: lower cavity retainer plate; 6: support plate; 7, 8:

ejector plates; 9, 10: movable-side clamp plates; 11: support pillar; 12: lower cavity insert; 13: upper cavity insert; 14: core pin; 15: insert; 16: flat bar; 17: ejector pin; 18: spme bushing; 19: centring disk; 20: O-ring; 21: spme ejector; 22: guide pin; 23: release bar; 24: latch; 25: latch pin; 26:

Four-cavity injection mold for nylon V-belt pulley halves

Example 36: 2 x %Cavity Hot-Runner Stack Mold for Yoghurt Cups Made from Polypropylene 115

Example 36, 2 x %Cavity Hot-Runner Stack Mold for Yoghurt Cups

Made from Polypropylene

Stack molds for thin-walled cups must be built

extremely ruggedly and precisely in order to avoid

variations in wall thickness Air ejection eliminates

the need for mechanical ejector mechanisms and

involves little wear

Stack molds are employed whenever parts with low

weight, minimal wall thickness and large projected

area have to be produced in large numbers

These polypropylene yoghurt cups weigh 13.4 g and

have a wall thickness of 0.63 mm A unique feature

of these cups is the bottom rim (raised bottom),

which requires special release techniques Depend-

ing on the molding material used, yoghurt cups have

wall thicknesses of 0.4 to 0.65mm The wall

thickness within the cavity requires great accuracy,

i.e positioning of core and cavity must be extremely

precise, so that the melt does not advance down one

side, displacing the core in relation to the cavity

Should this be the case, it will be impossible to

obtain properly filled parts

Mold

Figures 1 and 2 show how ruggedly the entire mold, including core and cavity, has been dimensioned Each core (1) and its allotted cavity (2) are aligned

by the ring (3) All part-forming components are hardened, while the mold plates are nickel-plated The mold has been designed with the aid of a CAD system and its components have been produced by means of CAM techniques

Mold Temperature Control

The minimal wall thickness of the molded parts allows for rapid cooling if the cooling system in the mold has been laid out correspondingly As is customary with such cup molds, the cooling channels in core and cavity lie close together just below the mold surface The cores are capped (8) with Cu-Be

The paths ofthe cooling channels are shown in Fig 3

1: core; 2: cavity; 3: locating ring; 4: cavity; 5: nozzle bushing;

6: locating ring; 7: core head ring; 8: core cap; 9: heated spme bushing;

10: manifold; 11, 12: heating coils; 13: heatednozzle; 14, 15: gear racks;

16: pinion; 17: support cover; 18: support shoe; 19: guide rod; 20: air jet;

21: air channel for cavity bottom; 22: air channel for core; 23: sliding adapter; 24: piston

2 x 8-cavity hot-runner stack mold

a: cooling for hot-runner plate; 6 : temperature control for gate insert

plate; c: cavity temperature control; d : core temperature control

Example 37: 2 x 2-Cavity Stack Mold for Covers Made from Polypropylene 117

Runner System/Gating

The melt to be injected flows to the cavities through

a heated spme bushing (9), which is bolted to the

manifold (10) The manifold itself is heated by two

heating coils (1 1) and (12) embedded in it Eight

healed nozzles (13) lead to the cavities from the

manifold (1 0)

There is a sliding adapter piece (23) where the melt

enters the heated spme bushing (9) When the molding

machine’s nozzle lifts off after injection, the adapter

piece follows the nozzle, thereby increasing the

volume of the manifold The melt in it is allowed to

expand, thus stopping the spme bushing from drooling

Guides and Supports

A pair of racks (1 4, 15) is mounted on either side of

the mold, with a pinion (1 6) in between They ensure

the synchronous movement of the two parting lines

when the mold opens or closes Support pillars (17)

above and below the racks absorb the radial forces

transmitted by the meshed teeth when in operation

The mold weighs 2330 kg and is supported on the machine base by shoes (18) There are also four guide rods inside the mold (19)

Part Release/Ejection

The rim on the bottom of the cup can only be safely released if the cups are freed from the cavity bottom before the main parting line I opens This is achieved with compressed-air pistons (24), which push the mold apart first at parting line I1 on mold opening (Fig 4) In order to prevent suction from occurring at the cup bottom, air is blown in The cups now remain between the cavity insert (2) and core (1) until parting line I opens The molded cups are pulled out of their cavities and then blown off the cores by compressed air This is achieved via two annular gaps between core head ring (7) and the adjacent components (1)

or (8) There is a moving air jet (20) at the base of each core As the mold opens, compressed air enters the air channel (21), the air jet (20) moves forward and an air blast blows the falling cups in a downward direction out of the mold

Example 37: 2 x 2-Cavity Stack Mold for Covers Made from Polypropylene

The cover for a coffee maker has a diameter of

135mm and is 13mm high Two small depressions

are located on the outside edge, while two snap fits

are found on the inside In addition, an “ear” is

found on the side of the cover

Mold

The mold has dimensions of 646 mm x 390 mm and

a shut height of 736mm, with a weight of 1000 kg

The part-forming inserts are made of through-

hardened steel (material no 1.2767)

For such a cover (large projected area, minimal height,

minimal weight), it makes sense to use a stack mold

The four cavity inserts (2) are arranged in opposite

pairs in the center plate (1) of the mold

Gating

The center plate also holds the four externally heated

hot-runner nozzles (4) and the hot-runner manifold (6),

that is heated with heater cartridges (5) Melt is con-

veyed to the manifold via the heated spme bushing (7)

The heated spme bushing (7) follows the motions

of the center block and is enclosed in a stationary

protective tube (8) that prevents any melt from

drooling into the stationary-side ejector housing

from the bushing plate (9)

A short runner (10) connects each of the four hot-

runner nozzles (4) to the “ear” of the cover via a

submarine gate

Sucker pins (1 1) pull the solidified runners away from the hot-runner nozzles and out of the tunnel gates upon mold opening and then eject them

Temperature Control

The cores and cavity inserts are provided with a system of cooling channels that cover their respec- tive surfaces Additional cooling lines are located in the center plate (1) to remove the unavoidable heat radiated by the hot-runner system

Demolding

To release the outer depressions, each cavity has two slides (13) actuated by cam pins (12) attached to the cavity insert and guided along the core The inner snap fits are released by lifters (14)

Ejector pins (1 5) are used to eject the molded part from the core Three moveable core pins (17) position the cover during ejection After a stroke “X”, the cover is stripped off the core pin by a sleeve ejector (1 6) The stationary-side ejector plate (1 9) is operated by hydraulic cylinders (2 l), while the moveable-side ejector plate (20) is operated by the machine’s ejector Both ejector plates run in ball guides (22) Two racks (23) connected to each other by means of

a pinion (24) are provided on the two narrow sides

of the mold to ensure synchronous opening and closing of both parting lines

1: center block; 2: cavity insert; 3: core; 4: hot-runner nozzle; 5: heater cartridge;

6: hot-runner manifold; 7: heated spme bushing; 8: protective tube; 9: bushing

plate; 10: runner; 11: sucker pin; 12: cam pin; 13: slide; 14: lifter; 15: ejector pin;

16: sleeve ejector; 17: core pin; 19, 20: ejector plates; 21: hydraulic cylinder; 22:

25

23 2L

Example 38: 2 x 5-Cavity Stack Mold for Cases Made from Polypropylene 119

Example 38, 2 x 5-Cavity Stack Mold for Cases Made from Polypropylene

For a case in which the base and lid are connected by

an integral hinge (Fig l), a stack mold has

been designed with five mold cavities in each of the

two parting lines This means that each shot

produces 10 complete cases Due to the surface

quality specified for the outside, the molded parts

are gated on the inside surface; base and lid each

require a separate gate

Figure 1

integral hinge (left opened, right closed)

Case in which the base and lid are connected by an

Mold

The mold mounting dimensions have been so

selected that it can be used on two different injection

molding machines with different distances between

tie bars Because of the mold’s weight, it is also

supported by shoes that fit over the tie bars of the

injection molding machine in addition to its own

four guide columns The mold shown in Figs 2 to 5

can be adapted to either tie bar spacing with the aid

of the reversible adaptor (10) and the two semi-

circular bearings (28) contained therein

The moving central section of the mold accom-

modates the hot-runner manifold (5), which is

heated by heater elements (63) cast in aluminum

The melt flows from the hot-runner manifold through a heated nozzle (42) to the respective gate in the base or lid of the case The individual cavities are formed by the inserts (17) and (18) For appearance reasons, the gates are positioned asymmetrically The hot-runner manifold (5) is fed by the machine’s nozzle through a spme bushing (20) which is heated

by the tubular heater (64)

The total installed heating capacity amounts to about 13.5 kW It is divided up as follows: 20 x 300 W for the hot-runner probes, 7000W for the hot-runner manifold and 450W for the tubular heater used around the spme bushing When in operation, the connected load is about 7.5kW The hot-runner probes can be independently controlled; their temperatures are monitored by built-in thermo- couples Four control circuits are provided for the hot-runner manifold The temperature of the spme bushing is controlled by the injection molding machine’s closed-loop control in the same way as is the nozzle on the machine

Mold Temperature Control

Twenty circuits connected to a water manifold by quick disconnect couplings have been provided for cooling the molded parts

Part Release/Ejection

To eject the cooled parts, the mold opens with synchronous separation of the two parting lines ensured by the action of the racks (6) and pinion (7) During the opening motion, the molded parts are retained on the central section until the racks actuate the ejector plates (3A) and (3B), thereby ejecting the molded cases and separating them from the gates During mold closing, pushback pins return the ejector plates to their original positions again

120 3 Examples - Example 38

Fig 2

Fig 3

2 to 5 2 x 5-cavity stack mold for cases

3& 3D: ejector plates; 5 : hot-runner manifold; 6: rack; 7: pinion; 10:

reversible adaptor; 17, 18: mold inserts; 19: mold clamp; 20: heated spacer bushing with filter element; 28: semi-circular bearing; 42: hot-

m e r probe; 47: locating ring; 63: heat element; 64: tubular heater

Example 38: 2 x 5-Cavity Stack Mold for Cases Made from Polypropylene 121

57

6

1A I4 2A 41 3A 40 4 30 16 20 I0 15

Figures 2 to 5 2 x 5-cavity stack mold for cases

3A, 3D: ejector plates; 5 : hot-runner manifold; 6: rack; 7: pinion; 10:

reversible adaptor; 17, 18: mold inserts; 19: mold clamp; 20: heated

spacer bushing with filter element; 28: semi-circular bearing; 42: hot-

runner probe; 47: locating ring; 63: heat element; 64: tubular heater

Example 39: 16-Cavity Hot-Runner Mold for Packaging of Medical Parts made from Polypropylene 123

Example 39, 16-Cavity Hot-Runner Mold for Packaging of

Medical Parts made from Polypropylene

The tubular medicinal packaging parts are internally

threaded on both sides separately and divided in

the middle by a thin wall They are produced from

an easily flowing polypropylene known for being

ropy To keep this effect from causing problems in

production and application, suitable measures had

to be taken with regard to the hot-runner system as

well as to thermal control In addition, it was also

necessary to comply with the strict requirements

of cleanroom technology, which involved conse-

quences for the choice of a suitable hot-runner

system

For the mold, an individually regulated 16-cavity

model with externally heated hot-runner manifold

and open, externally heated gating nozzles with

tips (Figs 1 and 2) was selected Special difficulty

was presented by the necessity to locate each of the

gating nozzles between the unscrewing spindles

(not adequately illustrated on the drawings) on both

the nozzle as well as the closing side The solution

arranged the gating nozzles horizontally to gate the

molded parts directly from the side Lateral con-

figuration without tips would be at least proble-

matical Depending on cycle time, materials, and

temperature, the gate in such a system tends to

freeze; any resulting “cold plug” would then be

injected into the cavity at the next cycle and could

cause unacceptable surface defects, for example

These problems can be solved with inside mounted

heat-conducting (torpedo) tips in conjunction with

optimum mold cooling To keep the melt from

dripping into the cavity, melt decompression (pres-

sure release, e.g., by screw retraction) is required

Each nozzle body is radially sealed and centered in the gating area by titanium alloy sealing rings chosen for their low thermal conductivity factor (to avoid heat loss in the gating area) The head mount

of the gating nozzle at the hot-runner manifold block

is a sliding seal face The reactive force resulting from both injection pressure and pressure-stressed difference surfaces has a desired sealing effect by generating surface pressure between the nozzle head and hot-runner manifold block The lateral forces are absorbed by the moveable cavity plate The mold inserts and gating nozzles with four cavities each can be dismounted, e.g., for maintenance, on the machine when the mold is open The hot-runner manifold block with a width of only lOmm in the nozzle area is a very compact design The drilled

runner channels are naturally balanced The narrow,

“sword-shaped’’ area of the hot-runner manifold block is indirectly heated Thanks to the twofold heat source (from hot-runner and nozzle), tempera- ture difference should be negligible

an ejector pin

124 3 Examples Example 39

Figure 1 16-cavity hot-runner mold

with so-called sword distributor and horizontally arranged heated gating nozzles with tips