Example 24, Injection Mold for an Angle Fitting from Polypropylene

90 3 Examples ~ Example 24/Example 25 Example 24, Injection Mold for an Angle Fitting from Polypropylene If ejectors are located behind movable side cores or slides, the ejector plate

90 3 Examples ~ Example 24/Example 25

Example 24, Injection Mold for an Angle Fitting from Polypropylene

If ejectors are located behind movable side cores or

slides, the ejector plate return safety checks whether

the ejectors have been returned to the molding

position If this is not the case, the molding cycle is

interrupted

This safety requires a switch on the mold that is

actuated when the ejector plate is in the retracted

position The ejector plate return safety thus h c -

tions only if the molding cycle utilizes platen

preposition, i.e., after the molded parts have been

ejected, the clamping unit closes to the point at

which the ejector plate is returned to the molding

position by spring force Only then does the control

system issue the “close mold” command In molds

requiring a long ejector stroke, spring return of the

ejector plate is often not sure enough For such

cases, there is an ejector return mechanism that

hlfills this h c t i o n Attachment of the ejector plate

return safety is shown in Figs 1 to 7

This single-cavity mold is used to produce an angle

fitting (1) Two long side cores (2) meet at an angle

of 90” The somewhat shorter side core is pulled by

a cam pin (3), while the longer core is pulled by a slide (4) The difficulty is that blade ejectors (5) are located under the two cores and must be returned to the molding position after having ejected the finished part before the two cores are set as the mold closes and possibly damage the blade ejectors Possible consequences include not only broken blade ejectors but also a damaged cavity Either of these could result in a lengthy interruption of production For this reason, a helical spring (6) that permits operation with platen preposition is placed

on the ejector rod This spring then returns the ejector plate

To ensure proper operation, a microswitch (7) is mounted to the clamping plate (S), while a pin (10) that actuates the switch is mounted in the ejector plate (9) After connecting the cable with the switch housing of the movable clamping plate, the ejector plate return safety is complete

Example 25, Mold for Bushings from Polyamide with Concealed Gating

A flanged bushing is to be injection molded in such

a way that any remnants of the gate are concealed or

as inconspicuous as possible The bushing would

normally require a two-plate mold with a single

parting line The molded part would then be released

and ejected along its axis, which coincides with the

opening direction of the mold The gate would be

located on the outer surface of the flange since it is

in contact with the mold parting line

In order to satisfy the requirement for an “invisible”

gate, the cavities (two rows of four) are placed

between slides carrying the cores (Fig 1) even

though there are no undercuts From a central sprue

the melt flows through conical runners in the cores

to pinpoint gates located on the inner surface of the

bushings As the slides move during opening of the

mold the gates are cleanly sheared off flush with the

adjacent part surface The flexibility of the plastic

selected is sufficient to permit release of the end of

the runner from the angled runner channel The parts

are now free and can drop out of the mold

11

12

9 ’ io

Figure 1

1: stationay-side clamping plate; 2: stationary-side backing plate; 3:

wedge; 4: slide; 5 : movable-side backing plate; 6: injection-side cavity half; 7: ejector-side cavity half; 8: core; 9: spme bushing; 10: locating ring; 11: part ejector; 12: sprue ejector

Mold for bushings with concealed gating

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Example 26: Injection Mold for the Valve Housing of a Water-Mixing Tap Made from Polyacetal 91

Example 26, Injection Mold for the Valve Housing of a Water-Mixing Tap -

Made from Polyacetal

Avalve housing (Figs 1 and 2) had to be designed

and produced for a water-mixing tap The problem

when designing the tool (Figs 3 to 7) resulted from

the undercuts in four directions Originally occurring

considerable differences in wall thicknesses have

been eliminated during optimization Demands for

high precision of the cylindrical valve seat in

Figure 1

places of core penetration

Company photo: ARCU, Altemo/Sweden

View of the interior of the valve housing, showing the

particular were negatively influenced by various recesses in the wall and adjoining partitions, which favored sink marks and ovalness

Polyacetal (POM) had been chosen as molding material The complete molded part had to have homogeneous walls, and be free from flow lines if at all possible, as it would be subjected to ever- changing contact with hot and cold water during an estimated long life span Inadequately hsed weld lines would be capable of developing into weak spots and were therefore to be avoided at all cost Provision has been made for an electrically heated spme bushing (30) (Fig 6) in order to avoid a long spme The resultant very short runner leads to the gate on the edge of the pipelike housing,

to be hidden by a part that is subsequently fitted to cover it

Two cores each cross in the pipe-shaped housing, i.e one core (1 6) each penetrates another core (1 9) This obviously presents a danger spot should the minutest deviation occur from the specified time- and movement-based coordination as well as from the accuracy in the mold

The hollow cores (19) are kept in position by mechanical delay during the first phase of mold opening, while the crossing cores (16) are each withdrawn by an angle pin (31, 32) Mechanical actuation has been preferred over a hydraulic or pneumatic one in this case in order to exclude the danger of a sequencing error (the so-called human factor) during set-up and operation

The cores (16, 33) consist of a copper-beryllium alloy They are cooled by heat conducting pins (27, 28)

Figure 2 View of the exterior of the valve housing

Company photo: ARCU, Altemo/Sweden

Figures 3 to 7 Injection mold for the valve

housing of a water-mixing tap

1, 2, 3, 4: O-rings; 5, 6, 7: core clamping rings; 8,

9: core retainer with angle pin hole; 10: core

retainer with angle guide; 11, 12: wedge; 13:

guide rail; 14, 15: guide plate for core retainer;

16: internal core; 17, 18: external core; 19: core;

20: upper mold cavity half; 21: lower mold cavity

half; 23: insert; 25: angle guide; 26: core baffle;

27, 28, 29: heat conducting pins; 30: heated spme

bushing; 31, 32: angle pins; 33: support core; 34,

35: ejector; 36: spme ejector; 37: return pin; 38:

locating ring; 38, 40, 41: stop; 43: screw; 44: lock

nut; 45: fixed mold plate; 46: retainer plate for the

upper mold cavity; 47: temperature control

medium connection; 48: lower mold cavity retai-

ner plate; 49: moving mold plate

(Courtesy: Seveko Fristedt & Sundberg, Karlskro-

na/Sweden, and Gustavsson Gravyr, Stockholm)

Example 27: Mold for a Lid with Three Threads Made from Polyacetal 93

Example 27, Mold for a Lid with Three Threads Made from Polyacetal

The lid is a rotationally symmetrical part with three

threads Threads I and I1 are of the same pitch and

can be formed by a single threaded core The

material employed is polyacetal The total number of

units to be produced is small The mold (Figs 1 to

5) is of simple design The external shape of the

molded part is formed by an insert (c), which is

housed in mold plate (b) and secured against rotat-

ing The temperature of this insert is controlled via a

ring channel (heating/cooling system A) Thread I11

is formed by two slides (d) The part is injected

through a diaphragm gate (e) The internal shape of

the lid is obtained from a main core cf), which is

housed in the mold plate ( p ) and is secured against

rotating The temperature of this core is controlled

via an internal tube (heating/cooling system B) Its

effectiveness is increased by the soldered-on spiral

(g) The threads I and I1 are formed by a single

threaded core (h) Because of the low number of

moldings required, the mold has been designed for

the threaded core (h) to be unscrewed outside the

tool The threaded core is inserted into an ejector

ring (i) and is retained by three springloaded detents

The mold opens at parting plane 1-1 positively

assisted by two latches (m) The threadforming

slides (d) are moved outward by this action After a distance of 18 mm the latches are released by the

control strips (n) and the mold opens at the main

parting plane 11-11 By actuation of the machine

ejector the threaded core (h) is pushed in the

direction of the fixed half by three ejector pins (0)

and the ejector ring (i) for a distance of 90mm (height of the molding plus 10mm) During the movement the threaded core strips the molding off the fixed core cf) Then the molded part, with the

threaded core (h), is pulled manually out of the

stripping ring (i) without any danger of damaging the fixed main core cf) Unscrewing takes place outside the mold with the aid of an unscrewing device To shorten the cycle time, several tempera- ture controlled threaded cores are employed While one part is being unscrewed, the next molded part is being produced

Figures 1 to 5 Mold for lid with three threads

a: molded part; 6 : cavity plate; c: insert; d : slides; e : diaphragm gate;

f : main core; g : spiral; h : threaded core; i: ejector ring; k : spring-

loaded detent; I : core; m: latch; n: control strip; 0: ejector pin; p : mold

Example 28: Two-Cavity Injection Mold for Coupling Sleeves Made from Polyamide 95

Example 28, Two-Cavity Injection Mold for Coupling Sleeves Made from

Polyamide

The coupling sleeve in Figs 1 to 5 had to be

produced in a PA 66 with 30% by weight glass fiber

reinforcement The injection molded part has a

center hole, entered by tapped M 10 holes that,

starting from the peripheral surface, are opposite

each other As set screws are screwed into each

tapped hole to push against a centrally fitted shaft, it

is not necessary to have a continuous thread in both

holes, which would have called for a bridging

threaded core that would have had to cross the center

core Apart from problems with sealing, the un-

screwing device also would have caused difficulty,

as it would have had to perform a larger stroke Use

of the molded part allows for two separate threaded

cores to be operated independently of each other, so

that they can be driven by one rack each To avoid

M h e r core pulls for the remaining shape of the molded part, it is put perpendicularly into the parting line of the mold by its axis of symmetry

Concerning direct operation of the threaded cores by racks, a check must be made to ascertain that adequate transmission can be achieved or if inter- mediate stages are required to avoid an excessively long rack stroke

The pitch of the metric thread M 10 is h = 1.5mm Allowing for a certain safety, an unscrewing distance

of 11 mm must be taken up, which results in 1111.5 = 7.33 rotations of the threaded core For a

Example 29: Injection Mold for the Housing of a Polypropylene Vegetable Dicer 97 pitch circle diameter of do = 12 mm and a modulus

of rn=O.Smm, the pinion of the threaded core

works out at t = 12/0.8 = 15 teeth and a pitch circle

circumference of 12 x 7c = 37.68mm For 7.33

turns this results in a required rack stroke of 7.33 x

37.68 = 276.19 111111

Standard hydraulic cylinders of 280mm stroke are

available Divided by the pitch d = 7c x m =

2.5 mm of the gear tooth system, this corresponds to

112 teeth on the rack, which with 15 teeth on the

pinion turns the latter 7.46 times during one stroke

From this results an unscrewing distance of

1 1.19 mm, which is sufficient It must be checked

whether the space available on the injection

molding machine allows installation of the mounting

hardware and the hydraulic cylinder under the

mold

The mold design (Figs 6 to 12) is such that two

sleeves (1) can be produced at the same time The

unscrewing equipment has been installed in the fixed

mold half (3) so that the hydraulic cylinder (14) does

not have to participate in the opening and closing

movement but can remain in position

The center bore of the coupling, which tapers toward

the moving mold half, is formed by two cores (4)

and (5) which are self-centering

The locators (6) for the threaded cores enter the core

(4), which is held in the stationary side of the

clamping plate, from both sides The threaded cores

are made up of the locators (6), the M 10 thread (7),

a guide (8), the 15 gear teeth (9), and the guide

thread (1 0) at the other end, which runs in the fixed

guide bushing (11) The two racks (12) and (13) have been arranged offset to each other so that opposite directions of rotation can be transmitted to the opposing threaded cores The hydraulic cylinder pushes the racks (12) and (13) up to unscrew the threaded cores The upper racks protrude from the mold and need to be guarded by a screen For interlocking with the machine’s control circuit for the cycle sequence, the racks contact switch (1 5) in the lower and switch (1 6) in the upper position By employing lateral submarine gating (1 7), the coupling sleeves are automatically degated from the runner (1 8) This is fed directly through a beryllium- copper nozzle tip (20), which is screwed into the female thread of the nozzle on the machine (1 9) to avoid the conventional tapered sprue penetrating the fixed mold half (3)

The operating sequence of the unscrewing mold takes place as follows:

The racks are moved in by the hydraulic cylinders, unscrewing the threaded cores from the molded parts Then the opening movement of the mold starts When finished, the hydraulic ejector of the machine, to which the ejector bar is coupled (21), pushes forward the ejector plates (22) and through them the ejector pins (23) for the coupling sleeves and runner For safety, the push-back pins (24) also move out simultaneously They have to return the ejector plate to the starting position in any case when the mold closes Once the mold is closed, the racks are pulled up again and the new cycle can start with injection

Example 29, Injection Mold for the Housing of a Polypropylene

Vegetable Dicer

Molded Part

The housing accommodates a cutting disc that is

driven by a hand crank (Fig 1) The shaft of the

crank drive is located in a bore in the housing

The underneath of the housing has a recess for

accommodating a suction cap to attach the device to

a table The top of the housing has a filling shaft which supplies the cutting disc with the vegetables

to be diced A feed hopper will be attached to this filling shaft The molded part weighs 386g

The mold was designed so that the dicing chamber

lies in the mold-opening direction The housing

base, the filling shaft and two other apertures are

ejected with the aid of splits, a core puller and slides

(Figs 4 and 5)

The slide (23), moved by the angle pin (24), forms

the inside contour of the housing base (Fig 2) In the

closed position, the split shoulder (28) lies against

punch (21) and so forms the bore for attaching the

suction cap to the housing base The cylindrical slide

lies in the mold parting line and each half is

Figure 2 Longitudinal section through the injection mold for the housing

1: ejector retaining plate; 2: ejector base plate; 3: cylinder pin; 4: ejector pin; 5: locating ring; 6: stop plate; 7: ejector rod; 8: core pin; 9: ejector sleeve; 10: locating pin; 11: screw; 12: return pin; 13: guide pillar; 14: guide bushing; 15: support plate; 16: buffer pin; 17: mold insert; 18: punch; 19: locating pin; 20: sprue bushing; 21: punch; 22: punch retaining plate; 23: slides; 24: angle pin; 25: adjusting plate; 26: wedge: 27: mold plate (nozzle side); 28: split shoulder; 29: cooling pipe; 30: mold plate (clamping side); 31: adjusting plate; 47: bar; 48: mounting plate

enclosed by the mold plates (27) and (30) Guide strips (50) (Fig 3) lead the slide on the mold plate (30) The slide supports itself against the effect of the cavity pressure via the adjusting plate (25) and the wedge (26) Bending of the wedge is prevented

by the adjusting plate (31) and the mold plate (30) The vegetable filling shaft and the passage to the dicing chamber are formed by the mobile core (33) (Fig 6) Its movement is provided by the angle pin (32) Figure 7 shows the core guide in the guide strip (45) The inserted core is locked via the wedge (35) and adjusting plate (34) The guide strip (37) (Fig 8) forms a rectangular opening in the side wall of the housing which lies half over and half under the mold parting line It is moved by two angle pins (38) and

is locked in the closed state by two bolts (39) A guide strip (49) which is bolted and doweled to the mold plate (30) is guided in a T-slot (Fig 9) Finally, a slit has to be formed in the housing wall that penetrates a reinforcement there Rectangular aperture and reinforcement are formed by the slide (40) (Fig 10) which is actuated by the angle pin (41) and locked by the wedge (42) Two bars (51) (Fig 11) serve to guide the slide on the mold plate (30)

Figure 3 Guiding of mold slides in Fig 2

Example 29: Injection Mold for the Housing of a Polypropylene Vegetable Dicer 99

Figure 4 View of the moving side of the injection mold for a PP

PP housing View of the stationary side of the injection mold for a

Since the angle pins traverse out from the slide, the

core and the guide bars on mold opening, each is

provided with ball catches that keep these guide

elements in the “open” position Bars (47) and rolls

(43) support the plate (1 5) on the clamp plate (48)

Part Release/Ejection

On side push the splits, cores and slides on the

opening, the angle Pins on the fixed

Runner System/Gating

The spme bushing (20) lies on the axis of the

housing bore, which accommodates the blade drive

shaft The end of the spme bushing forms the face of

an eye inside the dicing chamber that is a part of

the crankshaft mount A core pin (8) protrudes

into the bore of the spme bushing and divides

the spme into three pinpoint gates

Mold Temperature Control

The coolant is guided in bores and cooling channels

in the mold plates, inserts and punches The splits

(23) and (33) Offer sufficient space for

modating cooling channels (33) Figure 6 Demolding of the feed in a vegetable dicer

Figure 7 Core guiding for Fig 6

44: punch; 45: guide bar; 46: punch

Figure 8

37: slide; 38: angle pin; 39: locking bolt

Demolding the rectangular aperture

moving side so far outward that they release the

undercuts of the housing The molded part

remains on the moving mold side Ejector pins (4)

and ejector sleeve (9) push the molded part out of

the ejector-side mold cavities and off core pin (8)

Since the ejector pins are contour-forming, they

Figure 9

49: guide bar

Figure 10 Demolding a slot

30: slide; 41 angle pin; 42: wedge

Figure 11

51: guide bar (Courtesy: Plastor p.A., Oradea/Romania)

Slide guide for Fig 8

Slide guide for Fig 10

must be secured against twisting (pin 3) On mold closing, the ejector system is brought into the injection molding position by ejector-plate return pins (12) and buffer pins (16), and so too are the splits, cores and slides by their respective angle pins