WO2000066295A1

WO2000066295A1 - Manufacture of moulded products

Info

Publication number: WO2000066295A1
Application number: PCT/ZA2000/000090
Authority: WO
Inventors: Hendrik Jakobus Van Wyk
Original assignee: Hendrik Jakobus Van Wyk
Priority date: 1999-05-04
Filing date: 2000-05-04
Publication date: 2000-11-09
Also published as: AU5049800A

Abstract

Spin casting apparatus is described which comprises two mould plates (62, 90), which are rotatable about the vertical axis of a column (30). The lower mould plate (62) can be moved vertically towards and away from the upper mould plate (90) by means of a pneumatic cylinder (18) which displaces the shaft (52). The column (30) is rotated by means of a belt (44) and pulley (42) driven by a motor (46). Ejector pins (74) are provided for freeing a casting when the lower mould plate (56) is lowered by the cylinder (18). The ejector pins are advanced and retracted automatically by two stripper plates (70, 72).

Description

MANUFACTURE OF MOULDED PRODUCTS

FIELD OF THE INVENTION

THIS INVENTION relates to spin casting.

BACKGROUND TO THE INVENTION

Spin casting is a technique which has been used for the production of

articles in low melting point metals such as zinc. The mould used is made of hard

rubber and comprises an upper part and a lower part each of which is in the form of a

disc. The mould cavities are formed by recesses in the top surface of the lower part

which register with recesses in the bottom surface of the upper part when the upper

part is placed on the lower part. Once in register the mould parts are clamped between

upper and lower plates.

The upper mould part and the upper plate have registering central

openings into which molten metal is poured. The lower mould part does not have a

central opening but is unapertured. Thus molten metal entering via said central

openings drops onto the lower mould part. Runners cut in the lower mould part extend

outwardly from the central opening in the upper mould part to the mould cavities which

are arranged in an array around the common vertical axis of the two parts. The registering mould parts and the two plates are then spun about the

common vertical axis of the mould parts so that the molten metal flows outwardly from

the central opening along the runners to the mould cavities.

After spinning, the upper and lower plates are separated and the

registering mould parts removed from between the plates. The upper mould part is

lifted-off the lower mould part leaving the casting exposed on the lower mould part. The

casting is then lifted off the lower mould part, the lower mould part being distorted if

necessary to free the casting. The cycle described is then repeated.

The present invention seeks to provide improved spin casting apparatus

and an improved spin casting method which can be used particularly, but not

exclusively, with high melting point metals such as aluminium.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention there is provided spin

casting apparatus which comprises an upper mould plate mounted for rotation about a

vertical axis, a lower mould plate mounted for rotation about said axis, means for

displacing said plates towards and away from one another between a mould closed

position and a mould open position, ejector pins for ejecting a casting, and means for

retracting said ejector pins to inoperative positions as the mould plates are moved

towards one another and for advancing said ejector pins to operative positions as the mould plates are moved apart.

The spin casting apparatus can include means for lifting and lowering said

lower mould plate, means on which said ejector pins are mounted, an operating

element for displacing the ejector pin mounting means downwardly with respect to said

lower mould plate as the lower mould plate is lifted, and a further operating element for

lifting said mounting means with respect to said lower mould plate as the lower mould

plate is lowered. Preferably each ejector pin comprises a shank and a head and the

mounting means therefor comprises a pair of plates with said heads between them, the

shanks of the ejector pins passing through the upper plate of said pair of plates.

In a specific form said operating element for displacing the mounting

means downwardly comprises an element mounted on said upper plate of said pair of

plates and extending upwardly toward said upper mould plate so that it is forced down

with respect to the lower mould plate when its upper end encounters the upper mould

plate as said lower mould plate is lifted. In this form said operating element for lifting

said mounting is carried by a base plate which is itself below said pair of plates, the

operating element which lifts said mounting passing through the base plate and being

displaceable vertically with respect thereto to displace the mounting means upwardly

with respect to the lower mounting plate as the lower mounting plate is lowered.

The displacing means can comprise a pneumatic cylinder having a rod, a thrust bearing to one race of which said rod is connected, and a shaft connected to the

other race of said thrust bearing, said lower mould plate being mounted on said shaft

and being displaceable vertically with said shaft. The apparatus can further comprise a

hollow column, bushes within said column, said shaft sliding axially within said bushes,

and means for rotating said column, said upper mould plate being connected to said

column for rotation thereby.

According to a further aspect of the present invention there is provided a

spin casting method which comprises feeding molten material to a central space of a

mould comprising upper and lower mould parts, spinning the mould so that the material

flows outwardly from said space to a mould cavity to fill the cavity, separating said

mould parts, and advancing ejector pins from retracted inoperative positions to

advanced operative positions as the mould parts are separated thereby to eject the

casting from the mould cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the

same may be carried into effect, reference will now be made, by way of example, to the

accompanying drawings in which:-

Figure 1 is a diagrammatic side elevation of spin casting apparatus in

accordance with the present invention; and Figure 2 illustrates a detail of the apparatus of Figure 1 to a larger scale.

DETAILED DESCRIPTION OF THE DRAWINGS

The spin casting apparatus 10 illustrated in Figure 1 comprises a

framework only some parts of which have been shown. More specifically, the illustrated

parts of the framework comprise a lower channel 14, an upper channel 16 and an

intermediate channel 18.

A vertically positioned pneumatic cylinder 18 is mounted on the channel

14. The body of the cylinder is designated 20 and its piston rod 22. The lower race 24

of a thrust bearing 26 is connected to the upper end of the rod 22.

A rotatable structure 28 comprises a hollow column 30, a base plate 32

welded to the upper end of the column 30, a plurality of posts 34 arranged in a circular

array around the base plate 32, and a top plate 36 secured to the tops of the posts 34.

The column 30 is supported by and rotatable in bearings 38 and 40 which

are carried by the channels 16 and 18. A pulley 42 is secured to the column 30 and

connected by a drive belt 44 to an electric motor and gear box designated 46.

It will be understood that the column 30, base plate 32, posts 34 and top

plate 36 are all rotated by the motor and gear box 46. Within the column 30 there are upper and lower bushes 48 and 50

through which a shaft 52 passes.

The shaft 52 has its lower end connected to the upper race 54 of the

thrust bearing 26.

The upper end of the shaft 52 is fast with a lower mould structure

designated 56 (see also Figure 2). The structure 56 comprises a bottom plate 58 and

an array of columns 60 which join the bottom plate 58 to a lower mould plate 62. A

mould 64 having runners 66 and recesses 68 cut therein is bolted to the plate 62. This

facilitates changing of the mould 64 when other articles are to be manufactured.

Two further plates 70 and 72 are located between the upper and lower

plates 58 and 62. The plates 70 and 72 are restrained from moving sideways by the

columns 60 which pass through them.

At least one ejector pin 74 having a shank 76 and a head 78 is provided in

conjunction with each recess 68. Preferably there are a number of ejector pins per

recess. The shanks 76 of the pins 74 pass through the plate 62 and the plate 70, the

heads 78 of the pins 74 being between the plates 70 and 72. The ends of the shanks

76 remote from the heads 78 enter the mould recess 68 from below. Ejector pin operating elements 80 are carried by the plate 58, the

elements 80 having heads 82 and shanks 84. The heads 82 are above the plate 58,

the shanks 84 passing through the plate 58. The lower ends of the shanks 72 co¬

operate with the plate 32. Further ejector pin operating elements 86 are carried by the

plate 70 and protrude upwardly above the mould 64. Only one of the elements 86 has

been shown.

An upper mould 88 is bolted to the underside of an upper mould plate 90

which is itself bolted to the underside of the top plate 36. Recesses 92 are cut in the

underside of the mould 88. The plates 36 and 90 and the mould 88 have central

openings 94, 96 and 98 which register with one another and form a passage 100

through which molten metal enters the casting apparatus. It will be noted that, when

the moulds 64 and 88 are in contact, the mould 64 bounds the lower end of the

passage 100.

In use of the apparatus, the parts are initially as shown in Figure 2 of the

drawing. The cylinder 18 is used to push the shaft 52 upwardly. The entire lower

mould structure designated 56 is thus lifted until the lower mould 64 abuts the upper

mould 88. The recesses 68 in the lower mould thus register with the recesses 92 in the

upper mould 88 to form the mould cavities. The runners 66 join the passage 100 into

which molten metal is poured to the mould cavities. By pressing the moulds 66 and 88

together they are rendered fast in rotation with one another. As the structure 56 lifts the upper ends of the elements 86 encounter the

underside of the mould 88. Their movement is thus stopped and they slide with respect

to the plate 62. In so doing they move the plates 70 and 72 downwardly with respect to

the plate 62. This has the effect of retracting the ejector pins 74 from the mould

cavities.

A charge of molten metal is poured into the passage 100. The structure

28 is then spun by means of drive transmitted to the column 30 from the motor and

gear box 46 via the belt 44 and pulley 42. Because the moulds are in face-to-face

contact, the lower mould structure 56 also rotates. The molten charge flows outwardly

from the central passage 100, through the runners 66 and into the mould cavities. A

ring of material remains in the passage 100 and joins the inner ends of the strips of

material which remain in the runners 66.

After spinning, the motor is switched off and the rod 22 retracted to move

the structure 56 downwards away from the upper mould 88. The lower ends of the

shanks 84 of the elements 80 encounter the plate 32 before the structure 56 reaches its

lowermost position. These elements thus stop moving but the remainder of the

structure 56 continues downwardly. The stationary heads 82 are encountered by the

underside of the plate 72 and as a consequence the plates 70, 72 are in effect lifted

with respect to the lower mould 64. As the lower mould continues to move down the

shanks 76 of the pins 74 enter the mould cavities and lift the casting away from the mould 64. The casting can be gripped using tongs and removed from its position on

the mould 64. The cycle is then started again by raising the structure 56 by means of

the cylinder 18.

To compensate for misalignment of the moulds 64 and 88, the shaft 52 is

welded to a plate 102 which is itself connected to the plate 58 by rubber bushes 104.

Thus as the structure 56 encounters the mould 88, some tilting of the structure 56 is

possible.

The plate 58 can include two lugs 106 which protrude outwardly therefrom

and lie one on each side of a post 34. The lugs 106 thus form guides which ensure that

the moulds 64 and 88 are always in approximate alignment. Final alignment can be by

means of tapering pins (not shown) on the plate 62 which enter tapering bores (not

shown) in the plate 90.

Claims

CLAIMS:

1. Spin casting apparatus comprising an upper mould plate mounted for

rotation about a vertical axis, a lower mould plate mounted for rotation about said axis,

means for displacing said plates towards and away from one another between a mould

closed position and a mould open position, ejector pins for ejecting a casting, and

means for retracting said ejector pins to inoperative positions as the mould plates are

moved towards one another and for advancing said ejector pins to operative positions

as the mould plates are moved apart.

2. Spin casting apparatus as claimed in claim 1 , and including means for

lifting and lowering said lower mould plate, means on which said ejector pins are

mounted, an operating element for displacing the ejector pin mounting means

downwardly with respect to said lower mould plate as the lower mould plate is lifted,

and a further operating element for lifting said mounting means with respect to said

lower mould plate as the lower mould plate is lowered.

3. Spin casting apparatus as claimed in claim 2, wherein each ejector pin

comprises a shank and a head and the mounting means therefor comprises a pair of

plates with said heads between them, the shanks of the ejector pins passing through

the upper plate of said pair of plates.

4. Spin casting apparatus as claimed in claim 3, wherein said operating

element for displacing the mounting means downwardly comprises an element mounted

on said upper plate of said pair of plates and extending upwardly toward said upper

mould plate so that it is forced down with respect to the lower mould plate when its

upper end encounters the upper mould plate as said lower mould plate is lifted.

5. Spin casting apparatus as claimed in claim 3 or 4, wherein said operating

element for lifting said mounting is carried by a base plate which is itself below said pair

of plates, the operating element which lifts said mounting passing through the base

plate and being displaceable vertically with respect thereto to displace the mounting

means upwardly with respect to the lower mounting plate as the lower mounting plate is

lowered.

6. Spin casting apparatus as claimed in claim 1 and comprising a pneumatic

cylinder having a rod, a thrust bearing to one race of which said rod is connected, and a

shaft connected to the other race of said thrust bearing, said lower mould plate being

mounted on said shaft and being displaceable vertically with said shaft.

7. Spin casting apparatus as claimed in claim 6, and comprising a hollow

column, bushes within said column, said shaft sliding axially within said bushes, and

means for rotating said column, said upper mould plate being connected to said column

for rotation thereby.

8. A spin casting method comprising feeding molten material to a central

space of a mould comprising upper and lower mould parts, spinning the mould so that

the material flows outwardly from said space to a mould cavity to fill the cavity,

separating said mould parts, and advancing ejector pins from retracted inoperative

positions to advanced operative positions as the mould parts are separated thereby to

eject the casting from the mould cavity.