MACHINE FOR INJECTING THERMOPLASTIC MATERIAL

Abstract

A machine for injecting thermoplastic material into mould includes a frame, a bracket, a melt chamber supported by the bracket, a piston designed to plunge into the melt chamber per an injection axis through an upper opening and push a molten material contained in the chamber to the mould. The machine includes a head along which the piston slides, the head also having a hopper which contains the non-melted thermoplastic material, the head being mobile perpendicularly to the injection axis between an injection position, in which the piston is aligned with the melt chamber, and the hopper is blocked off by the bracket, and a feed position, in which the hopper is aligned with the melt chamber to feed it with thermoplastic material, and the movement of the piston is limited by the bracket.

Claims

1. A machine for injecting thermoplastic material into a mould, the machine comprising a frame, a bracket mounted on the frame, a melt chamber supported by the bracket, a piston designed to plunge into the melt chamber along an injection axis through an upper opening and push a molten material contained in the chamber into the mould, wherein the machine comprises a head along which the piston slides, the head further comprising a hopper that contains the non-molten thermoplastic material, the head being mobile perpendicularly to the injection axis between an injection position, in which the piston is aligned with the melt chamber and the hopper is blocked off by the bracket, and a feed position in which the hopper is aligned with the melt chamber to feed the melt chamber with the thermoplastic material and the movement of the piston is limited by the bracket.

2. The machine as per claim 1 in which head can swivel around column axis parallel to the injection axis between the injection position and the feed position.

3. The machine as per claim 1, in which the bracket comprises a plate extending perpendicularly to the injection axis on either side of it and opposite the piston and the hopper to block off the hopper, the plate including through a hole opposite the melt chamber.

4. The machine as per claim 3, in which the chamber comprises a heat insulation washer between the melt chamber and the plate.

5. The machine as per claim 1 in which the head has a base plate extending between the piston and the hopper, flush with the bracket to block off the melt chamber where the head is in an intermediate position between the injection position and the feed position.

6. The machine as per claim 1 in which the piston is operated by an arm mounted on the head.

7. The machine as per claim 1 in which the frame includes a column that has an axis parallel to the injection axis, the bracket being mounted in such a way it can slide along the column and comprising a stopping system for holding the bracket in position on the column.

8. The machine as per claim 1 in which the head includes a locking system to fasten the head in the injection position.

9. The machine as per claim 8 in which the locking system is formed by a bolt passing through the head and the bracket, one of the elements of the head and of the bracket comprising a bolt hole through which the bolt passes to enable the movement between the injection position and the feed position, the bolt being capable of being tightened to link the head and the bracket.

10. The machine as per claim 1, further comprising end-stops to stop the swivelling of the head in the injection position and in the feed position.

11. The machine as per claim 1, the melt chamber comprising an injection nozzle designed to come into contact with the mould by a movement of the melt chamber towards the mould with respect to the bracket.

12. The machine as per claim 11 in which a return system configured to keep an opening of the melt chamber as close as possible to the bracket, to enable the nozzle to come into contact against the mould when the piston raises the pressure.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] The invention will be better understood and other features and advantages will appear on reading the following description, the description referring to the appended drawings among which:

[0021] FIG. 1 is a perspective view of a machine conform to an implementation mode where the invention is in the feed position;

[0022] FIG. 2 is a view similar to FIG. 1 where the head is in the intermediate position;

[0023] FIG. 3 is a view similar to FIG. 1 where the head is in the injection position;

[0024] FIG. 4 is a view similar to FIG. 1 where the head is in the injection position and the piston is lowered at the end of the injection phase;

[0025] FIG. 5 is a cross-section view per the machine's injection axis with the head in the feed position;

[0026] FIG. 6 is a cross-section view per the machine's injection axis in the position shown in FIG. 4.

DETAILED DESCRIPTION

[0027] A machine used to inject thermoplastic material conform to an embodiment of the invention is shown in FIGS. 1 to 6. The machine is designed to inject molten material M into mould C, as shown in FIG. 6. Material M is fed in the form of solid particles, for example granules, by means of hopper 50 into melt chamber 1 where it is melted before being injected into mould C by piston 3.

[0028] The machine has a frame 2 including a base 20 that has a more or less flat shape designed to be placed horizontally and a column 21 that protrudes from base 20 per column axis A.

[0029] Bracket 4 slides along column 21 extending parallel to base 20 and includes a stopping system 40 to hold bracket 4 in position on column 21. The stopping system 40 has a slot 401 extending radially with respect to a bore 402 in bracket 4 which serves as the guide for bracket 4 on column 21, and a bolt 403 extending perpendicularly to the slot, bolt 403 being able to tighten bore 402 to tighten bracket 4 on to column 21. A nut on bolt 403 has a lever 404 to enable operation by hand.

[0030] Melt chamber 1 extends vertically per an injection axis I parallel to column axis A and is supported by bracket 4 by means of three small columns 41 that guide melt chamber 1 in a transfer movement per injection axis I. The small columns are fastened to a ring 14 fastened in the upper part of melt chamber 1 at the level of opening 10. The return system in the form of springs 42 placed around small columns 41 tend to maintain an opening 10 in melt chamber 1 as close as possible to plate 43 on bracket 4, in a direction opposite to base 20. Plate 43 extends perpendicularly to injection axis I in the upper part of bracket 4, that is to say opposite to base 20, and includes a through hole 430 opposite opening 10.

[0031] Melt chamber 1 has a heat insulation washer 11 between melt chamber 1 and plate 43, washer 11 being pressed against plate 43 by springs 42. Melt chamber 1 consists of a sleeve 12 with a tubular shape whose interior diameter is adjusted to the exterior diameter of piston 3, and a heater element 13 surrounding sleeve 12. The machine has an electrical regulation device, not shown, to supply heater element 13 with current and regulate the temperature inside melt chamber 1 by means of at least one temperature probe, not shown. Sleeve 12 is fastened to ring 14.

[0032] The machine also has a head 5 along which piston 3, designed to plunge into melt chamber 1 per injection axis I through upper opening 10, slides guided by bushing 52. Head 5 can swivel on column 21 around column axis A between an injection position and a feed position. A system of end stops 6 is provided to stop the swivelling of head 5 in the injection position or in the feed position. The end stops for example are two studs 6 fastened on to plate 43.

[0033] Head 5 also has a hopper 50 to contain the non-melted thermoplastic material. Hopper 50 is more or less funnel shaped, but may have a variety of shapes. Head 5 has a base plate 51 extending between piston 3 and hopper 50 flush with plate 43 of bracket 4. In the feed position, as shown in FIG. 1, hopper 50 is aligned with melt chamber 1 to feed it with thermoplastic material and the movement of piston 3 is limited by bracket 4, that is to say by plate 43 of bracket 4. In the injection position, as shown in FIG. 3, piston 3 is aligned with melt chamber 1 and hopper 50 is blocked off by bracket 4. In an intermediate position of head 5 between the injection position and the feed position, base plate 51 is opposite the hole in plate 43 of bracket 4 and blocked off by melt chamber 1.

[0034] Head 5 includes a locking system 7 for locking it in the injection position. Locking system 7 consists of bolt 70 passing through head 5 and bracket 4 that can be tightened to link head 5 and bracket 4 together. Head 5 has a hole 71 through which bolt 70 passes to enable the movement of head 5 between the injection position and the feed position. The nut on bolt 70 also has a lever 72 to enable operation by hand.

[0035] An arm 8 is connected to piston 3 swivelling around an axis perpendicular to injection axis I and to head 5 by means of two connecting rods 80 parallel with each other. So, arm 8 makes it possible to manually control the sliding of piston 3 in guide bushing 52 and in melt chamber 1.

[0036] Melt chamber 1 has an injection nozzle 15 designed to come into contact with mould C through the movement of the chamber towards mould C along small columns 41. Nozzle 15 has a blocking-off system, not shown, for closing melt chamber 1 outside of the injection phases. The blocking-off system can be controlled by various means, for example by pressing nozzle 15 on to mould C, or by raising the pressure of the material in melt chamber 1.

[0037] We are going to describe an example of the machine's operating cycle.

[0038] We consider that the initial position of head 5 is the intermediate position. In this position, hopper 50 is blocked off by plate 43 and can receive the thermoplastic material in the form of fragmented solids, for example granules. Piston 3 rests on plate 43 through the force of gravity. Mould C is in place on base 20 under melt chamber 1, with an injection hole P opposite nozzle 15. Stopping system 40 is tightened after the adjustment of the height of bracket 4 on column 21.

[0039] Regulation is started to heat melt chamber 1 up to a set temperature which depends on the material to be injected. Ring 14 serves as a thermal diffuser that limits the upwards progression of the heat. At the same time, we swivel head 5 with arm 8 to the feed position. Melt chamber 1 then fills up with the fragmented material delivered by hopper 50 passing through hole 430 and opening 10. When the chamber is full, we push head 5 back to the intermediate position and wait for the material to melt.

[0040] When the material has melted, we swivel head 5 to the injection position, and tighten locking system 7 to guarantee the injection position and stiffen bracket 4. We then lower piston 3 by means of arm 8, which compresses molten material M in melt chamber 1. While increasing the pressure on the material with piston 3, we push melt chamber 1 against the force of the springs 42 so that it moves towards base 20. Nozzle 15 then abuts against mould C and opens to allow material M to pass under pressure into mould C. Piston 3 slides in melt chamber 1 to push the material until mould C is full.

[0041] We then raise arm 8, so that nozzle 15 closes, melt chamber 1 rises to stop against plate 43 and piston 3 comes out of melt chamber 1. We loosen locking system 7 and swivel head 5 to the intermediate position. At the time of this last movement, we can leave the end of piston 3 to rub against plate 43 so as to scrape the residue of material off piston 3. The machine is ready for another cycle. If hopper 50 contains enough material, we can pass directly on to the feed position without stopping in the intermediate position.

[0042] The invention is not limited to the implementation mode that has been described as an example only. Arm 8 could swivel on head 5 and transmit its movement by means of a connecting rod or a pinion meshing with a rack. Piston 3 could be operated by an electric, hydraulic or pneumatic actuator. The end-stops could be replaced by a screw adjustment system.