DE3833220C2 - Needle valve nozzle in an injection mold for processing thermoplastics - Google Patents

Description

The invention relates to a valve gate according to the preamble of An saying 1 as described for example in DE 34 03 603 A1.

Injection molds of the type mentioned above are commercially available in numerous versions. In Fig. 1 such an embodiment is shown cal matically in section. It consists essentially of a in a tool block ( 2 ) built-in needle valve ( 1 ), which is electrically heated and the front conically tapering part ( 7 ) of an axially displaceable needle ( 8 ) periodically opens a sprue ( 9 ) and closes through which the thermoplastic material coming through the hot runner ( 3 ) is injected into the cavity ( 15 ) at approximately 200 ° C. under high pressure. The separable tool block ( 10 , 11 ) forming the cavity is cooled by a temperature control system ( 12 , 12 ', 12 ''). From DE 32 45 571 A1 it is known to assign a pre-centering body in the needle closure nozzle adjacent to the sprue opening, which ensures exact guidance of the needle. Due to the type of heating via heating tapes and the material properties of the pre-centering body, poor heat transfer must be feared.

There is also a hot runner system ( 2 ) composed of several levels, in which the hot runner ( 3 ) is incorporated, and with the use of multiple tools, for example 6-32 molded parts are injected simultaneously in one operation. Methods for producing such temperature control and hot runner systems are known, for example, from DE 36 32 574 A1 and DE 36 32 640 A1 from the applicant.

In the case of temperature control systems that are generally cooled with tap water Corrosion caused by aggressive additions of water, by the limestone The cooling channels can become clogged with prolonged use, causing the Tool life is reduced.

The needle control is generally done by a piston drive, which cher is accommodated in a tool plate ( 5 ), consisting of a Kol ben ( 14 ) which sits in a cylinder ( 13 ) with air or hydraulic oil slidable. Such a piston drive is known for example from DE 32 49 486 A1. In this patent, the sealing problems of the piston because of the high pressures required for the hydraulics are discussed and it is proposed to solve the problems by two interacting Kol ben, which are operated with compressed air. The proposed structure is very complicated, however, and should cause wear problems with prolonged use.

Furthermore, in many injection molding tools, the connection from the piston to the needle unsatisfactorily solved, so that after prolonged use - many sprays Casting tools accomplish well over a million injection molding processes - a significant one wear is observed and an exact guidance of the needle is no longer possible is guaranteed.  

Finally, most of the commercially available injection molding tools the disadvantage that they only imperfectly control the valve pin control and thereby produce a high scrap of molded parts, which reduces the cost-effectiveness of the machine or expensive quality of the end products.

Therefore, the task was to find a valve gate of the generic type mentioned, which

• - A low-friction flow of the thermoplastic to the gates in the Cavity guaranteed
• - Reduces the wear of the parts causing the needle guide
• - Ensure the optimal sliding and sealing ability within the valve housing accomplishes
• - Automatically causes the ejection of incorrectly produced molded parts.

According to the invention, this object is achieved by those mentioned in claim 1 Features resolved. Details of the invention emerge from the subclaims, the description and the drawings.

An exemplary embodiment of the invention is explained below.

Show it:

Fig. 1 shows a section through a conventional injection molding type,

Fig. 2 shows a section through an injection mold according to the invention in the upper (open) position of the valve pin and

Fig. 3 is a partial view of a spray nozzle according to the present invention.

According to Fig. 2 and 3 of a good heat transfer the Vorzen should be executed trier body integrally with the nozzle body (6) for the purpose of further to the heating (4) of the nozzle (1) by a thermally conductive material such as copper, in which the heating coils (28 ) are cast in, can be accomplished.

On the other hand, the heat transfer from the nozzle body ( 6 ) to the tool block ( 10 ) should be as low as possible, which is caused by titanium or ceramic sealing insulations at the transition point ( 41 ). Likewise, the nozzle body is thermally separated at its upper part against the tool block ( 23 ) by an analog insulation ( 42 ).

With regard to rapid filling of the cavity and optimal precentration of the needle ( 8 ), it was found that the cone angles (α, β) of the front and rear conical taper ( 7 ) of the needle ( 8 ) should not exceed 15 ° in each case, as can be seen from Fig. 3. In this figure the upper stroke state (open) of the needle and the closed position (lower stroke state) is shown in broken lines.

As shown in FIG. 2, the drive unit of the needle consists of a valve housing ( 13 ) with a cover ( 16 ) in which a piston ( 11 ) is axially displaceable. The piston is firmly connected by a screw connection ( 32 ) to a piston rod ( 14 ), which is also located in the Ventilge housing. To drive the piston ( 11 ) are compressed air feeds ( 19 ) which, depending on the position of the piston in the open position of the needle, the upper part of the valve housing ( 33 ) or in the closed position of the needle, the lower part of the valve housing ( 20 ) with air act upon. The sliding seal of the piston ( 11 ) is produced by a sealing ring ( 21 ) with a rectangular cross-section (trade name "Quadring"), which is made of silicone rubber, and is seated in an annular wall recess of the piston. The sliding seal of the piston rod ( 14 ) causes a Hutman collar ( 22 ) which sits in an annular recess in the valve housing and is pressed against the piston rod by a cylinder ring ( 12 ) which is screwed to the housing. Furthermore, the screw connection ( 32 ) is secured against solutions because of the frequent lifting operations, which are associated with considerable Wechselbe loads, secured by a so-called Schnorr disc ( 29 ) as a washer. This disc is provided on both sides with radially oblique corrugations. Alternatively, the screw can be permanently connected to the piston with a suitable adhesive, such as Loctite screw locking lacquer.

The connection of the piston rod ( 14 ) with the needle ( 8 ) is created by expanding it cylindrically at its upper end and this extension ( 15 ) is seated in a T-groove of the piston rod, into which it is inserted radially. The mutual fit of the T-slot and the cylindrical extension is such that the needle ( 8 ) has an axial play of at most 5 µm, but at the same time compensates for displacements between the piston drive ( 5 ) and the hot runner manifold ( 2 ) due to thermal influences in the radial direction . A further voltage compensation can be achieved by means of a plate disk ( 17 ) known per se, the resilient edges of which are bent upwards bear against the piston drive and the underside of which rests against the hot runner ( 2 ).

In order to reduce the wear resistance, the parts of the valve housing or piston rubbing against each other are coated, and preferably the piston ( 11 ) and piston rod ( 14 ) made of hardened steel are coated on the sliding surface with titanium nitride, the layer being 2-4 µm thick , as well as the inside of the valve housing, the needle ( 8 ) and the coupling pieces. The latter parts can also be plasma nitrided, the coating thickness being 10-50 µm. The permanent tightness and high lubricity between the needle ( 8 ) and the needle guide bush ( 18 ) is achieved by an additional plasma nitriding the inside of the needle guide bush. Alternatively, these parts can also be chrome-plated.

To control the injection molding process, a sensor ( 36 ) is attached to the outside of the Ventilgehäu ses ( 5 ), which builds up an inductive field which is influenced by the piston ( 11 ) when it is adjacent to the sensor ( 36 ), for example in the upper Stroke position. An electronic evaluation unit, not shown, registers whether there is a difference between the time of the piston control by the compressed air in the upper or lower stroke position and the time of the effective position of the piston in connection with the injection parameters. If a specified limit of the time difference for the corresponding stroke when the molded part in question is ejected, this is discarded as a committee. In the case of multiple tools, the procedure is analogous, since each valve housing has such a sensor, which are all connected to the evaluation unit, so that, if appropriate, all molded parts of a cycle can be rejected as faulty.

Claims (7)

1. Needle valve in an injection mold for the production of molded parts made of thermoplastic materials with a Na del, the lower part of which has a conically tapered paragraph and a centering body and the upper part is connected to a piston in a valve housing, which with air or Hydraulic oil for the axial displacement of the piston can be acted upon, the piston having an annular recess with a sealing ring with a rectangular cross section, characterized in that the upper part of the needle ( 8 ) ends in a cylindrical extension ( 15 ) which is radially displaceable in one T-groove of an axially displaceable piston rod ( 14 ) sits, which is firmly connected to the piston ( 11 ) by means of a screw connection ( 32 ) and is sealed by means of a cap sleeve ( 22 ) which sits in an annular recess in the valve housing ( 13 ) and through a cylinder ring ( 12 ), which with the go housing ( 13 ) is screwed to the piston rod ( 14 ) and that a control system for controlling the injection molding process is provided with a sensor ( 36 ) which determines the stroke state of the piston in which the piston ( 11 ) the inductive field of the Sensor ( 36 ) influenced. 2. needle valve nozzle according to claim 1, characterized in that the screw connection ( 32 ) is secured against loosening by a Schnorr disc ( 29 ) or by an appropriate adhesive. 3. needle valve according to claim 1, characterized in that the cone angle (α, β) of the needle ( 8 ) have at their ends adjacent to the sprue an angle of at most 15 ° to the central axis. 4. needle valve according to at least one of claims 1 to 3, characterized in that the sliding surfaces of the piston ( 11 ) and the piston rod ( 14 ), the inside of the valve housing ( 13 ), the needle ( 8 ) and the coupling connection ( 15th ) are titanium nitride coated or chrome-plated. 5. needle valve according to claims 1 to 3, characterized in that the sliding surfaces of the piston ( 11 ) and the piston rod ( 14 ), the inner surface of the valve housing, the needle ( 8 ), coupling connection ( 15 ) and the needle guide bushing ( 18 ) are plasma nitrided. 6. needle valve nozzle according to claims 1 to 5, characterized in that the nozzle body ( 6 ) against the clamping tool blocks ( 23 , 10 , 11 ) by insulating seals ( 41 , 42 ), consisting of titanium or ceramic, is sealed. 7. valve gate according to claim 1, characterized in that the Control system has an evaluation unit, which is constructed so that at incorrect timing of the piston control of the ejection of the produced Molded is caused as defective or with a multiple tool a corresponding registration of the ejection of all molded parts as is caused incorrectly.