Patent Application
20090004323
The present invention relates to a device for supplying casting materials in an injection moulding process, in particular for a hot runner system with a needle valve, which system has a particularly low installation height.
Needle shut-off moulds have the advantage of allowing a clean sprue for the processing of plastics materials. An injection mould is a mould consisting of a plurality of modules for producing large quantities of plastics material parts. A plurality of plastics material parts can be produced simultaneously at a plurality of parting planes in a mould. The plastics material is injected at high pressure into the cavities of the mould through the supply channels by means of a cylinder. Melted plastics material is kept at temperature in the hot runner. Hot runner systems can be divided into open or closed systems, the relevant factor being whether the feed point was actuated by a sprue needle pneumatically, mechanically, electrically or hydraulically. The hot runner ends in the hot runner nozzle which is the point of transition between the heated and unheated zone in the injection mould. Hot runner systems have what is known as a needle shut-off mechanism in which the injection nozzle is closed immediately after the injecting and subsequent after-pressing by a shut-off needle.
Various needle valve injection nozzles are known in the art. For example, DE 295 04 162 discloses an injection nozzle, the shut-off needle of which is exposed to as little heat as possible. EP 0 558 932 A1 discloses a multiple needle valve nozzle, two nozzles having a common piston drive. DE 32 49 486 discloses a needle valve nozzle with two drive pistons. US 2003/0180409 A1 discloses systems with various drives, each arranged after the nozzle, for actuating the shut-off needle.
The present invention is accordingly based partly on the object of providing a manifold unit having a lower overall height.
The core of the invention is to provide a manifold unit for supplying sprue material in an injection moulding system for processing thermoplastic materials via a hot runner system, which manifold unit has at least one needle valve nozzle which can be sealed by a shut-off needle. In this case, the shut-off needle can be moved by a hydraulic, mechanical, electric or pneumatic drive system. The needle valve nozzle has a first longitudinal axis and the drive system, which has at least one piston, has a second longitudinal axis, the first longitudinal axis being arranged parallel to and laterally offset from the second longitudinal axis.
In other words, the manifold unit according to the invention allows the drive system of a needle valve nozzle not to be arranged coaxially with the longitudinal axis and after the nozzle; instead, the drive system is arranged parallel and offset next to the needle valve nozzle, for example respectively next to a hot runner manifold block of the manifold unit. The longitudinal axis of the drive system is thus not aligned with the longitudinal axis of the needle valve nozzles.
In conventional hot runner systems, the drive system, i.e. the drive piston or the cylinder or the guide pillar, is arranged coaxially with the nozzle. The coaxial arrangement of, for example, two nozzles pointing in two opposite directions then causes a further two drive systems, i.e. two pistons or cylinders, also to be arranged coaxially between the two nozzles. The construction resulting therefrom is very wide or has a large overall depth. The positioning in accordance with the invention of the drive next to the nozzle allows a coaxial arrangement of two nozzles with a minimum installation depth.
A lateral arrangement of the drive system relative to the needle valve nozzle has the further advantage that the drive can be placed in the cold region (i.e. out of the region where hot material flows in the hot runner), thus allowing, for example, the use of a hydraulic drive. One drawback of a drive system arranged in the warm region is that its large amount of heat can weaken the system. The use of hydraulics allows the drive system to have a smaller diameter, as the medium is substantially non-compressible. In addition, the pressures of the needle movement can be set with greater precision. The smaller diameter of the piston allows smaller distances between the nozzles or distances between the cavities to be adhered to.
According to a first embodiment of the invention, the shut-off needle is driven by the piston via a lever arm, the shut-off needle being arranged substantially perpendicularly to the lever arm. The longitudinal axis of the piston is in this case arranged substantially perpendicularly to the lever arm, so the shut-off needle, the lever arm and the piston describe a substantially U-shaped arrangement.
According to a further preferred embodiment of the invention, the lever arm is capable of surrounding with its free end at least one needle head, which is arranged at an end of the shut-off needle that is remote from a material outlet, and preferably in addition a spacer sleeve partly encasing the shut-off needle. This surrounding couples the pneumatically or hydraulically triggered raising and lowering of the piston to the movement of the shut-off needle and thus also to the retraction and extension thereof, and the use of the spacer sleeve allows simple regulation of stop positions.
According to a further embodiment of the invention, the manifold unit has at least two needle valve nozzles, the longitudinal axes of which are preferably arranged coaxially, each needle valve nozzle having a nozzle head with an opening, which can be sealed by the shut-off needle, for the outflow of the casting material. The nozzle heads of the two needle valve nozzles preferably point away from each other in opposite directions (back-to-back arrangement). Preferably, the shut-off needles of each two needle valve nozzles, which are arranged coaxially with each other, can be moved by the drive system, the first drive system having a first piston and the second drive system having a second piston, and the two drive systems have at least one common guide element, the pistons preferably being arranged coaxially. The guide element which is common to the two shut-off needles may, for example, be a guide cylinder which is preferably arranged in an axial fastening hole in the first piston and in an axial hole in the second piston. In other words, two coaxially arranged pistons can advantageously have a common guide cylinder, preferably a guide cylinder arranged in an axial hole in the piston or pistons. The movement of the pistons is transmitted to the shut-off needles via lever arms.
In this case, the drive system advantageously also has a first cavity, in which the first piston having a first head region runs or is movably mounted, and optionally a second cavity in which the second piston, which has a second head region pointing in the opposite direction to the first head region, runs or is movably mounted. The head region can be formed integrally with the piston and/or configured in one piece with the lever arm.
Advantageously, the first piston is screwed to the guide cylinder by means of a fastening screw which is guided in the first axial fastening hole in the first piston, the guide cylinder being displaceably movable in the second axial hole in the second piston, the second axial hole preferably having a ball cage.
Preferably, the first and the second piston are configured to be capable of actuating via two lever arms, which are arranged parallel to each other, at least two shut-off needles which are movably mounted in needle valve nozzles which are preferably arranged coaxially with one another and oriented in opposite directions. In this case, the two pistons can jointly actuate at least two shut-off needles via two lever arms. It is however also conceivable for each piston to be coupled to two shut-off needles via two lever arms which are arranged parallel to each other. In particular, it is advantageous if both lever arms in the drive system are responsible for the two shut-off needles. In this case, the two lever arms preferably have the same cross section. A movement of the pair of lever arms induced by the piston or pistons presses the two lever arms apart in the direction of the respective nozzle head, thus forming a gap or a double stroke between the two lever arms. Each lever arm presses in turn, through its movement, the two shut-off needles coaxially apart, i.e. the needle heads, which are arranged at the base of the shut-off needles, move apart from each other as the needles are extracted. The two pistons, which are arranged coaxially with each other, preferably run in opposite directions.
According to a further preferred embodiment, the lever arm is capable of actuating at least one, preferably two or more shut-off needles which are mounted in needle valve nozzles which are arranged parallel to one another and oriented in the same direction.
According to a further preferred embodiment of the invention, the manifold unit has at least two needle valve nozzles, the longitudinal axes of which are arranged parallel to and laterally offset from one another, the nozzle heads of the two needle valve nozzles pointing in the same direction. In this case, each needle valve nozzle has a nozzle head with an opening, which can be sealed by the shut-off needle, for the outflow of the casting material and the shut-off needles of the needle valve nozzles can be moved by a common drive system.
The lever arm can be configured in a fork-like manner with at least two fingers, each finger preferably having at its free end a recess which is capable of surrounding the needle head and optionally the spacer sleeve of the shut-off needle.
Furthermore, it is preferable for two coaxially arranged pistons together to drive at least four shut-off needles. In this case, half of the four needle valve nozzles, in each of which a shut-off needle is received, are advantageously arranged on a first side of the hot runner manifold and the other half of the needle valve nozzles at a second side of the hot runner manifold opposing the first side. Preferably, the needle valve nozzles are arranged in pairs on the manifold unit.
According to a further preferred embodiment according to the invention, each lever arm has an even number of fingers, preferably at least two or four fingers, each finger being capable of actuating at least one shut-off needle. As an alternative to a parallel arrangement, the fingers can also be arranged on the lever arm around the piston in a circular or star-shaped manner.
According to a further preferred embodiment, the lever arm engages with at least one opening in the hot runner manifold block in which the at least one needle valve nozzle is arranged. According to the invention, it is preferable for the at least one drive system to be arranged outside the hot runner manifold block or the hot region in which the hot runner extends.
The drive system may also be capable of operating a plurality of needle valve nozzles arranged parallel to and laterally offset from one another, the needle valve nozzles being coupled to the piston either via a common finger or bar or via various fingers, which are arranged parallel to one another, of a lever arm. If a plurality of needle valve nozzles are arranged in series along a bar, it can be advantageous for the purpose of stabilization if a second drive system or a second piston is arranged at the other end of the bar.
As an alternative to the foregoing embodiments in which a guide cylinder is arranged in the manifold unit, it is also possible to provide a manifold unit where only the guide is arranged in the hot runner manifold block and the actual hydraulic mechanism or piston chamber can be locked if required, or for a hydraulic piston to be attachable if required to actuate the needle.
In the case of a precentred cylindrical needle valve, during the shut-off movement, the needle is first precentred and brought to the sprue hole by means of a cylindrical guide. US 2004/0256767 A1 mentions the possibility of a hydraulic or pneumatic drive for a valve and describes the problem that very precise adaptation of the shut-off valve is necessary, as the components thermally expand on heating. The final adaptation of the position of the needle is however highly complex and time-consuming. A further advantage of the present invention over the prior art is thus, if the above mentioned spacer sleeve is used, that the shut-off needle no longer has to be adapted or centred with such precision; instead, its position can deviate by the extent to which it expands on heating.
In addition, the present invention can prevent the leverage effect, as any force-conditioned angular misalignment of the components can be compensated for by a common guide. The path of the needle can be fixed and the piston and the shut-off needle do not move coaxially with each other and have their own front and rear stop.
Multi-level systems have the drawback that the plastics material is multiply deflected and that the residence time of the plastics material in the runners or holes is longer than in normal systems. In the present invention, the plastics material is introduced into the hot runner substantially in the centre of the manifold unit or in the hot runner manifold block and is then distributed to the various holes over paths of substantially the same length and with as few deflections as possible. This also reduces the residence time of the material in the system.
Further preferred embodiments of the invention are described in the dependent claims.
The invention will be described hereinafter in greater detail based on exemplary embodiments and with reference to the drawings, in which:
Exemplary embodiments will be discussed hereinafter to document the proposed manifold unit. This discussion of the exemplary embodiments is intended by way of support and should not be used restrictively to interpret the scope of protection such as is defined in the likewise appended claims.
a and 1b show part of a preferred exemplary embodiment of a manifold unit I according to the invention. The manifold unit 1 has a hot runner manifold block 25 which is heated via a block heating line 31 (cf.
The needle valve nozzle 2 has in a central hole a shut-off needle 3 which is mounted so as to be displaceably movable and also, coaxially therewith, a material channel 5 through which the material is guided from the inlet opening 33 to the needle guide or opening 4, arranged in the nozzle head 7 which is shown to be conical, of the needle valve nozzle 2. The shut-off needle 3 is capable of sealing the material channel 5 toward the needle guide or toward the opening 4, it being possible, but not necessary, for the shut-off needle 3 to issue in this case—as shown in the present document—from the nozzle opening 4. During sealing of the channel 5, the tips of the shut-off needles 3 of the two coaxial needle valve nozzles 2 shown move apart from each other. The needle valve nozzles 2 shown are arranged on the hot runner manifold block 25, or secured therein, but project beyond the cooled mould plates 26 attached to the hot runner manifold block 25.
The drive system shown according to a first preferred embodiment of the invention has two coaxial pistons 16, 17, the common longitudinal axis L2 of which is arranged parallel and laterally offset from the longitudinal axis L1 of the needle valve nozzles 2. The two pistons 16, 17 shown each have a central axial hole 19, 22 in which a guide cylinder 18 is received. The guide cylinder 18 is coupled to the needle valve nozzles 2 or the shut-off needles 3 thereof via two lever arms 9 which protrude from at least one piston 13, 14 at an angle of substantially 90 degrees. The lever arm 9 or the fingers 9a, b thereof surround with at least one recess 10 both the neck of a spacer sleeve 6 and the needle head 8. The spacer sleeve 6 strikes in the needle valve a stop at the edge 40 of the hot runner block 25 and thus determines the distance by which the shut-off needle 3 extends.
The respective lever arm 9 is fastened to the piston 13, 14 for example, as shown in
In the exemplary embodiment illustrated in
Each shut-off needle 3 has, at its end opposing the nozzle head 7 or at its base, a needle head 8 which is surrounded by a recess 10 in the lever arm 9 or one of the fingers 9a, b thereof. The longitudinal axis L1 extends centrally through the shut-off needle 3 substantially in the longitudinal direction. The axial movability of the shut-off needle 3 is backwardly limited by the finger 9a, b or the recess 10 therein for surrounding the needle head 8 and also by a protrusion 36 in the hot runner manifold block 25 in that the needle head 8 finds in the aforementioned elements a stop. The limitation of the needle movement forward (or in the direction of the nozzle head 7) is facilitated by the spacer sleeve 6 which defines the extended position of the shut-off needle 3. Spacer sleeves 6 of various sizes can be used in this case, thus allowing the extension or retraction path of the shut-off needle to be defined as desired. The spacer sleeve 6 is preferably configured substantially as a hollow cylinder with a peripheral incision with which the finger 9a, b of the lever arm 9 can engage. The single stroke 11a defined by the movement of the shut-off needle 3 is half the double stroke 11 arranged between two lever arms when the shut-off needles 3 of two coaxially arranged needle valve nozzles 2 are in the extended position. The leading rim of the spacer sleeve defines the front stop for the shut-off needle 3 at the edge 40 of the hot runner manifold block 25 and the rear stop is defined by the projection 36 in the hot runner manifold block 25. The lever arm 9, or the fingers 9a, b thereof, preferably engages both with the peripheral incision in the spacer sleeve 6 and also around the needle head 8 arranged at the trailing end of the spacer sleeve 6, the needle head 8 and the hollow cylinder portion, arranged at the back of the peripheral incision, of the spacer sleeve entering the recess 10 in the lever arm 9 or the fingers 9a, b thereof.
The plane E, which is arranged as a mirror plane in relation to the coaxially arranged needle valve nozzles 2 parallel to the surface of the hot runner manifold block 25 of the manifold unit 1, is a central centre plane perpendicular to the longitudinal axis L1.
a shows the two coaxial shut-off needles 3 in the retracted position, i.e. the channel 5 is open for the outflow of casting material. The lever arms 9 rest against one another substantially without a gap or without a double stroke 11 lying therebetween. The first piston 13 is located in the present illustration in a position where a first or second piston chamber 23a or 24a is formed between the head region 16, 17 and the lid 37. The U-shaped arrangement may be seen particularly clearly in
b shows, like
The first or second piston chamber 23a, 24a and the third or fourth piston chamber 23b, 24b are utilized hydraulically or pneumatically. In this case, a pneumatic system generates, for example, a pressure which can then be used to actuate the pistons 13, 14. This leads to a movement of the guide cylinder 18 in the axial direction along the longitudinal axis L2. The movement of the guide cylinder 18 is then transmitted to the lever arms 9 which control the shut-off needles 3 of the needle valve nozzles 2 via the needle head 8. The shut-off needle 3 can then be moved in the axial direction along the longitudinal axis L1, leading to extension or retraction of the shut-off needle 3. The stroke of the piston may correspond substantially to the stroke of the shut-off needle. The double stroke 11 between two lever arms is preferably, in the case of a coaxial arrangement of the needle valve nozzles 2 and a coaxial arrangement of the pistons 13, 14 driving the needle valve nozzles 2, substantially twice the single stroke 11a of the shut-off needle 3 or of a piston 13, 14.
a and 2b show four needle valve nozzles 2, the shut-off needles 3 of which can be jointly actuated by the two pistons 13, 14 shown via two lever arms 9. The two figures show that the needle valve nozzles 2 are coupled to the free ends of the fingers 9a, b. The needle valve nozzles 2 may be said to be arranged in pairs in the axial direction, i.e. along the longitudinal axis L1 of the needle valve nozzles 2 on a finger 9a, b, and two needle valve nozzles 2 may also be said to be arranged adjacently in pairs on a forked lever arm 9, wherein in the illustrated exemplary embodiment all four needle valve nozzles 2 can be operated simultaneously. Two seals 29a, b, which are for example rubber ring seals, surround the circumference of the head region 16, 17 and the neck of the piston 13, 14.
Whereas
Located in the hot runner manifold block 25 is a hot runner via which the liquid casting material, which is kept at temperature by the block heating line 31, is distributed to the various needle valve nozzles 2, which are heated by heating lines 32 in the jacket, via branches and manifolds. The casting material, which is heated by a block heating line 31, enters the hot runner manifold block 25 at a central manifold hole 12 and is led to the manifold in order then to be guided through inlet openings 38 into the individual needle valve nozzles 2 or material channels 5 thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1037/07 | Jun 2007 | CH | national |
