METHOD FOR ARRANGING A THROUGH-CHANNEL IN A SOLID BODY AND BODY OBTAINED WITH THIS METHOD

Abstract: The invention relates to a method for arranging at least one through-channel in a solid body,e.g. a hot runner. The invention has for its object to offer a method of the type described, using which a considerable improvement can be achieved in the quality of high grade injection moulded products. To this end the method comprises the following steps: (1) the providing of at least two solid blocks which are together sufficiently large to form the body, (2) complementary modelling where required of cor­ responding side faces of the blocks, (3) the forming of a groove in each of the said side faces, which pairs of grooves possess corresponding forms, (4) the placing against each other of the said side faces such that the grooves together bound a channel, and (5) the coupling of the blocks into a body. This method is preferably succeeded by the following step: (6) the passing of a liquid abrasive agent with force through the channel for a certain period of time in order to render the channel a desired rheological form through honing, which honing may be pulsating.

Description: The invention relates to a method for arranging at least one through-channel in a solid body, said method comprising the steps of: (1) providing at least two solid blocks which are together sufficiently large to form the body, (2) if required complementary modelling corresponding side faces of said blocks, (3) forming a groove in each of said side faces such that said grooves together bound a channel, (5) coupling said blocks to form a body, e.g. by vacuum-soldering. The pre-characterising portion of Claim 1 is based on the disclosure of the document EP-A-0 197 181. An example of a solid body of this type is a hot-runner, that is, a component for use in combination with an injection moulding device, which component comprises at least one channel for passage of heated plastic to the mould cavity of an injection moulding die. A single hot-runner comprises only one channel which is generally straight and which if required may possess a slightly tapering form. Such a channel can be obtained simply by drilling. For injection moulded products with a more complicated structure, the injection moulded product usually has to be manufactured via multiple gates. Use has to be made for this purpose of a hot-runner with one inlet opening which branches into a number of channels which each run out on the other side of the hot-runner. As will be apparent, these channels have to possess a form that is out of straight. The European patent application EP-A-0 197 181 describes a method of manufacturing an integral manifold for a multicavity injection molding system. The manifold has a melt passage which follows a tortuous path and is formed by milling matching grooves without any sharp bends in opposite surfaces of two plates which are then secured together. The manifold is formed of tool steel and also has an electrical heating element which is cast into a channel in its upper surface. The two plates are brazed together and the heating element is cast in the channel in a common heating step under a partial vacuum in a vacuum furnace. The French patent application FR-A-2 238 569 relates to a multiple hot-runner consisting of two blocks previously processed and afterwards unified. A major problem in injection moulding high-quality objects, such as compact discs, video discs, numerical optical discs and the like, is the relatively poor quality of the objects resulting from the rheological shapes of the hot-runners involved. It should be appreciated that the quality of such discs in the context of the invention is mainly related to their optical qualities that are to a substantial degree determining the fault-free operation of such information carriers. As a result of the defective flow properties of prior art multiple hot-runners high-quality information carriers of the types described above cannot be made within the required tolerances. The invention has for its object to provide a method of the type described above by which a considerable improvement can be achieved in the quality of high grade injection moulded products. It is a purpose of the invention to aim at only the highest possible quality of the objects, particularly in view of their homogeneous composition without local tensions tending to be accompanied by variations of the index of refraction of the transparent material. To this end the method comprises the following characterizing steps: (6) passing a liquid abrading agent with force through the channel for a certain period of time in order to render said channel a desired rheological shape by means of a honing operation, which honing may be pulsating, determining said period of time by (7) manufacturing a number of bodies, each with a different time interval, (8) establishing in which body is the channel which complies best with the required rheological shape, (9) determining said time interval of that body. According to the steps (7)-(9), the interval of time during which the liquid abrading agent has to be passed through in the so-called "slurry-honing" can be effected, which is of great importance in determining the required rheological form. It should be understood that as a result of the passing through of a liquid abrading agent there occurs a gradual abrasion of the wall of the or each channel, whereby at a certain point in time the "ideal" rheological characteristics are obtained. The above specified step (8) can now be performed by: (10) dividing the body into blocks in lengthwise direction along a sectional plane of the channel and establishing the form of the thus formed grooves forming the channel in the original body. In the case where the body to be manufactured is a hot-runner to be used together with an injection moulding device, the above specified step (8) can be performed by: (11) successively accomodating the hot-runners in the injection moulding device, (12) manufacturing at least one injection moulded object, for example a compact disc, with each of these hot-runners, and (13) establishing by means of which hot-runner the best object has been manufactured. For example in the case of optical information carriers that are manufactured from high grade and very transparent plastic, establishing which of the objects produced is the best can be carried out by determining the optical properties, this being done at a number of places on the formed injection moulded product. The invention will now be elucidated with reference to a drawing. In the drawing: Fig. 1 shows an exploded view of a hot-runner in twofold form; Fig. 2 is a view along the line II-II of a coupling plane of a hot-runner as in fig. 1, with the associated injection nozzles; and Fig. 3 shows a schematic perspective view of a hot-runner, the channels of which are optimised by means of slurry-honing. Fig. 1 shows an exploded view of a hot-runner 1. This hot-runner 1 comprises two solid blocks 2, 3 which each consist of two parts, 2, 4; 3, 5 respectively. The solid blocks 2, 3 display in this case surfaces 6, 7 to be set facing each other which are provided with grooves 8, 9 in a milling process. Grooves 8, 9 together form, in the case where the surfaces 6, 7 are placed onto each other, the bounding of through-channels. The second parts 4, 5, together with the respective blocks 2, 3, likewise bound straight channels for the accommodation of heating elements. For this purpose grooves are cut into the surfaces 10, 11 and 12, 13 facing each other, for example by milling, all these grooves being designated with 14 for the sake of convenience. The hot-runner 1 is assembled from the components in the manner indicated in fig. 1 with broken lines 15. Accurate positioning is obtained by means of holes 16 and positioning pins 17. This ensures the most accurate possible joining of the edges of the grooves 8. Such a precise connection is of importance with respect to the desired accuracy of the streamline form of the channels bounded by the grooves 8, 9. The blocks 2, 3 consist of a material suitable for a hot-runner, for instance a high quality tool steel. The surfaces 6, 7 are given a plane form with a high degree of precision. The grooves 8, 9 are arranged in the block on the surfaces 6, 7 by a milling process. The parts 2, 4 and 3, 5 are connected to each other by means of screws 18 after heating elements 29 have been placed in the channels bounded by grooves 14, as shown in fig. 3. Fig. 2 shows the smooth surface 6 of the block 2, wherein the grooves 8, 9 are arranged by means of milling. Located on either side of grooves 8, 9 and on the side edges of the surface 6 are vacuum-soldering zones 19. Present in these zones are nickel, copper, beryllium or other suitable metal which, through eddy-current heating in vacuum with the surfaces 6, 7 lying against each other, give an exceptionally strong adhesion between these surfaces 6, 7. The vacuum-soldering technique is generally known and requires no further discussion within the framework of this invention. The vacuum-solder zones can comprise paste, wire or foil of the relevant material, or also combinations thereof. After the whole hot-runner 1 has been assembled in the above described manner, an improvement of the streamline form, that is, the rheological characteristics of the channels bounded by the grooves 8, 9, can if required be realized by an arrangement as shown in fig. 3. As in this very schematically drawn disposition a liquid abrading agent, generally denoted as abrasive slurry and originating from a storage tank 21, can be pressed through the channels of hot-runner 1 bounded by the grooves 8, 9 by means of a regularly reversing pump 20. This per se known honing technique gives, in the context of the invention, the specific advantage that the streamline form of the channels present in a solid body is improved in very simple manner, and as it were automatically. The outlets 22, 23 of the channels are connected via a filter 34 to the pump 20 which is connected on the other side to the inlet 24. The pulsating action pump 20 pumps for a period to be specifically determined the abrasive slurry with force back and forth through the channels bounded by grooves 8, 9. After completion of the hot-runner 1 injection nozzles 25 are coupled to the outlets 22, 23. Via these injection nozzles the heated and therefore softened plastic is injected into the mould cavity of the injection moulding die. The invention offers a method which can be performed in very simple manner for arranging in a solid block channels of which the characteristics can be kept under very close control. A better controlled injection moulded product can therefore be obtained, since the degree of filling and the temperature distribution of the plastic in the mould cavity is better kept under control. It will be apparent that the invention is not restricted to hot-runners but extends in general to metal blocks with channels, the form of which is determined only with difficulty or not at all by simple processes such as drilling or milling, and the flow characteristics of which are of essential importance.

Claims: A method for arranging at least one throughchannel in a solid body (1), said method comprising the steps of: (1) providing at least two solid blocks (2, 3) which are together sufficiently large to form the body, (2) if required complementary modelling corresponding side faces (6, 7) of said blocks, (3) forming a groove (8, 9) in each of said side faces (6, 7), which pairs of grooves have corresponding shapes, (4) placing against each other said side faces (6, 7) such that said grooves (8, 9) together bound a channel, (5) coupling said blocks (2, 3) to form a body, e.g. by vacuum-soldering, characterized by (6) passing a liquid abrading agent with force through the channel for a certain period of time in order to render said channel a desired rheological shape by means of a honing operation, which honing may be pulsating, determining said period of time by (7) manufacturing a number of bodies, each with a different time interval, (8) establishing in which body is the channel which complies best with the required rheological shape, (9) determining said time interval of that body. The method according to claim 1, characterized in that step (8) is performed by: (10) dividing the body (1) into blocks in lengthwise direction along a sectional plane of the channel and establishing the form of the thus formed grooves forming the channel in the original body. The method according to claim 1, wherein the body (1) is a hot-runner to be used together with an injection moulding device, characterized in that step (8) is performed by (11) successively accommodating the hot-runners in the injection moulding device, (12) manufacturing at least one injection moulded object, e.g. a compact disc, with each of these hot-runners, and (13) establishing by means of which hot-runner the best object has been manufactured.

Inventors: VAN POORTEN, ANTONIUS
Applicants: GPT AXXICON B.V.
Application year: 1988
Main classification: B23P15
IPC codes: B24B31, B29C45, B23P15, B24C3