Abstract: A mold construction for allowing molding of parts having elements with a helical configuration. The helically configured portion is formed by a portion of the mold that is freely rotatable relative to the rest of the mold about the axis of the helically configured portion. The extraction of the molded component from the mold along a path coextensive with the axis of the helically configured portion produces driven rotation of the rotatable mold portion thereby releasing the molded component.

Abstract: A core lifter system is provided for a plastic injection mold, particularly for use in a mold in which an undercut is to be formed in the molded part. The system has a core blade and a support for the core blade, with the support being formed to be mounted for linear translation on an ejector plate. The system is configured for fixedly retaining the core blade on the blade support at a desired angle of inclination of the blade relative to the support. In one form of the invention, the blade is adjustable, and pinned in place. In another form of the invention, a separate, inclined blade support is provided for each different angle of inclination desired for the blade, and the blade and the support are pinned together.

Abstract: A mold for forming an article having one or more substantial radial protrusions. The mold includes a core movable along a molding axis, a stripper ring movable a limited distance along one set of guide rods with axes parallel to the molding axis, a split ring having segments movable adjacent to the stripper ring for the limited distance and movable relative to the stripper ring on a second set of guide rods at an angle to the molding axis, and a cavity. The article is removable from the mold when the core is moved away from the cavity, the stripper ring is moved its limited distance, and the split ring segments are moved with the stripper ring and then relative to the stripper ring at an angle to the molding axis.

Abstract: The present invention relates to a molding apparatus having a first mold half with a core portion and a second mold half with a cavity portion wherein the core portion moves relative to the cavity portion between mold open and mold closed positions. The molding apparatus further includes a carrier plate for receiving molded articles and holding inserts to be incorporated into the molded article. The present invention also relates to transferring the inserts to the mold cores prior to molding.

Abstract: Disclosed is a new method for making a component having interior and exterior threads. Such method includes the steps of providing a thread-forming apparatus having first and second circumferential threaded portions defining a space between them. Such space is filled with a flowable material, e.g., hot plastic, which is permitted to solidify and form the component. The apparatus and the component are then separated from one another by rotating such apparatus so that both threaded portions unscrew from the component. The finished component has interior and exterior threads which are simultaneously formed and substantially free of flashing. The new thread-forming apparatus has a first threaded portion and a pocket. A plug is in the pocket and has a second threaded portion spaced from the first threaded portion.

Abstract: A method of molding the main body of a Y-adapter that has a straight passageway extending from one extremity to the other and an arcuate passageway that is generated along the arc of a circle. Core pins for the straight and arcuate passageways are placed in a mold such that they merges together to form a single, smooth lumen in the Y-adapter. The arcuate core pin can be withdrawn from the finished Y-adapter as a result of its circular arc.

Abstract: A selectively-flexible, selectively-rigid, reusable, one-piece mold is used to fabricate a composite part having a complex shape on an outer surface of the mold. Disposed within the interior of the shell is a grid-type support truss structure having a plurality of individual support members attached at one end to headers that are attached by clips to the inside surface of the shell at predetermined locations. The support members are locked in place relative to each other by the use of pins placed in holes formed at various locations in the support members. When locked in place in this manner, the shell is stiffened, thereby facilitating the fabrication of the composite part on the mold. When the pins are removed, the shell is allowed to flex, thereby facilitating the removal of the cured composite part from the outer surface of the mold.

Abstract: A melt core constructed of a low temperature melting point alloy for producing a cavity in a structural part manufactured by injection molding, the melt core being formed as a hollow body. Depending upon the production process employed, the hollow body is provided with an opening, which is tightly sealed by a separately produced cover constructed of the same material as the hollow body that it seals.

Abstract: A collapsible mold core assembly facilitates formation of features such as channels and undercuts in interior regions of molded articles. The assembly includes a central, fixed pyramidial base member having a first plurality of obliquely oriented channels which receive a like plurality of first mold core segments and a second plurality of parallel channels interleaved with the first plurality of channels. The second plurality of channels receives a like plurality of intermediate members which, in turn, receive a like plurality of second mold core segments. The plurality of first mold segments withdraws from the mold and the plurality of second mold segments, which are constrained to move generally radially within the mold collapse radially inwardly to facilitate removal of the molded part.

Abstract: Methods and apparatus for separating a mandrel having a tapered end portion from an article formed thereon comprising: (a) providing the mandrel having an opening in the tapered end portion; (b) plugging at least a substantial portion of the opening with a member which presents a deposition surface for the formation of the article; (c) forming the article having a tapered end portion on the mandrel, including on the deposition surface of the member; and (d) pushing the member against the inside surface of the tapered end portion of the article to move the article away from the mandrel, thereby forming a gap between the article and the mandrel.

Abstract: Apparatus includes a female mold and a mold core cooperating with the female mold to form a mold cavity therebetween in the mold closed position for the formation of a threaded, molded article therein. A movable, rotatable stripper ring is provided over the core, and a rack and pinion are provided to rotate the stripper ring from a rearward to a forward position and thereby remove the threaded article from the mold core by rotating same.

Abstract: This invention relates to the use of a flexible, heat resistant mold member. The mold member is useful in molding processes such as dip or slush molding. The mold member maintains its structural integrity and may therefore be used as an insert in the article being molded to provide flexible stability at specific locations within the article. The mold member is made of a material which is substantially non-reactive with the molded article. The molded article may be any article made from a plastisol such as a binaural for a stethoscope having single or double lumens.

Abstract: An injection molded piece is removed from a mold by thrust pins. A jet of fluid is directed toward a surface of the piece during removal so as to hold the piece in a proper position on the thrust pins without damaging the piece.

Abstract: A method of manufacturing a moulded part using a first and second mould, wherein the first mould has a complementary design of the outer surface of the moulded part and the second mould has a complementary design of the inner surface of the moulded part and a boss cavity for forming an outer wall of a thin-walled boss to be moulded onto the inner face of the moulded part. The steps include seating a plug substantially co-planar with the complementary inner surface design and extending the plug into the boss cavity presenting an inner wall of the boss, wherein the thickness between the inner and outer wall of the boss is less than 60% of the thickness of the moulded part where the boss is moulded thereto. Closing the first and second mould forming a mould cavity. Injecting molten material into the mould cavity. Waiting a predetermined amount of time to allow the molten material to harden. Opening the first and second moulds. Extending the plug from the boss cavity.

Abstract: A cap is attached to a mold core with a T-shaped connector instead of screws. The core cap has an air distribution channel and the core has cooling fluid distribution channels which are maximized by using the T-connector. The fluid distribution channels promote maximum cooling of the core, and, along with the air distribution channel, facilitates ejection of small articles from the mold.

Abstract: The present invention provides an injection mold having an injection core mold for defining the inner wall of a lip portion in a preform having an undercut, a first lip cavity mold for defining the outer wall of the lip portion having no undercut, and a second lip cavity mold for defining the outer wall of the lip portion having the undercut. In the initial release after the injection molding process of the preform, the second lip cavity mold is first moved upwardly to secure a space wherein there is no obstruction around the outer periphery of the undercut. Thereafter, the injection core mold is upwardly moved such that the second injection core mold can be forcedly released from the molded preform while resiliently deforming the undercut in the outward direction, utilizing the space so formed. The barrel portion of the preform so molded is biaxially stretched to provide a so-called roll-on type biaxially oriented vessel having a ball received in the lip portion thereof.

Abstract: An elastic molding die is composed of an elastomer laminate film, of which the innermost layer is formed of an elastomer not containing fillers. The innermost layer elastomer is preferably an oil-resistant elastomer. Alternatively, an oil-repellent agent may be contained in the innermost layer elastomer. The outer layer may be formed of an elastomer containing fillers. Furthermore, an oil blocking layer can be provided between the inner layer and the outer layer. A master model is dipped in an elastomer solution not containing fillers, heat dried to form a gelled elastomer film, the film is coated with a coagulant, dipped again in an elastomer solution, taken out, gelation treated, and the elastomer film is peeled from the master model to obtain an elastic molding die. In another method, a once-formed hollow elastic molding die is turned inside out, pressed in with a gas to swell, the swollen die is coated with an elastomer solution not containing fillers, heat dried, and turned it again inside out.

Abstract: In accordance with the present invention there is provided a new and improved internal core lifter for molding and ejecting plastic parts having undercuts. The preferred internal core lifter has a core blade with a first end configured to cooperate with the surfaces of the mold for molding a plastic part and for assisting in safe ejection of the plastic part. The core blade may be pivotally mounted at an opposite end for being disposed at a predetermined molding angle in a range of angles for accommodating various molding angles of mold apparatus. In ejecting the plastic part, the first end of the core blade moves horizontally away from the undercut while moving vertical to assist in safe ejection of the plastic part.

Abstract: The present invention relates to a process and apparatus for injection molding thin-walled plastic articles. The apparatus includes a mold cavity and a mold core defining a cavity space in the shape of the article. The cavity space has a circumferentially extending region having a thickness greater than the thickness of a sidewall defining portion. This circumferentially extending region is preferably located at the approximate mid-point of the sidewall defining portion. At least two gates directly and simultaneously introduce plastic material initially into the circumferentially extending portion in a manner so as to minimize the creation of side loads and core shift. After the circumferentially extending region is filled, the plastic material fills the entire cavity space. The plastic material is thereafter cooled to form the desired article.

Abstract: A method of injection molding a container cap with a precision thread having a tamper indicating band depending from the bottom of the cap skirt. Collet jaws form at least a frangible connection between the bottom of the cap skirt and the top of the tamper indicating band, and these jaws are moved radially outward specified amounts during the molding process to provide clearance for stripping an inwardly directed retaining element on the band from the core and for ejection of the finished cap.

Abstract: A method of the device for producing a hollow columnar piece whereby a blend of essentially thermoplastic particles is melted into a billet, introduced into a mold, looped into layers inside the mold, and transformed into a piece, subsequent to which the piece is solidified by cooling and removed. The billet (3) is rotated around its axis and concentric with its face as it is introduced into a mold (4), the mold accommodates a core (20), space is left between the core and the inner surface (6) of the mold, the billet is laid along the circumference of the space, and the billet continues to be introduced into the space until the mold's inner surface and core are uniformly and continuously wet with constituents of the billet.

Abstract: An elastic mold consists of a product molding section in which a fluidized charging material is charged and solidified to form a molded product, and a mold holding section formed integrally with a take-out opening which is contiguous to the product molding section and which is smaller in size than the molded product. The take-out opening contiguous to the product molding section and the mold holding section is of uniform thickness and is curved smoothly.

Abstract: When removing a molded part (7), particularly from an injection mold, the part is moved to an intermediate position in a first partial movement (a) at low speed, then to the final position in a second partial movement (b) at higher speed. The first partial movement (a) can take place while the injection mold is opening and/or while a gripping tool (14) or handling device is being introduced. The injection mold used in the process has pressure operated stops (21) which act on the front face of an ejection plate (13) and hold it in the intermediate position or release it for the second partial movement (b) to take place.

Abstract: In the injection molding of closure caps, the problem of demolding the safety-seal strip, which is suspended at an intended break line and is necessarily provided with undercuts, is encountered. Here a clearance must first be created at the lower outer surface of the safety-seal strip, and the safety-seal strip must then be stripped from the mold core together with the closure cap. As a practical method step, the invention proposes to bring about the release of the lower portion of the outer surface of the safety-seal strip by lowering a mold ring which is displaceable relative to the stripper plate.

Abstract: An inside corner form for forming an inside corner of a wall structure for casting concrete includes a central member for forming the corner, side members for forming portions of the walls adjacent the corner, an actuator for expanding and contracting the inside corner form and a lid for five sided pours. Slide lugs are provided to engage the central and side members such that the members are maintained in their proper orientations, while still permitting the members to slide relative to one another during the expansion and contraction of the form. A flowable material is injected between the central and side members for lubrication and to form a barrier to prevent grout from seeping between the members of the inside corner form and lid.

Abstract: A plastic molding apparatus which produces the molded part on a centrally located core with this core being elongated and having a non-linear, longitudinal, center axis. The core is removed from the molded part by being pulled directly from the molded part which causes the molded part to assume a temporarily deformed shape with the molded part then springing back into its molded shape after removal of the core.

Abstract: An ejection and conveying device mounted in a rotary pressing tabletting machine having matrices supported by a rotating table, whereinto upper punches and lower punches enter and come out, while tablets come out at an ejection station; the device includes a plate fastened to the machine and positioned under the table. Part of the plate is located under the machine's ejection station, while a rotating disk is placed inside a raised border of the plate and has a plurality of hollows whereinto the ejected tablets fall so that the tablets are drawn by the disk up to be positioned above one or more holes made in the bottom of the plate and from which holes discharge channels depart. The tablets pass through the holes and are brought away by the channels.

Abstract: A film forming composition including a film forming substance having amphiphilic molecules and being dispersed in a gel-like carrier having a non-liquid state below about 20.degree. C. The carrier stabilizes the film forming substance, and inhibits diffusion of moisture and oxygen into the composition. This minimizes deterioration of the film forming substance, and also minimizes undesirable formation of agglomerations of such substance. When the composition is applied to a surface, an ultra thin substantially continuous film of substantially uniform thickness forms spontaneously and attaches to the surface. The excess composition is then washed away.

Abstract: Apparatus for producing plastic parts with a resilient projection, such as connectors for corrugated tubing. The apparatus includes means for flowing plastic material on a core provided with a recess to mould the resilient projection, plural core cam surfaces to extract the resilient projection out of the recess, after the mass of plastic material is solidified and extract the solidified part from the core.

Abstract: A method for manufacturing a drip irrigation emitter, including the steps of molding onto an injection-mold core having at least n different active diameters, n different, axially spaced apart members of the emitter, at least n-1 of the members being substantially annular, the inside diameter of at least one of the annular members being a tight fit on the outside diameter of the next smaller of the members, stripping the members off the core, starting from the member having the largest inside diameter, thereby causing the members to be tightly nested one inside the other, in a predetermined axial and angular relationship, and ejecting the thus fully assembled emitter from the mold. There is also provided an injection mold for producing fully assembled multi-part drip-irrigation emitters.

Abstract: A molding method is used to produce a module cover for an air bag device which has undercut portions in mounting edge portions thereof. A lower mold disposed inside the module cover to be produced is of the split type so that is includes a central mold disposed at the center and a plurality of lateral molds for molding of the undercut portions. The mating face of the central mold with each lateral mold is oblique so that its bottom is closer to the edge of the module cover than its top. Thus, the module cover produced can be detached from the lower mold by moving the lateral molds mutually inward.

Abstract: A molded article having an embedded bracket, such as a whirlpool tub, the mold and a method of molding the article are disclosed. The article includes a rigid shell having a non-finish side and a finish side. The non-finish side is coated with a polymeric material. The polymeric material encloses a bracket and distributes the weight of an attached object, such as a whirlpool motor, over adjacent polymeric material. The bracket is affixed to the rigid shell in a spaced relationship and includes a surface for attaching to an object by attachment means such as a blind bolt. The bracket may also be affixed to the rigid shell by supports which are welded to the rigid shell.

Abstract: An apparatus for molding reconstituted culled olive product in a slurry or plastic form comprising a plurality of molds, each of the molds being comprised of two halves which when brought together in face to face engagement define at least one cylindrical cavity; a plurality of elongated cylindrical rods, one for each of the cavities; a first endless belt to carry the molds vertically and incrementally over a predetermined horizontal course, and to return the molds back to the start of the course; an injection device disposed at a station below the horizontal course, the device being provided with a supply of the olive product in slurry form and adapted to inject a predetermined quantity of the product into each mold cavity having a rod inserted therein when the mold is disposed in the station; and a second endless belt adapted to carry the plurality of rods over a course which includes a rod insertion station disposed horizontally from the mold injection station, a tannic acid tank, a product coloring tank,

Abstract: In a molded intake manifold/fuel rail, a through-passage for the conveyance of combustion air is created by disposing two separably engaged core parts of the mold to occupy the entirety of the through-passage during the molding process. After molded material has solidified, the core parts are separated in generally opposite, but non-colinear directions. During the molding process, one core part occupies the entire length of the through-passage along a certain circumferential extent of the through-passage while along another circumferential extent, both core parts conjointly occupy the entire length of the through-passage.

Abstract: A process and apparatus for injection molding thin-walled plastic articles having comparatively thick lip portion. The apparatus has a mold cavity and a mold core defining a cavity space in the shape of the article and at least one injection gate adjacent a portion of the cavity space defining the lip portion through which molded plastic is injected into the cavity space. The direct lip gating approaches employed in the apparatus do not sacrifice core/cavity alignment and conventional mold motions along the machine axis and form plastic articles having substantially no gate vestiges on the lip sealing surface or on the outer perimeter of the lip.

Abstract: An apparatus for making concrete pipe having vinyl liners. An expandable core is used to hold a tubular vinyl liner. The core has over-center latches which lock the core in an expanded position to hold the liner against the outside surface of the core. The core is a flexible and expandable shell which can be deformed by a forming module into an exact desired shape prior to placing concrete arount the liner and the core. The liner and core are inserted along with a reinforcing cage into a dry-cast concrete form. Then the form is placed over the module and the module is actuated into engagement with the inside surface of the core. The module has a series of disc assemblies, each of which has a plurality of radially moveable shoes capable of being moved to expanded and retracted positions. The form is filled and immediately taken off the module.

Abstract: An internal core lifter in a mold is provided with both linear motion and pivotal seating in a universal coupling that slides linearly along an ejector plate. The pivotal seating allows the core blade to be used at various angles in different molds, thereby reducing the inventory of core blade needed. To resist high forces encountered during ejection and during the opening and closing of the mold, the preferred pivotal seating comprises wide arcuate dovetail surfaces on the lower end of the core blade and on a slidable support which has linear dovetail surfaces with the ejector plate. The upper end of the core blade may be configured to be part of the molding surfaces to mold an undercut in a plastic part. The upper end of the core blade is moved laterally from the undercut and then is shifted upwardly to engage and eject the part.

Abstract: A method and apparatus for molding a product having internal threads includes a threaded mold core and a device for rotating the mold core about the axis of its threads and for axially withdrawing the core from the mold at a rate that is related to the rate of rotation, according to the pitch of the threads. This is accomplished by a cam, which is rotated in synchronism with the device that rotates the core, and a follower for displacing the core as the cam is rotated. The cam follower is fixed with respect to the mold. The cam and threaded core are positioned on a carrier, along with the device for rotating the core, such that rotation of the cam displaces the carrier away from the mold. The core is inserted into the mold, prior to the molding process, by displacing the carrier toward the mold without rotating the core.

Abstract: A mold for making bathtubes is disclosed. The mold includes a mold receptor and an insert attached to the mold receptor face. The mold receptor receives a shell which has a finish side and a non-finish side. The shell is placed in the mold receptor leaving a void between the non-finish side of the shell and the face of the receptor. The insert is attached to the face of the mold receptor to reduce the cross-sectional area of a portion of the space between the shell and mold receptor face. A male mold engages the finish side of the shell, sealably retaining the shell to the mold receptor. A polymeric foam material is introduced into the void between the receptor and the shell. The polymeric material fills the void and coats the shell. The molded bathtub is then removed from the mold receptor after the male mold has been removed. The insert is then removed leaving an area of reduced thickness and a periphery on the non-finish side of the molded bathtub which defines a lip.

Abstract: A self-draining container and method of forming. The container includes a body and a wall extending upwardly from a body opening. The wall surrounds a dispensing spout which extends above the top of the wall. A web joins the wall and the dispensing spout to form a drain channel. A drain opening is defined adjacent the channel for draining fluid from the channel into the container body. A cap having a depending skirt defining a thread which mates with an internal thread on the container wall to close the container.

Abstract: A method and apparatus are described for forming a closure device having a cylindrical plug and a cylindrical collar extending coextensively and coaxially from a cap. The apparatus includes an outer mold defining an injection mold cavity. A cylindrical hollow outer core extends into the injection mold cavity and a cylindrical inner core extends into the injection mold cavity within the hollow outer core. Pushing means separate the molded part from the inner core. A stripper separates the part from the outer core by engaging an annular shoulder on the part. The part is pushed free of the mold's inner core after the outer mold is removed but before the stripper is advanced to engage the annular shoulder.

Abstract: A mold forms a portion of a part having a first cross-section of a first thickness further removed from a body of the part than a second cross-section of a reduced thickness. The mold includes pairs of mold pins which are moved between a molding position at which they define a cavity to form the portion of the part, to a release position at which they allow the portion to move outwardly of the mold so that the part may be released. In an embodiment, the mold pins are actuated by a first actuator, and a second actuator actuates a plurality of ejector pins to force the part off the mold. In this way, it is ensured that the part is forced off of the mold, which can then be operated without supervision. In a preferred embodiment, a ramp member moves a holder for the mold pins between first and second positions, which causes the mold pins to move between the molding and release positions.

Abstract: A CM block machine for casting masonry blocks includes a mold cavity formed between a mold box and a mold core containing one or more plungers selectively extending laterally into the cavity along a second axis which is normal to the axis of casting so as to form openings extending through portions of the block in the direction of the second axis. The plunger(s) is disposed in a cartridge housing contained within the mold core. An oversized vibrating ring wiper mounted in the cartridge housing engages the external periphery of the plunger to prevent CM material from entering the cartridge during plunger retraction. The plunger includes an annular relief chamber formed in a side wall thereof to provide an additional volume of air from within the cartridge to an air passage communicating with the plunger end face to prevent vacuum from impeding plunger retraction.

Abstract: A die casting mold part, which may be mounted on or applied to a die casting mold to provide for the molding and shaping of a variety of projections from the molded article and a simple and sure release from the mold of such projections including a plurality of projections lying closely adjacent to one another and extending outside the mold separation plane. The mold part includes segments, which are received in a bore that guides them and holds them together to form a die casting cavity, the segments together thus forming a mold at one of their ends. On their opposite end they flare outwardly and are mounted pivotally on a central control shaft so that they are caused to be opened where together they formed a mold, by relative movement between the control shaft and bore.

Abstract: An induction heating system for melting metal cores contained within articles or components made of plastic uses induction heating and redirects flux lines for efficient melting. The system includes a high permeability magnetic core, an induction heating coil about at least a portion of the magnetic core to produce flux circulation in a magnetic circuit formed by the magnetic core, and two magnetic nozzles attached to the magnetic core with a gap therebetween for insertion of a specific shape of plastic article, the magnetic nozzles shaped to direct and position a desired pattern of flux lines to heat and melt the metal core of the plastic article.

Abstract: An automatable tool can part an internal endless film from a mold. A preferred embodiment includes a lead member and a lap member having parallel axes, and rotating about an axis intermediate to their axes. The lead member may be provided with a separation tip used to initiate separation of a film from a mold. A trailer member can also be provided and all three members are inserted internal to a mold. The lead member is inserted so as to be on the outside of the film while the lap member and trailer member remain internal to the film. Upon rotation of a connection means between the lead and lap members, the film is wound up on the tool so that it may be removed from the mold.

Abstract: An apparatus for molding a cap (16) including a base portion (18) and peripheral skirt (20) extending axially from and about the base portion (18) includes an outer surface forming mold (44) for forming an outer surface of the base portion (18) and the peripheral skirt (20) and an inner surface forming mold (46) seatable within the outer surface forming mold (44) for forming an inner surface of the base portion (18) and the peripheral skirt (20). The outer surface forming mold (44) is retractable from seated engagement with inner surface forming mold (46) for exposing the molded cap (16) therebetween. The inner surface forming mold (46) includes a core portion (52) and lug forming mold portions (54) disposed radially peripherally thereabout, the lug forming mold portions (54) being able to project axially from and retract radially inwardly relative to the central core portions (52) for releasing and ejecting the molded cap (16) from the inner surface forming mold (46).

Abstract: A liquid tight connector for affixing, in a liquid tight manner, to a conduit having a ridge located adjacent to its end, wherein the conduit extends into a bore (5) and abuts against a sealing surface (6) and is held in liquid tight engagement therewith. A locking member (9) projects into the bore (5) and locks on to the ridge of the conduit.

Abstract: The unit has a conveyor belt (5) adapted to receive, transfer and cool the pellet elements, a cylindrical member (2) located above the conveyor belt and rotatable about an axis transverse to the feed direction of the conveyor belt, the peripheral speed of the cylindrical member substantially corresponding to the feed speed of the conveyor belt, at least a ring element (6) engaged in coaxial relation with and at the outside of the cylindrical member and exhibiting a number of projections (9) oriented radially apart from the cylindrical member (2), feed means (12) and dispensing means (14) adapted to distribute material to the fluid state onto the projections (9) and to form drop portions of the same thereon, each of the projections passing in the vicinity of the conveyor belt (5) so as to let one of the drop portions defining one of the pellet elements fall thereon.

Abstract: A single-block central plunger is manufactured, which is particularly suited for the production of boxes made of plastic material for electric accumulators. The mould includes a mobile plate (3) supporting some lateral cores (5) and a fixed plate (2) supporting a fixed central plunger (7), wherein the mobile plate (3) moves co-axially in relation to the fixed plate (2) by sliding on some guiding columns (4). The fixed central plunger (7) supported by the fixed plate (2) is made from a single block and its cores (8) are obtained from the same block, as well as its box angle-plate (11), preferably by machining them with wire cutting spark erosion tool machines.