ITAN20140073U1 - NOZZLE FOR INJECTION MOLDING AND RELATIVE TIP. - Google Patents

Description

DESCRIPTION

accompanying a patent application for a utility model entitled:

“NOZZLE FOR INJECTION MOLDING AND RELATIVE TIP”.

TEXT OF THE DESCRIPTION

This utility model patent application relates to a nozzle for injection molding of molten materials, in particular plastic materials and in particular refers to the tip of the nozzle.

With reference to Fig. 1 there is illustrated a system for distributing molten material for injection molds, according to the known art, indicated as a whole with the reference number (100).

The distribution system (100) includes:

- an inlet manifold (105) from which the material enters by increasing the delivery pressure,

- one or more distribution plates (106) that distribute the material by making it flow in channels (160) obtained inside the distribution plates,

- one or more nozzles (101) which convey the material into the mold, maintaining a temperature within a predetermined range.

The heat to the distribution plate is provided by tubular resistors (161) inserted in suitable grooves of the distribution plate (106).

The distribution system (100) is mounted in a seat made inside an injection mold and more precisely on the side of the mold matrix.

On the distribution plate (106) there are mounted supports (162), generally made of titanium, which are in contact with the mold and allow differential expansion between the distribution plate (106) and the mold, during the running of the distribution system (100).

After being injected into the mold cavity, the material must solidify. The molds are therefore equipped with one or more cooling circuits to remove excess heat.

The nozzle (101) includes a body (10) consisting of a steel cylinder provided with an axial channel (11) in order to allow the passage of the molten material.

The nozzle (101) has a base (12) equipped with appropriate connection systems to the distribution plate (106). The base (12) of the nozzle can rest on the distribution plate (106) and held in position by the pressure exerted by the metal plates that make up the mold or can be screwed to the distribution plate.

The nozzle (101) includes a head (13) at the opposite end to the base (12). The head (13) of the nozzle is intended to couple with the cavity of the mold to be filled. The head (13) of the nozzle is made in such a way as to let the material flow towards the mold, limiting the transmission of heat to the walls of the mold cavity.

With reference to Fig. 2, the head (13) of the nozzle inserted in a cylindrical seat (201) of a mold (200) is illustrated. The mold seat (201) continues with a tapered portion (202) having a decreasing diameter which ends in a hole (203) communicating with the cavity of the mold into which the plastic material is to be injected.

The head (13) of the nozzle includes:

- a centering ring (14) fixed to the nozzle body (10), to maintain concentricity between the nozzle and its seat (201) in the mold;

- a tip (102) comprising a body (20) and a conical tip (21) that protrudes from the body (10) of the nozzle to arrange itself in the tapered portion (202) of the mold seat; And

- a ring nut (103) which serves to fix the tip (102) to the body (10) of the nozzle.

The body (10) of the nozzle is generally heated by heating systems known per se and therefore not shown in the figures. The ring nut (103) is made with a cylindrical area (30) which, being in contact with the mold, causes the heat to flow from the nozzle to the mold.

The body (20) of the tip provides an axial duct (22) communicating with the duct (11) of the nozzle body. In the tip (2) one or more channels (123) are formed, communicating with the axial duct (22) of the tip. The channels (123) of the tip lead into a gap (I) defined between the external surface of the tip of the tip and the internal surface of the ring nut (103). The channels (123) of the tip allow the passage of the material from the axial duct (22) of the tip to the hole (203) which leads to the cavity of the mold.

The channels (123) of the tip are perfectly cylindrical and inclined with respect to the axis (A) of the nozzle by an acute angle (α) of about 45 °. Consequently, in the gap (I) between the external surface of the tip (21) of the tip and the internal surface of the ring nut (103), stagnation areas (R) are generated, above the channels (123), in which the material stagnates. plastic.

The nozzle shown in Fig. 2 is a free flow nozzle, ie without shutter.

With reference to Fig. 3, a nozzle equipped with a shutter (5), having the shape of a pin, axially arranged in the duct (11) of the nozzle body and in the duct (22) of the tip is shown. In this case, the duct (22) of the tip passes through to pass the pin (5) which passes through the tip of the tip.

The tip (21) of the tip is truncated cone and the lower end of the pin (5) protrudes inferiorly from the tip of the tip. The needle (5) can slide between two positions:

- a retracted position where the pin lets the material flow, e

- an advanced position in which the pin generates a sharp reduction in the surface of passage of the material.

The reduction of the passage of material, in steady conditions, first requires a control of the back pressure of the material and then the passage section will be blocked by solidified material. The needle can be hydraulically or pneumatically operated. The purpose of this needle valve system (5) is to control injection timing more precisely.

In this case, the nozzle with needle shutter does not provide a fixing ring and the tip (102) is directly fixed to the body (10) of the nozzle. The channels (123) of the tip are always located in the tip (21) of the tip and flow into a gap (I ') between the outer surface of the tip of the tip and the tapered portion (202) of the mold seat.

However, even in this case, stagnation of material (R) is formed, within the interspace (I '), above the channels (123) of the tip.

It must be considered that the molten plastic material that flows into the nozzle (1) is formed by threads of material which, flowing between them due to the differences in the speed of the melt, generate high shear stresses. With reference to Fig. 4, the shear stresses increase as the speed of the molten material increases and generate ever-increasing swirling areas of turbulence (T), in which the material stagnates.

Generally the nozzle assembly and in particular the tip (102) plays an important role due to said shear stresses which develop inside it.

This nozzle unit is made in such a way as to try to minimize the stagnation areas (R). In fact, it is known that the material to be injected can degrade if it remains in contact with hot surfaces for a long time. Furthermore, by minimizing the stagnation areas (R), the resumption of production after a color change of the material to be injected is also improved, preventing the new material from being polluted by the material present in the stagnation areas (R).

EP1602465 describes a nozzle assembly in which an attempt was made to minimize the areas of material stagnation.

However, with known nozzle assemblies, in order to change the color of the material to be printed, many cycles are required, during which non-conforming articles are produced to clean the stagnation areas.

In fact, it must be considered that many products made by injection molding are made in different colors. The operation to make the transition from one material to the next is called "color change". This color change operation requires cleaning the plasticizing cylinder of the injection molding machine, removing it from the mold and purging the material contained in the plasticizing cylinder, introducing the new material. When the new material comes out of the injector, the cylinder approaches the mold again.

At this point, to clean all the internal surfaces of the supply duct (manifold, distribution plates, nozzles), test prints are made. This allows the new material to replace the old. The color of the pieces produced therefore gradually changes from the old to the new, presenting an increasingly higher percentage of new material. The transition from one color to another is not immediate, because the molten material inside the nozzle ducts presents speed gradients moving away from the walls. The material has a low speed near the walls and a maximum speed in the center of the duct, thus arriving at different times in the cavity of the mold to be filled. In the presence of stagnation areas it is possible to find, even after hundreds of prints, small percentages of the old color, especially if it has a darker shade than the new material.

The material flows into the nozzle having as delimitation the following surfaces: the axial duct (11) of the nozzle body, the axial duct (22) of the tip body, the channels (123) of the tip, the interspace (I ) between the external surface of the tip of the tip and the internal surface of the ferrule, the gap between the external surface of the tip of the tip and the tapered portion (202) of the mold seat, the hole (203) of the mold that accesses the cavity of the mold. All these surfaces create very variable passage sections in terms of dimensions.

The object of the present invention is to eliminate the drawbacks of the known art, by improving the conformation of the tip of the nozzle in order to avoid the stagnation of material during the molding process and to allow rapid production changes, without the need to carry out several throwaway molds between the production changes.

This purpose is achieved in accordance with the invention, with the characteristics listed in the attached independent claim 1.

Advantageous embodiments of the invention appear from the dependent claims.

With reference to Fig. 5, a graph of two velocity profiles for non-Newtonian fluids within a circular duct is shown. The distance from the center of the duct is represented on the abscissa while the velocity on the ordinate. A lower average velocity corresponds to a flatter velocity profile and therefore lower gradients, moving away from the center of the duct.

On the basis of this experiment, the applicant found that if the speed of the material in the nozzle tip channels can be decreased, the areas of turbulence and stagnation decrease. This result can be obtained by increasing the section of the material passage channels as much as possible.

The injection molding nozzle according to the invention includes:

- a body provided with an axial duct through which the material to be injected passes, e

- a tip fixed to the body, called tip comprising:

- an axial duct communicating with the axial duct of the nozzle body, e

- a plurality of channels communicating with said axial duct of the tip and leading to the outside of the tip, each of said channels having an inlet section on the axial tip duct and an outlet section on the external surface of the tip.

The peculiarity of the invention is represented by the fact that the entrance section is smaller than the exit section and said channel has a tapered shape with increasing dimensions from the entrance section to the exit section. In this way the speed of the molten material decreases in the tip channel and decreases turbulence and stagnation of material at the exit of the tip channel.

Further features of the invention will appear clearer from the detailed description that follows, referring to its purely exemplified and therefore non-limiting embodiments, illustrated in the attached drawings, in which:

Fig. 1 is a sectional view illustrating a distribution unit for injection molding, according to the known art;

Fig. 2 is a sectional view, partially interrupted, showing a nozzle of the distribution unit of Fig. 1 inserted in a seat of a mold;

Fig. 3 is a view like Fig. 2, but illustrating a nozzle with a needle shutter according to the known art;

Fig. 4 are three two-dimensional simulations, illustrating the behavior of the flow of plastic material in a duct, with increasing shear stresses;

Fig. 5 is a graph illustrating two velocity profiles of a plastic material in a cylindrical duct, as a function of the distance from the axis of the duct,

Fig. 6 an axial sectional view of the head portion of a nozzle according to the invention;

Fig. 7 is a perspective view of the tip of the nozzle of Fig. 6, shown upside down;

Fig. 8 is a side view of the tip of Fig. 7;

Fig. 9 is a cross-sectional view, taken along the section plane IX-IX of Fig. 8;

Fig. 10 is a schematic view in perspective, illustrating the profile of a channel of the nozzle tip according to the invention;

Fig. 11 is a side view of a variant of the tip according to the invention;

Fig. 12 is an axial sectional view, taken along the section plane XII-XII of Fig. 11;

Fig. 13 is a side view of the nozzle ring nut of Fig. 6;

Fig. 14 is an axial sectional view, taken along the section plane XIV-XIV of Fig. 13;

Fig. 15 is a view like Fig. 6, but illustrating a needle shutter nozzle according to the invention;

Fig. 16 is a three-dimensional simulation of the flow of plastic material in the tip of the nozzle according to the invention, in an initial condition;

Fig. 17 is a simulation like Fig. 16, but illustrating the flow of plastic material in a final condition.

In the following, elements identical or corresponding to those already described are indicated with the same reference numbers and their detailed description is omitted.

With reference to Fig. 6, a nozzle according to the invention is shown, indicated as a whole with the reference number (1).

The nozzle (1) includes:

- a body (10) with an axial duct (11) for the passage of the molten material,

- a tip (2) provided with an axial conduit (22) communicating with the axial conduit (11) of the body and outlet channels (23) of the molten material communicating with the axial conduit of the tip, and

- a ring nut (3) to fix the tip to the nozzle body (10). The ring nut (3) has an upper edge (3 ').

With reference to Figs. 7-10, the tip (1) comprises a body (20) and a tip (21) having a substantially conical or ogive shape.

The body (20) comprises a first cylinder (24) and a second cylinder (25) having a smaller diameter than the first cylinder, so as to define an abutment surface (24 ') intended to abut the upper edge ( 3 ') of the ring nut (3).

The tip (21) of the tip has a circular base (26) disposed on the second cylinder (25) of the tip body. The diameter of the second cylinder (25) of the tip body is greater than the diameter of the base (26) of the tip (21), therefore an annular plane (27) protruding radially is generated on the second cylinder (25) of the tip body outward from the base (26) of the tip.

The axial duct (22) is obtained axially in the body (21) of the tip. The axial duct (22) is a blind duct and has a substantially concave bottom wall (22 ') (Fig. 7), corresponding to the annular plane (27) from which the base (26) of the tip of the tip starts.

The channels (23) of the tip open into the base (26) of the tip, under the annular plane (27).

With reference to Figs. 9 and 10, advantageously the tip (2) comprises four channels (23) arranged in diametrically opposite positions and equidistant from each other. Each channel (23) has an inlet section (23a) communicating with the axial duct (22) and an outlet section (23b) formed in the base (26) of the tip of the tip.

The inlet section (23a) has a smaller surface than the outlet section (23b). Therefore the channel (23) has a tapered shape with gradually increasing dimensions going from the inlet section (23a) to the outlet section (23b). In this way the material flowing in the channel (23) gradually decreases its speed and therefore the shear stresses between the material threads are minimized.

With reference to Fig. 9, the channel (23) advantageously has a taper angle (β) comprised between 20 ° and 40 °, preferably 30 °.

Advantageously, the inlet section (23a) and the outlet section (23b) have a rectangle shape in which the larger sides extend in a circumferential direction and the smaller sides extend in a direction parallel to the axis (A) of the duct (22 ) of the tip. In this case the channel (23) has a truncated pyramid shape with a rectangular base. Preferably the shorter sides of the rectangle are rounded in an arc of a circle or the inlet and outlet sections (23a, 23b) of the channel (23) can also have an ellipse shape, in which the major axis of the ellipse extends in circumferential direction and the minor axis of the ellipse extends in a direction parallel to the axis (A) of the duct (22) of the tip.

It should be noted that the channels (23) are not frusto-conical in order not to increase the axial dimensions of the tip too much and to have as little metal as possible between one channel and the other, that is, to obtain the outputs of the channels as close as possible. In fact, to obtain the same speed reduction results, truncated cone rather than truncated pyramidal channels would imply a longer tip, since the radius of a circular outlet section should be at least twice the length of the shorter side of the rectangular outlet section (23b ).

In addition, a tip with channels having a circular outlet section must provide for a greater amount of material between one channel and the other, that is, the outlet sections of the channels are more widely spaced than in the case of rectangular outlet sections. This greater distance between the channels implies problems in rejoining the plastic material exiting the channels, as will be explained below.

With reference to Figs. 11 and 12 show a variant of the tip in which the channel (23) of the tip has an axis (B) which forms an obtuse angle (α) with respect to the axis (A) of the axial duct of the tip which coincides with the nozzle shaft. This angle (α) is greater than 90 °, preferably between 90 ° - 100 °. In this way, the flow of plastic material coming out of the channels (23) is directed in the opposite direction with respect to the direction of travel of the material within the nozzle duct (11). Consequently, the flow of material is forced to flow in the opposite direction to the direction of travel of the material within the nozzle duct (11), improving the cleaning of the stagnation areas that are formed at the outlet of the channels (23) of the tip.

To make these channels (23) it is not enough to use a traditional numerical control lathe of the tool, but it is necessary to use five-axis lathes or wire EDM (after having made a first perfectly cylindrical-shaped through hole that allows to insert the wire).

As an alternative to wire EDM, an additive construction technique can be used. In this case, to reduce costs, it is possible to start from a tube already machined with traditional lathes and build only the passage channels (23) and the tip (23) of the tip with additive construction technique.

With reference to Figs. 13 and 14, the ring nut (3)

comprehends:

- a cylindrical body (31) threaded externally to be able to screw into the body (10) of the nozzle;

- a collar (32) that protrudes externally from the body (31) of the ring nut and is placed under the lower edge of the body (10) of the nozzle,

- a cylindrical portion (30) that comes into contact with the seat of the nozzle obtained in the mold.

Gripping areas for a tubular key are formed in the collar (32) of the ring nut.

The ring nut (3) includes a cylindrical duct (33) axially obtained in the body (31) of the ring nut which continues with a tapered duct (34) having a decreasing diameter going from top to bottom. A shoulder (35) is generated between the cylindrical duct (33) and the tapered duct (34).

With reference to Fig. 6, the shoulder (35) of the ring nut is located in correspondence with the annular plane (27) from which the base (26) of the tip of the tip starts into which the outlet channels (23) of the molten material open.

The upward orientation of the axis (B) of the channels (23) and the provision of the shoulder (35) of the ring nut in correspondence with the annular plane (27) from which the base (26) of the tip of the tip starts, eliminates the formation of stagnation in the gap (I) between the external surface of the tip of the tip and the internal surface of the ferrule.

In fact, the surface of passage of the molten material inside the ring nut (3), starts in coincidence with the shoulder (35) in correspondence with the channels (23) of the tip. This expedient, combined with the non-cylindrical shape of the channels (23), allows the new material to be able to remove all the material already present at each injection.

Advantageously, the tip (2) and / or the ring nut (3) can be coated with CVD (Chemical Vapor Deposition) processes using for example DLC (Diamond Like Carbon) coatings, in order to lower the friction of the material on the walls of the tip. and of the ring nut in contact with the material.

With reference to Fig. 15, a nozzle (1) provided with a needle shutter (5) is illustrated. In this case, the tip (21) of the tip is frusto-conical and the axial duct (22) of the tip is through and extends also into the tip (21), so that the lower end of the needle (5) can protrude from below from the tip (21). The shape of the channels (23) of the needle is the same as that of the free flow nozzle according to the invention.

In this case, a ring nut (3) equal to the ring nut of the free flow nozzle according to the invention is shown. However, the nozzle (1) according to the invention could be devoid of a ring nut and the channels (23) of the nozzle (1) can lead directly into the gap formed by the outer surface of the tip of the tip and the truncated cone portion (202) ( see Fig. 3) of the mold seat that houses the nozzle.

With reference to Fig. 16, a fluid dynamic simulation of the molten material flowing in the tip (1) of the nozzle according to the invention is shown, in an initial situation.

A flow of cylindrical material (322) flows into the axial conduit (22) of the tip. This cylindrical flow branches into tapered flows (323) which flow into the channels (23) of the tip. The tapered flows (323) exiting the channels (23) generate arcuate flows (326) which flow around the base (26) of the tip of the tip and rejoin each other, forming an annular flow in the cavity (I) between the external surface tip of the tip and the inner surface of the ferrule (3).

In Fig. 17 a final situation is shown in which the arcuate flows (326) have joined together along the seam lines (G).

It must be considered that the nozzle (1) according to the invention has the following advantages:

The material flows at high speed only in a small area, that is, in the inlet section (23a) of the tip channels, immediately slowing down. Consequently, lower average speeds of the material, compared to known nozzles with cylindrical tip channels, create a flatter velocity profile in the material (see Fig. 5), lower pressures, reduced shear stresses and less turbulence in the event of section changes , as at the output of channels (23).

As a result, with the nozzle according to the invention, a wider area is obtained, compared to known nozzles, where the fluid has a roughly constant speed. Consequently, the material that passes through the tip of the nozzle is renewed with reduced time differences and therefore in a smaller number of prints. Therefore, there is greater cleaning of the channels (23) during the color change.

Thanks to the velocity profile of the flatter material compared to known nozzles, the flow of fluid threads at different distances from the center of the duct has a zero or in any case less velocity gradient compared to known nozzles and therefore the material has shear stress ) lower than known nozzles.

By decreasing the speed and pressure (or keeping it high for a very small area) there are fewer pressure drops due to lower shear stresses. Consequently, the material has low residual shear stresses, thus improving the mechanical and thermal characteristics of the material.

As the material passes through multiple channels, it separates into multiple tapered streams (323) and when the material reaches the annular groove (26) of the tip, the tapered streams (323) rejoin each other. At the joining points, seams are formed (G). It must be considered that in particular constructions (transparent materials) or under certain conditions (polarized lenses), the effects of these junction lines (G) are visible. However, in the case of the nozzle according to the invention, the lines are still created due to the separation of the flows, but these junction lines (G) have a lower aesthetic and mechanical impact than in the case of known nozzles. This is due to the shorter space traveled by the material before encountering another flow and the lower velocity gradient between different melt paths.

Basically, with the nozzle according to the invention, the material better preserves its mechanical, aesthetic and optical characteristics and any color changes are facilitated.

Equivalent variations and modifications can be made to the present embodiments of the invention, within the reach of a person skilled in the art, which however fall within the scope of the invention.

Claims (10)

CLAIMS 1. Nozzle (1) for injection molding comprising: - a body (10) provided with an axial duct (11) through which the material to be injected passes, and - a tip (2) fixed to the body (10), said tip (2) comprising: - an axial duct (22) communicating with the axial duct (11) of the nozzle body, e - a plurality of channels (23) communicating with said axial duct (22) of the tip and opening outside the tip, each of said channels (23) having an inlet section (23a) on the axial duct (22) of the tip and an outlet section (23b) on the outer surface of the tip, characterized in that the inlet section (23a) is smaller than the outlet section (23b) and said channel (23) has a tapered shape with increasing dimensions from the inlet section to the outlet section. 2. Nozzle (1) according to claim 1, wherein the inlet section (23a) and the outlet section of the channel (23) have a substantially rectangular or elliptical shape, in which the shorter sides of the rectangle or the axis minor of the ellipse develop in a direction parallel to the direction of the axis (A) of the axial duct (22) of the tip and the longer sides of the rectangle or the major axis of the ellipse develop in a circumferential direction around the tip. 3. Nozzle (1) according to claim 2, in which the inlet section (23a) and the outlet section of the channel (23) have a substantially rectangular shape with the smaller sides arched. 4. Nozzle (1) according to any of the previous claims, in which the taper angle (β) of the channel (23) is between 20 ° and 40 °, preferably 30 °. 5. Nozzle (1) according to any one of the preceding claims, wherein the tip channel (23) has an axis (B) which forms an obtuse angle (α) with respect to the tip axis (A), preferably between 90 ° - 100 °. 6. Nozzle (1) according to any one of the preceding claims, wherein said tip comprises a tip (21) having a truncated conical or ogive shape, said tip having a base (26) arranged on the body (20) of the tip so as to defining an annular plane (27) which protrudes radially from the base (26) of the tip of the tip, in which said outlet section (23b) of the channels (23) of the tip is located in said base (26) of the tip of the tip, under said annular plane (27). 7. Nozzle (1) according to any one of the preceding claims, further comprising a ring nut (3) for fixing the tip (2) to the nozzle body (10), said ring nut (3) comprising an axial cylindrical duct (33) which continues with a tapered duct (34) having a decreasing diameter going from top to bottom and a shoulder (35) between the cylindrical duct (33) and the tapered duct (34), in which said shoulder (35) of the ring nut is located at the outlet section (23b) of the channels (23) of the tip. 8. Nozzle (1) according to any one of the preceding claims, wherein said tip (2) has a conical or ogive tip (21) and said axial duct (22) of the tip is blind and provided with a bottom wall (22 ') in correspondence with said input sections (23a) of the tip channels. 9. Nozzle (1) according to any one of claims 1 to 8, wherein said tip (2) has a frusto-conical tip (21) and said axial duct (22) of the tip is through and axially crosses the tip of the tip and the The nozzle further comprises a needle shutter (5) which passes through the axial duct (22) of the tip and protrudes from the tip of the tip. 10. Nozzle (1) according to any one of the preceding claims, wherein said tip (1) and / or said ring nut (3) are coated with an anti-wear coating