Method for producing a fan impeller

Abstract

The present invention relates to a method for producing a fan impeller, wherein the fan impeller has a plurality of impeller blades and a cover plate covering the impeller blades, wherein the fan impeller is injection molded from a plastic material in an injection mold using a cascade injection molding process, and the injection mold has a plurality of shut-off nozzles for supplying plastic material at different connection positions, the plurality of throttling nozzles having different opening times, wherein the number of the shut-off nozzles is determined according to the number of the impeller blades.

Description

Technical Field

[0001] The invention relates to a method for producing a fan impeller. Background Art

[0002] The production of fan impellers made of plastic material by injection molding is known in the prior art. Such plastic injection molded parts need to be of high quality to ensure the required strength at high rotational speeds and the centrifugal forces they generate. Fan impellers have critical areas that are susceptible to cracking when stressed. Such critical areas are in particular the cover plates covering the impeller blades.

[0003] Since the injection molding process used during manufacturing creates weld lines at the flow front of the plastic material, the risk of cracking in the weld line area is particularly high. It is therefore very important to place the weld lines in areas with the lowest possible tension. The standardized and compliant connection design of the injection molding process and the required number of connections lead to a corresponding number of weld lines on the cover. Therefore, the possibility of placing these weld lines in areas of low tension is severely limited. Summary of the invention

[0004] It is therefore an object of the present invention to provide a method for producing a fan impeller using a plastic injection molding process, which reduces the tendency to cracking in the region of the weld line.

[0005] This object is achieved by combining the following technical features.

[0006] According to the invention, a method for producing a fan impeller is provided, the fan impeller having a plurality of impeller blades and a cover plate covering the impeller blades, wherein the fan impeller is injection molded from a plastic material in an injection molding tool using a cascade injection molding process. For this purpose, the injection molding tool comprises a plurality of shut-off nozzles, in particular needle-shaped shut-off nozzles, for supplying plastic material at different connection positions, the shut-off nozzles having different opening times for the cascade injection molding process. According to the invention, the number of the shut-off nozzles is determined depending on the number of the impeller blades.

[0007] The cascade injection molding process is known to those skilled in the art. The cascade injection molding process is a type of sequential injection molding in which multiple shut-off nozzles are used, which allows the molded plastic molded part to be filled over multiple gates. It is also known to use a hot runner system in the cascade injection molding process to keep the plastic molding compound in a liquid state.

[0008] Basically, the cascade injection molding process is characterized by the fact that the filling of the cavity in the injection molding tool is set particularly advantageously, since the opening time of the shutoff nozzle can be set individually by the controller. The injection of the plastic material into the cavity of the injection molding tool initially takes place only through a specific shutoff nozzle. The resulting melt front flows and reaches a downstream shutoff nozzle, which is open or only opens subsequently. The shutoff nozzles are thus opened successively in a cascade-like manner. The plastic melt now flows into the cavity through the successively opened shutoff nozzles. On the one hand, the cascade technology reduces the number of weld lines, on the other hand, weld lines can flow through the shutoff nozzle that is opened later and can even be completely eliminated or at least significantly improved in quality.

[0009] According to the invention, the cascade injection molding process used to manufacture the fan impeller is used to reduce or eliminate weld lines in the strength-critical areas on the cover plate. The number of shutoff nozzles depends on the number of impeller blades connected to the cover plate, so that the melt front of the plastic material injected through the shutoff nozzles overflows the connection point between the cover plate and the impeller blades, and since the opening time of the shutoff nozzles is different in the cascade injection molding process, no weld lines are generated on the cover plate. This increases strength and reduces the tendency to cracking due to weak points.

[0010] An advantageous embodiment is that different connection positions are assigned to the cover plate. It is particularly advantageous if the different connection positions assigned to the cover plate are such that, viewed in axial projection, the connection positions of the cover plate are each located between the impeller blades in the circumferential direction. Viewed along the axis of rotation of the fan impeller, the cover plate and the impeller blades are axially adjacent to one another. The impeller blades can extend in a straight line or can extend in a curved manner forward or backward in the circumferential direction. However, the connection positions are preferably determined in such a way that they do not extend to the connection line between the cover plate and the impeller blades, but are at a distance from this connection line.

[0011] In one embodiment of the method, it is further provided that, in the case of an even number of impeller blades, the number of shutoff nozzles corresponds to the number of impeller blades. For example, in the case of six impeller blades arranged in the circumferential direction on a fan impeller, six shutoff nozzles are also arranged at the same distance in the circumferential direction. This ensures that the shutoff nozzles eliminate all weld lines due to their different opening times.

[0012] The method is also unique in that, in the case of an odd number of impeller blades, the number of shutoff nozzles is greater than the number of impeller blades. In particular, an advantageous embodiment provides that, in the case of an odd number of impeller blades, the number of shutoff nozzles is twice the number of impeller blades. For example, in the case of five impeller blades arranged in the circumferential direction on the fan impeller, ten shutoff nozzles are arranged at the same distance in the circumferential direction. This allows complete flow to be achieved with staggered opening times of the shutoff nozzles, thereby eliminating all weld lines.

[0013] A further development of the method is characterized in that the plurality of shutoff nozzles are respectively divided into a plurality of cascade groups and the cascade groups have opening times of the shutoff nozzles which are successive to one another. By assigning the shutoff nozzles to the cascade groups, the opening times of the shutoff nozzles can be controlled in groups by the controller. This means, for example, that for a fan impeller with six impeller blades, initially three of the six shutoff nozzles are opened simultaneously and then the other three shutoff nozzles are opened after a specified time period so that the plastic material is injected into the melt front of the plastic material from the first opened shutoff nozzle and the weld line is removed.

[0014] A particularly advantageous embodiment is characterized in that the shutoff nozzles of one cascade group are positioned exactly at the location of the weld line of the plastic supplied by the shutoff nozzles of another cascade group. Thus, the arrangement of the cascade groups of shutoff nozzles is precisely matched to the corresponding fan impeller and the corresponding number of impeller blades.

[0015] The method particularly relates to a radial fan impeller. Preferably, a fiber-reinforced plastic material is used as the plastic material.

[0016] Furthermore, the invention comprises a fan impeller produced according to the above method, which has an optional base plate, impeller blades and a cover plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other advantageous developments of the present invention are shown in more detail below together with the description of a preferred embodiment of the present invention with reference to the accompanying drawings. It is shown therein:

[0018] Figure 1 A perspective view showing a fan impeller in a first embodiment variant;

[0019] Figure 2 A perspective view of a fan impeller is shown in a second embodiment variant. DETAILED DESCRIPTION

[0020] Figure 1 A perspective view of a fan impeller 1 is shown in a first embodiment variant, which has a base plate 4, a cover plate 3 and impeller blades 5 formed axially therebetween. This exemplary embodiment relates to a fan impeller 1 designed as a radial fan with six impeller blades 5. Figure 1 A base plate 4 is shown, but it is also possible to produce a fan impeller without a base plate.

[0021] The fan impeller 1 is manufactured from a thermoplastic material in an injection molding tool using a cascade injection molding process by the method. For an impeller 1 having six impeller blades 5, six needle-shaped shut-off nozzles 6, 7 are provided as connection locations for supplying plastic material preferably via a hot runner system, and a supply device 9 is provided at connection locations equidistantly spaced in the circumferential direction, through which the plastic material is injected into the cavity of the injection molding tool.

[0022] The connection points of the needle shutoff nozzles 6, 7 are assigned to the cover plate 3, i.e. the liquid plastic material is fed into the region forming the cover plate 3. The connection points of the needle shutoff nozzles 6, 7 are located between the impeller blades 5, i.e. when viewed in the axial projection, they are adjacent to but not reaching the connection line between the impeller blades 5 and the cover plate 3. During the manufacture of the fan impeller 1, the liquid plastic material thus flows in the circumferential direction through the region of the cover plate 3 which represents the connection line between the impeller blades 5 and the cover plate 3.

[0023] The needle-shaped intercepting nozzles 6 and 7 are divided into two cascade groups, the needle-shaped intercepting nozzles 6 provided with reference numeral 6 form a first group, and the needle-shaped intercepting nozzles 7 provided with reference numeral 7 form a second group. The two cascade groups of needle-shaped intercepting nozzles 6 and 7 have mutually continuous opening times, so that when the needle-shaped intercepting nozzles 7 of the second cascade group are opened, the melt front of the liquid plastic material from the needle-shaped intercepting nozzles 6 of the first cascade group flows through the needle-shaped intercepting nozzles 7 of the second cascade group. The needle-shaped intercepting nozzles 7 of the second cascade group are accurately positioned at the position where the weld line of the plastic material supplied from the needle-shaped intercepting nozzles 6 of the first cascade group is located.

[0024] Figure 2 An alternative exemplary embodiment of a fan impeller 1 is shown. Its features are similar to Figure 1 The embodiment of the invention is substantially the same, but the number of impeller blades 5 and the connection position to the needle-shaped shut-off nozzles 6, 7 are different. The fan impeller 1 comprises not six, but only five impeller blades 5, i.e. an odd number of fan impellers. Figure 1 In the same manner as in the embodiment of FIG. 1 , the number of connection points and needle shutoff nozzles 6 and 7 is twice the number of impeller blades 5. Here, the plastic material is also injected between the impeller blades 5 in a cascade injection molding manner by the needle shutoff nozzles 6 and the needle shutoff nozzles 7 forming two cascade groups in a time-continuous manner, thereby eliminating the weld line.

[0025] The implementation of the invention is not limited to the preferred exemplary embodiments specified above. On the contrary, a wide variety of variants of the solution shown can be envisaged, even in the case of fundamentally different designs. For example, the method can also be used for axial fan impellers with or without a base plate. A preferred fiber-reinforced thermoplastic plastic material can also be used as plastic material.

Claims

1. A method for producing a fan impeller (1), the fan impeller having a plurality of impeller blades (5) and a cover plate (3) covering the impeller blades, wherein the fan impeller (1) is injection molded from a plastic material in an injection mold using a cascade injection molding process, and the injection mold has a plurality of shutoff nozzles (6, 7) for supplying plastic material at different connection positions, the plurality of shutoff nozzles having different opening times, wherein the number of the shutoff nozzles (6, 7) is determined according to the number of the impeller blades (5), the connection positions of the shutoff nozzles (6, 7) are assigned to the cover plate (3), wherein when the number of the impeller blades (5) is an even number, the number of the shutoff nozzles (6, 7) corresponds to the number of the impeller blades (5), and when the number of the impeller blades (5) is an odd number, the number of the shutoff nozzles (6, 7) is greater than the number of the impeller blades (5), and the impeller blades (5) are formed axially.

2. The method according to claim 1, It is characterized in that The different connection positions assigned to the cover plate (3) are such that, viewed in projection, the connection positions of the cover plate (3) are each located between the impeller blades (5).

3. The method according to claim 1 or 2, It is characterized in that When the number of the impeller blades (5) is an odd number, the number of the shut-off nozzles (6, 7) is twice the number of the impeller blades (5).

4. The method according to claim 1 or 2, It is characterized in that The plurality of shut-off nozzles (6, 7) are each divided into cascade groups, and the cascade groups have consecutive opening times of the shut-off nozzles (6, 7).

5. The method according to claim 4, It is characterized in that The shut-off nozzles (6, 7) of one cascade group are positioned at the location of the weld line of the plastic material supplied by the shut-off nozzles (6, 7) of another cascade group.

6. The method according to claim 1 or 2, It is characterized in that The fan impeller (1) is a radial fan impeller.

7. The method according to claim 1 or 2, It is characterized in that The plastic material is a fiber reinforced plastic material.

8. A fan impeller (1) produced according to the method according to any one of the preceding claims 1 to 7.

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