Method and mold for producing a plastic roller
Through the two-stage injection molding method and annular gate technology, the problem of forming joint marks when melt flow encounters is solved, and plastic roller manufacturing without joint marks is realized, which improves roller durability and reduces material losses.
Patent Information
- Application Number
- CN202380083649.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-12-06
- Filing Date
- 2023-11-27
- Publication Date
- 2025-08-08
AI Technical Summary
Prior Art When manufacturing plastic rollers, melt flow encounters in the molding cavity to form bond marks, resulting in weak points, affecting roller durability and increasing material loss.
Using a two-stage injection molding method, the basic structure is formed using the first and second molded parts, and the outer shell structure is formed on the support surface through the annular gate to avoid melt flow encounters, and the molded cavity is filled in the axial direction with the annular gate to eliminate bonding marks.
The manufactured plastic rollers have no joint marks, improve durability and reduce material waste, and the method is cost-effective.
Smart Images
Figure CN120457013A_ABST
Abstract
Description
Technical Field
[0001] The present invention firstly relates to a method for producing a plastic roller, in particular for a vehicle equipment device. A vehicle within the meaning of the present invention can be a land, air or water vehicle. Background Art
[0002] Plastic rollers are used, for example, in movable cargo floors or adjustable vehicle seats in the vehicle industry. In the prior art, plastic rollers are manufactured using, for example, multi-nozzles, which are injection molding nozzles with multiple nozzle tips and multiple gate areas. During production, multiple melt streams entering the mold cavity through these gate areas meet in the mold cavity, where the material streams connect. These so-called weld marks represent potential weak points in the component being produced, which can lead to failure during use and depending on the load.
[0003] One solution is to merge the melt streams outside the molding cavity. However, this solution is associated with high material losses. Summary of the Invention
[0004] For this reason, the object of the present invention is to provide a method in which no weld marks are produced in the mold cavity during production. Furthermore, material waste should be minimal. In this application, a weld mark is understood to be a meeting of melt streams that, depending on their state, form a more or less permanent connection. Such weld marks represent potential weak points, at least in critical areas of the plastic roller, which are to be avoided according to the present invention.
[0005] This object is achieved by a method having the features of claim 1 .
[0006] The method for producing a plastic roller for a vehicle equipment component comprises the following method steps.
[0007] Manufacturing occurs in a molding die comprising a first molding part, a second molding part, and a third molding part supported in an injection molding machine. The first molding part and at least one second molding part are used to create the first molding cavity. The first and second molding parts, which partially form the molding cavity, are typically movable into two relative positions in the injection molding machine: an open position and a closed position. In the closed position, the molding cavity is closed, and the injection molding process can be carried out. In the open position, the produced component can be removed from the molding die, ejected from the molding die, or a mold change can be performed.
[0008] First, using a first molded part and a second molded part, the basic structure of the plastic roller including the supporting surface is produced by injection molding a plastic melt into the first mold cavity. The supporting surface is used for the subsequent shaping of the outer shell structure in a two-stage process.
[0009] After the plastic melt cools, the forming mold is opened. The intermediate product, namely the basic structure of the plastic roller, remains in the first forming part, for example, the basic structure being arranged on a forming core. The second forming part is then replaced with a third forming part in the opened forming mold. Together with the first forming part, the third forming part is used to create a second forming cavity for producing a jacket structure comprising a cylindrical running surface on the supporting surface of the base part. The running surface is designed coaxially with the longitudinal center axis of the plastic roller.
[0010] For example, a second mold part can be replaced by a third mold part by using an injection molding machine with a mold changer, wherein one of the mold parts can be moved into an active position and the other mold part can be moved into an inactive position.
[0011] Furthermore, a ring gate is used when manufacturing the outer shell structure. This means that if a different gate is used when manufacturing the base structure, the gate is replaced. This can be done by replacing the hot runner nozzle or by replacing the gate. The ring gate can, for example, be formed on the third molded part, so that when the second molded part is replaced by the third molded part, the gate is replaced simultaneously.
[0012] The mold is then closed again, and the plastic melt is directed via a ring gate into the second mold cavity formed by the first mold part and at least a third mold part. When using a ring gate, the outer shell structure of the plastic roller is formed on the supporting surface of the base part. In other words, the second mold cavity is formed partially by the first mold part or the base structure supported on the first mold part, and partially by the third mold part. Other mold parts may also be involved. The melt is introduced into the ring gate, for example, using a central nozzle tip or multiple nozzle tips while maintaining a minimum temperature.
[0013] The melt is introduced into the second mold cavity in an annular manner at the ring gate, allowing it to expand in the mold tool parallel to the center axis of the mold cavity. The melt front develops uniformly, preventing weld marks. In other words, the mold cavity is filled annularly in the axial direction, without the melt streams coming into contact with one another.
[0014] The forming mold is then opened and the plastic roller is ejected.
[0015] The advantage of the method according to the invention is furthermore that the produced plastic roller has a greater durability due to the fact that no joint marks are contained in the outer shell structure. However, the method according to the invention can be implemented economically and advantageously.
[0016] For example, the basic structure is formed using a hot runner nozzle with a central gate, wherein the melt is ejected from the end face of the basic part. For example, the basic part is produced with a single nozzle, ie, an injection molding nozzle with a nozzle tip and a gate area.
[0017] After the basic structure has been produced, the central gate is replaced, for example, by a ring gate. This replacement is performed, for example, by replacing the second molded part with a third molded part, wherein the ring gate is formed on the third molded part.
[0018] For example, the annular gate can be implemented in the axial end region of the running surface. In this way, to produce an annular outer shell structure, the mold cavity can be filled with a substantially uniform axial progression of the melt front in a direction parallel to the center axis of the plastic roller to be produced, so that no melt streams come into contact with each other and thus no weld marks are formed. In this case, the cylindrical mold cavity is filled in the axial direction.
[0019] One embodiment provides that during the injection molding process, a mold core forms the base structure of one of the molded parts. The mold core can, for example, create a cavity in a plastic roller that is later used to accommodate a bearing and / or a shaft. The mold core can serve as a seat for an intermediate product, i.e., the base structure, when switching between the second and third molded parts.
[0020] According to one embodiment, the forming tool is designed such that the central axial section of the running surface is formed to protrude radially outward relative to the end regions. In other words, the central axial section disposed between the end regions has a larger diameter than at least one end region. This design of the running surface ensures that deviations from the theoretical installation angle do not affect the function of the roller. Due to the curved or convex running surface, the plastic roller functions completely properly in angle ranges deviating from the theoretical axis because it rests only on a substantially point-shaped or linear contact area.
[0021] In the case of a smaller difference between the middle diameter and the diameter on at least one end region of the running surface, even if undercuts are present, the shrinkage of the plastic material during cooling can allow axial demoulding. In this case, demoulding in two axial directions is possible.
[0022] For example, the running surface may be axially asymmetrical, with the diameter of the running surface at the second end region of the jacket structure being smaller than the diameter at the first end region of the plastic roller. For example, the second end region is the outer end region of the plastic roller, and the first end region is the inner end region of the plastic roller. The outer end region is the end region of the jacket structure that, after the plastic roller is mounted on the shaft, is located closer to the free end region of the shaft. The inner end region is the end region of the jacket structure in the axial region of the running surface facing away from the free end region. This allows for a larger tolerance range in the event of axial angular deviations of the plastic roller.
[0023] The asymmetrical convexity facilitates demoulding in the case of stronger undercuts, as will be explained in greater detail below.
[0024] With an asymmetrical convexity, the running surface can have its largest diameter in the central third region and a greater diameter difference in the second end region than in the free first end region. At the first end region of the running surface, for example, the diameter difference from the central region is so small that shrinkage allows demolding. Demolding at the outer ends is straightforward when demolding is performed parallel to the central axis in the direction of the first end region.
[0025] This embodiment offers the advantage that the plastic roller can be easily demolded even with large asymmetrical convexities. The diameter at the inner end region of the running surface is only slightly smaller than the maximum diameter of the running surface, so that shrinkage after the injection molding process is sufficient to demold the product. Demolding is not a problem at the second end region of the plastic roller, which has a large diameter difference from the third region, because there is no undercut.
[0026] The forming die has, for example, an immovable side and a movable side. The ring gate can be realized not only from the immovable side but also from the movable side.
[0027] The invention further relates to a forming tool for producing a plastic roller.
[0028] Such forming tools have already been mentioned above and have the disadvantage that they form joint lines in the outer shell structure of the plastic roller to be produced, which lead to failure of the plastic roller.
[0029] The object of the present invention is to provide a forming tool with which a plastic roller can be produced without seam marks.
[0030] This object is achieved by a forming tool having the features of claim 10 .
[0031] The forming tool according to the present invention comprises a first forming part, a second forming part, and at least one third forming part. Using this forming tool, an injection-molded part can be produced from one or more material components in a two-stage process. In other words, the forming tool can first produce an intermediate product, namely a base structure, and then at least one further structure, namely a jacket structure, can be injected onto the intermediate product, with a fixed connection to the intermediate product.
[0032] The first and second molding components create a first molding cavity, in which the base portion can be molded as an intermediate product. The first and third molding components create a second molding cavity, in which the at least one additional outer shell structure can be molded onto the intermediate product. The second and third molding components are interchangeable to form the first and second molding cavities. Injection molding machines with a mold changing function can easily replace and reposition molds.
[0033] The injection molding nozzle is provided with an annular gate, by means of which the melt can be ejected with an annular melt front into the cylindrical second molding cavity.
[0034] The advantage of the molding tool according to the invention is that the highly loaded outer shell structure of the plastic roller can be produced without joint marks. The molding tool according to the invention can be used to implement the method according to the first aspect of the invention. This method can be implemented with little effort, as a two-stage injection molding method is common and is assisted by a suitable injection molding machine. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] In the following description of the drawings, exemplary embodiments of the present invention are also described by way of example with reference to the drawings. For the sake of clarity—also insofar as different exemplary embodiments are concerned—identical or similar components, elements, or regions are denoted by the same reference numerals, sometimes with additional lowercase letters.
[0036] Features described with reference to only one embodiment may also be provided in any other embodiment of the invention within the scope of the invention. Such modified embodiments, although not shown in the drawings, are also encompassed by the invention.
[0037] All disclosed features are important to the present invention per se. The cited documents and the described prior art devices are hereby incorporated in their entirety into the disclosure of the present application, and for this purpose, single or multiple features of these documents are incorporated into one or more claims of the present application.
[0038] in:
[0039] Figure 1 shows a perspective view of the plastic roller from the inside;
[0040] Figure 2 shows a perspective view of the plastic roller as seen from the outside;
[0041] Figure 3 A side view showing the completed plastic roller;
[0042] Figure 4 Shown in accordance with Figure 3 Sectional view of the cutting line AA in;
[0043] Figure 5 A side view of a first molded part of a plastic roller including a base portion arranged thereon is shown after a first production step;
[0044] Figure 6 Shown in accordance with Figure 5 sectional view along the section line BB in , wherein the second molded part is represented imaginarily by a dashed line;
[0045] Figure 7 A side view of the forming mold after the second production step is shown, wherein only the nozzle tip is shown for the hot runner;
[0046] Figure 8 Shown in accordance with Figure 7 Sectional view of the cutting line CC in;
[0047] Figure 9 Showing an alternative molding structure according to Figure 7 View;
[0048] Figure 10 Shown in accordance with Figure 9 Section view along the cutting line DD in FIG. DETAILED DESCRIPTION
[0049] exist Figure 1 , a plastic roller 10 is shown. The plastic roller 10 has an axis of rotation a, about which the plastic roller 10 can rotate when assembled. Because the plastic roller 10 is designed to be rotationally symmetrical in this example, the axis of rotation a also serves as the center axis. The plastic roller has a base structure 11 and a jacket structure 12. The running surface 13 of the jacket structure 12 is designed to contact a rolling surface on which the plastic roller 10 can roll. The rolling surface is not shown.
[0050] In the present application, this is referred to below as the rolling surface, with which the plastic roller 10 is in contact during subsequent operation and along which it moves. Figure 1 The first end region 14 of the jacket structure 12 can be seen and is Figure 2The second end region 15 of the outer shell structure can be seen in FIG. In this example, the first end region 14 is the inner end region and the second end region 15 is the outer end region. Figure 3 A plan view onto the running surface 13 is shown in FIG.
[0051] exist Figure 4 As can be seen in the figure, the plastic roller 10 has a recess 16 with an opening 19, through which the recess 16 is accessible. Adjacent to the opening 19, the base structure 11 forms an annular flange 29, which projects radially outwards beyond the bearing surface 28. The recess 16 serves, for example, to receive a bearing (not shown) and / or a physical shaft (not shown).
[0052] A problem in the prior art in the production of such plastic rollers 10 is that during production, joint marks appear in the finished product, which form weak points. For the term "joint marks", please refer to the above definition. In particular, such joint marks in the area of the running surface lead to weakening and, not uncommonly, to failure of the roller. The joint marks are caused by the meeting of different melt flows in the forming mold. These melt flows are determined, for example, by a multi-nozzle with a plurality of nozzle tips, wherein a plurality of melt flows are ejected into the forming cavity and the melt flows meet in the forming mold. Alternatively, the joint marks can also occur due to inclusions or obstructions in the circulation of the plastic melt in the forming mold.
[0053] The method according to the invention provides that in a first working step, the basic structure 11 is produced in a molding die 31. For this purpose, a commercially available injection molding machine (not shown in the figure) is used. The injection molding machine can move the molding part between an open position and a closed position.
[0054] exist Figure 5 The first molding part 17 of the molding tool 31 can be seen in FIG. The molding tool 31 is supported in a known manner in an injection molding machine. To produce the basic structure 11, a first molding part 17 and a second molding part 18 are used, wherein the latter is Figure 5 Not shown and Figure 6 The following are only indicated in the figure.
[0055] In this example, the first molding part 17 is formed as a molding core. Figure 6As can be seen in the figure, the first mold part 17 forms a free end region 21, which forms part of the mold cavity 20. In this example, the gate 22 is centrally located parallel to the central axis a, in the direction x1 of the free end region 21 of the first mold part 17. Reference numeral 23 designates the region of the plastic melt solidifying in the gate funnel (not shown) of the mold. When the melt solidifies in the mold cavity 20, the mold is opened. The produced basic structure 11 remains on the first mold part 17 as an intermediate product. During the movement into the open position, the region 23 is separated from the basic structure 11.
[0056] The second molded part 18 is then replaced in the injection molding machine by a third molded part 24, which is Figure 7 and 8 For this purpose, the machine can, for example, have a forming tool changing device for holding different forming parts, which can be selectively moved into a movable position.
[0057] Furthermore, the central gate 22 is replaced by a ring gate 25 .
[0058] As in Figure 8 As can be seen in the figure, the second molding cavity 27 of the molding die 30 is defined by the support surface 28 of the base structure 11 supported on the first molding part 17, the annular flange 29, and the third molding part 24. The molding die 30 has the first molding part 17 and the third molding part 24. In the molding cavity 27, the jacket structure 12 is produced on the support surface 28 of the base structure 11. After the molding die is closed again, the plastic melt can be directly introduced into the second molding cavity 27 in an annular manner from the injection nozzle of the hot runner (not shown) through the melt channel 26 of the ring gate 25.
[0059] During the filling of the second molding cavity 27 (see Figure 8 ), the melt front advances annularly in a direction x1 parallel to the central axis a, thus preventing the formation of a weld mark. In this application, the material boundary of the melt flowing forward in the mold cavity is referred to as the melt front, also known as the flow front. The melt forming the outer shell structure 12, disposed in the second mold cavity 27, is positively connected to the support surface of the base part 11, thereby producing a one-piece plastic roller 10. Weld marks formed by the merging melt flows due to the melt front moving annularly in the same X position are not formed in the outer shell structure.
[0060] After the plastic melt has solidified, the molding tool 30 is opened and the finished plastic roller 10 is ejected from the molding tool 30 in the direction x2 , in this example relative to the molding part 17 .
[0061] Next, the features of the plastic roller 10 according to the invention which are advantageous with regard to production should also be mentioned.
[0062] The outer shell structure 12 can be (see Figure 3 ) has a diameter D1 in the first end region 14, a diameter D2 in the second end region 15, and a diameter D3 in a third region in the center of the outer shell structure 12. Diameter D3 can be greater than diameters D1 and D2. D1 and D2 can, for example, be the same size. The convexity, also known as the camber, ensures trouble-free operation of the plastic roller even if the axis a deviates from the nominal mounting axis by an angle.
[0063] The convexity of the outer shell structure 12 results in an undercut when demolding in the direction x1 or x2. Usually, the curvature, i.e., the difference between D1 and D3 and between D2 and D3, is small enough so that the shrinkage of the plastic during solidification is sufficient to allow demolding. In this case, the direction of demolding is not important. For example, the plastic roller 10 is demolded in the direction x2 on the nozzle side (see Figure 8 ).
[0064] If the convexity is so great that the undercut is not compensated by the shrinkage of the plastic during cooling, the jacket structure 12 can be formed asymmetrically according to the present invention. In such an asymmetrical production of the jacket structure 12, D3 > D1 > D2. This utilizes the fact that angular deviations are more noticeable at the second end region 15, that is, at the second end region 15 of the plastic roller 10, than at the first end region 14. Therefore, the plastic roller 10 is designed so that the difference between D3 and D2 is greater than the difference between D3 and D1.
[0065] According to the invention, the diameter difference between D3 and D1 is kept small. Therefore, the existing undercut can be compensated by shrinkage. When the plastic roller 10 is demoulded in the direction x1 of the first end region 14 (see Figure 10 ), the large diameter difference between D3 and D2 is unimportant since there is no undercut at this location.
[0066] Reference Signs List
[0067] 10 plastic rollers
[0068] 11 Infrastructure
[0069] 12-jacket structure
[0070] 13 running surface
[0071] 14 first end region
[0072] 15 Second end region
[0073] 16 gaps
[0074] 17 first molded part
[0075] 18 second molded part
[0076] 19 opening
[0077] 20 molding cavities
[0078] 21 Free end region (17)
[0079] 22 gates (in the center)
[0080] 23 Melt Funnel
[0081] 24 third molded part
[0082] 25 ring gate
[0083] 26 melt channels
[0084] 27 molding cavity
[0085] 28 support surface
[0086] 29 annular flange
[0087] 30 molding mold
[0088] 31 molding mold
[0089] x1 / 2 direction
[0090] aAxis of rotation
[0091] D1 / 2 / 3 diameter
Claims
1. A method for producing a plastic roller (10) for a vehicle equipment component, comprising the steps of: - producing a basic structure (11) of a plastic roller (10) including a support surface (28) in a molding tool (30) by introducing a plastic melt into a molding cavity (20) formed partly by a first molding part (17) and partly by at least one second molding part (18), - opening the forming die (30) after the plastic melt solidifies, - replacing the second molded part (18) with a third molded part (24) in order to produce a jacket structure (12) comprising a cylindrical running surface (13) on the supporting surface (28) of the base structure (11), - closing the forming mold (30) - introducing the plastic melt into a second mold cavity (27) using a ring gate (25), the second mold cavity being formed by the first mold part (17) and the third mold part (24), After the plastic melt solidifies, the forming mold (30) is opened and the plastic roller (10) is ejected.
2. The method according to claim 1, characterized in that The basic structure (11) is formed using a hot runner nozzle with a central gate (22), wherein the melt is injected into the mold cavity (20) from the end side of the basic structure (11) to be produced.
3. The method according to any one of the preceding claims, characterized in that After the basic structure (11) is produced, the central gate (22) is replaced by a ring gate (25).
4. The method according to any one of the preceding claims, characterized in that The forming tool (30) is designed so that a central axial region of the running surface (13) is formed to protrude radially outward relative to a first axial end region (14) and a second axial end region (15) of the running surface (13).
5. The method according to claim 4, characterized in that The forming tool (30) is designed so that the running surface (13) is shaped axially asymmetrically, wherein the diameter (D1) formed in the first end region (14) is larger than the diameter (D2) formed in the second end region (15).
6. The method according to claim 5, characterized in that The forming mold (30) is configured so that the plastic roller (10) can be demoulded in the direction of the diameter (D1).
7. The method according to any one of the preceding claims, characterized in that The forming tool (30) has a fixed tool half and at least one movable tool half, and the ring gate (27) is formed on the movable side.
8. The method according to any one of the preceding claims, characterized in that The annular gate (25) is realized in an axial end region (14, 15) of the running surface (13).
9. The method according to any one of the preceding claims, characterized in that During the injection molding process, a base structure (11) of at least one of the molded parts (17) is formed from the mold core.
10. A molding die (30), comprising a first molding part (17), a second molding part (18) and at least one third molding part (24), wherein: A first molding cavity (20) can be generated using a first molding part (17) and a second molding part (18), and a second molding cavity (27) can be generated using a first molding part (17) and a third molding part (18), wherein the second molding part (18) and the third molding part (24) can be interchanged with each other, wherein the injection nozzle is provided with an annular gate (25), by means of which the plastic melt can be injected into the cylindrical second molding cavity (27) with an annular melt front.