JP2004314310A - Bearing manufacturing method and injection mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing manufacturing method capable of preventing the damage of a product caused by an ejector pin at the time of extrusion of the product by the ejector pin and hard to yield wrinkles or warpage even in a molded product such as a thin film-like one or the like, and an injection mold. <P>SOLUTION: This injection mold is used for manufacturing a bearing for holding a bearing part and a film-like outer diameter part through a bridge part and equipped with a fixed template, the movable template mated with the fixed template, the cavity part, which is formed by the fixed template and the movable template so that the axial direction of the bearing part and the advance and retreat direction of the movable template become same, and the hollow part core provided to the movable template. The hollow part core advances and retreats in the same direction as the advance and retreat direction of the movable template. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a bearing having a special shape, particularly a rolling element for conveying a sheet of an image forming apparatus, and an injection mold used for the manufacturing.
[0002]
[Prior art]
When a bearing is used at a site where a thin material such as a film or a sheet is fed, a pressing mark of the bearing may remain on the thin material. For example, when a rolling element for sheet conveyance such as a discharge roller is used in a discharge section of a copying machine, a laser beam printer, or the like, a pressing mark of the rolling element is left on a sheet, and image quality may be deteriorated. Preventing the formation of traces is an important technical issue.
The cause of the pressure mark is a local contact pressure of the bearing against the sheet, and a parting line (hereinafter referred to as “PL”) formed on the outer diameter sliding contact surface of the bearing and an edge of the sliding contact surface end. It mainly occurs at the contact part with the part. In addition, in particular, in the case of paper discharge rollers used in an image forming apparatus, in addition to the above-described problem, the toner on the surface pressed by the paper discharge rollers is crushed, so that there is a problem that a difference occurs in image quality from other parts. Since the surface in contact with the paper roller is cooled faster than the other surfaces, there are problems such as a difference in image quality due to a difference in cooling speed.
[0003]
Conventionally, in order to cope with such a problem, the PL is provided at a central portion in the longitudinal direction of the discharge roller, and the outer diameter of the central portion in the longitudinal direction is smaller than both end portions of the sliding surface of the discharge roller. Rolling elements for use (see Patent Literature 1) and those in which a soft rubber such as foamed rubber is covered with a PFA tube or the like have been devised. Furthermore, in order to solve the problems that cannot be solved by these, the outer diameter sliding contact part is made into a film shape, so that the rolling member for sheet conveyance of the image forming apparatus in which the contact pressure between the rolling member and the sheet printing surface is reduced. It has been devised (Japanese Patent Application No. 2002-340640).
[0004]
FIG. 6 shows an injection step in the case where a conventional bearing such as a rolling element for sheet conveyance is manufactured by injection molding. FIG. 6 is a sectional view showing the vicinity of the cavity in the injection step.
In the injection mold 12, a fixed mold plate 13 and a movable mold plate 14 are abutted to form a cavity 15. Both mold plates are provided with hollow portions 13a and 14a for forming hollow portions of the bearing (FIG. 6 (a)).
The procedure of the injection molding process using this mold will be described below. That is, first, in a state where the fixed-side mold plate 13 and the movable-side mold plate 14 abut against each other and the mold is closed, the molding molten resin 16 is injected and filled into the cavity 15 through the gate 17 (FIG. 6B). )). After the filling, the resin 16 in the cavity 15 is cured through a pressure holding step and a cooling step, and then the mold is opened (FIG. 6C). After release, the protruding pin 18 is advanced to push out the molded product 19 and discharge it from the movable mold plate 14 (FIG. 6D).
Further, a method has been devised in which a rolling element for sheet conveyance excellent in non-adhesiveness of toner is manufactured by injection molding using a fluorocarbon resin or the like (see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-2000-355434 (Claims)
[Patent Document 2]
JP-A-10-114443 (Claims)
[0006]
[Problems to be solved by the invention]
However, when the injection molding of the bearing is performed by the above procedure using the injection molding die, when the protrusion is pushed out by a protruding pin or the like, the bearing is surrounded by the nest and other mold parts such as the outer diameter part of the bearing. If the bearing has a large frictional resistance and the outer diameter of the bearing is in a drum shape or the like, it cannot be forcibly removed, causing a problem that wrinkles and warpage occur.
In particular, when the outer diameter of the bearing is in the form of a film having a thickness of less than 1 mm, in the product extruding step after injection molding, the film is wrinkled or the film is torn. There is a problem that a protrusion pin penetrates a product and the like, and it is difficult to manufacture by injection molding. Penetration of a product by an ejection pin often occurs when molding an injection moldable fluororesin such as PFA, ETFE, and FEP. This is due to their low Shore hardness of D60 to D80 (ASTM D2240).
[0007]
The present invention has been made to address such a problem, and is directed to a method of manufacturing a bearing having a special shape such as a rolling element for transporting a film-like sheet by injection molding, and an injection mold used for the molding. A method of manufacturing a bearing and an injection molding die, in which a product is not damaged by a protruding pin when a product is pushed out by the protruding pin, and wrinkles and warpage hardly occur even in a molded product such as a thin film. The purpose is to:
[0008]
[Means for Solving the Problems]
In order to manufacture a bearing that holds the bearing portion and the film-shaped outer diameter portion via a bridge portion, the injection mold of the present invention includes a fixed side mold plate and a movable side that abuts the fixed side mold plate. A mold plate, a cavity formed by the fixed mold plate and the movable mold plate such that the axial direction of the bearing portion and the moving direction of the movable mold plate are the same direction, and An injection molding die provided with a lightening portion insert on a plate, characterized in that the lightening portion insert moves forward and backward in the same direction as the movable side mold plate.
Further, the bearing is a sheet conveying rolling element of the image forming apparatus.
[0009]
The method for manufacturing a bearing according to the present invention is a method for manufacturing a bearing for holding a bearing portion and a film-shaped outer diameter portion via a bridge portion, wherein the fixed-side mold plate and the meat that advances and retreats in the same direction as the abutment direction are provided. Abutting the movable-side mold plate having the withdrawal insert to form a cavity in which the axial direction of the bearing portion and the moving-back direction of the movable-side mold plate are in the same direction; and The method is characterized by comprising a step of injecting a resin and a step of retracting the hollow portion of the movable mold plate before extruding the molded product.
Further, the bearing is a sheet conveying rolling element of the image forming apparatus.
[0010]
By using an injection molding die having a lightening portion insert that can advance and retreat in the same direction as the movable side mold plate, and before extruding the product, only the lightening portion insert is retracted, so that the molded product is extruded at the time of extrusion. Since the mold is released from the insert nest and the resistance can be reduced, the wrinkle and outward warpage do not occur even if the outer diameter of the bearing is in the form of a film.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
An injection molding die for a bearing according to the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing the vicinity of a cavity of an injection mold.
In the mold 1, the fixed-side mold plate 2 and the movable-side mold plate 3 are abutted, and the cavity is combined with the fixed-side lightening portion insert 2a and the movable-side lightening portion insert 3c provided on each side. 4 are formed. In addition, 8 is PL in the figure.
A gate 5 for injecting the molten resin into the cavity 4 is formed on the fixed mold plate 2. The movable mold plate 3 is provided with a center pin 6 for forming a shaft hole of a bearing and a protruding pin 7 for pushing out a molded product.
The cavity 4 has an outer diameter sliding contact surface, and includes an outer diameter portion 4a whose both ends are in a film shape, and an image forming apparatus including a bearing portion 4c that holds the outer diameter portion via a bridge portion 4b. Of the rolling element for sheet conveyance.
[0012]
The movable mechanism of the mold according to the present invention will be described with reference to FIG. FIG. 2 shows a partial cross-sectional view of the injection mold. In FIG. 2, the gate 5 shown in FIG. 1 is not shown.
The fixed-side mold plate 2 and the movable-side mold plate 3 are connected by a tension link 9 to determine the opening / closing stroke of the mold 1 to be opened at PL8. Also, guide pins (not shown) are communicated with the two mold plates so that the two mold plates can be accurately abutted.
Further, the movable mold plate 3 is composed of a right mold plate portion 3a having a cavity 4 and a left mold plate portion 3b having a movable side lightening portion insert 3c and the like, and is fixed to the right mold plate portion 3a. the stop bolt 3d, the movable range L ₁ only the right type plate portion 3a and the left die plate portion 3b is a closable structure. Note that the stop bolt 3d may be fixed to the left mold plate 3b.
[0013]
The tension link 9 is connected only to the fixed template 2 and the right template 3a of the movable template 3, and the movable template 3 is retracted to the left in the drawing, and the fixed template 2 and the right Even after the template 3a is opened at a predetermined interval by the tension link 9, the left template 3b can be further retracted independently.
[0014]
The movable side lightening portion insert 3c is fixed to the left mold plate 3b. Therefore, when the left mold part 3b retreats to the left side in the drawing, the insert 3c retreats independently of the cavity 4 in the same direction as the left mold part 3b. Therefore, the movable-side recessed portions nesting 3c, in the state in which the right die plate part 3a and the left die plate portion 3b is open in a state of being withdrawn from only the cavity 4 movable distance L ₁ stop bolt. Incidentally, the movable distance L ₁ is a molded article formed between the movable-side recessed portions nesting 3c and the right type plate portion 3a, it may be any distance and該入Ko 3c is not in contact. For example, when the outer shape of the bearing portion is straight, it is desirable to completely pull out the insert 3c from the bearing portion. However, when the draft is formed, it may be merely retracted by about 1 mm, for example.
[0015]
Inside the left mold plate portion 3b, a protruding plate 7a for disposing the protruding pin 7 and a center pin plate 6a for disposing the center pin 6 are provided.
The protruding plate 7a is formed of two flat plates as shown in FIG. 2, and has a strength that does not cause bending against the protruding force. The protruding plate 7a is provided with the protruding pin 7 for the cavity 4 even when the right mold plate 3a and the left mold plate 3b are open when the movable side hollow portion 3c is pulled out of the cavity 4. In order not to change the position, the moving distance from the right mold plate portion 3a is restricted by the protrusion plate fixing pin 7b.
The center pin plate 6a is also composed of two flat plates like the protruding plate 7a, and when the right mold plate portion 3a and the left mold plate portion 3b open, the center pin 6 retreats in conjunction. In order to prevent this, the moving distance from the right mold plate portion 3a is restricted by the center pin plate fixing pin 6b.
[0016]
The protruding plate 7a and the center pin plate 6a are connected to the right mold plate portion 3a of the movable mold plate 3 by independent protruding plate fixing pins 7b and center pin plate fixing pins 6b, respectively. Even when the left mold plate portion 3b is opened, the distance between the protruding pin 7 and the center pin 6 and the cavity 4 can be kept constant, and only the protruding pin 7 can be moved independently when the product is pushed out.
[0017]
Any synthetic resin can be used as a molding material for the bearing filled in the cavity 4. In particular, when a rolling element for conveying a sheet of an image forming apparatus is molded, injection molding such as PFA, ETFE, and FEP can be performed. A suitable fluororesin is preferably used. Even if PFA, ETFE, or FEP is used, the molded product is not pierced by the ejection pin.
[0018]
PL8 can be located at any position. However, since the injection molding die of the present invention is used for molding a bearing, particularly a rolling element for conveying a sheet of an image forming apparatus, the injection molding die has an outer peripheral sliding surface. As shown in FIGS. 1 and 2, it is preferable to set the PL8 at one end of the outer diameter portion of the bearing so as to eliminate burrs and steps and prevent dirt on the paper.
[0019]
The method of manufacturing a bearing by injection molding according to the present invention will be described with reference to FIGS. 3 (a) to 3 (f) are views showing a manufacturing process of the bearing using the cavity peripheral sectional view, and FIGS. 4 (a) to 4 (d) are partial sectional views of the injection mold. It is a figure which shows the manufacturing process of a bearing.
Before starting the injection molding, the movable-side lightening portion insert 3c of the movable-side mold plate 3 moves forward, and the protruding pin 7 retreats (FIG. 3A). The steps will be described below in order with reference to FIGS. 3B to 3F and FIGS. 4A to 4D.
(1) Mold closing step (cavity forming step): The solid-side mold plate 2 and the movable-side mold plate 3 are abutted, and are combined with the fixed-side lightening portion insert 2a and the movable-side lightening portion insert 3c. A cavity 4 having the shape of a bearing is formed (FIGS. 3B and 4A).
(2) Injection Step (Resin Injection Step): The molten resin for molding 10 is injected and filled into the cavity 4 via the gate 5 (FIG. 3C).
(3) Mold opening step: After the resin 10 in the cavity 4 is cured through the pressure holding step and the cooling step, the movable side mold plate 3 is retracted leftward in the figure to open the mold (FIG. 3 (d) )). The mold opening stroke is determined by the tension link 9 as shown in FIG. The movable mold plate 3 is driven by driving means such as a hydraulic cylinder (not shown).
(4) Step of punching out the lightening portion insert: After the fixed mold plate 2 and the right mold plate 3a are opened at a predetermined interval by the tension link 9 and the right mold plate 3a is fixed in position, the left mold is removed. When the plate portion 3b independently retreats further leftward in the drawing, the movable-side lightening portion insert 3c fixed to the left mold plate portion 3b is released from the resin 10 portion (FIG. 4 ( c), FIG. 3 (e)). The distance to be withdrawn is a movable distance L ₁ stop bolt 3d shown in Figure 4 (a).
(5) Molded product extrusion step: The ejection pin 7 is moved rightward in the figure to extrude the molded product 11 in which the resin 10 has hardened and discharge it from the cavity 4 (FIG. 3 (f)). The protrusion pin 7 is moved by moving the protrusion plate 7a independently of the center pin plate 6a by driving means such as a hydraulic cylinder (not shown) (FIG. 4D).
After the steps (1) to (5) are completed, the movable-side cutout insert 3c and the protruding pin 7 of the movable-side mold plate 3 are returned to the state shown in FIG.
In addition, the molding conditions of the injection pressure and the holding pressure in each of the above steps are performed under the optimum conditions of the resin used.
In addition, (4) the step of removing the lightening portion insert may be performed before the step (3) of opening the mold as long as the resin 10 in the cavity 4 is cured through the pressure holding step and the cooling step.
FIG. 5 is a perspective view of a sheet transporting rolling element which is the obtained molded article 11.
[0020]
When the molded product is extruded with the protruding pin without pulling out the lightening portion insert, the outer diameter portion 11a receives a large frictional resistance between the lightening portion insert and the mold, and the shape is film-like. If the shape is thin, wrinkles and warpage are likely to occur in the portion. Further, when the rolling element for sheet conveyance is formed, as shown in FIG. 5, the outer diameter portion 11a has a drum-like shape and the product cannot be pushed out without force, so that wrinkles and warpage are particularly likely to occur.
On the other hand, in the manufacturing method of the present invention using the injection molding die of the bearing, after the above (2) injection molding step and before the above (5) molded product extrusion step, the above (4) insertion of the hollow portion is performed. By providing a step of retracting and pulling out the child, at the time of extruding the molded product, the hollow part of the hollow part becomes hollow, and the frictional resistance of the part in contact with the part is reduced, and the outer diameter of the bearing is reduced. Since the deformation in the inward direction is permitted, the bearing can be easily taken out of the cavity 4 without difficulty.
In this embodiment, the bearing portion has a hollow shaft hole. However, the bearing portion may be solid and provided with boss portions on both sides of the bearing portion.
[0021]
【Example】
Example 1
Using the injection mold shown in FIG. 2, the bearing shown in FIG. 5 (axial length: 12 mm, film outer diameter: 9 mm, film end: 0.5 mm, shaft hole) 2 mm and a bearing diameter of 4.5 mm). The molding resin is a PFA natural material (Shore hardness D64).
Example 2
It is the same as Example 1 except that the molding resin was changed to ETFE (Shore hardness D83) containing 15% by weight of carbon powder.
Comparative Example 1
A bearing having the same shape as that of Example 1 was molded using an injection molding die of the related art in which the movable-side hollow portion of the movable-side mold plate did not recede. The molding resin is a PFA natural material (Shore hardness D64).
Comparative Example 2
Comparative Example 1 was the same as Comparative Example 1 except that the molding resin was changed to ETFE (Shore hardness D83) containing 15% by weight of carbon powder.
[0022]
In the bearings of Examples 1 and 2, a bearing having the same shape as the cavity was obtained. However, in the case of the bearing of Comparative Example 1, the product could not be taken out because the protruding pin broke the molded product when the product was pushed out. . In Comparative Example 2, although the molded body was not broken by the protruding pin, the film portion had streaks, and it was determined that use was hindered.
[0023]
【The invention's effect】
In order to manufacture a bearing that holds the bearing portion and the film-shaped outer diameter portion via a bridge portion, the injection mold of the present invention includes a fixed side mold plate and a movable side that abuts the fixed side mold plate. A mold plate, a cavity formed by the fixed mold plate and the movable mold plate such that the axial direction of the bearing portion and the moving direction of the movable mold plate are the same direction, and An injection molding die having a lightening portion insert on a plate, wherein the lightening portion insert advances and retreats in the same direction as the moving-side mold plate advances and retreats. Resistance and the like can be reduced, and a molded article free of wrinkles, outward warpage, and the like can be obtained even when the outer diameter portion of the bearing is a film or the like.
[0024]
The method for manufacturing a bearing according to the present invention is a method for manufacturing a bearing for holding a bearing portion and a film-shaped outer diameter portion via a bridge portion, wherein the fixed-side mold plate and the meat that advances and retreats in the same direction as the abutment direction are provided. Abutting the movable-side mold plate having the withdrawal insert to form a cavity in which the axial direction of the bearing portion and the moving-back direction of the movable-side mold plate are in the same direction; and Since the step of injecting the resin and the step of retreating the cutout of the movable side mold plate before extruding the molded product are provided, before pushing out the product, only the cutout insert is retreated. In the case of extrusion, the molded product is released from the insert of the hollow portion, so that it can be extruded with less resistance. Therefore, even if the outer diameter portion of the bearing is in the form of a film or the like, no wrinkling or outward warpage occurs. .
[Brief description of the drawings]
FIG. 1 is a sectional view of the periphery of a cavity of an injection mold according to one embodiment of the present invention.
FIG. 2 is a partial cross-sectional view of an injection mold according to one embodiment of the present invention.
FIG. 3 is a diagram (a sectional view around a cavity) showing a manufacturing process of the bearing of the present invention.
FIG. 4 is a view (partial cross-sectional view of an injection molding die) showing a manufacturing process of the bearing of the present invention.
FIG. 5 is a perspective view of a molded product obtained by the production method of the present invention.
FIG. 6 is a view showing a manufacturing process of a conventional bearing.
[Explanation of symbols]
Reference Signs List 1 mold 2 fixed-side mold plate 3 movable-side mold plate 4 cavity 5 gate 6 center pin 7 protrusion pin 8 PL (parting line)
9 Tensile link 10 Molten resin 11 Molded product

Claims (4)

In order to manufacture a bearing that holds a bearing portion and a film-shaped outer diameter portion via a bridge portion, a fixed-side template, a movable-side template abutting the fixed-side template, and a shaft of the bearing portion A cavity formed by the fixed-side mold plate and the movable-side mold plate such that the direction and the moving direction of the movable-side mold plate are in the same direction, and a lightening portion insert in the movable-side mold plate. An injection mold provided with
An injection molding die, wherein the insertion portion of the hollow portion advances and retreats in the same direction as the direction in which the movable mold plate advances and retreats. The injection molding die according to claim 1, wherein the bearing is a rolling element for conveying a sheet of an image forming apparatus. A method for manufacturing a bearing for holding a bearing portion and a film-shaped outer diameter portion via a bridge portion,
The fixed-side mold plate and the movable-side mold plate having a lightening portion nest that advances and retreats in the same direction as the abutment direction are abutted, and the axial direction of the bearing portion and the advancing and retreating direction of the movable-side mold plate are aligned. Forming a cavity in the same direction;
Injecting a resin into the cavity,
Before extruding the molded product, the step of retracting the hollow portion of the movable mold plate is retreated. The method according to claim 3, wherein the bearing is a rolling element for conveying a sheet of an image forming apparatus.

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