JPH02165176A - Magnetic pole piece for magnet roll - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetic pole piece for a magnet roll produced by magnetic field injection molding and used in electrophotographic developing devices and cleaning devices such as RPC copiers and facsimile machines.

BACKGROUND OF THE INVENTION A magnetic pole piece 1 for a magnet roll produced by conventional magnetic field injection molding has a gate 2 for injection of resin in the form of a film on the long side end face, as shown in FIG. 3 in Figure 3
is the sprue and 4 is the runner. This is because in magnetic field injection molding of the magnetic pole piece 1, unless the resin is uniformly filled from the long side of the magnetic pole piece 1 parallel to the short side, the orientation of the ferrite in the resin will not be uniform. This is because it was thought that the magnetic properties of the magnetic pole piece 1 were not satisfactory.

Problems to be Solved by the Invention However, in the magnetic pole piece 1 having such a conventional film gate 2, (1) during injection molding of the magnetic pole piece 1, when resin is injected, the gate side a of the magnetic pole piece 1 and the opposite gate Because there is a difference in the resin temperature and resin pressure after filling in the sides,
The amount of molding shrinkage of the resin changes, causing the molded product to warp in the direction shown in Figure 4, and as a result, as shown in Figure 6, the magnet
When assembling the magnetic pole pieces 1 onto the shaft 9, a gap is created as shown in FIG. 6, making it impossible to attach the magnetic pole pieces 1 closely together. (2) The gate volume of the runner 4 next to resin injection is large, resulting in poor resin yield and increased material cost. (
3) Because the molding projected area of runner 4 and gate 2 is large,
Production is only possible with a molding machine that has a large mold clamping force. (4) Since the gate 2 is wide, there is a problem in that post-finishing of the gate 2 is costly.

Therefore, the present invention improves quality by reducing molding warpage of the magnetic pole piece, and reduces manufacturing costs by reducing gate cross-sectional area, reducing gate finishing man-hours, and reducing runner/gate volume. It is something.

Means for Solving the Problems The technical means of the present invention for solving the above problems is to provide a gate in injection molding on the short side of the magnetic pole piece or on the end face of the long side near the short side.

action The effect of this technical means is as follows.

In other words, with the gate provided on the short side of the magnetic pole piece or on the end face of the long side near the short side, resin is filled from the gate parallel to the long side toward the opposite side of the gate during injection molding, so the resin temperature and resin pressure are There is a difference between the short side near the gate and the short side away from the gate, but since there is no difference in resin temperature and resin pressure between the two long sides that would affect molding warp as in the past, molding warp will be reduced. Since it is possible to mold a magnetic pole piece without any cracks, and the gate area and runner/gate volume can be reduced, manufacturing costs can be lowered.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings.

In FIG. 1, the gate 12 in the injection molding of the magnetic pole piece 11 is provided on the end face of the long side near the short side. During the injection molding process, the molten resin injected from the molding machine passes through the sprue 13 and runner 14 of the molding die, which consists of an upper mold 17 and a lower mold 18 equipped with a coil 16 for magnetic field molding as shown in FIG. Then, it is injected from the gate 12 into the cavity 16 for forming the magnetic pole piece.

At this time, the resin is filled along the long plane direction while being cooled on the wall surface of the cavity 16 and reducing the resin pressure due to pressure loss, so the resin temperature distribution and resin pressure after filling are higher on the gate side C. , the anti-gate side d is lower, but on the long sides & and b.

There is no difference in resin temperature or pressure. In other words, the resin temperature difference and pressure difference between the long sides a and b, which are the cause of molding warpage that occurs when filling resin with the conventional gate position, are eliminated, and the resin temperature difference is brought to the short sides C and d, which do not affect warpage. It can be solved with.

Effects of the Invention As described above, according to the magnetic pole piece for a magnet roll with a gate of the present invention, the a-pole piece does not deform or warp due to the influence of resin temperature and pressure difference during magnetic field injection molding. When assembling the magnet roll onto the shaft, each magnetic pole heath can be attached in close contact with each other, improving the magnetic properties of the magnet roll in the circumferential direction.In addition, the gate cross-sectional area is small, making it easy to finish the gate after molding. In addition, the volume of the runner and gate is reduced, which improves the resin yield and reduces the cost of resin materials.Furthermore, the molding projected area of the runner and gate is reduced, so the mold clamping force required for injection molding is also reduced to approx. 60～
This has the advantage of being able to reduce the manufacturing cost by 70%.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an injection molded product of a magnetic pole piece for a magnet roll according to an embodiment of the present invention, Fig. 2 is a schematic sectional view of a magnetic field injection molding mold for a magnetic pole piece of the present invention, and Fig. 3 is a conventional injection molded product. A perspective view of an injection molded product of a magnetic pole piece having a gate; FIG. 4 is a plan view showing the direction of molding warpage of a conventional magnetic pole piece;
FIG. 5 is a perspective view showing a method of assembling a magnetic pole piece of a magnet roll, and FIG. 6 is a plan view of the magnet roll when a magnetic pole piece with a molded warp is assembled. 11...Magnetic pole piece, 12...Gate, 13...Sprue 14...Runner,
16...Cavity, 16°゛°°...Coil, 17...Upper mold, 18...Lower mold. Name of agent: Patent attorney Shigetaka Awano 1 person: 16
Lower mold diagram

Claims (1)

[Claims] A magnetic pole piece for a magnet roll, characterized in that a gate for resin injection in magnetic field injection molding is provided on a short side or a long side end face near the short side.