JPH0695371B2 - Method for manufacturing permanent magnet type erasing head - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a permanent magnet type erasing head mainly used for recording and erasing audio tapes.

2. Description of the Related Art Generally, as a method of erasing a record on a magnetic recording medium such as a magnetic tape, there are a current erasing method, a method using a permanent magnet, and a method using a combination thereof. A conventional permanent magnet type erasing head will be described with reference to the accompanying drawings. FIG. 3 shows the structure of a permanent magnet type erasing head, and FIGS. 4a and 4b show magnetic pole arrangement states and magnetic characteristics showing the erasing principle. As shown in the drawing, after the magnetic material 2 is inserted into the erasing head case body 1 or fixed in place by means such as insert molding, in order to improve the adhesion with the tape and the slidability, The tape was slid onto the curved surface to form the tape sliding surface 3 and was commercialized.

As shown in FIG. 4a, the tape sliding surface 3 alternates in the tape running direction with N → S → N ... And its magnetic field strength gradually decreases as shown in FIG. 4b. The principle is to magnetize and guide the data magnetized on the tape to the point where the magnetic field strength becomes zero and erase.

Problems to be Solved by the Invention However, in the conventional structure, the R polishing process is required to form the curved surface of the tape sliding surface 3, and the R polishing process cost in response to the ever-increasing demand for cost reduction in the market. Is a big problem.

The present invention is intended to provide a method of manufacturing a permanent magnet type erasing head which solves the above-mentioned drawbacks of the prior art and enables cost reduction.

Means for Solving the Problems In order to solve the above problems, the present invention prepares a magnet having a curved surface of a tape sliding surface in advance and insert-molds it into an erasing head case body, and also a synthetic resin for the case. The mold shrinkage of the material is assumed, and the curved surface of the magnet and the curved surface of the case obtained by molding are matched by designing a mold with a step between the curved surface of the magnet and the curved surface of the case. To do.

Working When looking at the tape sliding part of the erasing head case by this method, when the shrinkage after molding is completed, the curved surface that was previously provided on the magnet and the tape sliding surface match, and the boundary part of the magnet / resin material In this case, a stepless product can be obtained, and the work of performing R polishing on the tape sliding surface as in the conventional example is unnecessary.

Example An example of the present invention will be described below with reference to FIGS. 1 and 2. 2 shows an insert-molded magnet 4, and FIG. 1 shows an erase head in which the magnet 4 is insert-molded. The magnet 4 has a tape sliding surface 5 provided with a curved surface in advance. In this embodiment, a press-molded product having the shape shown in FIG. 2 is used.

The contents of insert molding will be described with reference to the front view of FIG. 1 (a) and the side view of FIG. 1 (b). Since the magnet 7 is inserted and fixed in a fixed position in the erasing head case body 6, the magnet is held in the case molding die except for the curved surface provided on the magnet, and the front-back direction of FIG. 1 (a) is used. The magnets 7 are set in the case molding die by using the two holding ratios 8, 8'and 9, 9'from the above, and one holding rod 10 and 10 'from the lateral direction in a sliding structure. After holding in position,
Resin is injected to mold the erase head case body 6.

In this embodiment, the case material is nylon resin,
Since the nylon resin has a molding shrinkage of 0.25%, the boundary surface between the tape sliding surface 5 provided on the magnet 7 and the tape sliding surface 11 of the adjacent case portion is a step in which the molding shrinkage of the nylon resin sinks. Therefore, in this embodiment, in order to correct the above difference, the step 12 having a content such that the case portion is higher than the magnet portion is provided in the molding die. Specifically, the total height of the magnet x molding shrinkage = 4 x 0.25%
= 0.01 mm is provided in the mold, the nylon resin shrinks after molding, and the curved surface of the magnet, that is, the tape sliding surface 5 and the case curved surface, that is, the tape sliding surface 11 of the case Match.

When a material other than nylon resin is used as the case material, it is advisable to calculate and correct the molding shrinkage rate of the material to be used as described above.

EFFECTS OF THE INVENTION In the present invention, the curved surface of the tape sliding surface is matched with the magnet and the case portion because the mold shrinkage rate is taken into consideration and the step is formed in the die, and the R polishing process is not necessary. This allows
The direct cost can be reduced by 1/5 to 1/4, and the contribution to the market demand for cost reduction can be greatly improved.

[Brief description of drawings]

FIG. 1 (a) is a front view of an erase head after insert molding showing a method for manufacturing a permanent magnet type erase head in one embodiment of the present invention, FIG. 1 (b) is a side view of the same, and FIG. 2 is an insert. FIG. 4 is a front view of a magnet used for molding, FIG. 3 is a front view showing the configuration of a conventional permanent magnet type erasing head, and FIG. 4 (a) is a magnetization state diagram of an alternating magnetic field showing the principle of erasing.
FIG. 6B is a magnetic field characteristic diagram showing the gradually decreasing alternating magnetic field. 5: Tape sliding surface, 6: Erase head case body, 7
...... Magnet, 8,8 ′, 9,9 ′, 10,10 ′ …… Holding bar, 11
…… Tape sliding surface of case, 12 …… Step.

Claims (1)

[Claims] 1. A erasing head case body for insert molding of a permanent magnet erasing head in which a synthetic resin is injected and molded into a portion of a magnet having a curved one end surface covering the periphery except the one end surface. The mold shrinkage rate of the synthetic resin material used is estimated, and the tape sliding part die of the case main body is made to protrude from the curved surface provided on the magnet to form a die structure having a step, thereby forming the curved surface of the magnet and the case. A method for manufacturing a permanent magnet type erasing head, characterized in that the curved surfaces of the tape sliding portion of the main body are matched.