JPH04277602A - Closed-type variable resistor - Google Patents

Abstract

PURPOSE:To avoid exposure of an aluminum board and keep airtightness, even when a gate part of the resin case is torn off while the resin case is removed from a mold after the molding, by giving a sufficient thickness of resin at a part between the gate of a resin case and an aluminum board, and moreover to allow high injection pressure that can prevent a shortage in charging resin, by making the aluminum board thin at only one part, which provides no decrease in antibreak strength for the aluminum board. CONSTITUTION:A closed-type variable resistor is characterized by an aluminum board 1 that is inserted by injection molding into a resin case 2, and a hole 1a that is positioned on the aluminum board at a part facing to a gate 2a in the resin case 2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed variable resistor, and more particularly to the shape of an insert injection molded alumina substrate.

0002

[Prior Art] Conventionally, a sealed variable resistor has an O-ring 4 made of an elastic material such as silicone rubber at the interface between a resin case 2 and a rotor 3 to shield it from outside air, as shown in FIG. inserted and sealed from the external atmosphere. Further, the resin case 2 is injection molded with the alumina substrate 1 inserted therein, and the alumina substrate 1 is sealed from the external atmosphere to obtain a sealed variable resistor.

0003

[Problems to be Solved by the Invention] In the conventional sealed variable resistor described above, an alumina substrate 1 on which a resistor is printed is insert injection molded into a resin case 2. There were problems like this. (1) When the resin case is made thinner, the resin wall thickness between the gate opening of the resin case and the alumina substrate becomes thinner, and when the resin case is released from the mold after molding, the resin at the gate part Since the alumina substrate is etched away and the alumina substrate is exposed, the airtightness with the outside air is reduced. (2) If the alumina substrate is made thinner, the transverse rupture strength of the alumina substrate will decrease, and during injection molding of the resin case, the alumina substrate will crack due to the resin injection pressure from the gate, and the resistor printed on it will also break. , electrical connection is lost. Further, as a countermeasure for the above-mentioned problem, if the resin injection pressure from the gate is lowered, resin filling becomes insufficient and injection molding becomes impossible.

An object of the present invention is to prevent the alumina substrate from being exposed even if the resin at the gate part is eaten away when the resin case is released from the mold after molding, and to maintain airtightness from the outside air. It is an object of the present invention to provide a closed type variable resistor which can ensure the properties of the alumina substrate without reducing the transverse rupture strength of the alumina substrate, can increase the resin injection pressure, and does not cause insufficient filling of the resin.

[0005]

[Means for Solving the Problems] The sealed variable resistor of the present invention is characterized in that a hole is provided in the surface of an alumina substrate insert injection molded into a resin case, which faces the gate opening of the resin case.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view of an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a state of injection molding of a resin case in which an alumina substrate is insert injection molded.

Reference numeral 1 in the figure denotes an alumina substrate with a hole 1a formed on the surface facing the gate opening 2a of the resin case.

The resin wall thickness of the gate portion of the resin case 2 is equal to the resin wall thickness of the hole 1a of the alumina substrate 1, so that a sufficient resin wall thickness can be ensured. Even if the resin at the gate portion is cut off when the mold is released, the alumina substrate 1 will not be exposed.

FIG. 3 is a sectional view showing the injection molding state of a resin case in which an alumina substrate is insert injection molded according to another embodiment of the present invention. It will be done. In this example, the alumina substrate 1
Since the hole 1a has a moderately curved surface, the injected resin has good fluidity during injection molding of the resin case 2, and is effective in preventing resin flow mark defects and color unevenness defects. be.

0010

[Effects of the Invention] As explained above, the present invention provides holes in the alumina substrate insert injection molded into the resin case on the surface facing the gate opening of the resin case.
It has the following effects. (1) Sufficient resin thickness is ensured between the gate opening of the resin case and the alumina substrate, so when the resin case is released from the mold after molding, the resin at the gate part is eaten away. Even if it is cut, the alumina substrate is not exposed, ensuring airtightness from the outside air. (2) Since only a portion of the alumina substrate is thinned, the transverse rupture strength of the alumina substrate can be ensured, and the alumina substrate will not be broken by the resin injection pressure from the gate during injection molding of the resin case, ensuring electrical connection. be done. Further, since the resin injection pressure can be made sufficiently high, insufficient filling of the resin does not occur.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view showing an injection molding state of an embodiment of the present invention.

FIG. 3 is a sectional view showing an injection molding state of another embodiment of the present invention.

FIG. 4 is a sectional view of an example of a conventional sealed variable resistor.

[Explanation of symbols]

1 Alumina substrate 1a Hole 2 Resin case 2a Gate entrance 3 Rotor 4 O-ring 5 Metal can case 6 Slider 7 Injection mold upper mold 8 Injection molding lower mold 9 Eject pin

Claims (1)

[Claims] 1. A sealed variable resistor comprising a rotor, a ring-shaped seal made of an elastic insulator, a metal case, and a resin case made by insert injection molding an alumina substrate on which a resistor is formed, wherein the alumina A sealed variable resistor characterized by having a hole in the surface of the resin case of the circuit board facing the gate opening.