JPS6164094A - Cartridge heater - 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] Industrial applications.

The present invention relates to a cartridge heater with a single-end terminal that performs instant heating underwater for heating molds for plastic molding, water heaters, and the like.

2. Prior Art Conventionally, this type of cartridge heater has a cylindrical insulating core wrapped around a heating wire inserted into a metal pipe with one end sealed. 'd! 111' is filled with electrically insulating powder, and a lead wire is led out from the opening at the other end. This heater is generally used in a state where the surface power of the heater is extremely high because it increases the rapid heating of a mold or is used as an underwater heater. Therefore, if abnormal heating occurs, it may burn out or break, creating a safety hazard. As an invention to prevent this abnormal heating, a method has been disclosed in which a metal having a melting point lower than that of the heating element is installed in series in the 7-Z heater, and the metal is fused at the time of abnormal heating.

(For example, Japanese Patent Application Laid-Open No. 59-56386) There are also products on the market in which a type pair is installed in a cartridge heater to prevent an excessive rise in temperature.

Problems to be Solved by the Invention When installing and melting a low melting point metal as described above,
If metal is installed inside the heater, the low-melting point metal is held by a buried insulating material, and even if abnormal heating occurs and the metal melts, it will maintain its shape, resulting in the disadvantage that it cannot effectively interrupt the current.

In addition, when using a thermoelectric heater installed internally for a mold, when abnormal heating occurs, the entire heater rises rapidly, making it an effective heater, but when used as an underwater heater, thermoelectric Performance is affected by the location where the pair is installed. For example, if the thermocouple is installed below the water surface when the amount of water decreases and a part of the heater is exposed above the water surface, abnormal heating of the heater cannot be detected and the exposed part of the heater becomes locally burnt out, resulting in burnout or damage. A disconnection occurs. These drawbacks become more pronounced as the cartridge heater becomes longer.

Means for Solving the Problems In the present invention, these drawbacks can be solved by providing a heat-sensitive wire having a positive temperature coefficient of resistance in close proximity to the heating element of the cartridge heater. Heat-sensitive wires include nickel and iron, which have large resistance changes.

Uses an alloy of nickel and iron.

If a cartridge heater equipped with a heat-sensitive wire is used in a water heater or the like underwater, the water will evaporate and the heater will be exposed, resulting in a complete burnout and an abnormally high temperature. As a result, the heat-sensitive wire provided near the heating element also becomes hot, and its specific resistance value increases. A safety circuit detects this change in resistance and shuts off the power. Even if a small amount of water remains in the container and only a portion of the heater burns out, a change in the resistance value of the heat-sensitive wire is detected and the safety circuit is activated to shut off the power.

Example An embodiment of the present invention will be described with reference to the drawings.

1 and 2 show cross-sectional views of the cartridge heater. Since it is often used underwater, it generally has good corrosion resistance.
One end of a metal pipe 1 made of A111 or stainless steel material is completely sealed with the same material. A heating element 5 made of nichrome or iron chrome is wound around the outer periphery of a cylindrical insulating core 2 having four through holes in a slightly crosswise direction. Both ends of this heating element 6 are joined to the heating element lead wires 4, respectively.

Reference numeral 5 denotes a heat-sensitive wire which is coiled and inserted into two of the through-holes of the insulating core 2, and its both ends are joined to a heat-sensitive lead wire 6. The heat-sensitive wire 5 is a thin wire made of nickel, iron, or an alloy of nickel and iron, which has a positive temperature coefficient of resistance.

In this way, the insulating core 22 heating element.

The heat-sensitive wire 5 is inserted into the metal pipe 1 in an integrated state, and the small spaces in each part are completely filled with magnesia insulating powder. Then, in order to further increase the light transmission rate, the diameter is reduced by applying external pressure. Thereafter, in order to prevent insulation from deteriorating due to moisture absorption, a cartridge heater is constructed by sealing with a material 7 having good airtightness, such as epoxy resin or glass.

If the cartridge heater configured as described above is not installed in a water heater, the water evaporates and the water level drops, and the heater also bulges out and becomes completely burnt out, causing abnormal heating. At this time, the heat-sensitive wire 5 provided inside the heater also becomes abnormally high temperature at the same time, and the resistance value increases accordingly. This increase rate is based on the resistance value when using underwater ioo'c.
When the heater surface temperature is 600°C, the increase is 2 to 6 times.

By detecting this sudden change in resistance, the power to the heating element 3 can be cut off using a safety circuit. In addition, even if some water remains in the container and the heater locally causes abnormal heating, the heating element 3 should be placed close to the heat-sensitive wire 5 to quickly catch the abnormal temperature and activate the safety circuit. The power to the heating element 3 can be cut off.

Abnormal heating has yet begun, and current flows through the heating element 6 for a short period of time due to the time difference until the power is shut off, causing a temperature rise, but even when the peak temperature at that time is actually measured using a heater with a power density of 25 to 30 w/crl, it is below 400°C. It can be held down.

Prevents rupture due to burnout that can easily occur when copper is used for the Gold kA Vibe 1, and when stainless steel pipes are used, 600℃
Heating above this level can avoid conditions that tend to cause intergranular corrosion.

Effects of the Invention As described above, according to the present invention, by installing a heat-sensitive wire having a positive temperature coefficient of resistance close to the heating element of the cartridge heater, it is possible to prevent complete burnout or localized damage when used in water or liquid. Prevent a total burnout.

Heater burnout and disconnection can be completely prevented. Also, even if the surface of the heater has a high density of d, does it peak after the power is shut off? A
Since the I'L IIJf can be kept quite low, even if copper is used for metal pipes, burnout or rupture will not occur, and if stainless steel pipes are used, conditions that tend to cause intergranular corrosion can be avoided, and it is possible to It is possible to provide an excellent cartridge heater for heating liquids and liquids.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of a cartridge heater showing an embodiment of the present invention. 1...Metal pipe, 2...Insulating core, Ro...
・Heating element. 4. Heating element lead wire, 5... Heat sensitive wire. 6...Heat-sensitive lead wire, 7/-lu material.

Claims (1)

[Claims] A heating element (3) is placed inside a metal pipe (1) with one end sealed.
Insert the cylindrical insulating core (2) wrapped around it, fill its surroundings with electrical insulating powder, and insert the lead wire (
4), a heat-sensitive wire (5) having a positive temperature coefficient of resistance is provided close to the heating element (3), and a heat-sensitive lead wire (6) is led out to the opening at the other end. A cartridge heater featuring: