JPS6318313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric heater that is assembled to the bottom of a container containing a liquid and uses a ceramic heater.

2. Description of the Related Art Various flat or tubular ceramic heaters in which a heating resistor is embedded in a ceramic substrate are known. However, although this type of ceramic heater has advantages such as chemical stability and small size and high output, it does not cause rapid heating or cooling, that is, rapid heating when a liquid is added and dry energization is applied, and cold water immediately after dry energization. It is extremely susceptible to distortion due to rapid temperature changes such as rapid cooling due to water injection, and the resulting expansion and contraction often causes cracks and cracks. For this reason, due to concerns about exposure of the heat generating part into the liquid to be heated, a structure in which the heat generating part is assembled to the back bottom of the container is common. However, these structures have poor thermal efficiency because the liquid to be heated is heated between the walls of the bottom of the container, and in order to improve the adhesion between the ceramic heater and the bottom of the container, a flat surface must be formed, and it is difficult to install the ceramic heater. It is necessary to mechanically press the entire surface of the ceramic heater without any gaps.
However, directly pressing the ceramic heater surface is dangerous as it may cause cracks, etc. Therefore, it is necessary to press indirectly and evenly over the entire surface, and this pressing structure is complicated and unreliable. For this reason, a ceramic heater is installed in the liquid to be heated, and a detection electrode and its detection circuit that detect the leakage current that occurs when the heat generating part is exposed due to cracks, etc. are installed separately from the ceramic heater. However, this type of structure requires a hole in the container for mounting the detection electrode, and also requires a watertight structure for mounting. Further, since the detection electrode is attached separately from the ceramic heater, there is a delay in detecting leakage current, and there is a drawback that prompt detection of leakage current and cracks cannot be performed.

The present invention has been made to solve the above-mentioned drawbacks, and embodiments of the present invention will be specifically described below with reference to the drawings. Reference numeral 1 denotes a first ceramic substrate made of inorganic powder such as alumina or zirconia, which is formed into a ceramic green sheet.The surface of the first ceramic substrate 1 has a corrugated or saw-shaped wiring pattern. Heating resistor pattern 2
is formed. The heating resistor pattern 2 is also formed by simultaneously printing the heating resistor terminals 3, 3 and the third electrode terminal 4 using a conductive paste such as tungsten or molybdenum-manganese. 5
Like the first ceramic substrate 1, this is a thin layer made of a ceramic substrate made from inorganic powder such as alumina or zirconia and formed into a thin ceramic green sheet. A through hole 6 is provided in the hole. Next, a third electrode 7 is formed by coating or printing a conductive paste of a corrosion-resistant conductive material, such as tungsten or silver, approximately at the center of the upper surface of the thin layer 5. Next, the thin layer 5 on which the third electrode 7 is printed and the first ceramic substrate 1 on which the heat generating resistor pattern 2 is printed are held together, and the heat generating resistor pattern 2 is clamped between the lower surface of the thin layer 5 and the first ceramic substrate 1. At this time, the through holes 6 provided in the thin layer 5 can come into contact with the third electrode terminals 4 provided on the surface of the first ceramic substrate 1 while avoiding the heating resistor pattern 2. Next, the through hole 6 is filled with a corrosion-resistant conductive material similar to the third electrode 7, such as a conductive paste such as the above-mentioned tungsten or silver material to electrically connect the third electrode 7 and the third electrode terminal 4. Sintered and integrated. Next, a pair of heating resistor lead wires 8, 8 and a third electrode lead wire made of nickel wire are formed by using silver solder or the like on the heating resistor terminals 3, 3 and the third electrode terminal 4 of the sintered and integrated product. Connect each 9 to complete.

When the ceramic heater of the present invention constructed as described above is assembled to the bottom of a container, a power supply of 100 V is connected to both ends of the heating resistor pattern 2 via the relay switch 10, and the third electrode 7 and one of the power sources are connected via the drive coil of the relay switch 10. Pour the liquid here and turn on the power.
When 100V is applied to heating resistor pattern 2, the 3rd
There is no conduction between the electrode 7 and one of the power sources, and the drive coil of the relay switch 10 does not operate, so the heating resistor pattern 2 starts generating heat. Next, when the ceramic heater cracks due to dry firing or water injection immediately after dry firing, a crack occurs and the heat generating part is exposed in the liquid, a current flows between the third electrode 7 and one of the power sources through the liquid. The drive coil of the flow relay switch 10 is actuated, turning off the relay switch 10, cutting off the current to the heating resistor pattern 2, and preventing electrical leakage immediately.

Since the present invention is constructed and operated as described above, it has excellent effects as explained below.

That is, in the ceramic heater of the present invention, the third electrode, which is the sensing electrode, is provided in a position extremely close to the heating resistor pattern via a thin layer and is sintered into one piece, so it is different from the ceramic heater in the conventional structure described above. The disadvantage of not being able to completely prevent electrical leaks due to the delay in detecting electrical leaks that occurs due to the detection electrodes being installed at separate and distant positions is eliminated, and the detection and electrical leaks can be detected quickly and electrical leaks can be prevented. It is highly reliable and eliminates the risk of electric shock due to exposed live parts, allowing safe liquid heating. Further, since the third electrode according to the present invention is integrally molded and sintered into a thick film on the top surface of the ceramic heater, it is strong and has a long life without being damaged by external stress, such as stress during internal cleaning. In addition, since it is sintered and integrated, it can be made into a single component, which makes assembly work easy and has excellent mass productivity. In addition, in the present invention, if a material such as platinum or rhodium is used as the corrosion-resistant conductive material of the third electrode, even when heating chemical liquids such as drugs, it will exhibit corrosion-proofing and other properties for these heated liquids, and will be extremely chemically This method has unique effects such as being able to obtain a third electrode that is physically stable and has a long life.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is a perspective view of a ceramic heater having the structure of the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. It is a circuit diagram explaining operation. DESCRIPTION OF SYMBOLS 1...First ceramic substrate, 2...Heating resistor pattern, 5...Thin layer, 7...Third electrode.

Claims (1)

[Scope of Claims] 1. A heating resistor pattern of a regular shape made of tungsten material or the like is embedded in the surface of a ceramic substrate, and a corrosion-resistant conductive material made of a corrosion-resistant conductive material is interposed on the upper surface of the heating resistor pattern of the ceramic substrate. A ceramic heater for heating liquids that also includes a third electrode made by printing and sintering conductive paste. 2. The ceramic heater according to claim 1, wherein the third electrode is made of platinum, rhodium, or the like.