【発明の詳細な説明】[Detailed description of the invention] 本発明はシーズヒータに関し、特に寿命が長く
かつ、完成初期および長時間使用後の使用状態に
おける絶縁抵抗値の高いシーズヒータを提供しよ
うとするものである。 一般にシーズヒータは第１図に示すように、両
端に端子棒１を備えたコイル状の電熱線２を金属
パイプ３に挿入し、この金属パイプ３にマグネシ
ア粉末等の電気絶縁粉末を充填してなり、必要に
応じて金属パイプの両端をガラス５や耐熱性樹脂
６で封口してなるものである。 ところが、従来のシーズヒータは、使用状態に
おける絶縁抵抗値（以下、熱時絶縁抵抗値と称
す）が時間の経過につれて低下してしまうという
欠点と、電熱線が断線するまでの時間が短かいと
いう欠点があつた。 これに対して、本発明者らは酸化ニツケル等の
酸化物を添加した電気絶縁粉末を用いることによ
り、寿命が長く、かつ長時間使用後の熱時絶縁抵
抗値が高いシーズヒータが得られることを見出し
た。 ところが、酸化ニツケルの固有抵抗値はマグネ
シアの固有抵抗値に比べて低いため、酸化ニツケ
ルを添加することによつて、特に完成初期の熱時
絶縁抵抗値が低下する欠点がある。 この対策として、非常に高純度のマグネシア粉
末を用いることにより完成初期の熱時絶縁抵抗値
が高められる。しかし、この高純度マグネシア粉
末は粒子表面が活性化しているため、種々のガス
水分、酸化物等と非常に反応しやすく、シーズヒ
ータ使用中に、酸化ニツケルとマグネシア粉末と
の反応や酸化ニツケルのマグネシア粉末への吸着
が生じ酸化ニツケル成分がマグネシア表面を通つ
て電子伝導により絶縁抵抗値を劣化させる。これ
らの理由により、高純度マグネシア粉末に酸化ニ
ツケルを添加した電気絶縁粉末を用いると長時間
使用後の熱時絶縁抵抗値が低下してしまうという
欠点がある。 本発明者らは電気絶縁粉末についてさらに検討
した結果、酸化カルシウム、酸化アルミニウム、
酸化鉄および酸化ケイ素を固溶したマグネシア粉
末に対し、酸化コバルト等の酸化物を0.1〜10重
量％の範囲で添加したものを用いることにより、
寿命が長く、かつ完成初期および長時間使用後の
熱時絶縁抵抗値の高いシーズヒータが得られると
いう結論を得た。 以下、本発明の実施例について説明する。 まず、マグネシア粉末に対し２重量％の酸化カ
ルシウム、0.5重量％の酸化アルミニウム、１重
量％の酸化鉄および0.7重量％の酸化ケイ素を添
加し、電融し、粉砕して上記酸化物固溶マグネシ
ア粉末を生成し、これに粒径2μｍの酸化コバル
トを0.5重量％添加して電気絶縁粉末４を準備し
た。 また、電熱線２として線径0.29mmのニクロム線
第１種を用い、これを巻径２mmのコイル状とし、
両端に端子棒１を接続した。 さらに、金属パイプ３として長さ324mm、外径
８mm、肉厚0.46mmのNCF2P（商品名インコロイ
800）を用いた。 この金属パイプ３に、上記端子棒１を両端に接
続した電熱線２を挿入し、この金属パイプ３に上
記電気絶縁粉末４を充填し、この後、圧延減径し
て金属パイプ３を長さ400mm、外径6.6mmとした。 さらにこの後、金属パイプ３を焼鈍し、金属パ
イプ３の両端開口を低融点ガラス５および耐熱性
樹脂６で封口してシーズヒータを完成した。 このようにして製造された上記構成のシーズヒ
ータを５本作製し、初期特性ならびに表面温度
950℃での耐久性能を調べるとともに耐久試験に
おける750℃での熱時絶縁抵抗値の経時変化を調
べた。なお、比較のために、従来品として上記構
成における電気絶縁粉末をマグネシア絶縁粉末の
みとしたものを５本作製し、同様に試験を行つ
た。 これらの試験結果のうち、初期特性および耐久
性能の結果を第１表に示す。なお、この第１表に
おいて、耐久性能については電熱線が断線するま
での日数で表示してある。 The present invention relates to a sheathed heater, and an object of the present invention is to provide a sheathed heater that has a particularly long life and a high insulation resistance value both at the initial stage of completion and during use after long-term use. Generally, as shown in Fig. 1, a sheathed heater is constructed by inserting a coiled heating wire 2 with terminal rods 1 at both ends into a metal pipe 3, and filling this metal pipe 3 with electrically insulating powder such as magnesia powder. Both ends of the metal pipe are sealed with glass 5 or heat-resistant resin 6, if necessary. However, conventional sheathed heaters have the disadvantage that the insulation resistance value during use (hereinafter referred to as insulation resistance value when hot) decreases over time, and that the time until the heating wire breaks is short. There were flaws. In contrast, the present inventors have found that by using electrical insulating powder to which oxides such as nickel oxide are added, a sheathed heater with a long life and high insulation resistance when hot after long-term use can be obtained. I found out. However, since the specific resistance value of nickel oxide is lower than that of magnesia, the addition of nickel oxide has the disadvantage that the insulation resistance value during heating decreases, especially in the initial stage of completion. As a countermeasure to this problem, by using extremely high-purity magnesia powder, the insulation resistance value during the initial stage of completion can be increased. However, since the particle surface of this high-purity magnesia powder is activated, it is highly reactive with various gas moisture, oxides, etc., and during the use of a sheathed heater, the reaction between nickel oxide and magnesia powder and the reaction between nickel oxide and nickel oxide. Adsorption occurs on the magnesia powder, and the nickel oxide component deteriorates the insulation resistance value due to electron conduction through the magnesia surface. For these reasons, the use of an electrically insulating powder made by adding nickel oxide to high-purity magnesia powder has the disadvantage that the insulation resistance value under heat decreases after long-term use. As a result of further studies on electrical insulating powders, the present inventors found that calcium oxide, aluminum oxide,
By using magnesia powder containing iron oxide and silicon oxide as a solid solution, an oxide such as cobalt oxide is added in a range of 0.1 to 10% by weight.
It was concluded that a sheathed heater that has a long life and a high insulation resistance value during initial heating and after long-term use can be obtained. Examples of the present invention will be described below. First, 2% by weight of calcium oxide, 0.5% by weight of aluminum oxide, 1% by weight of iron oxide, and 0.7% by weight of silicon oxide are added to magnesia powder, electrolyzed, and pulverized to form the magnesia solid-dissolved oxide. Electrical insulation powder 4 was prepared by producing a powder and adding 0.5% by weight of cobalt oxide having a particle size of 2 μm to the powder. In addition, a first type nichrome wire with a wire diameter of 0.29 mm was used as the heating wire 2, and this was made into a coil shape with a winding diameter of 2 mm.
Terminal bar 1 was connected to both ends. Furthermore, as the metal pipe 3, NCF2P (product name: Incoloy
800) was used. The heating wire 2 with the terminal bar 1 connected to both ends is inserted into the metal pipe 3, the metal pipe 3 is filled with the electrical insulation powder 4, and then the metal pipe 3 is reduced in diameter by rolling. 400mm, outer diameter 6.6mm. Furthermore, after this, the metal pipe 3 was annealed, and the openings at both ends of the metal pipe 3 were sealed with low melting point glass 5 and heat-resistant resin 6 to complete a sheathed heater. Five sheathed heaters with the above configuration were manufactured in this way, and the initial characteristics and surface temperature were
In addition to investigating the durability performance at 950℃, we also investigated the change in thermal insulation resistance value over time at 750℃ in the durability test. For comparison, five conventional products having the above structure in which magnesia insulating powder was used as the only electric insulating powder were manufactured and tested in the same manner. Among these test results, the initial characteristics and durability performance results are shown in Table 1. In Table 1, durability performance is expressed in terms of the number of days until the heating wire breaks.
【表】 第１表から明らかなように、本発明品は従来品
と比較して初期特性の熱時絶縁抵抗値は約1.5倍
であり、さらに断線するまでの日数は２〜３倍長
くなる。 さらに、熱時絶縁抵抗値については第２図に示
すように、特性曲線イで示す本発明品はほとんど
変化しないが、特性曲線ロで示す従来品は通電日
数の増加につれて徐々に低下し、１週間程度で初
期値の1/10程度に低下してしまう。このように本
発明品では熱時絶縁抵抗値について従来品に比較
して大きく改善されている。 なお、酸化カルシウム、酸化アルミニウム、酸
化鉄および酸化ケイ素の各固溶量はマグネシア粉
末に対し、それぞれ５重量％以下、３重量％以下
３重量％以下、５重量％以下とすると良いことが
確認された。 また、上記実施例では添加する酸化物として酸
化コバルトを用いたが、他の酸化物、例えば酸化
タングステン、酸化ガリウム、酸化スズ、酸化鉄
でも良く、さらにはこれらの酸化物の添加量は
0.1〜10重量％が良い。これは添加量が0.1重量％
以下では酸化物の効果が認められず、また、10重
量％以上では酸化物によつて絶縁抵抗値が低下し
てしまうためである。 以上の説明から明らかなように、本発明は酸化
カルシウム、酸化アルミニウム、酸化鉄および酸
化ケイ素を固溶したマグネシア粉末に酸化コバル
ト、酸化タングステン、酸化カリウム、酸化ス
ズ、酸化鉄の群から選ばれる少くとも一種の酸化
を0.1〜10重量％の範囲で添加してなる電気絶縁
粉末を用いてシーズヒータを構成したので、寿命
が長く、かつ完成初期および長時間使用後の熱時
絶縁抵抗値の高いものとなる。[Table] As is clear from Table 1, the initial characteristic thermal insulation resistance of the product of the present invention is approximately 1.5 times higher than that of the conventional product, and the number of days until wire breakage is 2 to 3 times longer than that of the conventional product. . Furthermore, as shown in Figure 2, the thermal insulation resistance value of the inventive product shown by characteristic curve A hardly changes, while that of the conventional product shown by characteristic curve B gradually decreases as the number of days of energization increases. It drops to about 1/10 of the initial value in about a week. As described above, in the product of the present invention, the thermal insulation resistance value is greatly improved compared to the conventional product. In addition, it has been confirmed that the solid solution amount of calcium oxide, aluminum oxide, iron oxide, and silicon oxide is preferably 5% by weight or less, 3% by weight or less, 3% by weight or less, and 5% by weight or less, respectively, based on the magnesia powder. Ta. Furthermore, although cobalt oxide was used as the oxide to be added in the above example, other oxides such as tungsten oxide, gallium oxide, tin oxide, and iron oxide may also be used, and the amount of these oxides to be added may vary.
0.1-10% by weight is good. The amount added is 0.1% by weight.
This is because if the content is less than 10% by weight, the effect of the oxide is not observed, and if it is more than 10% by weight, the insulation resistance value decreases due to the oxide. As is clear from the above description, the present invention provides magnesia powder containing calcium oxide, aluminum oxide, iron oxide, and silicon oxide as a solid solution, and a small amount selected from the group of cobalt oxide, tungsten oxide, potassium oxide, tin oxide, and iron oxide. The sheathed heater is constructed using an electrically insulating powder made by adding a type of oxidation in the range of 0.1 to 10% by weight, so it has a long life and a high insulation resistance value when heated, both at the initial stage of completion and after long-term use. Become something.
【図面の簡単な説明】[Brief explanation of the drawing] 第１図は一般的なシーズヒータの断面図、第２
図は本発明の実施例におけるシーズヒータおよび
従来のシーズヒータの通電日数と熱時絶縁抵抗値
の時間特性図である。 ２……電熱線、３……金属パイプ、４……電気
絶縁粉末。 Figure 1 is a cross-sectional view of a typical sheathed heater, Figure 2
The figure is a time characteristic diagram of the number of energization days and the insulation resistance value at the time of heat for the sheathed heater in the embodiment of the present invention and the conventional sheathed heater. 2... Heating wire, 3... Metal pipe, 4... Electrical insulation powder.