電熱反射爐的密(mi)(mi)(mi)封(feng)(feng)(feng)蓋(爐蓋),只承(cheng)受氣體的壓(ya)力,結(jie)構比較簡單。但電阻加熱爐的密(mi)(mi)(mi)封(feng)(feng)(feng)蓋見(jian)圖5-17中的7號件(jian),工作條件(jian)差,要(yao)求(qiu)嚴(yan)格,它需與坩堝密(mi)(mi)(mi)封(feng)(feng)(feng)配合(he);同時(shi)還要(yao)與升(sheng)液管密(mi)(mi)(mi)封(feng)(feng)(feng)配合(he);在保壓(ya)和澆注時(shi),它又(you)要(yao)和鑄(zhu)(zhu)型(xing)緊(jin)密(mi)(mi)(mi)接(jie)合(he),并(bing)承(cheng)受鑄(zhu)(zhu)型(xing)重量及開合(he)型(xing)機構的沖擊。因此密(mi)(mi)(mi)封(feng)(feng)(feng)蓋必(bi)須符合(he)下(xia)述要(yao)求(qiu):第(di)(di)1,在外力和熱作用(yong)下(xia)不(bu)易變形,密(mi)(mi)(mi)封(feng)(feng)(feng)性能良好;第(di)(di)二,與升(sheng)液管接(jie)合(he)部(bu)分(fen)的溫度(du)容易控制(zhi);第(di)(di)三(san),便于裝配,緊(jin)固。密(mi)(mi)(mi)封(feng)(feng)(feng)蓋材料一般用(yong)球墨鑄(zhu)(zhu)鐵或(huo)灰(hui)鐵鑄(zhu)(zhu)造,不(bu)宜用(yong)鋼(gang)材制(zhi)作。