電(dian)熱反射(she)爐的密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)蓋(爐蓋),只承受(shou)(shou)氣體的壓力,結構(gou)比(bi)較(jiao)簡單。但電(dian)阻(zu)加熱爐的密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)蓋見圖5-17中的7號件(jian),工作條件(jian)差,要(yao)(yao)(yao)求嚴格,它需(xu)與(yu)坩堝密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)配合(he)(he);同時(shi)還(huan)要(yao)(yao)(yao)與(yu)升液(ye)管密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)配合(he)(he);在保壓和澆(jiao)注(zhu)時(shi),它又要(yao)(yao)(yao)和鑄(zhu)型緊密(mi)(mi)(mi)接(jie)合(he)(he),并承受(shou)(shou)鑄(zhu)型重量及開合(he)(he)型機(ji)構(gou)的沖擊。因此密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)蓋必須(xu)符合(he)(he)下述(shu)要(yao)(yao)(yao)求:第1,在外力和熱作用(yong)下不易變形,密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)性能良好;第二,與(yu)升液(ye)管接(jie)合(he)(he)部分的溫度(du)容易控制(zhi);第三,便于裝配,緊固。密(mi)(mi)(mi)封(feng)(feng)(feng)(feng)蓋材料一般(ban)用(yong)球(qiu)墨(mo)鑄(zhu)鐵或灰鐵鑄(zhu)造,不宜用(yong)鋼材制(zhi)作。