電(dian)熱反射爐(lu)的密(mi)(mi)(mi)(mi)封(feng)(feng)蓋(gai)(爐(lu)蓋(gai)),只承(cheng)受氣體的壓(ya)(ya)力,結構比較簡(jian)單。但電(dian)阻加熱爐(lu)的密(mi)(mi)(mi)(mi)封(feng)(feng)蓋(gai)見(jian)圖5-17中(zhong)的7號件(jian),工作條件(jian)差,要(yao)求(qiu)嚴格,它需與坩堝密(mi)(mi)(mi)(mi)封(feng)(feng)配(pei)合(he)(he);同時還要(yao)與升液(ye)管密(mi)(mi)(mi)(mi)封(feng)(feng)配(pei)合(he)(he);在保壓(ya)(ya)和澆注時,它又要(yao)和鑄型(xing)緊密(mi)(mi)(mi)(mi)接合(he)(he),并承(cheng)受鑄型(xing)重量及開(kai)合(he)(he)型(xing)機構的沖擊。因(yin)此密(mi)(mi)(mi)(mi)封(feng)(feng)蓋(gai)必須符合(he)(he)下述(shu)要(yao)求(qiu):第(di)1,在外力和熱作用下不易(yi)變形,密(mi)(mi)(mi)(mi)封(feng)(feng)性能良好;第(di)二,與升液(ye)管接合(he)(he)部(bu)分的溫度容易(yi)控(kong)制;第(di)三,便于裝配(pei),緊固。密(mi)(mi)(mi)(mi)封(feng)(feng)蓋(gai)材料一般(ban)用球墨鑄鐵(tie)或(huo)灰(hui)鐵(tie)鑄造,不宜用鋼材制作。