同心異徑管又叫同心大小頭尺寸允許偏差應符合表4.2.2-3的規定.異徑管也叫大小頭,用來連接不同尺寸的管子,一般它分為同心異徑管和偏心異徑管兩種,當異徑管立起來后兩端口的投影是同心圓時,它就叫同心異徑管,而偏心異徑管的投影是小圓內切于外圓.
同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)的(de)(de)(de)(de)(de)制造工(gong)藝簡(jian)單(dan)，用壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)較(jiao)厚(hou)(hou)(hou)(hou)(hou)(hou)的(de)(de)(de)(de)(de)管(guan)(guan)(guan)(guan)作為(wei)(wei)(wei)毛坯，擴(kuo)大一(yi)端(duan)(duan)口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)或(huo)者用等壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)的(de)(de)(de)(de)(de)管(guan)(guan)(guan)(guan)作為(wei)(wei)(wei)毛坯，縮(suo)小(xiao)一(yi)端(duan)(duan)口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)均(jun)可。無(wu)論擴(kuo)口(kou)(kou)(kou)或(huo)縮(suo)口(kou)(kou)(kou)，一(yi)般(ban)是(shi)用模具(ju)壓(ya)制。當前(qian)國(guo)內(nei)(nei)普遍(bian)采用偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)模具(ju)逐級(ji)壓(ya)制偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)，用這種工(gong)藝生產的(de)(de)(de)(de)(de)三級(ji)以上的(de)(de)(de)(de)(de)偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)，在(zai)小(xiao)頭偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)端(duan)(duan)會產生嚴重(zhong)(zhong)缺口(kou)(kou)(kou)、內(nei)(nei)壁(bi)(bi)(bi)起(qi)瘤、壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)不(bu)均(jun)勻及橢圓(yuan)等現象。按斜截(jie)同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)截(jie)頭所(suo)得(de)結構代替偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)時，因為(wei)(wei)(wei)斜截(jie)面不(bu)是(shi)圓(yuan)面而(er)是(shi)橢圓(yuan)面，就會存在(zai)端(duan)(duan)面與直管(guan)(guan)(guan)(guan)之間的(de)(de)(de)(de)(de)錯邊、無(wu)法完全相接的(de)(de)(de)(de)(de)問題。如果采用新的(de)(de)(de)(de)(de)壓(ya)制工(gong)藝，即先用同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)模具(ju)壓(ya)制出同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)，再把壓(ya)好的(de)(de)(de)(de)(de)同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)放(fang)入(ru)偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)模具(ju)中壓(ya)制整型為(wei)(wei)(wei)所(suo)需要(yao)的(de)(de)(de)(de)(de)偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)，則其(qi)內(nei)(nei)、外(wai)表面光滑，小(xiao)頭平(ping)整，壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)均(jun)勻，圓(yuan)度(du)(du)(du)(du)合格，所(suo)用原(yuan)材(cai)料較(jiao)少。同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)的(de)(de)(de)(de)(de)質量應(ying)符合現行國(guo)家(jia)標準《鋼制對焊(han)無(wu)縫管(guan)(guan)(guan)(guan)件》GB/T 12459-2005的(de)(de)(de)(de)(de)規定,并應(ying)滿足下列要(yao)求:1) 同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)的(de)(de)(de)(de)(de)圓(yuan)度(du)(du)(du)(du)不(bu)應(ying)大于(yu)相應(ying)端(duan)(duan)外(wai)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)的(de)(de)(de)(de)(de)1%,且允(yun)許偏(pian)(pian)差為(wei)(wei)(wei)±3mm,同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)兩端(duan)(duan)中心(xin)(xin)(xin)(xin)(xin)線應(ying)重(zhong)(zhong)合,其(qi)偏(pian)(pian)心(xin)(xin)(xin)(xin)(xin)值允(yun)許偏(pian)(pian)差為(wei)(wei)(wei)±5mm.2) 同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)外(wai)觀不(bu)應(ying)有(you)裂紋,重(zhong)(zhong)皮,壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)應(ying)大于(yu)大徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)端(duan)(duan)管(guan)(guan)(guan)(guan)段(duan)的(de)(de)(de)(de)(de)壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou).12459-2005里面同(tong)(tong)(tong)心(xin)(xin)(xin)(xin)(xin)異(yi)(yi)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)標準允(yun)許偏(pian)(pian)差DN15-65 口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+1.6 -0.8 內(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±0.8 高度(du)(du)(du)(du)： ±2DN80-100 口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 內(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 高度(du)(du)(du)(du)： ±2DN125-200 口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+2.4 -1.6 內(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 高度(du)(du)(du)(du)： ±2DN250-450 口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+4 -3.2 內(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±3.2 高度(du)(du)(du)(du)： ±2DN500-800 口(kou)(kou)(kou)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+6.4 -4.8 內(nei)(nei)徑(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±4.8 高度(du)(du)(du)(du)：DN500-600 ±2 DN650-750 ±3 DN800 ±5壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)不(bu)小(xiao)于(yu)公稱壁(bi)(bi)(bi)厚(hou)(hou)(hou)(hou)(hou)(hou)的(de)(de)(de)(de)(de)87.5%圓(yuan)度(du)(du)(du)(du)偏(pian)(pian)差為(wei)(wei)(wei)正負絕(jue)對值之和(he)。但是(shi)一(yi)般(ban)500以下圓(yuan)度(du)(du)(du)(du)為(wei)(wei)(wei)4MM以內(nei)(nei)。