同心异径管又叫同心大小头尺寸允许偏差应符合表4.2.2-3的规定.异径管也叫大小头,用来连接不同尺寸的管子,一般它分为同心异径管和偏心异径管两种,当异径管立起来后两端口的投影是同心圆时,它就叫同心异径管,而偏心异径管的投影是小圆内切于外圆.
同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)(de)制(zhi)造(zao)工(gong)艺简单(dan)，用壁(bi)厚(hou)(hou)(hou)较厚(hou)(hou)(hou)的(de)(de)(de)管(guan)(guan)(guan)(guan)(guan)(guan)作(zuo)为(wei)毛坯，扩大(da)一端口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)或(huo)者(zhe)用等壁(bi)厚(hou)(hou)(hou)的(de)(de)(de)管(guan)(guan)(guan)(guan)(guan)(guan)作(zuo)为(wei)毛坯，缩小(xiao)一端口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)均(jun)可。无(wu)论扩口(kou)或(huo)缩口(kou)，一般是(shi)用模(mo)具压(ya)(ya)制(zhi)。当前国内普遍采用偏心(xin)(xin)(xin)模(mo)具逐级(ji)压(ya)(ya)制(zhi)偏心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，用这种工(gong)艺生产(chan)的(de)(de)(de)三级(ji)以(yi)上(shang)的(de)(de)(de)偏心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，在小(xiao)头(tou)偏心(xin)(xin)(xin)端会(hui)(hui)产(chan)生严重缺口(kou)、内壁(bi)起瘤、壁(bi)厚(hou)(hou)(hou)不(bu)均(jun)匀及椭(tuo)圆(yuan)等现象。按斜截(jie)同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)截(jie)头(tou)所得结构代替偏心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)时，因为(wei)斜截(jie)面不(bu)是(shi)圆(yuan)面而是(shi)椭(tuo)圆(yuan)面，就会(hui)(hui)存(cun)在端面与直管(guan)(guan)(guan)(guan)(guan)(guan)之间的(de)(de)(de)错边、无(wu)法完全相接(jie)的(de)(de)(de)问(wen)题。如果(guo)采用新(xin)的(de)(de)(de)压(ya)(ya)制(zhi)工(gong)艺，即先用同(tong)(tong)心(xin)(xin)(xin)模(mo)具压(ya)(ya)制(zhi)出同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，再把(ba)压(ya)(ya)好的(de)(de)(de)同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)放入(ru)偏心(xin)(xin)(xin)模(mo)具中(zhong)压(ya)(ya)制(zhi)整型(xing)为(wei)所需(xu)要的(de)(de)(de)偏心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)，则其内、外(wai)(wai)表(biao)面光滑，小(xiao)头(tou)平整，壁(bi)厚(hou)(hou)(hou)均(jun)匀，圆(yuan)度(du)(du)合(he)格(ge)，所用原材料较少(shao)。同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)(de)质量(liang)应(ying)符合(he)现行国家标准《钢制(zhi)对焊无(wu)缝管(guan)(guan)(guan)(guan)(guan)(guan)件》GB/T 12459-2005的(de)(de)(de)规定,并(bing)应(ying)满足(zu)下列要求:1) 同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)(de)圆(yuan)度(du)(du)不(bu)应(ying)大(da)于(yu)相应(ying)端外(wai)(wai)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)的(de)(de)(de)1%,且允许偏差(cha)为(wei)±3mm,同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)两端中(zhong)心(xin)(xin)(xin)线应(ying)重合(he),其偏心(xin)(xin)(xin)值允许偏差(cha)为(wei)±5mm.2) 同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)外(wai)(wai)观不(bu)应(ying)有(you)裂纹,重皮,壁(bi)厚(hou)(hou)(hou)应(ying)大(da)于(yu)大(da)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)端管(guan)(guan)(guan)(guan)(guan)(guan)段(duan)的(de)(de)(de)壁(bi)厚(hou)(hou)(hou).12459-2005里面同(tong)(tong)心(xin)(xin)(xin)异(yi)(yi)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)管(guan)(guan)(guan)(guan)(guan)(guan)标准允许偏差(cha)DN15-65 口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+1.6 -0.8 内径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±0.8 高(gao)(gao)度(du)(du)： ±2DN80-100 口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 内径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 高(gao)(gao)度(du)(du)： ±2DN125-200 口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+2.4 -1.6 内径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±1.6 高(gao)(gao)度(du)(du)： ±2DN250-450 口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+4 -3.2 内径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±3.2 高(gao)(gao)度(du)(du)： ±2DN500-800 口(kou)径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：+6.4 -4.8 内径(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)(jing)：±4.8 高(gao)(gao)度(du)(du)：DN500-600 ±2 DN650-750 ±3 DN800 ±5壁(bi)厚(hou)(hou)(hou)不(bu)小(xiao)于(yu)公称壁(bi)厚(hou)(hou)(hou)的(de)(de)(de)87.5%圆(yuan)度(du)(du)偏差(cha)为(wei)正负绝(jue)对值之和(he)。但(dan)是(shi)一般500以(yi)下圆(yuan)度(du)(du)为(wei)4MM以(yi)内。