浙江至德鋼業有限公司技術人員(yuan)，根據公司車(che)間生產工(gong)藝及檢驗發現不銹鋼管擠壓時，使用的空心坯(pi)可以由(you)以下三種方法獲得：

 1. 在實(shi)心坯料上，直(zhi)接(jie)鉆一個直(zhi)徑比擠壓芯棒直(zhi)徑略大(da)的孔。這(zhe)種方法用于(yu)得(de)到(dao)直(zhi)徑為50mm以下(xia)的孔。

 2. 在實心坯(pi)料上(shang)，先預(yu)鉆一個直徑為20~30mm的(de)小孔，然后在擴孔機(ji)上(shang)將孔擴大到(dao)指(zhi)定的(de)尺寸。這種方法(fa)用(yong)于得到(dao)50~100mm的(de)孔。

 3. 實(shi)心坯料在穿孔(kong)機上直接穿孔(kong)，得到所要求尺(chi)寸的孔(kong)。這(zhe)種方法用于大于100mm的孔(kong)。

  無論以何種方法獲得的空心坯料，其主要的質量指標是空心壞料的同心度及其內孔的彎曲度。在坯料進行穿孔或擴孔時，影響穿孔空心坯同心度和內孔看曲度的，同時也是影響其擠壓鋼管壁厚均勻度極限值的參數，主要是坯料的長度Lz,與其內孔的直徑dg的比值。一般情況下，為了確保空心坯的同心度和擠壓管壁厚均勻度的極限值，將參數L2/ds限制在一定范圍內。實心坯料穿孔時，L,/d8=5~7(碳素鋼7,不銹(xiu)鋼 5~6);空心坯料擴孔時，L/dg=10~12(最大L/dg可達到15)。

  L,/d比值的選擇主要取決于材料的變形抗力以及對擠壓不(bu)銹鋼管(guan)壁厚精度的要求。06Cr18N111Ti不銹鋼坯料穿孔后空心坯壁厚不均影響的試驗結果顯示，隨著L/ds的比值從4.4增大至6.1,穿孔后空心坯的壁厚不均增大15%.根據奧地利原VEW公司在34MN擠壓機上所得到的數據，空心坯的獲得方法對不銹鋼擠壓鋼管壁厚均勻度的影響示于圖2-23。由圖2-23可知，擴孔工藝比穿孔工藝具有更高的空心坯壁厚精度。

 55MN擠壓機上，采(cai)用ф210mm、ф280mm和(he)ф315mm 擠壓筒時的(de)芯棒(bang)直徑(jing)(jing)空心(xin)坯(pi)(pi)長度之(zhi)間的(de)關系示于圖2-24。圖中有細線的(de)區域(yu)表示可(ke)能的(de)芯棒(bang)直徑(jing)(jing)與空心(xin)坯(pi)(pi)的(de)長度的(de)比(bi)值。采(cai)用坯(pi)(pi)料的(de)孔工藝，將(jiang)使這(zhe)個區域(yu)向(xiang)較小(xiao)(xiao)的(de)空心(xin)坯(pi)(pi)長度方面明顯地縮小(xiao)(xiao)。在(zai)許多情況下，不銹鋼管縮小(xiao)(xiao)到一半(ban)。

 不銹鋼(gang)管坯料在穿(chuan)孔和擴孔時(shi)，必須滿(man)足以下(xia)條件：在一次(ci)行程中，孔的擴大(da)不(bu)應超(chao)過(guo)(guo)5倍；擴孔時(shi)的延伸(shen)系(xi)數不(bu)應超(chao)過(guo)(guo)1.45;穿(chuan)孔時(shi)的延伸(shen)系(xi)數不(bu)應超(chao)過(guo)(guo)1.60。

采用(yong)擴孔(kong)(kong)(kong)(kong)(kong)工藝的(de)(de)效(xiao)果隨著穿孔(kong)(kong)(kong)(kong)(kong)機(ji)噸位或擴孔(kong)(kong)(kong)(kong)(kong)芯棒直徑(jing)的(de)(de)減小而增加。在這種情況下(xia)，擴孔(kong)(kong)(kong)(kong)(kong)工藝可以(yi)用(yong)到擠壓(ya)(ya)筒(tong)的(de)(de)整個長度擴孔(kong)(kong)(kong)(kong)(kong)頭(tou)擴孔(kong)(kong)(kong)(kong)(kong)的(de)(de)坯料。所以(yi)，對于10~25MN擠壓(ya)(ya)機(ji)的(de)(de)擠壓(ya)(ya)穿孔(kong)(kong)(kong)(kong)(kong)芯棒穿孔(kong)(kong)(kong)(kong)(kong)車間，立式穿（擴）孔(kong)(kong)(kong)(kong)(kong)機(ji)的(de)(de)選擇應該是(shi)更(geng)簡(jian)單(dan)的(de)(de)擴孔(kong)(kong)(kong)(kong)(kong)機(ji)，而不是(shi)穿孔(kong)(kong)(kong)(kong)(kong)機(ji)。

 對于直徑超過150mm的孔(kong)，采用擴孔(kong)工藝是(shi)不合適的，因為(wei)這就需要使(shi)坯(pi)料(liao)的鉆孔(kong)直徑超過35mm,因而增加了金(jin)屬消耗(hao)，或者是(shi)需要進行2次(ci)擴孔(kong)。其結果是(shi)使(shi)擠壓生(sheng)產(chan)線的部分(fen)設備閑置，降低了整條生(sheng)產(chan)線的生(sheng)產(chan)的影(ying)響效(xiao)率。

 最直(zhi)接影(ying)響穿(chuan)（擴(kuo)(kuo)(kuo)(kuo)）孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)坯(pi)(pi)(pi)料(liao)(liao)同心(xin)度的(de)(de)(de)因素是穿(chuan)（擴(kuo)(kuo)(kuo)(kuo)）孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)坯(pi)(pi)(pi)料(liao)(liao)與(yu)(yu)穿(chuan)（擴(kuo)(kuo)(kuo)(kuo)）孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)襯(chen)(chen)之(zhi)間(jian)的(de)(de)(de)間(jian)隙。穿(chuan)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)時(shi)(shi)，由于實心(xin)坯(pi)(pi)(pi)料(liao)(liao)在穿(chuan)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)預先經過(guo)鐓(dui)粗(cu)(cu)工序，因此(ci)當(dang)鐓(dui)粗(cu)(cu)壞料(liao)(liao)的(de)(de)(de)鐓(dui)粗(cu)(cu)變形程(cheng)度足(zu)夠時(shi)(shi)，鐓(dui)粗(cu)(cu)后坯(pi)(pi)(pi)料(liao)(liao)與(yu)(yu)穿(chuan)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)襯(chen)(chen)的(de)(de)(de)牙孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)和擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)工藝之(zhi)間(jian)的(de)(de)(de)間(jian)隙，基本上應(ying)等于零，在這(zhe)種(zhong)情況(kuang)下(xia)，穿(chuan)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)坯(pi)(pi)(pi)料(liao)(liao)與(yu)(yu)穿(chuan)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)襯(chen)(chen)之(zhi)間(jian)的(de)(de)(de)間(jian)隙對于穿(chuan)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)后空心(xin)坯(pi)(pi)(pi)同心(xin)度的(de)(de)(de)影(ying)響非常小。而(er)當(dang)擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)時(shi)(shi)，由于預鉆孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)坯(pi)(pi)(pi)料(liao)(liao)在擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)不進行預先鐓(dui)粗(cu)(cu)，因此(ci)，當(dang)預鉆孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)坯(pi)(pi)(pi)料(liao)(liao)進行擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)時(shi)(shi)，預鉆孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)空心(xin)坯(pi)(pi)(pi)料(liao)(liao)外徑與(yu)(yu)擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)襯(chen)(chen)之(zhi)間(jian)的(de)(de)(de)間(jian)隙使(shi)擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)過(guo)程(cheng)的(de)(de)(de)穩定性降低，因而(er)直(zhi)接影(ying)響到(dao)擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)后空心(xin)坯(pi)(pi)(pi)的(de)(de)(de)同心(xin)度。在擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)時(shi)(shi)，對于坯(pi)(pi)(pi)料(liao)(liao)與(yu)(yu)擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)筒(tong)內(nei)襯(chen)(chen)之(zhi)間(jian)的(de)(de)(de)間(jian)隙應(ying)當(dang)特別引(yin)起注意，并且(qie)應(ying)盡可能(neng)地(di)做(zuo)(zuo)到(dao)最小，且(qie)做(zuo)(zuo)到(dao)精(jing)確(que)。這(zhe)是確(que)保擴(kuo)(kuo)(kuo)(kuo)孔(kong)(kong)(kong)(kong)(kong)(kong)(kong)后空心(xin)坯(pi)(pi)(pi)同心(xin)度的(de)(de)(de)關(guan)鍵。

另外，有資料認為(wei)(wei)(wei)碳(tan)鋼和低合金鋼穿孔(kong)時的(de)(de)延(yan)伸系(xi)數不(bu)(bu)應(ying)大于1.6,不(bu)(bu)銹鋼不(bu)(bu)應(ying)超過1.5,而擴孔(kong)時不(bu)(bu)銹鋼的(de)(de)延(yan)伸系(xi)數不(bu)(bu)應(ying)大于1.3。圖2-23所示為(wei)(wei)(wei)空心坯(pi)(pi)獲得方法對不(bu)(bu)銹鋼擠(ji)壓(ya)管壁厚均勻(yun)度的(de)(de)影響。坯(pi)(pi)料直徑為(wei)(wei)(wei)229mm,穿孔(kong)芯棒和擴孔(kong)頭(tou)的(de)(de)直徑為(wei)(wei)(wei)112mm。前者(zhe)(zhe) L/d,≈5,生產的(de)(de)不(bu)(bu)銹鋼管規(gui)格為(wei)(wei)(wei) ф127mm x10mm;后者(zhe)(zhe)L/d,≈6,生產的(de)(de)不(bu)(bu)銹鋼管規(gui)格為(wei)(wei)(wei)ф127mmx4mm.圖2-24所示為(wei)(wei)(wei)55MN 擠(ji)壓(ya)機210mm、280mm和315mm擠(ji)壓(ya)筒的(de)(de)芯棒直徑和空心坯(pi)(pi)長度之間的(de)(de)關系(xi)。