皮革拉力試驗機的測試范圍
皮革(ge)(ge)橡膠(jiao)在(zai)制(zhi)成皮鞋(xie)、皮服裝等制(zhi)品(pin)及在(zai)制(zhi)品(pin)的(de)(de)使用過(guo)程中,都要受(shou)到不(bu)同程度的(de)(de)拉伸作用而變形,了(le)解(jie)這種(zhong)變形的(de)(de)性(xing)質和大小在(zai)很(hen)大意義上(shang)可以(yi)了(le)解(jie)革(ge)(ge)的(de)(de)品(pin)質,以(yi)確定制(zhi)品(pin)的(de)(de)種(zhong)類,皮革(ge)(ge)拉力試(shi)驗機就會顯(xian)得相當重(zhong)要了(le)。
皮(pi)革拉力試驗機(ji)如何判斷彈性材料的柔(rou)軟度(du)、品質(zhi),伸長率(lv)
柔軟(ruan)的(de)革(ge)延伸性比(bi)較大(da)(da),而(er)板硬的(de)革(ge)則不易拉(la)伸,故此(ci)可以根據革(ge)試樣受到外力作用所表(biao)現(xian)的(de)變(bian)形(xing)情況和受力大(da)(da)小判斷革(ge)的(de)柔軟(ruan)性。
革的(de)(de)伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)對于輕(qing)革尤為重要,影響穿著時(shi)的(de)(de)舒適(shi)性(xing)(xing)、彈塑(su)性(xing)(xing),并與制鞋(xie)關(guan)系密切。伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)過(guo)小的(de)(de)面(mian)革在(zai)制鞋(xie)過(guo)程中(zhong)容(rong)易(yi)出(chu)現裂紋(wen),在(zai)穿用中(zhong)不(bu)能(neng)經受反復多次彎 由;伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)過(guo)大的(de)(de)面(mian)革,制成鞋(xie)后容(rong)易(yi)變(bian)形。故(gu)伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)既不(bu)能(neng)太大,又(you)不(bu)能(neng)太小,應為一個(ge)比較合適(shi)的(de)(de)范圍,如(ru)部頒標準(zhun)規(gui)定:服裝用橡膠(jiao)規(gui)定負(fu)(fu)(fu)荷(he)伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)為 25%~60%,鞋(xie)面(mian)用橡膠(jiao)規(gui)定負(fu)(fu)(fu)荷(he)伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)為55%。革的(de)(de)伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)是指革試樣在(zai)受到軸向拉伸(shen)(shen)(shen)后,其(qi)伸(shen)(shen)(shen)長(chang)(chang)(chang)的(de)(de)長(chang)(chang)(chang)度與原長(chang)(chang)(chang)度的(de)(de)比,在(zai)實際測定中(zhong)有:規(gui)定負(fu)(fu)(fu)荷(he)伸(shen)(shen)(shen)長(chang)(chang)(chang) 率(lv)(lv)(lv)、粒(li)面(mian)層伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)、斷(duan)裂伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)和永(yong)久伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv),其(qi)中(zhong)規(gui)定負(fu)(fu)(fu)荷(he)伸(shen)(shen)(shen)長(chang)(chang)(chang)率(lv)(lv)(lv)為國家(jia)標準(zhun)必(bi)測項目。
拉力機如何檢(jian)測彈性材料的彈塑性:
從力學性質上(shang)看,皮革橡膠的(de)(de)(de)變(bian)(bian)(bian)(bian)形(xing)(xing)有(you)兩種(zhong)(zhong)(zhong)情況,一(yi)(yi)種(zhong)(zhong)(zhong)是(shi)(shi)彈(dan)性變(bian)(bian)(bian)(bian)形(xing)(xing),一(yi)(yi)種(zhong)(zhong)(zhong)是(shi)(shi)永久變(bian)(bian)(bian)(bian)形(xing)(xing)(塑性變(bian)(bian)(bian)(bian)形(xing)(xing))。革是(shi)(shi)一(yi)(yi)種(zhong)(zhong)(zhong)彈(dan)塑性材料,當(dang)(dang)(dang)試樣受(shou)到軸向(xiang)拉伸時,長度(du)有(you)所(suo)增加,這(zhe)是(shi)(shi)由于(yu)試樣內的(de)(de)(de)纖(xian)維(wei)(wei)(wei)在作用(yong) 力的(de)(de)(de)方向(xiang)上(shang)發(fa)生r變(bian)(bian)(bian)(bian)形(xing)(xing)的(de)(de)(de)緣故,纖(xian)維(wei)(wei)(wei)束因變(bian)(bian)(bian)(bian)形(xing)(xing)而產生了(le)內力,這(zhe)種(zhong)(zhong)(zhong)內力力圖使纖(xian)維(wei)(wei)(wei)束恢復其原來(lai)的(de)(de)(de)位(wei)置(zhi)(zhi)和形(xing)(xing)狀,所(suo)以(yi)當(dang)(dang)(dang)外(wai)(wai)(wai)力除去(qu)后(hou),一(yi)(yi)部(bu)分纖(xian)維(wei)(wei)(wei)束的(de)(de)(de)延長部(bu)分在很大 程度(du)上(shang)恢復了(le)原狀,革的(de)(de)(de)這(zhe)種(zhong)(zhong)(zhong)變(bian)(bian)(bian)(bian)形(xing)(xing)叫彈(dan)性變(bian)(bian)(bian)(bian)形(xing)(xing);還有(you)一(yi)(yi)部(bu)分纖(xian)維(wei)(wei)(wei)當(dang)(dang)(dang)受(shou)外(wai)(wai)(wai)力拉伸時,因纖(xian)維(wei)(wei)(wei)與作用(yong)力的(de)(de)(de)方向(xiang)不(bu)同,改(gai)變(bian)(bian)(bian)(bian)了(le)原來(lai)的(de)(de)(de)位(wei)置(zhi)(zhi),并且(qie)超過了(le)它的(de)(de)(de)彈(dan)性極限,在外(wai)(wai)(wai) 力除去(qu)后(hou),不(bu)能恢復到原來(lai)的(de)(de)(de)位(wei)置(zhi)(zhi),這(zhe)一(yi)(yi)部(bu)分不(bu)可逆變(bian)(bian)(bian)(bian)形(xing)(xing)就稱為永久變(bian)(bian)(bian)(bian)形(xing)(xing),即塑性變(bian)(bian)(bian)(bian)形(xing)(xing)。對于(yu)橡膠來(lai)說,不(bu)管是(shi)(shi)外(wai)(wai)(wai)力多大,彈(dan)性變(bian)(bian)(bian)(bian)形(xing)(xing)和永久變(bian)(bian)(bian)(bian)形(xing)(xing)都是(shi)(shi)同時發(fa)生的(de)(de)(de)。
皮(pi)革(ge)(ge)橡(xiang)膠的彈性(xing)(xing)變(bian)(bian)形(xing)和永(yong)久變(bian)(bian)形(xing)都是很珍(zhen)貴的性(xing)(xing)質,因(yin)為在(zai)(zai)制(zhi)造皮(pi) 鞋(xie)等(deng)制(zhi)品(pin)(pin)以及在(zai)(zai)使(shi)用它(ta)們的時(shi)候,要(yao)求(qiu)革(ge)(ge)有一定程(cheng)度(du)的永(yong)久變(bian)(bian)形(xing),即有一定的成形(xing)性(xing)(xing),不然皮(pi)鞋(xie)、皮(pi)服(fu)裝等(deng)就(jiu)(jiu)無一固定的形(xing)狀。上海發瑞(rui)儀器提示:制(zhi)鞋(xie)過(guo)程(cheng)中,革(ge)(ge) 在(zai)(zai)繃(beng)楦時(shi)受(shou)力(li)而被(bei)拉伸(shen),取下(xia)楦后,則(ze)要(yao)求(qiu)它(ta)保(bao)持(chi)已賦(fu)予的形(xing)狀和尺寸。另(ling)外(wai),在(zai)(zai)皮(pi)鞋(xie)穿用初(chu)期,需(xu)要(yao)一定的最低限度(du)的永(yong)久變(bian)(bian)形(xing),因(yin)為,不管(guan)制(zhi)作時(shi)怎樣合理,鞋(xie) 的個別部位(wei)總要(yao)改(gai)變(bian)(bian)形(xing)狀以適(shi)應腳(jiao)形(xing)。在(zai)(zai)這種情況(kuang)下(xia),如果是絕對彈性(xing)(xing)的革(ge)(ge),由于需(xu)要(yao)經常地把力(li)消(xiao)耗于使(shi)革(ge)(ge)變(bian)(bian)形(xing),就(jiu)(jiu)會引起(qi)腳(jiao)的過(guo)早(zao)疲勞(lao)。另(ling)一方面,如果用來制(zhi) 鞋(xie)和服(fu)裝的橡(xiang)膠沒有彈性(xing)(xing)變(bian)(bian)形(xing),它(ta)在(zai)(zai)外(wai)力(li)消(xiao)除后,就(jiu)(jiu)不能恢復原來的形(xing)狀,使(shi)鞋(xie)、服(fu)裝等(deng)制(zhi)品(pin)(pin)變(bian)(bian)型(xing)(xing)。因(yin)此,這兩種變(bian)(bian)形(xing)都是必須的:靠(kao)塑(su)性(xing)(xing)來成型(xing)(xing),靠(kao)彈性(xing)(xing)來保(bao)型(xing)(xing)。 革(ge)(ge)的彈塑(su)性(xing)(xing)則(ze)可通(tong)過(guo)測(ce)定其伸(shen)長率來表征。
皮革(ge)(ge)橡膠由于天然結構(gou)特殊,其不(bu)同(tong)部位、不(bu)同(tong)方向(xiang)的(de)性質(zhi)差異較大,給革(ge)(ge)制品設計帶來一定困(kun)難。為(wei)了(le)減少革(ge)(ge)的(de)部位、方向(xiang)差別,在(zai)制革(ge)(ge)過程中采取了(le)很多措施,力(li)求(qiu)減少縱(zong)、橫(heng)向(xiang)延伸性的(de)差別。縱(zong)向(xiang)伸長(chang)(chang)率(lv)比橫(heng)向(xiang)伸長(chang)(chang)率(lv)越接近于1,革(ge)(ge)的(de)品質(zhi)越好。