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在(zai)目(mu)前國(guo)內(nei)外陶(tao)瓷成(cheng)形(xing)(xing)生(sheng)產(chan)中(zhong)，石膏(gao)(gao)模(mo)型(xing)仍然是成(cheng)形(xing)(xing)生(sheng)產(chan)的(de)主(zhu)(zhu)要(yao)輔助工具(ju)，而(er)石膏(gao)(gao)粉主(zhu)(zhu)要(yao)指指熟(shu)石膏(gao)(gao)粉，則(ze)是制作(zuo)石膏(gao)(gao)模(mo)型(xing)的(de)材(cai)(cai)料(liao)。由于(yu)石膏(gao)(gao)在(zai)我(wo)國(guo)分布(bu)廣泛，儲量豐富，且價格低廉；石膏(gao)(gao)粉又(you)是一種優(you)良的(de)膠(jiao)凝材(cai)(cai)料(liao)，與水混合攪拌(ban)后漿(jiang)體流動性(xing)能(neng)(neng)好，可(ke)(ke)以在(zai)制模(mo)過(guo)程中(zhong)注(zhu)出各種形(xing)(xing)狀，再(zai)加(jia)之其有(you)無(wu)可(ke)(ke)比擬的(de)凝結性(xing)能(neng)(neng)、吸水性(xing)能(neng)(neng)和(he)易加(jia)工性(xing)能(neng)(neng)，故用途廣泛。加(jia)上目(mu)前還(huan)沒有(you)找到可(ke)(ke)替代(dai)其廉價性(xing)質的(de)相似材(cai)(cai)料(liao)，所以國(guo)內(nei)外大(da)多(duo)數陶(tao)瓷廠仍將其作(zuo)為制作(zuo)模(mo)型(xing)的(de)主(zhu)(zhu)要(yao)材(cai)(cai)料(liao)。主(zhu)(zhu)要(yao)用于(yu)制作(zuo)陶(tao)瓷注(zhu)漿(jiang)成(cheng)形(xing)(xing)、滾(gun)壓(ya)成(cheng)形(xing)(xing)和(he)塑壓(ya)成(cheng)形(xing)(xing)的(de)模(mo)型(xing)。總(zong)之。用石膏(gao)(gao)粉制作(zuo)陶(tao)瓷生(sheng)產(chan)成(cheng)形(xing)(xing)模(mo)型(xing)具(ju)有(you)取材(cai)(cai)方便、成(cheng)本低、安排(pai)生(sheng)產(chan)便捷(jie)的(de)特點。
目前國內生(sheng)產(chan)(chan)(chan)(chan)石(shi)膏(gao)(gao)(gao)粉(fen)的(de)廠(chang)家眾(zhong)多。分布地(di)(di)域廣泛．由于石(shi)膏(gao)(gao)(gao)礦石(shi)的(de)性質(zhi)和開采方式不(bu)一．加(jia)上企(qi)業規模(mo)(mo)大(da)小(xiao)(xiao)、生(sheng)產(chan)(chan)(chan)(chan)工藝(yi)設備水平不(bu)一。因此生(sheng)產(chan)(chan)(chan)(chan)出的(de)石(shi)膏(gao)(gao)(gao)粉(fen)的(de)質(zhi)量(liang)(liang)(liang)參差不(bu)齊(qi)。一般(ban)而(er)言，一些石(shi)膏(gao)(gao)(gao)礦石(shi)儲量(liang)(liang)(liang)豐富、生(sheng)產(chan)(chan)(chan)(chan)規模(mo)(mo)較(jiao)大(da)、生(sheng)產(chan)(chan)(chan)(chan)工藝(yi)設備較(jiao)先進、管理嚴格、檢(jian)測(ce)手段和實驗(yan)設備較(jiao)齊(qi)全的(de)廠(chang)家所生(sheng)產(chan)(chan)(chan)(chan)的(de)石(shi)膏(gao)(gao)(gao)粉(fen)質(zhi)量(liang)(liang)(liang)較(jiao)好．且質(zhi)量(liang)(liang)(liang)均(jun)一穩(wen)定(ding)性好；而(er)一些加(jia)工工藝(yi)落后(hou)的(de)小(xiao)(xiao)廠(chang)生(sheng)產(chan)(chan)(chan)(chan)出的(de)產(chan)(chan)(chan)(chan)品質(zhi)量(liang)(liang)(liang)無(wu)保證，質(zhi)量(liang)(liang)(liang)均(jun)一穩(wen)定(ding)性差。從另一方面(mian)而(er)言，現(xian)在一些陶瓷制造(zao)企(qi)業生(sheng)產(chan)(chan)(chan)(chan)經營較(jiao)困難(nan)。資金短缺，使用(yong)的(de)石(shi)膏(gao)(gao)(gao)粉(fen)不(bu)斷變換供應廠(chang)家，來料來不(bu)及檢(jian)驗(yan)就投入(ru)生(sheng)產(chan)(chan)(chan)(chan)使用(yong)，石(shi)膏(gao)(gao)(gao)粉(fen)的(de)質(zhi)量(liang)(liang)(liang)與穩(wen)定(ding)性難(nan)以保證。因石(shi)膏(gao)(gao)(gao)粉(fen)質(zhi)量(liang)(liang)(liang)問題而(er)造(zao)成(cheng)的(de)生(sheng)產(chan)(chan)(chan)(chan)損失時有發生(sheng)，影響生(sheng)產(chan)(chan)(chan)(chan)的(de)正常進行。在這種情(qing)況下，企(qi)業的(de)技術質(zhi)量(liang)(liang)(liang)檢(jian)驗(yan)部門(men)，如何簡便(bian)、快捷(jie)、較(jiao)準確(que)地(di)(di)判斷出石(shi)膏(gao)(gao)(gao)粉(fen)質(zhi)量(liang)(liang)(liang)的(de)優劣，及時為企(qi)業生(sheng)產(chan)(chan)(chan)(chan)服務，顯得尤為重要(yao)。
石(shi)膏(gao)粉(fen)在(zai)生產中(zhong)能(neng)否使用，首要(yao)最基本的條件是能(neng)否滿足(zu)模型制作的注模操作要(yao)求。也(ye)就(jiu)是說石(shi)膏(gao)粉(fen)的凝結時間(初凝和終凝)應符(fu)合(he)(he)標(biao)準，長(chang)短合(he)(he)理，過(guo)長(chang)過(guo)短都(dou)不好。初凝(ning)時間過(guo)短，來不及操(cao)作。會注(zhu)桶影(ying)響生產；終凝(ning)時間過(guo)長(chang)，凝(ning)固時間慢，影(ying)響產量(liang)。陶瓷企業一般(ban)在新進石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉后，都(dou)會經過(guo)廠內(nei)質(zhi)檢部門進行全面的(de)(de)(de)物(wu)理化學(xue)檢驗合(he)(he)格后方(fang)能使用。其實，描述石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉質(zhi)量(liang)的(de)(de)(de)物(wu)理性能參數較(jiao)多．故(gu)判(pan)斷石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉質(zhi)量(liang)的(de)(de)(de)方(fang)法(fa)和手段也(ye)較(jiao)多。簡(jian)單而(er)言(yan)．有(you)時從外(wai)(wai)觀上(shang)即可初步判(pan)定石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉質(zhi)量(liang)的(de)(de)(de)優劣(lie)。但是(shi)．有(you)時觀察石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉的(de)(de)(de)外(wai)(wai)觀，除了顏色有(you)明(ming)顯的(de)(de)(de)可判(pan)定區別外(wai)(wai)．同一顏色的(de)(de)(de)石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉從外(wai)(wai)觀上(shang)很難判(pan)斷其質(zhi)量(liang)的(de)(de)(de)優劣(lie)．必須進一步采用化學(xue)分析或者物(wu)理檢驗的(de)(de)(de)方(fang)法(fa)才能判(pan)定。比如還需要測定石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉的(de)(de)(de)標(biao)準稠度(du)、流動性、凝(ning)結時間、抗折強度(du)、膨(peng)脹率等(deng)指標(biao)。本文根據生產實踐(jian)經驗，對此問題進行了探討，提出了判(pan)定和鑒別石(shi)(shi)(shi)(shi)(shi)(shi)膏(gao)(gao)粉質(zhi)量(liang)的(de)(de)(de)一些簡(jian)易和實用的(de)(de)(de)方(fang)法(fa)。
2 石(shi)膏(gao)粉質(zhi)量的簡易鑒別方法
2．1從(cong)外觀上判斷
通過外觀(guan)上(shang)觀(guan)察和手感可初步判斷石膏粉質(zhi)量的優(you)劣。觀(guan)察就(jiu)是(shi)看外觀(guan)包裝袋(dai)質(zhi)量情況和石膏粉的外觀(guan)顏(yan)色，手感就(jiu)是(shi)用手搓(cuo)一搓(cuo)石膏粉的糙細程度(細度)。
(1)若(ruo)包裝(zhuang)(zhuang)塑料(liao)(liao)(liao)編(bian)織袋的材(cai)質質量(liang)(liang)差、松軟(ruan)強(qiang)度低、做工粗(cu)糙、編(bian)織稀疏(單位面積內的經(jing)緯數目(mu)不(bu)達(da)標(biao))、顏色(se)發灰呈綠(lv)黑(hei)色(se)、內部(bu)沒有(you)(you)防潮塑料(liao)(liao)(liao)袋、出現(xian)撒(sa)料(liao)(liao)(liao)現(xian)象、三無產品(pin)或外觀(guan)標(biao)識或種類名稱、生產廠家、商(shang)標(biao)、重量(liang)(liang)、聯系方(fang)式等不(bu)齊(qi)全(quan)的石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)則很(hen)大可(ke)能不(bu)符合質量(liang)(liang)標(biao)準、檔(dang)次質量(liang)(liang)差，質量(liang)(liang)穩定性也不(bu)能保證。反之，那些包裝(zhuang)(zhuang)塑料(liao)(liao)(liao)編(bian)織袋用(yong)材(cai)好、做工精致、顏色(se)發白、強(qiang)度高(gao)(gao)、編(bian)織經(jing)緯密(mi)集、內部(bu)有(you)(you)防潮塑料(liao)(liao)(liao)袋、封口嚴密(mi)、外觀(guan)印刷清(qing)晰(xi)、標(biao)識齊(qi)全(quan)、不(bu)撒(sa)料(liao)(liao)(liao)的石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)一般質量(liang)(liang)較好、檔(dang)次高(gao)(gao)，質量(liang)(liang)有(you)(you)保證。一般使用(yong)這種包裝(zhuang)(zhuang)袋的石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)白度高(gao)(gao)、細度細。若(ruo)石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)是(shi)質量(liang)(liang)上乘的高(gao)(gao)檔(dang)、高(gao)(gao)附加值的高(gao)(gao)強(qiang)度石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)、特種石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)如母模(mo)石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)、原模(mo)石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)或樹脂石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)，其價格很(hen)高(gao)(gao)．是(shi)普通(tong)石(shi)(shi)(shi)膏粉(fen)(fen)(fen)(fen)的3～9倍。
(2)外觀上看(kan)，白度(du)高(gao)的(de)石(shi)膏粉細度(du)目數高(gao)，質量好。價(jia)(jia)格較高(gao)；而發灰發黑、里面有黑色雜質的(de)石(shi)膏粉質量較差(cha)。用手的(de)拇指和食(shi)指搓(cuo)捻石(shi)膏粉，手感發沙粗(cu)糙(cao)的(de)石(shi)膏粉細度(du)糙(cao)，質量較差(cha)、價(jia)(jia)格較低(di)；而手感細膩的(de)石(shi)膏粉說明細度(du)細并且均勻，質量較好，價(jia)(jia)格也會較高(gao)。
2．2測定(ding)結晶水含量
石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)是一種結(jie)(jie)晶(jing)(jing)(jing)(jing)混合物，其中會含(han)有生(sheng)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)、半(ban)水(shui)(shui)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)和無水(shui)(shui)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)(過(guo)(guo)燒石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao))。在炒(chao)制過(guo)(guo)程(cheng)中欠(qian)火(huo)夾生(sheng)會出現(xian)生(sheng)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)，或者火(huo)大、炒(chao)制時(shi)(shi)間(jian)(jian)過(guo)(guo)長(chang)造成過(guo)(guo)燒會出現(xian)無水(shui)(shui)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)，這些都會影響(xiang)(xiang)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)的(de)(de)凝(ning)結(jie)(jie)時(shi)(shi)間(jian)(jian)，影響(xiang)(xiang)生(sheng)產(chan)的(de)(de)正常使用(yong)(yong)。有時(shi)(shi)由于石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)放置時(shi)(shi)間(jian)(jian)過(guo)(guo)長(chang)受(shou)潮(chao)，也會影響(xiang)(xiang)正常使用(yong)(yong)。根據經驗(yan)和資料介紹，通過(guo)(guo)測定結(jie)(jie)晶(jing)(jing)(jing)(jing)水(shui)(shui)的(de)(de)含(han)量(liang)，可(ke)判斷(duan)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)質量(liang)的(de)(de)好壞。一般合格(ge)的(de)(de)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)結(jie)(jie)晶(jing)(jing)(jing)(jing)水(shui)(shui)的(de)(de)含(han)量(liang)在4．5～5．5％之(zhi)間(jian)(jian)。若石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)的(de)(de)結(jie)(jie)晶(jing)(jing)(jing)(jing)水(shui)(shui)含(han)量(liang)遠低于此(ci)標準值(zhi)(zhi)，則說(shuo)明(ming)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)過(guo)(guo)燒，注模時(shi)(shi)凝(ning)結(jie)(jie)時(shi)(shi)問太長(chang)甚至不凝(ning)固(gu)；若石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)的(de)(de)結(jie)(jie)晶(jing)(jing)(jing)(jing)水(shui)(shui)含(han)量(liang)遠高(gao)于此(ci)標準值(zhi)(zhi)，則說(shuo)明(ming)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)欠(qian)火(huo)或者受(shou)潮(chao)，注模時(shi)(shi)凝(ning)結(jie)(jie)時(shi)(shi)間(jian)(jian)短。以(yi)上兩(liang)種情況的(de)(de)石(shi)(shi)(shi)(shi)膏(gao)(gao)(gao)粉(fen)都不合格(ge)，在生(sheng)產(chan)中不能使用(yong)(yong)。
檢測石膏粉(fen)結晶(jing)水含量(liang)的(de)方法是：精確(que)稱(cheng)取(qu)40℃烘干后冷(leng)卻(que)至室溫的(de)試樣質(zhi)量(liang)G (一般為2～5g)，放置于恒(heng)重(zhong)的(de)鉑金(jin)坩堝(或瓷坩堝)中，精確(que)稱(cheng)取(qu)其(qi)質(zhi)量(liang)為G1 ；在230±5℃ 下(xia)灼(zhuo)燒3～4h，取(qu)出移入干燥器內，冷(leng)卻(que)至室溫后稱(cheng)取(qu)其(qi)質(zhi)量(liang)為G2，則其(qi)結晶(jing)水百分含量(liang)為：
(G1一G2)／G×100％。
2．3測(ce)定石膏粉的凝結(jie)時(shi)間
凝(ning)(ning)(ning)(ning)結(jie)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)包(bao)括初(chu)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)和終(zhong)(zhong)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)。石(shi)(shi)(shi)膏(gao)(gao)(gao)粉凝(ning)(ning)(ning)(ning)結(jie)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)質(zhi)量標準是(shi)(shi)：在(zai)標準稠度下．一(yi)般初(chu)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)不小于(yu)6min，終(zhong)(zhong)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)不大于(yu)25min。適(shi)宜(yi)的(de)(de)(de)凝(ning)(ning)(ning)(ning)結(jie)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)是(shi)(shi)石(shi)(shi)(shi)膏(gao)(gao)(gao)粉在(zai)生(sheng)產(chan)(chan)中(zhong)(zhong)正常(chang)使用(yong)的(de)(de)(de)先決和必要的(de)(de)(de)條件。初(chu)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)過(guo)(guo)短(duan)或(huo)終(zhong)(zhong)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)過(guo)(guo)長都不合適(shi)。如果在(zai)使用(yong)中(zhong)(zhong)初(chu)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)太短(duan)，小于(yu)6min，則證(zheng)明(ming)石(shi)(shi)(shi)膏(gao)(gao)(gao)粉沒有(you)炒熟夾生(sheng)，或(huo)受(shou)潮內(nei)(nei)部含有(you)生(sheng)石(shi)(shi)(shi)膏(gao)(gao)(gao)，影(ying)響注(zhu)(zhu)模操作(zuo)，表現(xian)為(wei)生(sheng)產(chan)(chan)中(zhong)(zhong)注(zhu)(zhu)桶，耽誤生(sheng)產(chan)(chan)；若終(zhong)(zhong)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)太長，遠大于(yu)25min，則說明(ming)石(shi)(shi)(shi)膏(gao)(gao)(gao)在(zai)炒制時(shi)(shi)(shi)(shi)過(guo)(guo)燒。里面含有(you)過(guo)(guo)燒石(shi)(shi)(shi)膏(gao)(gao)(gao)，表現(xian)為(wei)注(zhu)(zhu)模時(shi)(shi)(shi)(shi)易漏漿，甚至石(shi)(shi)(shi)膏(gao)(gao)(gao)漿不凝(ning)(ning)(ning)(ning)固，影(ying)響生(sheng)產(chan)(chan)。這兩種情況的(de)(de)(de)石(shi)(shi)(shi)膏(gao)(gao)(gao)粉在(zai)生(sheng)產(chan)(chan)中(zhong)(zhong)都不能(neng)(neng)使用(yong)。故通過(guo)(guo)凝(ning)(ning)(ning)(ning)結(jie)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)的(de)(de)(de)測定(ding)(ding)(ding)(ding)可判定(ding)(ding)(ding)(ding)石(shi)(shi)(shi)膏(gao)(gao)(gao)粉質(zhi)量的(de)(de)(de)優劣或(huo)者決定(ding)(ding)(ding)(ding)該(gai)石(shi)(shi)(shi)膏(gao)(gao)(gao)粉在(zai)生(sheng)產(chan)(chan)中(zhong)(zhong)能(neng)(neng)否使用(yong)。簡易測定(ding)(ding)(ding)(ding)方法為(wei)：(1)按(an)生(sheng)產(chan)(chan)的(de)(de)(de)膏(gao)(gao)(gao)水(shui)比例稱取100ml水(shui)所(suo)需的(de)(de)(de)石(shi)(shi)(shi)膏(gao)(gao)(gao)粉試(shi)(shi)(shi)(shi)樣(yang)(yang)，把(ba)水(shui)注(zhu)(zhu)入500ml容器(qi)中(zhong)(zhong)，將試(shi)(shi)(shi)(shi)樣(yang)(yang)在(zai)1min內(nei)(nei)均勻地(di)撒入水(shui)中(zhong)(zhong)，并(bing)靜置30s，快速攪拌30s，并(bing)把(ba)石(shi)(shi)(shi)膏(gao)(gao)(gao)漿體立(li)即倒人放置在(zai)玻璃(li)板上(shang)的(de)(de)(de)銅管內(nei)(nei)，隨后緩慢垂(chui)直(zhi)向上(shang)提起(qi)銅管2Omm，使石(shi)(shi)(shi)膏(gao)(gao)(gao)漿體平鋪成厚約5mm的(de)(de)(de)試(shi)(shi)(shi)(shi)餅；(2)用(yong)直(zhi)徑(jing)約5mm的(de)(de)(de)玻璃(li)棒(bang)(bang)劃(hua)割試(shi)(shi)(shi)(shi)餅，間(jian)(jian)(jian)(jian)(jian)(jian)隔30s劃(hua)一(yi)次，每次劃(hua)后用(yong)布(bu)將玻璃(li)棒(bang)(bang)擦(ca)凈。當(dang)劃(hua)痕兩邊的(de)(de)(de)料漿剛好(hao)不再合攏時(shi)(shi)(shi)(shi)即為(wei)初(chu)凝(ning)(ning)(ning)(ning)。以試(shi)(shi)(shi)(shi)樣(yang)(yang)投入水(shui)中(zhong)(zhong)開始至初(chu)凝(ning)(ning)(ning)(ning)的(de)(de)(de)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)間(jian)(jian)(jian)(jian)(jian)(jian)隔就是(shi)(shi)初(chu)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)；(3)在(zai)測定(ding)(ding)(ding)(ding)初(chu)凝(ning)(ning)(ning)(ning)后的(de)(de)(de)試(shi)(shi)(shi)(shi)餅上(shang)用(yong)大拇指以約50N的(de)(de)(de)力連續按(an)壓，間(jian)(jian)(jian)(jian)(jian)(jian)隔15s一(yi)次，當(dang)按(an)壓至印(yin)痕邊緣沒有(you)水(shui)份出現(xian)時(shi)(shi)(shi)(shi)即為(wei)終(zhong)(zhong)凝(ning)(ning)(ning)(ning) 以試(shi)(shi)(shi)(shi)樣(yang)(yang)投入水(shui)中(zhong)(zhong)開始至終(zhong)(zhong)凝(ning)(ning)(ning)(ning)的(de)(de)(de)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian)間(jian)(jian)(jian)(jian)(jian)(jian)隔就是(shi)(shi)終(zhong)(zhong)凝(ning)(ning)(ning)(ning)時(shi)(shi)(shi)(shi)間(jian)(jian)(jian)(jian)(jian)(jian).
根據檢測結果與(yu)質量(liang)(liang)標準或(huo)與(yu)正常大生(sheng)產中時(shi)的(de)石膏粉(fen)的(de)凝結時(shi)間數值進行對比，即可(ke)判(pan)定石膏粉(fen)質量(liang)(liang)的(de)優劣和決(jue)定其在生(sheng)產中能否使用(yong)。
2．4測定試餅直(zhi)徑(jing)
按生產(chan)(chan)中(zhong)石(shi)(shi)(shi)(shi)膏(gao)和(he)(he)水的(de)(de)比(bi)例(li)，可通(tong)(tong)過觀察和(he)(he)測量(liang)試(shi)(shi)(shi)餅(bing)(bing)的(de)(de)直(zhi)(zhi)(zhi)徑(jing)大(da)小(流(liu)動(dong)(dong)性(xing)(xing))，來判斷石(shi)(shi)(shi)(shi)膏(gao)粉(fen)質(zhi)量(liang)的(de)(de)優劣和(he)(he)決定其(qi)在生產(chan)(chan)中(zhong)能否使(shi)用(yong)(yong)。試(shi)(shi)(shi)餅(bing)(bing)直(zhi)(zhi)(zhi)徑(jing)的(de)(de)大(da)小與(yu)水量(liang)、膏(gao)水比(bi)例(li)以(yi)及石(shi)(shi)(shi)(shi)膏(gao)粉(fen)的(de)(de)質(zhi)量(liang)等因素有(you)(you)關。實(shi)驗檢測時應固定水量(liang)的(de)(de)大(da)小，所采用(yong)(yong)的(de)(de)器具和(he)(he)實(shi)驗方法應一(yi)致。在大(da)生產(chan)(chan)石(shi)(shi)(shi)(shi)膏(gao)和(he)(he)水的(de)(de)比(bi)例(li)下，若(ruo)以(yi)生產(chan)(chan)中(zhong)正常使(shi)用(yong)(yong)的(de)(de)合格石(shi)(shi)(shi)(shi)膏(gao)粉(fen)的(de)(de)試(shi)(shi)(shi)餅(bing)(bing)直(zhi)(zhi)(zhi)徑(jing)為(wei)D，待檢石(shi)(shi)(shi)(shi)膏(gao)粉(fen)試(shi)(shi)(shi)餅(bing)(bing)直(zhi)(zhi)(zhi)徑(jing)為(wei)d。如果d遠遠小于D，甚(shen)至不流(liu)動(dong)(dong)平鋪，則(ze)說明(ming)(ming)石(shi)(shi)(shi)(shi)膏(gao)粉(fen)質(zhi)量(liang)不好，沒有(you)(you)炒熟夾生。或受(shou)潮(chao)內(nei)部(bu)含有(you)(you)生石(shi)(shi)(shi)(shi)膏(gao)，影響注模(mo)操作甚(shen)至不能使(shi)用(yong)(yong)；如果d遠遠大(da)于D，漿體(ti)很稀(xi)流(liu)動(dong)(dong)性(xing)(xing)強，則(ze)說明(ming)(ming)石(shi)(shi)(shi)(shi)膏(gao)粉(fen)過燒(shao)，注模(mo)時凝結時間太長(chang)以(yi)至不凝固，也無法使(shi)用(yong)(yong)。用(yong)(yong)此方法也可以(yi)區分普通(tong)(tong)B 石(shi)(shi)(shi)(shi)膏(gao)粉(fen)和(he)(he)高強度a石(shi)(shi)(shi)(shi)膏(gao)粉(fen)。在同(tong)樣的(de)(de)膏(gao)水比(bi)例(li)下，若(ruo)漿體(ti)流(liu)動(dong)(dong)性(xing)(xing)強、試(shi)(shi)(shi)餅(bing)(bing)直(zhi)(zhi)(zhi)徑(jing)大(da)，則(ze)證明(ming)(ming)是a石(shi)(shi)(shi)(shi)膏(gao)粉(fen)；反(fan)之，若(ruo)漿體(ti)流(liu)動(dong)(dong)性(xing)(xing)差、甚(shen)至不流(liu)動(dong)(dong)，試(shi)(shi)(shi)餅(bing)(bing)直(zhi)(zhi)(zhi)徑(jing)小，則(ze)證明(ming)(ming)是B 石(shi)(shi)(shi)(shi)膏(gao)粉(fen)。
2．5生產中(zhong)試(shi)注
按生產中(zhong)石(shi)(shi)膏(gao)(gao)和(he)水(shui)的(de)(de)比例，確(que)保所采(cai)用(yong)(yong)的(de)(de)器具(ju)、操作人員、設備(bei)和(he)工藝方法一(yi)致，選(xuan)擇一(yi)個小型(xing)胎型(xing)母模進行生產模型(xing)的(de)(de)試注，與生產中(zhong)正(zheng)(zheng)常(chang)使用(yong)(yong)的(de)(de)合(he)格(ge)石(shi)(shi)膏(gao)(gao)粉(fen)(fen)的(de)(de)模型(xing)澆(jiao)注過程進行對比。若待測(ce)石(shi)(shi)膏(gao)(gao)粉(fen)(fen)凝(ning)(ning)(ning)結(jie)時(shi)間(jian)(jian)正(zheng)(zheng)常(chang)合(he)理(li)、操作順利(li)不注桶，則說明該石(shi)(shi)膏(gao)(gao)粉(fen)(fen)是(shi)合(he)格(ge)的(de)(de)石(shi)(shi)膏(gao)(gao)粉(fen)(fen)；若待測(ce)石(shi)(shi)膏(gao)(gao)粉(fen)(fen)凝(ning)(ning)(ning)結(jie)時(shi)間(jian)(jian)非正(zheng)(zheng)常(chang)，凝(ning)(ning)(ning)結(jie)時(shi)間(jian)(jian)太短注桶，或(huo)者凝(ning)(ning)(ning)結(jie)時(shi)間(jian)(jian)太長(chang)甚(shen)至不凝(ning)(ning)(ning)固，這樣的(de)(de)石(shi)(shi)膏(gao)(gao)粉(fen)(fen)不合(he)格(ge)，生產中(zhong)絕對不能(neng)使用(yong)(yong)。
