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濰坊學(xué)院本科畢業(yè)設(shè)計(jì)任務(wù)書
課題名稱： 長(zhǎng)筒塑料注射模具設(shè)計(jì)
課題類別： 工程工業(yè)設(shè)計(jì)
?！ I(yè)： 機(jī)械設(shè)計(jì)制造及自動(dòng)化
年 級(jí)： 2016 級(jí)
指導(dǎo)教師： 張 華 紅
學(xué)生姓名： 張 婕
2020年 03月 05日
一、 課題條件：
1. 學(xué)生對(duì)此課題感興趣并希望更深入的了解與掌握
2. 學(xué)過《機(jī)械設(shè)計(jì)》、《塑料成型與模具設(shè)計(jì)》等課程
3. 熟悉并掌握AutoCAD繪圖軟件
4．給定注塑零件
二、畢業(yè)設(shè)計(jì)主要內(nèi)容：
1. 根據(jù)零件要求，分析注射成形工藝；
2. 確定注射方案和模具結(jié)構(gòu)；
3. 繪制注射模具裝配圖和零件圖；
4. 制訂模具主要零件加工工藝
5. 3000~5000字英文科技文獻(xiàn)及翻譯
三、計(jì)劃進(jìn)度：
1.實(shí)習(xí) 2周
2.查閱資料，分析注射成形工藝 2周
3.確定注射成形方案和模具結(jié)構(gòu) 2周
4.繪制注射成形模具裝配圖和零件圖 3周
5.制訂模具主要零件加工工藝 1周
6.撰寫技術(shù)報(bào)告，整理資料，準(zhǔn)備答辯 2周
四、主要參考文獻(xiàn)：
[1] 劉俊，徐四紅，馮新紅.畢業(yè)設(shè)計(jì)指導(dǎo)與案例分析（機(jī)械類）[M].北京理工大學(xué)出版社，2009.
[2] 李德群.唐志玉.中國(guó)模具工程大典[M].北京電子工業(yè)出版社2007.3
[3] 閆閔.塑料壓縮成形與金屬模鍛成形對(duì)比研究[D].青島理工大學(xué)，2008.
[4] 劉金剛.CAD/CAM在高精密復(fù)雜模具設(shè)計(jì)與制造中的應(yīng)用[J].中國(guó)高新技術(shù)企業(yè)，2015，
27:61-62.
[5] 楊化林.基于知識(shí)的注塑模具設(shè)計(jì)若干技術(shù)研究[D].浙江大學(xué)，2006.
[6] 馮剛，張朝閣.我國(guó)注塑模具關(guān)鍵技術(shù)的研究與應(yīng)用進(jìn)展[J].塑料工業(yè)，2014，4:16-19.
[7] 何政軍.基于實(shí)例的注塑模具CAD/CAE/CAM技術(shù)研究與應(yīng)用[D].華北電力大學(xué)，2014.
[8] 許柳青.特征技術(shù)在注塑件及其模具設(shè)計(jì)中的應(yīng)用研究[D].湖南大學(xué)，2001.
[9] 吳啟峰.注塑模具零件分類體系及其參數(shù)化圖庫研究[D].大連理工大學(xué)，2004.
[10] 張新杰.基于成本核算的注塑模具報(bào)價(jià)系統(tǒng)的研究與開發(fā)[D].山東大學(xué)，2005.
[11] 陳兵.汽車塑件注射模設(shè)計(jì)[J].模具制造，2015，9:49-53.
[12] 李英，楊蘭玉，焦洪宇.基于UG的盒蓋注塑模三維設(shè)計(jì)[J].塑料科技，2015，12:82-84.
[13] 莊儉.微注塑成型充模流動(dòng)理論與工藝試驗(yàn)研究[D].大連理工大學(xué)，2007.
[14] 徐斌.微注塑充模流動(dòng)尺度效應(yīng)及其模具關(guān)鍵技術(shù)研究[D].大連理工大學(xué)，2010.
[15] 王雷剛，倪雪峰，黃瑤，王勻.微注射成型技術(shù)的發(fā)展現(xiàn)狀與展望[J].現(xiàn)代塑料加工應(yīng)
用，2007，1，55-58.
[16] 胡曉楠.基于CAD/CAE的冰箱接水盒注塑模具設(shè)計(jì)[D].東北大學(xué),2008.
[17] 李坤.注塑模具標(biāo)準(zhǔn)模架及其常用零部件和標(biāo)準(zhǔn)件三維參數(shù)化圖形庫的研究與開發(fā)[D].
大連理工大學(xué)，2000.
[18] 楊彬.模具高效加工方法與工藝規(guī)程制定[J].企業(yè)技術(shù)開發(fā)，2016，6:10-11.
指導(dǎo)教師 教研室主任
2020 年 3 月 5 日 年 月 日
塑料模具的編制和使用
M. B.鮑里索夫 華聯(lián)666.5:666.3.032
石膏模具被廣泛用于鑄造陶瓷行業(yè)所需的用具。除了具有一定的優(yōu)勢(shì)，由于它們工作表面下穿在體內(nèi)的水分和電解質(zhì)的行動(dòng)，所以還具有機(jī)械強(qiáng)度低，工作壽命短的好處。除此之外，在烘干機(jī)的溫度不能高于65度，高于此溫度石膏將被銷毀。
陶瓷產(chǎn)業(yè)開始安裝時(shí)，尋找替代石膏的必要性增加為半自動(dòng)成型和干燥加劇干燥條件機(jī)。我們的工廠1967年開始搜索替代石膏，并為此組織了一個(gè)研究小組，其中包含以下工人：AV Savel'eva，PS波利亞科夫，電訊管理局局長(zhǎng)Pashkova，弗吉尼亞州Kholkin，AV SarichevF. I. Lisov，和其他人。
該研究小組在國(guó)家陶瓷研究的數(shù)據(jù)指導(dǎo)研究所開始工作。但是，這并沒有回答一些工廠工作所產(chǎn)生的問題，例如：如何按模具設(shè)計(jì)和制造，以避免打擊在兩個(gè)平面的交點(diǎn)開裂面，一批每單位體積的模具，安排用什么熱處理，如何獲得均勻分布的孔隙，一般增加孔隙度，以及如何避免被人體堅(jiān)持等。
他們的研究結(jié)果之后，本集團(tuán)于1969年開始準(zhǔn)備開發(fā)PVC模具，并轉(zhuǎn)換其使用的工廠的生產(chǎn)線。
目前的時(shí)間有五板生產(chǎn)線，其中三個(gè)是在工廠淺200毫米板和兩個(gè)深200毫米板，以及七行杯。使用塑料生產(chǎn)模具的24000板和35-37,000杯每一天（24小時(shí)）。臨時(shí)的，每年可節(jié)省從所得只有一條生產(chǎn)線的引進(jìn)，為2500盧布。
世界杯生產(chǎn)的塑料模具的工作壽命達(dá)到4000個(gè)周期，仍然可以增加。板生產(chǎn)模具的生活仍然沒有得到確定。
他們的工廠于1969年舉辦了一個(gè)準(zhǔn)備模具部分（圖一）。原料是國(guó)內(nèi)的聚氯乙烯乳膠，L - 5級(jí)，或乳化聚氯乙烯，E級(jí)62。聚氯乙烯是氯乙烯聚合的產(chǎn)物。
（圖一）（圖二）
它是一個(gè)白色的細(xì)分散（沒有殘留于0056篩號(hào)）粉末，密度1.41克/厘米3。在溫度聚氯乙烯顆粒170-180℃和輕微的壓力下（具體壓力0.05公斤/厘米2）融化和凝聚。
在第一階段編制的模具是一個(gè)初步的振動(dòng)成型（上振動(dòng)表）確保統(tǒng)一的孔隙度。 振動(dòng)表執(zhí)行50振蕩幅度0.5/秒。 振動(dòng)成型是開展為15-20秒。
初步振動(dòng)成型是模具的過程中必不可少的一部分，因?yàn)?，在成型過程中，產(chǎn)生內(nèi)部應(yīng)力集中分子接觸點(diǎn)附近細(xì)顆粒的凝聚力。在燒結(jié)過程中，這種內(nèi)部的壓力是特別危險(xiǎn)的。它可以被刪除振動(dòng)，這幾乎完全打破了粒子之間的所有連接，并確保其均勻分布。
在這塊編制的塑料模具的基本設(shè)備是金屬?zèng)_壓模具（圖二）這是45級(jí)或圣3鋼。其內(nèi)部表面必須鍍鉻。
圖一、手壓；2）SNOL電加熱模具熱處理柜；3）內(nèi)閣
冷卻模具；4）表的組裝和拆除；5）站在準(zhǔn)備模具；6）存儲(chǔ)
站在塑料；7）電加熱干燥柜；8）完成的模具；9）表
塑料包裝；10）為測(cè)量出塑料表；11）振動(dòng)表。
圖二、按模。 A）組裝；B）拆除。
如圖扁平制品（板）塑料模具填補(bǔ)按模的過程（圖三）。
L-5粉末，以前在ll0℃在干燥柜干燥，然后篩選通過第05號(hào)篩，收費(fèi)是按模矩陣，并用專用工具夷為平地。 膠量取決于模具的類型（卷）。為淺200毫米板，它是600克，深200毫米板660克，碗碟400克，并為杯500-515克。按模具打孔，然后插入在這樣一種方式，它根據(jù)其自身的重量進(jìn)入，直到它與塑料接觸矩陣。要檢查裝配在這一點(diǎn)上的正確性，沖床旋轉(zhuǎn)矩陣。
組裝沖壓模具放在震動(dòng)表壓縮為15-20秒。壓縮之后，矩陣法蘭和打孔法蘭之間的差距應(yīng)該是8-10。
頂部，從而給了0.05公斤/厘米2的壓力。監(jiān)測(cè)溫度，溫度計(jì)插入因此，它觸及沖床中心。一個(gè)少量的塑料堆打孔法蘭，其顏色的變化，是用來評(píng)估模具的準(zhǔn)備。加熱過程持續(xù)2-3小時(shí)，在其完成的按模的溫度是170-175度。
熱過程完成后，溫度計(jì)被刪除并采取按模內(nèi)閣，并放置到通風(fēng)降溫的內(nèi)閣。按模，然后拆除使用一個(gè)提取螺絲。準(zhǔn)備的塑料模具被刪除，修剪邊緣光滑，經(jīng)檢查后已準(zhǔn)備就緒。
中空制品（杯）模具準(zhǔn)備根據(jù)以下的時(shí)間表。正確的聚氯乙烯塑料的金額投入矩陣（圖四），并穩(wěn)定下來。兩個(gè)22-24毫米厚的間隔被放置在法蘭矩陣1，矩陣2降低到使法蘭盤上休息的間隔。然后放進(jìn)沖3環(huán)，使法蘭與水平法蘭盤。
組裝沖壓模具，然后上交上震動(dòng)表法蘭下降，與打孔法蘭站在一個(gè)50 × 50毫米塊。然后墊片。從法蘭盤上取下，矩陣的底部放置8-10公斤的重量，定位，其中心軸沖壓模具。振動(dòng)器是打開背后的法蘭環(huán)塑料振搗15-20秒。在振動(dòng)矩陣和沖壓法蘭之間的間隙應(yīng)約5-7打孔法蘭和環(huán)約在10毫米之間。按模具，然后上交，和5-6毫米打孔法蘭奠定了厚厚的包裝，然后重量放在這給壓力的0.05公斤/厘米2的熱處理過程。
按模具的重量，放在一個(gè)粘土基地6-8厘米，在電干燥柜厚根據(jù)的1.5-2 h（圖5）的溫度加熱過程進(jìn)行了180-185℃水銀溫度計(jì)監(jiān)測(cè)溫度。在熱處理結(jié)束負(fù)載被刪除，記者將電柜壓在手上按直到環(huán)和沖壓模法蘭矩陣法蘭接觸。 10分鐘后保留下的新聞按模拆除，放置在通風(fēng)內(nèi)閣降溫至40-45℃按模被拆除和準(zhǔn)備的塑料模具中提取，修整后投入使用。
（圖3) （圖4）
（圖5）
圖3、1）停止墊圈；2）環(huán)；3）沖床；4）模具；5）聚氯乙烯。
圖4、 1）矩陣；2）環(huán)；3）沖床；4）螺釘；5）模具。
圖5、加工塑料模具的熱處理圖。
直徑為200毫米的鋼板。
在這些聚氯乙烯模具的準(zhǔn)備和他們?cè)诠S使用的經(jīng)驗(yàn)表明，從上述的準(zhǔn)備計(jì)劃的偏差，導(dǎo)致各種故障在外觀這表明，在與他們形成制品的過程中的模具顯示下按，材料的孔隙率空心模具的肩膀上，下環(huán)上的空心模具的干裂縫。
恒定控制調(diào)溫的干燥柜內(nèi)閣確保一個(gè)統(tǒng)一的期間的沖壓件的熱處理室的溫度，并確保均勻加熱對(duì)于所有的塑料厚度。由此產(chǎn)生的燒結(jié)均勻，防止模具生產(chǎn)與塑料之間的邊緣和中心熱膨脹系數(shù)不同。這大大降低模具的工作表面在使用過程中發(fā)生裂縫，并增加其工作生活。
積累使用的模具工廠經(jīng)驗(yàn)已經(jīng)表明，它是必要的支付注意：半自動(dòng)機(jī)底座下的模具持有人仔細(xì)調(diào)整;選擇成型的時(shí)間表;避免與身體接觸的時(shí)刻的輥突然降低;選擇正確的成型輥的速度（300-550 轉(zhuǎn)杯和板250-275轉(zhuǎn)）和模具持有人（750-800 轉(zhuǎn)杯和板300-500轉(zhuǎn)）為了避免生產(chǎn)廢“嗡嗡聲”和“呼呼聲”。如果不遵守這些要求，也可導(dǎo)致模具的損壞（崩過肩，并挖掘出與中空制品的底部）。
生產(chǎn)的模具，不同的顏色從玫瑰到深褐色，根據(jù)工期在不斷的壓力和電柜最后溫度的熱處理。深褐色的具有低孔隙度，并在實(shí)踐中不能使用。彩色的上升有足夠的工作性質(zhì)，但其機(jī)械強(qiáng)度低，大大降低了他們的工作生活。
獲得均勻分布的毛孔孔隙率31-35％的正常工作，并在同一同時(shí)保留必要的機(jī)械強(qiáng)度，在生產(chǎn)中最棘手的問題之一是模具。如果被迫熱處理，這迅速導(dǎo)致表面地殼的外觀原料在模具內(nèi)部。為了加快熱量，如果最終溫度升高高于210℃治療，這導(dǎo)致了塑料的分解與摧毀了表面的氣體演變模具。經(jīng)廣泛調(diào)查后，按模塑料的最佳加熱時(shí)間表，這給模具所需的質(zhì)量，如圖五。
在編制和使用的模具，塑料的正確金額的經(jīng)驗(yàn)，每單位體積模具被確定為0.9克/厘米3。這使其他因素保持不變，保持為不斷密度模具。
模具驗(yàn)收的技術(shù)標(biāo)準(zhǔn)，建立了工廠。他們必須有一個(gè)順利密集的工作表面和均勻的色彩匹配既定的標(biāo)準(zhǔn)。尺寸變化不得超過正負(fù)0.05％。模具必須有沒有變形。他們的孔隙率必須在31-35％之間。其吸水率決定在工廠開發(fā)出一種方法。
在這些模具制品的表面要求沒有進(jìn)一步的治療，這是一個(gè)商業(yè)優(yōu)勢(shì)。石膏的工廠消費(fèi)減少了每年500萬噸。勞動(dòng)力需求重型裝載/卸載工作是減少，勞動(dòng)者的工作/模塑解除，交通是釋放。
廠隊(duì)將繼續(xù)引進(jìn)更進(jìn)步的方法準(zhǔn)備工作加快增加輸出給每按模模具的熱處理工藝，塑料模具，并要提高其機(jī)械強(qiáng)度，同時(shí)保持高孔隙度。
參考文獻(xiàn)
1、S．M. Tsenter et al，Steklo i Keram，第1號(hào)（1969年）。
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THE PREPARATION AND USE OF PLASTIC MOLDS M. B. Borisov UDC 666.5:666.3.032 Plaster molds are widely used for casting wares in the ceramics industry. Apart from certain ad- vantages, they have a low mechanical strength and short working life due to wear of the work surface under the action of water and electrolytes in the body. Besides this, the temperature in the dryer cannot be higher than 65 as above this temperature the plaster is destroyed. The necessity of finding a substitute for plaster was increased when the porcelain industry began in- stalling semiautomatic machines for molding and drying, with intensified drying conditions. The search for a substitute for plaster began in our factory in 1967, and to this end a group was organized containing the following workers: A. V. Saveleva, P. S. Polyakov, T. A. Pashkova, V. A. Kholkin, A. V. Sarichev, F. I. Lisov, and others. At the start of their work the research group were guided by data from the State Ceramics Research Institute 1. However, this did not answer a number of questions arising from the working of the plant, such as: how to design and make press molds so as to avoid cracking in the plane of intersection of two surfaces, what batch to take per unit volume of mold, what schedule to use for the heat treatment, how to obtain uniform distribution of pores and increase general porosity, and how to avoid adhering by the body, etc. Following on the results of their research, in 1969 the group began developing the preparation of PVC molds, and converting the production line of the factory to their use. At the present time there are in the factory five production lines for plates, three of which are for shallow 200 mm plates and two for deep 200 mm plates, as well as seven lines for cups. Using the plastic molds a totalof24,000 plates and 35-37,000 cups are produced per day (24 h). The provisional annual saving accruing from the introduction of only one production line is 2500 rubles. The working life of the plastic molds in cup production reaches 4000 cycles and can still be increased. The life of the molds in plate production has still not been determined. A section for preparing the molds was organized in the factory in 1969 (Fig. 1). The raw material was domestic polyvinylchloride latex, grade L-5, or emulsified polyvinylchloride, grade E-62. Polyvinyl- chloride is the product of polymerization of vinyl chloride. It is a white finely dispersed (no residue on No. 0056 sieve) powder of density 1.41 g/cm 3. At a tempera- ture of 170-180 and under slight pressure (specific pressure 0.05 kg/cm 2) the polyvinylchloride par- ticles melt and cohere. The first stage in the preparation of the molds is a preliminary vibromolding (on the vibrotable) which ensures uniform porosity. The vibrotable performs 50 oscillations/sec with an amplitude of 0.5 ram. The vibromolding is carried out for 15-20 sec. This preliminary vibromolding is an essential part of the process for making the molds, since, during molding, internal stresses are generated which are concentrated near the points of contact of molec- ular cohesion of the fine particles. This internal stress is especially dangerous during the process of sin- tering. It can be removed by vibration, which almost completely breaks all connections between particles and ensures their uniform distribution. The basic piece of equipment in the preparation of the plastic molds is the metal press-mold (Fig. 2) which is made from grade 45 or St. 3 steel. Its internal surface must be chromium plated. Dulevo Porcelain Factory. Translated from Steklo i Keramika, No. 3, pp. 7-9, March, 1972. 9 1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 g/est 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $i5.00. 147 ,.- 13 500 l 2 3 45 6 fi IO 9 8 7 Fig. I Fig. 2 Fig. I. i) Hand press; 2) SNOL electrically heated cabinet for heat treatment of the molds; 3) cabinet for cooling the molds; 4) table for assembly and dismantling; 5) stand for prepared molds; 6) storage for the plastics; 7) electrically heated cabinet for drying; 8) stand for finishing the molds; 9) table for packing plastics; i0) table for measuring out plastics; ii) vibrating table. Fig. 2. Press-mold. a) Assembled; b) dismantled. The process of filling the press-mold for making flat ware (plates) plastic molds is shown in Fig. 3. L-5 powder, which has previously been dried in the eleetrodrying cabinet at ll0 and then screened through a No. 05 sieve, is charged into the matrix of the press-mold and leveled with a special tool. The amount of plastic depends on the type (volume) of the mold. For shallow 200 mm plates it is 600 g, for deep 200 mm plates 660 g, for saucers 400 g, and for cups 500-515 g. The press-mold punch is then in- serted into the matrix in such a way that it enters under its own weight until it is in contact with the plastic. To check the correctness of assembly at this point, the punch is rotated relative to the matrix. The assembled press-mold is placed on the vibrotable and compacted for 15-20 sec. After com- pacting, the gap between the matrix flange and the punch flange should be 8-10 ram. The press-mold is next inserted into SNOL electrocabinet for the heat process and a weight is placed on the top so as to give a pressure of 0.05 kg/cm 2. To monitor the temperature, a thermometer is inserted so that it touches the center of the punch. A small amount of the plastic is heaped on the punch flange, and its change in color is used to assess the readiness of the mold. The heat process continues for 2-3 h and at its completion the temperature of the press-mold is 170-175 After the completion of the heat process, the thermometer is removed and the press-mold taken from the cabinet and placed into the ventilated cabinet to cool. The press-mold is then dismantled using an ex- traction screw. The prepared plastic mold is removed, trimmed smooth at the edges, and after inspection is ready for use. The molds for the hollow wares (cups) were prepared according to the following schedule. The cor- rect amount of PVC plastic was put into the matrix Fig. 4) and leveled off. Two 22-24 mm thick spacers were placed on the flange of the matrix 1, and the matrix 2 lowered onto it so that the ring flange was resting on the spacers. The punch 3 was then lowered into the ring so that its flange was level with the ring flange. The assembled press-mold was then turned over and placed flange down on the vibrotable, with the punch flange standing on a 50 x 50 mm block. The spacers were then. removed from under the ring flange, and a weight of 8-10 kg placed on the bottom of the matrix, positioned to that its center lay on the axis of the press-mold. The vibrator was turned on and the ring held behind the flange vibrated the plastic for 15-20 sec. After vibrating the clearance between the flanges of the matrix and punch should be about 5-7 ram, and between the punch flange and the ring about 10 mm. The press-mold was then turned over, and 5-6 mm thick packing laid on the punch flange, and then the weight placed on this which gave the pressure of 0.05 kg/cm 2 for the heat process. The press-mold, with the weight, was placed in the electrodrying cabinet on a fireclay base 6-8 cm thick. The heating process was carried out according to the graph (Fig. 5) for 1.5-2 h up to a temperature of of 180-185 The temperature was monitored by a mercury thermometer. At the end of the heat treatment the load was removed and the press-mold taken from the electrocabinet and pressed on the hand press until 148 Fig. 3 tc 160 _ . =.: .iu/ 0 20 40 60 80 lOO Time, rain Fig. 4 Fig. 5 Fig. 3. 1) Stop washer; 2) ring; 3) punch; 4) die; 5) polyvinylchloride. Fig. 4. 1) Matrix; 2) ring; 3) punch; 4) screw; 5) mold. Fig. 5. Heat treatment graphs for processing plastic molds. 200 mm diameter plates. 1) For cups; 2) for shallow the ring and punch flanges made contact with the matrix flange. After retaining under the press for 10 min the press-mold was removed and placed in the ventilated cabinet to cool down to 40-45 The press-mold was dismantled and the prepared plastic mold extracted. After trimming it was ready for use. Experience in the preparation of these polyvinylchloride molds and in their use in the factory has shown that deviation from the above preparation schedules leads to the appearance of various faults in the molds which show up during the process of forming wares with them: underpressing, porosity of the ma- terial under the shoulders of the hollow mold, ring cracks on the stem of the hollow mold. Constant control of the electrodrying cabinet by means of the thermoregulator ensures a uniform temperature in the chamber during the heat treatment of the pressings, and ensures uniform heating of the plastic for all section thicknesses. The resultant uniformity of sintering prevents the production of a mold with different coefficients of thermal expansion between the edges and center of the plastic. This greatly reduces the occurrence of cracks in the working surface of the mold during use and increases its working life. Accumulated experience in the use of the molds in the factory has shown that it is necessary to pay attention to: careful adjustment of the mold holder under the pedestal of the semiautomatic machine; selec- tion of the molding schedule; avoiding sudden lowering of the roller at the moment of contact with the body; the selection of the correct speed for the molding roller (500-550 rpm for cups and 250-275 rpm for plates) and for the mold holder (750-800 rpm for cups and 300-500 for plates) in order to avoid the production of scrap in the form of humpers and whirlers. Failure to observe these requirements can also lead to damage to the mold (chipping off the shoulder, and digging out the bottom with hollow ware). The molds when produced vary in color from rose to dark brown, according to the duration of the heat treatment at constant pressure and the final temperature in the electrocabinet. The dark brown ones have low porosity, and in practice cannot be used. The rose colored ones have adequate working proper- ties, but their low mechanical strength significantly reduces their working life. Obtaining the normal working porosity of 31-35%, with uniformly distributed pores, and at the same time retaining the necessary mechanical strength, was one of the most difficult problems in the production of the molds. If the heat treatment was forced, this rapidly led to the appearance of a surface crust with a raw interior in the mold. If the final temperature was raised above 210 in order to speed up the heat treatment, this led to decomposition of the plastic with the evolution of gases which destroyed the surface of the mold. After extensive investigation, the optimum heating schedule for the plastic in the press-mold, which gave molds of the desired quality, was found and is shown in Fig. 5. From experience in the preparation and use of the molds, the correct amount of plastic per unit vol- ume of mold was established as 0.9 g/cm 3. This enables, with other factors remaining constant, to main- tain a constant density for the molds. The technical criteria for acceptance of the molds were established in the factory. They must have a smooth dense working surface and a homogeneous color matching the established standard. Dimensional 149 variations must not exceed =0.05%. The molds must have no deformations. Their porosity must fall within the limits 31-35%. Their rate of water absorption is determined by a method developed in the factory. The surface of wares made in these molds requires no further treatment, which is a commercial advantage. The consumption of gypsum by the factory is reduced by 500 tons per year. The labor re- quirement on heavy loading/unloading work is reduced, the work of the laborer/molders is relieved, and transport is released. The factory team continue to work on the introduction of more progressive methods of preparing plastic molds, on speeding the heat treatment process to give increased output of molds per press-mold, and on increasing their mechanical strength whilst preserving a high porosity. 1. LITERATURE CITED S. M. Tsenter et al., Steklo i Keram., No. 1 (1969). 150