Seramik sağlık gereçlerinde ikinci pişirme sırları
Başlık çevirisi mevcut değil.
- Tez No: 55880
- Danışmanlar: PROF.DR. SERDAR ÖZGEN
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 92
Özet
ÖZET Tüm üretim süreçleri sonunda olduğu gibi Seramik Sağlık (Vitrifiye) gereçleri üretim süreci sonunda da bazı hatalı mamuller ortaya çıkmaktadır. Bu hatalı mamuller emek, zaman ve para kaybına yol açmaktadır. Bu kayıpların oranı üretim sürecindeki birçok aşamadan herhangi birinden kaynaklanan bu hataların ek bir işlem ile giderilmesi eğilimini geliştirmiştir. Basit bir tamir işlemi ile, bu işlem sonucunda kazanılabilecek hatalı mamullerin değerinin İşlem maliyetini amortise edeceğinin görülmesi bu eğilimi hayata geçirmiştir. Seramikte son sözü ateş söyler realitesi gözönüne alınırsa herhangi bir pişirme işlemi yapmadan tam olarak tamir işlemi yapmak mümkün değildir. Dolayısıyla genelde yüzeydeki hataların giderilmesi mümkün olduğundan, bu yüzey hatalarını kapatacak ve aynı zamanda alttaki bünyeyi, pişmeden kaynaklanabilecek deformasyon ve çatlaklardan koruyacak bir pişirme süreci geliştirilmiştir. Bu süreç ikinci pişirme olarak adlandırılmıştır. İkinci pişirme rejimlerinde, eğer rejim tünel fırın rejiminden oldukça farklı ise normal işletme sırları kullanılmaz ve bazı değişiklikler yapılması zorunludur. Bu tez çalışmasında yerel bir Seramik Sağlık (Vitrifiye) Gereçleri fabrikasındaki tamir işlemi ve ikinci pişirme rejimi şartlan göz önüne alınmıştır. İkinci pişirme sıcaklığı blister ve deformasyon oluşumuna neden olmayacak kadar düşük, tamir yerinde matlık ve bozuk yüzey oluşumuna neden olmayacak kadar yüksek olarak programlanmıştır. Bu ikinci pişirme rejimi sabit tutulmaktadır. Dolayısıyla, bu tez çalışmasında yukarıda açıklanan şartlar altında ıskarta mamuller üzerindeki hatalı bölgeleri tatminkar bir şekilde kapatacak ve yeni hatalara yol açmayacak bir sır kompozisyon geliştirilmesine çalışılmıştır. Denemelerde başlangıç olarak tünel fırın rejiminde olumlu sonuç veren bir sır baz alınmıştır. Bu sır daha sonra ikinci pişirme rejimine tabi tutulmuştur. Bir sırın kullanımını belirleyen özellikleri olarak erirlik katsayısı, yüzey gerilimi, viskosite, akış davranışı gibi bazı kriterler yayında özellikle tamir yerinde sağladığı kamuflaj göz önüne alınmıştır. Yukarıdaki sırın ikinci pişirme rejiminde olumlu özellikler sağlamadığı görülmüştür. Daha sonra bu sırın kompozisyonunu değiştirilerek çeşitli denemeler yapılmıştır. Değiştirilen her sırın kompozisyonu ikinci pişirme rejimine tabi tutularak sonuç özellikleri incelenmiştir. Birçok sayıdaki denemeden sonra optimum özelliklere sahip ve mamuller üzerindeki hatalı bölgeleri tatminkar derecede kamufle eden bir sır kompozisyonu geliştirilmiştir. IX
Özet (Çeviri)
REFIRING GLAZES IN SANITARYWARE SUMMARY In so called China Sanitaryware production process, there have been five basic stages; which are 1 -Casting slip and Glaze slip preparation 2-Slip Casting 3 -Drying 4-Glazing 5-Firing In these stages the technologies, technigues and machines can vary, but this order never changes. In Batching, raw materials are classified as masse materials and glaze materials. This is because the masse and glaze is differently and seperately prepared. The masse materials are different types of Clay, especially Slip Casting Clays, Kuartz, Feldspars and Kaolens. The slip casting clays are high in alcali content and they are water purified and the kuartz is grounded into fine particles. Also all materials must have a spesific particle size distribution. In masse suspension production kuartz, feldspar and kaolen are wet milled in rotating mills. After milling and further sieving particle size distribution is controlled, if the result is in the chosen limitations, the suspension will taken to the blunger which is octangle in shape. Clays (plastic type) are added in this stage and a proper mixing has done also the electrolites like sodium silicate and sodium carbonate which are added also aids this mixage and gives suspension optimum slip properties. The casting slip is a suspension of the nonplastics and clays in water. It is necessary that the slip casting suspension should be of high concentration and yet be fluid enough to pump through pipe lines, to pour into the plaster moulds, to flow into every corner of the mould and so faithfully reproduce the shape intended, and to drain cleanly from the mould after casting. Casting-slips have to be made up at a higher concentration (measured as pint weight) so that the plaster mould is not required to remove too much water during the casting process, and so become saturated with water. At the high pint weights required for slip casting, the suspension would be extremely viscous and impossible to use if some deflocculantfor clay-containing bodies are sodium silicate and sodium carbonate, and these may be used either singly or more frequently together. The practical importance of the deflocculation is that it produces a suspension of high pint weight which is at the same time fluid enough to allow it to be slip cast. The deflocculant acts chiefly on the clay in the body and the nature of the clay is important in determining the effectiveness of any particular deflocculant. As well as pint weight and viscosity, there is a third important property of casting-slip, which has to be controlled for successful casting, i.e. thixotropy. If a clay suspension is well stirred, it may be fluid and easily pourable. If the suspension is then left undisturbed for some time it will gradually thicken, and in extreme cases it may thicken to such an extent that the container may be inverted without loss of the suspension. On vigorous stirring the suspension again becomes free flowing. This property of some suspensions to become more viscous with time when left at rest is known as thixotropy and is an important property of suspensions used in slip casting. Addition of a deflocculant to casting-slip as well as drastically reducing the viscosity also reduces thixotropy. It is desirable to leave a small amount of thixotropy in the slip to give extra firmness to the cast and to keep a reasonably high rate of casting. Too high a value of thixotropy produces a“flabby”cast which is easily distorted, and on shaking may return to the fluid state and flow. The amount of deflocculant added is therefore adjusted to give a high fluidity but to leave a small amount of thixotropy in the slip. The common use as deflocculant of mixtures of sodium silicate and sodium carbonate is due to the fact that in general the silicate gives high fluidity to a slip but tends to completely destroy thixotropy, whilst the carbonate leaves a considerable thixotropy in the slip on achieving the same fluidity as the silicate. If the two deflocculants are mixed, slip can usually be prepared with high fluidity and a small residual thixotropy and there slips give good casting properties. Once a casting-slip has been adjusted to the required values of pint weight, fluidity and thixotropy, it is desirable that these properties should remain reasonably constant until the slip has been used. As well as producing the required fluidity and thixotropy in the slip, the deflocculant should therefore also produce a stable slip in which the fluidity and thixotropy do not vary excessively with time. The glaze materials are Kuartz, Feldspars, Kaolen, Dolamit, CaCOî, BaC03, ZnO and Zirkon as the opacifier. All of these materials are in non - plastic character except kaolen. Kaolen Commonly used to avoid precipation of the glaze solution. XIThese materials are mixed in adequate proportions and wet milled further sieved. Also this glaze solution is controlled for particle size distribution. If it is adequate the prepared glaze is transported to the glazing lines. There are different types of slip casting which have different moulds are technologies but the principle of slip casting is very simple. While slip which contains a large volume of water loses its water, it takes the shape of the mould. Slip casting's conventional method generally uses plaster moulds. This moulds take the water of the slip because of capilar effect. The time and quality of this casting technique depends on the slip and mould properties. If the slip does not have the proper silicate amount or contains to much water it will cause many defects. For instance the slip stays in the plastic form very long and this will delay the period of proper thickness or sometimes no matter what the time has been passed the slip does not have the proper rigidity. The pore volume, size and distribution of the moulds also have fatal effect on slip casting efficiency. There are two main plaster mould slip casting methods; hand - slip casting and mechanized slip casting. In the hand slip casting fill in and out of the moulds is done by the workers and it is especially adequate for heavy products which are difficult to handle. This casting method needs very large place and takes very long time so other casting methods tried to developed. In the machanized slip casting fill in and out of the moulds done by the pressured vessels and a group of moulds squeezed by the presses. Thus, significant time and labor savings can be achieved. The time of dewetting of slurry İs the limiting factor of slip - casting, in plaster moulds this is relatively slow and this reduces the efficiency of manufacturing. The time can be reduced by using extra force but the moulds must be compatible to this force. This problem has been solved by using plastic moulds which have inner paths that water can be passed. Thus, the installation of pressured slip - casting machines come in to life. In this system a pressure is given to the slurry and casting time reduced significantly. Also this plastic moulds have a very long strength and product / time ratio reduces as expected. Although the shaped ware has a level of rijidity they need subsequent drying. If the products does not have the proper amount of water, the fast dewetting stage in firing may cause some deformations and cracks. Also these wet ware can not properly glazed. Furthermore this may cause unwanted glaze - masse reuctions and may decay the surface of the products. Drying is a pysical period and it depends on the temperature and time. Too high temperatures may cause thin fast dryed layer of surface which is non - permeable so the inner parts rescues wet. The much time causes over - drying. XIIAfter this stage glazing takes part. This the last stage before firing. The glazes commonly sprayed into the surfaces of products with air pressure. This method is called spray method and done by the help of special vessels called pistoles. The amount of glaze has an important role on the success of the finished product. Glazing can be done by human or by programmed machines. The permanent properties of this machines made them preferred over human The last and a very important stage of the process is firing. Almost all of the mistakes done in former stages that can not be seen, come into reality in this stage. Also the unadequate firing process may cause fatal defects. The firing rejime must be compatible with the optimized masse and glaze requirements. The final product must carry some specific properties so to ensure this properties we must propose the reactions in masse, in glaze and between glaze and masse. We must avoid from under and over - firing. The firing process commonly takes place in tunnel kilns in which the temperature zones are stationary and the ware moves through this zones. In these kilns the energy consume is relatively low and the reliability is very high. After all this stages against of the all care taken on the factors that can cause defects like; unexpected properties, labor faults, it is unable to eliminate defective wares. This defective wares reduces efficiency and profit. For this reason a tendecy to repair this defective wares has been growth. After an simple operation the defective wares must be repaired reliably. This is done by development of refiring processes. Refiring process must not cause further defects on repaired wares thus refiring rejime has been altered. Commonly the refiring time and maturing temperature is lower than tunnel kiln firing rejimes. For this reason there must be a glaze which is compatible with refiring requirements. This glaze must cover the defects and make no difference on sight of the surface of the finished ware. This thesis consists of altering refiring glazes in current circumtances of a domestic sanitary ware plant. Mostly the white wares are producted so this thesis commonly insists on refiring glazes of white wares. Glazes which have currently been used in the plant, have been designed for tunnel kiln regimes whose maturing temperature is 1250° C and the firing time is 16.5 hours. Obviously, when the wares which are repaired, are fired under this regime then deformations and blistering can be occured. Consequently a new regime has been developed by improving the quantatives of two factors: temperature and time. XIIIIn the factory which has been under observation, refiring regime comprises the maturing temperature and time whose values are respectively, 1190° C and 13 hours. Furthermore, due to do fact that repairing operation is variable and not permenant, the usage of shuttle kilns has been preferred. At these kilns, while the ware is constant, the temperature is variable. In this thesis, experiments for development of glaze which suits the above conditions have been made. Initially, since the maturing temperature is not very low, the addition of frit to the glazes has not been chosen. Subsequently a glaze formula which matures at 1250° C has constituted a starting point. After that, the proportions of the glaze constituents have been changed as each raw glaze which has been tried, has been fired in the shuttle kiln then the resulting properties have been observed. Next, when a suitable glaze formula for refiring rejime has been obtained it has been attempted to get the colour of the white wares which has to repaired. After wards, for this operation a ceramic stain has been added to the formula moreover with several trials, the proper colour has been endeavured to be obtained. Furthermore, the glaze should comprise thermal expansion and surface tension which do not cause any defect. Finally a proper glaze has been reached which is suitable for usage without any problem. XIV
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