H. Serdar MUTLU1, Yunis YILMAZER2
1 Assoc. Prof. Inonu University, Faculty of Fine Arts and Design, Ceramics Department,
Traditional shaping methods in plaster mold for ceramic production, are still in use with their thousands of years background. But as a result of the social life and urbanization by the beginning of industrial age, the high pressure method has been developed to meet the faster, easier, cheaper and quality ceramic production demand. This system has been developed in Switzerland and Germany in the 1960s for the production of various ceramics particularly of medical equipment, tableware ceramics and floor and wall tiles, and the operation requires setting up some specific equipment beforehand such as the preparation of cupping sludge, air pressure, heating, vacuum and water systems and the preparation of synthetic molds.
Compared to the traditional plaster mold production, faster, smoother products with high moist and dry strength within a smaller area makes it possible for the drilling, cutting and retouching operations to be carried out easier. This method has a high production capacity, allows for high quality products being produced with automation and needs less manpower. Durable, elastic, easy-to-assemble, easy-to-store molds used in the system do not require any re-drying process thus allow for energy saving and reduce the production costs. With these and suchlike advantages, high investment costs needed when there’s a product model change, may be considered as the only disadvantage of this method.
In this study, the high pressure cupping technology used in the production of medical equipment, are investigated on site with the purpose of contributing to the studies of researchers, undergraduate and postgraduate students in this field.
Keywords: Industry, Ceramic, High Pressure Method.
INDUSTRIAL CERAMICS PRODUCTION
Traditional production methods beginning with the invention of ceramic, has a thousands of years of history until they’re carried into workshops and further into factories by the invention of the lathe. But the industrial production of medical equipment with silica content, is as short as a century.
In the ceramics factories seen in the industrial age, the high pressure cupping method is preferred in the production of medical and tableware ceramics for faster, cheaper, quality products with high market competitiveness.
This study focuses on the use of high pressure cupping method in medical equipment. With more advantages compared to the traditional plaster mold production, this method requires some installations such as pressure, vacuum, heating and water systems and molds made of polymeric materials. With this method, the difficulties in the limited production of molds, the energy used in the preparation of molds for cupping and drying them, the loss of time and labor and the storing of molds, have been cleared up.
The cupping systems used to this day are separated into five categories; Hand Cupping, Battery Cupping, Mechanized Cupping, Capillary Cupping and Pressure Cupping System. The common purpose of all is to make fast and cheap production conforming the high quality standards. As the plaster molds are poorly resistant to 10-15 bars vacuum and air pressure, some molds containing concrete, sintered metal, synthetic plaster and various organic materials, have been tried in 1922 and in the end polymeric synthetic resin molds have been developed (1).
The high pressure cupping method has been brought in to the ceramics industry with the collaborative works of the Swedish Laufen company and the German Dorst company in 1960s. Later on, other ceramic machinery and mold manufacturers have also manufactured pressure cupping presses and molds such as the Sacmi in Italy, the Netzch in Germany, others from European countries and the Unimac, Ukcast and Genitec in Turkey (2). The computer technology and engineering used in this system allows for easier and faster production and provides stronger and smoother products coming out of mold. It leads to less retouching labor, high quality, fast production and low costs in the products.
Some pre-programmed systems such as; the Cupping Sludge System, Pressured Air System, Vacuum System and Water System are required in this production method.
HIGH PRESSURE CUPPING PARAMETERS
In the high pressure cupping production method, the parameters in basic are summed up and shortly explained below in 4 groups such as; the cupping sludge parameters, model parameters, mold parameters and the machinery and system parameters.
2.1. High Pressure Cupping Sludge Parameters
For a fast and continuous production, the cupping sludge is desired to have some variable properties such as physical, chemical, viscosity, thixotropy and rheologic properties. And these are observed to affect the grain size and granulation, filtration and mold operating time in general. Particularly the deflocculant type and the change in the water rate causes a change in rheologic properties therefore leads to a cupping clay including less water, lower use of deflocculant substance and a formation with more open pores so speeds up the filtration process.
Having a fluidity in an ideal cupping sludge depends on the use of various electrolytes at specific ratios and in the case of surplus in this ratio, the cupping sludge needs to be checked constantly in order to prevent glomeration.
2.2. Model Parameters in High Pressure Cupping
The prototype model designs also significantly affect the cupping parameters of vitrified products to be manufactured with high pressure cupping technology. The mold pressures to be used in the production of some models, should not be over 10 bars. This way, it’s possible to avoid fractures in critical vitrified products by increasing high pressure levels. All the details of a model should be examined well before transferring the designs of some models with very thick body and longer mold drying time, into cupping molds (1).
2.3. High Pressure Cupping Mold Parameters
While manufacturing the resiny molds to be used in high pressure cupping benches, the grain sizes of the mold’s raw materials and the polymerization of the resin need to be kept under control and the heating and mixture periods need to be particularly paid attention to. This way, it becomes possible to better adjust the pore size, pore distribution and the mechanical strength of the mold.
While manufacturing the resin mold composed of different parts, there are some stringent standard processes which need to be done in order for the properties of all the parts to be equal (3). As well as allowing for exposure to high pressure, water systems and pressured air, these molds should be prepared in a way to allow also for a negative pressure applied to the cupping part for the mold parts to be able to be attached to the mold. And to make it possible for all these to be taken under control, the mold needs to have a high mechanical strength. It's generally desired for the mold to have outer metal reinforcement suitable for a system of inner canals which provide homogenous distribution of air and water flows and vacuum application. For instance; Shown in Figure 1 are these such details on the technical drawing of the section of a sink mold. In the drawing, you can see the system combined of cylindrical canals of 15-20 mm in size and 10-12 mm in diameter, extending at a right angle to the cupping surface. The opening of these canals is connected to each other with the canals under the aluminum plate covering the mold from back. This way, it’s ensured to work a s collector for various liquids and vacuum distributed into the mold canals.
Figure 1. Schematic Drawing of a Sink Mold in Pressure Cupping (Yilmazer, 2020)
To get a high quality product with high pressure vitrified cupping, the pores of the mold should be homogeneous. On the contrary case, there will be fractions in the products generally during the drying process of the production. In addition, the cupping sludge to be used needs to be prepared suitable for production method and an ideal micro pore structure needs to be chosen for the production mold (3).
2.4. Machinery Parameters in High Pressure Cupping
The production machinery parameters in this system can be sorted as; the cupping pressure, the thickening time of the product, the temperature-discharge time-discharge pressure of the cupping sludge, the hardening time-pressure of the product in the mold and the demolding time-pressure of the product. Most of these parameters are dependent to each other.
Visual 1. High pressure sink cupping system bench (Bien Seramik, 2020)
For production is faster and constant in high pressure cupping, periodical maintenances and repairs of the resin molds and machinery should be carried out with detailed checks at every phase of the production (1), (Visual. 1).
3. PROPERTIES OF HIGH PRESSURE CUPPING TECHNOLOGY
These properties can be sorted as; the pressure’s, pore’s, rheology’s, the cupping sludge temperature’s effect on the thickening time of the cupping clay in the mold and the deflocculation status’s, specific gravity’s and the cupping sludge type’s effect on the dry shrinking. Brief explanations to these are given below. According to this;
1. The thickening time of the cupping sludge in the mold, varies relevant to the pressure applied on it. This variation is tended to be logarithmic or we can say that consecutive pressure increases on the cupping sludge leads to smaller increases in the formation speed of the product. (4).
2. The thickening time and ratio of the cupping sludge in the mold is understood to be independent from the pore structure of the resin mold (4).
3. The rheological structure of the cupping sludge, significantly affects the thickening time of the product in the mold. Rheology is a branch of science studying the deformation of materials exposed to some force from outside. The distribution and flow of the solid particles in the cupping sludge, shows rheological variances with the pressure applied to it. Using water in cupping sludge as a distribution media causes a double layer structure to be formed together with a self-subsisting electrical layer in the interface layers of the clay and other solid particles. This situation ensures a pull and push force to occur between the particles in the cupping sludge. Therefore, the cupping sludge’s rheology is highly important in medical equipment production.
The success of production with an ideal cupping sludge depends also on deflocculation status along with the product’s thickness, density and easy-drying- the well-accepted basic properties of the product (3). In general, the permeability of the high pressure cupping sludge being as low as possible, significantly reduces the thixotropy effect in the thickening time of the product (4).
4. Increasing the cupping sludge temperature reduces the thickening time of the product in the mold. This is because, it speeds up the cationic change reactions that cause the thixotropic properties of the cupping sludge to increase (4). To prevent this, the cupping sludge temperature needs to be changed as well as adjusting the thixotropy rate and conforming to reference viscosity and thixotropy values. By increasing the temperature in cupping sludge, the viscosity of the water in it is reduced (3) and the thickening time of the product in the mold is shortened.
5. The thickening times of the cupping sludges manufactured for different functions in the mold varies according to the deflocculation, thixotropy and viscosity properties. For this reason, the physical and chemical properties of the cupping sludge prescriptions need to be adjusted according to the type and the features of the functional product to be manufactured.
6. The cupping sludge’s type affects the thickening time in the mold. Both high pressure cupping sludge and resin molds should be prepared according to the product type preferred to be manufactured.
7. One of the properties with the most effect on the thickening time of the cupping sludge in the mold is the porous structure of the cupping sludge. This structure, with the thickening of the cupping sludge and the increase in the pressure applied to it, varies according to the following properties in basic; grain sizes and granulation of solid materials in the cupping sludge, grain structures and localization during the thickening process. In addition, the mobility of the cupping sludge grains makes it easier for the cupping sludge to form out and enhances the product’s resistance against water filtration with its’ even surface. This way, it increases the thickening time of the cupping sludge in the mold, ensures the particles to heap together in a specific surface and prevents plate layouts to be formed very close to each other (3).
3.1. Cupping Pressure’s Effect on Dry-Shrinking
In this part of the study, the cupping pressure’s effect on the dry-shrinking of the product is examined. In order to better determine the results of this process, same cupping sludge has been cupped both into a clay mold and a resin mold and the dry-shrinking of the obtained products were compared. As the product produced with the pressure cupping system contains less moisture, its’ dry-shrinking rate is found out to be relatively less than the traditional clay mold cupping (3).
The dry-shrinking of the product produced with the high pressure cupping technology, is very limited for it happens vertical to the cupping surface. It’s because, the cupping sludge grains are aligned well and tight-knitted to each other so the water molecules elevates to the surface in the same direction. The shrinking occurs parallel to the cupping sludge so the moist in the product structure decreases as much as the pressure applied to the cupping sludge increases (4).
3.2.Production System with the High Pressure Cupping Technology
The closure of the high pressure cupping molds are performed by a cylindrical piston controlled by the hydraulic unit and works with a pressure of 120-160 bars (5), (Visual. 2).
Visual 2. Closure of high pressure cupping molds. (Bien Seramik, 2020)
Heated to a temperature of 30-35°C in traditional clay mold production, the cupping sludge is heated to a temperature of 40-50°C and increased in viscosity in high pressure cupping technology to shorten the thickening time in resin molds. Then the cupping sludge is filled into the resin molds at a specific ratio to its’ own weight, exposed to a pressure of 10-15 bars and ensured to reach a thickness of 9-10 mm in 12-20 minutes. This process time is seen to take up to 60 minutes in productions with traditional clay molds.
The heating process and the applied pressure to quickly give thickness to the cupping sludge, rapidly cupping sludge to fill up the pores in the resin mold and ensures it to be removed out of the structure. This way, the thickening time of the product in the mold is shortened and afterwards the pressure valves are closed. The excess cupping sludge from the areas to be left empty according to the product type, is discharged with the pressured air applied into the mold. Then all valves are closed and the cupping system is taken into a full stop. Hot air at a pressure of 4-5 bars and a temperature of 30-40°C is repelled for 15-20 sec. to the inner surface of the product in the mold. This ensures the inner surfaces of the product to quickly dry out and harden. After the drying process of the inner surfaces is finished, the air is discharged out of the product and the mold is dismantled into parts. To remove the moist product from the mold and clean off the cupping clay water from the pores on the synthetic mold surface, air is pressured into the mold with 5 bars for 5-6 sec (Visual. 3-4). This way, the semi-wet product is removed of the mold parts with any deformation and easily taken onto the product jacket.
Visual 3. Taking the semi-wet product of from the high pressure mold without any deformation and taking it out onto the product jacket. (Genitec 2020).
Visual 4. Cleaning off the cupping sludge water from the pores on the high pressure mold surfaces (Genitec, 2020).
After process like opening assembly holes on the low moist product, it’s put on the drying vessels. The moist rate is relatively lower than the cupping with clay mold, that’s why the semi-wet products taken out from the pressure cupping allows for all kinds of processes on them without getting deformed easily (2), (Visual.5).
Visual 5. Being able to carry out all kinds of processes on the semi-wet product without getting deformed. (Bien Seramik, 2020)
3.4. Advantages of High Pressure Cupping System
The advantages of this automation-based production can be listed as;
The high quality production capacity between 20.000 and 100.000 pieces in a smaller area compared to traditional clay mold production,
It’s long-life, and no need for surface preparation on molds prior to cupping,
Little amount of labor and loss of time, easy mold assembly, production and storing (1),
Being in need of less manpower, ensuring size standards at high quality (4),
Obtaining products with smooth surfaces and carrying out less retouching in resin molds,
Semi-wet products gaining hardness for it contains lower amount of moist, thus allowing for instant drilling, cutting and retouching processes (4),
Ensuring faster and constant production, having less deformations in drying and firing the products (2),
Ensuring energy saving for synthetic molds are not dried out compared to clay molds and having more durable and easier mold assembly (1).
3.5. Disadvantages of High Pressure Cupping System
In general, it’s hard to specify a disadvantage of the high pressure cupping technology. But as it involves high investment costs (4), molds produced for a few models only are used for a long time and being unable to start a different model production and requiring high investment costs when starting a change in product model type, can be considered as a disadvantage(1).
Traditional production methods beginning with the invention of ceramic, has a thousands of years of history until they’re carried into workshops and further into factories by the invention of the lathe. But the industrial production of medical equipment with silica content, is as short as a century. Cupping system with high pressure method has been developed in turning the medical equipment, tableware ceramics and floor and wall tiles into faster, cheaper products with more quality and higher market competitiveness to meet the increasing demand of societies by the industrial revolution.
In this study, the system in the factory using high pressure method in medical equipment production, has been examined and its’ advantages and disadvantages compared to traditional clay mold production have been researched. It involves some installation used in high pressure production such as the pressure, vacuum, heating and water systems and information on molds made of polymer materials. The limited production of the clay mold, the preparation of molds for cupping, loss of energy and time and labor and difficulties in storing the molds are compared with this method. In addition, it’s examined in five categories of cupping production methods used to this day; hand cupping, battery cupping, mechanized cupping, capillary cupping and pressure cupping systems.
In the literature review carried out, it’s found out that the high pressure cupping system has been developed in 1960s by the Swedish Laufen and German Dorst companies. In the later years, the press and mold systems of this method have begun to be manufactured and used also in Italy, Germany, European countries and Turkey. For the production in this system is carried out with computer-assisted automation, the need for qualified manpower has diminished. For this reason, it allows for faster and easier production and the products taken out from the mold are higher in strength and smoothness compared to clay mold. It’s preferred because it shows less retouching labor, higher quality, faster production and lower costs in the products. It’s used in the production of various ceramics particularly of medical equipment, tableware ceramics, floor and wall tiles. It’s also determined that it ensures energy-saving and reduces the production costs with durable, elastic, easy-to-assemble and easy-to-store synthetic molds used in the system without any need to dry out the molds again. Alongside the advantages brought in by this system, requiring high investment costs only when a product model change is started, is taken as a disadvantage.
In conclusion, the high pressure cupping technology used in the production of medical equipment, has been examined on site in the production factories manufacturing in our country and the purpose is contributing to the studies of researchers, undergraduate and postgraduate students in this field.
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