History of refractory bricks Refractory materials

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I. The ironization of production tools and the development of the iron smelting industry: After the Warring States period, thanks to advances in iron smelting technology, changes in the social and economic system, and an increasing demand for iron in society, the extraction of iron ore, as well as the smelting and casting of iron, became important handicrafts that had a significant impact on the country’s economy and people’s livelihoods. As a result, the iron smelting industry began to develop. There were already many iron mines developed during the Warring States period. The work from that era, the \"Shan Hai Jing·Wu Cang Shan Jing\", lists 37 mountains that produced iron; among those mentioned as belonging to Nanyang is the mountain of \"Di?NF9A5?\", where \"there is much iron on its shady side\", located roughly between Biyang County and Nanyang County in present-day Henan Province ； The other location is the “Mountain of Rabbit Beds, where there is much iron on its sunny side,” situated roughly between present-day Songxian County and Nanyang County. During the Warring States period, all states had iron-smelting industries, among which those of Han and Chu were the most developed, with the greatest number of famous iron-smelting sites. At that time, Nanyang had already become a renowned iron-smelting center during the Warring States era. The chapter ‘On Military Strategy’ in Xunzi states: “Wan’s heavy iron weapons are fierce, like bees and wasps.” ”By the Qin and Han dynasties, ironware and iron smelting technology had been widely spread and used across large areas. Archaeological findings show that by the early Western Han Dynasty, iron farming tools and instruments had replaced those made of copper, bone, stone, and wood. By the middle of the Western Han Dynasty, with the advancement of iron-smelting technology, more forged iron tools appeared, and iron weapons gradually came to play a dominant role. By the Eastern Han Dynasty, all major weapons were made of steel, thus completing the process of ironization of both weapons and production tools. ?In the early Western Han Dynasty, the iron smelting industry could be operated by merchants. The Kong family of the Wei state was originally engaged in iron smelting; after the Qin dynasty conquered Wei, they were forced to move to Nanyang, where they became extremely wealthy through iron smelting. During the reign of Emperor Wu of the Western Han Dynasty, he appointed Kong Zhi, a iron merchant from Nanyang, as the \"Director of Agriculture\" in charge of salt and iron affairs, thereby overseeing the country’s salt and iron industry. Nanyang thus became one of the industrial hubs in the country where iron-related officials were stationed. At the Han Dynasty iron smelting site excavated in Wafangzhuang, Nanyang, iron-smelting relics from the Western Han period were discovered (furnace bases, refractory bricks, blast pipes, molds used for casting, as well as iron tools including iron plowshares, iron harrow shares, iron picks, adzes, axes, etc.). By the Eastern Han Dynasty, based on the foundations laid during the Western Han Dynasty, the iron smelting industry in Nanyang saw an increase in the number of smelting workshops, an unprecedented expansion in their scale, and significant improvements in technology. Iron smelting sites discovered near Nanyang after the founding of the country include: the iron casting workshop site in Wafangzhuang, Beiguan, Nanyang City; the Dazhangpi iron smelting site in Zhangpi Village, Tongbai County; the Tielu Village site in Tongbai County; the Taishanmiao and Caodian iron smelting sites in Nanzhao County; the iron smelting site in Zhaohe Village, Fangcheng County; the iron molds and castings site in Anguo City, Zhenping County; and the iron smelting stones in Baishijian, Xixia County. The Han Dynasty iron smelting site excavated in Wafangzhuang, Beiguan, Nanyang City from 1959 to 1960 covers an area of 2,800 square meters. A large number of remains and artifacts related to iron smelting were discovered there, including 9 furnaces for melting iron, 8 furnaces for tempering steel, and 1 forging furnace. It was found that, under the production conditions at that time, hot blast furnaces were used in the iron smelting process; these were furnaces that saved thermal energy and were used in China in the early days. There are nearly 40 types of molds and patterns used in casting. The artifacts unearthed through archaeological excavations show that Nanyang had already become a national center for metallurgy at that time. II. Development of iron smelting technology and processes: Iron smelting technology further developed during the Qin and Han dynasties. Blast furnace ironmaking has become an economical and effective method for iron production. In blast furnace ironmaking, material is fed from the top while air is blown in from below, creating a relative movement in which the charge descends and the gas rises. The high-temperature gas generated by the fuel rises through the material layer, transferring heat to the furnace charge; the carbon monoxide contained in it simultaneously acts as a reducing agent for iron oxide. In this way, the thermal and chemical energy of the fuel are both utilized to a fairly high extent; the material at the lower layer is gradually reduced until it melts, while the material at the upper layer slowly descends from the top of the furnace. The fuel is preheated, allowing for a higher combustion temperature. This is indeed a relatively reasonable smelting method, and thus it has retained its vitality and been used for a long time. The development of its smelting capabilities is reflected in the following aspects: First, the technology used for building blast furnaces for iron production has reached a high level. Some are constructed using rectangular or arc-shaped refractory bricks fired from yellow or red refractory clays with a high content of silicon trioxide. The fire-resistant bricks unearthed from the Wafangzhuang site in Nanyang vary in terms of the material used, thickness, and shape depending on the location. Some use white quartz sand particles with a diameter of 0.3–0.5 cm, mixed with a small amount of fine sand. Some are made by mixing grass with mud, yellow clay, and a large amount of quartz sand; the quartz sand used includes both natural varieties and those that have been processed and crushed. The fire resistance strength of these refractory bricks ranges from 1463°C to 1469°C, which is clearly the result of the incorporation of sand and gravel containing a high amount of silicon dioxide into the refractory soil. Given that the acidic slag produced by ancient blast furnaces in China contained a relatively high amount of silica, such acidic refractory material is appropriate. Second, most of the raw materials used in blast furnace ironmaking have been processed. Smelting workers have found through long-term practical experience that uniform particle size of the charge can reduce resistance to coal gas. Therefore, the raw materials had to be processed before smelting. At the site in Zhangfan Village, Tongbai County, thousands of tons of ore powder were unearthed, indicating that great attention was paid to the processing of ore at that time. In addition to blast furnace ironmaking, the crucible ironmaking technique was also discovered during the Western Han Dynasty. At the Wafangzhuang site in Beiguan, Nanyang City, 17 crucible furnaces were discovered, 3 of which are relatively intact and all are roughly rectangular in shape. One of them is 3.6 meters long, 1.82 meters wide, and has a remaining depth of 0.82 meters. The method of constructing the furnace involves digging a rectangular pit in the ground, leaving a door opening, and after ramming the surrounding walls, applying a thin layer of mud on them. The roof of the furnace is constructed from arc-shaped refractory bricks of varying sizes. The inner surface of these bricks is covered with a layer of refractory mortar about 1 centimeter thick; a thin layer of grayish-white magma remains on the surface of this mortar. The back side of the bricks is coated with a thicker layer of mud made from straw, about 5 centimeters thick. Part of it was built using adobe and mud mixed with grass. The furnace consists of four parts: a door, a chamber, a furnace body, and a chimney. The door is at the very front of the furnace and is used for loading the furnace and ensuring ventilation; both the left and right walls have been burned and are now brick-gray in color. The pool is inside the door, and its surrounding walls are also painted grayish-brown. There is a layer of fine sand about 1 centimeter thick on the bottom of the pool, which seems to have been used as a \"chimney\" for combustion. The furnace chamber is rectangular, with its surrounding walls coated in mud mixed with straw; the fire intensity is low. It was likely used to hold crucibles arranged in rows, as well as fuels such as wood and charcoal. There are 3 chimneys at the back of the furnace, intended for expelling the smoke from it. Some stoves are filled with wood ash, while the bottoms of other stoves contain many burned soil clods and fragments of bricks and tiles. Three crucibles were found; all were oval-shaped pottery jars with round bottoms. A layer of mud mixed with grass, about 3–4 centimeters thick, covered the outside of these jars. The interior of the mud had turned a red brick color, while the surface was a shiny dark black color, with a layer of grayish-white, shiny magma present as well. Additionally, fragments of iron slag were also stuck to the inner wall of another crucible. Based on the structure of the furnaces and the crucible iron-smelting method that was passed down through the ages, it can be inferred that the iron-smelting technique at that time involved first mixing crushed ore with charcoal and fluxes, placing this mixture in a crucible. Before putting the crucible into the furnace, a suitable amount of brick and tile fragments were laid at the bottom of the furnace to ensure proper ventilation there ； Many \"craters\" were left in which flammable materials could be placed to facilitate ignition; afterward, a layer of charcoal was spread over them, and crucibles were arranged in rows on top of the charcoal ； Then, another layer of charcoal is placed on top of this layer of crucibles, and more crucibles are arranged in rows on top of the charcoal. Once the furnace is filled, a flame can be ignited at the \"flame opening,\" and air can be blown in to reduce and melt the ore in the crucibles into pig iron. ?Third, the development of blower technology. The development of blast furnace ironmaking and iron smelting technologies is inseparable from the improvements in blast technology. In ancient China, leather ‘bladders’ were used as blowers in iron-smelting furnaces. Over time and with the accumulation of experience, people gradually changed the methods of blowing air. In large smelting furnaces, there is more than one blower; additional blowers and air ducts are used to ensure complete combustion of the fuel within the furnace, thereby raising its temperature and accelerating the smelting process. At the iron-smelting site in Wafangzhuang, a large number of blast pipes were unearthed; some of these were ceramic blast pipes with elbows. The inner diameter of the thicker end was approximately 100 mm, while that of the thinner end was 50 mm, and the length of these pipes was around 400 mm. Since the clay layer beneath the air supply duct in the pottery body was burned, it was determined that the burning temperature was between 1250°C and 1280°C. From then on, based on temperature and the artifacts unearthed, it can be determined that the iron-smelting furnaces in Nanyang during the Han Dynasty were equipped with hot blast systems (\"Iron Smelting in Nanyang during the Han Dynasty\", Zhongzhou Ancient Books Publishing House, December 1995, page 23). ). This device uses the residual heat from the furnace mouth to turn the cold air in the air ducts into hot air, which is then blown into the furnace. This not only increases the furnace temperature but also reduces the smelting time, thereby improving the quality of the molten iron. In terms of blowing power, there were human-powered blowing methods, as well as animal-powered blowing methods such as those using horses or cows. In the 7th year of Jianwu during the Eastern Han Dynasty (31), Du Shi served as the governor of Nanyang; he invented the \"water bellows\" which used water power for ventilation, and promoted their use. Using water-driven blowing to cast farming tools requires less effort while yielding better results compared to using manual blowing. The iron-smelting site discovered today in Zhangfan Village, Tongbai County, is located far from the mines and instead beside a river; this is likely because water wheels were used to blow air into the smelting process. The invention and application of water wheels not only improved the blowing capacity but also **reduced costs, which is why they were widely used in the iron smelting industry for a long time. Blowing machinery powered by water like this did not appear in Europe until more than 1,100 years later. ? Improvements in blast furnace technology promoted the development of iron smelting technology. In addition to the rapid development of iron casting technology, processes for softening cast iron were developed, giving rise to gray cast iron and ductile iron. Analysis of the iron artifacts unearthed from the Han Dynasty iron smelting site in Wafangzhuang, Beiguan, Nanyang City, shows that agricultural tools from that period were primarily made of malleable cast iron. Of the 12 farming tools tested, 9 were malleable cast iron, 2 were cast iron decarburized steel, and 1 was white cast iron. This indicates that softening techniques have been employed in the cast iron. In terms of quality, the cast iron softening technology at that time was already quite stable. The iron pick No. 135, unearthed from the Eastern Han Dynasty strata at the Wafangzhuang iron smelting site, has a graphite structure that did not form in its cast state but was created during high-temperature annealing; yet it has a regular shape close to spherical with smooth edges, which enhances the mechanical properties of the artifact. III. Steel refining, cast iron decarburization, steelmaking technologies, and casting techniques: To meet society’s demand for steel products, the \"steel refining\" technique was developed by the late Western Han Dynasty. This technique involves heating pig iron to a molten or nearly molten state and then refining it, thereby removing carbon from the iron to produce steel or wrought iron. ? Six furnace types identical to those found at the Han Dynasty iron smelting site in Tieshenggou, Gongxian County, were also discovered at the Han Dynasty iron smelting site in Zhaohe Village, Fangcheng County, Nanyang City. This type of iron frying furnace has a small volume, is barrel-shaped, and allows for concentrated heat ； Digging it underground turns it into a ground furnace, reducing heat loss and helping to increase the temperature ； The lower part of the furnace is designed in a \"pot bottom\" shape to facilitate material loading and mixing. In addition, several steel-firing furnaces were also found at the iron-smelting site in Wafangzhuang, Beiguan, Nanyang City; their design and construction methods were largely similar, with iron blocks present at the bottom of the furnaces. Based on the findings from this site, the iron-smelting workshops in Wafangzhuang, Nanyang, not only cast ironware but also used pig iron to produce steel or wrought iron, thereby forging tools and other components. Chisels, spades, and similar tools were also unearthed at this site; they were likely chisels, spades, etc. manufactured by the workshop itself. Archaeological evidence shows that by the Eastern Han Dynasty, steel refining technology was already widely used. An iron knife from the Eastern Han Dynasty was unearthed in the eastern suburbs of Nanyang. It has a rather unique design, resembling a knife used for cooking; there is a weld mark on its blade that runs parallel to it. The knife is 11.2 centimeters wide, about 17 centimeters long, and approximately 0.5 centimeters thick at the back. It is well-preserved and was forged from steel that had been heated and worked (Henan Provincial Museum et al.: “A Preliminary Study of Iron Smelting Techniques in the Han Dynasty in Henan”, Acta Archeologica Sinica, Issue 1, 1978). ). By the late Western Han Dynasty, simple steel-smelting furnaces had been invented, and the development of techniques for converting pig iron into wrought iron or steel marked a new stage in steel-smelting technology. This led to an **increase in steel production**, which was of great significance for the improvement of production tools and the wider use of steel products at that time. In ancient steelmaking, low-carbon pig iron or wrought iron was used as raw material, and steel was produced by carburization (a method still in use today); another approach involved using high-carbon pig iron as raw material and producing steel through decarburization in a solid state. During the Warring States period, softening treatment processes were already in use: pig iron was subjected to decarburizing annealing, resulting in cast iron and decarburized steel components with incomplete decarburization (Li Zhong: “A Study on the Development of Steel Smelting Techniques in the Early Feudal Period in China,” Acta Archeologica Sinica, Issue 2, 1975). ), this technique was still in use during the Han Dynasty. For example, the iron axes unearthed from the iron-smelting site in Wafangzhuang, Nanyang, have a white-metallic structure in their center, with a steel composition in their surface layer. Ironware similar to this has also been found at other sites. They are all made from white cast iron blanks, which are annealed in an oxidizing atmosphere to cause decarburization of the outer layer; moving from the surface inward, the structure becomes pure ferrite, hypoeutectoid, and eutectoid respectively. Due to incomplete decarburization, the interior remains iron, and it is actually a composite material composed of steel and iron. In another case, the decarburization is relatively complete, with all case structure removed, but some graphite precipitates in the inner layer. For example, an iron chisel unearthed in Wafangzhuang, Nanyang, appears to be a cast piece from its appearance, and metallographic analysis of its surface shows a steel structure, which can easily lead to the mistaken assumption that it is a steel casting. Under the technical conditions of the Han Dynasty, without high temperatures above 1500°C and the corresponding refractory materials, it was impossible to produce liquid cast steel. Another iron chisel unearthed in Wafangzhuang, Nanyang, was tested and found to have a hypereutectoid steel matrix with residual graphite in its interior, proving that it is a steel tool that has been decarburized. Furthermore, shaped thin iron plates were also unearthed at the Wafangzhuang iron smelting site in Nanyang; these plates had actually undergone decarburization treatment, becoming steel plates with a lower carbon content, and could be forged into utensils, thus representing the creation of a new steel-making process. This expands the range of uses for pig iron and increases the sources of high-quality steel, playing a significant role in steel production. ? The heat treatment techniques for cast iron saw significant development during the Han Dynasty, reaching a state of maturity. Of the 9 agricultural tools unearthed at the Wafangzhuang iron smelting site in Nanyang, 8 were found to be made of ductile cast iron with a black heart; they were of good quality, and some of them showed little difference from modern ductile cast iron with a black heart. There is also a type of white-heart ductile cast iron; this type can be used to manufacture hand tools that are resistant to impact and have excellent performance. Black-heart ductile cast iron, on the other hand, can be used to make agricultural tools that are resistant to wear. Among the cast iron products, some such as iron shovels, iron plowshares, and iron spades are white-heart ductile cast iron. ? Judging from the discovered iron-smelting sites from the Han Dynasty, some workshops were mainly engaged in iron smelting as well as the casting of ironware, while others specialized in the casting of ironware. The initial iron castings were made by pouring molten iron directly from the iron smelting furnace. During the Han Dynasty, specialized iron smelting furnaces were developed, which was highly beneficial for improving the quality of molten iron and producing high-quality castings. As can be seen from the Wafangzhuang site in Nanyang, the structure of the iron-smelting furnaces and the materials used in their construction differed significantly from those of iron-forging furnaces, indicating that the division of labor between iron smelting and iron forging was already well-defined at that time. ? Seven iron-smelting furnaces were unearthed at the Wafangzhuang iron-smelting site in Nanyang. The method of constructing them involved laying a layer of mud mixed with grass on a flat surface, with a diameter of about 2.6 meters and a thickness of 50 mm; this layer was then burned to an orange-yellow color to serve as the foundation for the furnace. The furnace bottom is hollow and consists of an integral base, corbelled supports, peripheral walls, and the bottom of the furnace bowl. The base is approximately 45 mm thick and is paved with refractory clay mixed with a large amount of coarse sand, the particle size of which is around 10 mm. The furnace-building materials for the surrounding walls and supports are slightly different from those of the base. It contains a large amount of fine-grained sand. The wall thickness is 40–50 mm, the diameter of the pillars is 70–120 mm, and their height is 70 cm. Based on the dimensions of the rectangular fire-resistant bricks found at the site, it is estimated that there might be around 15 pillars, with the bottom of the furnace chamber built upon these pillars. The furnace body is entirely constructed from arc-shaped refractory bricks. Based on the varying degrees of melting on the inner surface of these bricks, the furnace body can be divided into three zones: the furnace mouth and the three or four layers of bricks below it (with brick lengths of 36 cm, widths of 17 cm, and thicknesses ranging from 6 to 9 cm). In this zone, the refractory lining shows slight signs of melting and there are many crack patterns; it is the zone with the lowest temperature, serving as a preheating area. The third and fourth layers of bricks in the middle of the furnace, as well as the furnace lining, are all fired, indicating a high temperature; this must be the reduction zone. Three or four more layers of bricks down, the furnace lining generally melts and even completely flows away, exposing the brick structure; this is the area with the highest temperature, likely the oxidation zone near the air inlet. Based on the height of the refractory bricks and the aforementioned burning conditions of the furnace wall, the height of the blast furnace body is estimated to be around 3–4 meters. The furnace wall of the iron smelting furnace is divided into 3 layers: the arc-shaped refractory bricks are specially made shaped bricks covered with mud mixed with straw, with a thickness of about 15–50 mm; an inner lining is applied, with a thickness of about 40 mm. Based on the curvature of the 14 relatively intact refractory bricks found at the site, the minimum outer diameter of the iron smelting furnace was 1.16 m and its inner diameter was 0.92 m; the maximum outer diameter was 2.3 m and the inner diameter was 2.14 m. The average inner diameter was around 1.5 m. Upon inspection, the refractory bricks were all made from a mixture of sand particles and clay. In terms of the particle composition of the quartz sand, there were rounded as well as angular white quartz particles along with a small amount of feldspar, indicating that in addition to natural sand, artificially crushed sand particles were also used. The presence of cracks in the quartz particles, as well as the formation of needle-like mullite crystals within the glass phase along with a flow structure, all indicate that the iron oxidation furnace was capable of reaching quite high temperatures at that time. ?Judging from the large number of air supply pipes unearthed at the site, heat-exchange type hot air devices may have been used during iron smelting. There are ceramic air supply pipes covered with about 45 mm of mud mixed with straw; the upper layer of mud melts and drips, while the mud near the corners melts and flows down along the corners. According to temperature measurements, the melting temperature was likely between 1250°C and 1280°C. There is an explanation for this burning condition of the ducts: it might have been installed on top of the furnace to serve as a preheating duct. Furthermore, among the large number of iron fragments and slag unearthed, there are many trapezoidal iron plates as well as fragments of iron tools such as plows, spades, axes, hoes, and picks (with a thickness of about 40–70 mm). These relics may have been raw materials used in iron smelting furnaces; the square anvil and hammer served both as forging tools and as instruments for breaking down the raw materials. The large amount of charcoal residue indicates that the fuel used was charcoal; there were charcoal clumps remaining in the furnace, some of which were fused together with the slightly melted iron on the surface, and some of the vessel shapes could still be identified. It is speculated that this phenomenon may be the result of layered charging. Judging from the excavated furnace lining, its cross-section is clearly divided into three layers, indicating that the furnace was shut down and repaired at least twice; the material used for the repairs was the same as that used for the refractory bricks. Based on the artifacts unearthed, it is inferred that for a furnace of such size, operation was likely semi-continuous, with molten iron being produced at regular intervals to cast a batch of molds. The furnace should be shut down at the appropriate time when melting has lasted too long or the casting is complete. This shows that the craftsmen of the Han dynasty had already mastered the operating procedures for furnaces well. The casting technology of the Han Dynasty further developed upon the techniques used during the Warring States period for casting iron and bronze artifacts. At that time, the molds used for casting included clay molds, pottery molds, and iron molds; in particular, the use of iron molds improved both the quality and efficiency of iron casting to varying degrees. Judging from the various molds and patterns unearthed in Wafangzhuang, Nanyang, the manufacturing process is roughly as follows: mold makers select local yellow clay, mix in about 35% fine sand, add water to form the clay mixture, and create the molds. They then carefully carve the surfaces of these molds, shaping the various parts on each surface according to strict dimensional requirements. After the mold surface is prepared, paint it and let it dry; this is the first and essential step in mold making. Before casting, the mold is first closed, reinforced with clay, and then sent into a furnace for baking. Once it reaches the desired temperature, the baking process is stopped and the mold is taken out of the furnace; iron melt is then poured in while it is still hot. During pouring, the gates and risers are filled with iron melt to accommodate the shrinkage of the mold cavity. Once the iron mixture has solidified to a certain extent within the mold cavity, the reinforcing mud is removed, the mud mold is taken out, and then the gating iron is removed, thereby obtaining the iron casting mold. Then, the upper and lower molds of the cast iron are joined together, the iron core is inserted into the mold cavity, and some iron tool is used to secure the molds in place, so as to prevent cracking due to the thermal expansion of the molten iron during pouring. After the mold is assembled, it can also be placed in a furnace for heating; then molten iron is poured into it. Once the molten iron has solidified to a certain extent, the mold is opened and the gates and risers made of iron are removed, thereby yielding the final product. ? The development of casting techniques is also reflected in the field of laminated casting technology. The die-casting technique involves stacking multiple molds or mold pieces layer by layer, and using a single feeding channel to cast multiple castings at once. This method was invented during the Warring States period (Zi Xi: “On the Molds of Several Ancient Artifacts,” Cultural Relics Reference Materials, August 1957). ), it is mainly suitable for the mass production of small castings. During the Han Dynasty, the technique of stacked casting saw further development. For example, a Han Dynasty drying furnace was discovered in Wenxian County, Henan Province, from which more than 500 sets of stacked casting molds were unearthed. There were 16 types of castings and 36 different sizes; each set of molds consisted of 4 to 14 layers, with 1 to 6 castings per layer. In some cases, as many as 84 items could be cast at once, thereby **increasing production efficiency**. Several stacked and slightly melted artifacts, as well as three to five stacked V-shaped iron plow share components, were unearthed at the Wafangzhuang iron smelting site in Nanyang, providing strong evidence that Nanyang was one of the earliest regions to employ the double-stack casting technique in iron smelting. ?The design of the molds is also quite scientific; the layer of clay between the mold cavities is very thin, which helps to minimize the amount of clay used and keep the mold surfaces compact. In some molds, the gates are designed to be oval in shape, and the tenon-and-mortise alignment mechanisms used for joining the molds are arranged according to this principle as well. The shape of the mold corresponds to that of the casting cavity; in many cases, the corners of the mold are removed to ensure as uniform a wall thickness as possible. This not only reduces the volume of the mold and the amount of clay required, but also promotes more even heat dissipation, thereby improving the quality of the castings. For the fabrication of Fan Xin, in addition to using a built-in clay core, those with a simple shape have clay strips pressed into the core holder. Complex ones, such as the mud core for vehicle hatches, are made using mud-based split-core molds. The multi-stack casting molds (die mouths) from the Eastern Han Dynasty discovered in Wafangzhuang, Nanyang, feature vertical parting lines that divide the mold blocks in two. The two stacks of casting molds share a single sprue, which results in a higher metal yield and shorter pouring time, indicating further development in casting technology.