First, the test plan
(1) Main raw materials and auxiliary materials
The main raw material: the base material with self-produced high-temperature alumina as the filter medium, the material does not react with the aluminum liquid, does not dehydrate during the roasting process, the shrinkage rate is very small, and the physical and chemical properties (see Table 1) are relatively compared. stable.
The auxiliary materials mainly include: kaolin , feldspar and bentonite . The chemical composition is shown in Table 2.
Table 1 High-temperature alumina physical properties %
Al 2 O 3 | SiO 2 | Fe 2 O 3 | Na 2 O | CaO | MgO | True specific gravity / g · cm 3 | Median diameter D 50 /μm |
93.4 | 0.09 | 0.036 | 0.475 | 0.084 | 0.0084 | 3.89 | 0.688 |
Table 2 Chemical composition of auxiliary materials
Component | SiO 2 | Fe 2 O 3 | Al 2 O 3 | CaO | MgO | Na 2 O | K 2 O | Burning down |
Kaolin | 60.81 | 0.10 | 24.5 | 1.20 | Trace | 0.16 | 5.29 | 5.59 |
Feldspar | 68.49 | 0.39 | 13.0 | 2.19 | 0.21 | 3.44 | 3.73 | |
Bentonite | 60.20 | 6.24 | 16.00 | 1.80 | 2.57 | 0.18 | 1.58 | 10.0 |
(2) Low temperature binder
Low Temperature Synthesis of binder: aluminum hydroxide or pseudoboehmite Shanlv production of industrial water and phosphoric acid was synthesized by the following reaction:
Al 2 O 3 ·nH 2 O+6H 3 PO 4 →2Al(H 2 PO 4 ) 3 +(n+3)H 2 O (1)
Al 2 O 3 ·nH 2 O+3H 3 PO 4 →Al 2 (HPO 4 ) 3 +(n+3)H 2 O (2)
Al 2 O 3 ·nH 2 O+2H 3 PO 4 →2AlPO 4 +(n+3)H 2 O (3)
(1) The Al(H 2 PO 4 ) 3 and the Al 2 (HPO 4 ) 3 formed in the formula (2) have cohesiveness, and the former has the most cohesiveness, and the latter is the second, and in the formula (3) The aluminum phosphate is non-adhesive. In order to ensure that aluminum dihydrogen phosphate is produced instead of aluminum phosphate, excessive phosphoric acid should be added during the reaction.
Bonding mechanism: The aluminum dihydrogen phosphate will react as follows during re-sintering:
2Al(H 2 PO 4 ) 3 →Al 2 (H 2 P 2 O 7 ) 3 +3H 2 O
The resulting aluminum pyrophosphate undergoes molecular polymerization of metaphosphoric acid as the temperature increases:
Al 2 (H 2 P 2 O 7 ) 3 →nAl 2 (H 2 PO 10 )+1/2H 2 O
Al(PO 3 )2+nH 2 O→[Al(PO 3 )] n
(3) Forming carrier
The shaped carrier is the key material in the manufacturing process, and the polyurethane foam is used as the molding carrier. The carrier mesh is uniform and has good elasticity. When used, it can be restored to its original state after coating the slurry. The mesh size and specifications are shown in Table 3.
Table 3 Specifications of the molded carrier
Size / cm | Aperture / PPcm (1) |
430×430×40 | 5.0 |
360×360×40 | 8.0 |
450×450×40 | 13.0 |
Note: (1) PPcm refers to the number of holes per unit centimeter.
(4) Production process
(5) Technical points
1. Preparation of slurry The slurry used in the test is a water-based suspension of various components mainly composed of Al 2 O 3 . When the blank is produced, the slurry can be firmly bonded to the foamed plastic mesh. When grouting, the slurry should not be too thick or too thin. Too thick, the slurry is not easy to be poured onto the foamed plastic mesh; too thin, it is easy to settle on the plastic mesh to form uneven slurry. Therefore, controlling proper moisture is the key to preparing the slurry. In addition, the slurry has a moderate cohesiveness. In the test, it was found that when too much low-temperature binder was added and the slurry was too strong, the excess slurry was extruded (the purpose was to prevent the blank from being generated by the billet). After that, the foamed plastic mesh is more difficult to recover; if too little binder is added and the slurry is too weak, the slurry cannot be more and more firmly bonded to the foamed plastic mesh. After deplasticization, The test block has no strength and even falls apart. Even if there is a certain strength, since the slurry on the embryo body is too thin, the mesh structure is very fragile and the overall strength is poor.
2. Formulation of drying and firing system The test uses a metal mesh to make an oven plate. As a pallet for the foam test block baked after the pulp is placed, it is naturally dried at room temperature and then dried by hot air.
Firing is a crucial step in the process of making porcelain. Mastering the changing rules of the baked product during high-temperature roasting and formulating the correct firing system is the key to burning high quality products. The study of the changes in the heating process of each component is the basis for determining the firing system. Taking the study of kaolin as an example, the differential heat curve, dehydration curve, and expansion and contraction curve are shown in Figures 2 to 4.
 Through the differential thermal analysis of the kaolin used, combined with the current research on the change of its heating process, the lattice water begins to slowly discharge at 400-450 °C, and the lattice water is quickly discharged at 450-550 °C. It can also be seen on the thermal curve that there is an obvious endothermic peak around 600 °C, which is caused by the structural water. The initial temperature at which the kaolin dehydrated product continues to undergo structural transformation is 925 ° C. There is a strong exothermic peak at 925 to 1050 ° C on the curve, which is caused by crystal transformation. In addition, when the kaolin is heated to 900 to 1020 ° C, a severe volume shrinkage occurs. According to these characteristics, the low temperature heating or heat preservation operation is adopted in the corresponding temperature zone at 400 to 550 ° C and 920 to 1020 ° C in the test.
Evaporation period: It is advisable to raise the temperature at a slow speed. The purpose of this stage is to remove the crystal water in the foam test block.
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Second, the results and analysis
(1) Determination and calculation of components
The basic components with high temperature Al 2 O 3 , kaolin and feldspar are selected as the basic components, and the proportion of the components is calculated according to the composition [3] , and the basic formula is determined. On this basis, the amount of other small component raw materials added is adjusted. The amount of bentonite is generally fixed at about 3%, and then Al 2 O 3 is X parts, kaolin is Y parts, feldspar is Z parts, and the reference composition is:
SiO 2 31.69%, Al 2 O 3 55.40%, Na 2 O 0.621%, K 2 O 0.21%, CaO 0.13%, MgO 0.015%, calculated :
X/Y/Z=40/22.5/20
Generally, the amount of fixed feldspar is 20 parts, and the amount of bentonite is 3 parts, including: 40 parts of alumina, 22.5 parts of kaolin, 20 parts of feldspar, and 3 parts of bentonite. Converted to percentage: alumina 46.7%, kaolin 26.3%, feldspar 23.36%, bentonite 3.6%.
(II) Test results and discussion
The physical and chemical analysis of the laboratory products, the results are listed in Table 4, the XRD pattern of the product is shown in Figure 5. From the results of the physical and chemical analysis, the laboratory products meet the requirements of general industrial applications.
Table 4 Results of physical and chemical analysis of products
chemical composition/% | Physical properties | ||||||||
Na 2 O | SiO 2 | Al 2 O 3 | Fe 2 O 3 | CaO | K 2 O | strength | proportion | Aperture PPcm | XRD |
0.47 | 34.86 | 53.3 | 0.512 | 2.2 | 0.822 | 0.64 | 0.70~ | 7.5 | Square quartz α-Al 2 O 3 |
(III) Effect of heating rate on product strength Figure 7 shows the relationship between firing system and product strength.
At the end of the test, a reasonable firing system was established, such as holding at 400-550 °C for 2 h, 920-1020 °C for slow heating and holding for 2 h. By strictly controlling the firing process, the strength of the obtained product is greatly improved, and the average strength reaches 0.64 MPa, as shown by curve 1 in FIG. In the early stage of the test, the firing system was directly heated to 1260 ° C and kept for 2 h. As shown by curve 2 in Figure 7, the strength of the obtained product did not meet the requirements for use, and the average strength was only 0.038 MPa. Therefore, the establishment of a reasonable firing system and strict control of the heating rate is the key to ensuring the strength of the product.
Third, the conclusion
(1) Tests on the physical and chemical properties of laboratory products show that the indicators meet the requirements of general industrial applications and have entered the industrial application test stage.
(2) Since the main raw materials and binder raw materials used are self-produced by Shan Aluminum, the production process is simple, the cost is below 1000 yuan/m 2 , and the price of purchased products is above 1800 yuan/m 2 . If all the self-made ceramic foam filter plates are used, the annual cost savings will be 1 million yuan.
"Gravity Die Casting. A permanent mould casting process, where the molten metal is poured from a vessle of ladle into the mould, and cavity fills with no force other than gravity, in a similar manner to the production of sand castings, although filling cn be controlled by tilting the die."
Gravity Die Casting
Sometimes referred to as Permanent Mould, GDC is a repeatable casting process used for non-ferrous alloy parts, typically aluminium, Zinc and Copper Base alloys.
The process differs from HPDC in that Gravity- rather than high pressure- is used to fill the mould with the liquid alloy.
GDC is suited to medium to high volumes products and typically parts are of a heavier sections than HPDC, but thinner sections than sand casting.
There are three key stages in the process.
- The heated mould [Die or Tool] is coated with a die release agent. The release agent spray also has a secondary function in that it aids cooling of the mould face after the previous part has been removed from the die.
- Molten metal is poured into channels in the tool to allow the material to fill all the extremities of the mould cavity. The metal is either hand poured using steel ladles or dosed using mechanical methods. Typically, there is a mould [down sprue" that allows the alloy to enter the mould cavity from the lower part of the die, reducing the formation of turbulence and subsequent porosity and inclusions in the finished part.
- Once the part has cooled sufficiently, the die is opened, either manually or utilising mechanical methods.
Advantages
- Good dimensional accuracy
- Smoother cast surface finish than sand casting
- Improved mechanical properties compared to sand casting
- Thinner walls can be cast compared to sand casting
- Reverse draft internal pockets and forms can be cast in using preformed sand core inserts
- Steel pins and inserts can be cast in to the part
- Faster production times compared to other processes.
- Once the tolling is proven, the product quality is very repeatable.
- Outsourced Tooling setup costs can be lower than sand casting.
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