China Luoyang Hengin Heavy Technology Co., Ltd.

China Luoyang Hengin Heavy Technology Co., Ltd.

Home / SAG Mill Liner / SAG Mill Liner Casting
SAG Mill Liner Casting

 

■ Chemical Composition Control
◆C:
Considering that the basic property indicators of liners steel mainly lie in high wear resistance, high hardness, high strength and certain impact toughness, the initial composition range is 0.8% and 0.9% so as to make sure that there are sufficient amounts of pearlite (P) in the steel substrate, a certain number of cementite (Fe3C) as well as some dispersed alloy carbides that can interact with some alloying elements, which is consistent with the high wear resistance and hardness required by the material apparently. However, the excessively high content of C leads to weak plasticity and toughness of steel grades easily.
◆Si:
Apart from certain de-oxidation and improvement of fluidity of molten steel, adding a certain amount of Si into the material mainly plays a role in strengthening matrix structure through solid solution strengthening. Moreover, the strengthening effect is very remarkable. It can be said that Si is primary alloy element in terms of improvement in the strength (especially for the yield strength) and hardness of materials.
It is noteworthy that the carbide in the steel tends to precipitate along grain boundaries and coarse grain size of the steel is likely to decrease the toughness and wear resistance of the steel, thus leading to cracking of the steel when the content of Si is excessively high (> 0.6%).
◆Mn:
Generally, Si and Mn (displacement solid solution) are major elements that strengthen matrix in cast steel. Therefore, adding a certain amount of manganese (Mn) into steel can firstly improve the strength of matrix greatly from the point of view of solid solution. In addition, the addition of manganese (Mn) can also increase the relative content of pearlite, and further improve the strength of steel.
At the same time, it is rather beneficial to the impact toughness of steel than harmless when the addition of Mn is less than 1%. Therefore, it is reasonable to add Mn with its content in 0.6% - 1%.
◆Cr:
In the iron and steel industry, the addition of chromium (Cr) mainly strengths solid solution and improves the hardenability of steel grades. It exists in the form of (Fe, Cr) 3C with the little amount content of Cr (1% - 3%) of is, which brings about subtle effect in solid solution.
Expect for this, the solubility of chromium (Cr) in steel can also boost the corrosion resistance and oxidation resistance of steel (formation of dense oxide film Cr2O3). The range of Cr 2%-2.5% is reasonable.
◆Mo: 
Mo plays a role in improvement in steel grades by precipitation or dispersion precipitation (mainly in the form of MoC and Mo2C) in subsequent processes after austenitizing solid solution, which mainly attributes to the fact that Mo belongs to a strong carbide forming element, and these precipitated carbides are dispersedly precipitated mainly in the form of particles when the content of the carbide is within a certain range. In addition, the carbide itself is high in hardness and wear-resistant. In sum, a certain amount of molybdenum exerts an obvious effect on the property optimization of steel species in terms of strength, plasticity, toughness or wears resistance.
At the same time, the addition of 0.25% - 0.4% can satisfy the effect taking into account the high economic cost of Mo.
◆Ni:
As the atomic radius of Ni is similar to that of iron, Ni can be dissolved in the matrix with a subtle effect. It is noteworthy that adding a certain amount of Ni can enhance the plasticity and impact toughness of steel, but nickel can hardly interact with other alloying elements in steel, so it is unnecessary to add Ni.
◆Cu:
Adding a certain amount of copper to the liners mainly serves as a dense protective film for antioxidant. The general content of copper is not more than 0.25%, while this performance indicator should be replaced by Cr.
◆Nb:
Being a strong carbide forming element, niobium plays an important role in refining grain of liner plate steel with carbide (NbC,Nb (C, N), etc.) formed by niobium. Meantime, it also has an effect on dispersion strengthening well. According to some concerned researches, adding about 0.03% -0.05% of Nb to steel can has a significant effect on refining grain and strengthening properties. BesidesNb is capable of preventing austenite grain growth.
◆Re/Ti:
Roughly 0.3% Re and Ti alloy are used to modify molten steel, refine grain size, and further reduce non-metallic inclusions such as S and P (< 0.04%) in molten steel during melting. Moreover, deoxidizers such as silicon-calcium alloy are efficiently used to reduce oxygen content in molten steel, crack sources with micro-cracks, segregation and enhance wear resistance of liner plates.
All the above alloying elements (except for Mn) have ability to prevent austenite grain growth and refine grain, especially the carbide forming elements Mo and Nb. Furthermore, most alloying elements can improve the hardenability of steel.
The above material composition renders high strength and toughness comprehensive performance to the grinding mill pearlite liners , and it also endows liners with superior wear resistance and impact resistance, thus realizing the ideal use effect.
■ Casting Technology Requirements
◆ Process Parameters Design
The parameters of gating system, riser and process product yield are determined, and the casting process design is validated by Procast simulation software.
◆ Model Design
The model process is strictly made in line with the standard of the first-class wood model, and different reduced scales of liners in all directions are determined with general range of 2.0-2.4%. The casting number and marking of liners must be clear and accurate.
◆ Riser Design
The diameter of riser is determined to be 1.5 times that of hot pitch circle to improve the filling effect of riser. Moreover, the pouring height of riser is 1.5 times riser diameter so as to play a role in reinforcing shrinkage as well as reduction in microporosity exists in the structure of liners.
◆ Modeling Requirement
The strength of sand mold shall be improved so as to prevent sand sticking due to the increase of pouring temperature, and the worse heat dissipation condition of liners caused by sand adhesion. Meanwhilethe outgassing effect of sand mold should be also improved. 
◆ Molten Steel Refining
After the molten steel is out of furnace, refining is carried out in the ladle to remove harmful gases and inclusions, and further ensure the purity of molten steel. Meanwhile, the temperature of molten steel shall be adjusted to a reasonable range, which is conducive to the pouring process.
◆ Pouring Temperature Control
Pouring temperature shall be strictly controlled and it shall be not too high or too low so as to enhance the mass transfer effect in solidification process of castings, improve the density and uniformity, reduce the possibility of defects in porosity casting, and ensure the punching effect of molten steel.
◆ Release Casting Stress
Liners must be well insulated for a long time after pouring, so that the casting stress can be fully released in the sand mold and cooled naturally below 300 C before it can be taken out and then it is placed at room temperature.
◆ Clear
It is forbidden to use flame cutting tools so as to ensure no cracks of castings when parts of liners like gating system, riser, flying edge are cleared. 
■ Casting Production
◆ Modeling
We use assembly line of resin sand liners for modeling, which can achieve 20000 tons / year molding ability, offer accurate size of liners, good appearance quality and no sand sticking phenomenon. Besides, the nigh core is made of chromium iron ore sand.
◆ Melting
Melting equipment for liners refers to electric furnace with 12 ton medium frequency to endow with accurate chemical composition. In order to ensure the purity of molten steel, slag removal, inclusions, gas and reduction of sulfur and phosphorus content shall be limited within the required range.
■ Inspection of Liners
◆ Mechanical Property Test
We achieve the performance testing objections after heat treatment by strictly controlling the manufacturing process under the premise that the mechanical properties of pearlite chromium-molybdenum steel mill liners meet the standards.
Yield strength σs≥830MP, tensile strength σb≥960MPa, hardness HB330-370, impact toughness aK≥25J, which have good wear resistance and impact resistance.
◆4.2 Metallographic examination
Pearlite structure formed by heat treatment shall be closely and uniformly spaced, the net carbide and strip carbide is eliminated, and massive carbide existing in the structure is improved with the purpose of achieving ideal structure; Pearlite + granular carbide is listed as a typical wear-resistant material combined with matrix structure and hardening.
 
123123
123123123