Development tendencies of moulding and core sands

Further development of the technology for making moulding and core sands will be strictly limited by tough requirements due to protection of the natural environment. These tendencies are becoming more and more tense, so that we will reach a point when even processes, that from technological point of view fulfill high requirements of the foundry industry, must be replaced by more ecologically-friendly solutions. Hence, technologies using synthetic resins as binding materials will be limited. This paper presents some predictable development tendencies of moulding and core sands. The increasing role of inorganic substances will be noticed, including silicate binders with significantly improved properties, such as improved knock-out property or higher reclamation strength. Other interesting solutions might also be moulding sands bonded by geo-polymers and phosphate binders or salts and also binders based on degradable biopolymers. These tendencies and the usefulness of these binders are put forward in this paper.

Influence of wet activation of used inorganic binder on cyclically refreshed water glass moulding sands hardened by microwaves

The paper presents the research results of using an innovative method to reclaim the waste moulding sands containing water glass. Two of the examined processes are connected with "dry" or "wet" activation of inorganic binder in waste moulding sand mixtures physically hardened by microwave radiation. The sand mixtures consisting of high-silica sand and water-glass with average molar module 2.5, were subjected to the following cyclical process: mixing the components, compacting, microwave heating, cooling-down, thermally loading the mould to 800 °C, cooling-down to ambient temperature, and knocking-out. After being knocked-out, the waste moulding sands were subjected to either dry or wet activation of the binder. To activate thermally treated inorganic binder, each of the examined processes employed the surface phenomenon usually associated to mechanical reclamation. The study also covered possible use of some elements of wet reclamation to rehydrate waste binder. To evaluate the effectiveness of the two proposed methods of waste binder activation, selected strength and technological parameters were measured. After each subsequent processing cycle, the permeability, tensile strength and bending strength were determined. In addition, the surface of activated sand grains was examined with a scanning electron microscope. Analysis of the results indicates that it is possible to re-activate the used binder such as sodium silicate, and to stabilize the strength parameters in both activation processes. Permeability of the refreshed moulding sands strongly depends on the surface condition of high-silica grains. The wet activation process by wetting and buffering knocked-out moulding sands in closed humid environment makes it possible to reduce the content of refreshing additive in water-glass. The moulding sands cyclically prepared in both processes do not require the addition of fresh high-silica sand. The relatively high quality achieved in the refreshed moulding sands allows them to be reused for manufacture of next moulds. Thus, the two proposed methods for cyclically processing used moulding sands containing sodium silicate, subject to microwave hardening, are suitable for economic and ecological circulation moulding mixtures.

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand, and zircon sand moulds) under different freezing temperatures and water contents was studied. Results show that with the decrease of freezing temperature and the increase of water contents, the tensile strength and air permeability of the sand moulds are gradually improved. Meanwhile, computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water. The results show that in silica sand moulds, the form of water film is lumpy, and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds, while in zircon sand moulds, the form of water film is membranous. At the same freezing temperature and water content, the tensile strength of zircon sand mould is the highest, and 100-mesh silica sand mould is the lowest. A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould. The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting, but the primary α-Al phase grows in the form of dendrites, and the eutectic silicon phase is coarse needle-like in the resin sand mould casting. The difference of microstructure is caused by the different cooling rate. The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.

Criteria for an advanced assessment of quality of moulding sands with organic binders and reclamation process products

Reclamation of used moulding and core sands has been defined as a treatment of waste moulding refractory materials, enabling a recovery of at least one of the components having properties similar to those of the fresh component, and reuse for production of casting moulds and cores. However, at present, there is a lack of a reclaimed material assessment index, which could be applied to each type of moulding sand and reclaim. Modern investigation methods and equipment for the estimation of the quality of the moulding sands matrices with organic binders, in their circulation process, are presented in this paper. These methods, utilizing the special equipment combined with the author's investigation methods developed in the Faculty of Foundry Engineering, AGH - University of Science and Technology, allow the better estimation of the matrix quality both in an aspect of its application as a fresh sand substitute in the preparation of moulding sands, and also with regard to the environmental protection. The most important criteria for the technological assessment of the reclaimed materials and the quality of sands with organic binders are presented in this paper.

A Model for Predicting Dynamic Cutting Forces in Sand Mould Milling with Orthogonal Cutting

Cutting force is one of the research hotspots in direct sand mould milling because the cutting force directly a ects the machining quality and tool wear. Unlike metals, sand mould is a heterogeneous discrete deposition material. There is still a lack of theoretical research on the cutting force. In order to realize the prediction and control of the cut?ting force in the sand mould milling process, an analytical model of cutting force is proposed based on the unequal division shear zone model of orthogonal cutting. The deformation velocity relations of the chip within the orthogonal cutting shear zone are analyzed first. According to the flow behavior of granular, the unequal division shear zone model of sand mould is presented, in which the governing equations of shear strain rate, strain and velocity are estab?lished. The constitutive relationship of quasi?solid–liquid transition is introduced to build the 2D constitutive equation and deduce the cutting stress in the mould shear zone. According to the cutting geometric relations of up milling with straight cutting edge and the transformation relationship between cutting stress and cutting force, the dynamic cutting forces are predicted for di erent milling conditions. Compared with the experimental results, the predicted results show good agreement, indicating that the predictive model of cutting force in milling sand mould is validated. Therefore, the proposed model can provide the theoretical guidance for cutting force control in high e ciency mill?ing sand mould.

Biodegradable materials as binders for IVth generation moulding sands

This paper focuses on the possibility of using the biodegradable materials as binders(or parts of binders' compositions) for foundry moulding and core sands. Results showed that there is a great possibility of using available biodegradable materials as foundry moulding sand binders. Using biodegradable materials as partial content of new binders, or additives to moulding sands may not only decrease the toxicity and increase reclamation ability of tested moulding sands, but also accelerate the biodegradation rate of used binders, and the new biodegradable additive(PCL) did not decrease the strength and thermal properties. In addition, using polycaprolactone(PCL) as a biodegradable material may improve the flexibility of moulding sands with polymeric binder and reduce toxicity.

Investigations of physicochemical properties of dusts generated in mechanical reclamation process of spent moulding sands with alkaline resins

Mechanical reclamation processes of spent moulding sands generate large amounts of postreclamation dusts mainly containing rubbed spent binding agents and quartz dusts. The amount of postreclamation dusts, depending in the reclamation system effi ciency and the reclaim dedusting system, can reach 5%-10% in relation to the total reclaimed spent moulding sand. The proper utilization of such material is a big problem facing foundries these days. This study presents the results of investigations of physicochemical properties of post- reclamation dusts. All tested dusts originated from various Polish cast steel plants applying the mechanical reclamation process of moulding sands with alkaline resins, obtained from different producers. Different dusts, delivered from foundries, were tested to determine their chemical composition, granular characterization, physicochemical and energetic properties. Presented results confi rmed assumptions that it is possible to utilize dusts generated during mechanical reclamation of used sands with organic resins as a source of energy.

Effect of Varying Corn Cob and Rice Husk Ashes on Properties of Moulding Sand

The use of rice husk and corn cob ashes as aggregates for foundry moulding sand has been studied. 5-12.5 weight percent of rice husk and corn cob ashes were added to the sand mixture and the sand properties determined. A mixture of equal proportion of rice husk and corn cob ashes was also used. In each case, four weight percent water and clay were added to the sand mixture. Some of the properties of the sand tested are: permeability, green compression strength, dry compression strength, green shear strength, dry shear strength, moisture content and permeability. The results showed that the green compression strength, green shear strength, moisture content and permeability decrease with increase in the additives (rice husk ash, corn cob ash, and (50% rice husk and 50% corn cob ashes). While dry compression strength and dry shear strength increase with increase in weight percent of the additives.

The Study of Green Compression Strength of a Green Sand Mould Using Statistical Approach

The study of green compression strength of a green sand mould using statistical approach has been undertaken. Empirically generated data in National Metallurgical Development Centre, Jos Sand Testing Laboratory were used for the study. Coefficient of correlation, coefficients of determination and coefficient of multiple determinations were used to explain the relationship existing between the two independent variables of clay and moisture content and green compression strength, the dependent variable. The study showed that the coefficient of determination for Ys: X1 was 0.88 while the coefficient of correlation was 0.94, coefficient of determination for Ys: X2 was 0.90 while the coefficient of correlation was 0.95 and the coefficient of multiple determination was 0.72;these coefficients assisted tremendously in the study of green compression strength. A mathematical model was developed for the prediction of green compression strength;it was tested and proved to be a good estimation tool for estimating green compression strength values on the foundry shop floor. The study has clearly shown that statistical approach is a good tool for studying green compression strength of green sand moulds.

基于砂型3D打印技术的壳体低压铸造工艺开发与验证

壳体型腔复杂且壁薄,采用传统工艺不仅造型困难,而且从模具设计到整体铸造工艺开发与验证,所用周期长、效率低,生产成本高。基于砂型3D打印技术快速制样优势,本文对壳体浇注系统采用随形设计方案,实现了型腔、叶片一体化结构成形制造,结合数值仿真计算分析,对浇注工艺进行设计优化,开展了浇注试制与铸件实物检测。结果表明,选用3D打印砂型整体成形工艺可实现复杂结构壳体的短周期、低成本与高精密制造,实现工艺样件的快速制造。

6缸柴油机高强度球墨铸铁曲轴的研制

通过成分设计、凝固模拟、铁模覆砂铸造和等温正火复合新工艺应用,研制了一种高强度6缸柴油机球墨铸铁曲轴,分析了其内部质量、显微组织和力学性能.中试结果表明:采用复合新工艺研制的6缸球墨铸铁曲轴,其组织致密,没有内部铸造缺陷;与树脂砂铸造工艺相比,球墨铸铁曲轴的基体组织更均匀,共晶团数增多,晶粒显著细化,基体组织中索氏体比例大于90%,自由渗碳体比例小于1%.6缸球墨铸铁曲轴沿轴向不同位置的平均拉伸强度R_(m)、平均伸长率和基体平均硬度分别为946 MPa、5.6%和287 HB.负荷为2900N·m下,其弯曲疲劳试验加载次数达到10×10^(7)次而未出现裂纹和开裂现象,各项性能指标均超过L6R040301Q曲轴的技术要求,可代替现用的45锻钢和42CrMo锻钢曲轴,成本分别降低44.0%和66.2%.

硅砂、陶粒砂和宝珠砂铸造工艺性能研究

研究了鄂尔多斯硅砂、通辽硅砂、海南海砂、陶粒砂和宝珠砂的形貌,用其做原砂的碱酚醛树脂砂的抗拉强度,原砂抗机械破碎和粉化能力等。结果表明:鄂尔多斯硅砂形貌最差,呈尖角、片状;通辽砂、海砂较好,呈圆形、多角形;陶粒砂和宝珠砂最好,呈圆形。型砂24 h时抗拉强度,鄂尔多斯硅砂最低,只有0.277 MPa;通辽硅砂和海砂较高,接近0.6 MPa;宝珠砂最高,接近0.9 MPa;陶粒砂为0.667 MPa,高于硅砂,低于宝珠砂。经机械搅拌破碎试验得出:鄂尔多斯硅砂强度较低,抗破碎能力最差,易破碎粉化,粉尘含量由0.03%提高到0.812%;通辽硅砂和海砂强度都较好,粉化较轻,粉尘含量由0.016%提高到0.32%;陶粒砂强度也较好,粉化较少,粉尘含量由0提高到0.195%;宝珠砂破碎和粉化率极低,粉尘含量基本无变化。

基于砂型3D打印技术的薄壁筒形件铸造成形技术

近年来,砂型3D打印技术取得了重大进展,利用有机粘结剂和树脂结合自硬化技术制作砂型已成熟,可运用于铸造行业,这解决了传统铸造方法普遍存在的生产效率低、工艺设计复杂等问题。采用差压铸造能够生产出性能优异的高质量铸件,当与3D打印技术结合时,能够快速获得复杂、精密的铸造成形零件。本文将3D砂型精密打印技术与差压铸造成形技术结合,采用ZAlSi7MgA铸造铝合金材质,试制了具有复杂内腔结构的薄壁筒形结构件。结果表明:产品附铸试样性能远优于国标要求,其中抗拉强度平均值达到348 MPa,提升18%,断后伸长率平均值为5.5%,提升83%,产品内部质量达到Ⅰ类铸件水平;经尺寸扫描分析,产品内腔单侧尺寸公差范围为-0.0976~+0.1089 mm,满足±0.3 mm的设计指标,实现了薄壁复杂筒形结构件的差压精密铸造成形。

不同添加剂配比对镁合金砂型铸造用树脂砂性能的影响研究

针对镁合金砂型铸造中使用的树脂砂,探讨了混砂时加入树脂、固化剂、阻燃剂、硅烷等添加剂的配方及作用。通过测定树脂砂的可使用时间、起模时间、抗压强度等参数,分析了不同添加剂配比对树脂砂性能的影响。研究结果表明,在确保树脂砂强度的基础上,尽量减少树脂和固化剂的配比量,可减少铸件气孔缺陷,改善高温性能,提高铸件质量,降低生产成本。该研究结果可为镁合金铸件的高质量生产提供技术支持。

砂型增材制造设备用铺砂器清理机构的设计

砂型3D打印设备采用增材制造的逐层打印造型技术取代了传统的流砂翻箱造型技术,大幅改变了传统铸造行业“傻大黑粗”的形象,实现了铸造行业的转型升级。但在砂型3D打印设备产业化的过程中,也出现了各种各样的问题。本文主要解决了砂型3D打印设备在产业化使用过程中铺砂器的清理问题,使得铺砂器在铺砂作业过程中能够始终保持良好的状态,保证了铺砂层面的质量,提升了砂型3D打印设备的有效作业率。

铁型覆砂铸造工艺在轨道交通电机机座类铸件上的应用

分析电机机座类铸件结构特点与技术要求,选其中一种电机机座铸件为例,根据铁型覆砂工艺特点确定半封闭式浇注系统,分析该铸件铁型覆砂工艺设计及砂芯设计要点,采用有限元软件对铁型覆砂铸造工艺方案进行验证及优化,经生产实践表明,该电机机座铸件铁型覆砂铸造工艺方案可行,铁砂比为1∶6,工艺出品率为90.8%,产品合格率为95%。经济效率显著,已实现批量生产。

压下制动盘的国产化试制

分析制动盘的结构特点,采用铁模覆砂铸造工艺,通过原料成分控制,炉前工艺控制,铁型砂箱改进等措施,均衡整个圆盘温度场分布,消除缩孔等缺陷,实现铸件内部组织致密,确保制动器试制成功。

A new numerical simulation model for high pressure squeezing moulding

High pressure squeeze is the most popular moulding process applied in modern moulding machines.Because of the unique characters of moulding sand and nonlinearity of squeezing process,the mechanical model is of key importance for computer simulation.Drucker-Prager/Cap is a typical soil mechanical theory model and it was used to simulate the squeezing process in this study,while ABAQUS software is used to simulate dynamic stress/strain evolution during the process.The simulation agrees well with the experimental results.We conclude that Drucker-Prager/Cap is an appropriate model for the squeezing compaction of moulding sand,and that the associated nonlinearity can be solved well with ABAQUS software.

Iron casting skin management in no-bake mould – Effects of magnesium residual level and mould coating

The relative performance of coatings for furan resin sand moulds [P-toluol sulphonic acid(PTSA) as hardener] [FRS-PTSA moulds], was compared by analyzing the surface layer for degenerated graphite in Mg treated iron with 0.020 wt.% to 0.054 wt.% Mgres. It was found that the iron nodularising potential(Mg, Ce, La content) and whether the mould coatings contained S, or were capable of desulphurizing were important factors. These moulds have S in the PTSA binder, which aggravates graphite degeneration in the surface layer, depending strongly on the Mgres with lower Mgres increasing the layer thickness. The application of a mould coating strongly influenced graphite deterioration in the surface layer of castings. It either promoted graphite degeneration to less compact morphologies when using S-bearing coatings, or conversely, limited the surface layer thickness using desulphurization type coatings. Independently of the S-source at the metal – mould interface, the presence of sulphur had an adverse effect on graphite quality at the surface of Mg-treated irons, but its negative effect could also reach the graphite phase within the casting section. If the coatings employed desulphurization materials, such as Mg O, or a mixture(Ca O + Mg O + Talc) or Mgbearing Fe Si, they protected the graphite shape, improving graphite nodularity, at the metal – mould interface, and so decreased the average layer thickness in FRS-PTSA moulds. Fe Si Mg was highly efficient in minimizing the casting skin by improving graphite nodularity. It is presumed that the Mg O or(Mg O + Ca O + Talc) based coatings acted to remove any S released by the mould media. The Mg-Fe Si coatings also reacted with S from the mould but additionally supplemented the Mg nodularising potential prior to solidification. This dual activity is achievable with coatings containing active magnesium derived from fine Mg-Fe Si materials.

Impact of Moisture Variation on Some Foundry Properties of Fori Silica Sand

Moulding Sand for metal casting is usually sourced from either natural deposit or synthetic mix of refractory sand grain binder and moisture. Each of the mix constituent is important in determining the characteristics of sand. The binding agent is responsible for bendability thereby determining the size of voids within the sand grain, while moisture level determines the plasticity of the foundry sand. Tests using American Foundry Society (AFS) Standard were followed in carrying out the experiment on Fori sand deposit to determine its suitability for foundry use. The sand was collected from the river bank of Fori, in Fori Community, Maiduguri, Borno State. The experimental test equipment includes: laboratory sand mixer, sand rammer, universal strength testing machine, permeability-meter, oven, mouldability machine, and as well as quick moisture teller. The chemical composition of the materials was carried out using atomic absorption spectrophotometer (AAS) model PG990AFG. The silica content in the material sample is about 78.65%, and with the traces of other elements, such as CaO (1.07%), Fe2O3 (0.76%), Al2O3 (15.81%), MgO (1.01%), TiO2 (2.21%), K2O (3.87%), and Na2O (1.16%), respectively. These percentages are within acceptable limits. The results of the physical properties revealed that the sand sample has clay content of 15.32% which is above the standard range of 10% - 12% recommended for natural moulding sands required for producing good quality castings. Other foundry properties of Forinatural moulding sand conducted include “moisture content” in the following ranges of percentages, 7.6%, 6.5%, 5.8%, 4.2% and 2.9% with the corresponding value of green compressive strength of (43.95, 53.47, 69.56, 68.21 and 61.16 KN/m2), dry compressive strength (93.50, 96.52, 105.50, 146.50 and 152.49 KN/m2), and permeability No. of 340, 390, 410, 430 and 440 respectively. It is clear from the test that, the lower the moisture content, the higher the dry compressive strength of the materials. The refractoriness value of the materials is 1400 ℃. The results of the physical and other foundry properties carried out show that Forisilica sand is suitable for casting non-ferrous alloys like bronze, brass and aluminium, and cast iron.