Mould Permeability Research Articles

Simulation and experimental research on extra-squeeze forming method during gradient sand molding

The flexible extrusion forming process (FEFP) is a sand mold patternless manufacturing technology that enables digital near-net shaping of complex sand molds. But, it is difficult to achieve the gradient sand molds with high surface strength and strong interior permeability by FEFP. To solve this problem, an extra-squeeze forming method based on FEFP for gradient sand mold was developed. To further reveal the extra-squeeze forming mechanism, based on the Johnson-Kendall-Roberts (JKR) theory and “gluing” notions, the single and double-sided squeeze models of gradient sand molds were established using the EDEM software. The squeezing processes of sand molds with different cavity depths of 60, 100, 140, 180, and 220 mm were systemically studied under single and double-sided squeeze conditions. The variation in the void fraction of sand mold as also investigated at a variety of extra-squeeze distances of 2, 3, 4, 5, and 6 mm, respectively. Simulation and test results show that a deeper cavity depth weakens the extrusion force transmission, which leads to a decrease in strength. The sand mold permeability and void fraction are identified to be positively correlated, while the tensile strength and void fraction appear to be negatively correlated. The void fraction of sand molds decreases with a longer extra-squeeze distance. A 6 mm extra-squeeze distance for the sand mold with 220 mm cavity depth results in a 26.8% increase in tensile strength with only a 5.7% reduction in the permeability. Hence, the extra-squeeze forming method can improve the quality of the sand mold by producing a gradient sand mold with high surface strength and strong interior permeability.

Experimental investigation on influence of mould wall thickness and hardness on green sand mould permeability

The green compression strength, mould permeability and hardness are the three important properties of the green sand mould. These mould properties are influenced by the sand type, sand grain size, grain shape, clay type, water content, ramming and mould wall thickness. The poor mould permeability and hardness value result in gas related casting defect and poor casting surface finish. Hence in this work, to predict the green sand mould permeability, the exponential models are developed for mould permeability, mould wall thickness and mould hardness value. The mould specimens of 50 mm diameter, 30/40//50/60/70 mm thickness with the hardness value of 87, 90 & 93 are prepared from the moulding sand. The permeability and hardness tests are carried out in the prepared specimens. Using these test results, graphs are plotted between the permeability and mould wall thickness for 87, 90 and 93 hardness values. The exponential model for each hardness value is developed to predict the permeability value for the different mould wall thicknesses.

Investigation on the Influence of Different Additives on Properties of Green Sand Mould

Green sand mixtures which are used for moulding purposes in foundry industries should possess sufficient green compression strength, flowability, toughness and air-permeability. Usually, the aforementioned properties for a particular casting differ due to variation in composition of the moulding sand mixtures, sand grain shape and size, bonding capacity of the binder, type and quantity of additives used, etc. The present work focuses on the effect of various additives namely, camphor powder, coconut shell ash, mixture of camphor powder and coconut shell ash at diverse proportions on permeability and green compression strength of the sand moulds. The quantity of the aforementioned additives for experimentation was varied from 0.5 to 3.5 wt. %. It was found that the mould’s permeability increased on addition of 1 wt. % additives for all cases. Similarly, the optimum quantity of additives that needs to be added to the sand mixtures for enhancing green compression strength was found to be 2 wt. %. Among all the additives used for improving the mould’s permeability, substitution of camphor exhibited best results. The green compression strength was found to be highest for the coconut shell ash containing sand mould. The moulding sand containing a combination of camphor powder and coconut shell ash between 1 to 2 wt. % exhibited fine mould permeability along with sufficient green strength.

Properties of silica sand and GBF slag moulds practiced by Nishiyama process

ABSTRACTInvestigations were carried out to use Granulated Blast furnace (GBF) slag as mould material for either full or partial replacement of existing silica sand in foundry industry. Nishiyama process was adopted for evaluating the same. A series of sand tests were carried out on sand and slag individually and also combinations of these two. Three types of moulds were made with sand, slag individually and combination of these two. Both laboratory and industrial castings of ferrous and non ferrous materials were performed. Results of mould permeability, compression and shear strength of GBF slag reveal that is a suitable candidate for either partial or full replacement of molding sand. During casting of both laboratory and industrial, neither fuse, dripping nor collapse of the mould walls was observed; this is true for both ferrous and non ferrous castings. Castings with good surface finish, no surface defects and porosity were made by slag moulds.

Investigation of process parameter effect on anisotropic properties of 3D printed sand molds

The development of sand mold three-dimensional printing technologies enables the manufacturing of molds without the use of a physical model. However, the effects of the three-dimensional printing process parameters on the mold permeability and strength are not well known, leading the industries to keep old settings until castings have recurring defects. In the present work, the influence of these parameters was experimentally investigated to understand their effect on the mold strength and permeability. Cylindrical and bar-shaped test specimens were printed to perform, respectively, permeability and bending strength measurements. Experiments were designed to statistically quantify the individual and combined effect of these process parameters. While the binder quantity only affects the mold strength, increasing the recoater speed leads to both greater permeability and reduced strength due to the reduced sand compaction. Recommendations for optimizing some 3D printer settings are proposed to attain predefined mold properties and minimize the anisotropic behavior of the sand mold in regard to both the orientation and the position in the job box.

Experimental characterization of ceramic shells for investment casting of reactive alloys

The investment casting of reactive Ti and TiAl alloys requires the use of selected ceramics in the face-coat layer to prevent the reaction between the cast metal and ceramic shell, avoiding the formation of a hard layer at the metallic components surface. This work aims to study the influence of ceramic shells composition in some of its characteristics such as flexural strength, friability and dimensional accuracy. The microstructure of the shells was evaluated by SEM. Changes in the face-coat and back-up ceramic shells composition determines the ceramic shell strength to withstand the casting stage with adequate mould permeability and thermal conductivity, and a compromise resistance for knock-out. All the non-conventional ceramic shell systems with interest for reactive alloys, based on fumed alumina binder and alumina sand for the back-ups, present higher dimensional stability (low shrinkage or expansion) compared with traditional systems based on colloidal silica binder and zircon and aluminosilicates back- ups. In this work, better mechanical strength and lower friability were obtained with non-conventional face-coats of alumina and polymer binders, both with yttria flour and stucco, followed by alumina back-ups. Selecting the right ceramic shell composition, it is possible to achieve adequate properties for casting titanium alloys.

Molding and casting behavior of ferro chrome slag as a mold material in ferrous and non-ferrous foundry industries

ABSTRACTIn the present investigation, efforts are made to use Ferro Chrome (Fe-Cr) slag as a mold material for the replacement of silica sand in the foundry industry. The sodium silicate-Fe–Si process is adopted for evaluating the same. The process parameters considered for this investigation are % of sodium silicate, % of Fe–Si powder as a binder, and mold setting time. A series of sand tests are carried out on sand, slag individually, and for various combinations of these two. Three types of molds are made with sand, slag individually, and combination of these two with 6% sodium silicate and 1.5% Fe–Si. Various ferrous and non-ferrous castings are performed on these newly developed slag molds. The results reveal that the Fe-Cr slag with mold permeability, compression, and shear strength is a suitable candidate for either partial or full replacement of silica sand. During casting neither fusing, dripping, nor collapse of the mold walls is observed in slag molds; this is true for both ferrous and non-ferrous castings. Castings with good surface finish and no surface defects are made by slag molds. Faster heat transfer in slag molds enable to obtain castings with enhanced metallurgical and mechanical properties.

Ferro Chrome Slag: An Alternative Mould Material in Ferrous and Non-ferrous Foundries

Various efforts are being made to use industrial wastes as an alternate moulding material in the foundry industry. Ferrochrome (Fe–Cr) slag has many of the same attributes of sand. Hence, in this paper, investigations were carried out on the suitability of Fe–Cr slag as mould material for either full or partial replacement of existing silica sand in the foundry industry. Owing to the superiority, sodium silicate–CO2 process was adopted for evaluating the same. The process parameters considered for this investigation were percentage of sodium silicate and CO2 gassing time. A series of sand tests were carried out on silica sand, Fe–Cr slag individually and various combinations of these two. Three types of moulds were made with Fe–Cr slag, silica sand individually and combination of these two with 8 %sodium silicate and 15 S CO2 gassing time. Various ferrous and non-ferrous castings were performed on these newly developed slag moulds. Results reveal that mould permeability, compression and shear strength of Fe–Cr slag are suitable candidates for either partial or full replacement of moulding sand. During casting, no burning, dripping nor collapse of the mould walls was observed in slag moulds; this is true for both ferrous and non-ferrous castings. Castings with good surface finish, no surface defects and without porosity were made by slag moulds. Slag moulds show faster solidification rates than sand moulds. Faster heat transfer in slag moulds enables obtain castings with enhanced metallurgical and mechanical properties like, hardness, compression and tensile with improved elongation.

A NEW CERAMIC CASTING MOLD MADE BY GEL CASTING USING SILICA SOL AS A BINDER

This Paper presents a new ceramic casting mold made by gel casting using silica sol as a binder. The new ceramic mold is consisted of an alumina-mullite-zirconia matrix with the ratios of 38.332 wt. % alumina, 34.378 wt. % mullite, and 27.294 wt. % zirconia respectively, the slurry is mixed then the gelling agent is added and poured into the pattern. After gelation the mold is extracted and left to dry, then sintered. There are three main defects appear in the mold fabrication process. The 1st defect is the mold cracking, as a result of forced shrinkage of mold into pattern. The 2nd defect is the bad gelation behavior of mold, as a result of non equal gelling time. The last defect is mold surface cracks, due to increased silica ratio added to the mixture. As zirconia increased the bulk density and apparent porosity is increased, leading to higher mold permeability which is important to eliminate trapping of residual gases. The increased zirconia content decreases the micro hardness and the cold crushing strength, but increases the thermal shock resistance due to phase transformation during sintering. The ceramic mold is applicable for nodular cast iron so that the mold is hard enough to withstand the forces of spheroidal graphite formation when nodular cast iron is poured into the ceramic mold. The surface roughness no. of metal cast into ceramic mold is 0.582 μm, while of the metal cast into sand mold is 5.187 μm.

Influence of steel shot size on the permeability of mould

Summary Casting is one of the commonly used techniques in industries for the manufacturing of metal products. Although sand is used as a mould material for casting, its permeability and thermal conductivity are very low and hence affects the microstructure and mechanical properties of the cast product. Therefore using alternate material for the mould may result in better permeability, heat transfer rate and thereby better properties. In the present work, steel balls are used as mould material and the effect of grain size on the permeability of the mould material is studied. Steel balls of different diameters namely 0.18 mm, 0.6 mm and 1 mm which are commercially available were used. From the experiments conducted, it is confirmed that coarser steel balls showed more permeability and thereby can help in easy escape of hot gases (from the molten metal and mould material) during pouring of molten metal into the mould.

High Carbon Ferro Chrome Slag – Alternative Mould Material for Foundry Industry

High silica sand is commonly used in foundry industry for sand moulds making. Various efforts are being made to use the industrial wastes as an alternate molding material in foundry to conserve the natural resources; and effective utilization of the industrial waste to sustain the industrialization. Ferro chrome (Fe-Cr) slag has many of the same attributes of the sand. In this paper investigations were carried out on comparative mould and casting properties of high silica sand and Fe-Cr slag for foundry applications. A series of sand tests were carried out on silica sand, Fe-Cr slag individually and various combinations of these two. The process parameters considered for this investigation were % of Sodium silicate, CO2 gassing time, and mould setting time. Two types of moulds were made with 100%Fe-Cr Slag and 100% Silica Sand individually with 8%Sodium Silicate and 15Seconds CO2 gassing time. AA2024 Aluminium alloy cylindrical castings were made through these two moulds; castings were investigated for its microstructure and hardness studies. Results reveal that standard samples with Fe-Cr slag can be prepared; these shows smooth surface finish and accurate dimensions on par with the sand samples. The mould permeability, compression and shear strength results showed Fe-Cr Slag will be a suitable candidate for either partial or full replacement of molding sand. Enhanced mould properties were observed for Fe-Cr slag than silica sand. Good surface finish castings with enhanced mechanical properties and fine grain microstructures were produced by Fe-Cr slag moulds.

An alternative approach in ceramic shell investment casting of AZ91D magnesium alloy: In situ melting technique

In this research, the possibility of ceramic shell investment casting of a magnesium alloy using in situ melting technique was explored. AZ91D granules were charged into shell investment mould and in situ melted under various processing parameters including heating temperature, flux application, shell mould thickness and permeability. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques were used to characterise the cast samples. Thermal analysis was employed to further investigate the effect of mould thickness on the solidification behaviour of the metal. It was found that mixing flux with the granules not only reduced the temperature at which melting can be achieved, but it also contributed to produce castings with acceptable surface quality. The use of thinner mould provided higher solidification rate, which is believed to favour in situ melting of the granules. It enabled melting of the granules at 650°C, which in turn helped to suppress the mould–metal reaction and produce castings with good surface quality. Shell mould permeability showed no influence on suppressing the mould–metal reaction at 650°C.

New Investigation Method of the Permeability of Ceramic Moulds Applied in the Investment Casting Technology / Nowa metoda oceny przepuszczalności form ceramicznych stosowanych w technologii wytapianych modeli

Abstract The new investigation method of a permeability of ceramic moulds applied in the investment casting technology, is presented in the paper. Some concepts of performing permeability measurements are shown. Investigations in which the influence of the solid phase fraction in the liquid ceramic moulding sand (LCMS) on a permeability of a multi-layer ceramic mould were performed and discussed. The permeability was estimated during two the most important stages of the technological process: in the first - after wax melting and in the second - after mould annealing. Also an influence of the matrix grain sizes (material for sprinkling) on a ceramic mould permeability was estimated.

The influence of polymer content and sintering temperature on yttria face-coat moulds for TiAl casting

Abstract Yttria is an important primary coat material in investment shells for casting extremely reactive TiAl alloys and polymer is usually added to slurry to improve strength of the shell. In this investigation, systems that vary the polymer content through 0%, 6% and 30% were produced and the samples were sintered at 1000 °C, 1200 °C and 1400 °C. The results suggest that polymer content and sintering temperature appear to have little effect on the hardened alpha layer of the cast alloy, which is elevated by near-surface oxygen content. Silica from the backing coat is seen to travel through the primary coat and diffuse into the alloy regardless of the shell system. Firing temperatures above 1200 °C increase the shell strength undesirably but the friability of the primary coat decreases as firing temperature increases. Higher mould permeability was found in the mould containing higher polymer level and this would be advantageous for complete mould filling.

An In-situ Device for Rapid Determination of Permeability for Granular Bases

Abstract This paper describes a new in-situ Air Permeameter Test (APT) device developed for estimating the hydraulic conductivity of drainable granular base materials. The device is assembled from commonly available components including air flow meters and differential pressure gages. Using prescribed air flow and pressure measurements from the APT, a theoretical relationship is derived to calculate the saturated hydraulic conductivity. The geometric factors for the device, sample boundary conditions, partial saturation, compressibility and viscosity of the permeant fluid (i.e. air), and the Brooks-Corey pore size distribution index are considered in the derivation. Attempts at correlating in-situ APT calculated hydraulic conductivity values for compacted granular base materials to hydraulic conductivity values from reconstituted laboratory compaction mold permeability tests show that the in-situ values are generally higher and more variable. The in-situ variability is attributed to segregation and is shown to be spatially correlated to the fines content (passing No. 200 sieve).

2種の圧力型歯科チタン鋳造機における鋳造圧

This study theoretically examined the relationship between mold permeability and the casting pressure acting on the molten titanium in two types of pressure casting equipment [two-chamber and one-chamber] for preparing titanium dental castings in order to select the most effective investment material and optimal casting conditions. The casting pressure exerted on the melt can be defined as the pressure difference between the melting chamber and the mold cavity after the molten titanium drops and seals the entrance to the cavity sprue. Differential equations describing the pressure in the mold cavity were derived from the equation of the state of gas as a function of time. Analysis revealed that mold permeability and the operation of each casting unit affect how the casting pressure acts on the melt: a low-permeability mold is appropriate for the one-chamber type but intermediate permeability molds are desirable for the two-chamber type. Using the results of this study and published permeability data on investments, an optimum investment material can be selected for each type of equipment.

Correlation of technological parameters and quality of castings obtained by the EPC method

In this paper, a part of the results of investigations and developments of the new evaporative patterns casting (EPC) method is presented. For successful development of the technology, it is necessary to establish initial material characteristics—polymers for making evaporative patterns, as well as conditions of their shaping in the special tools by machining. Accent is given to investigation of influence of construction and properties of the expanded polystyrene patterns of density 15 and 20 kg/m 3 on the quality of silumine castings. In addition, a survey of other technological parameters of the EPC method—casting temperature, thermophysical characteristics of cordierite and talc coatings produced by original recepture, mould permeability and pouring system construction—whose selection is performed according to the specific characteristics of the new technology, is given.

Casting Pressure in Two Types of Titanium Casting Equipment

This study theoretically examined the relationship between mold permeability and the casting pressure acting on the molten titanium in two types of pressure casting equipment [two-chamber and one-chamber] for preparing titanium dental castings in order to select the most effective investment material and optimal casting conditions. The casting pressure exerted on the melt can be defined as the pressure difference between the melting chamber and the mold cavity after the molten titanium drops and seals the entrance to the cavity sprue. Differential equations describing the pressure in the mold cavity were derived from the equation of the state of gas as a function of time. Analysis revealed that mold permeability and the operation of each casting unit affect how the casting pressure acts on the melt: a low-permeability mold is appropriate for the one-chamber type but intermediate permeability molds are desirable for the two-chamber type. Using the results of this study and published permeability data on investments, an optimum investment material can be selected for each type of equipment.

Investigation of fibre modified ceramic moulds for investment casting

The incorporation of nylon fibres in a water based silica binder to replace the costly liquid polymer addition in investment casting mould were investigated in this work. Ceramic moulds produced with fiber modified binder were found to be 13% thicker at flat section and 40% thicker at sharp edges and radii than polymer modified system. The firing strength after fiber and polymer burn out was comparable for both systems. The extra shell thickness in the fibre system, especially at edges, gives a higher load bear capacity. This has the advantage of resisting cracking during de-wax and mould wall movement during alloy casting which lead to costly defects. A much higher mould permeability at casting temperature of fibre modified system also proves advantageous to complete mould filling. The unique properties of fibre modified system lead to a promising alternative for the standard investment casting industry.

Theory of Filtration of Ceramics: II, Slip Casting on Radial Surfaces

The theory of filtration of slip casting of incompressible beds of ceramic materials in planar molds is extended to deposition on internal and external cylindrical surfaces. Formulas are developed for (a) calculating the variation of the liquid pressure in both cake and mold as a function of the radius and (b) determining the time to produce a given thickness of a consolidated body. Assuming that the mold permeability Km and capillary suction Pcap are related by an inverse parabolic relation, KmPcap2=J, there is a mold with a specific permeability that produces a maximum rate of deposition from the slip. The theory presented in this paper strictly applies only to incompressible cakes and should be used cautiously with moderately compactible beds. For highly flocculated slurries yielding highly compressible bodies, the equations would not be expected to yield reliable results. Radial geometry leads to mathematical complexities not encountered in analyses of planar molds.