Mold Coatings Research Articles

Release red mud-based coatings for foundry steel molds

Release red mud-based coatings for foundry steel molds

An Indirect Evaluation Method of Mold Coating Thickness in AlSi Alloy Permanent Mold Casting Production

Permanent mold casting produces the second most aluminum cast parts among all casting processes. In this process, mold coating changes the heat transferred from the molten metal to the mold by acting as an insulating layer. Moreover, the coating thickness is a significant variable regarding the coating’s thermal resistance, which strongly influences the microstructure of cast parts and the thermal shock on expensive molds. However, in casting production, coating peeling-off and repeated recoating result in an inhomogeneous coating thickness distribution. Due to the high working temperatures of the molds, no efficient online coating thickness measurements exist. We propose an indirect evaluation method based on the as-cast surface corresponding to the coating area. Our experiments analyzed as-cast and coating surfaces at nine different coating thicknesses. The results show a close correlation between the as-cast surface roughness parameter of arithmetical mean height Sa and the coating thickness. Based on this correlation, we can derive the coating thickness from the corresponding as-cast surface analysis. Furthermore, the coating peel-off area and other casting surface defects are easily recognized in these surfaces. In our next work plan, an affordable optical camera and proper light conditions will be tested by taking photos of as-cast surfaces, and an algorithm for the real-time automatic evaluation will be developed.

Influence of the injection molding thermal boundary conditions on the filling flow of PET

During the filling phase of the injection molding process, the polymer in contact with the wall solidifies, developing the so-called skin layer. Although the no-flow temperature is often exploited in numerical simulations to model the skin layer formation mechanism, there is still an incomplete understanding of what happens for semi-crystalline PET. In fact, for this polymer, the high shear stresses near the cavity wall combined with the thermal gradient at the polymer-mold interface can cause the so-called flow-induced crystallization. This work aims to experimentally investigate the skin layer formation at different injection molding processing conditions. A full-factorial experimental plan was performed using a commercial PET injected into an open-cavity mold. The thermal and mechanical boundary conditions at the polymer-wall interface were varied using insulating coatings and different flow rates, respectively. The mold coatings were applied to different steel substrates to consider the substrate thermal conductivity contribution. Different flow rates were imposed, varying the cavity thickness and the injection speed. The in-line acquisition of the cavity pressure allows for assessing the contributions of the modified boundary conditions to the solidified skin layer formation. The results show that the insulating mold coating changes the thermal boundary conditions, leading to a maximum pressure decrease of 14 %. The cavity pressure vs. filling time curves for the uncoated inserts show an evident derivative discontinuity, suggesting the onset of flow-induced crystallization.

Advanced technologies for development of non-stick anti-burn coatings for iron casting

Burns on iron castings produced in non-metallic molds is still an urgent problem in the foundry industry. Its removal results in high costs as well as a noticeable deterioration in production ecology. However, recently this issue has been neglected in spite of the fact that in the processes of burns formation there is still a lot to consider. This paper is aimed at surveying technologies for increasing the efficiency of anti-burn molds for iron casting. According to conducted analysis, the use of anti-burn coatings for molds and cores is certain to be an important part in the manufacturing iron castings. A poor-quality coating can be caused by non-compliance with such requirements as the percentage of paint, the technology of its application and surface drying of the casting mold. Therefore improving the efficiency of antiburn coatings remains an urgent problem even nowadays. Currently scientific research concerning with this problem is focused on developing the following three directions: the search for new cost-effective initial components of coatings (fillers, binders, additives); technologies development for improving the physical and mechanical properties of coatings initial components by individual or complex activation methods as well as improving methods for studying the structure and properties of the coating at all stages of its properties formation.

Sand casting of surface alloyed butterfly valve with improved hardness and corrosion resistance by incorporating metal powders in-mold coatings

A cost-effective procedure to surface alloy WCB steel butterfly valve sand castings using mold coatings incorporating metal and ferroalloy powders has been described. The tooling, mold design, and casting conditions similar to plain WCB castings were successfully used to produce sound surface alloyed butterfly castings under industrial conditions. The surface alloying was achieved by adding powders of Ni, Cr, Fe–Si, Fe–Mn, and Mo to the slurry containing a binder coated on the mold surface. The surface alloyed coatings on the surface of WCB steel butterfly valve castings were enriched in Ni, Cr, Mo, and Mn up to 6.4, 23.2, 3.3, and 1.1%, respectively. The depths of coatings were as high as 420 µm. After normalizing and tempering heat treatment, the surface alloyed layer exhibited an increase in corrosion resistance as compared to base metal WCB steel.

Improving appearance quality of injection molded microcellular parts through mold coating of PTFE and zirconia

AbstractThe application of microcellular parts in the field of high appearance quality is limited due to its appearance defects. In order to improve the appearance quality of microcellular parts, low heat transfer coefficient mold coating with PTFE and zirconia was employed in this study. The appearance quality of microcellular was evaluated by the surface roughness of microcellular parts. The numerical and experimental results show that delayed heat transfer between the melt and the mold can be achieved through both mold coatings, which improve the melt fluidity and reduce the shear force of the mold on the melt effectively. It is demonstrated that the PTFE has a better effect of delay heat transfer under thinner coating. The polished zirconia coating shows more conducive to the melt wall slip due to its stable molecular structure and smooth surface, resulting in microcellular parts with better appearance quality.

The Formation and Frictional Behavior of Ni and Cu Aluminide Coatings on Copper

The microstructure and frictional behavior of candidate protective coatings for steel continuous casting copper molds were studied. A number of conventional coatings, consisting of the hard chromium deposited by electroplating, nickel-phosphorus deposited by electroless plating, and WC-17Co deposited by high-velocity oxy-fuel spraying, were compared with copper aluminide and nickel aluminide coatings. The copper aluminide coating was formed via pack cementation diffusion and aluminized in the Al-AlCl3-Al2O3 powder mixture at 500 °C. The nickel aluminide coating was obtained using the same aluminizing treatment, yet after depositing an electroless nickel-phosphorus interlayer. The microstructure of the coated specimens was characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy and x-ray diffraction phase analysis. Cu9Al4 was identified as the main phase of the copper aluminide coating, whereas Ni2Al3 and NiAl phases were identified in the nickel aluminide coating. The evaluation of the coatings frictional behavior through a pin-on-disk machine applying a 12 N loading showed that the copper aluminide coating is worn away and that the nickel aluminide coating remains intact up to the end of the test. The reference coatings revealed negligible wear with the material transfer from the pin to their surface. The copper aluminide coating demonstrated the least friction coefficient among the entire evaluated coatings.

Gaseous Atmosphere During Gas Forming Tendency Measurements of the Selected Protective Coatings for Sand Moulds

Gaseous Atmosphere During Gas Forming Tendency Measurements of the Selected Protective Coatings for Sand Moulds

Plastic intensity reduction using thermally insulating coatings for injection molds

The use of plastics in today's world is still increasing despite its enormous burden for environmental sustainability. The urge to reduce plastics impact is driving the development of novel technological solutions. The high viscosity of thermoplastic polymer melts often leads to the design of oversized plastic parts having wall thickness higher than structural requirements. This work proposes a novel approach to wall thickness reduction, exploiting the thermally insulating effect of mold coatings. Four different mold coatings were characterized using inline rheological testing carried out on a PET using a slit-die open mold. The thermal boundary condition of a numerical model was calibrated by fitting the numerical to experimental pressure values. The thickness reduction associated with the use of a specific coating was then quantified for a case study geometry using the calibrated model. The results indicated that it is possible to reduce the thickness of the part by 12%, leading to material consumption and cycle time reduction of 8% and 22%, respectively.

Microstructure and Wear of (CrN/CrAlN)/(CrAlN/VN) and (CrN/TiAlN)/(TiAlN/VN) Coatings for Molds Used in High Pressure Casting of Aluminum

Molds made of tool steels used in aluminum high-pressure die casting should routinely withstand tens of thousands of injection cycles, but repeated loading and temperature spikes result in their frequent premature wear. Extending their lifetime could be sought by nitriding or application of coatings of even higher hardness or both. Therefore, in the present experiment the arc-deposited Cr/(CrN)/nx(CrN/CrAlN)/mx(CrAlN/VN) or Cr/(CrN)/nx(CrN/TiAlN)/mx(TiAlN/VN) nano-multilayer stacks were deposited on glow discharge nitrided X40CrMoV5.1 steel. The scanning and transmission electron microscopy backed by Energy Dispersive X-ray Spectroscopy measurements of local chemical composition helped to confirm that the coatings are built of nanolayers of respective nitrides of period less than 10 nm. They also showed that droplets being characteristic for arc deposition method were enriched either in chromium, aluminum or vanadium but not in titanium. Both coatings presented comparable hardness of ~25 GPa, but the one covered with TiAlN/VN was roughly twice as wear resistant as the CrAlN/VN. Simultaneously, they were ~200 and ~100 more wear resistant than X40CrMoV5.1reference steel.

The Study of lithic assemblages on deflation surfaces. The case study of Arroyo Verde, Northern Patagonia coast, Argentina

This paper focuses on surface lithic artefacts from Holocene coastal hunter gatherer occupations of Arroyo Verde archaeological locality (Rio Negro province, Northern Patagonia, Argentina). The study of lithic assemblages collected at a deflation surface surrounded by stabilised sand dunes near the coastline, shows that wind produce significant corrasion (wind abrasion) of artefacts and affects preservation of small and medium size artefacts. The sample is mainly composed of chert knapping debitage with abraded and polished edges and surfaces. The artefact size distribution suggests that a subset of the assemblage exhibits good preservation, possibly due to the recent subaerial exposure. Furthermore, carbonate and mould coatings were recorded over the artefacts surface in contact with the ground, which indicates the presence of humid conditions in the sand dunes deflation area. In order to explore the factors that affected assemblage stability conditions in the locus, a machine learning based decision tree was applied. The model predicts and defines a threshold at which the occurrence of instability conditions may appear. Also, it suggests that relative altitude of artefacts within the deflation hollow is the primary variable explaining the exposure conditions recorded in the artefacts and it points out processes of differential deflation over time. The data presented here illustrates how wind alters local surface materials and emphasizes that a taphonomic perspective is needed to assess the formation processes within northern Patagonia coastal archaeological assemblages.

Tribological effects of mold surface coatings during ejection in micro injection molding

The effects of different mold coatings on the ejection force in micro injection molding were experimentally investigated. Two diamond-like-carbon and chromium titanium niobium nitride coatings were selected in accordance with their potential affinity with the considered injected polymers. The obtained results were correlated with the wetting properties for all the combinations of injected polymers and surface coatings. Moreover, the tribological properties of the different coatings were evaluated using an off-line friction test. The ejection force peak was correlated to the static friction coefficient. For each polymer a good linear correlation between the online and the offline friction characterization was identified, indicating the effectiveness of the proposed procedure in evaluating the tribological properties of different coatings for different polymers.

Functional coatings for titanium casting molds using the replica technique

The quality of titanium cast parts depends not only on the corrosion reaction of the mold in contact with the titanium alloy melt, but also on the dimensional accuracy and the surface quality of the investment casting mold. Usually, the ceramic mold is produced by dip-coating. This contribution investigated the coating properties of green calcium zirconate (CaZrO3) coatings produced by the replica technique. Thus, the effect of different coating slurries as well as different coating technologies on important coating properties was analyzed. In all cases, centrifuging and spraying produced thinner coatings compared to dip-coating. Using an appropriate coating slip, particularly centrifuging revealed a cohesive homogeneous coating surface and is therefore a promising technology for the production of functional coatings for titanium casting molds.

Effect of Mould Coatings and Pouring Temperature on the Fluidity of Different Thin Cross-Sections of A206 Alloy by Sand Casting

Thin-wall castings of the A206 alloy can pose a manufacturing problem associated with mould filling which results in fluidity defect. The mould coating generates a smooth surface, and reduces the friction between the melt and mould contact, thus reducing the heat-transfer coefficient, which in turn leads to enhancement of fluidity and mechanical properties. The fluidity of A206 alloy was observed in various cross-sections of the thin channels at three altered pouring temperatures i.e. 700, 750 and 780 °C for uncoated and coated green sand moulds. The Graphite and Soapstone powder coatings were used as sand mould coatings in the present investigation. It was found that the fluidity of aforesaid alloy was significantly increased with the Soapstone powder mould coating at pouring temperature of 750 °C. The characterization of the coating materials was performed by the X-ray diffraction analysis and scanning electron microscope test with EDAX.

Thin-wall injection molding of polystyrene parts with coated and uncoated cavities

Low-friction mold surface coatings can be used to promote filling of thin-wall parts through reduction of the melt flow resistance by causing wall slip at the polymer-mold interface. This work investigates the effects of different mold coatings (DLC, CrN and CrTiNbN) on the flow resistance of molten polystyrene in thin-wall injection molding. The design of the mold allowed high-speed visualization of the molten polymer flow during the filling phase and measurement of the velocity profile across the cavity thickness. The evaluation of the speed profiles allowed the characterization of the wall-slip phenomenon, indicating the absence of conventional ‘fountain-flow’ filling mechanism. The results indicate that a DLC deposited on a chrome substrate can significantly reduce the flow resistance of polystyrene, by increasing the slip velocity of polymer melt in contact with the mold surface. Moreover, the contact angle of molten polystyrene over the considered coatings was found to be inversely proportional to the melt flow resistance, indicating the importance of the adhesion at the polymer-mold interface.

Replication of micro-structured injection molds using physical vapor deposition coating and dynamic laser mold tempering

AbstractPlastics parts with micro-structured surfaces enable the development of innovative products such as optical components in sensors or light management systems for laser and LED applications. Moreover, micro-structured parts can be utilized in the medical and packaging industry for hydrophobic or antibacterial products. The production of micro-structured parts causes challenges in molding and demolding. Rough surfaces of the laser-structured mold inserts offer flow resistance during injection phase as well as increased demolding forces which cause failures of the replicated structures during ejection. Therefore, an innovative approach combines coated mold inserts by means of physical vapor deposition (PVD) and a highly dynamic laser tempering system to improve the replication of micro-structured plastics parts. Both uncoated and coated micro-structured mold inserts were used in a series of molding experiments by means of conventional and dynamic mold tempering. Based on the results, it can be shown that significant improvements of the replication of micro-structures of different sizes can be achieved by use of PVD mold coatings. This is attributed to the tribological interactions between coating and plastics melt. Furthermore, results indicate an influence of the thermal conductivity of PVD coatings to enhance replication quality.

Inductively Coupled Plasma Assisted Magnetron Sputtered Nanocrystalline Vanadium Nitride Coatings for Corrosion Protective Molds

Inductively Coupled Plasma Assisted Magnetron Sputtered Nanocrystalline Vanadium Nitride Coatings for Corrosion Protective Molds

Effect of Mould Coating on Skin Formation and Nodule Characteristics of Thin Wall Ductile Iron Casting

Thin wall ductile iron (TWDI) has the potential alternative for lightweight aluminium use in automotive parts. The main problem in TWDI, however, is the formation of skin during the casting, which may reduce its mechanical properties. This casting skin is formed by the decomposition of nodular graphite at the mould interface during the casting process. One of the ways to work around this problem is by using mould coating to control the cooling process. In this work, three variables of mould coatings were used, i.e. graphite, MgO, and MgO/graphite double layers. The results showed that the average casting skin thickness in double layer coating was the lowest (30.41 μm), 57% lower than that of in MgO (71.46 μm) and 60% lower than that of graphite (74.44 μm). The reduction of casting skin thickness increased the mechanical properties of TWDI (346 MPa), 69% higher than that of MgO (223 MPa) and 26% higher than that of graphite (297 MPa). The same is true for ductility (2.7%), which was higher than that of MgO (1.43%) and that of graphite (1.43%).

Gas Evolution Rates of Graphite Protective Coatings in Dependence on the Applied Solvent and Kind of Atmosphere

Abstract The results concerning emission of gases from two commercial graphite protective coatings for moulds and cores (water and alcoholic) are given in the hereby paper. Investigations were performed in two systems. One of the systems was corresponding to conditions occurring inside the mould cavity immediately after its pouring with liquid metal (Method 1), while the second was simulating conditions deep inside the mould at a certain distance from the casting (Method 2). Investigations were carried out in the CO2 atmosphere and in the air. The water protective coating generated 1.5 to 3 times larger volume of gases than the alcoholic coating (in dependence on the measuring method and atmosphere). The smallest differences occurred in the air atmosphere, while the largest in the CO2 atmosphere.

Evaluation of nano ceramic coating on radiographic defects of thin-walled AL4-4 aluminum alloy sand casting

Internal defects are among the problems in gravity casting of aluminum parts. The main internal volumetric defects are gas and shrinkage defects which form during solidification of the melt and drastically reduce the quality of the produced parts. These defects adversely affect the mechanical properties of thin walled castings parts. In this study, ceramic nanoparticles coatings were applied on the sand mold and the effect of mold coatings on the reduction of defects were investigated. X-ray radiography was used to detect defects in sand molds with ceramic nanoparticles coatings. For comparison, this test was performed on molds with micro-ceramic and graffiti coatings and uncoated sand mold. The results showed that the maximum amount of gas and shrinkage defects was observed in casting parts from AL4-1 alloy in uncoated molds. On the other hand, the minimum defects were found in molds coated with ceramic nanoparticles. It seems that the reduced defects in casting parts in molds coated with ceramic nanoparticles may be due to high thermal and chemical stability and higher heat transfer rate of the coating. These results can facilitate the production of high quality aluminum alloys parts using nanotechnology.