Examination of Interpenetrating Polymer Networks of Polyurea in Silicone Molds Arising during Vacuum Casting Processes

We present an in-depth investigation of the aging effects in silicone molds for vacuum casting processes. Their lifetime is limited to a few production cycles due to contamination with the diisocyanate component of polyurethane casting materials. Using thermogravimetric analysis measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and helium-ion-microscopy the chemical and physical mechanisms of the aging process have been identified. It has been shown that a diffusion process of diisocyanate into the cavity surface leads to the formation of interpenetrating polymer networks of polyurea derivatives in silicone rubber. This has been proven by extracting and analyzing polyurea of low molecular weights from the silicone.     

Examination of the Aging Effects of Silicone Molds During Vacuum Casting Processes via Scanning Electron Microscopy

We present an in-depth investigation of contaminated silicone molds by use of scanning electron microscopy, that provides additional insight into the aging process of the molds. The molds lifetime in vacuum casting processes of polyurethane is limited due to contamination with the diisocyanate compound of the PUR resin. SEM investigations, combined with FIB cross-sections and EDX measurements show that three different types of particles are distributed in the contaminated silicone matrix. The particles differ in shape and size, with a range from 50 nm to 50 µm. This explains the loss in transparency and the hardened haptics of contaminated molds.     

聚乙烯加工流变改性剂在LLDPE电缆护套料中的应用

介绍了有机硅型聚乙烯加工流变改性剂ＱＬＹ在ＬＬＤＰＥ电缆护套料中的应用。对加有ＱＬＹ的ＬＬＤＰＥ护套料的流变性能进行了试验研究，测试了该护套料的物理机械性能并举了应用实例。结果表明，在ＬＬＤＰＥ电缆护套料中，加入少量的有机硅型改性剂后，能使熔体的表观粘度下降，从而解决了加工困难的问题提高了产量，降低了能耗，也解决了电缆涂布中发生的熔体破裂现象，消除了产品外观产生的鲨鱼皮现象，使国产ＬＬＤＰＥ电缆护     

Development of New Cordierite‐Based Refractory Coatings for Casting Applications

In this study, new refractory coatings based on synthesized cordierite for the casting applications were developed. The investigation included starting raw materials characterization, synthesis of the cordierite, design of the refractory coating as final product, and its application testing. The obtained results pointed out that coating suspension sediment stability was crucial quality parameter. Design and optimization of the coatings composition, with controlled rheological properties included, were achieved by application of different coating components, namely different suspension agents and by alteration of the coating production procedure. Cordierite, used as filler, was obtained by means of synthesis in the solid‐state reaction on the basis of talc, kaolin, and alumina. The investigation showed that the application of these particular types of water/alcohol‐based coatings has positive influence on surface quality and structural and mechanical properties of the castings of aluminum alloys obtained by casting into sand molds by means of evaporable models method, that is, evaporate pattern casting process.     

Modification of polyolefins with silicone copolymers. I. Processing behavior and surface characterization of PP and HDPE blended with silicone copolymers

Permanent surface modification of polypropylene and high‐density polyethylene was obtained by blending with small (0.1 to 5.0% by weight) amounts of silicone copolymers. A triblock polycaprolactone‐b‐polydimethylsiloxane copolymer and a multiblock polydimethylsiloxane–urea copolymer were used as modifiers. Blends were prepared in a twin‐screw extruder. Influences of the type and amount of the additive on the processing behavior and surface and bulk properties of the resulting systems were investigated. During processing, the additives also acted as very efficient processing aids, increasing the extruder output dramatically, up to 200%. Surface characterization by water‐contact angle measurements and X‐ray photoelectron spectroscopy clearly showed the formation of silicone‐rich surfaces even with very small amounts of additives, such as 0.1% by weight. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1625–1634, 2002     

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.     

Rotational molding cycle time reduction through surface‐enhanced molds,Part B: Experimental study

Rotational molding is a process used to manufacture hollow plastic products, and has been heralded as a molding method with great potential. Because of long production cycle times, which are limited by the time required to heat‐up and cool‐down the mold and the product, its productivity is hampered. To address this issue, exterior mold modification techniques (i.e. the application of extended and rough surfaces) have been employed to enhance heat transfer to and from molds, ultimately reducing cycle times. Extended surfaces have the potential to enhance heat transfer by increasing the surface area. Roughness elements are utilized in conjunction with turbulent flows, also producing significant increases in heat transfer rates. Experimental results presented here demonstrate very significant cycle time reductions through the use of surface‐enhanced molds. The experimental savings are in the order of 18 and 28%, whereas the predicted cycle time reductions are around of 21 and 32% for roughness‐enhanced and pin‐enhanced molds, respectively. Although the prediction methods have been unable to forecast the exact experimental cycle times very accurately, they have proved to be useful for predicting the approximate cycle time reductions and the relative rankings of the plain and the surface‐enhanced molds. POLYM. ENG. SCI., 47:1420–1429, 2007. © 2007 Society of Plastics Engineers     

Slip casting molds produced by hot isostatic process

Slip casting can produce large green bodies of fairly complex shape with high homogeneity. In this work, porous alumina produced by hot isostatic process (HIP) is evaluated to apply as slip casting molds. HIPed porous alumina molds have higher water suction rate than conventionally sintered ones with a same open porosity. The high water suction rate of HIPed molds is due to the low specific surface area of HIPed porous materials. The high water suction rate of HIPed porous alumina molds allows high casting rates.     

Improving the design and technology of molds for ceramic articles

Ways of improving the design and the manufacturing technology of porous and poreless molds for shaping ceramic articles by the methods of slip casting and plastic molding are considered. New techniques for the production of porous molds are suggested, which make it possible to decrease the cost of the molds and optimize the processes of slip casting and plastic molding of ceramic articles.     

Hydrolysis and other phenomena affecting structure and performance of polyamide 6 membrane

The rate of hydrolysis of polyamide 6 in membrane casting solution containing strong mineral acid has been studied by determining changes in molecular weight, as estimated from dilute solution viscometry measurements. Hydrolysis is shown to be first order with a long half-life of about 250 days. A two-step dissolution process for polyamide 6 is proposed. The effect of extended dope maturation time upon polyamide 6 membrane preparation and performance has been examined. At short maturation times where protonation of polymer chain is occurring, flux is relatively low. A major increase in flux occurs after about 10 h, when protonation appear complete and hydrolysis has begun. Hydrolysis reduces polymer chain entanglement, and so quite different mechanisms for membrane formation exist as dope maturation time proceeds. With chains less than the critical entanglement length, nodular top layer membranes and alveolar walls lead to high water flux. However, such membranes are quite fragile.     

A freeze method of obtaining ceramic based on fused quartz

Conclusions The technology of producing materials based on fused quartz by freezing the blank in a liquid nitrogen medium has been studied.The advantages of this method over slip casting in porous molds are: a reduction in the molding time; the production of articles with a large variety of wall thicknesses and complexity of surface; the possibility of firing the blanks immediately after molding; the production of strong articles with a porosity of 40-0%; the possibility of making articles with specified dimensions without mechanical treatment; and the simplicity of the process.Assistance was given in the manufacture of the molds and the molding of the specimen material.Translated from Ogneupory, No. 7, pp. 49–52, July, 1980.     

有机硅防水涂料的研制与施工

研制了一种新型有机硅防水涂料。涂料中的有机硅分子与基材表面的羟基紧密结合,形成网状疏水性硅氧烷膜,成为一种防水性、耐久性优的防水剂。介绍了该产品的配方组成、工艺流程、施工工艺及产品技术指标等。     

Experimental casting of multichamotte refractories from slip

Conclusions The possibility of casting refractories from multichamotte slip with a maximum moisture content of 15% has been investigated; a preliminary treatment of the slip under vacuum is recommended as well as a brief vibration of the gypsum molds within a certain period after pouring.The high rate of moisture loss and solidification of multichamotte slip castings allow production on an industrial scale.Multichamotte kaolin mixtures yield castings up to 100 × 80 × 80 mm which acquire the following properties after firing at 1470° C: bulk density –2.17–2.26 g/cm³; porosity –12 to 18%; compressive strength –420 to 800 kg/cm²; loss on ignition –2. 7 to 4. 3; total shrinkage in relation to the size of gypsum molds –4 to 5%.The casting process is of practical value for the manufacture of multichamotte products (including high-alumina refractories) since molding the latter by means of pressing is either impossible or extremely difficult.Industrial tests are conducted for the verification and more accurate determination of technological parameters and the technical and economic effectiveness of the method.     

Surface properties of polyamides modified with reactive polydimethylsiloxane oligomers and copolymers

Surface modification of polyamide-6 (PA-6) was investigated by melt blending with silicone-urea copolymers or organofunctionally terminated polydimethylsiloxane oligomers. Blends were prepared in a laboratory scale high-shear melt mixer. Surface characteristics of the blends were determined by static water contact angle measurements and X-ray photoelectron spectroscopy. Effect of the type, composition, average molecular weight and amount of the silicone additive in the blends, on the surface properties were determined. Influence of the thermal history of the samples on the surface properties was also investigated. All of the blends showed formation of silicone rich surfaces. Surface modification was permanent due to either the formation of chemical bonds between additive and polyamide and/or very strong hydrogen bonding between urea and amide groups.     

High precision pulp-based sacrificial molds: A solution towards mass production of hollow ceramic spheres for deep sea applications

Hollow ceramic spheres are considered as an excellent buoyancy unit for deep-sea applications (> 5,000 m). However, there is no successful commercialization due to the low productivity of conventional slip casting because of the short life span of gypsum molds. In this work, we have developed single-use pulp-based molds for ceramic slip-casting applications. The developed robust pulp mold offers the advantage of being combustible in a controlled manner during the ceramic sintering process. The smooth, wrinkle-free inner surfaces, controlled water swelling, high wettability, and ability to retain shape during wet casting make the molds highly suitable for producing hollow ceramic spheres on an industrial scale. Alumina-based spheres with 52.8 mm diameter, 1.08 mm wall thickness, 0.46 g/cm³ density, and 54% buoyancy were successfully produced in pulp molds after sintering at 1630 °C. The spheres show exceptionally high hydrostatic failure pressures of above 200 MPa (> 20,000 m) and can be safely operated at depths greater than 5,000 m below sea level. We envision this approach to facilitate the mass production of ceramic spheres with the possibility of creating other complex-shaped ceramics via slip casting in pulp-based molds.     

Fabrication of bioceramic scaffolds with pre-designed internal architecture by gel casting and indirect stereolithography techniques

A new technique of combining the gel casting and indirect rapid prototyping methods was utilized to fabricate macroporous β-tricalcium phosphate (β-TCP) scaffolds, which provided an excellent control over the internal architecture of scaffolds and enhanced their mechanical properties. A stereolithography apparatus was used to produce resin molds for ceramic gel casting. These molds were filled with a water based thermosetting ceramic slurry which solidifies inside the mold. After burning the resin mold and sintering, the β-TCP scaffolds with designed pore architecture were obtained. The pore morphology, size, and distribution of the resulting scaffolds were characterized using a scanning electron microscope. X-ray diffraction was used to determine the crystal structure and chemical composition of scaffolds. The mechanical measurements showed that the average compressive strength was 16.1 ± 0.8 MPa.     

“Memory” of the substrate/solution interaction in the properties of ultrafiltration membranes prepared by the phase-inversion method

The productivity and some structural properties of membranes made by the casting of aromatic polyamide on various substrates are found to be sensitive to the wetting characteristics of the used substrate. The influence of the interaction substrate/solution expands through the membrane bulk up to the “free” surface which was not in contact with the substrate. © 1996 John Wiley & Sons, Inc.     

Fabrication of antibacterial silicone composite by an antibacterial agent deposition,solution casting and crosslinking technique

The key problems faced in developing indwelling catheters are how to incorporate antibacterial agents into the substrate and how to improve the antibacterial effectiveness. In this study, an antibacterial composite coating layer is inversely in situ formed on the silicone substrate by a novel technique involving deposition of an antibacterial agent, solution casting and crosslinking of a silicone resin. The antibacterial particles were strongly bonded to the matrix silicone and evenly dispersed on the coating surface. Moreover, energy‐dispersive X‐ray analysis revealed the gradient distribution of the antibacterial agent, perpendicular to the composite surface. The co‐instantaneous crosslinking within the coating layer and polymer substrate as well as the graded structure formed lead to good adhesion between the two parts. The silicone composite shows a highly efficient antibacterial activity with no cytotoxicity to HL‐60 cells. Compared with the commonly used methods of incorporating antibacterial agents into the silicone substrate, such as multiple dip‐coating, surface grafting or simple blending, the proposed process is easily operated and is promising for forming a percutaneous or subcutaneous device with the capacity for efficient sterilization in an economical way. Copyright © 2011 Society of Chemical Industry     

聚酰胺供需状况和我国发展建议

综述了国内外聚酰桉生产、消费、市场、生产厂家和产品开发特点，并根据中国聚酰胺工业现状、供需状况与国外的差距，提出了加快发展中国聚酰胺工业的建议。     

Enhancement of convective heat transfer to polymer manufacturing molds

Many complex and dimensionally stable plastic products are manufactured using processes such as blow molding, thermoforming, injection molding, and rotational molding due to various advantages offered by these techniques. However, in many cases, product cycle times—and hence productivity—are limited by the time required to heat up and cool down the mold and the product. This is particularly true for rotational molding of thermoplastics. Due to the complex rotation of the mold, heating and cooling are most commonly achieved by convection to the external surfaces of the mold using air as the transfer medium. The objective of this work is to achieve substantial enhancement in convective heat transfer to mold exteriors and ultimately to reduce production cycle times. In this paper, the application of extended surfaces and roughened textures to molds is investigated. Extended surfaces have the potential to enhance heat transfer by increasing the surface area. Roughness elements are utilized in conjunction with turbulent flows, also producing significant increases in heat transfer rates. A steady state analysis using well‐established techniques has been performed to estimate the heat transfer enhancement, and a series of simple experiments have been carried out. The predicted enhancements to heat transfer are substantial, and have been verified by the preliminary experimental results. POLYM. ENG. SCI. 45:114–124, 2005. © 2004 Society of Plastics Engineers