Study on nitrogen barrier protection of an airend oil-free compressor bearings in H2 compression

The oil free compressors were specially designed for air compression. The National Research and Development Institute for Gas Turbines COMOTI gained a great deal of experience in producing/designing certified oil injection screw compressors for the natural gas field and for several years it has been focusing its research on the use of “dry” (oil-free) compressors in natural gas compression and more recently in hydrogen compression. Working with an explosive gas, one of an idea was to use a nitrogen barrier in oil bearing sealing, which are open source of gases in the atmosphere for such compressors. Worldwide, on-site nitrogen generators have been developed for a purity range of 95…99.5%, and that nitrogen can be supplied in any environment conditions. The present paper will address nitrogen flow with low percentage of oxygen for bearing sealing at the working pressure, the nitrogen consumption, ideas for H2 re-injection and the influence over the global efficiency of the process. Due to the Energy Strategy worldwide, and the studies regarding production, transport and storage of hydrogen in natural gas network, COMOTI has involved researches in developing such possibilities and to express a point of view in existing research in the newly created industry.

Analysis on vibration characteristics of screw in filling process of dynamic injection molding machine

This paper presents a study of the characteristics of axial vibration of a screw in the filling process for a novel dynamic injection molding machine. By simplifying a generalized model of the injection screw, physical and mathematic models are established to describe the dynamic response of the axial vibration of a screw using the method of lumped-mass. The damping coefficient of the screw is calculated in the dynamic filling process. The amplitude-frequency characteristics are analyzed by the simulation and experimental test of polypropylene. The results show that the amplitude of a dynamic injection molding machine is not only is related to structure parameters of the screw and performance of the material, such as non-Newtonian index, but also depends on the processing parameters, such as vibration intensity and injection speed.

Design analysis of a standard injection screw for plasticising polycarbonate resins

The industrial use of plastic injection moulding machines is widespread. However, few studies have examined the injection screw, which is one of the key components of moulding machines. Studies have demonstrated that a properly designed injection screw improves both the moulding quality and the production rate. Factors that affect the plasticisation properties of conventional standard reciprocating screws include the screw geometry, the screw operation settings, and the processed resins. An ideal standard reciprocating screw exhibits a high plasticising capacity and excellent melt temperature homogeneity; however, these properties typically conflict. Through simulation analysis, this study investigated the optimal design of a standard reciprocating injection screw used for plasticising polycarbonate resins. First, the Taguchi method was integrated with a commercial simulation programme to identify the key control factors affecting the plasticising rate of a screw and the temperature uniformity of the melt. Simulation results revealed that the screw diameter, rotation speed, metering channel depth, ratio of the screw length to the screw diameter, and compression ratio substantially influence performance. Consequently, grey relational analysis was adopted to optimise the design of an injection screw that ensures sufficient quality according to the plasticisation rate and the homogeneity of molten plastic.

Strength Enhancement of Styrene Acrylonitrile Co-Polymer via Delay Pack Injection Molding

This study investigates the effects of processing of styrene acrylonitrile (SAN) by injection molding using a delayed packing stage. The concept of Delay Pack Injection Molding (DPIM) evolved from an in-situ study of vibration-assisted injection molding (VAIM) which indicated that the beneficial effects of VAIM came not from the vibration itself, but rather from the delay in the onset of packing resulting from the application of the vibration. Conceptually, DPIM involves normal filling of the mold immediately followed by a slight retraction of the injection screw for a specified time period before the final packing pressure is applied. Application of DPIM results in increased birefringence in the molded parts and increases in the ultimate tensile strength of molded parts very similar to the effects seen using VAIM. A parametric study using a design of experiments framework was carried out to determine the delay pack parameters affecting SAN and resulted in a maximum increase in UTS of 11.6%. Observation of birefringence patterns in Delay Pack processed samples shows a significant impact on molecular orientation while observation of failed specimens and their fracture surfaces shows distinctly different modes of crack growth and failure. Growth of craze cracks resulting from tensile loading appeared to be arrested by oriented areas surrounding the part core allowing the specimen to sustain higher loads relative to conventionally molded parts. All of the above observations are consistent with the observed effects of vibration-assisted injection molding.