Papers by Keyword: Extrusion Pressure

Abstract: In order to find out optimum filler to increase manufacturability (extrudability) of composites based on ultra-high molecular weight polyethylene (UHMWPE) matrix as well as to develop polymer-polymeric composites with improved tribological characteristics, the structure, mechanical properties and wear resistance of UHMWPE mixtures with elasticizing block-copolymer PA-b-LLDPE (UHMWPE + PA-b-LLDPE) was investigated under dry sliding friction. Applied aspect of the study is related to the selection of commercially available fillers being compatible with UHMWPE for manufacturing anti-frictional extrudable nanocomposites. It is shown that as compared with pure UHMWPE mechanical properties (ultimate strength, value of elongation at failure) do not vary substantially, but the wear rate under dry sliding friction of polymeric composites UHMWPE + n wt.% PA-b-LLDPE is reduced only when block copolymer weight fraction is less than ≤ 5 wt.%. By the polymeric filling an important technological characteristic - specific pressure of extrusion (that is proportional to melt flow index) might be decreased. Permolecular structure and wear track surfaces of polymer-polymer composites UHMWPE + n wt.% PA-b-LLDPE was examined and numerically characterized.

Abstract: Surface finish and Manufacturing process has a prominent role in the fatigue life of a machine component. Fatigue strength of a material generally increases with the surface finish. But the super finishing process like electro polishing reduces the fatigue strength of the material. In Abrasive flow machining it is found that surface finish and fatigue strength always increasing. In Abrasive flow machining the fatigue strength is mainly governed by the process variables extrusion pressure, abrasive concentration and mesh size. This research studies the influence of the process variables on the fatigue strength of the material. In this study an approximate surface finish of 4μm is obtained after AFM. The effect of three process variables on the response function selected, fatigue strength, were studied. A statistical 2³ full factorial experimental technique is used to find out the main effect, interaction effect and contribution of each variable on fatigue strength. The instron machine is used to find out the number of cycles to failure of the material. The fatigue strength is obtained with S-N curve analysis.

Abstract: The content of magnesium in various parts of a nodular iron casting is measured by using spectrum analyzer. The results show that the skin of castings has an enrichment of magnesium, and the inner has a gradient distribution of magnesium, not an average distribution. Discussions on the results indicate that bubbles in the liquid metal would not move upward under the action of buoyancy, but migrate toward all directions and the bubble stranded below the surface of the liquid metal form blowholes, because these bubbles can not migrate with the obstruction of oxide films and dendrites. The results of production practices show that increasing carbon equivalent in the liquid metal is helpful to avoid blowhole defects.

Abstract: According to the theory of extrusion pressure by molding in barrel of the single screw extruder specially designed for pure UHMWPE, extrusion pressure generated during the process must be sufficient while extrusion molding with single-screw extruder. The mathematical model for formation of extrusion pressure in feeding section during single-screw extrusion molding has been established. This paper conducted a research on theory of extrusion pressure which is part of n-lamina model of non-plug flow solid conveying in feeding section by single-screw extrusion molding.

Abstract: While extrusion molding with single-screw extruder, extrusion pressure comes into being from feeding section; it is one of the basic conditions to ensure that extrusion process can be carried on normally, in order to ensure molding process goes smoothly, it must meet the following requirement: extrusion pressure generated during the process must be sufficient. Therefore it has certain engineering significance to design structure of a single screw correctly that a mathematical model for formation of extrusion pressure during single-screw extrusion molding will have to be established. This paper conducted a research on theory of extrusion pressure when powder of pure UHMWPE resin is still in feeding section by molding in barrel of the single screw extruder specially designed for pure UHMWPE, and established a n-lamina model of powder materials or grain materials which is in feeding section and at the state of non-plug flow solid conveying, and it provided a method to calculate extrusion pressure of the n-lamina model, thus it enriched and perfected theory of single-screw extrusion molding.

Abstract: In this paper, the extrusion process of bimetallic tubes is discussed, and the extrusion pressure is calculated based on the method of energy conservation, according to the three categories of metal flow that may occur during the process. A number of parameters, geometry of bimetallic tube, mechanical properties of material components and friction conditions, are highlighted in this analytical method. Compared with the data of TP304l/20G bimetallic tubes which were extruded at 1100-1200 °C, the calculated results show a good agreement with the industrial results, with the error less than 10 %. It also proves that the friction between the two layers play an important role in the process.

Abstract: Plastic deformation process resulting in ultra fine grained materials which are rapidly grasping applications due to their superior mechanical properties remain an area of continued research interest. Generally, the influence of die land length and web to flange ratio in grain refinement subsequent to plastic deformation process have not being adequately exploited especially in complex die opening geometries. In the present study, the effect of these parameters on extrusion pressure and morphological change in I-shaped die opening geometry is investigated and reported. A forward extrusion rig is designed and manufactured for the purpose of experimental investigation. The upper bound analysis shows that increasing die land length leads to increasing relative extrusion pressure. Optimum web to flange ratio of 0.45 is numerically simulated and recommended to extrude I-shaped lead alloy with minimum load requirement. The experimental results reveal that increasing area ratio leads to quasi-sinusoidal pattern in surface hardness of I-shaped section irrespective of strain rate value. Increasing web to flange ratio, therefore, leads to increasing anisotropy of the I-shaped lead alloy. The extruded sections were examined with optical metallurgical microscope, and it is observed that increasing strain rate results in profound refinement of grain and inclusions in lead alloy even at room temperature.

Abstract: The main emphasis of this study is to utilize thixoextrusion process for improving extrudability of 7075 Al wrought alloy. In the present study, the influences of thixoextrusion parameters, such as initial ram speed and die bearing length, on mechanical properties of thixoextruded 7075 Al wrought alloy were investigated. The results of thixoextrusion experiments about microstructures and mechanical properties were compared with conventional extrusion results. The maximum extrusion pressure of thixoextrusion processes was seven times lower than that of conventional hot extrusion processes. The hot extruded bars show a large amount of grains which are stretched along the extrusion direction and asymmetry of grains was formed to extrusion direction, while the microstructures of the thixoextruded bar did not show any asymmetry and grains were homogeneously distributed. The hardness values of thixoextruded bar were higher than that of conventional hot extruded bar.

Abstract: The present study discussed extrudability improvement for 7000 series Al wrought alloys by thixoextrusion, with emphasis on controlling thixoextrusion parameters, such as initial ram speed, die bearing length and extrusion temperature of billet in semisolid state. The results of thixoextrusion experiments about microstructures and extrusion pressures were compared with conventional hot extrusion results. The maximum extrusion pressure for thixoextrusion was greatly decreased than that of conventional hot extrusion. This will contribute to extrudability in terms of extrusion pressure, which in turn means that shorter process time is required and smaller extrusion machine can be applied for the same operation. It is also possible to make complex shape components of 7000 series Al wrought alloys, which is not possible by conventional hot extrusion processes. The elongated grains to extrusion direction were generally observed during conventional hot extrusion, while the thixoextruded microstructures were isotropic.

Abstract: Thixoextrusion process has been developed for improving productivity, reducing extrusion pressure, extending die life and even cost saving due to low energy consumption compared with conventional extrusion process. The present study focuses on AZ31 Mg wrought alloy to investigate the potential industrial applications of thixoextrusion process. The maximum extrusion pressures of thixoextrusion process were very lower than that of hot extrusion process. The average grain sizes of thixoextruded specimens were bigger than average grain sizes of hot extruded specimens. However, the grains of the thixoextruded specimens did not show any asymmetry. Also, the microstructures of thixoextruded specimens did not show any dendrites or rosette-like structures. The values of tensile strength and hardness of thixoextruded specimens were lower than that of hot extruded specimens. The specimens manufactured by the thixoextrusion were usually rather soft and their tensile strength was lower than those of hot extruded specimens. If necessary, their low tensile strength can be improved through appropriate heat.