雙軸式和面機設計含開題及8張CAD圖,雙軸式,和面,設計,開題,cad 英文原文 New energy-saving mechanical mixer and Overview of adaptable die design for extrusion Abstract In the work there are described the results from the laboratory researches of the basic characteristics (performance) of one new type of energy-saving mechanical mixer, conditionally named ‘Eleron’. These characteristics (performance) are compared with respective results of the other known in the literature and successfully used in practice mixers. The mixer is designed for mixing and aerating liquid systems and it will be effective for mixing in the ferment reactors for biochemical industries, where the processes are energy absorbing. Keywords: Mixer; Air-saturation; Power-number; Heat and mass-transfer during mixing; Aeration-number 1. Introduction In implementing a long-term, energy-saving program for industry [1], the department of Heat and Mass-Transfer Technics in TU-Sofia, under the guidance of the author, has conditionally created for patent an original construction of energy-saving mixer. It has a universal function for mixing liquid systems in chemical, food, wine, tobacco, and biochemical industries. We expect our mixer to take its place with dignity in fermentation technics, because of its easy manufacture, good results in air-saturation and low energy consumption. Till now it was the investigated laboratory version of ‘Eleron-1’ mixer, which is a small type, with D=(0.25/0.35)T. Universal appearance of mixer is shown in Fig. 1. It consists of a central round disk (1), which is carrying pap (2) and four wings (3). The wings are cut through in the middle (a–a) and in the beginning, near the round disk (c–c), and the receiving pieces are bend arch-shaped up and downward, making four blades with radius R=(0.05/0.07)D. Their length is L=0.8pR, as (considered) from line of bend. The blades on each following wing are in different order in bend direction, and because of this in working conditions there are circumstances for vortexes. This is very important when there is more than one mixer on a shaft (Figs. 1 and 2). When mounting, we observe the axial flows, created by curved blades, to meet each other (if we aim air saturation) or to pass each other, when we aim mixing without aeration. In this way we create multitude of symmetrical current lines (vortexes), which spread symmetrically vessel. 2. Experimental For researching characteristics (performances) of mixer ‘Eleron-1’ there are used two identical laboratory reactors with plane bottom and releasers, respectively with volumes 6.5 and 24 dm3. Reactor’s diameters are, respectively 190 and 300 mm, and mixers are make up with D_0.35T. As pattern substances there are used water and die thylene glycol, which under 20°C have dynamical viscosity and Pa · s. Reactor’s configuration is on Fig. 2 and the experiment tal installation, which is used, is on Fig. 3. With this installation’s configuration we are researching the power consumption, working with and without aeration , heat-transfer during mixing with ‘Eleron-1’, that is why reactors have heat-transfer bogies-worm-pipes (serpentines) with respective tube diameter d1 and wind up diameter dS, which are on Fig. 2. For measuring DO2 (dissolved oxygen) in liquid phase during aeration, installation also has a bottle with nitrogen, air-compressor, sensor for DO2and a writing instrument, which register on the tape the oxygen absorption (Fig. 3). Fig. 1. Scheme of mechanical mixer ‘Eleron-1’ in appearance from above. 2.1. Power coefficient determination For this mixer’s characteristic are usedtwo reactors and two pattern substances, and the rotation frequency of mixer’s shaft is changing from 100 to 1200 min_1. Rotation frequency is chosen and fixed and after that is controlled with electronic cyclometer. Eu-number is determined under equation and it is read net power consumption P, for respective rotation frequency . The dependency is in Fig. 4 and is compared with the dependency of Rush ton-turbine. 2.2. Aeration-number determination This exponent is defined under known methods, which is adopted for mixing technics. In our reactor with volume 6.5 dm3, with the help of air-distributed mechanism, the air is entranced with flow of qG_0.1 to1.5 V . The researching results are on Fig. 5 and are compared and heat-transfer surface (serpentine). Fig. 2. Configuration of laboratory reactors with mechanical mixer Fig. 3. Scheme of experimental installations: 1, thermostat; 2, reactor; 3, pressure vessel; 4, heat-transfer surface (serpentine) 2.3. Mass-transfer coefficient determination during mixing with ‘Eleron-1’ There are used two reactors with different volumes, which have air-distributed mechanisms and sensor form easuring and registering of CO2 in water. We work under 20°C, and the liquid phase, before each attempt, is scavenged with nitrogen until initial oxygen concentrationC0, which is changing progressively and is writing on the tape till establishing an equilibrium (saturation concentration) . 3 Traditional Mixer 3.1 Different ways to classify the mixers. 3.1.1 According to the number of mixing spindles .There are single-spindle mixers and double-spindle or even triple-spindle mixers. 3.1.2 According to their mixing speed .There are slow-speed mixers(less than 30rev/min), high speed mixers (above 35rev/min), and variable speed mixers. 3.1.3 According to their operation mode. They can be classified into batch mixers and continuous mixers. 3.1.4 According to the axis position of the mixing spindle from which the mixing arms receive torque and motion .They can be classified into vertical mixers and horizontal mixers .In this chapter, he machines will be discussed in terms of this classification. Investigations show that horizontal mixers are still the dominant mixing equipment in today’s modern bakery and snack industry, for they are of simple construction, simple in operation, and cheaper to run. They also have varied capacities and can be used for a wide variety of mixtures from a thin batter for cookie depositing to extremely tough dough for Chinese snack casing. 3.2 HORIZONTAL MIXERS Horizontal mixers are characterized by having a horizontally located mixing spindle on which the mixing arms are fixed into the mixing bowl .Fig.2.1 is a typical front view of this kind of mixer. 3.2.1 Construction A typical horizontal mixer consists of a mixing bowl，one or two mixing spindles by which the mixing arm(s) is or are driven through transmission mechanisms，and a main frame made of either cast iron or unitary construction of heavy steel plate，One or two motors are mounted below for mixing and bowl tilting functions together with a facia control and an electric interlock system to prevent access when the machine is running. There are two types of weighing systems: one is separate from the mixer; the other calculates the weight change of the complete mixer before and after the addition of an ingredient, the mixer being located on a suitable weighing scale or platform. In this case the mixer is often referred to as a weigh-mixer. 3.2.2 Mixing bowl The bowl of the horizontal mixers is of trough-like design with a curved bottom (U-shaped in cross section) and flat ends. The bowl surfaces in contact with the dough are commonly of stainless steel or stainless clad steel. This is the usual construction for the bowl ends, where the bearings are fixed to support the mixing spindles. The bowls of large modern mixers are generally double-‘skinned’in the form of a jacket through which chilled water or refrigerant can be circulated to prevent the dough warming up to too high a temperature as a result of mixing friction. To avoid flour and other ingredients splashing, especially at the beginning of mixing, and for safety as well as food hygiene, the bowl is always equipped with a lid which is either removable or hinged for dough discharge and cleaning. For large mixers, he lid usually has provision for assisted ingredients feed. There are two methods of dough discharging: by tilting the bowl(110。to 180。),or by mechanically sliding down the door in front of the stationary bowl to allow the dough to fall into an underlying hopper. For a ground-floor installation, the dough is often discharged into a dough tub which is usually fabricated in heavy gauge stainless steel and is supplied separately by the manufacturer. The bowl-tilting operation is generally carried out by a worm-gear mechanism in which the worm-gear is fixed on the bowl sidewall. Feeding of the bowl is carried out either manually for small mixers, or automatically through the corresponding pipes above the mixer and by means of a weighing system for large horizontal mixers. Bowls are manufactured in a wide range of volumes which allow from a few kilograms up to 1500 kg of food materials to be mixed in them. The larger the bowl size, the greater the required power of the mixing motor, so that bigger batches of dough can be mixed, resulting in a higher rated capacity for the mixer. For most large mixers, the bowl is tilted by a separate reversible motor ranging from 0.75 to 2.26Kw. 3.2.3 Mixing arms Mixing speed The mixing operation is directly performed by the mixing arms, while its power is transmitted by its driving spindle (shaft or axle).That is, the speed of the mixing arm is dependent on the speed of its spindle. Horizontal mixers are designed in either a single or dual mixing speed mode. For the dual mode, its lower speed is half the rated maximum speed. As dough mixing is often carried out in two stages-blending of the ingredients, and developing the gluten-it is essential that the first stage should be accomplished at a lower speed(for example 36 rev/min) and the second stage at the rated speed (which will be 72 rev/min).Generally speaking, the machine with a mixing speed below 30rev/min is referred to as a slow-speed mixer, and that with a speed above 35rev/min as a high-speed mixer.Modern mixers commonly cover a wide range of speed variation from 20 to 145 rev/min or even up to more than 200 rev/min, which high speed allows a quick development of gluten elastic dough by means of suitable mixing arms. The slow-speed mixers are generally used in short and soft dough mixing since a much longer time would be needed for hard and bread dough。 For of the mixing arms The mixing arms are designed in various configurations and cross-sections for different mixing functions such as blending, dispersing, beating, shearing, scraping, stretching, or kneading to form either a uniform mass or a dispersion or a solution, or aeration (that is, either a soft dough or hard dough, a sponge dough or batter or topping with other food material). Some mixing tools have a floral-hoop type, oval-type, or twisting-plate type and comprised only one or two loop-like arms without a centre shaft; they are referred to as‘shaftless’a agitators or mixing arms. The corresponding machines are referred to as ‘shaftless’ mixers. In the group, there are some other types of arm such as Z-type and S-type. Their cross-section is large to ensure strength . Their relatively complex configurations are commonly cast in one piece or are welded after forging .Attention should be paid to the coaxiality of the two sides of the arm during manufacturing to avoid severe trouble in the later mixing operation. This type of mixer can be used for a wide range of dough with different consistencies, from thin batter to extremely tough dough., as the ‘shaftless’ arms are especially efficient in dealing with extensible dough, since in their rotation orbit there is always a limited clearance from the bowl inner walls, which is beneficial in showing the dough to be stretched and kneaded repeatedly to form an oriented gluten network. Some other mixing tools (agitators) comprise simple shaped arms and a centre shaft. This kind of segmented construction is easy to manufacture and assemble, and its maintenance is lower than that of those described earlier. However, to deal with sticky dough, this group of agitators are at a disadvantage since the tendency of sticky dough is to adhere to the shaft, and the circular velocity at the centre shaft area is very low, resulting in a dead space and therefore improper mixing. Sometimes the centre shaft is covered by dough, layer upon layer. The term “adaptable die design” is used for the methodology in which the tooling shape is determined or modified to produce some optimal property in either product or process. The adaptable die design method, used in conjunction with an upper bound model, allows the rapid evaluation of a large number of die shapes and the discovery of the one that produces the desired outcome. In order for the adaptable die design method to be successful, it is necessary to have a realistic velocity field for the deformation process through extrusion dies of any shape and the velocity field must allow flexibility in material movement to achieve the required material flow description. A variety of criteria can be used in the adaptable die design method. For example, dies which produce minimal distortion in the product. A double optimization process is used to determine the values for the flexible variables in the velocity field and secondly to determine the die shape that best meets the given criteria. The method has been extended to the design of dies for non-axisymmetric product shapes. ? 2006 Elsevier B.V. All rights reserved. Keywords: Extrusion; Die design; Upper bound approach; Minimum distortion criterion 1. Introduction New metal alloys and composites are being developed to meet demanding applications. Many of these new materials as well as traditional materials have limited workability. Extrusion is a metalworking process that can be used to deform these difficult materials into the shapes needed for specific applications. For a successful extrusion process, metalworking engineers and designers need to know how the extrusion die shape can affect the final product. The present work focuses on the design of appropriate extrusion die shapes. A methodology is presented to determine die shapes that meet specific criteria: either shapes which pro-duce product with optimal set of specified properties, such as minimum distortion in the extrudate, or shapes which produce product by an optimized process, such as minimum extrusion pressure. The term “adaptable die design” is used for the method nology in which the die shape is determined or modified to produce some optimal property in either product or process. This adaptable die design method, used in conjunction with anupper bound model, allows the rapid evaluation of a large number of die shapes and the discovery of the one that can optimize the desired outcome. There are several conditions that need to be met for the adaptable die design method to be viable. First, a generalized but realistic velocity field is needed for use in an upper bound model to mathematically describe the flow of the material during extrusion through dies of any shape. Second, a robust crite- rion needs to be established for the optimization of the die shape. The criterion must be useable within an upper bound model. The full details of the method are presented elsewhere [1–6]. In the present paper, following a review of previous models for extrusion, the flexible velocity field for the deformation region in a direct extrusion will be briefly presented. This velocity field is able to characterize the flow through a die of almost any configuration. The adaptable equation, which describes the die shape, is also presented. The constants in this die shape equation are optimized with respect to a criterion. The criterion, which can be used to minimize distortion, is presented. Finally, the shape of an adaptable die, which produces of an extruded product with minimal distortion, is presented. The objective of the present paper is to provide a brief overview of the adaptable die design method. 2. Background 2.1. Axisymmetric extrusion Numerous studies have analyzed the axisymmetric extrusion of a cylindrical product from a cylindrical billet. Avitzur[7–10] proposed upper bound models for axisymmetric extrusion through conical dies. Zimerman and Avitzur [11] modeled extrusion using the upper bound method, but with generalized shear boundaries. Finite element methods were used by Chen et al. [12] and Liu and Chung [13] to model axisymmetric extrusion through conical dies. Chen and Ling [14] and Nagpal [15] analyzed other die shapes. They developed velocity fields for axisymmetric extrusion through arbitrarily shaped dies. Richmond[16] was the first to propose the concept of a streamlined die shape as a die profile optimized for minimal distortion. Yang et al. [17] as well as Yang and Han [18] developed upper bound models for streamlined dies. Srinivasan et al.[19] proposed a controlled strain rate die as a streamlined shape, which improved the extrusion process for materials with limited workability. Lu and Lo [20] proposed a die shape with an improved strain rate control. 2.2. Distortion and die shape analysis Numerous analytical and experimental axisymmetric extrusion investigations have examined the die shape and resulting distortion. Avitzur [9] showed that distortion increases with increasing reduction and die angle for axisymmetric extrusion through conical dies. Zimerman and Avitzur [11] and Pan et al. [21] proposed further upper bound models, including ones with flexibility in the velocity field to allow the distorted grid to change with friction. They found that increasing friction causes more distortion in the extruded product. Chen et al.[12] con-firmed that distortion increases with increasing reduction, die angle, and friction. Other research work has focused on non-conical die shapes. Nagpal [15] refined the upper bound approach to study alter-native axisymmetric die shapes. Chen and Ling [14] used the upper bound approach to study the flow through cosine, elliptic, and hyperbolic dies in an attempt to find a die shape, which minimized force and redundant strain. Richmond and Devenpeck [16,22,23], instead of assuming a particular type of die shape, decided to design a die based upon some feature of the extruded product. Using slip line analysis and assuming ideal and frictionless conditions, Richmond [16] proposed a stream-lined sigmoidal die, which has smooth transitions at the die entrance and exit. The streamlined die shape is the basis for many efforts in axisymmetric extrusion die design. Yang et al. [17] , Yang and Han [18] , and Ghulman et al. [24] developed upper bound models using streamlined dies. Certain materials, such as metal matrix composites, can be successfully extruded only in a narrow effective strain rate range, leading to the development of controlled strain rate dies. The control of the strain rate in the deformation zone came from studies that showed fiber breakage during the extrusion of whisker reinforced composites decreases when peak strain rate was minimized [25] . Initially developed by Srinivasan et al. [19] , the streamlined die shape attempts to produce a constant strain rate throughout a large region of the deformation zone. Lu and Lo [20] used a refined slab method to account for friction and material property changes in the deformation zone. Kim et al. [26] used FEM to design an axisymmetric controlled strain rate die. They used Bezier curves to describe the die shape and minimized the volumetric effective strain rate deviation in the deformation zone. 2.3. Three-dimensional non-axisymmetric extrusion analysis Both the upper bound and finite element techniques have been used to analyze three-dimensional non-axisymmetric extrusions. Nagpal [27] proposed one of the earliest upper bound analyses for non-axisymmetric extrusion