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鞍山科技大學本科生畢業設計（論文） 第 1 頁THE SELF-GRINDING MECHANISM AND AFFECTING FACTORS OF BULK MATERIAL IN FLUID MOTIONAbstract: The fluidity and classfication of bulk material (loose body) were introduced, the self-grinding mechanism and the affecting factors bulk materials in various forms of phase, state and motion were investigated. A rotational-flow-state centrifugal autogenous grinder was developed on the basis of applying self-grinding mechanism of bulk material, the result tested by the autogenous grinder was compared with extremely high specific area were obtained. The feasibility lf the developed new-type artogenous grinder in the view of fluid motion of bulk material was proved.Key words: motion of bulk material; self-grinding mechanism; new developed mill1 IntroductionComminution except coarse grinding in most commintors or crushing machines is performed in the course of motion of bulk materials. Only in a few comminting equipments such as rollermill and extruding milll, the vomminuted materials are stationary or fluid motion was provided through grasping the characteristic of fluid motion in the course of comminuting.2 Fluid Motion of Bulk Materials2.1Fluidity of bulk materialsIn unconsolidated media mechanics, bulk material is also named loose body, it is the aggregate of interrelated solid particles, where a single particle presents the characteristic of solid and is the skeleton of the loose body. However, in macroscopic view, it also presents fluidity and some characteristics of liquid: (a) being the same with liquid, bulk material can not keep a certain shape; (b) both bulk material and liquid can not bear a tension force but bear a pressure force. The difference between bulk material and liquid is that there exists an inner friction (inner friction angle) in the bulk material. This is to say, if an external condition is exerted on bulk material to alleviate or eliminate the inner friction angle, the bulk material will be fluidized. For example, adding some media such as water and colloid materials to bulk material or exerting special external forces (resonant force etc.) on bulk material, the bulk 鞍山科技大學本科生畢業設計（論文） 第 1 頁material can be fluidized.2.2 Affecting facters of bulk material motionAs stated above, the most predominant factor affecting the motion of bulk material is the existence of inner friction angle. The smaller the inner friction angle is, the easier the motion of bulk material becomes. In the conctrte, the factors can be: (a) the lumpiness of single particle in bulk material, the lumpier the particle is, the more difficult the motion of bulk material will be;(b) the unit weight of bulk material, the beavier the rnit weight is, the more difficult the motion will be;(c) the looseness (porosity) of bulk material, the looser the bulk material is, the easier the motion will be;(d) the humidity of bulk material, bulk material starts to flow when the humidity exceeds a critical, whereas, for some bulk materials, the increment in humidity conversely brings about the increment of inner friction angle and leads it difficult to flow;(e) the morphology and surface roughness of single particle, the inner friction angle is colsely related to the morphology and roughness of particle of bulk material;(f) it is more difficult for momideal bulk material to flow than for ideal bulk material to.2.3 Classification of fluid motion of bulk materialThe fluid motion of bulk material can be classified according to whether there is energy-carrier medium or not:() Single-phase flow. When there is not energy-carrier medium in the bulk material, or there are media, for example, air and water, but the media do not play the role of energy-carrying, the flow is all regarded as single-phase flow.() Biphase flow, when there are quantities of energy-carrier media in the bulk material, the particles of bulk material are suspending or near to suspending, the flow is biphase flow.The flow velocity of bulk material is an impoetant parameter for self-grinding. According to the velocity, the fluid motion can be classified:() ultimate low velocity (9m/s); () low velocity (9100m/s);() medium velocity (20100m/s);()high velocity (100200m/s); () ultrahigh velocity (2501000m/s). The efficiency of self-鞍山科技大學本科生畢業設計（論文） 第 1 頁grinding is very low when the flow velocity is in the ultimate low velocity range, the velocity is hardly chosen as a parameter in autogenous grinder. The low velocity is often chosen as a parameter in horizontal cylindrical autogenous grinders. The medium velocity is usually chosen as a parameter in vertial shaft centrifugal comminutors, and high velocity and ultrahigh velocity are adopted in ultrafine comminution.3 Analysis of Fluid Motion Mechanisn3.1 Classification of self-grinding modesThe self-grinding modes of fluid motion can be classified into:(a) impact self-grinding. In this mode, particles collide each other and reduction takes place;(b) delaminating self-grinding. Particles impact and shear each other, the particles are delaminated and reduction take place;(c) fatigue rupture self-grinding. Materials are fatigued to rupture under the condition of high-frequency altenating pulse stresses. The fatigue rupture self-grinding can make tough mateials to be comminuted in the way in which brittle materials are comminuted.3.2 Analysis of self-grinding mechanismThe flowing forms of every kinds of bulk materials are composed of two basic flowing forms:linear flow and rotational flow. In practice, an independent flowing form is usually present in grinding machine, in a very few case, two flowing forms are compositely present in centrfugal autogenous grinder. Hence, respectively studying the self-grinding mechanism of the two basic flowing forms is the basis for investigating the self-grinding mechanism of bulk material. Moreover, difference in phase and state of flowing bulk material must also be considered.3.2.1 linear flow(a) Single-phase linear flow. The forms of self-grinding are impacting and delaminating of particles. For example, he principle of vertical shaft impact comminutor is that a strong centrifugal force field caused by a high-speed rotating centrifugal disk brings about a high-speed linear jet of bulk material, the jet collides and impacts the particles remained the wall of cylinder. Meantime, the difference in velocity of jet particles caused by different sizes and morphologies also brings about impacting and delaminating of particles, but the degree of wearing and delaminaing is limited.鞍山科技大學本科生畢業設計（論文） 第 1 頁(b) Biphase linear flow. Similar to flow of liquid, the biphase linear flow also includes laminar flow and turbulent cuttent. The flow is stable when it is in the district of laminar flow, the velocity of particles in a layer is same but that in various layers is different. The friction of particles between different layers takes place. However, as well-known, the flow velocity in laminar flow district is very low, so the degree of self-grinding caused by laminar flow is limited.The comminution mainly takes place in the district of turbulent vurrent due to higher or very high velocity of current and occurrence of violent turbulence in the district. Violent collision between particles exists in the trubulence, and impact comminution is formed. If several jets intersect each other, the intersected particles will violently collide and impact. The higher the velocity is, the more efficient the self-grinding will be. For example, air-current comminutor works in gas-solid biphase self-grinding.3.2.2 Rotational flowRotational flow is formed by an external force such as in an anular pipe and cylindrical container. The centrifugal force field caused by rotating flow radially acts on the particles, the particle jet pressures the walls of pipe or container and particles remained on the walls, thus lesds to friction and shear force between the particles. The peculiar shear force in rotational flow is a predominant factor contributing self-grinding.(a) Single-phase rotational flow. The state and velocity of each particle of bulk material are different owing to the difference in size and morphology of each particle. Consequently, the fricting shear force between particles caused centrifugal pressure is a kind of alternating and pulse stress, the higher the flowing velocity is, the higher the altermating frequency and intension wil be. The high-frequency alternating and pulse shear stress make particles fatigue ruptured, the fatigur rupture which is expressed as brittle fatigue comminution is also a predominant form of self-grinding in rotational flow.(b)Biphase rotational flow. The self-grinding foem stated in single-phase flow above obviously is present in biphase flow. However, the self-grinding form is relatively weak owing to the fact that the viscid effect of energy-carrier medium hinders the flow of particles. Similar to those of biphase linear flow, the occurrence of violent turbulence ta high rotational 鞍山科技大學本科生畢業設計（論文） 第 1 頁velocity brings about the collision of particles and impact comminution is formed. The self-grinding form also occupies a place in biphase rotational flow.4 Factors Affecting Self-grindingOn the basis of analyses of comminution mechanism stated above, the factors affecting self-grinding can be summarized as following:(a) The instinctive structure and physical properties of bulk material such as fragility, hardness, brittleness, toughness, joint, cleavage and natural defects. All these factors are of importance to every comminution form. (b) The state of flowing. Linear flow and biphase rotational flow are applicable to brittle material, and single-phase rotational flow is applicable to tough material, the reason is that the high-frequency pulse shear effect renders tough material brittle failute. (c) The velocity of flowing. Whether in linear flow state or in rotation flow state, the velocity of flowing is one of the most important factors affecting the efficiency of self-giending. The higher the velocity is, the more efficient the self-grind will be, and the finer the obtained particles will be.(d) The concentration (for biphase flow) or the looseness(for single-phase flow). On the basis of probability theory, the increment in concentration raises the probability of collision between particles, thus improves the efficiency of comminution. Comsequently, increment in comcentration fo bulk material in biphase flow state and decrement in loosemess of bulk material in single-phase state are effective ways to improve the effectiveness of self-grinding.5 Practical Application鞍山科技大學本科生畢業設計（論文） 第 1 頁A new-type rotational-flow-state centrifugal autogenous grinder has successfully developed by applying self-grinding machanism of bulk material in Wuhan University of Technology. The schematic diagram of principal machine is shown in Fig.1. The evident difference betweeen the developed autogenous grinder and other vertical shaft centrifugal comminutor is that the working pan of the developed autogenous grinder is in conical shape. When the conical working pan rotates at a high speed, the resolutes of centrifugal force field acting on material including horizontal force and vertical force, thus the material in the ore-grinding cylinder cyclically and spirally flows upwards, and the material can be fully comminuted in the rotational flow. The horizontal flow and radial flow are shown in Fig.2 and Fig.3 respectively. 鞍山科技大學本科生畢業設計（論文） 第 1 頁The results of comminution efficency by the developed autogenous grinder were compared with those(listed in Table 1).The results in Table 1 show that such indexes as the granularity and fineness of product, throughput, enery-consumption and noise by the centrifugal autogenous grinder are all superior to those by 4R Raymond mill. This reveals that the new type autogenous grinder which is develop on the basis of the viewpoint of fluid motion is feasible.鞍山科技大學本科生畢業設計（論文） 第 1 頁自動磨碎機以及散裝流體材料對其的影響摘要：在不同階段的形狀、狀態和運動的情況下，通過被采用的液體和散裝材料（主體松軟材料） ，對自動磨碎機以及散裝流體材料的影響所做的調查。在散裝材料磨碎機應用的基礎上，一種新型的循環流體狀態自生磨碎機已經發展起來了，自生磨碎機的實驗結果與 4R 雷德蒙工廠的實驗結果通過比較，及其高精確地獲得了更小的微粒。在對散裝材料磨碎方面，這種新發展起來的自動研磨機的可行性是被證明成功的。1、介紹粉碎除了在大多數粉碎機的磨碎過程或是壓縮機在散裝材料運動中被壓碎的過程，只有在很少的一些設備例如軋輥機和擠壓機粉碎時采用的材料才是固定的或可以說是比較固定的。因此，一種關于流體狀態的散裝材料自動磨碎機的新的構想，通過深刻領會流體材料在研磨過程中的特性而被提出來了。2、散裝材料的流體狀態2.1 流體散裝材料在機械學的分支介質機械學中，散裝材料同樣被叫做主體松軟材料，它是相互關聯的固體微粒的集合體，在這里，每一個單獨的微粒都代表著固體的特性，并且是主體松軟材料的骨骼。然而，肉眼可見的方面分析，它同樣代表流體和流體的一些特性。（a） 與流體一樣，散裝材料不能保持固定的形狀；（b） 散裝材料和流體都不能承受拉力但可以承受壓力。散裝材料與流體的不同是散裝材料可以承受較小的正切力，而流體不能，這是由于在散裝材料里存在內部摩擦（內部摩擦角） 。也就是說，如果用外部條件施加在散裝材料上用以減輕或削減內部摩擦角，散裝材料將被流體化。舉例來說，把一些如水和膠體材料的介質加入到散裝材料中或是在外部施加特殊的力（諧振力等）在散裝材料上，散裝材料將會被流體化。2.2 散裝材料狀態的影響因素如上所述，影響散裝材料狀態最主要的因素是其內部存在摩擦角。摩擦角越小，散裝材料的狀態越容易得到。具體說來，影響因素包括：（a） 散裝材料單獨微粒體的塊狀程度。微粒的塊狀程度越大，散裝材料的狀態越難得到。（b） 散裝材料單元體的重量。單元體的重量越大，散裝材料的狀態越難得到。鞍山科技大學本科生畢業設計（論文） 第 1 頁（c） 散裝材料的疏松（多孔性）程度。散裝材料越疏松，散裝材料的狀態越容易得到。（d） 散裝材料的潮濕程度。當濕度超過臨界值時，散裝材料開始流動，然而，對于某些散裝材料，在濕度反面附加的東西反過來也帶來摩擦角影響因素并且導致散裝材料不易流動。（e） 微粒的形態和表面粗糙程度。內部的摩擦角與散裝材料微粒的形態和粗糙程度有著密切的關系。（f） 對于理想狀態的散裝材料，實際狀態的散裝材料更難流動。2.3 散裝材料流體狀態的分類散裝材料流體狀態根據是否有承載能量的介質可分類為：（）單階段流動。但散裝材料中沒有承載能量的介質，又或者是有介質，如水和空氣，但不能起到承載能量作的介質，這樣的流動形式都被認為是單階段流動。（）雙階段流動。當散裝材料中存在大量的能量承載介質，散裝材料的微粒是懸浮的或是接近懸浮的，這樣的流動形式被認為是雙階段流動。散裝材料的流動速度對于自磨來說是主要參數。根據其速度，流體的狀態可分為：（a） 最低速度(9m/s) ；（b） 低速(9100m/s)；（c） 中速(20100m/s)；（d） 高速(100200m/s)；（e） 超高速(2501000m/s)。當流動速度在最低速度范圍內時，自磨的效率是非常低的，作為自動磨碎機來說這種速度幾乎不能作為參數。低速經常被拿來作為水平圓柱磨碎機的參數。介質的速度經常被選來作為縱向離心磨碎機的參數，并且極細粉碎中采用高速和超高速。3流體磨碎機的分析3.1 自磨形式的分類流體的自磨形式可以分為：（a） 自磨的沖擊。在這種形式下，微?；ハ嗯鲎膊⑶覝p??；（b） 自磨的分層。微?；ハ嘧矒艋ハ嘞鳒p，發生微粒分層、減少的現象；（c） 自磨的疲勞破裂。在高頻率交替脈沖的重壓下，材料因疲勞而導致破裂；疲鞍山科技大學本科生畢業設計（論文） 第 1 頁勞破裂的自磨過程，用脆性材料被研磨的方式，可以使較硬的材料被研磨。3.2 自動磨碎機的分析各種各樣的散裝材料流動形式都是由以下兩種流動形式組成：直線流動和旋轉流動。實際上，獨立的流動形式常出現在自磨機上，在一些情況下，兩種流動形式在離心自磨機中合成。因此，為了研究散裝自磨機，把自磨機的這兩種流動形式分開來研究。而且，流動時不同的階段和狀態會帶來不同的自磨形式。因此，散裝材料的階段和狀態也必須考慮進去。3.2.1 直線流動（a）單直線流動。自磨的形式是微粒的撞擊和分層?？v向沖擊自磨機的原理是：一個高速的旋轉離心圓盤產生的巨大的離心力場，帶動散裝材料產生高速直線噴霧，噴霧互相撞擊，并且微粒停留在圓筒壁上。同時，不同大小和形態導致噴霧微粒在速度上的不同，致使微粒撞擊和分層，但是磨損和分層的程度是有限的。（b）雙直線流動。與流體的流動形式相似，雙直線流動同樣包括層流和亂流。在層流區域流動是穩定的，微粒的速度在同一層上是相同的，而不同層上的速度不同。不同層上的微粒產生摩擦。然而，總所周知，層流區域的速度是非常慢的，因此層流自磨的程度是有限的。研磨主要發生在亂流區域，因為在這個區域發生高速流動和強烈騷動。亂流中產生強烈的微粒撞擊，形成撞擊粉碎。如果幾條噴霧相交，交錯的微粒會強烈的碰撞和沖擊。速度越高，自磨得效率越高。如，氣流自磨機以固體、氣體雙直線流動的自磨下工作。3.2.2 旋轉流動旋轉流動是在如密閉管子或圓筒形容器中的產生的外力的作用下形成的。由旋轉流動產生的微粒的徑向運動形成的離心力場，使微粒噴霧對管壁和容器壁產生壓力，并且使微粒停留在壁上，因此導致微粒間摩擦力和剪切力。旋轉流動中產生的特殊的剪切力是促成自磨的主要因素。（a） 單旋轉流動。由于散裝材料的每個微粒大小和形態的不同，導致每個微粒的狀態和速度不同。因此，微粒間的摩擦剪切力導致的離心壓力是一種交替和脈沖的壓力，流動的速度越高，交替的頻率和強度越高。高頻率的的交替和脈沖剪切力使微粒疲勞破裂，這種被認為是脆性疲勞自磨的疲勞破鞍山科技大學本科生畢業設計（論文） 第 1 頁裂是自磨在旋轉流動的主要形式。（b） 雙旋轉流動。單旋轉流動的自磨形式，明顯地存在于雙旋轉流動中。然而，由于承載能量的介質的粘度妨礙介質的流動，自磨得形式相對較弱。與雙直線流動相似，高旋轉速度的亂流導致微粒的撞擊和自磨得沖擊。雙旋轉流動在自磨中同樣占據一個重要位置。4自磨的影響因素如上所述的自磨機的基本分析，自磨機的影響因素可以總結如下：（a） 散裝材料的本質結構和物理性質有脆性、硬度、易變性、強度、連接、裂開和自然缺陷。這些因素對每個自磨形式都非常重要。（b） 流動狀態。直線流動和雙旋轉流動適用于脆性材料，單循環流動適用于硬性材料，原因是高頻率脈沖剪切的影響使硬性材料脆性斷裂。（c） 流動速度。無論是在直線流動狀態或是在旋轉流動狀態，流動的速度是影響自磨效率的一個主要因素。速度越高，自磨得效率越高，獲得的微粒越細。（d） 集中性（雙流動）松散度（但流動） 。在可行性理論的基礎上，集中材料的增加會加劇微粒間的撞擊，因此影響自磨得效率。因此，雙循環中集中材料的增加和單循環狀態松散材料的減少是提高自磨效率的有效途徑。5實際應用鞍山科技大學本科生畢業設計（論文） 第 1 頁圖 1 機器原理略圖 1-縱軸 2-底盤 3-工作盤 4-錘板 5-安裝網 6-刮削器 7-自磨筒 8 空氣進入筒 9-分離器 10-材料入口一種旋轉流動離心自磨機已經被武漢科技大學成果的研制出。機器的主要圖表如圖1。這種自磨機與其它縱向自磨機的明顯區別是它的工作盤是圓錐形的而其它的事平的。當圓錐工作盤在高速下旋轉，強烈的橫向的和縱向的離心力作用在材料上，材料在圓筒中處于螺旋循環上升狀態，材料可以在旋轉流中被完全磨碎。圖 2 和 3 分別是水平和軸向運動方向。圖 2 水平流動 圖 3 縱向流動這種自磨機工作效率的結果與 4R 雷蒙德工業公司的相比較：表 1 與 4R 雷德蒙工廠的實驗結果的比較工廠 加入材料的大小產品的顆粒 產量t/h能量消耗 噪音4R 雷德蒙工廠150mm-4mm 96%過-200網眼3.2 18.2kw 99dB800 離心自磨機150mm 98.5%過-200網眼3.52 15.8kw 82dB從表 1 中可以看出這種產品的粒度和細度、產量、消耗量和噪音等指數都好于 4R鞍山科技大學本科生畢業設計（論文） 第 1 頁雷蒙德工廠的。顯示出在流體觀點的基礎上研制的新型自磨機是可行的。