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鞍山科技大學(xué)本科生畢業(yè)設(shè)計（論文） 第4頁
圓錐破碎機腔型對性能的影響及改進
1、前言
圓錐破碎機是破碎石料的重要設(shè)備，由于它的生產(chǎn)效率高、出料細、均勻，被廣泛用于礦石、建筑行業(yè)的石料加工處理。它可以將石料從350mm破碎到10mm以下不同級別的顆粒。為了生產(chǎn)不同等級產(chǎn)品的需要，破碎機又可分為中碎、中細碎和細碎，相對于的腔型為標準型、中間型和短頭型，而決定腔型的關(guān)鍵是襯板，因此，我們對腔型的研究，就是對襯板形狀的研究。
2各種腔型的區(qū)別
所謂腔型，即破碎機動錐襯板和定錐襯板圍成的空間和形狀。圓錐破碎機腔型劃分為標準型、中間型和短頭型。但何為標準型呢，以7英尺圓錐破碎機為例，我們把緊邊平行帶的長度在240mm左右、入料口寬度為105mm的定為細腔型；平行帶長度在163mm左右、入料口寬度為334mm的定為標準型，如表1和圖1腔型斷面圖。腔型不同的破碎機在破碎工藝中所處的位置也不同。以7英尺圓錐為例，標準型的給料粒度在0~250mm，處理能力在600t/h，80%產(chǎn)品粒度≤50mm,因此作為二級破碎，即中碎。短頭型的給料粒度在0~50mm，處理能力在400t/h，80%產(chǎn)品粒度≤12mm,因此作為三級破碎，即細碎。中間型介于二者之間，因此既可作中碎又可作細碎。
3腔型在運行中的變化和影響
一塊襯板從安裝到報廢更換，短則2個月，長則4個月，在這一生產(chǎn)磨耗過程中，腔型隨襯板的磨損而不斷發(fā)生變化，各種型腔之間的區(qū)別顯得越來越小，破碎機的性能隨著腔型的變化也在發(fā)生變化，直到更換襯板。如果襯板的更換是因為襯板的磨損量已到極限范圍，則襯板適得其所。但往往在襯板還很厚時，其處理能力已大幅下降，因此不得不更換襯板，如7英寸Symons圓錐中碎，當襯板使用2個月，襯板磨損余量還有很多時，其處理能力已大大下降，因此，有必要對原腔型進行分析研究，使其適合生產(chǎn)需要。
3.1細碎腔型的變化規(guī)律
以7英尺Symons圓錐為例，當一件新的動錐襯板和一件新的定錐襯板組成一個細碎腔型時，其初始狀況如圖2a，各項參數(shù)如表1;使用一個月后，平行帶長度為265mm，入料口緊邊寬度為92mm,其腔型狀況如圖2b,(根據(jù)經(jīng)驗，襯板平均每天磨損0.5mm) ;當運行到第三個月時，平行帶長度為450mm，入料口緊邊寬度為34mm,其腔型狀況如圖2c。平行帶的長度在逐漸變長，入料口緊邊寬度在變窄，處理量在下降。
3.2中碎腔型變化規(guī)律
以7英尺Symons圓錐為例，當一件新的動錐襯板和一件新的定錐襯板組成一個中碎腔型時，其初始狀況如圖3a，各項參數(shù)如表1;使用一個月后，平行帶長度為190mm，入料口緊邊寬度為273mm,其腔型狀況如圖3b;(根據(jù)經(jīng)驗，襯板平均每人磨損0.5mm) ;當運行到第三個月時，平行帶長度為254mm,入料口緊邊寬度為187mm,其腔型狀況如圖 3c。平行帶的長度在逐漸變化，入料口遠小于始值334mm，各項數(shù)據(jù)越來越接近表1中細碎腔型的數(shù)據(jù)，處理量也在下降。但這時襯板的厚度還遠未磨損到需要更換的尺寸。
4 對中碎腔型配置的改進
出現(xiàn)襯板磨損后平行帶變長，入料口變窄的情況，一般可以采取以下兩種改進措施:①加厚平行帶處襯板厚度;②襯板厚度不變，加大定襯板上口尺寸;使腔具有更大的入口尺寸。如果采取措施①可以預(yù)測，仍將不能徹底解決襯板合理地最大限度地磨耗的目的，雖然襯板的使用壽命延長了，但剩余厚度未變，浪費大，因此不是好的解決辦法;如果采取措施②，加大定錐襯板上口直徑，這受調(diào)整環(huán)尺寸影響，可行性不大;在實踐中我們采用了第二種辦法:新、舊襯板配置，如圖4a。這是一種最簡便易行的措施，它不需要對現(xiàn)有設(shè)計、條件作任何修改。配置后平行帶長200mm，入料口寬度260mm;到動錐襯板磨損更換時，平行帶長250mm，入料口寬度240mm，比最大石料尺寸略小，如圖4b;新動錐襯板配舊定錐襯板同。從圖中可以看出，舊的襯板能充分磨損，更換舊襯板時，破碎腔入料口仍能保持足夠大的尺寸，對通過能力沒有太大影響。
5對細碎腔型配置的改進
對中碎腔型的配置改進方法能否用于細碎呢?首先讓我們來看一下配置后襯板磨損的變化規(guī)律見圖5。
從圖5中可以看到A：定新動舊配(新定錐襯板配舊動錐襯板)。動錐的下口最大直徑處出現(xiàn)了凸緣。B：定舊動新(舊定錐襯板配新動錐襯板)。定錐襯板的下口內(nèi)卷，也是有凸緣，由于細碎的排礦口很小，只有7mm~8mm，這樣很容易發(fā)生襯板碰襯板的現(xiàn)象，更重要的是，由于凸緣的形成，阻礙了礦石的通過，降低了通過速度。但中碎的排礦口較大，在22mm~25mm,并且定錐襯板比細碎的陡10° ,雖同樣有凸緣問題，但對通過速度影響也不大，不會出現(xiàn)襯板相碰情況。因此，這種新舊搭配適合于中碎而不適合在細碎中使用。中碎在襯板磨損后期，造成處理量下降的因素是入料口減小，礦石難以通過入料口進入破碎腔。細碎在襯板磨損后期，造成處理量下降的因素是平行帶太長，礦石通過平行帶時間延長，造成過粉碎。因此，細碎腔型可以采取第一種方法：襯板加厚，同時背隙加大，如圖6;這樣可以達到延長襯板使用時間目的。由于細碎的粒度較細，在破碎腔的上部，對礦石的破碎也是礦石相互擠壓破碎;而中碎，由于粒度大，很大一部分礦石是直接破碎;因此，細碎動錐的上部可以不用相應(yīng)加厚，甚至可以減薄。通過這種改進，細碎的處理能力波動小，襯板也能合理磨損，如圖6b。到后期，平行帶長400mm,但緊邊入口寬度為51mm,最大物料能夠進入破碎腔，對處理能力不會有太大影響。
現(xiàn)在有的圓錐設(shè)計廠家，為了避免細碎腔型平行帶在磨損過程中越來越長，將襯板設(shè)計成如圖7的形狀，這樣，襯板到更換時，其平行帶入口尺寸也基木保持不變，平行帶不僅不變長，反而有所縮短，這應(yīng)該說也是確保細碎型圓錐性能穩(wěn)定的一個好辦法。
6 結(jié)論
通過以上對圓錐腔型的改進、使用，有效地達到了延長襯板使用壽命的目的，消除了造成圓錐處理能力波動的因素，實現(xiàn)了破碎機的平穩(wěn)運行。
鞍山科技大學(xué)本科生畢業(yè)設(shè)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(tài)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(diào)查。在散裝材料磨碎機應(yīng)用的基礎(chǔ)上，一種新型的循環(huán)流體狀態(tài)自生磨碎機已經(jīng)發(fā)展起來了，自生磨碎機的實驗結(jié)果與4R雷德蒙工廠的實驗結(jié)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(fā)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(shù)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(shè)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(guān)于流體狀態(tài)的散裝材料自動磨碎機的新的構(gòu)想，通過深刻領(lǐng)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(tài)
2.1流體散裝材料
在機械學(xué)的分支介質(zhì)機械學(xué)中，散裝材料同樣被叫做主體松軟材料，它是相互關(guān)聯(lián)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(nèi)部摩擦（內(nèi)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(nèi)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(zhì)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(tài)的影響因素
如上所述，影響散裝材料狀態(tài)最主要的因素是其內(nèi)部存在摩擦角。摩擦角越小，散裝材料的狀態(tài)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(tài)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(tài)越難得到。
（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(tài)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(dǎo)致散裝材料不易流動。
（e） 微粒的形態(tài)和表面粗糙程度。內(nèi)部的摩擦角與散裝材料微粒的形態(tài)和粗糙程度有著密切的關(guān)系。
（f） 對于理想狀態(tài)的散裝材料，實際狀態(tài)的散裝材料更難流動。
2.3散裝材料流體狀態(tài)的分類
散裝材料流體狀態(tài)根據(jù)是否有承載能量的介質(zhì)可分類為：
（Ⅰ）單階段流動。但散裝材料中沒有承載能量的介質(zhì)，又或者是有介質(zhì)，如水和空氣，但不能起到承載能量作的介質(zhì)，這樣的流動形式都被認為是單階段流動。
（Ⅱ）雙階段流動。當散裝材料中存在大量的能量承載介質(zhì)，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(shù)。根據(jù)其速度，流體的狀態(tài)可分為：
（a） 最低速度(ν<9m/s)；
（b） 低速(9<ν<100m/s)；
（c） 中速(20<ν<100m/s)；
（d） 高速(100<ν<200m/s)；
（e） 超高速(250<ν<1000m/s)。
當流動速度在最低速度范圍內(nèi)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(shù)。低速經(jīng)常被拿來作為水平圓柱磨碎機的參數(shù)。介質(zhì)的速度經(jīng)常被選來作為縱向離心磨碎機的參數(shù)，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(fā)生微粒分層、減少的現(xiàn)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(dǎo)致破裂；疲勞破裂的自磨過程，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(zhuǎn)流動。實際上，獨立的流動形式常出現(xiàn)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(tài)會帶來不同的自磨形式。因此，散裝材料的階段和狀態(tài)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(zhuǎn)離心圓盤產(chǎn)生的巨大的離心力場，帶動散裝材料產(chǎn)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(tài)導(dǎo)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(qū)域流動是穩(wěn)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(chǎn)生摩擦。然而，總所周知，層流區(qū)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(fā)生在亂流區(qū)域，因為在這個區(qū)域發(fā)生高速流動和強烈騷動。亂流中產(chǎn)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(zhuǎn)流動
旋轉(zhuǎn)流動是在如密閉管子或圓筒形容器中的產(chǎn)生的外力的作用下形成的。由旋轉(zhuǎn)流動產(chǎn)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(chǎn)生壓力，并且使微粒停留在壁上，因此導(dǎo)致微粒間摩擦力和剪切力。旋轉(zhuǎn)流動中產(chǎn)生的特殊的剪切力是促成自磨的主要因素。
（a） 單旋轉(zhuǎn)流動。由于散裝材料的每個微粒大小和形態(tài)的不同，導(dǎo)致每個微粒的狀態(tài)和速度不同。因此，微粒間的摩擦剪切力導(dǎo)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裂是自磨在旋轉(zhuǎn)流動的主要形式。
（b） 雙旋轉(zhuǎn)流動。單旋轉(zhuǎn)流動的自磨形式，明顯地存在于雙旋轉(zhuǎn)流動中。然而，由于承載能量的介質(zhì)的粘度妨礙介質(zhì)的流動，自磨得形式相對較弱。與雙直線流動相似，高旋轉(zhuǎn)速度的亂流導(dǎo)致微粒的撞擊和自磨得沖擊。雙旋轉(zhuǎn)流動在自磨中同樣占據(jù)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(jié)如下：
（a） 散裝材料的本質(zhì)結(jié)構(gòu)和物理性質(zhì)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(tài)。直線流動和雙旋轉(zhuǎn)流動適用于脆性材料，單循環(huán)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(tài)或是在旋轉(zhuǎn)流動狀態(tài)，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(chǔ)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(huán)中集中材料的增加和單循環(huán)狀態(tài)松散材料的減少是提高自磨效率的有效途徑。
5．實際應(yīng)用
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(wǎng) 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(zhuǎn)流動離心自磨機已經(jīng)被武漢科技大學(xué)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(qū)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(zhuǎn)，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(huán)上升狀態(tài)，材料可以在旋轉(zhuǎn)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(jié)果與4R雷蒙德工業(yè)公司的相比較：
表1 與4R雷德蒙工廠的實驗結(jié)果的比較
工廠
加入材料的大小
產(chǎn)品的顆粒
產(chǎn)量
t/h
能量消耗
噪音
4R雷德蒙工廠
150mm-4mm
96%過-200網(wǎng)眼
3.2
18.2kw
99dB
Ф800 離心自磨機
150mm
98.5%過-200網(wǎng)眼
3.52
15.8kw
82dB
從表1中可以看出這種產(chǎn)品的粒度和細度、產(chǎn)量、消耗量和噪音等指數(shù)都好于4R雷蒙德工廠的。顯示出在流體觀點的基礎(chǔ)上研制的新型自磨機是可行的。
鞍山科技大學(xué)本科生畢業(yè)設(shè)計（論文） 第1頁
THE SELF-GRINDING MECHANISM AND AFFECTING FACTORS OF BULK MATERIAL IN FLUID MOTION
Abstract: 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 mill
1 Introduction
Comminution 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 Materials
2.1Fluidity of bulk materials
In 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 material can be fluidized.
2.2 Affecting facters of bulk material motion
As 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 material
The fluid motion of bulk material can be classified according to whether there is energy-carrier medium or not:
(Ⅰ) 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.
(Ⅱ) 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:(ⅰ) ultimate low velocity (ν<9m/s); (ⅱ) low velocity (9<ν<100m/s);(ⅲ) medium velocity (20<ν<100m/s);(ⅳ)high velocity (100<ν<200m/s); (ⅴ) ultrahigh velocity (250<ν<1000m/s). The efficiency of self-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 Mechanisn
3.1 Classification of self-grinding modes
The 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 mechanism
The 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.
(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 flow
Rotational 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 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-grinding
On 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
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.
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.
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