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學院：機械與動力工程學院 專業(yè)：機械設計制造及其自動化 班級： 姓名： 學號：3 指導老師： Hammer mills: hammer-mills In the feed processing process there may be a number of ingredients that require some form of processing. These feed ingredients include coarse cereal grains, corns which require particle size reduction which will improve the performance of the ingredient and increase the nutritive value. There are a many ways to achieve this particle size reduction, here we are looking at using hammer-mills, for information on roller mills, see the related links at the bottom of this page. Both hammering and rolling can achieve the desired result of achieving adequately ground ingredients, but other factors also need to be looked at before choosing the suitable method to grind. Excessive size reduction can lead to wasted electrical energy, unnecessary wear on mechanical equipment and possible digestive problems in livestock and poultry. For more in depth information regarding what actually occurs to the ingredients during size reduction please refer to this link: particle size reduction. Hammer-mills Advantages: - are able to produce a wide range of particle sizes - Work with any friable material and fiber - ease of use -Lower initial investment when compared with a roller mill - Minimal maintenance needed - Particles produced using a hammer-mill will generally be spherical, with a surface that appears polished. Disadvantages: - Less energy efficient when compared to a roller mill - may generate heat (source of energy loss) - produce greater particle size variability (less uniform) - Hammer-mills are noisy and can generate dust pollution General Design The major components of these hammer-mills, shown in the picture, include: - a delivery device is used to introduce the material to be ground into the path of the hammers. A rotor comprised of a series of machined disks mounted on the horizontal shaft performs this task. - Free-swinging hammers that are suspended from rods running parallel to the shaft and through the rotor disks. The hammers carry out the function of smashing the ingredients in order to reduce their particle size. - a perforated screen and either gravity- or air-assisted removal of ground product. Acts to screen the particle size of the hammer mill to ensure particles meet a specified maximum mesh size. Feeder design Materials are introduced into the paths of the hammers by a variable speed vein feeder. This type of feeder can have its motor slaved by a programmable controller to the main drive motor of the hammer mill. The operational speed of the feeder is controlled to maintain optimum amperage loading of the main motor. Hammer design and configuration The design and placement of hammers is determined by operating parameters such as rotor speed, motor horsepower, and open area in the screen. Optimal hammer design and placement will provide maximum contact with the feed ingredient. Hammer mills in which the rotor speed is approximately 1,800 rpm, should be using hammers which are around 25cm (~ 10 inches) long, 6.35cm (~2.5 inches) wide, and 6.4mm (0.25 inches) thick. For a rotor speed of about 3,600 rpm, hammers should be 15 to 20 cm (~ 6-8 inches long, 5 cm (~ 2 inches) wide, and 6.4 mm (0.25 inches) thick. The number of hammers used for a hammer mill of 1,800 rpm, should be 1 for every 2.5 to 3.5 horsepower, and for 3,600 rpm, one for every 1 to 2 horsepower. Hammers should be balanced and arranged on the rods so that they do not trail one another. The distance between hammer and screen should be 12 to 14 mm (~ 1/2 inch) for size reduction of cereal grains. The velocity or tip speed of the hammers is critical for proper size reduction. Tip speed is the speed of the hammer at its tip or edge furthest away from the rotor, and is calculated by multiplying the rotational speed of the drive source (shaft rpm) by the circumference of the hammer tip arc. See the following formula: A common range of tip speeds seen in hammer-mills is commonly in the range between 5,000 and 7,000 m/min (~ 16,000 and 23,000 feet per minute). When the tip speeds exceed 23,000 feet per minute, careful consideration must be given to the design of the hammer mill, the materials used in its construction, and the fabrication of all the components. Simply changing the rotational speed of the drive source is not a recommended method of increasing hammer speed in excess of 23,000 feet per minute. Impact is the primary force used in a hammer-mill. Anything which increases the chance of a collision between a hammer and a target; increases the magnitude of the collision; or improves material take-away provides an advantage in particle size reduction. The magnitude of the collisions can be escalated by increasing the speed of the hammers. Screen Design The amount of open area in a hammer mill screen determines the particle size and grinding efficiency. The screen must be designed to maintain its integrity and provide the greatest amount of open area. Screen openings (holes) that are aligned in a 60-degree staggered pattern optimize open area while maintaining screen strength. This method will result in a 40 percent open area using 3.2 mm (1/8 inch) holes aligned on 4.8 mm (3/16 inch) centers. Feed producers need to pay particular attention to the ratio of open screen area to horsepower. Recommended ratio for grains would be 55 cm2 (~ 8-9 inches square) per horsepower (Bliss, 1990). Not enough open area per horsepower results in the generation of heat. When the heat generated exceeds 44C to 46C (120-125F), capacity may be decreased as much as 50 percent. The removal of sized material from a hammer-mill is a critical design feature. Proper output of material affects not only the efficiency of operation, but also particle size. When the correct ratio of screen area to horsepower is used and proper distance between hammers and screen face is maintained, most of the correctly sized particles will exit the screen in a timely manner. Anderson (1994) stated the particles that do not pass through the screen holes become part of a fluidized bed of material swept along the face of the screen by the high-speed rotation of the hammers. As these particles rub against the screen and each other their size is continually reduced by attrition. This excessive size reduction is counterproductive. Energy is wasted in the production of heat, throughput is restricted, and particles become too small. Most new hammer mills are equipped with an air-assist system that draws air into the hammer mill with the product to be ground. Systems are designed to provide reduced pressure on the exit side of the screen to disrupt the fluidized bed of material on the face of the screen, thus allowing particles to exit through screen holes. Some full circle hammer mills are designed so the screen is in two pieces. It is possible to use a larger whole size on the upward arc of the hammers to further reduce the amount of material on the face of the screen. Hammer Mills Hammers Hammers are used inside the hammer-mill to impact smash ingredients up into smaller particles, making it more suitable for uniform mixing and usage in feed. Hammers are available in a huge range of configurations, shapes, facings and materials. Hammers are available as single holed or with two holes, with two holes allowing the hammers to be used twice as the wear is done to one end of the hammer; the hammer can be rotated and used a second time. The hole fits onto a rod inside the hammer mill and swings to hit the material. Dimensions of a hammer ? A: Thickness ? B: Width ? C: Diameter to fit rod size ? D: Swing Length ? E: Total Length Hammer Mill Perforated Screens Hammer mills screens are used inside a hammer mill to separate particle sizes. Particle of small enough diameter that has been successfully grinded by the hammer mill passes through the screen and leaves the hammer mill with the aid of the pneumatic system. Particle Size Reduction Size Reduction: The initial reduction of cereal grains begins by disrupting the outer protective layer of the seed (hull), exposing the interior, see the picture. Continued size reduction increases both the number of particles and the amount of surface area per unit of volume. It is this increased surface area that is of primary importance. A greater portion of the grain's interior is exposed to digestive enzymes, allowing increased access to nutritional components such as starch and protein. The enhanced breakdown of these nutritional components improves absorption in the digestive tract. The overall effect is increased animal performance. Size reduction is also used to modify the physical characteristics of ingredients resulting in improved mixing, pelleting, and, in some instances, handling or transport. Hammer mills: Reduce the particle size of materials by impacting a slow moving target, such as a cereal grain, with a rapidly moving hammer. The target has little or no momentum (low kinetic energy), whereas the hammer tip is traveling at a minimum of 4,880 m/min (~16,000 feet per min) and perhaps in excess of 7,015 m/min (~ 23,000 feet per min) (high kinetic energy). The transfer of energy that results from this collision fractures the grain into many pieces. Sizing is a function of hammer-tip speed; hammer design and placement; screen design and hole size; and whether or not air assistance is utilized. Because impact is the primary force used in a Hammer mill to reduce the size of the particles, anything that; increases the chance of a collision between a hammer and a target, increases the magnitude of the collision, or improves material take-away, would be advantageous to particle size reduction. The magnitude of the collisions can be escalated by increasing the speed of the hammers. Anderson (1994) stated that when drive speed and screen size were kept constant, the increased hammer-tip speed obtained from increased rotor diameter produced particles of smaller mean geometric size. Particles produced using a hammer mill will generally be spherical in shape with a surface that appears polished. The distribution of particle sizes will vary widely around the geometric mean such that there will be some large-sized and many small-sized particles. Hammer Mill Rods Hammers are attached to rods inside the hammer mill, which are what they are swung on. Dimensions of rods are dependant on brand and style of the hammer mill. Roller mill Roller mills accomplish size reduction through a combination of forces and design features. If the rolls rotate at the same speed, compression is the primary force used. If the rolls rotate at different speeds, shearing and compression are the primary forces used. If the rolls are grooved, a tearing or grinding component is introduced. There is little noise or dust pollution associated with properly designed and maintained roller mills. Their slower operating speeds do not generate heat, and there is very little moisture loss. Particles produced tend to be uniform in size; that is, very little fine material is generated. The shape of the particles tends to be irregular, more cubic or rectangular than spherical. The irregular shape of the particles means they do not pack as well. For similar-sized particles, bulk density of material ground on a roller mill will be about 5 to 15 percent less than material ground by a hammer mill. Roller mills Advantages: - energy efficient - uniform particle-size distribution - little noise and dust generation Disadvantages: - little or no effect on fiber - particles tend to be irregular in shape and dimension - may have high initial cost (depends on system design) - when required, maintenance can be expensive General Design There are many manufacturers of roller mills, but they all share the following design features shown adjacent picture: - a delivery device to supply a constant and uniform amount of the material to be ground - a pair of rolls mounted horizontally in a rigid frame - one roll is fixed in position and the other can be moved closer to or further from the fixed roll - the rolls counter rotate either at the same speed or one may rotate faster; roll surface may be smooth or have various grooves or corrugations - bar; pairs of rolls may be placed on top of one another in a frame. To ensure optimum operation, material must be introduced between the rolls in a uniform and constant manner. The simplest feeder is a bin hopper with an agitator located inside it and a manually set discharge gate. This type of feeder is best suited for coarse processing. For grinding operations, a roll feeder is suggested. In this type of feeder, the roll is located below the bin hopper and has a manually set or automatic adjustable discharge gate. If the gate is adjusted automatically, it will be slaved to the amperage load of the main motor of the roller mill. The rolls that make up a pair will be 9 to 12 inches (23 to 30.5 cm) in diameter, and their ratio of length to diameter can be as great as 4:1. It is very important to maintain the alignment between the roll pairs. Sizing of the material is dependent upon the gap between the rolls along their length. If this gap is not uniform, mill performance will suffer, leading to increased maintenance costs, reduced throughput, and overall increased operation costs. The gap may be adjusted manually or automatically through the use of pneumatic or hydraulic cylinders operated through a computer or programmable controller. Each pair of rolls is counter rotating. For improved size reduction one of the rolls rotates faster. This results in a differential in speed between the roll pair. Typical differentials range from 1.2:1 to 2.0:1 (fast to slow). Typical roll speeds would be 1,300 feet per minute (~ 395 m/min) for a 9-inch (~23 cm) roll to 3,140 feet per minute (~957 m/min) for a 12-inch (~30.5 cm) roll. Usually a single motor is used to power a two high roll pair, with either belt or chain reduction supplying the differential. In a three high roll pair, the bottom pair will have a separate drive motor. In addition, the roll faces can be grooved to further take advantage of the speed differential and improve size reduction. By placing (stacking) pairs of rolls on top of one another, two or three high, it is possible to reduce particle sizes down to 500 microns, duplicating the size-reducing capability of a hammer mill for grain. For coarse reduction of grain, a roller mill may have a significant advantage (perhaps as high as 85 percent) over a hammer mill in terms of throughput/kwh of energy. For cereal grains processed to typical sizes (600 to 900 microns) for the feed industry, the advantage is about 30 to 50 percent. This translates into reduced operating expense. 錘磨機：錘片式粉碎機 在飼料加工過程中可能存在的成分需要某種形式的處理方式來完成。這些飼料成分包括粗糙的谷類植物，按要求減小玉米粒度可以提高原料的性能和營養(yǎng)價值。有許多不同的方法可以減小飼料微粒的粒度。在這里我們主要介紹錘磨機和滾子磨機，具體介紹如下： 錘片式和滾子式粉碎機都可以加工出滿足要求的圓形飼料，但是要選擇其他機器來滿足同樣要求的飼料粒度時就需要再加工前選擇合適的加工方式。過度減小飼料粒度將會浪費電能、造成機械設備不必要的磨損和家畜的消化問題。為了深入了解實際加工過程中產生材料粒度減小的原因請參考一下內容：微粒尺寸減小。 錘片式粉碎機 優(yōu)點： —可以生產的飼料粒度范圍廣 —可以用于加工脆性材料和纖維 —操作簡單 —相對于滾子式粉碎機來說它的早期投入低 —需要的維護很少 —它粉碎的飼料微粒一般都是圓形的而且表面光滑 缺點： —相對于滾子粉碎機它的效率較低 —產生熱量（能量損失） —微粒大小不均勻（相差大） —易產生噪音和灰塵、污染環(huán)境 總體設計 如圖所示，錘片粉碎機的主要零件包括： —傳送部分：用于將物料送到粉碎室的通道。 —轉子部分：由一系列錘片組成的轉子裝在水平軸上工作粉碎物料，錘片可以自由轉動并懸浮平行于軸桿穿過轉子盤。錘片的作用是擊碎物料減小它們的粒度。 —篩板：利用重力和空氣的輔助來分離飼料微粒。粉碎機篩孔要能確保粉碎粒度最大物料的通過。 粉碎室設計 材料引入到粉碎室的路徑由一個變量的速度靜脈接駁。這種類型的路徑有它自己的發(fā)動機由可編程的控制器連接錘片式粉碎機的主傳動電機。各線路接駁的速度控制，以保持最佳電量的主電機負載。 錘片的設計和布局 錘片的設計和布局由操作參數，如轉子轉速、電動機功率和篩板間隙決定。錘片的的最佳設計和布局可以提供最大的飼料原料接觸。粉碎機中轉子的轉速大約為1800轉/分時應當用的錘片為25厘米（~10英寸）長，6.35厘米（~2.5英寸）寬，6.4毫米（~0.25英寸）厚。對于轉速約為3600轉/分的的錘片一般應為15到20厘米（~6-8英寸）長，5厘米（~2英寸）寬，6.4毫米（~0.25英寸）厚。 對于轉速為1800轉/分的錘片式粉碎機來說，錘片數量應該是2.5~3.5/馬力，而對于轉速為3600轉/分的粉碎機來說錘片的數量為1~2/馬力。錘片應該是平衡的，而且它們在軸桿上的排列在運動時不至于相互碰撞。錘片和篩板之間的距離一般應為12~14毫米（~1/2英寸）為了減小谷粒的大小。 錘片末端線速度是微粒粒度的關鍵，末端線速度是錘片末端或者遠離轉子邊緣的速度，它可以通過軸的轉速乘以軸的直徑和圓周率再除以12in/ft來求得，詳見下面公式： 英尺/分=D×n/12 D —轉子直徑 n —轉速 在錘片粉碎機中常見的速度變化范圍一般為5000-7000米/分（~16,000-23,000英尺/分）。當末端線速度增大到23000英尺/分時就必須要考慮粉碎機的材料和所有零件結構是否能滿足要求。在轉速為2.3萬英尺/分時改變軸的轉速是不值得推薦的方法。 粉碎機中主要的力是沖擊力。在錘片和飼料顆粒之間增加的任何距離;增加距離的重要性；或者有利于改善飼料微粒的大小。距離的增大可以通過提高錘片的速度來實現。 篩片設計 粉碎機中篩板的篩孔數量取決于微粒大小和粉碎效率。篩板設計必須保證飼料的最大微粒通過和提供最大的開放面積。在保證篩板強度的情況下篩孔的最佳排列方式直線排列與開放區(qū)域呈60°角交錯。這種方法可以設計出的篩片有40﹪的用的是3.2mm（1/8英寸）的篩孔并直線排列兩孔中心距為4.8mm（3/16英寸）。 操作者應該特別注意粉碎機篩板有效面積與功率的比值。對于小麥類植物一般推薦使用的比例為55平方厘米/馬力（~8-9平方英寸）（Bliss1990）。如果沒有足夠的功率面積比將產生熱量。當溫度達到44℃-46℃（120-125F）時粉碎機的生產能力將下降50﹪. 飼料的排出是粉碎機設計的標準。粉碎機的度電產量不僅受生產效率的影響還受物料粒度的影響。當選用正確的有效篩板面積百分比和合適的錘篩間隙是粉碎的物料就能及時的從粉碎室中排出。Anderson(1994)曾聲明物料微粒不能全部通過篩片是因為一部分物料流在環(huán)流層外層( 靠近篩面)隨著轉子高速旋轉。這些微粒通過與篩片表面和彼此之間的摩擦來減小自身的尺寸。但過度減小微粒的尺寸也會產生反效果：能源都浪費在熱量上，產量也會受到限制物料微粒也會變得過小。 多數的新型錘片式粉碎機都有吸風系統(tǒng)，可以將空氣吸進粉碎室用于粉碎物料。吸風的目的是造成粉碎室負壓, 打破篩片表面的物料流促使室內殘留的物料通過篩孔。有些粉碎機設計有兩片篩片，這種篩片可以使用大的篩孔便于更多的減少滯留在篩片表面的物料數量。 錘片式粉碎機—錘片 錘片式粉碎機中錘片用來沖擊物料使其尺寸變小，使得它更用以與其他物料混合。錘片的布局、形狀、材料都是很重要的。錘片有單孔的和雙孔之分，雙孔的錘片可以使用兩次，一端磨損還可以使用另外一端。錘片安裝在粉碎機軸桿上轉動擊打物料。 錘片的外形尺寸 A— 厚度 B— 寬度 C— 軸孔半徑 D— 錘片伸出長度 E— 錘片總長 錘片粉碎機常用篩片 粉碎機中篩片是用來分離物料微粒的。粉碎機可以將物料粉碎的的足夠小，通過空氣壓縮系統(tǒng)的輔助微?？梢皂樌耐ㄟ^篩孔。 粒度： 粒度大?。汗阮愔参锸菑淖钔鈱娱_始被擊碎的而后是微粒內部。微粒的大小不僅與篩片表面的微粒數量有關而且還與粉碎速度有關。增加表面積是最重要的。對消化系統(tǒng)來說谷物的內部物質是重要，像淀粉和蛋白質等營養(yǎng)成分。這些營養(yǎng)成分可以改善消化道的吸收作用，增加動物的體能。微粒的成球形、物理性能可以提高物料的混合性便于轉載和運輸。 錘片式粉碎機 粉碎機是通過高速旋轉地錘片不斷地打擊物料來降低其微粒尺寸的。錘片以4880米/分（~16,000英尺/分）或者7015米/分（~23,000英尺/分）的線速度轉動。能量的轉移可以將物料達成許多微粒。微粒的大小取決于錘片線速度、錘片設計和布局、篩片的設計和篩孔大小以及吸風系統(tǒng)的共同作用。 因為錘片粉碎機中主要用來粉碎物料的力是沖擊力，所以增加錘片與物料間的沖擊可以提高物料的卸出，對粒度的減小也是有利的。Anderson(1994)聲稱當擊打速度和篩孔的大小保持不變時，可以通過增加轉子直徑來增加錘片的末端線速度，進而生產出粒度更小的物料。錘片粉碎的物料一般是圓形的且表面光滑。微粒大小不一也就是說既有大微粒也有小粒度微粒。 粉碎機軸桿 錘片式粉碎機的錘片是固定在軸桿上的，并可以繞軸桿轉動。軸桿的大小取決于粉碎機的設計。 輥子粉碎機 輥子粉碎機是通過力和機器特性相結合的方式來實現物料粉碎的。如果輥子以相同的速度旋轉則粉碎時用的力主要是壓力。若輥子以不同的速度旋轉粉碎時主要的力有切應力和壓應力。如果是帶槽的輥子將會撕裂或粉碎物料，槽寬的輥子粉碎機比細槽的粉碎機粉碎的物料粒度要小。設計合理的輥子粉碎機噪聲低且低污染、維護方便。輥子粉碎機的運轉速度較低因而不易產生熱量而且物料水分損失也較少。 粉碎的微粒大小幾乎一樣，也就是說物料微粒很均勻。微粒形狀不規(guī)則大多是長方體或立方體而不是圓形的。相對于錘片式粉碎機來說輥子式粉碎機中小尺寸微粒在輥子上的附著率要低5﹪—15﹪。 輥子粉碎機 輥子粉碎機 優(yōu)點： —效率高 —微粒粒度均勻 —低噪聲、低污染 缺點： —幾乎不用于粉碎纖維類植物 —粉碎的微粒形狀不規(guī)則 —前期投入可能要高（取決于系統(tǒng)的設計） —必要時維護保養(yǎng)費用要高 總體設計 有很多制造公司生產輥子粉碎機，但他們都有共同的設計特點如下所述： —傳送部件將物料連續(xù)的送到粉碎室以供粉碎 —一對輥子水平固定在支架上 —一個轉子固定不動另一個輥子間歇地靠近或遠離它 —輥子大都是以相同的速度反向旋轉或者其中一個轉動較快，輥子表面也許是光滑的也或許是有許多溝槽。 —軸桿，幾對輥子可能是固定在另一個支架的輥子上的 粉碎機中物料通常以連續(xù)不變的速度通過輥子以保證粉碎機輥子的最佳運轉。最簡單的粉碎系統(tǒng)是一個儲料器和一個手工操作的卸料門。這種類型的粉碎室最適合于粗糙的加工過程。對于研磨來說輥子粉碎是值得提倡的。這種類型的粉碎機中輥子位于儲料器的下方，有一個手工操作或自動控制的可調卸料門。 一對輥子的直徑是9~12英寸（23到30.5厘米），它們的長徑比可以達到4：1。輥子之間的排列方式是非常重要的，物料粒度取決于輥子之間的間隙。如果間隙不一致其粉碎性能將變壞從而導致維護成本增加、生產率下降，總之生產成本增加?？烧{節(jié)的間距,通過使用自動或手動氣動或液壓缸通過電腦操作或可編程序控制器來實現。 每對輥子都是反向旋轉的。輥子快速旋轉可以提高物料的粒度，每對輥子的轉速不同粉碎得到的物料粒度也不同。典型的范圍是1.2:1到2.0:1（由快到慢），對于一個9英寸（~23厘米）的輥子典型的速度是1300英尺/分（~395米/分），而對于一個12英寸（~30.5厘米）的輥子來說速度為3140英尺/分（~957米/分）。對于靠單獨電機驅動的兩個高速旋轉地輥子可用皮帶或鏈輪來減小速度。在底部的第三對高速滾子可以有單獨的驅動電機，另外輥子表面的凹槽可以改善速度的差異并提高粉碎效率。 輥子粉碎機通過將一對輥子撞到另一對輥子之上，第二對裝在第三對之上的方式來提高粉碎效果，這種方式產生的微?？梢越档?00微米，其粉碎能力是錘片式粉碎機的兩倍。粉碎粗糙類谷物時輥子粉碎機比錘片式粉碎機有優(yōu)勢其度電產量可能要比錘片式粉碎機高85﹪，飼料生產行業(yè)中谷類植物的典型粒度為600-900微米，降低了生產成本。