滚压机设计——影响喂料系统的压应力#中英文翻译#外文翻译匹配

滚压机设计 影响喂料系统的压应力 P. Guigon 杨丽丽 译（有删节） 摘要 在文章的第一部分，叙述了滚压机的主要特点。 然后 ,讲述了喂料和挤压质量之间的关系。 对于某个静态差距 (无负载 ) ，滚压机的处理量是由螺旋喂料速度决定的 ,与滚筒的速度快慢和需要压实的生产材料无关。当处理量是多种多样的时候，控制差距是一个获得相同质量压坯的好方法。对强烈环节紧凑的应力分布的解释和说明，这些应力是分布在由一根周期旋转的螺杆喂料的滚压机上的。 关键词 ：辊压； 喂 料 装置； 压坯异质； 差距控制 1 引言 由于 滚压 机 简单、低营运成本的 理念 ， 而且 用材广泛， 所以 被用在了许多不同的行业 (化工、制药、 食品加工、采矿、矿产、冶金 )上 。 广泛 的垃圾回收或处理 就是一个 新兴的应用领域。滚压机的挤压要比第一眼看上去的复杂。 对很多参数和对滚压机理的缺乏了解导致 了滚压机没有 产品的 优越性 。 这篇文章将讲述滚压机的主要部分。 文中 将注意力集中在了解喂料装置是如何影响压实质量的。 2. 滚压机的概说 1-5 滚压机的滚压是一个连续的过程。 功能原理很简单 ：料粉是通过重力方式或者通过一根连接两个方向相反正在旋转的辊子的螺杆喂入。 由材料和滚 筒表面产生的摩擦在辊子之间的狭小空间里带出料粉，在这些空隙里粉末产生的强大应力导致了其结构紧凑。 如果滚筒是平滑的或者是槽型的，物料被压紧成致密片 而口袋卷筒将形成煤球型的 (如图 1 所示 )。 1 图 1：滚压机中的压块和压坯 2.1. 压实机制 辊子之间的空间，一般分为三区，在这三个区由不同的机制作用。喂料区：在这个区颗粒的整理应力很小而且致密性很纯粹； 压实区：在这个区挤压力作用明显；挤压区：颗粒开始塑性变形和 /或被压碎。在喂料区和压实区之间的角度是钝角或者是锐角。 图 2：由压电传感器测量的应力分布 2.2. 典型应力 辊子间隙间的压应力的正常分布如图 2 所示。在喂料区当滚筒作用在粉末上的压力很小时 (小于 0.1 兆帕 )， 它不能用压电传感器测量。 只有压实区的应力才可以用它测量。 应力扩增在小于直角的情况下发生。 应力增加至最大值，这个最大值相当于到达中性角度。 在许多情况下，角度的改变不和辊子间隙成比例，是因为材料覆盖在滚筒的表面。 直角之后，压坯被排出。 弹出物对应的压力急剧下降。 2 2.3.滚压机所具有的优缺点： 滚压机滚压物料有以下几个优点： (1)允许连续运行和有多功能的高生产能力 :适合重工业每小 时几百吨的生产 (矿产、肥料 等 )。 (2)压实成本低。 带动滚筒和螺杆运转的能量是有限的。通常，干燥这一步是不需要的。 (3)需要压实的热材料的气温高达 1000摄示度是可能的。 然而，这项技术目前还有一些弊端： 压坯的外形和尺寸 比冲模挤压出来的不规则。料粉的泄漏 也 要重点解决 。未压碎的料粉 也需要 再挤压。使用真空除尘系统可以大大减少 (可降百分之几 )细粉的泄漏2。 图 3：滚压机的结构 2.4.技术 无论制造商是谁，滚压机的原理都是一样的 ,而且 滚压机 都有相似的结构配置。 市场上卖的滚压机的辊子 有水平放置的，有垂直放置的，有倾斜放置的， (如图 3 所示 )。两种不同的结构设计 要 根据滚压机放置位置的合理性来选择最优的设计 方案 。 在悬臂轴设计中，棍子是被置于框体外面的（如图 3所示）。 这种设计通常被用于小型机器；这样的设计便于辊子的维修。 比较大型的机器用中间轴的设计结构，这就意味着，轴的两端是由铰链连接轴承旋转的，而且辊子是位于框体里面的。制造商对 3 A、 B、 C三种结构的优点持有不同的意见。一般来说，一个辊子的轴承在机体里的作用是固定不变的，然而其他可移动的辊子的轴承是靠水压力调节的 2.5.滚动和挤压系统 辊子选择的 方法 一般有两种 :几何特征 (光滑、槽、 和容器设计 )和表面硬度。 对于压块，容器造型的优先使用，这是为了减少排除物的问题和挤压造成的破坏：作用于压坯上的最大允许压力很大程度上取决于辊子的直径。 越大的压力被用于越大的机器上。 辊子的驱动组件必须 保证两根轴间有一个恒定的转距和一个相等的速度，这是为了阻止辊子 较早的 被 磨损坏和破坏压坯的剪应力的形成。为了防止压块，两个辊子间的旋转速度必须一样。一般来说 ,液压系统是用来维持滚动轴承座的 . 采用这种系统，应用力的调整范围可以更广泛。 2.6.喂料系统及隔离 喂料系统是一个好的挤压过程的关键。它必须完成一个统一的连续的物料流动，这是为了恰当而充 分 的填满辊子间的量从而使压坯形成不均匀质。 该喂料系统还用于密封和除尘装置。 两种不同类型的喂料系统主要是依靠流动特性和粉末的密度来区分使用的。致密性需要制作压坯 有 足够的质量保证：重力的自由向下喂料和强迫喂料 (粉末是被一个或几个螺杆推向辊子的 )。 2.7.粉末的除尘 粉末中的空气有两种逃走的方法 :通过料粉的轴中心，来到喂料装置处；通过辊子之间的空隙和面夹板。 一些空气可以在棍子内被压缩， 这是一个限制生产量和压实 质量的关键因素 2。 在压实区使用真空除尘可以有效的优化辊压质量和减小未挤压的粉末的泄漏。 3. 在实验室滚压机中喂料和压实相互关系的阐述 3.1.实验室滚压机 实验室进行实验的过程如图示 4 所示。 滚压机配备了垂直安装的 130 毫米直径50毫米宽的圆盘。滚压机的详细描述和须知将在 3-6给出。 4 图 4：实验室的滚压机：（ 1）辊子（ 2）轴承座（ 3）辊轴（ 4）水平支撑系统（ 5）螺旋喂料（ 6）搅拌器（ 7）喂料漏斗（ 8）金属夹（ a）压电变换器（ b）移动变换器 3.2. 滚压机的吞吐量 对于细粉而言，滚压机的 进料 量是由两个因素限制的。一方面， 进料 量是由细粉的除尘能力限制的。而另一方面，压实速度又是由颗粒的弹性度限制的。一般来说，当达到临界流量时压实的质量比较差。在这种情况下，要么是由压实引起的风流影响了喂料（除尘能力差），要么是压实的速度太快。这项研究的所有实验都将在低于这个临界流量时进行。因此，当出现细粉压实没有产生带钢或者带钢的质量差的问题时，不是由除尘能力差或滚压速度过高（挤压时间短）引起的。 3.3.挤压率好的挤压场合 挤压速度和螺杆转速的范围大可在实验室滚压机中得到解决。因此，我们研究了在挤压带钢成形中滚 压速度和螺杆速度对它的影响。为了清楚地发觉高低滚压速度的限制对挤压成形的影响我们使螺杆速度固定选择它的挤压速度。在滚压速度低时将发过度挤压，而在滚压速度高时将不形成带钢。 三个操作条件规定如下： 当喂料不足时，由螺旋喂料提供的大量粉末的操作滚压率会太小。在这种情况下，不能挤压微粒物质。 当喂料过多时，由螺旋喂料提供的大量粉末的操作滚压率会太大。滚 子 与滚 子 之间 空隙的 增大 是很重要的。在 喂料过多的 情况下，挤压出来的物质质量会差而且 未 挤压的粉末的 流 失 也很 严重。 好的挤压率是在处于喂料不足和喂料过多之间的挤压率。当挤 压材料时产生的带 5 钢具有足够的凝聚力和力学强度时，才会有好的挤压率。 图 5：不同辊子对应不同旋转速度的压坯的输出 图 6：辊子的不同速度对应不同的旋转速度而且物料的输出依靠旋转速度而不是和辊速成正比 当螺杆转速固定时，滚压吞吐量是由多种能够形成好的挤压的滚压速度衡量的（如图 5 所示）。对于固定的旋转速度，滚压机的吞吐量也是个常数。在图 6 中，吞吐量是由多种滚压速度下的旋转速度决定的。这个吞吐量要比螺杆单独作用时的吞吐量小。由滚动产生的压力改变了粉末在螺杆内的滑动状态。 3.4. 轧辊辊缝的变化 如果上布的 轧辊能纵向移动，当传动力是恒定时轧辊的缝就能从初值增加到一个恒定值。恒定值是轧辊作用在压实材料上的平均压应力的作用。它也是辊速度 vr的作用，轧辊的生产量是 QC,材料的压实密度是 Qs，轧辊宽是 L，压实材料的摩擦系数 6 是 f3： e=Qc LVr s(1- ) 辊缝测量有许多工作要点（辊速度和螺旋转动速度），国际质量曲已给出 (如 图 7所示 )。 图 7：辊子和螺杆的速度之间的标准间隙差距，初次间隙是 0.8mm 3.6. 应力的波动与镭的不同成分的关系如表 6 紧凑的密度分布的特点是通过衡量一个氯化钠晶体的传 递分布 。 适当的压力能使氯化钠晶体支离破碎 。 因此 ， 同样 的 氯化钠晶体 不是到处都能传递光的 。 因为氯化钠的透光性能是与局部紧凑地方的压力有关 的 。 承受较少压力的地方因此出现暗色 (如 图 11 所示 )。 机械性能良好可以作为获得紧凑性的特点 ， 例如粉碎被使用过的氯化钠 (硼粉 74 时 )。 施加在物料 上的压力既不 符合 辊宽度也不符合时间常数 。 期刊的分布不均 。 周期现象就是螺旋反馈线的周期 。 事实上 ， 施加在滚轴间隙上的压力分布与 喂料 系统 压力的分布 有关。 喂料 系统的 压力 有 来自螺旋馈线 的 。 喂料压力的不均匀是由于最后螺旋的螺杆的传动力不均 匀 。 7 图 11：氯化钠的透光性（氯化钠 d50， Am74），上图 氯化钠照片的标准灰色度，下图 4. 结论 喂料和压缩特性之间相互作用得到了证明 。 因为使用螺旋给料器，大的压应力产生了 ， 并 被 当作滚动和转动的作用 力 。 压力的 大小 仅由螺杆 给料器决定 ，和生产 材料 以及棍子的转速都没有关系 。 结果表明差距曲线可以近似 于 国际质量曲线 。 因此 ，当压力的量不同时 ， 控制差距是一个好方法 ，可以用这种方法来 获得相同的压应力。对墙的观测表明 ， 颗粒运动喂料区不是连续的 。 螺杆自转 的应力 周期得到了证明 。 从单螺杆喂料的应力分布 看， 如果 它们有相同周期 就可以 被观察到。 8 Roll press design influence of force feed systems on compaction P. Guigon *, O. Simon1 Universite de Technologie de Compiegne, BP 20529, 60205 Compiegne cedex, France Abstract In the first part of the article, the main features of roll compactor design are reviewed. Then, the interaction between feeder and compact quality is demonstrated. For a given static gap (no load), the throughput of the press is only a function of the screw feeder speed no matter of the roller speed as long as compacted material is produced. Control of the gap is a good way to obtain compacts of the same quality when throughput is varied. The strong link of the stress distribution of the compact issued from a roll press fed by a single screw with the periodicity of the screw was demonstrated and explained. Keywords: Roll compactor; Feeding device; Heterogeneity of compact; Gap control 1. Introduction Because of their conceptual simplicity and low operating cost, roll compactors are used in many different industries (chemical, pharmaceutical, food processing, mining, minerals, and metallurgical) for a wide variety of materials. A new emerging application is the vast field of waste recycling or disposal. 9 Compaction in a roll press is more complicated than it looks at first sight. Many parameters are involved and a lack of understanding of compaction mechanisms results in products that do not possess the required characteristics. This article will review the main features of roll compactors. Then, attention will be focused on the understanding of how the feeding device influences the quality of compacts. 2. Generality about roll compaction Compaction in a roll press is a continuous process. Functional principle is simple: powder is fed by gravity or by means of a screw through two counter currently rotating rollers. Friction between the material and roller surface brings the powder towards the narrow space between the roll (gap), where the powder is submitted to high stresses leading to the formation of compact. If the rolls are smooth or fluted, material is compacted into dense sheets, whereas pocket rolls will form briquettes (Fig.1). 10 P. Guigon, O. Simon / Powder Technology 130 (2003) 41 48 42 Fig. 1. Briquetting and compaction in a roll press 2.1. Compaction mechanisms The space between the rolls is generally divided into three zones, where different mechanisms occur: the feeding zone, where the stresses are small and densification is solely due to rearrangement of particles; the compaction zone, where the pressing forces become effective and the particles deform plastically and/or break; and the extrusion zone. The limit between the feeding and the compaction zone is the gripping angle or nip angle 2.2. Stress profile A typical distribution of the normal stress versus the position in the gap between the rolls (roller angle) is represented in Fig. 2. 11 Fig. 2. Stress profile measured by the piezoelectric transducers. As the stress exerted by the rollers on the powder in the feeding area is very small (less than 0.1 MPa), it can not be measured by piezoelectric transducers. Only the stress exerted in the compaction area is observable. The stress augmentation takes place below the nip angle. The stress increases until a maximum which corresponds to the neutral angle. In many cases, the neutral angle does not coincide with the roll gap because the material slips along the roller surface. After the neutral angle, the compact is ejected. The ejection corresponds to a rapid decrease of the stress profile. 2.3. Advantages and drawbacks of roll compaction Agglomeration in roll presses has the following advantages: The process is continuous and allows with multiple units of high production capacities: several hundred tons perhour are suitable for heavy industry (mineral, fertilizers, ). The compaction costs are low. The energy consumption is limited to the power to drive the rolls and the screws. Normally, no drying 12 step is necessary. Compaction of hot materials with temperatures up to 1000 is possible. However, this technique presents some drawbacks: Aspect and dimension of compacts made by briquetting are less regular than those produced by die pressing. Powder leakage can be important. It is usually necessary to recycle the uncompacted powder. Use of vacuum desecration systems can greatly reduce (down to few percent) the leakage for very fine powder 2. 2.4. Technology Whatever manufacturer, the roll presses consist of the same elements and have similar configurations. Commercially available roller compactors have rolls mounted in a horizontal, vertical or even inclined position as shown in Fig. 3. Two different frame designs exist which are distinguished by the location of the press rollers with respect to the frame. 13 Fig. 3. Configuration of roll presses. In cantilever-shaft designs, the rollers are located outside the frame (Fig. 3). This design is normally used for smaller machines; it allows easy access to the rolls for maintenance tasks. Most larger machines use the mill-shaft frame design. This means, both ends of the two shafts are pivoted by bearings and the rolls are located within the frame. Manufacturers are not unanimous about the advantages of configurations A, B, and C. Generally, bearings of one of the rollers are fixed in relation to the frame,while the bearings of the other movable (floating) roller are maintained by an adjustable hydraulic force. 2.5. Rolls and pressurization system Roll choice is essential in two ways: geometrical characteristics 14 (smooth, fluted, and pocket design) and surface hardness. For briquetting, pocket shapes are optimized in order to diminish ejection problems and breakage of compacts: maximum applicable stress on the compact depends greatly on roll diameter. Higher stresses are used on larger machines. Roll drive assembly must ensure a constant torque and an equal velocity of the two roll shafts in order to prevent early wear of the rolls and shearing forces which will fracture the compact. In the case of briquetting, both rolls must rotate with exactly the same speed. Generally, a hydraulic system is used to maintain the bearing blocks of the movable roller. By using such a pressurizing system, the applied force can be adjusted within wide limits. 2.6. Feeding systems and confinement The feeding system is the key to a good compaction process. It must achieve a uniform and continuous flow of material in order to fill the nip between the rollers correctly and sufficiently, so that the formed compacts are not heterogeneous. The feeding systems are also used as densification and desertion devices. Two different types of feeding systems are used depending on the flow properties, the density of the powder, and the densification needed to produce compacts of sufficient quality: 15 （ 1） gravity feeder for free flowing particles and force feeder (powder is pushed towards the rolls by one or several screws). 2.7. Powder desecration The air fed with the powder can only escape by two paths: axially through the powder, counter currently to the feed; and through the gap between rolls and cheek plate. Some air can be compressed inside the compact. This is a key factor limiting compaction production throughput and compact quality 2. Use of vacuum desecration before the nip roll region is efficient in optimizing roller compaction and minimizing uncompacted powder leakage. 3. Demonstration of the interaction between feeding and compaction in a laboratory roll press 3.1. Laboratory roll press Experiments were carried out on a laboratory roll press (KomarekR B100QC) shown in Fig. 4. The roll press was equipped with 130-mm diameter and 50-mm wide smooth rolls, which were vertically arranged. Detail description of the roll press and instrumentation is given in Refs. 3 6. 16 Fig. 4. The laboratory roll press: (1) roll, (2) bearing block, (3) roll shaft, (4) supporting hydraulic system, (5) screw feeder, (6) paddle mixer, (7) feed hopper, (8) cheek plate. (a) Piezoelectric transducers, (b) displacement transducer. 3.2. Roll press throughput For fine powder, the roll press throughput is principally limited by two factors. On one hand, the throughput is limited by the powder deaeration ability, and on the other hand, the compaction speed is limited by the elasticity of the particles. Generally, a poor quality compaction takes place when a critical throughput is reached. In this case, either the airflow generated by compaction disturbs the feeding (bad deaeration) or the compaction is too fast 1. All experiments in this study were conducted below this critical throughput. Therefore, when no strip of compacted powder was produced or when the strip was of poor quality, the problem was not due to poor deaeration or to a too high roller speed (too short compaction time). 17 3.3. Compaction rate, good compaction settings A wide range of roller speeds and screw feeder speeds can be set on the laboratory roll press. Therefore, we investigated the influence of roller speed and screw speed on the formation of a compacted strip. The screw feeder speed was fixed and the roller speed was chosen in order to detect visually the higher and lower limits of roller speed that enabled the compaction. At low roller speeds, overcompaction occurred, and at high roller speeds, no strip was formed. Three operating conditions were defined as follows. The subfeeding, corresponding to the operating rate of the roll press when the amount of powder that is provided by the screw feeder is too small. In this case, the particulate material is not compacted. The over-feeding, which corresponds to the operating rate of the roll press when the amount of powder provided by the screw feeder is too large. The compact is extruded between the rolls and the roll gap increase is important. In this case, the compacted material is of poor quality and the powder loss as noncompacted powder is very important. The good compaction rate is an operating rate between sub- and overfeeding. It corresponds to the production of a strip 18 of compacted material that exhibits enough cohesion and mechanical strength. For a fixed screw speed, the roll press throughput was measured for several roller speeds Vr, enabling production of a good compact (Fig. 5). For a constant screw speed Vs, the roll press throughput is constant. In Fig. 6, the throughput is measured as a function of Vs for various Vr. This throughput is smaller than the throughput of the screw alone. The counter pressure created by the rollers modifies the slip between the powder and the screw barrel. Fig. 5. Compactor throughput versus roll speed for different screw speeds. 19 Fig. 6. Compactor throughput versus screw speed for different roll speeds and comparison with throughput delivered by the screw when not coupled with the roll. 3.4. Roll gap variation If the upper roll can move vertically, the roll gap increases from its initial value to an equilibrium value when the powder is compacted. This equilibrium value is a function of the mean stress applied by the rolls on the compacted material. It is also a function of the rollers speed Vr, the roll press throughput Qc, the density of the compacted material qs, the rolls width L, and the slip of the compacted material on the roll surface f 3: e=Qc LVr s(1- ) The roll gap was measured for many working points (sets of Vs and Vr), and iso-gap curves were computed (Fig. 7). 20 Fig. 7. Calculated iso-gap curves (mm) versus roll and screw speed. Initial gap is 0.8 mm. 3.6. Heterogeneity of compact in relation to the fluctuations of stress 6 Distribution of the compact density was characterized measuring the distribution of light transmitted through a sodium chloride compact. The fragmented sodium chloride crystals are oriented by the applied stress, and therefore, light is not diffused similarly in all directions. For sodium chloride, the light transmission property is linked with the stress that has been applied locally on the com