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1、2003中国聚氨酯行业整体淘汰ODS国际论坛论文集运用控制压力技术(CPT)生产连续性和非连续性产品Giorgio Pallanza Vittorio Mariani(意大利OMS集团公司)摘 要:CPT(控制压力技术)是一种不同的聚氨酯发泡技术:现在它不但可以作用在化学参数上,而且可以作用在物理参数上(压力),从而在发泡过程中获得真正的益处。CPT(也称为VPF:变压发泡)是在高海拔的地方进行第一次块状发泡试验后开发出来的。经过了几次成功的真空试验(压力在50100 kPa),也在有一定压力(最大到130 kPa)的情况下进行试验。连续生产和非连续生产都可以采用控制压力技术。在连续发泡设备上
2、,传统设备的结构根据密封区域的需要被复制。事实上,总共需要5个阶段来进一步的说明:1)在第一个密封区域内当压力到达预定值时聚氨酯泡沫开始发泡。2)在不间断发泡的同时,泡沫块被切割并且在打开第一扇门后,泡沫块通过传送带被传送到第二区域。所有这一切都发生在相同的控制压力下。3)泡沫块到达卸料传送带后将根据生产传送带以更快的速度被传送。4)在生产传送带和泡沫块卸料传送带之间的门被关闭,在卸料区的压力将逐渐恢复到大气压力下;然后泡沫块就被更快地卸放。5)在中间的门仍然关闭的情况下,卸料门被关闭,泡沫卸料区的压力恢复到所选的变压发泡值。在非连续系统上,泡沫是在一个包括所有发泡设备的大围房内生产,其中计量
3、设备是在围房的外面。当方形块状物放进装置内部后,主门被关闭,压力调整到设定值。接着,所有组分在放置在发泡箱底部的混合筒内混合。混合料放在模箱底部时,开始混合原料。在缓慢地泡沫发起过程(避免溅出)结束后,泡沫块被放在上部的成方工位下,在那里停留足够长的时间与完成反应。这一过程完成后,压力逐渐恢复到正常值,生产出来的泡沫被移出机器,操作重复开始。使用不同的加工压力可以改变聚氨酯的特性和泡沫的属性。使用控制压力技术的优点不止一个:可以生产密度非常低的产品,真空替代了发泡剂(如水),因此节省TDI。这一新技术的另一个重要方面是所使用的生产设备是完全的环保型设备,而且对环境和工作场所都没有危险,因为其带
4、有气密的围房,所有产生的气体都被活性碳吸收。最后一个积极的方面是可以在泡沫中加入填料,容易获得更高的硬度,并降低了原料成本。1 引言在生产低密度聚氨酯泡沫时,辅助发泡剂被广泛的使用。最近几年,辅助发泡剂已被大量地缩减,以不增加对臭氧层的破坏和温室效应。这种替代发泡剂的更换给泡沫生产厂家造成许多麻烦。在替代发泡技术中,许多环保型系统采用了LCD(液态二氧化碳)和CPT(控制压力技术),控压技术也称为VPF(变化压力发泡)。CPT技术的开发是在多年之前的事,当时确定大块泡沫生产在海拔2000 m以上的高度进行,在此高度下大气压力为78.5kPa (785mbar),在此低真空度下能使用在海平面上的
5、生产配方生产出较低密度的产品。在所有控制压力技术生产过程中,不需要发泡剂,这种技术即用于大块软质聚氨酯泡沫的连续生产,也用于非连续生产,既用于高密度泡沫块也用于低密度泡沫块的生产。在增加发泡装置的情况下,在一个给定真空度的条件下,泡沫膨胀,泡沫密度可以低于20 kg/m3,甚至可以得到密度为10 kg/m3的泡沫;在一定的压缩空气的压力下,可得到高于20 kg/m3的泡沫密度。在控制压力(CP)生产设备中,创造一种真空和/或压力的条件,泡沫的发起过程(即从乳白时间到泡沫大块的形成阶段)是在一个通道中进行的。在此通道内通过辅助的设备,使通道内的真空或压力保持在预先计算好的范围内。应该指出真空的范
6、围是从50100 kPa,而压力范围则为100130 kPa。这种创新技术的另一个重要方面是生产设备完全是环保型的,并且被封在密封的通道内,产生的所有气体都被活性炭捕集装置保留。最后,但并不是不重要,使用CPT技术生产的泡沫产品比采用环境压力技术的产品降低3%5%的成本。2 CPT控制压力技术原理聚氨酯泡沫的发起(膨胀)是由气体(二氧化碳或发泡剂)的膨胀引起的,而气体膨胀则受周围环境压力和温度的影响。物理学的定律决定着这种泡沫的膨胀,其源于气体膨胀定律:Px/Dx Pa/Da即 Px (DxPa)/ Da式中:Px控制的压力值,Dx在控制压力下的密度,Pa绝对大气压,Da在Pa(绝对大气压力)
7、下的密度。作为此公式的结果,我们可以预设工作压力,也就是为了得到所要求的密度在不调整化学组分的前提下算出工作压力。泡沫的硬度可通过下一公式计算:Hx (Px2/ Pa2)Ha式中:Hx在控制压力下泡沫硬度;Px控制压力值; Ha在Pa(绝对空气压力)下的硬度。图1为密度随压力和/或真空度的变化关系。 密度 kg/m3 27.6 21.0 18.0 17.0 14.012.5 10.5 50 60 70 80 90 100 130 压力/kPa 大气压 图1 密度随压力和/或真空度的变化关系例如:要从密度为22 kg/m3的泡沫和硬度为120N得到15 kg/m3和55.5N硬度的泡沫需要控制压
8、力为68 kPa。虽然这种公式是用于气体的,但获得泡沫的数据几乎用同样方法进行计算。3 连续控制压力工艺(CCPP)整套设备有一个气密通道组成(包括前部进口门和出口门),通道的尺寸以达到内部最大130 kPa压力和真空度为最大50 kPa为准。此通道由两个区域组成:第一个区域装有连续生产线或所谓的“干”设备:槽(2),落料板(6),生产传递器(9/1),开卷和再卷系统及剪切机(8)。在此之后是一个自由滚子传送器(10)和一传送器(9/2),在此传送器的终端是一中间气密门(3/1)。通道的第二个区域装有一个传送器(9/3),此传送器通过气密出口门(3/2)将泡沫块卸到常压下的泡沫块固化系统内。深
9、灰色颜色标明所形成的泡沫块,而浅灰色表示在所需操作值下的压力。所有计量线都有高压计量泵组成并且放在通道的外边。每一条线的计量都有一个质量流量计控制,流量计通过一个闭环系统自动变化泵的运转速度使输出量保持在所需要的值内。在我们的成套设备(如Maxfoam类似Foamax)中,混合枪头放置在压力控制通道之外,枪头与安装在通道内的槽底部的连接是通过高压管连接而成的。在通道内每个区域内的真空和/或压力值都是由与之相对应的独立的系统(4/1和4/2)进行设定和控制的。一个复杂的电子控制系统通过对真空/压力泵速度的调节,控制所需要的压力值。(1)在阶段1,进行以下的运行:a.中间气密门打开(3/1)b.气
10、密出口门关闭(3/2)c.只有当第一通道内的压力到达所需要的数值时(用黄色标出),大块泡沫生产(用红色标出)开始。(2)在阶段2,泡沫块进入传送器(9/2);当泡沫达到所需要的长度时,将泡沫块切开(8),然后加速进入传送和卸料区(通道2)。两个传送器(泡沫块生产和传送器)的运行速度是同步的(9/1和9/2)。(3)在阶段3,当剪切机将泡沫块切开后,传递区的传送器加速到原速度的15倍多,将泡沫块传送到泡沫块卸料传送器上(9/3)。传送器9/2和9/3的速度是同步的。在传送过程中,生产用传送器(9/1)泡沫块传送到自由滚子传送器(10)上。这个系统可使生产传送器的速度保持不变。自由滚子传送器的长度
11、是由泡沫块到达卸料传送器(9/3)之前所允许的时间决定的。当泡沫块到达卸料传送器时,此滚子传送器回到与生产用传送器同步的速度。在进行生产之前,通道中的两个区域的真空度都要保持在一个稳定的数值内,在生产阶段3中用黄色标出。在生产阶段4/1中表示泡沫块已经传送到第三个传送机(9/3)上,此传送机称为卸料传送机。当这种传递结束后,泡沫块通过自由滚论(自由传送器)到达传送机9/2上,传送机9/2的传送速度与传送机9/1同步。中间气密门关闭(3/1)及卸料区域内的气压回复,通过一个预定的时间达到大气的压力(常压)(用绿色标出)。如黄颜色所标出的,通道中第一个区域的压力是保持恒定的,除了在通道中区域2的压
12、力被释放时。在生产阶段4/2中,泡沫块被卸到固化设备上,在图中没有用颜色标出。当通道中区域2的气压重新回到大气压时,气密出口门(3/2)打开。传送器(9/3)将泡沫块送到泡沫块固化系统的传送器上。生产阶段5,当泡沫块被送到通道第二区域以外后,气密门(3/2)关闭。只有在通道2区域内的控制压力回复到通道的压力(黄色标出)时,中间气密门(3/1)才打开。通道中的两个区域,每一个都有独自的真空和压力控制。如上述的生产阶段1所示,生产周期现开始重复。发泡过程示意图见图2,分5个生产阶段。生产阶段1:开始发泡生产阶短2: 继续发泡生产阶段3:泡沫块按尺寸切割生产阶段4/1: 准备卸送泡沫块生产阶段 4/
13、2: 正在卸放泡沫块 生产阶段5:重新生产循环1.混合枪头, 2.槽, 3/1.中间气密门, 3/2.气密出口门, 4/1-2.真空或压力系统, 5/1-2.活性炭气体捕集器,6.落料板, 7.泡沫块, 8.剪切机, 9/1.带式运送机1,9/2.带式运送机2, 9/3.带式运送机3,10.自由滚子传送器 图2 连续控制压力工艺生产过程示意图4 非连续工艺工程应用控制压力技术的非连续聚氨酯泡沫块的生产是用一个非连续的软泡设备(工作在常压下的)和一个控制压力封闭围房内容易产生泡沫膨胀的辅助设备组成的。非连续法DCPP4-C软泡整套生产设备由以下部分组成:=每个组分的储料罐=每个组分的计量泵组带有
14、计量器,预设定混合比例,气动驱动的混合缸(筒)在模箱内对大量的组分进行混合。=泡沫块成方系统=围房工作压力在50130 kPa。=泵的运转使箱内保持一定的真空和/或压力(数值是预先调好的,通过电子仪器进行监测)。=活性炭捕集装置此类设备的生产工艺过程是:阶段1:将混合缸(筒)放入到模箱内;此阶段表示使用气动系统(3)将混料缸(筒)放到模箱的底面上,可以看到密封圈(4)安放在混合缸(筒)的底部。阶段2:在混合缸(筒)内组分进行计量和混合;此图表示四种组分在混合缸(筒)内进行计量和混合,混合缸(1)抵住模箱(2)的底部。阶段3:发生反应的混合料分布在模箱内;在阶段3中,当混合停止时,混合缸被释放并
15、且缓慢地向上移动在模箱内发生反应但不飞溅的混合料。阶段4:反应后的混合料发起和泡沫形成方块;在泡沫发起(上升)(第4阶段),当防滴落系统(3/1)盖住混合缸的底部后(盖住底部的目的是防止混合料的滴落形成飞溅的泡沫),模箱移动到成方工位。经过一个设定的技术上确定的时间后,在围房内的真空和/或压力恢复到大气压下。将我们竞争对手的一套设备放在围房内,此围房内的真空度或压力达到了预先要求的数值并保持恒定,以上第二、第三和第四阶段的过程都发生了。为了更好地描述此过程,请看图3。 阶段 1:将混合缸(筒)放入到模箱内 阶段 2: 在混合缸(筒)内组分进行计量和混合 阶段 3: 发生反应的混合料分布在模箱内
16、 阶段 4: 反应后的混合料发起和泡沫形成方块图3 非连续控制压力工艺生产过程示意图5 泡沫的机械特性表1表示了使用同样的配方在不同的气压条件下所获得的泡沫塑料块的机械性能。在表1中使用的化学配方如下: 常规多元醇或聚合物多元醇 100 H2O水 4.6 添加剂 1.7 二氯甲烷或其它发泡剂 TDI指数110绝对压力和密度的关系参照表1。压力控制法软泡生产技术不需要任何发泡剂。表1 发泡压力对泡沫物性的影响配方多元醇种类压力kPa密度kg/m340%硬度daNCLD 40%kPa50%压缩变定 %拉伸强度kPa聚合物多元醇10022.319.64.752.48115.8聚合物多元醇8516.2
17、11.42.622.72116.4聚合物多元醇6514.17.72.244.0397.4常规多元醇10020.716.34.042.87153.6常规多元醇8515.99.82.072.89145常规多元醇6512.77.61.684.831396 结论使用CPT(控制压力技术)生产的低密度泡沫块在技术上很有竞争力,经济效益明显,与其他生产方式相比具有更好的物理机械特性。1化学配方节约成本考虑泡沫的成本,在生产很低密度的泡沫(1516 kg/m3),因采用压力控制技术而不使用发泡剂,节约的成本是明显的。进一步与常压技术相比,压力控制技术需要一定量的水,这样就减少了TDI 80/20的使用,而T
18、DI 80/20是成本很高的化学组分。2物理机械特性对泡沫的分析,特别是低密度泡沫的硬度是非常重要的,这也促使控制压力技术的成功。与常用的发泡剂相比,低压效应对泡沫的硬度有很大的影响。积极的方法是有可能在泡沫中增加添加剂,使其得到较好的密度而又降低化学配方的成本。因液体二氧化碳系统带有过滤器就不能使用添加剂。CPT克服了这些不利因素,因它不需要添加与臭氧层和/或温室效应有关的发泡剂,而完全是环保型技术。在混合反应过程中产生的氨气和异氰酸酯挥发气体,在排放到大气之前被保留在活性炭捕集器内。因CP生产设备是被密封在气密通道内,生产过程对环境绝无影响,对环境和工作间没有危险性。作者简介:Giorgi
19、o Pallanza 1972出生,化学工程博士,曾任聚氨酯组合料技术市场经理,2001年加入OMS公司,目前是该公司远东市场销售经理。Vittorio Mariani 工业化学博士,OMS集团的创始人之一,曾任公司研发经理、连续发泡块状聚氨酯泡沫生产经理。 Continuous and Discontinuous Production with Controlled Pressure Technology (CPT) Giorgio Pallanza, Vittorio Mariani(OMS Group, Italy)ABSTRACTThe CPT (controlled pressure
20、 technology) allows a different approach for the PU block foaming technology: now it is possible to act not only on the chemical parameters but also to physical ones (pressure) to gain substantial advantages in the foam expansion.It has been shown that CPT (also known as VPF: variable pressure foami
21、ng) was born from the first trials of block foaming at high altitudes above the sea. After some positive feedback at vacuum like pressures (500 to 1000 mbar), also experiments with some compression (up to 1300 mbar) have been tried.Both continuous and discontinuous process have been positively adapt
22、ed to CPT.In the case of a continuous plant, the structure of conventional plant is replicated according to the exigency of sealed compartments. In the facts, a step more is introduced, arriving to a total of five phases:1) the foaming of PU takes place when in the first sealed compartment the press
23、ure reaches the desired value2) without interrupting the foaming, the foamed block is cut and accelerated to a second compartment of the conveyor, after the first gate is opened. All this happens at the same controlled pressure3) the foamed block reaches the discharge conveyor, running at faster spe
24、ed with respect to the production conveyor4) the gates between the production conveyor and the block discharge conveyor closes and the pressure in the discharge area is carried gradually to the atmospheric one; then the block is quickly discharged5) the discharge gate closes and, while the intermedi
25、ate gates is still closed, the pressure in the block discharge area is carried back to the chosen VPF valueIn a discontinuous system, the block is produced in a big cabin enclosing all the foaming devices, while the metering part is outside.After the squaring block is positioned inside the device, t
26、he main gate is closed and the pressure is adjusted to set value. Then the mix of the components is made inside the mixing cylinder, when positioned on the bottom of the box. After this last slowly rises (to avoid splashing), the squaring block is positioned under the top squaring station, where it
27、stays for the necessary time to complete the reaction. When this process is finished, the pressure gradually returns to normal values, the produced foam is removed from the machine and the operations can restart.The formulation of the polyurethane as well as the foam properties change according to t
28、he pressure one wants to use for the process.The CPT bring with it more than one advantage: with extremely low density products, vacuum replaces blowing agents, and above all water, leading therefore to a saving in TDI 80/20.Another important aspect of this innovative technology is that the producti
29、on plant is entirely environmentally-friendly and danger-free for both the environment and the workplace, being enclosed within an airtight tunnel and all gases developed are retained by activated carbon traps.At the end, a positive aspect is the possibility of introducing fillers in the foams, achi
30、eving easily a better hardness and a lower formulation cost.INTRODUCTIONIn the last years the use of ABAs has been gradually reduced not to increase the ODP and GWP effect. These ABAs are needed to produce the most widely used low density PU foams and their replacing cause problems to the foam manuf
31、acturers.To obviate this elimination of ABAs, some environmental-friendly systems have been adopted like LCD (liquid carbon dioxide) and CPT (control pressure technology), also known as VPF (Variable Pressure Foaming).CP-technology was developed some years ago when it was ascertained that slabstock
32、foaming plants operating at 2000 meter above sea level -about 785 mbar, therefore at low vacuum degree- can produce lower foam densities from production formulations made at sea level.No alternative blowing agents are needed in all CP foaming processes, applied to both continuous and discontinuous p
33、roduction of PU blocks either at low or high density.The foam expansion is mechanically obtained by creating above the foaming device either a given, accurate vacuum degree to get foam density lower than 20 kg/m3 reaching even 10 kg/m3 or a certain compressed air pressure degree to get foam density
34、higher than 20 kg/m3.To create such vacuum and/or pressure conditions in these CP plants the foaming process -from the cream time up to the block discharge phase- occurs in a tunnel where either vacuum or compressed air pressure are kept to a pre-calculated degree through pertinent equipment.It shou
35、ld be noted that the vacuum ranges from 500 to 1000 absolute mbar, while the compression ranges from 1000 to 1300 mbar.Another important aspect of this innovative technology is that the production plant is entirely environmentally-friendly being enclosed within an airtight tunnel and all gases devel
36、oped are retained by activated carbon traps.Last but not least, foams produced under CPT are 3%5% less expensive than those produced adopting the atmospheric pressure technology.CPT PRINCIPLEThe PU foam rise is based on the gas expansion (CO2 or blowing agent) being influenced by surrounding tempera
37、ture and pressure degree.Physical laws governing this expansion come from the law governing such gases:Px/Dx Pa/DaFrom which we get:Px (DxPa)/ DaWhere: Px is the controlled pressure value, Dx is the density at controlled pressure, Pa is the absolute atmospheric pressure, Da is the density at Pa.As a
38、 result of this formulation, we can foresee the working pressure without modifying the quantity of the chemical components to get the required density.The foam hardness can be calculated by applying the following formula:Hx (Px2/Pa2)HaWhere: Hx is the foam hardness at controlled pressure, Px is the
39、controlled pressure value, Ha is the density at Pa.For example: from a 22 kg/m3 foam density and 120 N hardness it is necessary to work at a 680 mbar to obtain a 15 kg/m3 density and 55,5 N hardness.Though these are formulas for gases, the data obtained for foams are most likely the calculated ones.
40、CONTINUOUS CONTROLLED PRESSURE PROCESS (CCPP)This plant is composed of an airtight tunnel (provided with front access and exit doors) duly dimensioned for reaching an inside pressure of max 1300 mbar and an inside vacuum of max 500 mbar.This tunnel is divided into two sections.The first section of t
41、he tunnel houses the continuous production line or so called “dry” equipment: the Trough (2), the Fallplate (6), the production conveyors (9/1), the Unwind and Rewind systems and the Cut Off Machine (8). Afterwards there is a free roller conveyor (10) and a transferring conveyor (9/2) at which end t
42、here is the intermediate airlock door (3/1).The second section of the tunnel houses a conveyor (9/3) discharging the foam block through the airlock exit door (3/2) to the block curing system at atmospheric pressure. The colour red highlights the foam block making, whereas the yellow highlights the p
43、ressure is at the desired operating value.All metering lines are manufactured with high pressure metering pumps and are located outside the tunnel.The metering of each line is controlled by a pertinent mass flow meter which, through a closed loop system, changes automatically the pumps speed to keep
44、 constant their outputs at the desired value.In plants like our Maxfoam (similar to Foamax), the mixing head is fitted outside the tunnel under CP. The connection between the mixing head and the bottom of the trough which is housed in the tunnel is by high pressure hoses.The vacuum and/or pressure v
45、alues inside each of the sections of the tunnel are set and controlled by suitable independent systems (4/1 and 4/2).A sophisticated electronic control system holds the desired pressure value accurate by balancing the vacuum/pressure pumps speed.During phase 1, the following operations occur: 1. Int
46、ermediate air lock door opens (3/1)2. Airlock exit door closes (3/2)3. Only when the pressure inside the first tunnel is at the desired value (marked in yellow), the block foam production (marked in red) startsIn phase 2, the foam block goes toward the transferring conveyor (9/2); when the foam block has reached the desired length, the block is cut off (8) and then accelerated into the transferring and discharge area (second tunnel). The running speeds of both conveyors (foam block production and transferring conveyor) are synchronised (9/1+9/2).In phase 3, as soon as t