中国中部大型混凝土预制管片生产企业.doc

中国中部大型混凝土预制管片生产企业A Big Work-shop for the Production of Concrete Prefabricated Segmentsin the Heart of China 1997年6月3日，世界银行指导委员会正式批准向中国最大的水利工程之一黄河万家寨引水工程贷款4亿美元。 万家寨引水工程位于山西省，是将黄河水从万家寨引入太原和大同。这一地区的人口约600万。工程总投资约120亿元人民币(约合14亿美元). 这个项目包括建设万家寨至平鲁的主线，平鲁至太原的南线，平鲁至大同的北线和其它支线.修建的水渠、隧洞和水管桥总长约450公里。 山西是中国最重要的煤炭生产基地，也是世界上最大的煤矿区之一。山西还是中国最干旱地区之一。 为了促进整个地区的工业发展，解决人畜用水和灌溉土地，因此万家寨工程是重中之重。尽管当地政府开展了植树造林运动努力阻止沙漠化的扩大，但该地区仍然几乎不长草木。 早在50年代初就提出了这个项目,但是直到1993年才经全国人大批准。由于该项目投资大，又缺少设备和技术,因此项目进展缓慢。 1993年在得到意大利财团3千万美元的贷款后工程开工。当时意大利拉韦纳的CMC公司和罗马的SELI公司开始对主线6号、7号和8号隧洞进行施工。隧洞直径为5.46米。 这三个隧洞均采用隧道掘进机掘进,用25厘米厚的六边形混凝土预制管片衬砌，于1998年完工。 世界银行随后提供的贷款加快了这项工程进度。最近山西黄河引水项目公司对标1、标2和标3发标，这项工作正在进行。 标2和标3已与万龙联营体签订合同。该联营体是由意大利Impregilo公司(48%), 意大利拉韦纳的CMC公司(42%)和中国第四水电工程局（10%）组建的。标2和标3包括南线的4个隧洞，地下工程总长90多公里。 隧洞掘进采用4台全断面隧道掘进机（三台ROBINS和一台NFM），衬砌采用六边形混凝土预制管片，内径为4.2米和4.3米。厚22厘米和25厘米，用环形密封密接。 意大利Novate Milanse 的CIFA 公司制造混凝土衬砌预制件的成套设备。这家公司专门设计和制造混凝土设备和机械,已有70多年的钢模技术。 四台隧道掘进机同时施工需要四套预制衬砌管片的设备。每套设备的生产能力为每24小时工作日生产90个六边形衬砌管片。 一套设备在店湾,照搬CMC-SECI财团的设计和新提供的钢模。另三套设备在温岭，置于同一间厂房内，靠近隧洞口。 每个六边形管片长1.4米,平均周边90度,构成一个预制衬砌环的四分之一.因此,每套设备每天衬砌管片产量为30米以上,这样,四套设备每天衬砌管片总产量为120米以上。 预制管片成套设备呈旋转木马型，钢模架在上面，在轨道上滑行。生产周期的每一道工序(装配、放置钢筋条，浇注混凝土，强化凝结，拆模和清洗钢模)在相同的工作台上进行，且不时地移动所有的钢模。 每套设备的生产线上有10个工作台。在强化混凝土凝结的加热间内有二条平行生产线，共22个钢模。 采用液压推进机移动生产线上的钢模。生产线间用起重车移动钢模，也采用液压驱动。 设备的所有操作和驱动由PLC程序和控制台控制。各个工作台的所有操作一完成，PLC程序和控制台就能操纵钢模的移动，生产线上的所有钢模都移动至下一个工作台。接着，程序控制将生产线上所有的钢模放入凝结线。同时准备对带有衬砌管片的钢模拆模。 每套设备的工作周期，即生产线上所有工序和移动钢模所花费的时间大约是15分钟。 采用液压开启的加料斗和移动系统将混凝土放入混凝土存储罐。混凝土存储罐位于钢模的正上方。一条混凝土传送带将混凝土从混凝土搅拌站输送到存储罐。用装有多频电子振捣器的移动式工作平台将振动传递给钢模。这个移动工作台在整个放置过程中借助气垫和液压抓手装置将钢模从轨道上移开。气垫还阻止振动传向地面。 几乎所有的预制设备需采用强化凝结以缩短放置和拆模之间的时间和限制所用钢模的数量和所占场地的大小。 强化凝结的目的是为了尽可能快地达到拆模和提起衬砌管片所需的混凝土最低强度。工艺要求混凝土温度升高约60C,升温梯度低于15-20C/h,在预凝结期保温，并以同样的梯度降温，整个过程大约需要5小时。 加热凝结室要避免用新鲜蒸气直接处理，因为车间温度很低（冬天气温可能低于零下20C），水马上就会结冰。我们用细管传热，通入少量的新鲜蒸气保持必需的湿度以加速衬砌管片的凝结。 由于室外温度低，衬砌管片拆模后在工厂放置约24小时。 采用旋转木马型而不是固定式的设备具有很多操作上的优点，包括优化使用的场地、专用设备（起重机，混凝土搅拌设备等)、原材料采购(钢筋件，置于衬砌管片中的各种衬料）和劳动力。 特别是，虽然所用的当地劳动力在生产成本中所占的比例可以不予考虑，但是，采用旋转木马型设备可将工时降至最少。 这种生产流程类似于一条装配线,允许细分和计划各道工序，在独立的工作台完成这些工序。这样消除了固定式预制件设备可能发生的问题。采用固定式预制件设备，在整个生产过程中，所有的工作台都要消耗固定的原材料和使用一定的劳动力。 旋转木马型设备允许减少所用钢模的数量，较好地计划强化凝结，因此采用这种设备，产品质量较好，产量稳定，不浪费生产率。 4套预制管片设备共配备了128个钢模。每套设备配备32个钢模，一套设备的钢模直径为4.2米，厚22厘米，二套设备的钢模直径为4.2米，厚25厘米，还有一套设备的钢模直径为4.3 米，厚22厘米。 钢模的设计和制造要达到隧道衬砌预制管片很小的尺寸公差，特别是周边表面。对于密封，周边表面要有很高的精度，在装配时，要与邻接的衬砌管片完全拼接。其目标是确保最终在隧道衬砌时做到紧密的水封和结构密封。 除了精确的模板结构外，制造这种类型钢模的每道工序都需要特殊加工，例如，使边标准化的热处理，对边、端和底面进行的机加工，部件与模板的装配。这样，衬砌管片宽度和长度的尺寸公差约1毫米,周边连接处等高线为十分之二。 特别要注意钢模结构的尺寸；每个钢模将反复使用1500次。为了确保在整个使用期间保持钢模的尺寸特性,需要制造特别坚固的钢模结构。 另外，为避免液体混凝土的泄漏和保证生产的衬砌管片具有完全的特性再现性，钢模的边、端和底面之间的连接精确是非常重要的。 为了缩短准备和拆模时间，设计的钢模只有很少几个快速开/关装置。该装置采用气压螺栓启动的圆锥形联结器结构。 这些成套设备所配备的钢模的最重要之处是，钢模基本上是在中国制造。一个钢模制造厂在河南洛阳，另一个在内蒙古包头。 这样做是出于减少制造成本，减少运输时间和费用。这意味着CIFA设计的钢模必须适于中国能够提供的原材料，并符合中国工厂的生产特点。在制造的所有阶段还要进行监理和提供帮助。 CIFA已经将中国工厂生产的钢结构用于中国其它大的工程，例如用于小浪底大坝大型隧洞的钢模(钢结构约3300吨重，用于建造30个不同的结构)和三峡大坝生产能力为每小时360立方米混凝土搅拌站(钢结构约500吨). 不过，对于万家寨工程项目，所选择的隧道衬砌管片钢模的中国生产厂家不仅要能够生产出高质量的钢结构，还要具备在要求的时间内完成精密机加工的技术实力。 完全排除采用数控切削机加工钢模的周边，因为中国新近才引进这些设备，难以达到需求的产量。因此采用铣削加工边。这些铣床一般是80年代意大利制造的设备，目前已全部被计算机控制的数控设备取代。不过，这些设备仍能够到达标准公差尺寸，满足生产的时间要求，尽管与混凝土接触的较粗糙的表面费事，还需要在设计上作某些调整以改造这种设备有限的操作性能。 不过，要用数控机床加工钢模的端，因为六边形钢模所具有的特殊尖顶形状，变换加工形式就生产不出合乎质量要求的产品。 中国提供的钢铁材料一般比欧洲的差，也需要进行一些结构调整。例如增加与混凝土接触的表面厚度。 钢模连接的机械部件，由于磨损和尺寸的原因，需要用很坚固的材料制造。鉴于难以在中国得到这些特种钢，这些部件在意大利制造。 由于与CIFA长期的合作，CIFA提供了预制件成套设备和钢模的技术及经验。IMPREGILO在中国已有很长时间，包括修建二滩和小浪底大坝，容易克服与中国生产厂家在工作方面的交流和交往的困难，在中国的中部建立了一个最大的预制管片生产企业。BACK HOME On 3rd June 1997, the Steering committee of the World Bank officially approved a 400 million dollar loan for the construction of one of the largest hydraulic projects in the whole of China: the Wanjiazhai Yellow River Diversion Project. The project, which has a total value of some 12,000 million yuan (approx. 1400 million dollars), is situated in Shanxi province, and is designed to divert the Yellow River from Wanjiazhai to the cities of Taiyuan and Datong, which have around 6 million inhabitants between them. The project comprises the construction of a main line running between Wanjiazhai and Pinglu, a southern line between Pinglu and Taiyuan, a northern line between Pinglu and Datong and other secondary lines, making a total of some 450 km of canals, tunnels and aqueducts. Shanxi, the most important coal-producing and mining region in China and one of the biggest coal-mining regions in the world, is also one of the most parched regions of China. The Wanjiazhai project is therefore considered a top priority in order to supply water for the industrial development of the entire region, for civil use and for irrigation of the soil, which produces little vegetation, despite planting campaigns undertaken by the local authorities in a continual effort to hold back the advance of the desert. The project, originally devised in the early Fifties, was not approved by the Council of State until 1993, and its progress was further slowed by the high overall cost and the lack of local equipment and technology. Work began in 1993 with the aid of a $30 million loan from Italian consortium, when CMC of Ravenna and SELI of Rome started work on tunnels 6,7 and 8 of the main line, with a diameter of 5.46 metres. The tunnels, excavated with TBMs and lined with 25 cm thick hexagonal prefabricated concrete linings, were completed in 1998. The loan subsequently offered by the World bank finally speeded up the work, and the Shanxi Yellow River Diversion Project Corporation recently awarded the tenders for lots 1,2 and 3, which are currently under way. Lots 2 and 3 have been contracted out to the Wan Long Joint Venture, set up by Italian companies Impregilo(48%) and CMC of Ravenna(42%) and the China Water Conservancy and Hydropower Engineering Bureau no. 4(10%); they involve the construction of four tunnels constituting part of the southern line of the project, with a total length of over 90km. running underground. The tunnels are made with four TBMs (three ROBINS and an NFM) of the full-face type with metal shield, which position a final lining consisting of prefabricated hexagonal lining sections with an inner diameter of 4.20 m and 4.30 m and thickness of 22 cm and 25 cm, fitted with perimeter seals. The concrete lining prefabrication plants were constructed by CIFA S . p. A. of Novate Milanese, Italy, a company which specializes in the design and manufacture of concrete plant and machinery, and has over 70 years experience of steel form technology. Four TBMs operating simultaneously required the construction of four manufacturing plants to make prefabricated lining sections; each of these plants has an average output potential of approx. 90 hexagonal lining sections in a 24-hour working day.One of these plants, located in Dianwan, is working on the same layout as used by the CMC-SELI consortium with newly-supplied steel forms. The other three plants are located in a single building at Wenling, near one of the tunnel openings. Each hexagonal segment is 1.4 metres long, with an average circumference of 90o, and constitutes a quarter of a prefabricated lining ring. Each manufacturing plant therefore allows the daily production of over 30 m of tunnel lining, which corresponds to over 120 m of lining a day for all four plants. The prefabrication plants are of carousel type. in which the steel forms are trailer-mounted and slide on rails. Each operation in the production cycle (setting up, placing of reinforced rods, concrete casting, forced curing, dismantling and cleaning of the steel form) is performed at the same workstation, to which all moving forms are conveyed at intervals. Each plant consists of 10 workstations along the production line, and 22 steel forms in two parallel lines contained in heated chambers for forced curing of concrete. The forms are moved along the lines by hydraulically operated pushers, and between the lines by traversing trucks, also with hydraulic drive. All operations and drives of the plant are controlled by PLC program and control board, from which the movement of the forms can be controlled as soon as all operations at the various workstations have been performed. All forms are moved simultaneously along the production line to the next station. In sequence, the program controls the insertion of the last form on the production line into the curing lines, and the simultaneous output of a form containing a lining section ready for dismantling. The cycle time of each plant, ie. the time taken to perform all operations on the production line and traverse the forms, is approx. 15 minutes. The concrete is placed at the concrete placing station on the production line through a hopper with a hydraulic opening and traversing system which is positioned directly above the form and fed by a concrete belt connected to the mixer of the concrete-mixing plant. The vibration is transmitted to the form by a mobile platform fitted with multi-frequency electric vibrators which can lift the form off the tracks throughout the placement stage by means of air cushions and hydraulic grippers. The air cushions also prevent dispersion of the vibrations into the ground. As in nearly all prefabrication plants, forced curing is needed to shorten the time between placement and dismantling, and therefore to limit the number of forms used and the size of the prefabrication area. The purpose of forced curing is to reach the minimum concrete strength required for dismantling and lifting of the lining sections as quickly as possible; it basically involves raising the temperature of the concrete to approx. 60oC with gradients not exceeding 15-20oC/hour, maintaining that temperature for a pre-set period, and cooling with an equal gradient. The whole process takes a total of approx. 5 hours. To heat the curing chambers, direct treatment with live steam was avoided because of the very cold environmental temperatures on site (which can fall below -20oC in winter) which would immediately cause the discharge water to freeze. Instead, we used heat transmission through finned pipes, still accompanied by a small input of live steam to maintain the essential moisture level required for accelerated curing of the lining sections. Also because of the cold external temperatures, the lining sections are kept inside the factory for approx. 24 hours after dismantling. The use of carousel rather than stationary plants involves a number of operational advantages, including optimisation of the areas used, the dedicated equipment (cranes, concrete-mixing plant, etc.), material procurement(reinforcing cages, various inserts to be positioned in lining sections) and labour. In particular, although the percentage of local labour used does not account for a significant proportion of the production costs, the use of a carousel plant minimises down time. The production process, similar to an assembly line, allows subdivision and planning of the individual operations, which are physically performed at separate workstations. This eliminates the interference which can take place with the stationary type of prefabrication plant, where the input of materials and labour throughout the production sequence must necessarily take place at all workstations, which are fixed. Carousel plants also allow a reduction in the number of forms used, better planning of forced curing, and therefore a more easily quantifiable, constant output, without any loss of productivity. A total of 128 forms were made for the four prefabrication plants: one plant with 32 forms with a diameter of 4.20 and a thickness of 22 cm, two plants with 32 forms with diameter of 4.20 and a thickness of 25 cm, and one plant with 32 forms with a diameter of 4.30 and a thickness of 22 cm. The forms are designed and manufactured to comply with the very small dimensional tolerances required for prefabricated tunnel lining sections, especially on the perimeter surfaces, which require high precision for the seal seatings and a perfect fit with the adjacent sections at the time of installation, the overall aim being to ensure the perfect hydraulic and structural seal of the final tunnel lining. In addition to precise template construction, the forms therefore required all the manufacturing processes specific to this type of product, such as heat treatment to standardise the sides, machining of sides, ends and bases, and assembly of the components with templates, the aim being to achieve dimensional tolerances of around 1 millimetre on the width and length of the lining section, and 2/10ths on the contour of the perimeter joints. Special attention was given to dimensioning the form structures; particularly strong structures were made in order to ensure that the dimensional characteristics would be maintained throughout the duration of the job, despite the 1500 re-uses to which each form will be subject. In addition, the precision of the joints between the sides, ends and base of the forms is very important to avoid leakage of liquid concrete and guarantee perfect replicability of the characteristics of the lining sections produced. To minimise setting up and dismantling times, the forms were designed with a small number of fast opening/closing mechanisms equipped with conical spigots activated by pneumatic screwers. But perhaps the most significant aspect of the forms installed in these plants is that they were largely manufactured in China, at two different factories, one at Luoyang in Henan province, and the other at Bautou in Inner Mongolia. This decision, dictated by the need to reduce manufacturing costs and transport times and costs, naturally meant that CIFA had to design forms suited to the materials available in China and the production characteristics of Chinese factories, and provide continuous supervision and assistance at all stages of manufacture. CIFA had already used Chinese factories to make the steelwork used on other major Chinese jobs, such as the steel forms used for the great tunnels of the Xiaolangdi dam (approx. 3300 tones of steelwork for the construction of 30 different structures) and the 360 cu.m/hr concrete-mixing tower for the Three Gorges dam (appox. 500 tones of steelwork). For the Wanjiazhai project, however, the construction of forms for tunnel lining sections required a selection of Chinese factories not only able to produce high-quality steelwork, but also equipped with the technological potential needed to perform precision machining in the required times. The use of numerical-control cutters to machine the circular sides of the forms was immediately ruled out, as these machines were only introduced into China relatively recently, and it would have been difficult to obtain much output from those available.