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2022

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Three major problems that may exist in low temperature and low pressure technology of domestic paperboard


最近,国内纸板行业正悄然流行“低温低压”技术,该技术的发展成熟将给国内纸板企业的生产力带来又一技术性革命。目前,国内部分纸板企业充当先锋勇于尝试,将“低温低压”技术率先应用在日常生产中。那么,究竟什么才是“低温低压”技术?另外,纸板生产中,配置多少蒸汽压力才算符合“低压”技术呢? 现状:国内低温低压技术应用情况并不乐观 曾有业内专家走访了国内数家运用“低温低压”技术较为成功的纸板企业,但明显发现“低温低压”技术实际运用情况并不乐观,如瓦线设计和实际生产情况均不乐观,致使产品质量也不稳定。此外,还发现当瓦线运行一段时间后,蒸汽压力又要恢复到以往的高压才能生产。 与欧美相比,我国低温低压技术上可能存在3大问题 该专家就低温低压技术,专门参观访问了欧洲发达国家多家纸板企业。通过交流和学习,基本了解了目前国外纸板企业所掌握的高新技术,与我国国内纸板企业所提出的“低温低压”概念,还是有偏差的,是值得商榷的。为此,笔者就以下几点心得与业内同仁分享: 控制各层纸和纸板的温度,控制低材质和高材质的温度 国内高速瓦线普遍采用“防弯翘系统”程序,通过检测和控制瓦线各关键点的纸板温度,确保纸板出驱动轮后的温度控制在合理的范围,致使纸板平整而不易变形。因此,我们需要控制各层纸和纸板的温度,控制低材质和高材质的温度。 在此提醒的是三层和五层纸板对热量的需求是不同的,如若采用统一的“低压”值生产纸板,那么瓦线供给的热量是无法满足纸板生产的热量需求 各部位的蒸汽压力并不是采用统一的“低压”值 笔者从国外提供的瓦线看其各部位配置的蒸汽压力情况,发现其蒸汽压力的分配也是有侧重点的。如一条幅宽2500mm,车速350m/min的瓦线,其蒸汽主管道蒸汽压力14kgf/cm².其压力分配大致如下:   (1)高定量纸板,双面机热板压力10-12 kgf/ cm².瓦楞棍压力8 kgf/cm².预热缸4-6 kgf/cm (2)低定量纸板,双面机热板压力6-8 kgf/ cm².瓦楞棍压力6 kgf/cm². 预热缸2-4 kgf/cm 从压力分配表中,我们可以看出,纸板定量不同,蒸汽供给压力量也是不同的。所以在瓦线生产过程中,各部位的蒸汽压力并不是采用统一的“低压”值。尤其是需要“高压”的瓦线部位,还是要采用“高压”生产,唯有如此才能确保瓦线的高效生产和纸板品质。 不能盲目跟学国外经验 从某种程度上看,对于300m/min车速的高速瓦线,如此蒸汽压力供给确实对我们来说算是一种“低压”了,但我们并不能盲目跟学。 笔者分析其主要原因如下:   <1>国外高速瓦线所配置的瓦辊和双面机热板,均是周边加热型的,相对于我们国内腔式加热容器,其热效能高,温度转换快,是我们无法效仿的。 <2>国外瓦线各加热容器为满足纸板加热温度,均实施了蒸汽压力自动调整。同时在关键部位加装了很多弧形加热器进行热量补偿,这是我们容易忽略的。 <3>国外纸板厂粘合剂工艺和使用的原料,也与我们有较大的差异。他们采用的是小麦淀粉,糊化温度一般控制在53摄氏度左右,而我们一般用的是玉米粉或木薯粉,糊化温度在56-60摄氏度之间。

国内纸板低温低压技术上可能存在的3大问题

Recently, the domestic paperboard industry is quietly popular "low temperature and low pressure" technology, the development of the technology will bring another technological revolution to the productivity of domestic paperboard enterprises. At present, some domestic paperboard enterprises act as pioneers and have the courage to try, and take the lead in applying "low temperature and low pressure" technology in daily production. So, what is the "low temperature and low pressure" technology? In addition, in the production of cardboard, how much steam pressure is configured to meet the "low pressure" technology?

Status: domestic low temperature and low pressure technology application is not optimistic

Some industry experts have visited several domestic cardboard enterprises that have successfully used "low temperature and low pressure" technology, but it is obvious that the actual application of "low temperature and low pressure" technology is not optimistic, such as tile line design and actual production situation are not optimistic, resulting in unstable product quality. In addition, it is also found that when the tile line runs for a period of time, the steam pressure has to return to the previous high pressure to produce.

Compared with Europe and the United States, China's low temperature and low pressure technology may have three major problems

The expert on low temperature and low pressure technology, specially visited the European developed countries a number of cardboard enterprises. Through the exchange and learning, the basic understanding of the current foreign cardboard enterprises to master the high-tech, and China's domestic cardboard enterprises put forward by the "low temperature and low pressure" concept, or a deviation, is debatable. To this end, the author on the following experience to share with colleagues in the industry:

Control the temperature of each layer of paper and cardboard, and control the temperature of low and high materials

Domestic high-speed tile line generally adopts the "anti-bending system" program, through the detection and control of the tile line of the key points of the cardboard temperature, to ensure that the cardboard out of the driving wheel after the temperature control in a reasonable range, so that the cardboard flat and not easy to deform. Therefore, we need to control the temperature of each layer of paper and cardboard, and control the temperature of low and high materials.

In this reminder is the three-layer and five-layer cardboard on the heat demand is different, if the use of a unified "low pressure" value of the production of cardboard, then the heat supply of the tile line is unable to meet the heat demand of cardboard production.

The steam pressure of each part is not a uniform "low pressure" value.

The author looks at the steam pressure of its various parts from the tile line provided by foreign countries, and finds that the distribution of its steam pressure is also focused. For example, if a tile line with a width of 2500mm and a speed of 350 m/min, the steam pressure of its main steam pipeline is 14kgf/cm. The pressure distribution is roughly as follows:
 


(1) high quantitative cardboard, double-sided machine hot plate pressure 10-12 kgf/ cm. Corrugated rod pressure 8 kgf/cm². Preheating cylinder 4-6 kgf/cm

(2) Low-weight cardboard, double-sided machine hot plate pressure 6-8 kgf/ cm. Corrugated rod pressure 6 kgf/cm². Preheating cylinder 2-4 kgf/cm

From the pressure distribution table, we can see that the amount of cardboard is different, and the amount of steam supply pressure is also different. Therefore, in the production process of the tile line, the steam pressure of each part is not a unified "low pressure" value. In particular, the need for "high pressure" tile line parts, or to use "high pressure" production, the only way to ensure the efficient production of tile line and cardboard quality.

Can not blindly learn from foreign experience

To some extent, for a high-speed tile line with a speed of 300 m/min, such steam pressure supply is indeed a "low pressure" for us, but we cannot blindly follow suit.

The author analyzes the main reasons as follows:

 

<1> the tile rollers and double-sided hot plates configured by foreign high-speed tile lines are of peripheral heating type. compared with our domestic cavity heating containers, they have high thermal efficiency and fast temperature conversion, which we cannot imitate.

In order to meet the heating temperature of cardboard, all heating containers of foreign tile line have implemented automatic steam pressure adjustment. At the same time, many arc heaters are installed in key parts for heat compensation, which is easy to ignore.

<3> The adhesive process and raw materials used in foreign cardboard mills are also quite different from ours. They use wheat starch, and the gelatinization temperature is generally controlled at about 53 degrees Celsius, while we generally use corn flour or tapioca flour, and the gelatinization temperature is between 56-60 degrees Celsius.

Keywords: printing machine