|
|
|
|
|
|
THE FIRST VIETNAMESE NON-ASBESTOS PRODUCTION LINE - A CASE STUDY
|
|
Based on the machine and equipment research and development for the non-asbestos technology at RITM, in 2007 the first production line for PVA cement corrugated sheets was set up in the Northern part of Vietnam. All the Hatschek machine and equipment implemented have been fabricated by RITM. For the first step, the factory aims to a capacity of 2 millions square meters of corrugated sheets per year.
The PVA cement production line of TTC contains two main units, namely the Hatschek machine and the set of equipment for raw materials treatment. The set of the raw material treatment is totally new, and it is not necessary for asbestos cement technology. As seen from the Figure 8, this set of equipment for the raw material treatment has been designed in a compacted way, and it does not require much space. The size of the non-asbestos production line at TTC, thus is not much larger than that of the asbestos one. In addition, this raw material treatment unit has been positioned just at the beginning of the Hatschek machine, and thus minimizes the pipeline and energy necessary for transporting the treated materials to the Hatschek machine.
In addition to the above-mentioned two main units of the PVA production line, some equipment for product forming and de-moulding is also necessary for producing high quality PVA cement sheets. The equipment should be highly automated to prevent crack and defect formation during the forming and de-moulding process. The equipment for product forming at TTC company is positioned just at the end of the production
line. The equipment designed and fabricated by RITM is fully automatic. In the latest version, the forming machine designed and fabricated by RITM has a cycle time of 15 seconds.
After 3 years from the date of installation, all the machine and equipment at the TTC company are working well, and no major repair has been required. The machine and equipment are maintained monthly, mainly cleaning and lubrication. The simple operation of the machine and equipment and environment oriented
design of the factory, where natural light has been used as mush as possible, ensure the effectiveness and efficiency of the production line.
PVA technology. Various types of fibers, including the natural fibers and Kraft pulp can be used as substitution for asbestos (Savastano Jr et al., 2000; Savastano Jr et al., 2003). However, since the question of durability of natural fibers in the high alkali environment of cement matrix is remaining, the PVA is the most favourable for this
purpose. In this regards, we select PVA fibers as asbestos replacement at the TTC company.
In our research, PVA fibers with commercial name Kuralon, made by Kuraray of Japan are employed. Kraft paper, silica fume and bentonite have been used as additional raw materials for the non-asbestos Hatschek process. Typical raw material dosages for PVA cement sheets are as follows: PVA fibers 2%, Kraft pulp 4%,
Silica fume 5%, Bentonite 4%. The remaining is ordinary Portland cement. A small amount of flocculant, pre-mixed with water is added to improve the process, including the retention, dewatering and formation.
However, care should be taken in choosing a suitable flocculant and the way in that this type of chemical is applied since bad flocculant and wrong way of using it results in decreased strength of the final products (Negro et al., 2005; Negro et al, 2006).
It is necessary to mention that many problems, including low cement yield, fiber balling, delamination, cracks, low bending strength have occurred at the beginning of our work. Among that crack formation on the products such as that shown in Figure 3 is the most common problem. The problem is the most difficult to solve in the non-asbestos technology.
Thanks to the team of Japanese and Vietnamese engineers, all the problems of PVA cement sheets at TTC were solved in time. To reduce the defects and to use the metal moulds in an efficient way, a steam curing system based on Japanese know-how has been developed at TTC company. The system allows the products
attaining the strength necessary for de-moulding after 8 hours from the time of moulding. Thus, the metal moulds can be reused in very short time, which helps the production line to be more economical.
Product properties:
Various tests, including the bending strength, specific gravity, water absorption, breaking load of full-size products have been performed. The test has been performed in accordance with JIS A 5430:2004, in which the bending test specimens have been kept in the well-vantilated room for at least 5 days after curing before testing (air dried condition). The bending strength samples with size of 180mm x 50mm x 6.3mm have been
cut out from the real corrugated sheets and tested in bending using three-point bending scheme.
The testing data are transferred to a computer
and the stress-deflection curves of the test are drawn.
The bending strength of all tested specimens exceeds 22 N/mm2, which is over the
requirement of the Japanese Industrial Standard, JIS A 5430:2004. With the large deflections, the curves show the high ductility of the composite as evidenced by the large area below the curves.
The corrugated PVA cement sheets with dimensions in accordance with Japanese and Vietnamese standards were tested to determine the breaking load and water absorption. The test was done in accordance to the Korean Industrial Standard, KS L 5114: 2003. As seen from the figure, the breaking load exceeds the load
required by the Korean and Japanese standards, which is more than 3,920 N. The water absorption, which obtained in the test is 26.9%, also meets the requirement of the standards (less than 29%). In consequence, this shows that the PVA corrugated cement sheets produced by RITM Hatschek machine and equipment
have good performance, and satisfy strict requirements of Japan and Korea market. In practice, the PVA corrugated cement sheets of TTC have been exported to the Korean market.
CONCLUSIONS
The paper presented a sheet production machine and accessory equipment for the production of nonasbestos cement products by using the principle of the Hatschek process which was originally developed for asbestos cement. Some features of the non-asbestos technology were also addressed. The first Vietnamese
PVA cement sheet factory using the modified Hatschek machine and equipment mainly designed and fabricated by RITM based on the Japanese know-how, was built at TTC, a joint Stock Company in Vietnam in 2007. The main conclusions of the paper can be summarized as follows:
The non-asbestos fiber cement technology is very different from the asbestos cement technology.
Although the modified Hatschek machine used in the non-asbestos technology looks very similar to
that used in the asbestos cement technology, many characteristics are different. Thus, a Hatschek machine used in the asbestos production line requires the necessary modifications before using in the non-asbestos products.
(Extract from DO QUOC QUANG and NGUYEN DINH KIEN - RITM - Report)
|
|
|
|
|
|
|
|
