HAMECO, established in 1958, is situated in Nguyen Trai Road, Thanh Xuan District, Hanoi City. The first objective in constructing this factory was to establish a modern mechanical plant as the flagship of the machine tool industry. At the time, the factory was the largest in Southeast Asia.

Company products include machines tool such as cutting, planing, and drilling equipment. Currently, HAMECO ranks first in manufacturing equipment for the sugar industry. The foundry, with a designed capacity of 8,000 tonnes of cast-iron and steel per year, is the most important part of the production process. Now, because of a slump in the manufacturing sector, foundry capacity has been reduced to 4,000 tonnes/year.

HAMECO operates two foundries:

Steel foundry

Steel scraps and ingots are melted in two electric-arc furnaces with capacities of 1.5 tonnes and 3 tonnes per batch, respectively. The molten steel is poured into ladles, which are then transported by crane to "green sand" moulds, where the molten metal is poured. Castings may be as large as 4,000 kilograms. Cooling time before removing the moulds is four days for large articles and one day for small ones. Mould removal employs vibrating grids, while casts are cleaned by hand.

Cast-iron foundry

The cast-iron is melted in 250-kilogram batches in induction-type furnaces. With castings weighing more than 250 kilograms, the iron is melted in an electric-arc furnace and transported by crane from the steel workshop. Both green sand and dry moulds are used. Moulds are shaken out and casts are cleaned by hand. The used sand is screened and reused.

All foundry processes – mould making, metal melting, mould removal, cast cleaning, mould drying, etc. – generate dust. Most of the equipment was provided by the former Soviet Union, and, after 40 years of use (1958-1998), much of it is in poor repair, especially the ventilation and exhaust systems. Obsolete technology together with ailing dust and fume control systems exacerbate any hazardous conditions.

Given the nature of foundry production, all processes are on line and unpartitioned one from the other (excluding a drum-shaped cleaning machine situated in a separate room), so dust spreads easily from one work area to another. Consequently all areas of the foundry, including the manager’s office, are polluted.

As seen in Table 7, all dust samples exceeded the standards by a minimum of 1.3 times (in the area near the steel-melting furnace) and by a maximum of 14.3 times (where cleaning casts with a pneumatic machine). The percentage of free silica fluctuated between 8 and 30 per cent, especially in the mould-removal and cast-cleaning areas, which were considered the most dangerous because of their high dust concentrations and close exposure.

According to statistical data for 1995-1998, foundry worker numbers tended to decrease, from 157 people in 1995 to 121 in 1998. (See Table 8.)

The data in Table 9 shows changes in the number of foundry workers with the same work history (in percentages).

The number of workers with a work history of fewer than 20 years tended to remain unchanged or increase slightly, but those with more than 20 years tended to decrease. The latter had retired or transferred to other work.

The number of female workers had changed very little, with 15 per cent in 1995 as opposed to 14.8 per cent in 1998. (See Table 8.) This was probably because most of them were working in the mould-making area, where work intensity was less and dust concentrations were low, so they were able to work more years than their male counterparts.

According to statistical data regarding worker health for 1995-1998, the percentage of those in "excellent" health was low (2-9 per cent), while those in the "normal" category was highest. This was a disadvantage for workers who enjoyed normal health and worked in hazardous environments, since the possibility of contracting silicosis was higher than it was among the workers in "good" health.

HAMECO conducts good health care and occupational disease examinations. Examination results for silicosis follow:

5. Some confirmed silicosis cases were transferred to other jobs, some to other enterprises or retired, and two cases died. The majority remained in the foundry.

Article 4: Coefficients for production units

The manager regularly audits the workplace to check whether workers are respecting regulations, and awards marks for each component of the point system. So the workers’ income depends on how well they respect regulations in the course of all work activities. This method contributes to raising worker awareness of OSH matters in general, and silicosis prevention in particular.

HAMECO organizes an annual training course for its own workers, aiming to raise awareness of OSH issues. However, there has never been a training course specializing in the topic of silica dust prevention. This has instead been incorporated into the course of OSH.

In order to increase product quality and market competitiveness, HAMECO has borrowed 160 billion VND from the Government, including 60 billion VND for new foundry technology, including measures to ameliorate areas and processes wherein workers are most exposed to silica dust:

• Mould-making. Furan (an organic by-product of oil refining) will be substituted for water and glass liquid, and a mix of Furan and diluted acid will be used to make moulds that are easily broken and which therefore emit less dust.
• Steel and cast-iron melting furnaces. Steel and cast iron will be melted in high-capacity, induction-type furnaces that emit less dust and fumes.
• Mould removal and cast cleaning. These processes will automated and contained in rooms with fume- and dust-control systems.

The project to improve the foundry technology began at the end of 1998 and is going to finish in 2000.

Technical processes at the Hanoi Mechanical Company and the Electrical Engineering Company are similar in many ways. We discuss only those features that are different, in the section below.

Only cast iron is produced with capacity of 1,200 tonnes a year. Cast iron is melted in cupolas. Other processes are similar to that of in HAMECO.

According to these measurements, dust pollution levels in this foundry are not high.

In the period 1995-1998, the number of workers remained relatively stable. Workers with 11-20 years of experience were in the majority with 64.7 per cent (1995), 72.2 per cent (1996), and 62.5 per cent (1997-1998). The percentage of female workers was relatively high: 29.4 per cent (1995), 35.18 per cent (1996), and 34.4 per cent (1997-1998). As in HAMECO, most female workers worked in the mould-making process, where working conditions were less harmful and the work was relatively light.

Workers’ health has worsened year by year.

2. The percentage of silicosis cases among female workers is low (tab.24)

Besides the classic methods applied in other enterprises, some improvements are evident in the foundry cleaning process:

• Cleaning of castings is restricted to an isolated room, far from the main production building.

• Sand and water shot-blasting is used to clean castings. This equipment is compact, easy to use, efficient, and inexpensive (about 20 million VND per unit).

Collection of gases is difficult and complicated, and the most costly part of the system is the cleaning device.

In order to trap fumes effectively, foundries have to install hoods both above the furnace and again in the upper zones under the roof. However, installing a hood directly above the furnace obstructs furnace operations. Thus, the hood is often installed only higher, under the roof. This option is not very effective. It requires much more exhaust air, for one thing, and wind blows the fumes away from the hood opening, further reducing its effectiveness.

Among other things, appropriate cleaning devices also have to be highly efficient at collecting gases and resistant to high temperatures. To meet these requirements, imported technology often uses a baghouse as a gas filter. Such filters, with an air-flow rate of 100,000 cubic metres per hour, were installed in Viet Thanh and VICASA steel mills at an investment of US$550,000 each. Not only are the capital investment costs beyond the means of many companies, operation costs (power consumption, maintenance, etc.) also present big problems.

The NILP suggests using scrubbers for collecting dust instead of baghouses. These devices have been applied at the Duyen Hai Mechanical Company (Hai Phong City) and the Hai Phong steel mill. Their effectiveness of trapping fumes at the hood is about 70 per cent, and their dust-cleaning efficiency is about 85 per cent. In combination with its high rate of discharge, this kind of system can maintain concentrations of dust at ground level within permissible limits. Total costs for such a fume- and dust-control system run about 600 million VND.

• For other dust sources such as material belt conveyers, stone-crushing machines, and grinding machines, the NILP proposes the popular cyclone with spiral vane guide dust-control method. This device has been used with success in many factories throughout the country. It collects soil, stone, and cement dust with an efficiency of 80 per cent. Among its advantages are simplicity of manufacture, low costs of capital investment and maintenance, moderate dust-trapping efficiency, and stability of operation. With an estimated cost of 200 million VND for a complete dust exhaust system of 30,000 cubic metres per hour, this is an appropriate means of control for most dusty processes.

• For dust sources where it is impossible to install exhaust ventilation system, various kinds of water suppression systems may be applied. The NILP has produced a good axial ventilator which can operate as mist equipment. This fan performs two functions: while it suppresses dust it also cools. The NILP has also studied a method that uses spray nozzles with good effect.

In conclusion, depending on specific conditions, various dust-control measures may be appropriate:

• dust collection and cleaning by scrubber;
• dust collection and cleaning by cyclone with spiral vane guide; or
• dust suppression by axial mist fans or spray nozzles.

Updated by PAP/SUT/TRS. Approved by BKL. Last updated on 21 November 2000