In the last couple of decades, various types of plastic products have been actively replacing metal products from the market. But due to their durability, excellent hydraulic properties and anti-corrosion resistance, cast-iron lines continue to be widely used for laying strategic underground utilities. They well withstand the load on the sewer networks in places where drain mechanisms are most actively used. In addition, cast-iron sewer pipes have a much longer service life than plastic ones.
Cast iron pipes for sewer installation
In the process of construction of any structure, it is imperative to carry out a set of works on laying main underground communications. Among the systems that are part of them is sewerage. It is the better and more durable, the better the semi-finished products used during installation. Access to the underground part of communication facilities is often difficult. Therefore, they should be made of durable and resistant material.
The most suitable material for the installation of underground sewerage is cast iron. It is perfect for sewer drains of enterprises whose activities are due to large hydraulic loads:
- meat processing plants, dairies and poultry farms;
- catering shops;
- farms and slaughterhouses;
- healthcare institutions.
Cast iron, an iron-based alloy with a high (above 2%) carbon content, is smelted using various technologies. Four types of finished metal are used for drawing:
- Grey. It contains lamellar graphite.
- White. Carbon in the crystal lattice of the cooled metal is in a bound state.
- High strength. Contains graphite in the form of microscopic spherical molecules.
- Malleable. This grade is most often subjected to redistribution, so graphite has the appearance of easily destroyed flakes.
The least popular are products with the Cheka marking, made of nodular graphite. The technique involves mandatory passivation with cement to form a thin silicone film. Products are used for sewerage in places where aggressive fecal liquids are discharged. Their cost is very high, and the level of demand, on the contrary, is extremely low.
The quality of pipe manufacturing is ensured subject to the requirements for the pouring process. It is done in three ways:
- semi-continuous. It consists in the gradual pouring of molten iron into the mold and its gradual solidification. Next, the not completely frozen metal is drawn into pipes and cut to size.
- Centrifugal. Liquid iron is poured into rotating molds. After pouring, the cast iron cools down completely. To avoid the appearance of layers and surface defects, the maximum deviation of the wall thickness should not exceed 2 mm. One of the varieties of this method is the modern method called De Lavo casting.
- Casting in a mold. For smelting pig iron, a specially made form of sand (chill mold) is used. Sand, clay, sodium silicate and other substances are used to bind sand.
To counteract corrosion, the pipes are coated with a special compound.
Cast iron product range
For the manufacture of products of various diameters used for the installation of main sewers, gray cast iron is the most suitable in terms of composition and properties. The requirements of GOST 6942-98 establish three types of nominal passages. This is how the table looks like, according to which it is possible to determine the diameters of sewer pipes of various lengths:
GOST tables allow you to determine only the approximate weight of the pipes. The actual dimensions of cast-iron main sewer pipes can vary by up to 5% in one direction or another.
Depending on the installation method (channel and non-channel laying by flange or socket method), products can be manufactured and supplied to customers with or without sockets, as well as longer lengths than established by the requirements of GOST.
Pressure sewer lines are made of cast iron castings with an internal diameter of 65 to 1000 mm, with a wall thickness of 6.7 to 22.5 mm. They are much stronger than those used in the upper communication block and can withstand internal pressure up to 1.0 kgf / cm2. When operating such products, there is one prerequisite: cast iron products cannot be subjected to shock loads due to the brittleness of the metal associated with a high carbon content in the chemical composition. Another disadvantage of cast iron products is their large mass. This can cause some difficulties in the process of installing trunk communications.
The most popular are main pipes 3 m long and socket pipes — for sewer outlet branches and supply lines to buildings and structures:
for a unit,
|SML 100||socketless||3000||3 840|
|SML 150||socketless||3000||6 867|
|50 GOST 6942-98||bell-shaped||2000||1499|
|100 GOST 6942-98||bell-shaped||2000-2100||2387|
|100 GOST 6942-98||bell-shaped||2000||4 369|
According to the type of socket connections, products are divided into three classes — A, B, and LA.
Marking on sewer pipes made of cast iron ChK or VChShG is applied to their fittings. Indelible paint is used for application. The place of marking is the end or reverse side of the socket. After reading the imprint, the buyer can find out the following information about the product:
- manufacturer’s trademark;
- designation characterizing the product;
- manufacturing standard.
Packing of pipes from which the main sewage system is mounted is carried out in three ways:
Cast iron products, with all the mass of advantages, have one significant drawback. The metal is not bendable, so the installation of transitions and turns of highways requires the use of various additional elements. They are called fittings. Finished products manufactured using modern technologies have improved mechanical properties. In particular, to increase the ability to bend, modifier substances are introduced into the composition of cast iron during crystallization.
Separately, on pallets with boxes or in containers, fittings for sewer installation are laid:
Another element, called revision, is used to clean clogged parts of highways.
Plastic, with all its undoubted advantages and low price, is not able to withstand such gigantic loads. Therefore, it is not used for the installation of pressure sewers. Due to the thick walls, cast iron products have minimal noise characteristics. The average service life of cast iron main sewer pipes is more than half a century. If the operating conditions are observed and timely preventive maintenance is carried out, it is possible to increase the maximum service life of main communications up to 80-100 years.
This is facilitated by the high performance of cast iron products:
- resistance to the formation of a corrosion film on the surface;
- high rate of resistance to linear stretching;
- excellent sound-absorbing properties;
- immunity to sharp fluctuations in ambient temperature;
- small coefficient of thermal expansion.
In addition to the above properties, finished cast iron castings are free of seams, cracks and crevices. This causes an extremely high resistance of products for the installation of sewers to physical wear. Therefore, in the near future, a massive transition is hardly expected during the installation of sewage from a cast-iron pipe to a plastic one.