Metal comes from mined ore. When metal ore is brought to the process plant, the ore may contain considerable quantities of dust known as fines which may create problems as well as easily become lost in handling.
The fines can be recovered to increase productivity, yet the abrasive nature of the dust will increase the potential for wear and lubrication problems if not properly handled. There are processing operations used to recover the fines and utilize other metal wastes. The following materials present a problem with lubricated equipment:
- flew dust from blast furnaces
- exhaust dust from the sintering process
- mill scales from rolling operations
- limestone dust
- carbon coke dust
- powdered coal
Aside from contamination from dust and fines, water and process chemicals can contaminate lubricating oils. The increase load demand as well as the extreme temperatures will lead to the premature breakdown of the lubricating oil if not properly attended to. Lubricating oils play an important role in the overall production of metal. Without lubrication, the machinery would not function.
In the steel industry, oils are used for a wide variety of purposes were operating conditions do not dictate the use of a grease.The most significant use of oil in a steel plant would be in the primary and secondary forming process in the rolling mills. The following common oils used include circulating oils, extreme pressure (EP) oils, rust and oxidation inhibited (R&O) oils, rolling mill oils, and hydraulic fluids.
Circulating oils are oils that are distributed throughout an assets componentry and include gasoline engine oil, turbine oil, automatic transmission fluid, process circulating oils, and diesel engine oils. These are oils used for the lubrication of plain bearings, slides, machine tool bearings, low and normal load enclosed closed gears, pistons and cylinders in the engine were common applications include diesel locomotives turbines and power transmission systems.
Extreme pressure (EP) oils are used in applications involving high pressure metal to metal contact. These lubricants are used in enclosed gearboxes. Applications include water pump gear drives, blast furnace and crane reduction drives, rolling mill screw downs, and sheer drives in rolling mill collar drives.
Rust and oxidation inhibited oils (R&O) are used in applications that require oil but do not require extreme pressure characteristics. They frequently are used in recirculation systems where typical applications include plain Babbitt bearings, coil bearings, rolling mills plane bearings, turbo blowers, air compressors, steam turbines, and backup roll bearings.
The roll mill oil is typically a low viscosity, oxidation and rust resistant oil made from a well refined base stock or a synthetic base oil designed for dual function of roll oil (directly applied to the metal for ease of processing) and as a lubricant for mill components. Different types of oils are used for different types of steels. Low viscosity mineral oils are used for heavy gauge metal, fatty polar types are used for stainless steel, and paraffinic oils are used for carbon and silicon steels.
Oil analysis for these applications can be used to identify dangerous contaminates such as particulates from dust and fines. Particle size analysis (ISO 4404) as well as Particle Quantification Indexing (PQI) can be used in conjunction with elemental analysis (ICP) to determine the source of particulates. Karl Fischer (KF) for moisture analysis as well as Infrared Spectroscopy (FTIR) can be used to help identify liquid contaminates.
Hydraulic fluids are used considerably throughout the plant. These fluids are either oil based (synthetic, mineral, or a blend), inverted emulsions, phosphate ester fluids, water glycol fluids, and R&O hydraulic oil. Some of these oils may be formulated with heavy duty anti-wear additives. Oil based hydraulic fluid is typically used in rolling stock with a typical flashpoint between 145°C to 315°C (300°F and 600°F). These flash points may not be a fire hazard for heavy equipment use yet because they are used under high heat and pressure situations if they leak through hoses or seals they may create a mist or spray which would be a fire hazard. The oil based anti-wear hydraulic fluids are used in precision stationary hydraulic units where there is a negligible fire hazard.
Other hydraulic fluids used for their fire-resistant properties in high heat environments or where there is the possibility of an open flame source or ignition include inverted emulsions, water glycol fluids, and phosphate esters.
Inverted emulsions are finely divided droplets of water which are dispersed throughout a continuous outer phase of oil. They are used for fluid power systems that are subject to fire hazards and suitable for hydraulic pump pressures limited to vane pumps up to 2,000 psi, gear pumps <2,800 psi, and piston pumps <3,500 psi system pressures that are prone to shock loads or high shear stresses. Normal operating temperature ranges from 48°C - 55°C (120°F - 130°F). Operating temperatures above 150°F (65.5°C) can cause water evaporation from the solution, which increases the viscosity and decreases the fire resistance of the fluid. These fluids are least expensive fire-resistant hydraulic fluids. The inverted emulsion fluids are used in coke battery pushers, hot strip mill coil conveyors, and the primary and secondary mill roll balance systems.
Water glycol fluids are also used in areas subject to fire hazards with normal operating temperatures of 48°C to 55°C (120°F-130°F). Operating temperatures above 150°F (65.5°C) can cause water evaporation which increases the viscosity and decreases the fire resistance of the fluid. To ensure proper water content and corrosion protection, the fluid must be monitored on a regular basis in close tolerance systems using a hydrometer or density meter and refractive index to ensure the water glycol ratio is correct. These fluids are not suitable for power systems operating above 2000 psi. The typical uses are in the open-hearth dolomite machine, electric arc furnace, tilting mechanisms, electrode systems, continuous caster pinch roll, and cut off torch systems.
Phosphate ester fluids are used in hydraulic systems that are subject to high degree of fire hazards. These fluids are suitable for high pressure operating systems operating at 5000 psi and high temperatures of 107°C (225°F). Phosphate ester fluids are the most expensive type of fire-resistant hydraulic fluid. A typical application would be the tractors used in the removal of pit slag and operational use would be the hydraulic systems scarfing machine, king pits, rotary furnaces, and regulators.
The oil based hydraulic fluids should be monitored for oxidation, acid formation as well as particle concentration, viscosity, and elemental analysis. The water-based fluids should be routinely monitored for particulates as well as water concentration, viscosity, and elemental analysis.
While the lubricants are in operation, basic properties in which a lubricant should adhere to would be to reduce oxidative degradation of lubricant, reduce deposition of harmful deposits, minimize rust and corrosion, control wear, reduce the tendency to foam or form stable foam over time.
ALS Tribology helps the steel industry by provide a comprehensive testing program for a wide range of assets. Various lubricants as well as fuel, coolants, and DEF are tested using the most up to date instrumentation and diagnosed by industry experts to provide the highest level of condition monitoring service.