On the basis of application of electrochemical machining method in various industries for many years using SFE electrochemical machines, Limited Liability Company Manufacturing and Commercial Enterprise STANKOFINEXPO specialists recommend to use 12% water solution of industrial sodium nitrate (NaNO3) (ammonium nitrate) GOST 828-77 with 120g/l concentration as electrolyte solution, as it has good tracing characteristics and ensures high accuracy of processing.
- Electrolyte NaNO3 is a water solution of a neutral mineral salt; its components are cheap, available, non-toxic and non-combustible.
- Use of industrial sodium nitrate (NaNO3) GOST 828-77 in the technological process of electrochemical machining is cost-effective. An average price of 50 kg pack of NaNO3 GOST 828-77 in Kirov city (regional) as of February 2012 amounts to 500 roubles.
- To operate electrochemical machines of SFE-4000М and SFE-5000М models 150 kg of industrial sodium nitrate (NaNO3) GOST 828-77 dissolved in water are required.
- To operate electrochemical machine of SFE-8000М model 200 kg of industrial sodium nitrate (NaNO3) GOST 828-77 dissolved in water are required.
- The frequency of electrolyte solution change (additional expenses for purchasing NaNO3) depends on the intensity of machine operation.
Electrolyte Solution Feeding And Preparing System in SFE Electrochemical Machines
- SFE-4000M and SFE-5000M machines include an electrolyte solution preparing station, that consists of a welded tank (volume = 850 liters) made of sheet stainless steel 12X18H10T, an electrolyte solution feeding pump made in Belarus or by Grundfos (at Customer’s option), corrosion-resistant variant, with a capacity of 3 kW/h and a pressure regulator. The pump and the regulator are placed at the tank.
- SFE-8000M machine includes an electrolyte solution preparing station, that consists of a welded tank (volume = 1600 liters) made from stainless steel 12X18H10T, a Grundfos pump with a capacity of 4 kW/h (corrosion-resistant variant) and a pressure regulator. The pump and the regulator are placed at the tank.
- On a contractual basis we may install an additional filter of fine electrolyte purification.
Electrolyte Purification with SFE Machine
SFE copying and broaching ECM machine is equipped with an in-built electrolyte filtering and cleaning system, designed for electrolyte filtering, cleaning and feeding to machine with controlled pressure characteristics.
The easiest and the cheapest method of electrolyte cleaning is the sedimentation method.
Slime sediments with the time, the upper layer of clean electrolyte is pumped into machine tank, slime is removed.
Collected slime is removed as a paste-like consistency and goes to the plant disposal facility. Slime liquid state is the electrolyte (12% NaNO3).
Wolframium, molybdenum, vanadium ions are collected in electrolyte.
Due to high humidity of slime, some part of electrolyte is lost with slime removal, which makes necessary to correct electrolyte level at times by adding the required quantity of freshly-made solution.
Adding fresh electrolyte provides that its composition stays stable and prolongs electrolyte service time significantly.
Preparation of Electrolyte
Electrolyte composition is selected depending on the processed material and technological requirements.
For processing a wide range of tool steel types the water solution of sodium nitrate (NaNO3) GOST 828-77 with 120 g/l concentration is used, as it has good tracing characteristics.
Electrolyte preparation and dissolution process
- It is better to prepare electrolyte in a separate tank, dissolving salt in hot (+70o) water, because dissolution process extracts heat.
- Pour salt into the tank, dissolving it with hot water from a hose (dissolution process extracts heat). Add salt to the tank as it is dissolving.
- After 150 kg for SFE-4000M and SFE-5000M machines and 200kg for SFE-8000M machine of NaNO3 salt are completely dissolved fill pump station tank with cold water up to the indicated level.
- Electrolyte volume in tank (0.85 or 1.6 m3); pump should be completely submerged in electrolyte solution.
Check hydrogen index pH = 6…7 and electrolyte density p =1.080…1.090 g/cm3.
Ideal density is p = 1.085 g/cm3 for a freshly-made solution.
If the solution density after dissolution is lower than required, it is necessary to adjust it to the stated level, dissolving more salt.
Initial solution density may be several times lower due to incomplete dissolution of salt.
It is necessary to mix the salt collected at the tank bottom and repeat the measurement.
For better mixing of a freshly-made solution pump electrolyte through interelectrode spacing for 2 hours.
Electrolyte Characteristics Control
Electrolyte density is measured by areometer (AOH-1).
When preparing electrolyte, NaNO3 salt dissolution in water ensures 12% solution, during machine operation process electrolyte is not worn out and used up.
Constant operating control of density is not required, it is enough to measure electrolyte density once a week.
- Electrolyte temperature
Principle of SFE ECM machines operation does not strictly limit electrolyte temperature.
- Operational temperatures range is rather wide – from +10oC to +35oC, but electrolyte temperature may increase even higher during intensive machining of large areas.
For cooling and maintaining stable temperature a pipe cooler is installed in the tank, through which cooling water is pumped.
Pipe cooler may be connected to a water-supply network as well as to a cooler (a system cooling device for a closed circuit cooling system).
- Cooler is an additional option
At the maximum machine loading tap water consumption is Q = 6 l/min.
Technological current source (TCS) is cooled with the same water.
Parallel as well as consecutive connection is possible, because TCS should be cooled constantly, and it is not required to cool electrolyte when small areas are machined.
Temperature is controlled with thermometer (it is possible to install a digital thermometer)
- A digital thermometer is an additional option
- pH acidity control
Performed with litmus paper. It is possible to install a pH controlling device for constant measurement of hydrogen index.
- A pH controlling device is an additional option.
Electrolyte Cleaning with Press-Filter
- Tank design provides electrolyte cleaning with natural sedimentation, during intense operation a press-filter can be used.
There are two connecting pipes in the tank for collecting sediments and draining clean electrolyte.
Electrolyte cleaning from slime in SFE machines may be performed by filtering with an additionally installed press-filter.
- Collected slime is removed from press-filter to a container as a paste-like consistency with a humidity of ~ 85-90% and goes to the plant disposal facility.
- Press-filters are rather widely spread and have various characteristics depending on their price.
Customer can buy a press-filter himself or order it together with the machine as an additional option.
- Press-filter is an additional option.