Question: We are a purely mechanical company and stamp parts made of copper, copper alloys and steel, among other things. Our customer is complaining that two identical parts, one made of copper and one made of steel, have too much of a burr. The parts are very delicate, so mechanical finishing such as barrel finishing is out of the question. We are now considering a chemical solution. What options can you recommend?
Answer: We would generally advise you to visit a specialist company. They are equipped for this in terms of occupational safety and environmental protection. They also have experience in handling chemicals on metal. You are sure to find a suitable company in our industry guide [1] - also available online [2].
The chemicals used are highly concentrated, very aggressive and sometimes have to be operated at high temperatures. If you are thinking about adding a chemical deburring department to your business, there are many points to consider. For example, tanks, the nature of the floor, extraction, protective equipment, equipment for handling the chemicals, water and waste water, to name just a few elementary points.
There is also pre- and post-treatment. The parts must be degreased and thoroughly cleaned before treatment so that the deburring process is successful. After successful deburring, they are rinsed and dried. So you need a lot more chemicals, equipment and know-how.
Nevertheless, we would like to pass on some recipes. Mainly to clarify the extent of the points mentioned above.
A distinction is made between chemical and electrochemical processes, both of which have their advantages and disadvantages. The implementation of purely chemical processes involves less effort. They also have advantages when handling small parts, especially filigree bodies.
Electrochemical processes have a shorter dwell time because the removal rate is much higher. If handled correctly, the results are also better. However, there is a certain amount of effort involved in controlling such processes for the parts described.
Electrochemical processes
Copper and copper alloys
- Phosphoric acid: 58-60% by weight
- Sulphuric acid: 12-15% by weight
- Temperature: 20-80 °C
- Current density: 10-100 A/dm2
Low alloy steel
- Phosphoric acid: 63 % by weight
- Sulphuric acid: 15 % by weight
- Temperature: 50-60 °C
- Current density: 50-100 A/dm2
In any case, you would need rectifiers, cathode plates and a corresponding device for these processes. If the volume of parts is small, we recommend using a bell or a vibrating plate that is immersed in a suitable tank and energized. The drum method is not suitable for such sensitive parts. Racks are very expensive.
Chemical processes
The transition between deburring, leveling, shining and polishing is fluid and is defined differently depending on the literature and the company. The following solutions are often used for polishing, but fine burrs can also be removed.
Copper and copper alloys
- Phosphoric acid (90 %): 550 ml/L
- Ethanoic acid: 250 ml/L
- Nitric acid (62 %): 200 ml/L
- Temperature: 55-80 °C
This produces nitrogen oxides (nitrous gases, NOx)! Without appropriate extraction, this leads to lung damage or even asphyxiation.
In the case of non-ferrous metals, there are different recipes and parameters for the various alloys in order to achieve the optimum result.
Low-alloy steel
- Oxalic acid: 25 g/L
- Hydrogen peroxide (30 %): 13 g/L
- Sulphuric acid (90 %): 0.1 g/L
- Temperature: 20-30 °C
The duration must be determined depending on the type of steel. In general, it is 20-40 min. Due to the decomposition of hydrogen peroxide, we recommend not working above room temperature.
Literature
[1] https://www.leuze-verlag.de/shop/fachbuecher-galvanotechnik/branchenfuehrer-galvanotechnik-17-detail
[2] https://www.leuze-verlag.de/fachzeitschriften/galvanotechnik/branchenfuehrer-galvanotechnik
