Bath Chemistry during bronze coating

Bath Chemistry during bronze coating

We are looking for a solution to automate the bath chemistry during the bronze coating of wires.

Bronze (an alloy of copper and tin) coating is achieved on steel wires by passing clean (electro-pickled) wires at a speed of up to 450 m/min through two baths with increasing concentration of copper sulphate (CuSO4) and desired concentrations of sulphuric acid (H2SO4), tin sulphate (SnSO4) and total iron (Fe). During the coating process, controlling process parameters such as the concentration of CuSO4, H2SO4, SnSO4, and Fe in CuSO4 baths is of prime importance.  These baths (refer Figure 1) are of 5500 liters capacity each and the bath temperature varies between 20 – 70 oC. In the current setup, copper sulphate and tin sulphate is added in the second bath, sulphuric acid is added in the first bath, while total iron gets released from the wires in the form of oxides or sulphate. The concentration range of these components is mentioned below in Table 1.

Table 1: Desired concentration of chemical compounds

Serial No.ChemicalConcentration range(g/liter)Desired accuracy (g/liter)
1Copper sulphate (CuSO4)5 – 800.05
2Tin sulphate (SnSO4)0.01 – 0.80.01
3Sulphuric acid (H2SO4)10 – 800.5
4Total iron (Fe)0 – 450.5

Since copper sulphate and tin sulphate gets consumed in the process, they need to be added continuously. As the number of wires and the size of wires (varying from 0.89 to 1.6 mm in diameter) keeps changing in the line, the amount of copper sulphate and tin sulphate required also keeps changing. This needs to be adjusted. Currently, concentrations of the above salts/elements in baths are intermittently measured in a laboratory by volumetric titration of the samples collected. Based on this laboratory test report, the operator corrects the concentrations of the bath by manually controlling the flow rate of dosing pumps of CuSO4 and SnSO4.

This manual testing of the sample and manual correction is a bottleneck in reducing the variance of the elements in the bath. Hence, we are looking for an automated system, which will maintain the concentration of various components (CuSO4, H2SO4, SnSO4, and Fe ions) in the bath within the pre-decided limits.


The proposed solution should meet the following criteria:

  • The system should be able to maintain the concentrations of CuSO4, SnSO4, H2SO4 and Fe in the bath with an accuracy of 0.05, 0.01, 0.5 and 0.5 gm/liters respectively.
  • It should also measure the bath temperature with an accuracy of ± 0.5 oC.


  • There are multiple wire lines running in parallel with varied thickness of the wires – 0.89 mm, 0.96 mm and 1.6 mm.)
  • Variation in customer requirements of coating thickness, adhesion value and tin content.

Awards:- INR 8,00,000

Deadline:- 30-06-2020

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