supply to railway

Please guide us on following issues supply to Railway-regarding

1. Under excise we were supplying Machined Railway Parts (Finished) under chapter 86079990. Now under Notification No. 1/2017-Integrated Tax (Rate) and schedule I chapter 8607990 falls under 5%.

2. We are selling Cast Railway Parts (Rough Casting). Now casting falls under 18% and Railway parts falls under 5%. What would be the rate of tax ? Please clear whether we should charge 5% or 18% supply of cast railway parts (Rough Casting).

with regards