Impairment of Assets

A Company has one molding units. there are four separate six molding machines. the company is not using 50% of them, i.e., three machines for several years and charging depreciation normally. all the four machines are independent of each other. can impairment of those machines be directed. If yes, how to calculate the impairment. because they did not maintain realisable value or Replacement cost. Only written down value of the machine will be available.