A Middletown steelworkers' union says it has approved an agreement with a company that is shutting down a steel-coating plant. The Armco Employees Independent Federation said its members voted today to accept the deal with Material Sciences Corporation, which applies coatings to steel coils for various customers. Material Sciences plans to close its Middletown plant on Monday, eliminating 62 union-covered jobs and about 20 administrative jobs. Depending on length of service, the union members may receive health insurance benefits for an additional two weeks to eight months and severance pay allowances ranging from five to 29 weeks beyond the plant's closing. Material Sciences, based in suburban Chicago, announced in May that it was closing the Middletown plant because of declining business at the facility.