WASHINGTON – American manufacturers expanded again last month, though more slowly than in December.The Institute for Supply Management, a trade group of purchasing managers, reported Thursday that its manufacturing index dipped to 59.1 in January from a revised 59.3 in December. But any reading above 50 signals growth, and U.S. factories have been expanding for 17 straight months.Among 18 manufacturing industries, 14 grew in January, led by textile mills and makers of fabricated metal products. Export orders grew faster, while manufacturers’ new orders, production and hiring increased more slowly.Overall, American industry remains strong, thanks in large part to a pickup in global economic growth and a weakening dollar, which makes U.S. products less costly in foreign markets.Last week, the Commerce Department said orders for long-lasting manufactured goods rose 2.9 per cent in December, the fastest pace since June, lifted by a surge in orders for commercial aircraft. Excluding the volatile transportation sector, durable goods orders still rose a healthy 0.6 per cent.The American economy as a whole appears to be generally healthy. Economic growth clocked in last year at 2.3 per cent, up from 1.5 per cent in 2016. Unemployment has dropped to a 17-year low 4.1 per cent.