Narrowly beating a midnight deadline, Congress voted Monday to renew an expiring ban on plastic firearms that can evade airport detection machines. But Republicans blocked an effort to toughen the restrictions — the latest defeat for gun-control forces in the year since the grade school massacre in Newtown, Conn.

By voice vote, the Senate gave final congressional approval to a 10-year extension of the prohibition against guns that can slip past metal detectors and X-ray machines. The House voted last week for an identical decade-long renewal of the ban, and the measure now goes to President Barack Obama for his signature.

Obama, traveling to Africa for ceremonies honoring the late South African president Nelson Mandela, was expected to sign the bill before midnight using an auto pen, a White House official said. The device has been used for the signatures of traveling presidents since the administration of president George W. Bush.

GOP senators rejected an effort by Sen. Chuck Schumer, D-N.Y., to strengthen the ban by requiring that such weapons contain undetachable metal parts. Some plastic guns meet the letter of the current law with a metal piece that can be removed, making them a threat to be slipped past security screeners at schools, airports and elsewhere.