Blackhawk Foundry & Machine Co., 323 S. Clark St., Davenport, has laid off about 30 employees, company president Jim Grafton said Monday. And that action came after about 10-20 previous employees were laid off in the past two months, he said. “We had two different groups in the past two to three months,” he said. “The last go-around was 30 people, one to two weeks ago. “Typically, this is our slow time of…