Citing lower shipment volumes and higher production costs, Keystone Consolidated Industries Inc. posted net income of $5.9 million during the third quarter, down 75.5 percent from nearly $24 million in the same quarter last year, on net sales that slid 45.2 percent to $100.4 million.

Throughout the quarter, customers continued just-in-time order philosophies, which resulted in the lower shipment volumes and additional production costs due to...