Complex sentence: Rivets were placed in the furnace and heated to a glowing hot temperature, at which time the furnace operator would use tongs to individually remove and throw them to catchers stationed near the joints to be riveted.
Split into simpler sentences: Rivets were placed in the furnace and heated to a glowing hot temperature. The furnace operator used tongs to individually remove rivets and throw them to catchers stationed near the joints to be riveted.