Which preposition to use with puddlers

in Occurrences 1%

The Northwestern rang Mitchell to say good-by forever and to hope his nose was broken; the Big Four promised that her brother, who was a puddler in the South Chicago steel mills, would run in and finish the rate clerk's job; Miss Gratz, of the C.&E.I., was tearfully plaintive and, being German, spoke of suicide.

Which preposition to use with  puddlers