Where the
world gathers for metal finishing
Q&As since 1989


-----

Zinc deposits on O.D. of 2nd end of pipe while I.D. blowing

DEPOSITION OF ZINC ON OUTER DIA OF PIPE ON THE SECOND END WHILE INSIDE BLOWING
DURING HOT DIP GALVANISING.THE EXTRACTION ANGLE IS 20 DEGREE. THE INSIDE BLOWING IS BY STEAM.

JITENDER GULATI
WORKING IN G.I. PIPE INDUSTRY - DELHI, INDIA
October 5, 2011

---

October 7, 2011

Sir:

What you are describing is "blow back." There are several solutions to this problem. In India, a plant cut a few inches off the bottom of the pipes so they could be threaded. In the USA there was a plant that had a line of natural gas burners to remelt the zinc on the outside of the pipe and have it drip on the floor. This was done while the pipes were on the walking beam between the outside and inside blows. A much better solution is to increase the ACN of the flux so the zinc is more fluid and drains more fully prior to the internal blow. Other technology has also solved this problem.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA