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Small Shop Galvanization

We build small water powered turbines in Bolivia and would like to use hot dip to protect some of the steel parts. Is there a low cost design available for a unit able to process sheet 50 cm by 50 cm pieces of 1/8 inch steel and pieces of 1.5 inch angle iron up to a meter long?

Ron Davis
turbine builder - Campo Nuevo, La Paz, Bolivia
December 16, 2009

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December 18, 2009

Sir:

Just looking at the kettle aspect--It would be very narrow, and fairly deep, and fairly long. Firebox steel (virtually pure iron) would be required and exactly matching weld rod. Drossing would be somewhat difficult. All this would only work economically if you had a very large number of items to galvanize.

Regards,

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

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December 18, 2009

Its possible to build a galvanizng plant to almost any size. The smallest kettle I've seen was about 200 mm x 200 x 200 mm, it was an experimental one for test pieces, but could have been used more commercially.

Spinning plants with dimensions <1 m x 1 m x 1 m are built often.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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December 29, 2009

Why don't you try zinc plating.The thickness will be less but for small items it will be a lot cheaper.
Good luck and God bless.

Khair Shishani
aircraft maintenance - Al Ain, UAE

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January 13, 2010

Geoff,

I do not agree that a 1m by 1m by 1m kettle is a viable spin galvanizing plant except possibly for extremely small product and extremely low production.

I just did a short report for a foreign galvanizer and the kettle size is 1.5 meters wide by 1.5 meters long by 2 meters deep. All four sides are to be heated. With a 30 inch diameter by 36 inch long "spin-a-batch" basket with product, the temperature of the kettle will decrease by 11.8 C deg (clearly unacceptable). Once the thermocouple turns on the burners to high fire it will take about 10 minutes for the heat to go though the kettle walls, meanwhile the basket and steel will have a frozen zinc cast around them. It is not possible to meet the required 10 minute (6 baskets/hour) cycle time to produce the required tonnage.

There are many other problems that I encountered in doing these calculations. For temperature drop feel free to do your own calculations. Just so you will know, there are problems in melting and heating replacement zinc, drossing problems, ash recovery problems, quality problems; the list goes on.

Regards,

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

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January 13, 2010

"I do not agree that a 1 m by 1 m by 1 m kettle is a viable spin galvanizing plant..."

Don't think I said that it was viable. Rather that its possible to build one.
Never the less, "viable" depends on may factors, most of which we don't know here as not given. If it was worth enough for someone to have a few small items galvanized it could be viable.

I can think of three kettles under 1 m3, and I'm sure there are more.

Yes, your example of a big heavy basket in a tiny kettle would freeze the zinc, that would be silly, but a proportionate size/mass basket can work. And what of the work? If its heavy then yes, some thermal inertia required, but 1:100 (kg:kg, Fe:Zn isn't uncommon ratio)

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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January 15, 2010

Geoff:

I stand by my quoted statement. Certainly there are exceptions such as being on an island or too far from any galvanizer or not being able to attain the required quality of product. Beyond a very few exceptions, the economic and operational aspects of a small kettle, especially a square kettle are very problematic.

The case in point was designed for 50 MT/day. This would be about 30,000,000 pounds of product/year. Even in my early days, from experience, if a galvanizer can get 1,000,000 pounds of steel galvanized for every foot of kettle length he would be doing quite well. And make a decent profit. Thus to do 30,000,000 pounds in a five foot long kettle would be six times more than what I consider a very productive operation and would be quite unlikely. I talked to a few galvanizers about doing 30,000,000 pounds/year in a five foot long kettle and it took them quite a long time to stop laughing.

For the case in point the spin-a-batch basket (already delivered) plus product weighs 0.651 MT/basket (to attain a 10 minute cycle) and the kettle has 30 metric tons of zinc in it. Thus the ratio would be 30/0.651 = 46 (46 to 1) and the temperature drop is 11.8 C.deg. For your 100 to 1, if the temperature drop is inversely proportional then the temperature drop would be 46% of 11.8 = 5.4 C deg (9.8 F deg.), which for me is still not acceptable. There is also the issue of overshoot by the burners (maximum zinc temperature).

Many other problems exist including having only one spin basket in the kettle at a time. Thus cook-off time of a single basket would severely limit production. Having to add make-up zinc every 4 1/2 hours and wait for it to melt and heat up also stops production for an hour or so. Drossing every 5.2 days with a clam is not my idea of a picnic. Not having space to have an ash box to recover dry ash makes ash 4 times greater. Not having kettle space for the spin inclosure for the spun off zinc to drop zinc directly back into the kettle. Having short kettle life due to low and high temperature variations from set point.

I trust that you and I really do not disagree. The thing is I calculated about a 3.15 MT/hour capacity for this kettle (10,000 Btu's/sq ft/hour for sidewall heating area, all four sides), whereas the required heat requirement is 3.91 MT/hour. Then all these other side issues came up (ash, drossing, replacement zinc, cook-out time, kettle life, and others). The proposed galvanizing plant just has too many problems (especially the small kettle) to be viable.

Five nights ago it was -30 F here. Last night my 9 year old son caught four three pound rainbows on a dry fly. How sweet it is.

Thank you Geoff for your opinions.

Regards,

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

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January 16, 2010

Geoff,

Is your 1 : 100 ratio based on a per lift (per basket + steel in this case) basis or on an hourly basis? I answered already as if it is on a per lift basis. However if it is on a per hour basis my response would be very different. If the basis is 1 : 100 on a per lift basis, as I have assumed, then the number of lifts/hour would have to be specified. So how many lifts/hour are you specifying?

Regards,

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

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My 1:100 ratio was with 1 tonne lift of steel needs about 100t zinc in the kettle at about 4-5 dips per hour.

But all that's a bit irrelevant to the original poster who asked if its possible to build a small kettle.
He didn't ask about economics which must be very variable according to the local conditions. We don't know what its worth for him to perhaps even do 2 dips per day of his material.

Its certainly possible to build a small kettle. Its been done before, and will be done again by someone.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

January 18, 2010