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topic 2995

Help for chilling plant for anodising



A discussion started in 1999 & continuing through 2017

(1999)

Q. We are doing hard anodising in India. We are having chilling plant for cooling our sulfuric bath by indirect chilling method. We want to chill our bath by direct immersion of coils in H2SO4 bath. Can we use SS 316 tubes or lead tubes for this purpose? Inside the tube we are using R22 gas. Please give us your suggestions.

ELANGOVAN DAMODARAN
- INDIA


A. Yes, this has been done with lead coils. However, I think you are making progress in the wrong direction. Here in the U.S. many shops are doing exactly the opposite: converting from direct cooling to indirect! Most seem to think it's inappropriate to be pumping refrigerants around a shop and into vulnerable coils in tanks like that.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(1999)

A. Although direct cooling is more efficient, the chance of acid being introduced into the chiller is a very real and serious problem. In addition, with indirect cooling more precise control is possible with modulating valves. Also, indirect cooling provides a cooling buffer to minimize chiller on and off.

Jeff Pernick
- Detroit, Michigan, USA


(1999)

Q. Thank you for your advice and we are doing chilling by maintaining a brine chilling solution in a separate tank and from there we are circulating this chilled water through lead coils to H2SO4 solution in the anodising bath (tank). So there is a temp drop always between brine solution and H2SO4 bath solution. To avoid this we want to chill the H2SO4 solution directly by immersing lead or SS316 tubes in H2SO4 solution. This lead or SS tubes will have freon gas R22 inside them for chilling .

This is our question, kindly help us out of this problem.

Thanking you,

ELANGOVAN DAMODARAN [returning]
- INDIA


(1999)

A. A common way of handling the problem, but it is not cheap, is to use an external heat exchanger. The "brine" flows through one circuit and the H2SO4 through the other. Since there is high velocity and large surface area, it is possible to maintain a small temperature difference (less that 10 degrees F) between the "brine" and the H2SO4. (I put "brine" in quotation marks because we actually use ethylene glycol in the water, not salt brine).

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(2001)

Q. We are in a service of anodising since 1978. But we have a traditional & orthodox procedure but now I want to apply modern technique through you. So please help me to do so. Thanking you.

SACHIN SHARMA (B.E)
- delhi INDIA



(2001)

Q. We are doing anodizing in india, we need help for chilling plant we don't know how it's possible. Please guide us.

Manish Pande
- Nagpur, Maharashtra, India


(2003)

A. We have a solution to your need in form of chilling your H2SO4 solution directly through M-22 refrigerant gas, in an all stainless steel heat exchanger outside your finishing tank.This way you can reduce your temperature losses and maintain your acid very close to the refrigerant gas temperature. Also you will avoid refrigerant gas leaking into your finishing tank.

Jittin Gupta
- Delhi, India



(2004)

Q. Kindly assist in the calculation of cooling required in a Sulphuric Acid Hard Anodising solution. What size chiller plant is required in a 1000 litre 20 % Sulphuric acid solution using a 1000 Amp rectifier up to 80 V for the purpose of hard anodising up to 60 micron thickness.  What percentage of current will be transformed into heat.

Thank you,

John Kleyn
Plating Plant and Equipment - Cape Town, South Africa


(2004)

A. Hi John. I have been involved in correcting a number of undersized cooling plants over the years, and I have never seen any indication that less than 100 percent of the anodizing power is converted to heat.

If you are running at 1000 Amps and 80 volts, you will be generating 80 KW of heat. If you are anodizing at this current and voltage 60 minutes out of every hour, you are generating 80 KW-hours of heat or 273,000 BTUs per hour. 12,000 BTUs per hour is a ton of refrigeration, so you're looking at 22.75 tons. Please check my conversion factors because this was a quick on-the-fly thumbnail sketch.

But usually you don't run a rectifier flat-out, and you need to ramp up your voltage, so it can't always be 80 V either. After looking into those duty factors, you'll probably come up with 15 to 20 tons of chilling required.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(2006)

Q. The conventional chilling plants use Brine (Calcium Chloride) as a media for indirect cooling of H2SO4 solution contained in Hard Anodizing Bath. In our firm too a Brine Chilling plant is in operation to maintain -8 °C in Anodizing bath. As brine solution is highly corrosive in nature we are encountering problems, viz., puncture of pipe line due to rust, heavy rusting of pumps and surrounding environment etc due to which plant is under frequent breakdowns. We learnt from you that Ethylene Glycol solution is an alternative for Brine. Please elaborate this by giving the Technical/Chemical/Thermal comparison (from heat transfer point of view) of both the solutions to establish the superiority of Glycol.

Arun Kumar Khamithkar
Plating shop Employee - Hyderabad, Andhra Pradesh, India


(2006)

A. Hello, Arun. Ethylene glycol is automobile antifreeze, and the thermal properties of brine/water and glycol/water are probably reasonably similar. But commercial antifreeze probably includes descaling and corrosion-fighting additives that will somewhat reduce the tendency of scales to form which interfere with the "U factor". If you want to take that tip and run with it, please do. Or if you want to retain a consultant to do an engineering and economic study of the two heat transfer systems for you, please see our Directory of Consultants. But this is a public forum for camaraderie and sharing of quick tips, so we need to warn you that there is little point waiting for someone to undertake a detailed engineering study for you for free :-)

Good luck with it.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


July 18, 2011

A. I have a suggestion and I think that you wanted to eliminate these problems
1. Improve the efficiency
2. Reduce the heat gained during the circulation of indirect cooling.

You can make a safe approach:
cascade the cooling coils with freon inside a SS case filled with brine(...) immerse this in the tank( cool pack method) that will prevent your coils with freon from being damaged and also avoid to a greater extent the mixing of H2SO4 in the freon or vise versa.

But this will increase your maintenance work in terms of regular check by NDT for any possible hole or thinning of the outer SS shell which contains the brine.

Ayzaz hussain
- Bangalore, India but currently Kuwait


November 8, 2012

Q. Greetings,
Over the last several months we have had to replace our Type III Anodize stainless steel heat exchanger twice due to it being eaten up. It appears that the stainless steel is being etched away. The welds are attacked first but the tubes are being attacked as well. The Steel is 347 stainless. Our Solution has been within spec and we have checked for stray current on the heat exchanger itself with none found. The heat exchanger is electrically isolated. We have not had this problem before and prior heat exchangers have lasted for years. Any thoughts?
Best Regards,
Peter

Peter Doyle
Engineer - Phoenix, Arizona, USA


November 13, 2012

A. Hi Peter.

Regardless of whether or not you are reading stray currents, make sure that you have dielectric unions, or lengths of radiator hose, or some positive electrical insulation in between the anodizing tank and the heat exchanger.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



February 17, 2013

Q. While running a chilling plant, what should be the control parameters to make the plant trouble free? How should be root of the water, control of chilling unit, water pump, etc.

If chillers cooling tube get burst, what is the solution to rectify same?

Paripooran Watsayan - Delhi, India


September 11, 2014

A. We are manufacturing chilling plants for Hard anodizing, the Sulphuric acid solution is coming directly into the Evaporator. We are using 316L tubes, Tube plates & Shell.
We have had no leakage problems in the evaporators.

RAJEN MEHTA
CHILLERS - New Delhi INDIA



September 16, 2017

Q. Is there a separate water inlet to a chilled water plant? Or from the cooling water inlet they get water for making chilled water?

Janaka Bandara
SNT automation works pvt Ltd - Sri Lanka


September 2017

A. Hi Janaka. Unfortunately, that is impossible to answer definitively. Although many systems (including most anodizing chillers) recirculate the chilled water, some chilled water systems might be open loop: for example if you go to a water fountain in your shop, it may chill the potable tap water before serving it to you.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


September 19, 2017

Q. What is a thermowell mounting in a chilled water line?

Janaka Bandara [returning]
NST Automation Works Pvt Ltd - Sri Lanka


September 2017
wikipedia
Thermowell

A. Hello again Janaka. In certain situations it can be impractical to insert a thermometer or other temperature sensor directly into the liquid. In that case the piping is specially built with a sort of a nest into the pipe so the temperature sensor can be in the middle of the flow but protected from it by metal; this also allows quick change-outs without draining anything.

If at all possible you should try to get a look at this chiller system because it is problematical to design a control system if the things you are trying to control are too ethereal :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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