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October 14, 2016

Wave Soldering System Nitrogen Use

How can I calculate the amount of nitrogen used in my wave soldering system?


Experts Comments

The best way to determine you N2 consumption is to hook up a mass flow meter to the incoming N2 source line.  These meters will provide you with an accurate consumption.
John Norton
Eastern Manager
Vitronics Soltec
John Norton started his soldering career in 1983 for Hollis Engineering. He has also worked with Electrovert as a technical training manager and Vitronics Soltec for the last ten years. He has held various technical development and sales positions.
You'll need some type of flow meter somewhere. The best solution is an electronic, totalizing flowmeter installed directly upstream of the wave solder system. The meter will record usage and give you a running total of the usage. A simpler strategy would be to install a mechanical flowmeter, such as a "rotameter" type meter, again preferably installed directly ahead of the wave machine. The latter will give you the instantaneous flow, and you'll need to calculate usage based on duty cycle and machine up-time. 
If the only flow meter available is up-line far enough to encompass more than one usage point, you can still work with this by taking the difference in the flow with the wave on and off. This assumes you can control the state of the other devices on the line, and that the flowmeter has enough resolution to distinguish. 
Finally, if it is not possible to tap into the line to the equipment to install a flow meter, there are non-invasive techniques on the market, e.g. ultrasonic flow measurement. These can be expensive, however. 
With any of the above techniques, you need to compensate for the temperature and pressure at which you are measuring the flow. You will have to convert flows measured at the line pressure and temperature to flow at "standard" pressure and temperature, typically in SCFH (Standard Cubic Feet per Hour). Some electronic meters can perform this conversion because they have temperature/pressure sensing incorporated into them.
Fritz Byle
Process Engineer
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
Many wavbe soldering machines come equipped with flowmeters for air & nitrogen. These flowmeters usually measure Cubic Feet per Minute or Liters per Minute.  In a steady-state system all you need to do is to log the flowmeter reading vs. time the equipment is using Nitrogen.
Edithel Marietti
Senior Manufacturing Engineer
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
A simple answer to your Q is put in a flow meter and measure it. However, I sense that you do not have a flow meter, hence, the calculation request.

Air velocity formula is as follows: Air Velocity in a Pipe Using the equation and typical values of V, D and L explained to the right approximate values of P are computed as follows:

V = air velocity in feet per second
D = pipe inside diameter in inches
L = length of pipe in feet
P = pressure loss due to air friction in ounces/square inch formula from B.F. Sturtevant Company

Whether you have all these data inputs is unknown. However, some online examples of this formula show that velocity is about 30 fps. Hence, for a good estimate for your wave solder machine usage is to  multiply the cross-sectional area of the pipe or tubing that you're using by 30 to get cubic feet, and then convert ft3 of N2 to lbs if that Is needed.  
Lee Wilmot
Director, EHS
TTM Technologies
Lee Wilmot has 20+ years doing EHS work in the PCB/PCBA industries, including environmental compliance, OSHA compliance, workers compensation, material content declarations, RoHS & REACH compliance. Active on IPC EHS committee and c-chaired committees on IPC-1331, J-STD-609A on labeling & marking, IPC-1758 on packaging and others.
If your wave soldering system came with a nitrogen inerting option, it should have a flowmeter somewhere on the nitrogen line going in to the machine, or built into the controls or display of the machine. Now, because nitrogen, like all gases, is compressible and changes volume when placed under pressure, or is heated or cooled, a given volume of nitrogen under one set of pressure and temperature conditions is not equivalent to the same gas under different conditions. Keep this in mind when attempting to measure volumes of gas.  

A manual display flowmeter looks like this: http://www.amazon.com/ESAB-639749-L-32-Flowmeter-Inlet/dp/B007PJIBKA/ref=sr_1_5?ie=UTF8&qid=1428950749&sr=8-5&keywords=nitrogen+flowmeter. These can be configured as either a display-only flowmeter, or as a controlling valve, ie, they may be installed in series on the nitrogen gas line to both control the nitrogen gas rate to the chamber AND see the gas flow rate. The gas flow rate is usually measured in gallons per minute (GPM), liters per minute (LPM), cubic feet per minute (CFPM) or SCCM (standard cubic centimeters per minute) or whatever other foreign, obscure, and generally-misunderstood flow rate you wish to choose from.  

I recommend you look at Davis Instruments or just Google up "flowmeter, gas" and you will see a huge selection. There are even non-intrusive Ultra-Sonic Doppler flow meters meant for tracking the amount of gas flow inside a pipe. Or you may have a really fancy technogeek style digital electronic flowmeter like this: http://www.amazon.com/Digiflo-1000-770-Digital-Flowmeter-sccm/dp/B00NI4G7IO/ref=sr_1_5?ie=UTF8&qid=1428951246&sr=8-5&keywords=davis+instruments+flowmeter; programmable in all of the above-mentioned measurement rates and some others you understand even less, such as acm/h (actual cubic meters per hour), sm3/sec (standard cubic meters per second), kscm/h (thousand standard cubic meters per hour), LFM (linear feet per minute), or MMSCFD (million standard cubic feet per day).  

Anyway... that is how the flow rate is measured.  

So, with the chamber operating at a desired oxygen level in parts per million (50 ppm or less is a good nitrogen blanket for a wave solder machine)... what do you mean you don't know what the oxygen level is? Well, how do you know how much nitrogen is needed to get the oxygen level below 50 ppm if you don't have an oxygen monitor like this one installed? http://aoi-corp.com/oxygen-analyzers/percent/series-2520.  

Ok, now that you are able to monitor the oxygen level in the wave solder chamber, and you have finally adjusted the in-line nitrogen flow rate so the oxygen monitor shows around 50 PPM or less, you can simply multiply the nitrogen rate times the number of hours of wave solder operation to come up with the total usage. For example, if your required nitrogen flow rate for your machine is around 6 liters per minute, and the machine is run 8 hours per day, your total usage would then be approximately 6 liters/min times 60 minutes times 8 for a total of 3,840 liters per 8 hour shift.  

What does that mean to you? Well, think of it as 3,840 of those biggie-sized bottles of Diet Coke, but instead of Coke they were filled with nitrogen. That is how much you would use every 8 hours of machine operation time. So, if you ran two shifts, or 7,680 Coke bottles per day, times 5 days per week that would be 38,400 Coke bottles of nitrogen used every week, times 51 weeks per year (after holidays are subtracted) then you are looking at 1,958,400 Coke bottles of nitrogen used every year. That's almost two million Coke bottles of gas every year!  

How much does that cost?  Well, I can buy 80 liters of 99.995% nitrogen for about $5. So, if I divided 1,958,400 by 80 I get 24,480 tanks, times $5 per tank, I get $122,400 per year, plus installation and maintenance costs. Nitrogen tanks require special handling, read the OSHA rules. One OSHA fine for not having the tanks handled and secured properly can be another $50,000!  

And that answers your question. Have fun with that!
Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.
To calculate this can be quite complex. Typically the manufacture will have this in the machine specification sheet. If you are worried that you are over consuming or under consuming nitrogen then I suggest that you fit a air flow sensor which can track the flow rate of the nitrogen. This sensor data will also show you the total amount lost due to planned and unplanned maintenance cycles.
Kishan Sarjoo
Process Engineering Manager - Electronics
Altech UEC, South Africa
Currently with Altech UEC and responsible for technology road map in PCBA electronic manufacturing and technical support for PCBA electronic manufacturing for Altech UEC and its JDM's. Over 7 years in SMT, Radial Insertion, Wave solder & Test Applications.
Reader Comment
N2 mass flow meter is the best practical way to read your N2 flow. Volumetric flowmeter is a reliable tool (not as precise as mass flow meter) but check if it is for N2 (not for air) and if its calibration pressure is the same as your working pressure. Check pressure changes from time to time, it may change and then influence in your volumetric flow readings.
Luiz Felipe Rodrigues, Air Liquide
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