Welding, Thermal Spray and Cutting
Browse previously asked/answered questions below.
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What are the advantages of using hydrogen as the fuel gas versus traditional hydrocarbons for HVOF operations?
There are only a few types of fuels to use for combustion in traditional HVOF (High Velocity Oxy-Fuel) systems, i.e., hydrogen, kerosene, methane (natural gas), propane and propylene. While each fuel has some distinct advantages, hydrogen offers some unique advantages:
- Because of its higher thermal conductivity, hydrogen achieves the best heat transfer from the flame to the powder particles despite having an overall lower flame temperature in comparison with the conventional hydrocarbon fuels.
- The performance of the HVOF process depends on the type of fuel, stoichiometric ratio, and combustion pressure, as well as gun design features. The ability to run rich hydrogen flows creates a reducing atmosphere, which lowers oxide production and further improves the quality of the coating.
- Due to the complete combustion of the stoichiometric reactants of hydrogen and oxygen, there are no unburned residuals deposited on the coating.
In addition, hydrogen can be delivered at sufficient pressures in tubes and bulk liquid tanks that do not require heating pads during the winter months in order to assure sufficient fuel flow to your HVOF booth.
To learn how hydrogen fuel can benefit your HVOF operation,
I know my flowmeter tells me that I have a certain gas flow rate, but how can I be sure?
|Flowmeters must be sized properly for each particular application, type of gas, gas pressure, and operating range. First, make sure that your flowmeter is calibrated for the specific gravity of the gas that you are metering. Check the label or the glass tube of the flowmeter or call the manufacturer to be sure. Second, operate the flowmeter only at the pressure for which it was calibrated. As an example, a variable-area flowmeter calibrated for 80 psi and reading 1000 scfh will really only be delivering 760 scfh if it is operated at 40 psi. This is a 24% error! Third, for best accuracy and to allow room for adjustment, size the flowmeter so that your normal flow rate falls within 30%–70% of full scale. These three steps will help ensure that you have good control over your gas flows and, ultimately, your process. |
For a free copy of Gas Atmosphere Analysis Guidelines, please call 800-654-4567.
Could gas purity be the reason for the variability in my thermal spray coating density, hardness and adhesion?
||Zbigniew Zurecki |
Gas purity, pressure and flow rate fluctuations can all cause inconsistent coatings. When troubleshooting plasma spray and HVOF applications, it’s important to look for things like properly sized valves, regulators and stainless steel lines from gas source to spray gun, plus bulk gas supply utilization, which provides higher purity and flow consistency than cylinders. Potential trouble spots include inferior rubber gaskets and diaphragms, greasy O-rings, acrylic flowmeters and many quick disconnects. Also, leaks from loose fittings and connections can entrain ambient air, resulting in gas impurities and a safety hazard.
Air Products can help troubleshoot your purity, pressure and flowrate challenges through a diagnostic audit that includes a gas analysis and piping design review. To schedule, call 800-654-4567.
Hear Robert Swan, Applications Engineer at Air Products, expand on Zbigniew's answer.
I use high-pressure gas cylinders and am concerned about safety. Is there a better way?
||John Tapley |
Microbulk Business Development Manager
Traditionally, high-pressure gas cylinders have been the supply mode for users in the low- to medium-volume range. This has left companies vulnerable to safety risks associated with moving cylinders and exposure to high pressure. Consolidating to a centralized microbulk system eliminates the need to handle cylinders and reduces the risk of product mix-up. Further benefits include decreased exposure to high-pressure containers and reduced traffic congestion with less frequent supplier deliveries.Air Products developed the microbulk supply option as a cost-effective, reliable alternative to high-pressure cylinders for nitrogen, argon, oxygen and carbon dioxide supply. In addition to efficient and flexible storage systems, innovative piping solutions are available to help you have a smooth transition from cylinders to microbulk.
How does hydrogen compare to traditional hydrocarbon fuels for my HVOF operation?
||Rob Hostinak |
Traditional HVOF (High Velocity Oxy-Fuel) systems use a few types of fuels for combustion, typically kerosene, methane (natural gas), propane, propylene and hydrogen. While each fuel has its benefits, hydrogen offers some unique advantages. Because of its higher thermal conductivity, hydrogen achieves the best heat transfer from the flame to the powder particles, despite having an overall lower flame temperature than the hydrocarbons. Excess hydrogen in the flame also creates a reducing atmosphere, which lowers oxide production. Since the stoichiometric reactants of hydrogen and oxygen completely combust, unburned residuals are not deposited on the coating. As the lightest gas with the highest speed of sound properties, hydrogen has the highest potential particle velocity—allowing for higher particle adhesion. Plus you don’t need heating pads in the winter to ensure sufficient fuel flow to your booth as you do with other fuels.
To learn how hydrogen fuel can benefit your HVOF operation, call 800-654-4567.
Can I remotely monitor what’s happening in my furnaces and other process equipment while I’m away from my plant?
||Chris Ward |
With the proper instrumentation and controls, you can securely monitor and control your heat treating or thermal process from nearly anywhere in the world! This is possible using a variety of hardware and communication methods, including Internet, dial-up, and cell phones. Alarm and warning notifications can also be proactively delivered to you so you can react to upsets, trends, and events before it’s “too late.” It’s important to identify the key parameters, equipment and instrumentation you want to monitor, and then select the hardware and software that best match your needs. Contact Air Products’ team of remote process monitoring and control specialists at 800-654-4567 for an assessment and recommendations as to how to get started.
How do I know if I’m wasting gas due to leaks in my gas piping?
Gas piping leaks can result from various conditions, including improper thread sealing, missed brazed joints, defective piping, over pressurization, or even vibration and shocks. A pinhole leak can cost you tens of thousands of dollars per year, depending on the size, number and severity of the leak(s). There are many ways to detect leaks; for instance, using soap tests, pressure drop tests, mass spectrometry or thermal conductivity tests. They all have their place; however, they also often come with limitations in precision, speed, difficulty or cost.
Air Products’ leak detection service can identify and repair costly leaks in your piping to help improve your part quality and bottom line.
In a short video, various methods for identifying leaks are described in more detail. You can view it online at www.airproducts.com/experts2. If you’d like to speak to a specialist about a leak detection audit of your facility, give us a call at 800-654-4567, and mention code 833.
Do you need to weld titanium in a glovebox? What are some of the gas considerations?
||Matt Thayer |
Principal Industry Engineer
No, titanium does not have to be welded in a glovebox; it's been welded outside gloveboxes for over 30 years. To help ensure quality welds and avoid contamination, use separate grinding and shielding tools.
The shielding gas should be supplied until the molten weld is below 800°F to prevent air contamination. During GTAW and GMAW, argon or helium shielding gases with a dew point below –50°F provide the required protection. Separate gas supplies are required for the primary shielding of the molten weld puddle, secondary trailing shield to cool the weld deposit and associated heat affected zone (HAZ), as well as a backside weld shield for the HAZ. Argon is generally preferred over helium due to its higher density, better arc stability and cost advantages. Argon-helium mixtures may be used if higher voltage, hotter arc and greater penetration are desired. Helium, with its lower density, is sometimes used for a trailing of back-up shielding when the weld is above the device.
An Air Products representative can help you select the gas or gas mixes to meet your needs. To learn more, contact us online or call at 800-654-4567 and mention code 749.
How can I address a cooling issue within my process?
In its liquid state, nitrogen is -320 degrees Fahrenheit! This makes it one of the most effective coolants available. Depending on your process, liquid nitrogen can provide temperature control, shorten cycle time, and improve product quality. Nitrogen is also a green product, as it leaves no residue and is sourced from the air we breathe. It’s used in many industrial processes and can be adapted to heat treating, machining, thermal spray, and many other applications that have problems related to excess heat.
If this is an issue for your applications, please give us a call at 800-654-4567, to learn how nitrogen can help improve your process.