Through-flow impeders are the most commonly used impeder type. They are also the least expensive. All EHE impeders use high-performance fluted ferrite to ensure low eddy current losses and to maximize cooling efficiency. Impeders are normally supplied with SAE flare fittings. ISO metric, NPT and BSP pipe fittings and quick connect couplings are available at a small extra cost. Flare nuts are not normally supplied with impeders, since they can be re-used many times.
They are available in packs of 10, 25 and 100 from us, or from most hardware and industrial supply outlets. Standard impeders have outer casings that fully enclose and protect the ferrite. Exposed ferrite impeders are used where weld spume or coatings such as aluminum or zinc tend to build up on conventional impeders and shorten their life. Exposed ferrite impeders often permit a larger impeder to be used, since there is no casing at the narrowest part of the tube.
These impeders also work well in air- or gas-cooled installations. Laminar flow of coolant over the exposed ferrite makes these impeders self-cleaning, and therefore highly resistant to damage from weld spume.
Epoxy/Glass - NEMA grade G-11/12 is a high temperature, high strength glass fiber reinforced epoxy resin composite which exhibits excellent wear properties, and extended life at elevated temperatures. It is widely used and is the least expensive type of casing for most impeder sizes.
EHE's G-11/12 epoxy glass will withstand temperatures 100° higher than the more common G-10 material.
Silglass™ - NEMA grade G-7 is an ultra high temperature silicone resin bonded glass fiber material used primarily for return flow impeders. It has poor wear characteristics & impeders must be protected from contact with the moving strip. Silglass™ is inorganic so it does not char when exposed to excessive temperatures. This reduces the amount of radiant heat absorbed by the impeder from the weld area. Ferroglass™ is a high temperature, ferrite impregnated glass fiber tube manufactured specifically for impeder use.
The additional ferrite present in the casing can increase weld speeds by as much as 40%. This improved efficiency is most noticeable at small diameters where the Ferroglass™ casing contributes a higher percentage of the total ferrite in the impeder. Ferroglass™ also has the best wear resistance of all materials normally used in impeders.
Coolant should be clean, preferably filtered. A pressure of 3 bar (45 PSI) will ensure adequate cooling under most operating conditions. Coolant flow requirements vary widely due to inlet temperature, weld power, frequency & weld area geometry.
In high power density situations & at high ambient temperatures, a small refrigerating chiller for impeder & work coil coolant can greatly improve efficiency. Cooling by air or other gas is not recommended, but can be useful in special situations where the presence of water inside the tube cannot be tolerated.
Gasses such as nitrogen have a density that is at least 1000 times less than that of water, so coolant volume must be increased accordingly. An impeder that can be cooled using 1/2 gallon of water per minute would require a minimum of 15 cubic feet per minute of nitrogen. The cost of this is prohibitive in most cases.
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