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Case Studies : |
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How Friction Welding Can Save Food Manufacturing OEMs on Material Costs ?
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The challenges of material price versus performance in pump shaft manufacturing have gotten tougher with each price increase for raw materials. FRICTION WELDING is a way to reduce costs is a viable option for design engineering and new product development. This article provides some background on FRICTION WELDING for pump shafts manufacturing.
Although the term “welding” is used in defining the Fiction Welding process, it bears no resemblance to conventional welding as no filler material is involved. Instead, two components are rubbed together at a controlled rotational speed, which creates the friction and heat that allows both components to reach a plastic state and forge together into a bond. Friction Welding involves the use of very unique technology incorporating state of the art monitoring controls.
FRICTION WELDING allows pump manufacturer the ability to use composite rather than one piece shafts, promoting more ease in selecting the best materials to suit an application with lessened concern on raw material costs. In essence, this creates a better balance in selection of optimum material without the heavy price tag.
Cost versus performance criteria, abrasion or corrosion resistance, mechanical strength for operating loads, FDA-mandated sanitary characteristics, etc. are realized without sacrificing performance. With 60% of the shaft replaceable with lower cost materials, significant savings can be realized for virtually any size and quantity of shafts, considering today’s costs of stainless steels and high nickel alloys. |
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Dry End Versus Wet End Shaft Considerations |
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Pump shafts have two distinct ends, the dry end and the wet end. The dry end is sealed and encased ( Typically in oil ) within the housing itself and wet end outside the pump enclosure comes in contact with the application. The dry end plays a less critical role in a given application, so less costly materials such as low carbon steel can be used for this portion of the shaft, provided sufficient strength for the application exists.
Conversely, the wet end of shaft is where “the rubber meets the road” due to its direct contact with the external ambient conditions of the specific application. This is where the critical needs reside and where much more costly, exotic high nickel alloys such as Hastelloy and high strength stainless are often required.
Cost savings are realized by constructing the composite shafts with the typical two third of the shaft’s less critical dry end replaced with lower cost steels. Considering the current challenges of both prices volatility and surcharges to nickel based materials, these savings can be substantial for OEMs while also promoting significant cost and profit stability on the end product. With proper selection of the two materials for dry and wet end, strength properties of the original material can typically be met or exceeded.
For all food related Friction Welding Applications close state of the art control via monitoring and visual graphing during the weld process and post weld ultrasonic inspection ensures consistent weld joint integrity through a very robust process. Production controls monitor RPM, Axial load and Displacement of material during welding. Parts are typically rated for loads far exceeding the intended applications. |
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Metallurgical Integrity of Friction Welding |
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Comparing friction welded to conventional welded joints, the heat affected zone (HAZ) is less extensive and has a narrower width than HAZ of a conventional weld that incorporates a filler material. HAZ mechanical properties are similar to the base metal, but depending upon the temperature achieved during welding, the cooling rate and post weld thermal treatment, all three can change the weld properties. If all are controlled correctly, welds will have necessary integrity.
The successful friction weld will be free of porosity, lack of fusion and oxide inclusions. If done right, none of these will be present. |
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Key Material Considerations |
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On the shaft wet side, a wide variety of stainless steels and nickel based alloys are typically used based upon particulars of the application. For instance, 304 stainless, 316 stainless or 174PH stainless can also be incorporated in friction welding for higher mechanical properties, providing a balance between strength and corrosion resistance.
On the dry side of the pump shaft, the options are virtually endless. Medium and low carbon steels as well as stainless on this end can be incorporated for corrosive resistance if needed. Even with using stainless on this end, cost reductions are often realized. As far as weld integrity is concern, the 1100 and 1200 series carbon steels with their re-phosphatized and re-sulfurized content (typically manufactured to enhance machinability) needs to be avoided since the addition of higher sulfur or lead can create complications in the welding process. Although these materials can be welded, mechanical strength cannot be guaranteed but steel may be within what’s needed for a customer application.
Many alternatives exist to avoid such complications while new weld developments using exotic combinations are being devised constantly with great success. |
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A Broad Range of Options |
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When using FRICTION WELDING, more options are available than only the cost of materials. In designing solutions for pump applications, pump manufacturers can more broadly consider material properties such as strength and corrosion resistance. On the dry end, specific wear resistance, longevity in length of service and related fatigue and the types of loads that shaft will be receiving are all important factor where ideal materials can be more easily integrated into a solution.
Manufacturability benefits can also be realized with friction welding. Shafts can be designed for optimum manufacturability and machinability with significant reduction of machine labour. This reduces perishable tooling cost with faster feeds and speeds, longer life on perishable tools, more uptime on machines and higher output due to faster times on existing equipment. At times, up to 15% savings can be realized, buying 15% to 20% more capacity on expensive machine tools.
For practically any selected blank for pump shaft, endless opportunities exist with respect to size, type, length and configuration, including the use of two different shaft diameters.
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FRICTION WELDING and Cost Savings |
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Based upon the particulars of an application, savings of up to 50% to 60% on raw material costs can be realized using FRICTION WELDING after factoring in the cost of the weld.
Although FRICTION WELDING has been around for more than 50 years, it continues to be one of the manufacturing’s best kept secrets. Specific to today’s cost challenges for high strength, nickel based materials, the ability of FRICTION WELDING to replace large percentage of this costly material without loss of strength or structural integrity is a strong consideration for cost conscious pump OEMs. It is one of the most economical welding processes available providing increased design flexibility, superior strength and significant cost savings. |
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