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Galvanic corrosion (also known as bimetallic corrosion or dissimilar metal corrosion) is the breakdown of metallic surfaces as a result of the difference in electrical potential of adjacent metals and the presence of an electrolyte.
Stated differently, when two dissimilar metals are in contact in a corrosive environment, one of the metals will begin to corrode. This process is the same one that occurs inside of a battery. The metal that will be corroded and the speed of this breakdown are dependent on the difference in metals and the environment.
Conditions for corrosion:
For galvanic corrosion to occur, three conditions must be met:
All metals have an electrical potential assigned to them, based on their nobility. Metals such as platinum, silver, and monel have lower corrosion potentials whereas metals such as copper, aluminum, and tin have much higher potentials. Any two dissimilar metals will have a galvanic mismatch and therefore a change of corrosion.
In situations of EMI shielding, the electrical path is inherently created by the conductivity of the gasket, coating, or sealant.
Examples of such fluids can include atmospheric humidity or salt fog environments. As this mist or moisture condenses and collects at the flange or gasket interface, it will create the electrolyte needed to start breaking down the metals.
Preventing galvanic corrosion while EMI shielding:
For aluminum substrates that are going to be exposed to harsh environments such as military and industrial applications, chromate conversion coatings (also known as chem filming) are recommended. On top of this coating would be a conductive or non-conductive top coat. For steels and coppers, nickel or tin plating is often used.
Corrosion-resistant conductive coatings, such as CHO-SHIELD 2000 series conductive paints, are developed with stabilizers to create a very conductive and galvanically inactive surface for high-level EMI shielding in harsh environments.Matching EMI gasket fillers to substrates
Because EMI shielding gaskets are in direct contact with structural metal substrates, the corrosion potential must be considered. Historically, conductive fillers have needed to adapt to increasing requirements of galvanic corrosion resistance. Only within the last couple of decades have filler systems such as silver-plated aluminum replaced traditional silver-plated copper or nickel-plated graphite, to dramatically improve corrosion resistance in enclosures that experience moisture and salt fog.Nickel-plated aluminum
Despite the excellent performance of silver-plated aluminum fillers, the development of a nickel-plated aluminum filler has set the gold standard for both EMI shielding levels as well as corrosion resistance. This filler system, utilizing inherently stable compounds, exhibits the best results on chem filmed aluminum flanges relative to any other filler system, with a 20-50% reduction even compared to silver-plated aluminum.
Design guide for corrosion control:
A properly designed interface requires a moisture-sealing gasket whose thickness, shape and compression-deflection characteristics allow it to fill all gaps caused by uneven flanges, surface irregularities, bowing between fasteners and tolerance buildups. If the gasket is designed and applied correctly, it will exclude moisture and inhibit corrosion on the flange faces and inside the package.
Follow the below steps to maximize corrosion resistance in enclosures:
Where other requirements are met, select nickel-aluminum filled elastomers for best overall sealing and corrosion protection.
Use silver-aluminum gaskets as the next best alternative to nickel-aluminum filled materials.
In aircraft applications, a “seal-to-seal” design can be used with the same gasket material applied to both flange surfaces.
Use a Co-extruded or Co-molded gasket – extruded or molded in parallel, these gaskets consist of a conductive and non-conductive elastomer in one piece. The non-conductive material is placed outboard to interface with the moisture, effectively minimizing a key condition causing galvanic corrosion.
Coat surfaces with a corrosion resistant plating.
Avoid designs that create areas for moisture to pool. Use drainage holes to allow liquids to flow away from the interface.
Avoid sharp edges or protrusions such as dovetail grooves that can damage gaskets.
Select the proper protective coating and use additional environmental sealants.
In order to conduct direct comparative shielding effectiveness testing of gasket panel sets before and after environmental exposure cycling in a standardized test set-up, Parker Chomerics established CHO-TP09. This test method is based on IEEE-STD-299 and takes into account environmental aging conditions such as salt fog, humidity, and extreme temperature cycling.
Proper enclosure design and the implementation of conductive filler systems engineered to minimize galvanic corrosion are key drivers in extending the life span of electronic enclosures and lowering long term maintenance/replacement costs.
24 Apr 2019
Manufacturing businesses have witnessed the rapid ascension of industrial networks, and in the pneumatics industry, there’s a real desire to ensure the benefits that connectivity can bring are leveraged. To maximise this opportunity, those looking to connect pneumatic valve manifolds to an industrial network will want to make sure of an optimised outcome. But how?
To begin with, select the network and communications protocol that is best suited to the application.
Common Ethernet networks and protocols, such as PROFINET IO, EtherNet/IP, EtherCat and Modbus TCP, have been around for some time now. However, the high cost of adopting such systems has restricted the range of their application to those requiring the highest levels of system sophistication. This factor is precisely why cost-effective fieldbus networks like PROFIBUS DP, DeviceNet, CANopen and AS interface have become popular for more straightforward operations.
And yet these too, are getting squeezed out of the picture. To find out why we only need to look at rapidly emerging technologies like wireless networks and open communications protocols. A clear case in point can be seen with IO-Link, which thanks to simple installation, better control and enhanced diagnostics capabilities, has already secured a large user base.
In support of IO-Link’s increasing stature, Parker has released its P2H network node, an addition to the H Series ISO valve platform. The good news is that P2H delivers a robust way of connecting H Series valves to the IO-Link network, therefore saving total system and installation costs compared with Ethernet or hard wiring.
Applications include vehicle body welding and assembly, along with systems for applying adhesives and sealants, end of arm tooling (EOAT) for robots, riveting machines, blow moulding machines and case erectors, to list but a few.
Regarding network connectivity, flexibility and modularity are the factors underpinning ease-of-use and space saving. The value of our P2M IO-Link node module, for example, is as a low-cost network connection with simple integration and easy-to-use local diagnostics. In addition, voltage monitoring and cycle counting are available through the network, simplifying diagnostics and supporting the take-up of predictive maintenance strategies.
Many general pneumatic control applications can benefit from such modules, including packaging machines, automotive systems and factory automation. In fact, if you happen to visit any automotive or packaging facility, the ‘elephant in the room’ will be clear to see: the big controller cabinet housing the PLCs and contactors. These cabinets consume valuable floor space, but now they are set to shrink in size. Safety relays are increasingly moving out of the cabinet, and trends indicate that PLCs are soon to follow. This ‘do more with less’ business model should encourage any of you who typically still hard-wire valve manifolds, to make that leap towards industrial networks.
24 Apr 2019
Using mechanical energy produced by a machine’s engine, a hydraulic pump can move hydraulic fluid from the pump’s own reservoir, to a connected hydraulic motor, converting the mechanical energy to hydraulic energy. The incoming fluid/energy triggers the hydraulic motor to begin rotation, which can be used to actuate a component outside the system, such as a wheel or axle. The power of hydraulics allows for machines to do more with less, such as traversing tough terrain or lifting heavy loads.Why a piston pump?
In the world of hydraulics, the performance range of gear pumps and piston pumps overlap for low-speed, high torque applications. Being the case, why would a consumer select one over the other? What kinds of advantages and disadvantages do piston pumps have compared to gear pumps?
Piston pumps provide robust and precise performance for a myriad of applications. Compared to a gear pump, a piston pump can operate at higher pressures with the same flow performance. Typically, gear pumps are rated for around 3,000 psi, but some models reach as high as 5,000 psi. On the other hand, piston pumps can be rated to as high as 30,000 psi.
Piston pumps have the ability to produce variable displacement. Variable displacement is the act of adjusting flow during the usage of the pump, while maintaining the same motor speed. Conversely, pumps that use fixed displacement can only operate at one flow specification. By using internal controllers, like springs and dampeners, a piston pump can change displacement while maintaining the same motor speed. Gear pumps require external valving to attain this effect, which can increase the cost of the overall unit.
While a piston pump provides greater pressure ratings and flow controls, a gear pump is the more cost-effective option. The gear pump’s interlocking gear design is simpler and easier to produce on a large scale, allowing for consumers to purchase the product at a lower cost. If an application requires a lower pressure rating and is able to operate using fixed displacement, a gear pump may be the proper solution.
Parker changes the game
The engineers at Parker Pump and Motor Division have developed the HP Series of pumps, ideal for the low-speed, high torque (LSHT) applications. The HP Series is the only line of closed loop, variable displacement pumps, designed specifically for LSHT applications, with an integrated oil reservoir, filter, and cooling fan. This compact model saves an engineer space within a design, and reduces the numbers of components from 72 to 5. HP pumps are designed for superior performance and longer life; up to 20% more efficient than other pump and motor systems. They are compact and able to fit in small machine platforms where space is limited. They also easily connect to various Parker Torqmotors, providing ultimate design flexibility.
"The HP series was designed to complement our transmission technology by addressing specific customer needs. Those requirements included durability, compactness, integrated features to lessen leak points and reduced OEM assembly time. HP1 single pumps incorporate a proven design with integrated filter, reservoir and a low center of gravity pulley attachment point. HP2 dual pumps can be direct mounted to a horizontal shaft engine, so there is no need for belts and pulleys. Like the HP1, the HP2 has an integrated filter, reservoir and fan for cooling. Both units, paired with our LSHT motors, provide design versatility to better serve our customers."
Somer Malone, senior engineer, Parker Hannifin.
The Pump & Motor Division is a market leader in gear pump and low speed-high torque gerotor motors. the division continues to blaze a trail by developing new technologies, while maintaining a high level of service synonymous with the name Parker. Between two facilities in North Carolina and Tennessee, PMD employs decades of industry experience to better serve you and your application.
Article contributed by C.T. Lefler, marketing product manager, Pump & Motor Division, Parker Hannifin Corporation.
23 Apr 2019