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Maintaining a normal oil temperature in all hydraulic systems is important for successful system operation. Normal operating temperatures for hydraulic systems is 110 to 130° F (unless specified by the equipment manufacturer). At high temperatures, oxidation of the oil is accelerated. This oxidation shortens the fluid’s useful life by producing acids and sludge, which corrode metal parts. These acids and sludge clog valve orifices and cause rapid deterioration of moving components. The chemical properties of many hydraulic fluids can change dramatically by repeated heating/cooling cycles to extreme temperatures. This change or breakdown of the hydraulic media can be extremely detrimental to hydraulic components, especially pumping equipment.Coolers extend the service life
Overheated hydraulics can be caused by decomposing fluid, wear, or damaged seals and bearings. Coolers can prevent overheating and extend the service life of your hydraulic system. However, smaller hydraulic systems with lower operating temperatures can often be cooled through natural convection. If natural convection is not enough, it becomes necessary to add a cooler.
Coolers are also crucial for systems with temperature requirements such as needing to stabilize the hydraulic fluid’s viscosity by keeping it at a specific temperature, or equipment with a history of hot oil problems that shortened seal life and break down the fluid. Hot fluid is always a concern with large mobile equipment, as well as commercial and industrial processing equipment. Specifying a properly sized cooler saves time, money and maintenance.
Selecting the best cooler
The process to select a cooler is driven by the type of system that needs to be cooled. Parameters to consider include heat load, power source, noise, operating costs, space available, environmental conditions, and more.
Actual heat generation varies throughout the machine’s cycles, as well as changing environmental factors and ambient temperatures. This can make it challenging to accurately define your cooling needs. When considering the application and sizing of coolers, the hydraulic fluid’s ideal operating temperature and the time it takes to arrive at that temperature must be used.
For new designs and retrofits, the first step in selecting the right cooler is identifying the challenges and performing the necessary calculations. Virtual design and sizing tools are available from most manufacturers to help determine the best fit for your application. Some companies provide online sizing calculators and other interactive resources that let engineers plug in specifications to get an idea of what is needed. Parker offers a comprehensive suite of online cooler sizing software. For instance, Parker offers an online cooler selector tool for each of the different types of coolers including brazed plate, shell and tube and air-oil coolers.Air-oil coolers
To select the best air-oil coolers, you’ll need as much information about the application as possible, including, but not limited to the following:
If the required heat dissipation is not known, it can be estimated assuming 20-30 percent of the installed horsepower will be converted into heat load. The most accurate way to calculate the heat load is to record the time it takes the oil to get up to temperature without a cooler in the system.Water-oil coolers
For water-oil coolers, which include Parker’s ST and OAW series coolers, you also need to know the inlet temperature and flow rate of the cooling water. Most manufacturers’ literature includes examples, steps and simplified equations to properly size coolers. For instance, Parker provides engineering specifications for their ST series water-oil coolers, such as cooling capacity, flow rate, working pressure, sizing, and connection thread in their online tools to enhance the specifying process. Once the heat-load parameters and other key influencing factors are defined, the next step is choosing an air-oil (air-cooled) or water-oil (water-cooled) cooler.
How air-oil coolers work
Air-oil coolers remove heat from the oil in a cooler by using the ambient air around the cooler. Air-oil coolers convect heat, which makes them ideal when no water source is available or when the preference is to remove heat from the oil by using ambient air. In air-oil coolers, hot oil passes through channels that contain turbulators to prevent laminar flow from developing in an effort to promote heat transfer from the fluid to the channel wall. The channel wall is always constructed of metals with high thermal conductivities.
The cores of air-oil coolers are constructed in two different styles: tube-and-fin or bar-and-plate construction. Tube-and-fin construction consists of round or oval tubes mechanically connected to an array of external fins. The tube-and-fin design is lightweight and offers low pressure drop across the core. The tubes in a tube-and-fin design can be susceptible to damage from pressure spikes and external debris that can be encountered in any application. Bar-and-plate construction uses compact and efficient cores that offer more cooling per cubic-inch than a tube-and-fin design. They consist of finned chambers separated by flat plates which route fluids through alternating hot and cold passages. The bar-and-plate design creates a honeycomb structure that resists vibrations and shocks. This core is usually made of aluminum and is furnace brazed in a controlled atmosphere or high vacuum. With all the bar-and-plate design characteristics that provide certain benefits over the tube-and-fin design, it can be seen that bar-and-plate coolers can offer design engineers greater system design flexibility.
Both types of air-oil coolers typically have a fan driven by a hydraulic or electric motor. Off-road or mobile equipment used in construction, forestry, or material handling typically use either a hydraulic-driven or DC electric-driven fan motors. Industrial equipment such as Hydraulic Power Units (HPU) use AC electric-driven motors to drive the fans. Cooler manufacturers offer a lot of motor configurations, voltages, and displacements to fit various applications. For instance, Parker offers a variety of air-oil coolers with AC, DC, hydraulic fluid, and engine driven fans.
Cooler manufacturers offer a lot of motor configurations, voltages and displacements to fit various applications. For instance, Parker offers a variety of air-oil coolers with AC, DC, hydraulic fluid and engine driven fans. Parker’s two most popular air-oil coolers are the ULDC Series (DC fan motor) and the ULAC Series (AC fan motor).
How water-oil coolers work – shell and tube design
Water-oil coolers remove heat from oil by using a second fluid (typically water). For more than 50 years, shell-and-tube oil coolers have been an industry mainstay when considering water-oil coolers. However, newer designs have been developed that increase efficiency while providing an equivalent heat-transfer surface in a smaller package at a reduced cost.
Shell-and-tube (bare tube) coolers have an outer flanged shell with end bonnets appropriately sealed to each shell end. Inside, a precise pattern of tubing runs the length of the shell and terminates in the endplates. Tube ends are fastened to the endplates, which seal each end of the shell. Cool water flows through the tubes while hot oil flows around the tubes within the shell. The tubes run through several baffle plates that provide structural rigidity and create a maze through which the hot fluid must traverse. This maze created by the baffles lengthens the path the hot oil must flow through. This elongated path increases the amount of heat transfer from the hot fluid to the water by forcing the hot fluid to travel around the tubes for a longer period of time.
As mentioned above, there are shell-and-tube designs in the market now that mechanically add fins to the external surface area of the internal tubes, which increases heat transfer and efficiency. Parker does offer this type of high-efficiency “hybrid” design in the ST Cooler Series. The way the hybrid design works is that the fins add surface area and improve heat transfer, letting the overall size be smaller than standard shell-and-tube exchangers without fins on the tubes (bare-tube). However, due to the increased time the hot fluid has to traverse the interior of the cooler, the pressure drop can be higher than shell-and-tube coolers without the increased flow path created by the baffles.
How water-oil coolers work – brazed plate design
Another type of water-oil cooler is the brazed-plate style. In this cooler design, heat-transfer surfaces are a series of stainless-steel plates, each stamped with a corrugated pattern for strength, efficiency, and resistance to fouling by creating turbulence in the flow of both fluids. The number and design of the plates varies depending on the desired heat-transfer capacity.
Plates are stacked with thin sheets of copper or nickel between each plate. The plate pack, endplates, and connections are then brazed in a vacuum furnace to join the plates at the edges and all contact points. This design can be used with several different types of inlet and outlet connections.
Brazed-plate coolers are compact, rugged and provide high-heat transfer capacities. They hold approximately one-eighth of the liquid volume of a thermally comparable shell-and-tube cooler. Their stainless-steel construction permits flow velocities up to 20 feet per second. Higher velocities, combined with turbulent flow, provide heat transfer at three to five times the rate of shell-and-tube coolers. A good example of the increased horsepower is Parker’s OAW Series that offers up to 275 horsepower of cooling at an entering temperature difference of 60°F, based on a 2:1 water flow. The higher heat transfer rate requires less heat-transferring surface area for a given capacity.
Due to their compact construction, brazed-plate coolers are ideal when space and size are design requirements. One drawback of using a brazed plate cooler is that there can be higher pressure drops when compared to an equivalent shell-and-tube design. In addition, tests prove brazed-plate designs handle particles up to 1-mm in diameter without issue. Filters or strainers should be used if larger particles will be encountered. Due to their construction, brazed-plate coolers require chemical, rather than mechanical, cleaning.
ROI of coolers
When properly specifying the right cooler into a hydraulic system, a system will maintain the correct working temperature, which yields numerous economic and environmental benefits, including:
Given the many variables involved when specifying coolers, it is always best to directly contact a cooler supplier such as Parker, with any questions you have. Manufacturers will have additional resources that you can use in the selection process, including specialized sizing software and testing equipment like wind tunnels and cooler design simulation software. Lastly, it is important to take advantage of and rely on your manufacturer’s expertise and available resources to ensure you successfully size and implement the best cooler for your application. To view Parker’s wide range of coolers, visit www.parker.com/ACD.
This article was contributed by Francis C. Gradisher Jr., product marketing manager - KleenVent & Coolers, Parker Hannifin's Accumulator and Cooler Division.
How to Specify the Proper Sized Heat Exchanger for Your Hydraulic System
2 Jul 2020
Prevention is better than a cure. In coal mining, these words offer particularly good guidance. Underground mining presents numerous hazards ranging from structural collapses, flooding and explosions. The tremendous amount of dust generated by activities in a coal mine creates breathing-related problems for workers as well as maintenance issues for machinery. Dust can also create a potentially explosive environment. Injuries and deaths occur every year either from accidents or health issues caused by exposure to coal dust. Mining companies can dramatically reduce these risks by applying rigorous dust suppression safety measures.
This blog investigates dust suppression methods and evaluates preventative versus corrective techniques that can effectively be used to suppress dust in underground coal mines, reducing the risk to workers and equipment.
Coal dust is a known carcinogen that causes miners’ lung disease (pneumoconiosis). Dust in the atmosphere can also create an ignition hazard when mixed with gas. Coal dust buildup is often a root cause of premature maintenance and failure of mining equipment. To this end, preventative suppression is critical.
There are a variety of ways to suppress dust in coal mines that offer a varying degree of effectiveness and efficiency. The most common methods are:
Bag filter system uses fans to circulate the air and trap the solids in a bag. However, this type of system is maintenance-intensive and requires bag filter change-outs — which is not conducive to work in an underground mine.
Dry fog system requires electricity, making it impractical for work below ground level.
Water is an ideal solution because it takes advantage of the mine's existing water supply, forming it into a spray to suppress the dust as soon as it is generated at the coal extraction point and all other areas where dust is generated.
Preventative vs. corrective dust suppression using water Preventative dust suppression
Logically, if a problem can be prevented from happening, then the time and cost of fixing it can be saved. Preventing dust from becoming airborne is critical in dust suppression. Three important elements to successful preventative suppression using water include:
Control pertains to how the water is controlled. It may be controlled by the presence of coal on the conveyor or by the belt’s motion. In either case, the water is isolated before entering the system.
Filter technology is used to remove contaminants from the water to assure reliable system operation.
Spray refers to a predetermined volume and pattern in which the water is delivered to the coal before the dust is generated.
The figure below shows a typical belt conveyor transfer point dust suppression system has two options: paddle valve (A) or belt-driven valve (B). Both are designed to operate only when there is coal on the conveyor.
Corrective or symptomatic dust control is implemented after the dust is created and is more challenging than preventative dust control. Dust particles come in a range of sizes with some as small as 10 µm which is invisible to the human eye. These small particles are the most dangerous to workers and equipment because they can remain airborne for long periods of time and eventually find their way into miners’ lungs, onto and into machinery as well as outside of the mine itself. Small particles are also the most difficult to remove from the atmosphere. Airborne coal dust can be addressed correctively using sprays. The principal is that the dust agglomerates with the water, causing it to fall under gravity. However, if the water droplets are too large, then the airborne dust particles are just moved around, resulting in very little dust being removed. To effectively remove the dust, the water droplets and dust particles must be the same size. Hence, the design of the spray head is of great importance. With preventative suppression, the size of the particle is less important.
Dust suppression in Columbia | case study
Parker Conflow, a leader in the industry, works continuously with mining companies and equipment manufacturers to enhance products for preventative dust suppression. In one case, at CI Milpa in Colombia, a manufacturer of metallurgical coal, Parker Conflow engineers designed two dust suppression systems for a mine as well as a fire suppression system on a roadway.
“We are focused on continually improving the efficiency and safety of our production sites and the Parker Conflow systems are an important part of this. We chose to work with Parker Conflow, because of the company’s expertise in the manufacture and installation of dust and fire suppression systems and are very pleased with the result.”
— David Fernando Jaimes Mojica, CI Milpa
Preventive coal dust suppression is vital to ensuring the health and safety of workers and protecting mining equipment from costly downtime and failure. For over 60 years, Parker Conflow has been providing dust suppression, fire suppression and water control equipment and services that help protect workers in the coal mining industry worldwide.
After more than a century of experience serving our customers, Parker is often called to the table for the collaborations that help to solve the most complex engineering challenges. We help them bring their ideas to light. We are a trusted partner, working alongside our customers to enable technology breakthroughs that change the world for the better.
This blog was contributed by Gary Wain, product manager, Parker Conflow.
2 Jul 2020
Will additive manufacturing (3D printing) replace all traditional, long-established manufacturing methods? Not any time in the foreseeable future. It may take a small bite out of some methods, but the real play is in enhancing the capabilities and possibilities for the processes that we use every day.
Additive manufacturing enables many avenues, but many people only know or tend to focus on a few. With seven technical families (ASTM F42) and many “sub” families or technologies within, there are lots of different ways to grow parts. We are using many of these different methods to help our operations in all three of the business realms: Prototype, Indirect Manufacturing, End-Use Production. Consider the following possibilities to find your business’s winning combination of traditional and additive manufacturing.
Of course, there are the well-known avenues such as display parts, checks for form, fit and function, and sales/marketing demos, but there is so much more to keep in mind with prototyping. Consider clear parts for fluid flow or level studies, even on dynos. How about running a weaker plastic version of your new design through your manufacturing systems to look for interferences or accessibility? For complex, multi-part assembly operations, create a printed “buck” for Design for Assembly (DFA) activities to find the issues requiring redesign. Does anyone ever have actual parts to design dunnage or lift assist tooling at the necessary time? And of course, if waiting for components to run validation tests, bridge parts can be printed and used until production parts are available. Printing prototypes can quickly provide the opportunity for many design iterations and the Design of Experiments (DoE), enabling better optimization and higher quality products.
Indirect manufacturing realm
This realm is all about manufacturing optimization and flexibility, but custom tooling, fixtures, and gauges are just the start. Internally ported tools or robotic end effectors that eliminate external piping or wiring are just as valuable. Conformally cooled injection molding tools create higher quality at faster cycle times. How about conformal machining or shipping fixtures for those hard to hold parts? An additive can even print compound curved paint stencils.
For castings, why spend money on tooling until it becomes a cost-effective solution and the design is fixed? Use sand castings--print the molds and cores out of the sand. As the volumes increase, tool the big, simple parts and use “hybrid” mold sets. Even in high rate production, very complex internal cores can still be printed at an advantage. Investment castings offer similar opportunities. The sacrificial patterns can be printed out of many different materials and burned/melted out during the process. The flexibility of printing molds or patterns also enables optimization through the Design of Experiments (DoE).
This is where most companies want to focus but is the most difficult realm especially if you need to certify with the FAA, FDA, or other authorities. There are great opportunities to optimize saleable items using additive manufacturing technologies. Combining parts eliminates machining, inventory, part numbers, and their supply chain, as well as joints which may leak or fatigue — not to mention fasteners. Printing frees up design constraints to use curved and non-round passages, embedded features, “designer” or even blended materials and unique geometry. The products can take advantage of new design technologies like topology optimization in which the computer provides optimal variations for stress, heat transfer, stiffness, flow path, and other important characteristics at minimal weight. Getting to production with additive manufacturing can give your products a distinct advantage.
Additive manufacturing- a single tool in your toolbox
Additive manufacturing is only one tool in your toolbox but is advantageous for many things. Speed, turn-around, and flexibility make it the choice for things like one-off obsolete parts or broken machine details. But remember: just because you can, doesn’t mean you should. There are many factors and traditional manufacturing still has significant advantages in many areas. Remember to consider all the many Additive Manufacturing technologies. Choosing the correct method for the application is extremely important to obtain the desired results.
Will Additive Manufacturing replace traditional like a one-size-fits-all application? Not any time in the foreseeable future. But it does add capabilities and offers many more options to traditional manufacturing. Investigate and choose the right combinations of traditional and additive manufacturing, and watch great things happen to your organization’s quality, delivery, and cost!
As the global leader in motion and control technologies, we play a pivotal role in applications that change our world. Our broad and diverse range of hydraulics, pneumatics, electromechanical, filtration, process control, climate control, fluid and gas handling, and engineered materials technologies support advancements in a wide range of aerospace, industrial and mobile equipment applications. As we look to the future, changes in how people live, developments in technology, and dynamic markets depend on a partner that advances modern progress. Parker is that partner. Download our Leading with Purpose book to learn more.
Article contributed by Paul Susalla, corporate manufacturing technology advancement director, Parker Hannifin. Originally published in Manufacturing Technology Insights Digital Magazine.
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1 Jul 2020