THE CLARKSON COMPANY SAVES TIME AND MONEY IMPROVING PIPING VALVE WITH ALGOR'S MECHANICAL EVENT SIMULATION SOFTWARE

Ranging in size from 2 to 20 inches in diameter, the Clarkson Wafer Type Knife-Gate Valve is lighter, thinner and can operate at higher pressure than other knife-gate valves. The Clarkson Company used ALGOR's Mechanical Event Simulation software to simulate the valve in action on a computer, reacting to the severe pressure and temperature of the slurry piping system's flowing materials. This enabled the optimization of the valve's performance in various applications.

December 4, 1998, Pittsburgh, Pennsylvania -- Mining, power and paper companies all over the world require dependable, efficient piping structures to transport newly excavated minerals or pulp stock to processing plants where it is converted to electricity, jewelry, paper and other valuable commodities. The Clarkson Company, a family-owned design and manufacturing company in Sparks, Nevada, revised a major component of these piping systems using Mechanical Event Simulation software by ALGOR, Inc. The redesigned part creates a more efficient piping system that can operate without maintenance interruption, saving miners time and money while maintaining revenue.

The Clarkson Company was able to simulate a knife-gate valve in action on a computer, reacting to the severe pressure and temperature of the piping system's flowing materials. The software provided a comprehensive analysis of the event that allowed Clarkson to modify the material, size and shape of the valve's elastomer seal to optimize its performance in various applications. Conducting this virtual experiment improved the company's valve technology and reduced the length and cost of the design cycle by avoiding weeks of prototype building and testing.

Clarkson's Knife-Gate Valve Reduces Maintenance Time

Mining, power and paper companies use piping systems to transport newly mined minerals, such as gold, copper and coal, or pulp stock to their processing plants. The excavated materials are crushed and suspended in a liquid medium, generically called slurry, for easy flow. An efficient slurry handling system is crucial to timely mineral and pulp processing, which is necessary for fast delivery to a worldwide market.

The slurry flow can be extremely abrasive and corrosive to the hundreds of valves that direct its materials. In mining, the newly crushed ore has a sharp surface, can be extremely hot, and flows quickly, constantly and often at high pressure. A slurry valve must be designed to withstand these severe conditions to minimize maintenance time and replacement costs.

The Clarkson Company has worked to advance metal and mineral processing for over 65 years. Clarkson designs and manufactures knife-gate and control valves that can quickly halt and isolate sections of a slurry flow. Such control is necessary when the slurry must be delayed, inspected or redirected to another location. Mining, power and paper companies all over the world rely upon their equipment, including Newmont Gold Company, Taiwan Power Company and International Paper. About 50 percent of Clarkson's products are exported from the U.S. to almost every continent.

The Clarkson Company created a unique type of slurry valve in the 1970s, the KG Series Knife-Gate Valve. This valve's knife-like steel gate lowers into the slurry flow automatically or manually to create a bubble-tight shutoff seal. When the knife-gate closes, it isolates sections of the slurry piping system from slurry flow in either direction. The valve has two matching, smooth elastomer sleeves that seal against each other when the valve is open, allowing slurry to flow through unobstructed and against both sides of the gate when the valve is closed. The elastomer sleeves resist abrasion and corrosion and cover the valve's metal parts to shield them from rapid wear and subsequent premature failure.

The Clarkson Knife-Gate Valve was a new concept because it replaced conventional metal seats and gate guides with easily replaceable snap-in elastomer sleeves that are more durable, versatile and handle higher pressure and temperature. Conventional metal seats and gate guides fill with hardened slurry and then fail to open or close.

Clarkson customers value the elastomer's long life because each seal costs between $75 and $500 to replace. More important, they lose revenue when they suspend the slurry system for maintenance repairs.

The Clarkson KGD Wafer Type Knife-Gate Valve is the newest in the Knife-Gate Series. Developed in 1991, the Wafer Type Valve is lighter, thinner and can operate at higher pressure, up to 150 psi, than other knife-gate valves. Customers appreciate the manageability of a lightweight, narrow valve that fits into smaller spaces, is quick and easy to maintain and gives them more options when designing their slurry pipe systems. The Wafer Type Valve's dimensions meet a nationwide standard, giving customers greater flexibility when choosing a valve supplier because the valves are interchangeable.

The Clarkson Knife-Gate Valve replaced conventional metal seats and gate guides with easily replaceable snap-in elastomer sleeves that are more durable and handle higher temperature and pressure. Using ALGOR's Mechanical Event Simulation software, the Clarkson Company was able to develop a greater variety of elastomer seals for the Wafer Type Valve Knife-Gate Valve to increase its efficiency in different applications.

Striving for a Better Seal

Clarkson wanted to develop a greater variety of elastomer seals for the Wafer Type Valve to increase the valve's efficiency in different applications. For example, power companies prefer synthetic types of elastomers like neoprene, butyl or viton, which handle high temperatures and corrosive materials, and mining companies prefer elastomers like natural gum rubber for abrasive slurries.

Also, Clarkson had been recommending seals made from various elastomers to customers based on published data and past trial and error in the field. The company wanted to give its customers more scientific suggestions by physically testing the elastomers in a laboratory. But each rubber mold prototype is expensive and takes weeks to produce. Clarkson decided to test virtual prototypes on the computer.

Nick Williams, a project manager in Clarkson's Engineering Services Department, used ALGOR's Accupak/VE Mechanical Event Simulation for Virtual Prototyping with Linear and Nonlinear Analysis software to test different nonlinear elastomer materials for the Wafer Type Valve's seal. "I chose Accupak/VE because it can simulate both mechanical events, like the knife-gate closing and contacting the seal, and physical conditions, like the slurry's heat and pressure. The software predicted how various nonlinear elastomer materials respond to those loading conditions," Williams said.

Accupak/VE combines traditional finite element analysis (FEA) with the physics of time, motion and impact to determine the development and outcome of a linear or nonlinear event. Engineers insert known physical data into the program, like weight and directional movement, but do not need to specify force because stresses in ALGOR's Mechanical Event Simulation are calculated based on the physics operating during the event.

Simulating a Slurry Valve in Action

Clarkson's product development team designed a steel knife-gate model and an elastomer seal model using CoCreate's H.P. Solid Designer CAD software. In preparation for Mechanical Event Simulation, Williams used ALGOR's Houdini product to convert the CAD solid models into one 3-D solid brick finite element model. He inserted contact elements between the elastomer and the steel.

Williams used ALGOR's Merlin Meshing Technology to refine the surface mesh. He specified a coarse mesh in parts of the seal he knew were inconsequential to the load applications and omitted small, irrelevant features. Analyzing fewer elements reduced processing time, but still produced an accurate analysis. Williams later used Houdini to refine the mesh in areas that indicated high stress in the analysis, such as where the sleeve seals against the knife-gate.

Williams set boundary conditions to constrain the seal's four corners, replicating its attachment to the valve body and neighboring pipe flanges. Then he applied a load curve based on previous physical testing data that represented the rise in pressure during a true pipeline event. In additional analyses, he applied pressures specified by the American National Standard Institute (ANSI), which requires that the elastomer in the valve withstand pressure one and one-half times its maximum operating pressure. He also applied prescribed displacement to move the knife-gate, which would cause displacement in the seal.

Laboratory testing of elastomer samples at high temperatures determined the stress-strain curve for each material. Williams then calculated the Mooney-Rivlin values and used them to define the material properties of each elastomer. He utilized the von Mises material model with isotropic hardening for the properties of steel.

Williams created 10 to 20 virtual experiments using the ALGOR software, modifying the elastomer's geometry and material properties after each analysis as necessary. "ALGOR fits into the design phase well because it is so easy to apply different pressures and use different material properties," he said.

ALGOR's Monitor utility tracked the progress of each event simulation making it easy to identify problems during the actual analysis process. "I simulate more models with Accupak/VE software than ever before because I can terminate an analysis immediately if the Monitor utility indicates that the elastomer material will fail in its current conditions," said Williams. "I saved many hours and even days of processing each time this occurred."

The elastomer material's deflection was also considered. Williams had designed holes in the elastomer sleeve to give the elastomer an area in which to deflect. He wanted to be certain that the rubber moved into these areas when the loads were applied.

Using ALGOR's Mechanical Event Simulation software, Project Manager Nick Williams simulated the Wafer Type Valve's knife-gate closing the valve and contacting the elastomer seal. He had to ensure that the elastomer sleeve would deflect into the designated holes.

"Before ALGOR's Mechanical Event Simulation software, we had to design and machine a mold to produce a prototype for each design iteration. Each prototype can cost thousands of dollars and involves weeks of manufacturing," said Williams. Clarkson was able to determine which elastomer candidates had a high probability for success without performing numerous, costly physical tests. The increase in the variety of elastomer materials used in the Wafer Type Valve's seal gave the company a competitive edge in the slurry handling industry and increased customer satisfaction.

"We felt we were compromising important data with limited linear analysis," said Williams. "We are now more comfortable manufacturing a prototype. Plus, we are saving time and have a smaller margin of error."

He also noted that ALGOR's Mechanical Event Simulation results could reveal the need for a new design feature or even an entire product line. When an engineer sees a model in motion, an opportunity otherwise unavailable, he or she may be inspired to create another design improvement or create a completely new design.

Where to Flow From Here?

Williams and Clarkson's product development team are still working to improve the Wafer Type Valve. They continue to study current elastomer options and explore other elastomer materials.

Clarkson Knife-Gate Valves are used in other industries including industrial scrubber systems, wastewater treatment systems and industrial process water systems. The Clarkson Company intends to use ALGOR software to contribute to the advancement of knife-gate and control valves used in all types of slurry handling systems.

"ALGOR FEA with a good solid modeler are two valuable tools in engineering. They will take you on the fast track and substantially reduce the probability of having to do more than one prototype test," said Williams.