Simple Solutions That Work! Issue 10

CHRIS DOERSCHLAG Consultant PALMER MANUFACTURING & SUPPLY, INC. – KLEIN DIVISION ARTICLE TAKEAWAYS: • Troubleshooting Guide • Difference between Dilute Phase and Dense Phase conveying. MAINTENANCE & TROUBLESHOOTING OF PNEUMATIC CONVEYING SYSTEMS FOR SAND IN A FOUNDRY N o doubt, minimizing maintenance costs ranks near the top priority when planning new foundry equipment investments. Maintenance is an integral function of the foundry equipment; therefore, the foundry engineer can greatly influence and predict such costs at the time a particular piece of equipment is selected. The more that is known about how a system functions (and the various factors influencing its operation), before the final decision to made to purchase is made, the better the chances of controlling future maintenance costs and loss of production. Typical cases where this specifically applies are in the pneumatic conveying systems for transferring sand in a foundry. Often these systems are tucked away in a corner or the basement of the plant and the only time attention is paid to its operation is when the system has stopped to operate. Ideally decisions to purchase should be based on understanding the difference in possible maintenance requirements for each option. Pneumatic conveying systems can generally be divided into two broad categories. Dilute Phase and Dense Phase conveying. Dilute Phase conveying works by vacuum or low pressure air of up to 20 psig and velocities in the pipeline of 4,000 FPM and higher, while Dense Phase works by medium pressure air of 10 – 90 psig and pipeline velocities of 450 – 2,500 FPM. The concept of dilute and dense phase systems in pneumatic conveying goes back 130 years. However, what works in one industry may not necessarily be applicable for another industry and when it comes to moving sand in a foundry, dilute and dense phase systems have simply been copied from other industries for foundry applications. As experience has shown, however, that these are not necessarily the best solutions! The terms “dilute” and “dense” refer to the material to air ratio (loading ratio) of the respective conveying system. In a Dilute Phase system the loading ratio is only about 0.06 to 0.3 pounds of material per cubic foot of air. High velocity air is necessary to entrain the particles and while in suspension bounces them along the pipeline to the receiver. It’s like a hurricane in a pipe, and only powders and “soft” materials can survive such a trip. Dilute Phase is definitely not a good choice for moving sand pneumatically. Most Dense Phase systems have a higher loading ratio of 40