Welcome to the initial post of the Interface Devices, Inc. Technoblog. We have created this to keep current with our valued customers and distributors. Entries should be posted on a weekly basis and cover any company news, product development, changes to our distribution network as well as an ‘Application of the Week’ describing a particular system or interesting application of our products. Feedback to any of these posts is welcome.
Application of the Week: Air Driven Pump for Underwater Plastic Pelletizer
Have you ever wondered where all the millions of pounds of plastic used every year comes from? We’ve all seen footage of the huge furnaces, forges and buckets of molten metal for the production of iron and steel, but have you seen the process for manufacturing raw plastic materials?
The bulk of commodity plastic used today is a polyolefin; specifically some form of polyethylene or polypropylene. These materials are produced in large petrochemical plants in a process that converts a hydrocarbon based material such as natural gas into ethylene or propylene gas. This in turn is “polymerized” in a reaction process creating the raw polyolefin usually in a fine powder form. The conversion of this somewhat volatile and unstable raw product into a salable bulk commodity product requires the powder to be melted down and blended with additives to enhance the properties and protect the raw material from things like UV rays. Yes, plastic does degrade in the presence of sunlight without these additives.
The final stage of this process converts the molten plastic into small pellets. The machinery to accomplish this is called an Underwater Pelletizer. Molten plastic is pumped through a large heated die with thousands of holes. On the other side of the die, water is circulated to freeze the polymer as it exits the die holes. Running on the surface of the die plate is a ring with multiple knives spinning in the water that cuts the just frozen plastic into pellets. The pellets are swept away by the flowing water and sent to a water separator. The pellets are then transferred to large silos or rail cars to await transport to their final destination.
How does this tie together with an IDI product? The knives that are spinning underwater are held in place with two hydraulic cylinders. As the knives wear out they must continue to feed themselves in to maintain pellet uniformity. IDI developed a system to make this happen. A P-Series Air Driven Liquid Pump with servo-pressure control hydraulic valves along with pressure transducers precisely control the force of the knives running on the die to ensure pellet quality while maximizing knife life. This design also allows the flexibility to automatically alter these forces that change with different grades of plastic and different production rates. The P Series Pump and servo valve are controlled by a very sophisticated control system that also monitors and controls all stages of the production process.
Modern plants produce plastic pellets at a rate in excess of 100,000 lbs/hr (40,000 kg/hr) and operate 24/7/365, so reliability is a primary concern. The IDI Air Driven Pump solution has proven to live up to this by maximizing knife life while providing a critical function to maintain quality.
Comments/Questions addressed to Mike Hotchkiss at +203-878-4648 or mhotchkiss@interfacedevices.com