Gear Metering Pump Provides Manufacturer Continuous Pulse-Free Process
A global manufacturer of scented plastic garbage bags was looking for an alternative to the use of pre-scented plastic pellets. A serendipitous encounter at a tradeshow led them to a precision gear metering pump solution that gave them accuracy and consistency at the low flow rates required, while also reducing their costs and improving worker health.
Seeking an Alternative for Costly Pre-Scented Plastic Pellets
A global manufacturer of scented plastic garbage bags was looking for an alternative to the use of pre-scented plastic pellets, which required a dedicated silo for each of the 20 available fragrances. The pellets are pneumatically conveyed to each silo from either tanker trucks or rail cars and the manufacturer was experiencing logistical issues associated with keeping the silos filled. They also had to carry high costs for maintaining the inventory of the pre-scented pellets.
In addition, the heavily concentrated scents had been causing health concerns for the workers who complained of headaches. To mitigate this issue, each extruder line was fitted with a vacuum exhaust hood to expel the fumes to the outdoors. On occasion, these emissions led to complaints from neighbors and citations from the United States Environmental Protection Agency.
The company was seeking a way to use plain plastic pellets and apply scented oil directly to the plastic sheet immediately after the extrusion process to reduce costs, logistical challenges, and energy use. They had tried to build such a system in-house but had struggled to achieve accuracy and consistency at the low flow rates they required. They decided to seek a pump-based solution that could directly spray fragrance on the warm melted sheet plastic because the in-house solution could not meet rigorous quality control standards requiring the spray-on scent to exactly match that of pre-scented pellets.
Finding a Solution on a Tradeshow Floor
Design engineers from the plastic bag manufacturer attending the PackExpo show observed a working demonstration of precision gear metering pumps made by Zenith and asked application experts if the pumps might be a fit with their application. After collecting information on the application, an area manager for the pump manufacturer with extensive experience in dosing and blending systems visited the plant to get a firsthand view of current operations and gather additional information.
Working with the pump manufacturer’s design group they developed a system solution using a Zenith B-9000 Series rotary positive displacement pump specifically designed for single-stream chemical duty applications. The pump features an accurate, repeatable, pulse-free flow in a compact design ideal for dosing additives such as colors, flavors, and fragrances.
This type of pump is defined as rotary because the drive shaft is rotated as compared to other types of pumps using a reciprocating motion and is also considered to be a positive displacement type because the displaced volume is constant and does not vary.
Pumping action is achieved by filling the gear teeth spaces and transporting the fluid around the outer diameter of the gears. When the gear teeth mesh, the fluid is displaced and forced to the outlet side of the pump. The flow rate can only be adjusted by increasing or decreasing the speed at which the shaft is rotated. The pump selected offers precision grinding and lapping processes that result in a precision metering instrument, producing precise, pulse-less, and repeatable fluid flow.
The pumps offer extremely tight operating clearances to minimize fluid slip. Manufacturing tolerances on many parts are to +/- 50 millionths of an inch with surface finishes as smooth as four micro inches or better. The pumps are offered with an AC “closed-loop” motor speed controller to maintain 0.1% pump speed accuracy.
The Zenith 9000 series pump is available in 11 sizes with capacities ranging from .003 to 300 GPH. Wetted parts are available in through hardened 440C series stainless steel, specialty treated 316 stainless steel, and high-quality tool steels such as D2, M2, M4, and CPM-M4 to provide good corrosion and abrasion resistance.
The bag manufacturer selected a model with a magnetic drive (mag-drive) sealing option, which can eliminate shaft leakage of fluids, increasing plant safety, and reducing volatile organic compound emissions. The use of a magnetic coupling also eliminates downtime due to mechanical seal failures and eliminates the need for buffer fluids.
New Solution Reduces Costs and Offers Uniform Fragrance Distribution
The Zenith pump system gave the scented bag manufacturer a continuous, pulse-free process, which guarantees equal and uniform fragrance distribution. By adding the scent directly to the bags after leaving the extruder, the plastic bag manufacturer not only eliminated the need to have separate pellet silos for each scent but also eliminated the need to vent the fumes that come from the pellets as they travel from the silos to the extruders.
The manufacturer purchased the first system and after successful trials, ordered six additional systems. Over the past two years, they have purchased more than 30 systems, with plans to order more. The manufacturer is also interested in having Zenith conduct annual field calibrations of each system.
After two years of operation, the manufacturer estimates a yearly savings of approximately $480,000 per skid in operation. With 30 skids now running, the return on investment for each system purchase can be measured in weeks.
To date, there have been no odor complaints since the customer installed the Zenith systems.
Mike Libbey is the Area Sales Manager at CIRCOR. Bob Limper is the Business Development Manager at CIRCOR.