Gear metering technology can improve seal dispensing
Insulating glass manufacturers strive for accuracy, repeatability and consistency in seal dispensing.
Selecting the proper sealant is critically important; how to accurately dispense the material to maximize performance and minimize waste is just as important.
Equipment suppliers offer a variety of pumping systems for insulating glass manufacturing, including piston pumps and spur gear pumps. Understanding pumping methods, sealant characteristics and application requirements helps in selecting the best method to properly pump and accurately dispense materials. Material viscosity, how it cures, application temperature, flow rate, deposition weight, accuracy, continuous or intermittent output, and manual versus robotic application are all essential factors in selecting equipment to maximize performance.
Piston pumps consist of a reciprocating air piston that drives a hydraulic plunger. The action of the plunger, along with check balls within the plunger, causes the pump to pull material in and then discharge it. Piston pumps experience a “wink” or pressure drop when shifting stroke cycles that does not lend itself well to continuous output applications. It can create inaccurate or unrepeatable deposition weights. A compensator or regulator is often used with a piston pump to minimize wink and stabilize hydraulic pressure. Piston pumps can dispense large volumes and can be used with high viscosity materials.
Spur gear pumps use counter-rotating spur gears inside a pump assembly. They have variable pressure and can be used in constant flow applications. They are manufactured to tight tolerances and are excellent for applications requiring accurate deposition weights. The rate of flow is dependent upon the size of gears and speed at which they turn.
For applications requiring extreme accuracy and repeatability, spur gear pumps placed at the dispense head offer superb metering capability. In conjunction with robotic devices, servo-driven, spur-gear pump metering heads can achieve deposition weights as accurate as plus or minus 1 percent. A spur gear pump metering dispense head combines gear metering technology with compact size to provide precision and control in dispensing high-viscosity silicones, butyls, epoxies and hot melt materials.
Viscosity and abrasiveness of sealants play a key role in selection of the pumping system.
Piston pumps handle a wider range of viscosities, from 50 centipoise to 10,000,000 cps, and can handle abrasive materials with their open design, compared with the tight interlocking fingers of a gear pump.
Reduced maintenance for gear pumps
Users believed that spur gear pumps, due to close tolerances of the spur gears, could only handle materials with viscosities fewer than 500,000 cps and that abrasive materials would wear gears prematurely. Recent testing demonstrates that these concerns can be alleviated by pump design and selection of the proper-sized spur gear pump. For extreme materials and applications an optional hardened-steel spur gear pump could be used.
Gear pump systems typically require less maintenance than piston pump systems due to their seal-less design. Piston pumps are under higher pressures than gear pumps, and routinely suffer seal failures and have material seeping out from the pump area. Additionally, compensators and regulators that accompany piston pumps require maintenance and rebuilding.
Gear pumps can help minimize waste of sealant material. Since piston pumps do not meter material, fluctuations in bead size are common, leading to excess material weights, and additional cost if insulating glass units require cleaning due to inconsistent deposition. Spur gear pumps with metering capability can place the proper amount of material exactly where intended. This minimizes waste and saves money.
Specifically with insulating glass, lack of the proper amount of matrix material in the spacer channel can lead to field failures and increased warranty claims. Warranty calls might decrease with gear pump production since the proper amount of material creates a more consistent finished product.
“When I arrived at LBL Windows about a year ago, they were using a piston pump system for the secondary IG seal,” says Viktor Olenin, director of manufacturing for LBL Windows in Troutdale, Ore. “Both from my personal experience and basic industry knowledge, it is generally given that gear pump systems are accommodating of the stop-and-go nature of IG production, as well as being forgiving of possible inconsistencies or changes in adhesive/sealant materials. So, back in May 2007 we installed a Nordson DuraDrum IG bulk melter. Since working through the initial installation and setup, we have enjoyed seeing the consistency of flow and volume associated with gear metering systems.”