Peter J. Bankert Market Development Manager Graco Inc. Farmington Hills, Michigan

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1 NEW PANT CRCUUTON PUMP TECHNOLOGY Peter J. Bankert Market Development Manager Graco nc. Farmington Hills, Michigan Presented at: "Finishing '93 Conference and Exposition" October 25-28, 1993 Dr. Albert B. Sabin Convention Center Cincinnati, Ohio

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3 ntroduction Paint circulation is one of the most demanding pumping applications in the industry. Many new high solids paints require constant flow to eliminate settling. n fact, automotive paints generally require a fluid velocity of 60 Wmin. to eliminate settling. The paint circulation pump must be capable of operating continuously - 24 hours per day, seven days a week, 52 weeks a year. This pump literally must operate 8760 hours per year to keep paint from settling in pipes and hoses. Continuous movement of paint through the circulation system can cause paint shear degradation. This paper will review laboratory results of this shear degradation and suggest ways to minimize it. Paint Shear Degradation Continuous pumping of paint can cause shear degradation. degradation can result in: This ) ncrease in paint temperature with a resultant reduction in viscosity, evaporation of solvents, and possible thermal degradation. 2) Breakdown in paint rheology which can result in lower paint viscosity. 3) Degradation of metallic flakes which can cause a darkening of the color of the paint. Metallic flake degradation has been recognized by the automotive industry as a cause of color match problems. Additional shear degradation problems are now associated with some of the newer paint technologies, such as waterborne paint. Many times these problems do not arise until new paint formulations are field tested - and even then they may not become readily apparent due to the different shear levels of different systems. There is no single parameter to measure shear degradation. Every paint is different and it will have a different reaction to the shear from the handling equipment. The purpose of this paper is not to evaluate different paints, or

4 to describe what happens to the paint under high shear. The purpose of this paper is to evaluate equipment and system designs which may reduce shear. - Laboratory tests were performed in order to evaluate various equipment configurations. The paint chosen for all equipment tests is an automotive topcoat with large metallic flakes. A single paint was used in all tests to simplify the test design and have a common baseline for all test results. The key parameter of evaluation in the tests is the colorimeter readings - in particular the near specular delta L parameter which is a measurement of lightness of the coating. This parameter is chosen because previous lab tests and field reports show this to be a consistent measurement of metallic flake damage due to shear degradation. Sources of Shear Dearadation Previous lab tests have isolated three primary causes of shear degradation: 1) Back Pressure Requlators (BPR): These devices have small orifices which are used to create large pressure drops. These regulators are also in the circulation loop. t is not uncommon for paint to go through the BPR times before it is sprayed. Fluid regulators which are located at the spray device also have small orifices and high shear, but the paint only goes through this regulator once. Other fluid regulators in the circulation system (wall regulators in 3-pipe systems) are also primary causes of degradation because they are "multiple pass" reg u ators. 2) Pumps: This is an obvious source of paint degradation due to its mechanical operation, energy input, and objective of increasing paint pressure. t is expected that different pump types have different shea; degradation eve s. 3) System Desian: The circulation system design translates the system ~~ needs (flow, velocity, paint demand at spray guns) into equipment specifications (pump pressure, BPR pressure, pipe diameters). The system designer can reduce paint degradation by reducing paint pressures and choosing low shear equipment.

5 Desians to Minimize Shear Degradation Equipment: The selection of low shear fluid regulators and low shear pumps can reduce shear degradation. Low shear regulators create pressure drops through special designed orifices which reduce fluid velocity and fluid shear. Most fluid regulators achieve pressure drop with a ball and seat orifice. n this regulator the paint is squeezed through the tiny opening between the ball and seat. n this type of regulator, the fluid velocities can reach 10,000 ft/min. A low shear regulator has a more laminar fluid path and achieves similar pressure drops at a greatly reduced fluid velocity. These low shear regulators are used by many automotive manufacturers to reduce paint degradation. System Desian: New system designs can reduce paint degradation. One system in particular - Smart njection - has been shown to reduce paint degradation. This concept reduces degradation by eliminating the BPR, and by reducing pump pressure requirements. n order to understand Smart njection, it is necessary to understand how a traditional pumping system works. Diagram shows a traditional circulation system with a pump taking paint from a mix tank and pressurizing the paint to 200 PS. The paint flows clockwise around the loop and retums to the BPR. The BPR pressure in this example is 100 PS on the upstream side. Downstream of the BPR is the mix tank which is at 0 PS (atmospheric). Every cycle through the system, the paint will go from 100 PS to 0 to 200 PS as it goes through the BPR to the mix tank and then through the pump. Paint in a circulation system would make this cycle on the average of 3 times an hour or 72 times per day. Diagram is a schematic of a Smart njection System. Notice that the BPR is removed, and the pressurized paint is fed directly into a circulation pump. The circulation loop is always pressurized, it never returns to the atmospheric mix tank. New paint is supplied to the pressurized loop with an injector pump. This pump must be a positive displacement, variable speed pump which will stall at a set pressure. n the example shown, this pump injects paint into the circulation loop at the outlet of the circ pump. The injector pump sets the system pressure, and is stalled until paint leaves the loop. As soon as

6 ~ paint leaves the loop through a spray gun, the injector pump senses a reduced pressure in the loop and cycles on to make up for the lost paint. The advantage of smart injection includes: Reduced Paint Deqradation: This is directly due to the elimination of the BPR and reducing the circulating pumps pressure requirement from 200 PS (i.e ) to 100 PS (i.e ). Reduced Pump Enerw: Again this is a direct benefit of not 'Yhrowing away" the energy in the paint at the BPR. n the example shown, the BPR pressure "saved" is 100 PS. This is 50% of the pump pressure of 200 PS, and the energy savings is about 50%. Paint Usaqe Reporting: The injector pump only supplies new paint to the loop when paint is used. A flow meter on this line, or a "smart" pump can measure flow at this point and report paint usage. Back-up Pump: With two pumps in a system it is possible to provide alternate piping and valves to enable the system to continue operating if one pump were to fail. Reduced Maintenance: Pump wear and maintenance is directly related to pump output. The pump energy savings is a direct indicator of reduced output, and should relate directly to reduced maintenance. Reduced Solvent Loss/Temperature Loss: The mix tank is often the place where circulated paint can lose temperature, lose solvents, and become aerated. Eliminating the mix tank from the circulation loop reduces these risks. Summary: Lab experiments have been performed by Graco to document the shear ~~ degradation of regulators, pumps and the benefits of the Smart njections System. The results were not available for inclusion in this written report, but will be presented in the October 1993 presentation.

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