Project Number: P13656

Transcription

1 Multidisciplinary Senior Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York Project Number: P13656 AGITATOR REDESIGN FOR CORROSIVE ENVIRONMENT Kate Karauda Mechanical Engineering Luigi Abbate Chemical Engineering William Fritzinger Mechanical Engineering Peter Torab Mechanical Engineering ABSTRACT The purpose of the following paper is to introduce the Senior Design Project completed by Team P13656 during the fall of 2012 and spring of The goal of the project was to select, optimize, and implement and off-the-shelf ultrasonic cleaning unit to replace a mechanical agitation system used by the customer: Coating Technology Inc. This new ultrasonic cleaning system was chosen for its potential to significantly reduce the time required to complete a coating removal process, as well as its higher reliability when compared with mechanical agitation design concepts operating in a corrosive environment. Optimal operating conditions for were determined for the ultrasonic unit prior to its implementation. Also, the customer was provided with a set of operating instructions and future steps which would further assist the customer in the introduction of the new process. INTRODUCTION 1) Customer Requirements & Specifications: While working with the customer during the initial stages of the design process, the team was provided with a set of specifications for the parts used by the customer. These parts consisted of two honeycomb extrusion dies with diameters of 15 and 8 inches respectively. The tank size used by the customer for the setup was 36 x 40 x 37.5 inches for a double size bath and 22 x 24 x 35 inches for a single size bath. With that setup in place, the time required to strip the parts was 6 days. The customer requested that the turn-around time be lowered and the maintenance time (about every year) as well as failure time of the agitation unit (about 5 years) be increased. 2) Initial Setup: Initially, the team was presented with a mechanical agitator that would agitate the parts in the corrosive bath and thus increase the speed and intensity of the stripping process. The initial setup consisted of the following items: - Gearbox, - Wash-down motor, - Drive gear, - Bushings, - Crank arms, - Gearbox shaft, - Part basket, - Mounting Bracket, - Tank.

2 Proceedings of the Multidisciplinary Senior Design Conference Page 2 Figure 1: Initial Setup. The team received a motor and a gearbox for disassembly and analysis to determine the failure modes. It was found that the mechanical setup was deficient in several respects: - Lack of resistance to the corrosive effects of the bath (see Figure 1). o Corrosion of the crank shaft assembly due to bath vapors, o Gearbox oil seal degradation, o Motor coil corrosion, o Bushing failure due to corrosion. - Poor mechanical design -- significant evidence of excessive wear was discovered in the gearbox due to a lack of maintenance, lubrication, and a design that placed a large amount of stress on the gearbox. This excessive wear was also noticed in other elements of the setup and the customer confirmed that the time between mechanical failures is less than ideal. Failure modes included: o Shearing of gearbox drive gear teeth due to jerk caused by wear at the crankshaft keyway, o Gearbox shaft keyway failures, slop is introduced over time due to loading, o Crank arm bolt failures. - Gearbox oil loss due to seal degradation; Figure 2: Wear & Tear: Motor Coil Corrosion. Project P13656

3 Proceedings of the Multi-Disciplinary Senior Design Conference Page 3 Figure 3: Wear & Tear: Stripping of Gearbox Drive Gear. - Safety concerns -- since the initial setup included an open tank with the corrosive bath inside and the moving parts suspended above the tank, employees in charge of switching and cleaning the parts were exposed to the corrosive bath as well as the moving parts of the agitator. This exposure to both the corrosive bath and the multiple pinch points on the mechanical agitator posed a safety concern. Figure 4: Initial Setup Safety. - Maintenance -- the initial setup, due to the use of many mechanical components as well as moving parts, required more maintenance than the customer was capable of easily providing. As a result, the lifetimes of parts were compromised by both the jerking loads and corrosion and needed frequent replacement.

4 Proceedings of the Multidisciplinary Senior Design Conference Page 4 PROCESS After the initial design process and analysis of the mechanical agitation system designed by the customer, several ideas were laid out and considered to determine which would best satisfy the customer. However, given the constraints, the team chose to move away from redesigning the agitation system currently in place. Instead, an alternative cleaning system, the ultrasonic cleaning system, was chosen to replace the mechanical setup due to the following: - Significant decrease in cycle time, - Increased safety: o Containment of all chemical vapors, o Lack of moving parts, o Closed of system, - Significant decrease in required maintenance, - Savings in the amount of solution necessary for the stripping process, - The unit s versatility and ability to be adapted to different processes running in the factory, - Higher efficiency when compared to conventional methods in removal of coating, - Increased lifespan of components than those cleaned by other methods. The improved surface finish reduces wear and damaging friction. - Reduced cost of materials since fewer parts have to be rejected through inefficient or damaging cleaning, - Ability to reach into small crevices and remove surface soils effectively due to inherently small size of the cavitation jet and relatively high energy, - Despite the high capital costs, reduced solvent expenses pay for a system in a short period of time. Although presenting a high potential in current a future applications, several concerns were presented to the team while considering the ultrasonic cleaning unit: - Cavitation erosion: o Loss of surface material due to microscopic bubble implosion (however, the simultaneous processes of surface cleaning and of surface erosion allow the optimization of parametric settings to maximize the cleaning efficiency, while minimizing the level of erosion damage) - Need for testing to obtain optimum combination of cleaning solution concentration and cavitation level: o Process dependent upon many controllable factors, o Optimal operating conditions have to be defined. TEST PLAN a) Variable Testing: The purpose of this testing was to establish the correlation between the temperature, ultrasonic frequency and the rate at which the coating was being removed from the surface of the samples using the ultrasonic technology. A small scale ultrasonic unit was used to determine the impact of time and temperature on stripping rate. The testing was then continued in a large scale ultrasonic tank to show a 100% increase in strip rate when compared with current process at same 140 F process temperature. Several different temperature ranges as well as different power setting on the unit were used to give a better understanding of the process and variables with the most impact on the stripping rate. b) Validation Testing: The goal of this testing was to determine the amount of time required to strip TiCN coating from the surface of 304 stainless steel test tabs in the SevereClean SC-11 ultrasonic cleaner using a hydrogen peroxide cleaning solution. The ultrasonic cleaner was to be tested in 4 different configurations of temperature and power level. Temperature was regulated using an external heating and cooling unit. After 1 hour of each process, all samples were checked visually every 15 minutes. Samples that appeared to be fully stripped were tested using the CTI method to detect any residual coating. c) Solution Conductivity and Absorbance: The purpose of this testing was to show correlation between the absorbance of the solution used during the variable testing as well as the Ti concentration remaining. The solution in which the samples were tested during the variable testing was collected and then run through chemical engineering equipment to establish the baseline for the remaining concentration of Ti and the absorbance. Project P13656

5 Proceedings of the Multi-Disciplinary Senior Design Conference Page 5 d) Residual Coating Testing: The purpose of this testing was to verify whether the samples previously tested during the validation and variable testing have been stripped completely of the TiCN coating. All samples were submitted to treatment with a 17% nitric acid solution, which was then mixed with a small amount of peroxide solution. Any residual TiCN would have caused a change in color of the solution from clear to yellow, indicating that the sample had not yet been stripped completely. e) Peroxide Titration Testing: Several samples of the peroxide solution used to strip the variable and validation test samples were tested for the remaining active peroxide concentration after the variable and validation testing was completed. The purpose of the test was to explore the rate at which the peroxide disintegrates from the solution. Recommendation were planned to be made to the customer on how often the bath should be replaced with fresh solution based on the test results. RESULTS AND DISCUSSION After completing all of the aforementioned testing the following results were found: a) Surface Coating Removal: Temperature has the biggest influence on the stripping rate, although the use of ultrasonics significantly decreases the stripping time, especially at elevated temperatures. It was also found that the ultrasonics will cause the temperature to increase steadily; therefore cooling of the hydrogen peroxide bath is required. Table 1: Surface Coating Removal Conditions. Group Samples Power Level Set Temperature % 100F % 140F % 100F % 140F 5 (Control) % (SONICS OFF) 140F Figure 5: Surface Coating Removal Stripping Rate.

6 Proceedings of the Multidisciplinary Senior Design Conference Page 6 b) Mock Die Coating Removal: After the Surface Coating Removal test results were confirmed, mock dies were also tested in the ultrasonic unit. Mock dies were furnished with 1/16 in blind holes to determine the effectiveness of the ultrasonice on the holes in the extrusion dies. After the test it was found that the larger mass of the mock dies (when compard with the mass of the 1x1 in tabs tested in earlier testing) did not seem to have a significant influence on the coating removal rate. The ultrasonics were also powerful enough to completely strip inside the blind holes. Figure 6: Mock Dies Coating Removal Results. Project P13656

7 Proceedings of the Multi-Disciplinary Senior Design Conference Page 7 CONCLUSIONS AND RECOMMENDATIONS Overall, the testing performed yielded expected results. When compared to the control group (still, 140 F) ultrasonics decrease the stripping time by half of the original results. They are also much safer and more efficient to use than the previous, mechanical setup. Ultrasonics have proved powerful enough to clean even the blind holes within the time that the surface was also cleaned which further increases their efficiency. The team recommends that an indirect method of contact between the tank and the solution be used. The tank of the ultrasonic unit should be filled with water. Later, glass or ceramic containers large enough to accommodate the parts in need of stripping, as well as the stripping solution, should be submerged in the tank. This is due to several reasons: - Corrosive nature of the bath used by the customer to strip titanium coating from the honeycomb extrusion dies. If no contact occurs between the tank and the stripping solution, the lifetime of the tank is extended and the risk of tank corrosion is minimized. - Exothermic nature of the solution used by the customer. Since the unit has to contain enough liquid that its surface is only 2 inches from the cover of the unit if the solution were to enter its exothermic region and evaporate the unit itself would sustain significant damage to the transducers and thus become inoperable. - Ergonomics -- only enough stripping solution is required to fill a glass/ ceramic container versus a tank itself. This will result as a saving to the customer since less solution will be used. After performing several tests the team acknowledged that more information can be collected in the future, based on the needs of the customer as well as the direction of further development of the process involved with the ultrasonic unit. Some steps that should be considered, given that time and resources allow it, would be: - Performing further ultrasonic testing with a larger sample size for better accuracy, - Determining the impact of ultrasonics on part substrate over the part s lifetime, - Using of a heating/ cooling system to maintain precise operating temperatures. REFERENCES N/A ACKNOWLEDGMENTS 1. Rochester Institute of Technology: Eric Peterson, General Manager Matt Smitley, Plant Manager 2. Rochester Institute of Technology: Prof. Edward Hanzlik, Faculty Guide Dr. Mario Gomez, Faculty Champion Dr. Patricia Taboada-Serrano Dr. Christian Richter Dr. Surendra Gupta Paul Gregorius Robert Kraynik MSD Staff 3. Severe Clean Ultrasonics: Robb Jones, Product Manager Rich Farr, Development Engineer 4. Dayton Coating Technologies: Robbie