PURAFIL AND AEC CALL ON ALGOR AS PART OF PRODUCT IMPROVEMENT PLAN

Purafil, Inc. is one of the leading manufacturers of air purification systems for industrial and high-tech industries. The company's products can be found protecting computers, electronic components and control equipment from potentially corrosive gases and other air-borne impurities.

Major Plan

Recently, Purafil completed a lengthy and comprehensive product improvement plan which was designed to further enhance the reliability and maintenance of its modular filtration cabinets, while reducing vibration-induced noise levels. To assist them in the effort, Purafil retained Applied Engineering Concepts (AEC), a Gainesville, GA based engineering consulting firm, to design and analyze a family of fan support frames.

The team that conducted the analyses: AEC Principal Larry O'Keefe with Purafil Engineers Beth Guler and Rick Gulakowski.

First Model Reality-Based

Larry O'Keefe, AEC Principal Engineer, began the project by creating an Algor FEA model based on an existing Purafil support frame which had undergone vibration testing during its original development. "The data from the development tests were compared to the results of a dynamic analysis of the existing frame," says Mr. O'Keefe. "The test data showed resonant peaks at the motor drive frequency and the fan rotational frequency. The Algor modal analysis results matched the actual vibration test results."

Time History Analysis

"Next, we performed time history runs on the validated model," continues Mr. O'Keefe, "imposing sinusoidal loads at the two critical frequencies on the bottom of the fan to simulate an imbalance situation. This process was repeated with progressively higher loads until the stresses exceeded the strength of the metal in the support frame.

"The analysis results showed maximum stress levels at the same location where additional structure had been required on the existing design during development testing. This further validated our analysis. We now had a reliable model on which to base the new designs."

Time history analysis results visualization from Superview for the new Purafil fan support structure. The analyses were carried out as part of an overall product improvement program by Applied Engineering Concepts of Gainesville, FL.

A Series of Analyses

Working with Purafil Engineering and Design Manager Beth Guler and Design and Service Group Supervisor Rick Gulakowski, Mr. O'Keefe began a series of design variations and analyses. The goals were to allow improved access to fan components, reduce vibration-induced noise levels and provide sufficient strength to meet the worst in-service conditions.

"The derived failure load was used as the basis for analysis of the new designs," says Mr. O'Keefe. "Modal and time history analyses were performed in three axes to simulate a worst-case vibration condition and 10 G static loads were applied in the same axes to simulate transportation and handling loads. In addition to having stresses below the material's allowable yield strength, the new design had to limit deflections in order to maintain the correct clearance between fan and the inlet cone."

Cabinet Also Analyzed

In parallel with the support structure analysis, Mr. O'Keefe performed a modal analysis on the outer cabinet of the filtration module. The results showed that the resonant frequencies of both the fan assembly and the cabinet were close to the motor frequency. This confirmed vibration transmission as a potential source of noise in the cabinet.

"In all," says Mr. O'Keefe, "we performed Algor design and analysis on two different fan sizes, using three materials and two orientations. The final design provided better fan belt accessibility, improved motor adjustment capabilities and more precise fan alignment. It also retained the required level of strength. Vibration isolators were added to decrease energy and sound transmissions to the cabinet and other sound deadening techniques were used to reduce overall noise levels."

Many Processors Used

Mr. O'Keefe used several Algor processors to optimize the final design. In his words: "Algor's modal analysis processor successfully reproduced the vibration modes shown in the original testing. The Timeload preprocessor generated the sinusoidal forcing function which simulated fan imbalance. The time history processor provided the complex stress and deflection response of the structure to the forcing function. We used the same modeling and analysis process to simulate the existing design and to refine and verify the various new designs."