ALGOR FEA HELPS ITALIAN FIRM OPTIMIZE AUTOCLAVE DESIGN

The firm of Belmonte ing. Claudio, located in Vicenza, Italy, recently completed the design of a high pressure autoclave using the Algor Finite Element Analysis (FEA) System. Autoclaves utilize superheated steam under extreme pressure and are used for a wide variety of purposes in industries such as rubber, glass, aerospace and healthcare.

The challenge faced by Claudio Belmonte, company president, was to optimize the sealing properties of the autoclave cover and shell prior to ordering materials and initiating machining operations. It was essential that the vessel withstand severe internal pressure while allowing users to easily open and close the cover several times each day to insert and remove materials.

Claudio Belmonte, president of Belmonte ing. Claudio, Vicenza, Italy, utilizes Algor FEA in the design of many different mechanical structures.

"The analysis utilized was nonlinear stress [GAP elements] due to the fact that we had two objects resting against each other," Mr. Belmonte explains. "The analysis shows the actual behavior of the material under internal pressure, where the maximum pressure occurs, and its precise value. If the value is too large, it is then possible to modify the model in the exact location where the problem occurred."

The finite element model of the autoclave consists of 1432 type 5 brick elements which were used to model a 20 degree section of the door and shell. A total of 452 boundary elements were used to enforce the conditions at the edges of the section. The model contains 2736 nodes.

Sealing of the autoclave vessel is accomplished by inserting a flange, machined around the edge of the door, into a ring at the top of the shell. The door is then twisted so that a series of 18 wide teeth machined into the door flange are captured behind a like number of teeth in the shell ring.

When internal pressure is applied, the door flange teeth are forced up against the shell ring teeth preventing forward motion. To properly represent the nature of the compressive contact stress between the two sets of teeth, Mr. Belmonte inserted 25 gap elements at the area of contact.

Portion of the model that contains the maximum stress is in the corner of the tooth of the shell.

Like most Algor users in European countries, Mr. Belmonte utilized SI units of measurement in his analysis of the model. Based upon the maximum internal pressure of 15 bar, the Tresca equivalent stress was found to be just over 20 kilograms of force per millimeter squared. The analysis was performed using the SSAPOGH processor and required approximately 15 hours to complete. Mr. Belmonte used a COMPAQ 386/25 equipped with 13 megabytes of RAM.

Although Belmonte ing. Claudio specializes in the design of pressure vessels, they have also utilized Algor FEA software in the design of many other mechanical structures. These include centrifugal hydroextractors, heat exchangers and frame supports.

"I like Algor FEA's flexibility and the reliability of the results," states Mr. Belmonte. "All of the calculations for the autoclave were submitted to either Italian or other European technical committees. Their test results using actual products matched the Algor FEA analysis."