SPIREX CORPORATION USES ALGOR FEA TO DESIGN PARTS THAT SAVE TIME AND MONEY FOR CUSTOMERS

A sliced linear stress analysis of one of the working models used in the development of the new Spirex components.

When a company sets out to design a new, innovative product, the goal is often to reduce production time, material costs or in some other way make the product better from the producer's point of view. Spirex Corporation of Youngstown, Ohio, recently used Algor FEA software to develop several new injection molding components which are designed to save time and money for their customers.

Spirex is a leading supplier of injection molding machine components to both original equipment manufacturers and companies that use injection molding to produce products. The new "Quick Change" endcap and barrel assembly was analyzed by Design Engineer Michael J. Senediak and is currently patent pending. This design is meant to shorten and simplify a time consuming, difficult chore that is common to virtually all injection molding equipment.

The Injection Molding Process

To understand the significance of the new Spirex components, it is important to have a basic understanding of how injection molding equipment works. As the name suggests, injection molding means literally injecting melted plastic, or another material, into a mold under very high pressure.

The plastic, which begins the process as pellets, enters a barrel which contains a screw with a non-return valve attached to its tip.

As the screw turns inside the barrel, the plastic travels toward the mold through the channels formed by the screw's flights. The plastic is melted and mixed during this process. As the screw turns, the molten material is pumped through the non-return valve filling up the cylinder and endcap, allowing the screw to recover to a preset value. The next phase of the cycle injects the molten material into the mold.

The pressure created in this process averages 20,000 psi and can be as high as 30,000 psi. This pressure is most apparent at the point where the endcap is attached to the barrel.

The Old Way

On a standard injection molding assembly, the endcap is attached with a series of high alloy bolts. In order to replace the screw and/or non-return valve, which is often necessary because different resins require different mixing properties or pressures, the machine operator must remove as many as 20 bolts to take off the endcap and gain access to the inside of the barrel. This can take a great deal of time and cost quite a lot of money since the bolts, which cost between $5.00 and $25.00 each, should be replaced every time they are removed.

Spirex Innovation

The new Spirex "Quick Change" endcap and barrel assembly is designed to make this job much easier and less costly. The design replaces the costly high alloy bolts with interlocking tabs which are incorporated into the ends of both components. This enables an operator to rotate the endcap slightly, once a small positioning block has been removed, until the tabs disengage allowing the endcap to be easily removed.

The time savings offered by the new "quick-change" design are dramatic. In Mr. Senediak's words, "With our new system, the entire procedure generally takes less time than it does to properly tighten one high alloy bolt on a conventional assembly. Our quick-change assembly will save countless hours of labor now spent on changing screws and valves, not to mention the cost of the bolts themselves."

Design and Analysis

Safety was the primary issue in creating the new design. According to Mr. Senediak, "Our main concern was the ability of the tabs to adequately handle the loading conditions produced by the high internal pressure. Also, we needed to be certain that the areas of the barrel wall where machining was necessary to create the tabs would be able to handle the stresses with a reasonable factor of safety."

A 3-D brick element model was created for each of the two pieces using Algor FEA software on a Compaq Deskpro 486/25," continues Mr. Senediak. "Linear stress analyses were run on a series of models representing different design options."

Analysis Results

"The preliminary results showed us two areas for concern," says Mr. Senediak, "First, the area of the barrel that had been removed for the tabs was too thin. Second, the tabs on the barrel were strong enough to withstand the force, but the model of the endcap produced some high stresses in the location where the tabs connect to the base. Once these areas were identified, proper modifications were made and subsequent models showed a considerable improvement over the initial design. That's when we really knew we had a winner."

Final Testing

The last step, prior to actual production, was testing components based on the final FEA-based design. According to Mr. Senediak, "We created a quick-change barrel and endcap assembly for two of Spirex's lab machines. Both were thoroughly tested and performed without a problem. Currently, the product is in full production and we are able to offer a time saving device to the plastic industry."

Other FEA Applications

About Algor software, Mr. Senediak says, "Spirex has used the Algor package to analyze other barrel applications as well as the drive end of injection molding screws. We are currently working with the fluid flow processor to perform further research on our non-return valve designs with the hope of additional improvements in this area.

"Algor is a powerful finite element package at a reasonable price. The number of options available to the user is continuing to grow each year, allowing for more analysis capabilities. Also," says Mr. Senediak, "Continuous upgrades to the software make Algor easier to learn and manipulate. Finally, the compatibility with other software packages is always a plus."