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Replacing Zinc with Polyamide 66 (Case Study)

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By: Michelle Maniscalco

Replacing zinc with PA 66 means an end to corrosion issues along with bonus savings.

This screen shot from IDES Prospector software compares materials that meet search criteria, including North American availability, tensile strength of more than 36,000 psi, and flexural modulus greater than 2,800,000 psi. The final filter locates all PA 66 materials that meet these three targets.

Comparing the top materials found in the search can help designers ask the right questions when they follow up with material suppliers. (Complete results are not shown.)

In this first installment of IMM's new Materials Specifier feature, a plumbing component manufacturer seeks to switch from zinc to thermoplastic as a means of eliminating corrosion. Along the way, the OEM also realizes that it will save steps in both finishing and assembling the components, thanks to the molding process. IDES is graciously performing searches for this series with its Prospector software, which can be trialed at www.ides.com. Then we have expert commentary from Jack Avery, formerly with GE Plastics (now known as SABIC Innovative Plastics) and currently a consultant, who gives context and commentary for the search results. Search results are meant to point designers in the right direction and to serve as the basis for further investigation during rigorous application development. (We are unable to show you the component discussed in this article because of proprietary concerns.)

Application: A plumbing component (fitting) traditionally made with zinc

Goal: Replace zinc with an injection moldable thermoplastic while maintaining the mechanical characteristics of zinc.

Criteria and most important properties:

Eliminate corrosion
Maintain strength and stiffness of zinc
Be available in North America
Be a readily available and moderately priced material

IDES search notes:
First, we chose to narrow our search by only selecting polymers available in North America, which narrowed the field from 70,740 globally available resins down to 49,880 materials.

Next, the strength and stiffness requirements needed to be considered. We filtered for all of the materials with a tensile strength greater than 36,000 psi, which narrowed our list to 101 grades.

For stiffness, we searched for materials with a flexural modulus greater than 2,800,000 psi, which returned a total of 66 grades, most of which were exotic materials like PEEK and polyimide (PI). We noticed that there were also 12 nylon 66 (PA 66) grades from three material suppliers that matched our requirements and were injection moldable. The top three matches were sent from two of the suppliers to the component manufacturer, who followed up by contacting the material suppliers for further details and application development.

Commentary by Jack Avery:
The two material suppliers identified are both reliable and well-known. RTP is a full-range, global compound supplier and Techmer PM is a specialty compounder.

All three materials identified were carbon-filled:

RTP compound 289: 50% carbon-fiber-filled material
RTP compound 289 TFE 10: 50% carbon-fiber-filled plus 10% TFE
Electrafil J-1CF/40BK, which can be either 40% carbon-fiber-filled or a combination of carbon fiber and carbon powder.

While none of these carbon-filled materials is price competitive with diecast zinc on a per-pound basis, there are other factors that figure into the overall part cost. For example, injection molded parts do not need the additional finishing steps that diecast zinc requires. Designers may also be able to consolidate several parts into one via molding, thereby eliminating assembly steps as well.

Results of this search illustrate why designers and engineers use this type of data as a starting point for further discussion with material suppliers-an initial step rather than the definitive answer. Here we have three materials that will fulfill specific material properties (strength and stiffness), but we don't yet know if they will meet the application design and performance requirements. Without further exploration, for instance, the higher cost of the carbon-filled materials might lead to a decision that they are not cost competitive rather than enabling the design team to determine an overall cost by factoring in parts consolidation and the elimination of assembly and finishing steps.

It's always wise to consult with application engineers at potential suppliers and give them as much information about the application as possible. They can identify critical requirements and work with the OEM, toolmaker, and molder to develop the product design and select an appropriate material that meets performance, productivity, and cost requirements.