New compound keeps Shuttleworth on a roll

Edited by the Engineeringtalk editorial team Apr 29, 2002

When Shuttleworth decided to develop a single roller design that could be used in a number of conveyors, the company needed a material capable of performing in the most demanding applications.

When Shuttleworth of Huntington, IN, an international manufacturer of material handling equipment, decided to develop a single roller design that could be used in a number of its conveyors, the company needed a material capable of performing in the most demanding applications - moving food, pharmaceuticals, glass, metals or electronics through the manufacturing process.

Using a single material would allow it to lower its costs and provide a faster response to customer needs.

Shuttleworth turned to specialty compounder RTP Company, of Winona, MN, who formulated a conductive and lubricated polyphenylene sulfide (PPS) compound that enabled it to meet these exacting requirements.

Klaus Daenzer, Senior Plastics R and D Engineer at Shuttleworth explained, "Since some of our customers' processes involve high and low temperatures, extreme temperature resistance was also mandatory".

In addition, continuous rotation dictated that lubricity and wear resistance be central properties and, for the electronics industry, the material had to be both electrically conductive and free of silicone oil.

Working closely with Shuttleworth's R and D department, RTP Company formulated an RTP 1300 Series PPS-based thermoplastic compound.

With a tensile strength of 62MPa and specific gravity of 1.54, the new material yields a sufficiently strong, yet lightweight part.

Adds Daenzer, "Because the new rollers are so much lighter than conventional steel rollers, our EP-0047 rollers had to maintain a high strength to weight ratio to achieve a low line pressure of less than 4%".

The inherent properties of PPS offer a continuous use temperature of 204C and excellent chemical resistance.

"The rollers easily passed our 6-month long heat durability test", said Daenzer.

To ensure the material's suitability for ESD (electrostatic discharge) sensitive applications, RTP Company engineers added a conductivity package resulting in a volume resistivity of 1kohm-cm maximum and maximum surface resistivity of 100kohm/sq.

"These properties allow the rollers to harmlessly bleed dangerous static charges away from any sensitive electronic parts they may be conveying", explained Daenzer.

A major challenge in creating the custom compound was the fact that the electronics industry prohibits the use of silicone additives - a traditional approach for reducing friction between surfaces in contact with each other.

"At times, a high loading of silicone will cause blooming to the part's surface, creating a source of potential contamination", explained Daenzer.

To meet the challenge, RTP Company tailored a combination of PTFE and Flouroguard synthetic oil into the PPS compound, providing lubricity that is superior to that of silicone.

"The addition of Flouroguard allowed us to achieve the necessary lubricity and eliminate the plate-out that's common during the moulding and wear process with higher loadings of PTFE", said Daenzer.

He also credited RTP Company's processing assistance with further enhancements to the rollers' surface appearance and smoothness.