Cleveland — Officials from Rotaloc International LLC gave a lesson in threaded inserts to attendees of the Society of Plastics Engineers' Rotational Molding Conference.
Rotaloc owner Steve Harris said customers often ask him how strong is a particular insert or what is the torque strength? To give some answers, Harris introduced Connor Landsverk, an engineer with Rotaloc in Littleton, Colo.
Landsverk explained things like tensile strength and pullout strength.
"The weakest part is going to nearly always be the plastic surrounding the insert," he said.
During the cooling cycle of rotomolded parts, shrinkage of the material can cause tension in the molded-in insert, Landsverk said. Rotoloc rests its inserts for the effect of material deformation on pullout strength, he said.
In general, the deforming plastic has a huge impact on pullout strength, although there is a lot of variation, the engineer said. That area needs more research, he added.
"The torque strength is all about the design of the insert," Landsverk said.
In a rotomolding plant, Harris said, inserts can get dirty as operators spray mold release on them or touch them with mold release on their hands. He advises molders to provide clean, disposable gloves to operators handling the inserts.
"Cleanliness has a lot to do with insert strength and torque strength," Harris said.