Page 38 - 2021 Connectivity Components: Everything but the Connectors eBook

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For medical applications, the overmolding must perfectly adhere to both cable and connector in order to limit the proliferation of bacteria in the areas of the assembly that are not accessible for cleaning or sterilization. The cable assemblies must be perfectly sealed against possible contamination, not only in the connecting area but also in the branch area when a cable assembly is made with several branches. The harness must be protected by a Y-shaped overmolding. Overmolding materials (thermoplastic polymers such as PVC, TPU, and TPE, and other plastic materials or silicones) are chosen for both their suitability to the methods of sterilization and for the levels of biocompatibility required by the customer.
Overmolded shapes are also designed to make cleaning easier. In the medical field, it is imperative to have smooth finishes, and to design out any “fiddly” areas that could trap bacteria and allow it to grow.
Ensuring sealing
Whatever the connection, a system or mini-system often needs a certain amount of sealing to guarantee its operation or longevity. Airtightness to prevent oxidation, watertightness to ensure proper electrical operation, oil and gas tightness to prevent chemical degradation, and dust and dirt tightness to ensure cleanliness in medical and space applications are common protection strategies.
The level of waterproofing is governed by an international standard that determines the IP (ingress protection) level. IP00 is a level with no protection from solids or liquids and IP69 is the maximum level of protection, allowing no dust to pass through and resisting water sprayed at high pressure.
The sealing of a system or connection can be achieved by various means. The best known is the elastomeric O-ring positioned in the groove of the part. When the dimensions require it, when the environment becomes severe (pressure, temperature, gas), when maximum adhesion is required, or to address the particular requests of customers, the O-ring may not be sufficient. Overmolding of technical materials (such as TPU, silicones, and SEBS) then becomes necessary.
» A circular connector made with 2 O-rings on the left and a 100% overmolded connector on the right protected by bi-injection for better sealing.
The adhesion effect is strongly increased by the compatibility of the materials (the more the molecular chains are compatible, the stronger the adhesion will be) and the shrinkage effect of the injected material. The choice of materials and the study of the shapes become essential to the integrity of these seals, which can then reach very high levels of protection (IP68, IP69).
Connecting is not necessarily only synonymous with connectors. For applications with severe integration constraints, overmolding techniques can help create a reliable connection. The role of upstream co-engineering with the customer, therefore, becomes essential.
Visit Axon’ Cable to learn more.