March 8th, 2021

Extrusion Factors for Medical-Grade Silicone Products

Silicone extrusions for various medical applications have been instrumental in facilitating patient care during COVID-19. This includes silicone-based products needed by the biopharma industry for vaccine manufacturing and distribution as well as direct medical products such as catheters and kink-free, coiled tubing. In this blog, we’ll discuss key extrusion-related factors that support functional requirements of medical-grade silicone products while supporting your profitability.

Whether you’re already making these high-demand extrusions or looking to expand into this market, it’s essential to match the right equipment to the silicone materials being processed as well as the application(s). Examples of medical silicone applications that Davis-Standard supports include single and multi-lumen medical tubing, coextruded or striped tubing, reinforced silicone hose, silicone profiles and silicone tapes. Davis-Standard also supports the production of these products with complete in-line curing systems, both vertical and horizontal, along with supervisory line control systems to integrate the equipment into a complete production process. Each product and process has its own set of specifications that need to be discussed with your equipment supplier to optimize your process.

When we advise customers on machine selection, we focus on evaluating several factors including:

    • Tooling back-pressure
    • Screw design
    • Feed-stock composition, and
    • Compound formulation

These dynamics have the greatest influence on output rate and extrudate temperature, directly impacting your profitability.

This prompts a series of questions to arrive at the best solution. For example:

(1) What is the product size and shape, operating pressure, durometer and viscosity of the compound, and maximum processing temperature the silicone compound will accept before pre-cure initiates?

(2) What is the ideal L/D ratio for the feedscrew, and is this a vented or non-vented process?

(3) In terms of die selection, what size, land, screens and pressure considerations are there?

(4) What is the required RPM to achieve desired feet per minute or pounds per hour?

Typically, extruders used for medical silicone processes range in size from 1-inch to 3.5 inches (25 to 90mm) with 10:1 to L/D ratio. In cases where porosity and air entrapment presents itself, this ratio can go up to 20:1 to allow for vacuum venting. It is also important to consider that most medical silicone processes are low to medium pressure, which means a pressure range of 1,000 to 3,500 PSI and max RPM around 40. This will influence gearbox design and horsepower requirements.

In terms of components, the overall design should be focused on extrudate precision, stability and consistency to achieve the desired results within the desired physical footprint. We recommend the following:

    • Extruder components such as a torque-controlled feed roll drive system for stability
    • A breaker plate/screen pack arrangement for filtration
    • High-efficiency barrel cooling design for precise temperature control to optimize green strength and processability of the silicone extrudate
    • Parts such as breaker plates should be stainless steel and the feed section should be chrome-plated to reduce the opportunity of staining of light color or clear silicone compound formulations
    • Barrels be made with less iron content for longevity
    • Feedscrews, in either single or double-flighted designs, should be chrome-plated or made of stainless steel
    • Process controls and automation features should promote ease of operation and exacting product specifications

For in-line curing of tubing and hose, we suggest a vertical in-line curing system with OD closed-loop control. A typical vertical curing tower includes at least two infrared heat zones, precision and automated product guiding systems, aperture sealing systems to contain heat, and a precisely controlled pull-up capstan. These systems can be adjusted from the operator control system or HMI display to guide the product, adjust line speeds, and control the curing temperature for optimum, complete cure.

Finally, equipment should adhere to strict cleanroom guidelines. Low levels of environmental pollutants such as dust and chemical vapors are important, as well as controlled contamination levels, protective clothing for staff, and adhering to various regulations. Regular maintenance and machine updates, and having equipment surfaces that are easy to clean and maintain are essential. Equipment should run cleanly without excessive vapors or oil from machine components that can introduce particulates into the environment.

We wish you well in your medical silicone extrusion endeavors. In the meantime, do not hesitate to contact us for emergency Davis-Standard equipment service and/or spare parts (844 MYDAVIS).


Have comments or questions about this blog? Comments below.

Stay safe and healthy! For any other questions, e-mail marketing.

The D-S Connect Blog Team

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