The best possible production should not only consider the performance requirements of a finished component, but ensure the most economically-beneficial and waste-eliminating molding processes.
As the leading supplier of highly-engineered, precision molded rubber parts, Rahco considers each design as a new entity. No part, production process, or formulation is ever the same. Each intricate detail is a priority. We use traditional methods as well as the latest technology and advanced automations to ensure first-time-through efficiencies via state-of-the-art molding systems.
While Flashless molding has become a growing part of our business, not all parts can be molded flash free.
What is Flash?
A byproduct of the molding process, Flash refers to the excess rubber or unwanted trim that protrudes from the surface of a part commonly resulting from injection, transfer and compression molding. With high-precision parts, even a small amount of trim can impact quality, performance, or assembly in an end-product.
Cryogenic de-flashing systems are computer controlled to precisely control flash removal without negatively impacting to the part, and are often more accurate and certainly more economical compared to tear or hand-trimming methods.
How Does Cryogenic De-Flashing Work?
Cryogenic de-flashing cools molded parts to the embrittling point of the material or below the elastomer’s glass transition temperature (Tg). The excess material becomes hard and brittle, and the parts are subjected to a fine mesh media which helps to break off the excess flash.
Rahco has incorporated a 9,000-gallon liquid nitrogen tank to its facility that feeds a rotating bin that quickly clears flash; avoiding the need for a labor-intensive manual operation, which helps avoid secondary operations and added waste.
The main chamber houses a de-flashing basket that ranges in size from 1 to 5 cubic feet. The basket rotates at varying speeds to expose rubber parts to the plastic shot-blast media. The plastic media, which can be recycled and re-used several times, is expelled from the throw wheel at speeds up to 10,000 RPM. Once the de-flashing process begins, the chamber fills with liquid nitrogen causing parts to go from ambient to freezing temperatures ranging from 0F to -175°F.
The process can clear internal features of a component and hard-to-reach part geometries without impacting the properties of the elastomer. However, dialing in the proper parameters is crucial to successfully removing flash without damaging parts. Based on part geometry, size, polymer, and basket volume, we can determine the appropriate temperature, RPM (speed of the throw wheel), cycle time, pulsation of recycled plastic media and basket rotation speed.
For example, a silicone part will require a colder de-flashing cycle because the brittle point is much lower. What’s more, a part with overflow flash will need a longer cycle and likely a higher RPM speed as opposed to parts with thin or feather flash.
Elastomers and Applications
Today, cryogenic de-flashing is used with parts that are molded from a variety of elastomers, including silicone, EPDM, nitrile and butyl rubber.
According to “Cryogenic deflashing for molded rubber parts,” an article published in Rubber World1:
Examples include block shaped silicone implants for surgical applications, and silicone bumper stops for shock absorption. Cryogenic de-flashing is an especially good choice for removing flash from the silicone distal handles that are used with handheld surgical instruments. When a medical molder wanted to replace hand trimming, Nitrofreeze Cryogenic Solutions saved the molder over six hours of de-flashing labor for every 1,000 distal handles.
In addition to silicone o-rings, gaskets and housings, cryogenic de-flashing is used with silicone overmolded springs, a type of rubber-to-metal bonded assembly. For a 60 durometer silicone part that measured just 1 cubic inch, Nitrofreeze Cryogenic Solutions removed parting line flash that was 0.005” thick and extended 0.200”. The batch sizes were thousands of parts per week, an amount that would have required a significant amount of hand labor.
Cryogenic de-flashing can also remove mold flash from fluorosilicone seals and gaskets that provide increased resistance to fuels, oils, chemicals and high temperatures. Often, molded fluorosilicone parts are used in military and aerospace applications.
EPDM rubber costs less than silicones or fluorosilicones, but molders still need to de-flash molded EPDM cost effectively. In the automotive industry, cryogenic de-flashing can support the fast and accurate removal of flash from high volumes of EPDM hoses, seals and gaskets. Because of its resistance to high temperatures, EPDM rubber is also used in electrical insulation and industrial gaskets. With the increasing popularity of alternative energy technologies, additional applications are being developed, including de-flashing molded EPDM parts for solar panels and battery energy storage systems.
In various industries, cryogenic de-flashing applications for molded EPDM include grommets for wires and cables. When a rubber molder asked Nitrofreeze to remove flash from 50 durometer EPDM grommets, it was especially critical to remove material from inner diameter (ID) holes to support smoother feeding. Cryogenic de-flashing also removed the outer diameter (OD) flash that could distort the part’s cone shaped features. Manual parts trimming could remove this OD flash, too, but it could not match cryogenic de-flashing for important ID dimensions.
Nitrile, a synthetic rubber that resists oil and abrasion, is also a strong candidate for cryogenic parts de-flashing. Molded nitrile parts are used in a wide range of industrial and automotive applications, but especially seals, gaskets, o-rings and hoses. Buna-N, as nitrile is also known, is sometimes used in the aerospace industry with fuel system components, and in the medical industry with catheter kits. As with other elastomers, the design of the part and the thickness of the flash are factors that a cryogenic de-flashing service will consider in defining the right recipe for a molded nitrile part.
Like other elastomers, butyl rubber is also a suitable material for cryogenic de-flashing because it can withstand low temperatures without becoming overly brittle and cracking. Butyl supports compression, transfer and injection molding, but is prone to flashing if there are issues with tooling or processing. Because of its airtight and water resistant properties, butyl is used in seals and gaskets for building and construction applications. Butyl’s inertness and low extractable levels also make it a good choice for the molded vials and syringe plungers used in medical applications. To ensure sealing and insulation, all of these parts require a flash-free surface.”
Overall, molding processes and systems must be aggressively structured to ensure that all required materials, tools, and processes are designed to support superior quality and manufacturing efficiency.
If you’re developing new products, facing performance challenges with existing ones or concerned about the materials in your current parts and their alignment to specification — Rahco Rubber can help.
“Cryogenic deflashing for molded rubber parts,” by Ryan M. Taylor and Steve Melito, Cryogenic Institute of New England: Rubber World, July2023