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For over 4,000 years, the evolution of the filter has been directly linked to the improvement of human health and life expectancy. The first great civilizations, like the ancient Egyptians, used sand and gravel as filter media to improve the taste and appearance of water. Today, filters have become an essential component to our entire way of life. They are found in countless industries, manufacturing facilities, processes, and in many cases, the end products themselves. More importantly, filters are enabling the tools and devices that are essential to defeating this invisible enemy and returning the world to some semblance of normalcy.
Since the onset of this pandemic, our society has gained a new appreciation for respirators, ventilators, and vaccines, as well as the vital role they play in saving lives and preventing future outbreaks. Like everything else in our modern industrial society, these life-saving tools all rely on specialized filter media and advanced filtration technology to function. It is obvious how filters are utilized in equipment like respirators and ventilators, but when it comes to vaccines the use of filter technology is not immediately apparent.
How are filters used for making vaccines?
A successful vaccine is the result of complex scientific processes that include the concentration of proteins and enzymes, blood plasma purification, virus and bacteria concentration and removal, as well as cell harvesting, clarification and washing. These procedures are all enabled by specialized filters and equipment.
Some common methods used in bioprocessing include membrane filtration, tangential flow filtration, centrifugation, and depth filtration. Implementing the proper filtration technology can have a positive effect on yield, product consistency, and overall efficiency of the entire operation.
What types of filters are used?
Hollow fiber filters possess excellent filtration performance and are commonly used in dialysis, water purification, reverse osmosis, separation of components from biological fluids, and cell culture devices to name a few.
Tangential flow filtration (TFF) systems are used extensively in the production of vaccines and other pharmaceutical drugs. They can be used to remove virus particles from solutions, clarify cell lysates, harvest and retain cells, and they can concentrate and desalt sample solutions ranging in volume from a few milliliters up to thousands of liters.
A HEPA (High Efficiency Particulate Air) filter works by forcing air through a fine mesh that traps harmful particles such as dust mites, pollen, pet dander, smoke, and even airborne viruses. HEPA filters are used in applications where contamination control is required, such as the manufacturing of semiconductors, disk drives, medical devices, food and pharmaceutical products, as well as in homes, vehicles, and hospitals.
How is Hapco involved in the filtration and ultrafiltration industry?
Hapco has been custom formulating adhesives, sealants, and potting compounds for some of the world’s largest filter manufacturers for over 40 years. Our materials and processing equipment are a key component to manufacturing a wide variety of specialized filters. As a preferred supplier to corporations like MilliporeSigma, Pall Life Sciences, and Koch Membranes, we take pride in our ability to provide customers with the highest quality polymers and the most reliable processing equipment available.
As we look to a post-pandemic future, our chemists are developing new formulations and processing methods to meet the needs of filter manufacturers around the world. We are currently conducting in-house testing on Filter-bond™ R-3590: a new epoxy formulation for the filtration market that is both Bisphenol-A (BPA) and nonylphenol-free.
What other Hapco products are used to manufacture filters?
The Filter-bond™ series was first developed in the 1980’s for various filtration and ultrafiltration applications. It includes formulations that do not contain aromatic amines or carcinogenic or mutagenic materials, systems that can be used to pot moist membrane material in place without foaming, and systems that are easily trimmed when used for pre-potting filters. Filter-bond™ includes a line of flexible and rigid materials to meet a wide variety of filtration applications. All Filter-bond™ products are compatible with Hapco’s MiniFIL™ and RapidFIL™ dispensing machines, which are used for potting or encapsulating various filter media.
Filters are one of mankind’s greatest achievements and a major reason our life expectancy has increased dramatically over the past 200 years. They clean the air we breathe, the water we drink, the fuel that moves us forward, and the medicine that keeps us healthy. Without them, there is simply no way to manufacture the life-saving and preventative drugs that offer us a light at the end of this tunnel.
Fun Fact: Hippocrates (460-370BC) was the first major proponent of water filtration in recorded history. He advised people to first boil, then filter water through two sewn together pieces of cloth which eventually came to be known as a Hippocrates’ Sleeve.
Part 1 – Making the Mold
In this article, we show you step by step, how to duplicate a complex pattern using Hapco’s high performance materials and equipment.
After taking measurements of the pattern and creating a drawing to outline our plan, we constructed a mold box using medium density overlay.
Orient the pattern inside the mold frame in a manner that will maximize the flow of material and minimize the amount of air that could get trapped. The paper represents cutouts that will reduce waste and save on material costs.
Pieces of cardboard were cut and layered to follow the shape and contours of the unicorn. This creates a foundation for a layer of clay that will represent the parting line for the two mold halves.
The clay is carefully smoothed out up to the halfway point to raise the part from the board and create a parting line along the middle.
Hapsil™ 360 is mixed thoroughly and degassed in an X-Vac™ Chamberto remove any trapped air before pouring.
Hapsil™ 360 is slowly poured over the pattern until it reaches the top of the mold box.
The silicone is left to cure overnight at room temperature.
Once the silicone has cured, the cardboard and clay are removed. The cured silicone mold half is temporarily removed from the frame for easier cleaning.
The pattern is temporarily removed allowing the mold to be cleaned thoroughly with isopropyl alcohol.Grease-It™ 5 release agent is also sprayed on the mold.
Once the unicorn pattern and mold are placed back in the frame, a final coat of Grease-It™ 5 is evenly applied over the surface.
Step 5 is repeated and the Hapsil™ 360 is poured evenly over the part in a thin, steady stream. It is best to pour from one side to allow the air to escape as it’s filling.
The uncured silicone is allowed to cure at room temperature overnight.
The silicone is removed from the frame and separated. Once the pattern is demolded, the silicone is cleaned thoroughly with isopropyl alcohol.
It is important to understand how the mold will be oriented and to consider where air may get trapped. Vents are carved out of one mold half to give air bubbles a path to escape.
The two mold halves are separated and placed in an oven at 125°F for 8 hrs. It is important to separate the mold halves to allow any oils or
residue to flash off.
A hole is cut where the material will be poured into. This represents the top of the mold.
The silicone rubber is completely supported by the wooden box. The two side pieces are screwed into place and the mold is rotated so that the hole is on the top. It is now ready for casting.
To learn how we cast a clear part using Ultraclear™ 480N-40, view Part 2- Casting the Unicorn.
Q. What is the difference between vacuum degassing and pressurizing?
A. Vacuum de-gassing expands the air trapped during mixing or pouring, causing the bubbles to grow, rise to the surface, and in most cases, release. After a period of time the amount of trapped air decreases. The material’s viscosity and surface tension will determine how easily the air will escape. Certain materials appear to bubble indefinitely until the vacuum pump is turned off. In order to maximize the vacuum’s potential for air removal, the pump must be capable of pulling 29.6 inHg.
Vacuum Degassing using the X-Vac™ Chamber
When placed under pressure, any air bubbles entrapped from the mixing and pouring process shrink to the point where they are no longer visible. Pressure ranging from 60-80 psi significantly reduces the chances of visible air bubbles. For pressure to be effective, the liquid thermoset material must remain under pressure until it has reached its gel time, otherwise the bubbles may expand once the pressure is relieved.
Pressure Casting using the X-11 Molding Chamber
Q. Is one method preferred over the other?
A. One method really isn’t preferred over the other. Whether you choose to use vacuum or pressure depends on the application, your capabilities, and budget. In fact, we often recommend vacuum degassing your product after hand mixing, pouring into the mold, and then using pressure to make sure all parts of the mold are filled. When using dispensing equipment, there is no air introduced during mixing. That doesn’t mean air cannot be introduced while shooting into your mold, especially one with many thin walls, sharp corners, or intricate details.
If you find yourself in a situation where you absolutely need a bubble free part (e.g., using a plaster mold or a large quantity of expensive material) it’s best to play it safe and employ both methods. If neither option is in your budget and you need a void free surface, we recommend using low viscosity materials, mixing slowly and thoroughly, and brushing a thin coat onto the mold or pattern’s surface. Using a hair dryer while brushing the thin coat will help to ease surface tension and reduce bubbles.
In the past, we’ve discussed the importance of temperature control when casting with thermoset resins. In this article, we will focus on the post cure process for molds or parts made with thermoset resins.
What is post-curing?
Post curing is the process of exposing a part or mold to elevated temperatures to speed up the curing process and to maximize some of the material’s physical properties. This is usually done after the material has cured at room temperature for at least 12 hours. In general, thermoset materials will achieve full cure at room temperature over a period of 7-10 days. After a full cure is achieved at room temperature, post curing will have no effect on the material’s properties.
Why is post curing necessary?
Post curing will expedite the cross-linking process and properly align the polymer’s molecules. Much like tempering steel, post curing thermosets can increase physical properties (e.g., tensile strength, flexural strength, and heat distortion temperature) above what the material would normally achieve at room temperature.
Post curing is extremely important when an application requires secondary machining.
Fred DeSimone of Hapco says, “Post curing your parts prior to machining is critical to ensure dimensional stability, particularly when trying to maintain tight tolerances. Elevated temperature acts as a catalyst to complete the cross-linking process and stabilizes the cured plastic so that it does not continue to creep over time. Although most thermosets will appear to be cured after several hours at ambient room temperature, the reality is that it can take up to two weeks for the material to fully cure. If secondary machining is completed during this time on non-post cured parts, they can either shrink or grow out of specification while the polymerization process is still occurring.”
How should I post cure my parts?
An oven is best for applying uniform heating, but we don’t recommend using the one in your kitchen. Applying too much heat to some materials may result in dangerous fumes being emitted or a material may melt, ruining your oven. Digital, vented lab ovens are ideal for post curing parts and molds; however, this can also be done in an X-Series Molding Chamber.
During elevated temperatures, thin-walled parts may bubble or deform. Keeping them in the mold or using a fixture during post cure is recommended. Make sure that anything you place in an oven can take the heat.
Is there an ideal post cure temperature?
Generally speaking, rigid materials are post cured at 175F for 8-24 hours and flexible materials at 140F for 8-24 hrs. Be aware that post cure temperatures vary for different materials. Please review the Material Handling & Safety Notes supplied with your specific Hapco products, or contact Hapco’s Technical Support for more information.