The Ins & Outs of PMF: Everything you want to know about pre-mixed and frozen (PMF) polysulfide aviation sealants
What Are PMF Sealants?
The majority of our sealants are available to ship in PMF form - pre-mixed and frozen in a dry ice mixture at our production facility in Magnolia, Texas. We oversee every aspect of production and have high quality control standards that meet or exceed those established by NADCAP. Our customers find our PMF packaging to be easy, convenient, and reliable because the product is precisely measured and air-free. Ready-to-use PMF is ideal for high volume production.
How Does PMF Packaging Work?
The PMF process starts with thoroughly mixing multi-component materials. The components are carefully mixed so as not to entrap air. After this, the product is flash-frozen at -80˚F in a slurry of 100-percent isopropyl alcohol and dry ice. This rapidly brings down the product's temperature and the product is left in this "bath" for a minimum of 20 minutes to prepare for storage in a freezer which is maintained at -80˚F .
The PMF Freezing Process
The PMF products remain stored at -80˚F until time for shipment, and shipping usually takes place within a week of packaging. At NSL, we have a security system on the freezer that is programmed to alert us of any power failure or shortage. In the event of a power disruption, the monitoring would send automated messaging to manufacturing leadership's phone and e-mail, describing which freezer system has the problem. This allows for a quick repair so that no product is wasted. Our customers can always trust our processes, which are part of a quality management system (QMS).
Each cartridge of PMF product goes through a rigorous inspection check before it is shipped to the customer. Each tube is filled and assigned a number, which corresponds to a number on something called a "button board." On this board is a dab of each tube's product. The buttons are allowed to cure, then sliced and examined for any sign that air has been introduced in the final product. Air bubbles are the primary indicator of this. The only exception to this process is tubes filled with part A products, which are too fluid to create a "button dab" - the material would run. This inspection also ensures that the two components are thoroughly mixed.
Layout Spread Sample Inspections
In addition to the "button board," for every 100 tubes that are filled in a run, two are pulled for further testing in our in-house lab. There, they are normalized in the lab freezer at -40 ˚F for no less than 24 hours. Upon removal, they are defrosted for 30 minutes. The product is smeared on a layout board at a thickness of 0.125 inches. The sample is then left to cure in the stability chamber for the amount of time called for in the product's TDS. For example, A2 is checked after 72 hours, B4 is checked after 96 hours, etc.
After the allotted time, the sample is then removed from the layout board, trimmed, cut horizontally, and folded in half to get the 0.25-inch thickness called for by the specification. A durometer is then used to test the hardness of the material according to the international standard for hardness measurement of rubber, plastic, and other non-metallic materials. The sample is also checked for accurate application, tack-free, and cure time.
Pros and Cons of PMF
Before deciding on pre-mixed and frozen (PMF) polysulfide aviation sealants, we encourage customers to consider the pros and cons. Here they are as we see them:
- The customer doesn't have to worry about mixing the kit or having air introduced into the product
- Hand-mixing is tiring and fatigue can cause an inconsistent mix of the base and catalyst
- No mixing is required and the product arrives ready to use
- Guaranteed that all chemical properties are properly mixed
- Used for large mass operations who are looking to have trusted product ready-to-go and in-hand (i.e. manufacturers like Boeing, Lear Jet, Cessna, Gulfstream, and more)
- Can't have a large backstock of PMF due to short shelf life
- The shelf life of the product is sped up tremendously. Instead of the typical nine-month shelf life, PMF only allows for four to six weeks
- PMF is more expensive to package and ship
- Expensive equipment to store product for both distributor and end-user
- Electricity shortages can cause trouble and loss of material, resulting in lost revenue