Introduction: Filled two-component potting resins change between the drum and the nozzle, and heated tanks with stirring, recirculation and vacuum degassing are how feed systems keep that change under control.
Most two-component resins do not sit still while they wait. A filled epoxy, polyurethane or silicone gel in a storage tank is a suspension — solid filler particles held in liquid resin — and gravity keeps pulling those particles down while temperature works on the liquid around them. By the time material reaches the mixing valve, the A and B sides may no longer behave the way they did on the first day. this guide looks at what actually changes inside a tank and what heating, stirring, recirculation and tank degassing each contribute before dispensing begins.
Why filled two-component potting resins separate and change viscosity in storage
Filler is the reason filled potting resins behave differently from unfilled ones. Silica, alumina and similar powders are added to control thermal expansion, thermal conductivity, hardness and cure shrinkage, and they are considerably denser than the resin that carries them. In a still tank, those particles slowly sink. What forms is a gradient rather than a clean split: the lower part of the drum becomes richer in filler and noticeably heavier, while the upper layer turns leaner and more fluid. A 40 L A-side tank and a 20 L B-side tank will each drift in their own way, because the two components usually carry different filler loads and different starting viscosities. The practical consequence shows up downstream. When the filler load in the pumped material drifts, the dispensed mixture no longer matches what was validated during process development, and cure speed, final hardness, thermal performance and shrinkage can all shift with it. Abrasive filler concentrated near the tank outlet also wears metering pumps and valve seats faster. Viscosity drifts for a second reason as well: a tank that cools overnight feeds thicker material in the morning than it did the previous afternoon, so the same pump setting produces a different flow. Settling and viscosity change are two separate problems, and they need two separate answers.
What heated tanks, stirring and recirculation each change before dispensing
These three mechanisms often sit under one feed-preparation heading, but they do different jobs, and keeping them apart makes a tank specification much easier to read. Spec sheets written by a vacuum potting machine manufacturer normally list heating, stirring, level monitoring, degassing and recirculation as separate functions for exactly this reason.
1. Heating Lowers Viscosity but Does Not Stop Filler Settling
Warm resin flows more easily, which makes it simpler to pump, easier to push through lines and easier for entrained bubbles to rise out of the bulk. That is the main job of a heated jacket or immersion heater: it holds the material in a workable flow state instead of letting it stiffen overnight. Heat changes how the resin moves; it does not change where the solids sit. Lower viscosity actually lets filler particles sink a little faster, because there is less resistance against their movement, so a warm tank without agitation is a tank where settling continues quietly while the surface still looks perfectly even.
2. Stirring and Recirculation Keep the Bulk Feed More Uniform
Stirring is the function that works against gravity. A slow paddle or anchor agitator keeps filler particles in motion so they cannot pack into a dense layer on the tank floor. Recirculation complements it from outside the tank: a pump draws material out and returns it, which keeps fluid moving through the outlet, the feed line and the pump inlet — the places a paddle cannot reach. The two are usually paired for that reason. On an automatic vacuum potting machine, the loop also keeps the line primed and warm between dispense cycles, so the first shot after a pause behaves like the tenth. Veady's MFS4020 feed unit shows this layout in practice: a 40 L A tank and a 20 L B tank with integrated heating, stirring, level monitoring, vacuum degassing and recirculation, feeding the dispensing head as one split system.
How vacuum degassing in the tank prepares resin for the dispensing chamber
Tank degassing addresses air rather than filler. Resin that has been pumped, stirred and transferred picks up entrained air, and pouring it into a drum traps more of it. Under reduced pressure in the tank, those bubbles grow and break at the surface, so the bulk material arrives at the metering pump carrying far less gas that could otherwise be released later inside the dispensing chamber. Stirring helps this along, because moving the material brings bubbles up to the surface instead of letting them sit in a pocket near the wall. NASA's published work on vacuum degassing in aerospace bonding and welding processes treats degassing as a standard step for pulling gas out of viscous polymers before they go into critical assemblies, which is the same principle a production feed tank applies on a smaller scale. The distinction that matters for process planning is that tank degassing and chamber degassing act on different volumes. Tank degassing treats the bulk supply: it removes air picked up during handling and transfer and gives the metering pump a more predictable fluid to work with. Chamber degassing acts around the workpiece, where the goal is filling tight gaps and windings without leaving voids behind. When someone asks a vacuum potting equipment supplier about degassing, the useful question is which volume the vacuum acts on — the tank, the chamber, or both. The VPS-431 off-line vacuum potting machine is built around that split: a feed unit that prepares the resin and a vacuum chamber that applies pressure around the part. Epoxy, polyurethane and silicone gel each behave differently in both stages, so settings that work well in one shop are rarely a universal answer.
Conclusion
Consistent potting starts well before the mixing valve. Filler settles because it is denser than the resin around it, viscosity drifts with temperature and time, and entrained air travels with the material into the dispensing chamber. Heating, stirring, recirculation and tank vacuum degassing each handle one part of that, and a split feed design puts those functions where an operator can see, service and top up the tanks without disturbing the rest of the system. Anyone who wants to see how these functions are configured on one machine can review the VPS-431 specification and match its tank volumes and integrated feed features against their own resin and part geometry.
FAQ
Q：Why do filled two-component potting resins settle in storage tanks?
A：Filler powders such as silica and alumina are much denser than the liquid resin that carries them, so gravity pulls them downward whenever the material is standing still. The result is a gradient — a filler-rich, heavier layer near the bottom and a leaner, thinner layer at the top — and it grows the longer a tank sits without movement. Warm material settles faster still, because low viscosity offers less resistance to particle movement.
Q：What do heating and stirring each do for A/B resin before vacuum potting?
A：Heating lowers viscosity so resin pumps more easily, moves through lines with less effort and releases trapped air more readily, which is why feed tanks are temperature controlled. Stirring keeps filler in suspension so it cannot build a dense layer on the tank floor. Heating governs how the material flows; stirring governs where the solids sit. Most feed systems use both together, because neither one alone keeps a filled resin uniform.
Q：Does tank vacuum degassing replace degassing inside the vacuum chamber?
A：They treat different volumes, so both stages matter. Tank degassing removes air entrained during handling, transferring and stirring, which means the metering pump receives a more predictable fluid and less gas travels toward the part. Chamber degassing applies vacuum around the workpiece itself, which is where winding gaps and tight cavities need to be filled. Running the tank stage makes the chamber stage easier rather than unnecessary.
Sources / References
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