Under Tested’s Fuse 1 demo, a viewer who’d run Formlabs resin printers asked two things: how much the powder costs, and does it expire? Expired material had been “the biggest problem” with their Form printers. It’s a fair question to ask before you buy a pallet, and the answer on SLS powder shelf life depends on which Formlabs page you read.
Does SLS powder expire?
Not on a hard date, if you store it right. Formlabs’ powder care page says that when stored as directed, its SLS powders “do not have a defined shelf life or expiration date.” The Nylon 12 technical data sheet, though, lists a 2-year shelf life and storage between 0 and 45 °C. I’d plan around the datasheet number and treat anything older as something to test first.
What does “stored as directed” mean?
Closed containers, original packaging until use, and low humidity. Formlabs wants the room around the printer, the Sift and your storage at 50% RH or less at all times. It says humidity “affects shelf life significantly,” and that higher humidity leads to clumping, underdosing and failed prints. Opened bags get zip-tied or taped shut.
What does long SLS powder shelf life do to parts?
A study in the International Journal of Advanced Manufacturing Technology looked at EOS PA2200, a PA12, stored for 5.5 and 6.5 years and compared it with powder made half a year before testing. The mechanical changes were minor. The parts came out noticeably more yellow, though, and the molecular chains had shortened. The authors put that down to used-up stabilisers and expect those parts to age faster.
Their advice is practical: don’t use long-stored powder for critical parts or parts that’ll live in strong light or humidity, and keep it out of your closed-loop recycling. For long storage they suggest a sealed bag somewhere dark, under 25 °C and under 30% RH.
So how do you manage old stock?
Write the delivery date on every container and use the oldest first. If something has sat past two years, run it through a test build of cosmetic parts before it touches a customer job. Keep it out of the Sift so it doesn’t mix into your recycled stock. Yellow parts from old powder are an easy thing to spot and a hard thing to explain to a customer.
Related on the Solvi blog: MJF Humidity: How Room Conditions Affect Your Builds; SLS Nylon Yellowing: Why White Parts Turn Yellow; SLS Material Changeover: Is Switching Powders Worth It?.
Sources: YouTube: Formlabs Fuse 1 demo (Tested), viewer question; Formlabs: Powder care, storage, and disposal; Formlabs Nylon 12 Powder technical data sheet; Int. J. Adv. Manuf. Technol.: prolonged shelf time on PA12 LS powder.