Test pallets through a bake without warping the rack

A tray of test pallets going into a bake is two ratings at once. The boards have a moisture spec to satisfy, and the rack holding them has a temperature its own materials have to survive. Only one of those shows up in the work instruction, which is why racks come out of ovens bent.

What actually warps

Not the frame. The aluminum pillars and the steel base take oven heat without complaint. It is the side panels, and on a standard rack those are conductive polymer. Past their rating they soften, and once they soften the slot pitch stops being true.

That is the damage that matters, because the pitch is what the rest of the line depends on. A rack whose slots have drifted a millimetre still looks fine on the bench, then jams a loader that expects boards every 10 mm. The boards get handled twice, and the second handling is the one that chips edges.

Match the rating to the profile, not to the oven

• 80 C racks do not go in. They are for transport, storage and feeding a line. There is no bake in that list.
• 120 C. Low-temperature moisture removal at 90 to 110 C.
• 200 C, metal base. The full 125 C accelerated profile in J-STD-033, and conformal-coat cure up to 200 C.
• 300 C, all-aluminum. No polymer anywhere in the rack. Lead-free reflow peaks, and anything above a cure.

The rating is a property of the rack, not of the batch. Running a 125 C profile in an 80 C rack once, briefly, is still the run that bends the panels.

Pallets change the arithmetic

Bare boards weigh nothing. Test pallets do not. Two numbers move:

• Weight. A loaded rack carries up to 85 kg on the aluminum pillar and steel frame, 50 kg on the all-plastic chassis. That is the whole rack, not per slot, and a pallet load reaches it far sooner than boards ever would.
• Thickness. A pallet with hardware on it is thicker than a board. Standard slots are 5 mm wide, the all-aluminum rack is 7.5 mm. Measure the pallet at its thickest point, over the standoffs and latches, not across the plate.

Mass also slows the soak. A full rack of pallets reaches temperature later than a rack of boards, so the profile timer starts when the load is at temperature, not when the oven is.

Check the rack after the bake, not the boards

Boards get checked as a matter of course. The rack rarely does, and it is the part that changes shape. After a cycle, slide a pallet into several slots across the width and along the length, top and bottom. It should drop under its own weight in every one. Anything that needs a push is a panel that moved.

If the pitch has drifted, the frame is usually still good. The side panels are the replaceable part and come as kits, so a rack that failed one cycle can go back to service without buying a new chassis.

The short version

Pick the rack by the hottest step its load will see, weigh what you are actually putting in it, and inspect the slots after the first cycle rather than after the jam. The J-STD-033 bake guide walks the profile itself, the all-aluminum racks cover everything above a cure, and if you send us the pallet's length, width and thickness, we will check them against the slot before you buy. Ask a question.