Why microwave claims are lost in production

A container that passes a lab test can still warp in a customer's microwave after four minutes on high power. The difference is rarely the resin batch; it is how the sheet crystallised, how the corners were drafted and how the load sat on the base. Shantou Longsheng Industry Co., Ltd. builds the extrusion, thermoforming and mold side of this problem in one place.

Three variables that decide heat performance

• Sheet thickness distribution — a base 0.15 mm thinner than the wall acts as a hot spot and deforms first
• Crystallinity from extrusion — cooling too fast leaves the sheet under-crystallised, and the part softens sooner
• Corner radius and draft — sharp internal corners concentrate stress when the material expands

On our DSI-PP multi-layer co-extrusion line the sheet recipe is set for these conditions, and the LSI series PET/PLA single-screw extruder with drying and crystallising system gives comparable control with recycled or heat-stabilised grades.

Warp control belongs to the mold

A PP container usually warps because the base cools before the sidewall. Our molds for microwave containers use a temperature-balanced cooling circuit and, where needed, a slightly crowned base so the part settles flat after shrinkage. A mirror-polished base releases heat more evenly than a rough one.

Venting and lid matching

Containers intended for microwave use should carry a peel-back vent patch position or a lid with a steam port. We match the rim geometry of container and lid in the same tool set, so seal height and vent position stay aligned lot after lot.

Which machine fits your volume

• FS-8556 full-servo cup making machine for round containers and bowls with tight rim tolerance
• Multi-station thermoforming machines for rectangular meal boxes, trays and compartmented formats
• Vacuum forming machines for short runs and prototype tooling before mass production

All of them run PP, PS, HIPS, PVC, PET, PLA, PE and biodegradable blends, so one supplier covers both a conventional PP line and a compostable alternative.

About Shantou Longsheng

Founded in 1998 in Shantou, Guangdong Province, the company operates a 30,000 m² plant, holds the "Longsheng" trademark, 25 granted patents (1 invention and 24 utility models) and is certified as a high-tech enterprise. Product lines cover sheet extruders, multi-station thermoformers, vacuum forming machines, cup making machines and precision molds.

Learn more at https://www.stlongsheng.com