What are the solutions of rotational molding technology?

What are the solutions of rotational molding technology?

Rotommoulding technology may have various problems during the production process. The following are some common problems and solutions:

Bubble or hole
Causes: The air in the mold expands due to heat and it is difficult to discharge the gas; the mold is not tightly closed, and air enters during heating or cooling; the special shape of the powder particles causes air to remain bypassed.
Solution: Adjust the position of the vent pipe and the filling material; the mold slowly heats up, increase the furnace temperature or extend the heating time; apply Teflon coating on the inner surface of the mold; preheat the insert and some surrounding areas; use materials with higher melt flow rates and materials with lower density, etc.
Poor resin coating
Causes: The insert has poor heat transfer performance and low end temperature; the insert is too high relative to the product surface; the insert is too close to the adjacent side surface of the product, blocking material flow.
Solution: Make the insert have a good heat transfer structure; the height and volume of the insert relative to the surface of the product should be as small as possible; the depth and width of the stop or anti-pull groove on the insert are suitable for the rotation molding requirements; preheat the insert during rotation molding.
Uneven wall thickness
Cause: The mold structure is unreasonable, such as the thickness at the inner concave corner of the product, the angle at the outer convex corner is too small; the mold temperature is uneven; the rotation speed is uneven.
Solution: Fix the rotary mold in an appropriate position on the mold frame and adjust the balance; maintain the rotation speed of the main and secondary shafts to maintain the proportion and the speed is uniform; the heating furnace ensures that the mold is heated evenly; preheat or reduce the influence of insulation factors in the parts where the thickness of the desired product increases; add heat insulation materials in the parts where the thickness of the desired product decreases.
Rough surface
Causes: The particle size is too large, the temperature is too low, the heating time is short, the resin powder cannot be completely melted; the powder has a large foreign substance mixed in; the particle size is too small, the rotation speed is improper, or the rotation speed is uneven.
Solution: Select powder of the appropriate particle size for the product; control the heating and cooling temperature and time, and keep the temperature basically stable; determine the appropriate spindle speed and main and secondary shaft speed ratio, and keep the speed uniform; avoid mixing the same material with foreign matter or larger particles in the raw materials.
Uneven color
Causes: Improper selection of toners, such as using organic dyes that are not resistant to high temperatures or inorganic mineral pigments with poor quality; uneven mold temperature control; excessive spraying of release agents.
Solution: Use inorganic mineral pigments that can withstand high temperature for a long time, with a smaller particle size than the powder particle size; control the heating, cooling temperature and time, and keep the temperature basically stable; avoid uneven heating of various parts of the mold; try not to use a mold release agent, if it is inevitable, pay attention to the appropriate amount.
Warp deformation
Causes: The product has complex shape, uneven wall thickness, incomplete symmetrical, and the cooling rate and shrinkage rate in different parts are inconsistent; the mold release temperature is too high, and the artificial control factors are strong, so the shrinkage of the product is difficult to control.
Solution: When designing products, try to avoid large planes, use structural forms such as reinforcement ribs to reduce the plane area; adjust the position of the mold on the mold frame; make fixed tooling or fixed tooling with moving parts according to the structural characteristics of the product; take reasonable cooling measures to ensure that the cooling rate of each part of the product is consistent.
The surface is not shiny
Causes: The molding temperature is too high or low; the surface of the mold is not polished, and the adhesion between the product and the mold during production is large, which causes the product to be strained or woven when it is strongly removed; the mold release agent is improperly used.
Solution: Coat the inner surface of the mold with polytetrafluoroethylene coating; adopt an appropriate forming temperature; try to choose an alkaline release agent, and maintain the appropriate amount; choose the appropriate pigment particle fineness.
Insert exposed
Cause: After the product is demolded, it continues to cool and shrink, so that the outer surface of the insert is higher than the product surface; the insert is too close to the side of the product or the distance between the fixed end surface of the insert and the mold surface is unreasonable, and interferes with each other during the rotomolding process.
Solution: Before forming, add a gasket of appropriate thickness and size between the mold and the insert; the insert structure must be well designed, and the distance between the fixed end surface of the insert and the inner wall of the mold must be appropriate or flush with the inner surface of the mold.