SMC Molding Common Problems And Solutions

Problem 1: cavity not filled fully

*The edge of product not filled fully

Solutions: increasing the quantity of feeding, decreasing the molding temperature, shortening the closing time, increasing molding pressure, increasing the feeding area, etc.

*Small area on the edge of product not filled fully

Solutions: increasing the quantity of feeding, discharging carefully, reducing the fitting clearance and increasing the fitting length, if the defect is small, increasing the molding temperature or adding excess SMC material, etc.

*Although the entire edge of product is full, some areas are not filled fully

Solutions: increasing the quantity of feeding, improving the feeding method & area, using three-half mold structure or allow air to be discharged form the ejector pins, if the defect is small, increasing the pressure, etc.

Problem 2: coking (the surface areas which are incompletely filled is dark brown or black)

*Trapped air and styrene vapor are compressed to raise the temperature to the ignition point.

Solutions: to improve the feeding method so that the air flows out with the raw material, and no trapping occurs. If brown spots appear in the blind holes, you can use the three-half mold structure or use the ejector pin to exhaust air.

Problem 3: internal cracking

*Due to excessive shrinkage stress in individual layers of thick walled products, bosses or ribs.

Solutions: reducing the feeding area so that the fibers are better interwoven between the layers and reducing the molding temperature.

Problem 4: many small surface holes

*If there are too many small holes in the surface it will be difficult to release the fiberglass molding products.

Solutions: reducing the feeding area and adding small material sheet at the top of the large sheet; repairing the clipping edges; reducing the initial viscosity of the resin paste, increasing the work roll in the impregnation area, and replacing the glass fiber; reducing mold temperature and adding inhibitor to resin paste; when using the anti-seepage film to wrap the SMC material, the quantity of zinc stearate can not be prepared too much; increasing the thickening time or increasing the thickening temperature to increase thickening viscosity level; increasing the molding pressure.

Problem 5: swell (a semicircular swell on the surface of solidified fiberglass compression molding part)

Solutions: removing the interlayer air by pre-pressing method and reduce the feeding area to facilitate the discharge of air; lowing tooling temperature; extending solidifying period; reducing the viscosity of the resin, installing more work rolls in the impregnation area, and heating the dip rollers, replacing the glass fiber; carefully removing the burrs in cavity of tooling; increasing the rhickening of fiberglass SMC raw material or increasing the content of thickener.

Problem 6: Mucosa

*The fiberglass molding part is difficult to remove from the mold, and the fiberglass sheet, sticks to the mold in some areas.

Solutions: increasing the mold temperature; extending solidifying time; always keeping the fiberglass sheet sealing before using them; using release agent to help demolding for first several cyclings; getting better surface polishing.

*It's difficult to demold the solidified fiberglass molding parts. In some areas the fiberglass raw material sticksto the mold, and the surface of the final parts has some microholes and scars.

Solutions: reducing the feeding area and adding small sheet at the top pf the large sheet.

Problem 7: warpage

*The fiberglass compression molding part is slightly warped.

Solutions: Cooling fiberglass molding parts in fixture; using low or no shrinkage resin; reducing mold temperature difference.

*The fiberglass compression molding part is seriously warped.

Solutions: increasing the feeding area, shortening the process and using low shrinkage or shrink free resin in the formulation.

Problem 8: surface ripple

*Ripple on the long, vertical and thin surface, which is at right angles to the direction of flowing. Also due to other adverse flow conditions (wall thickness difference) may result in irregular surface ripple.

In most cases it cannot be completely eliminated, but can be improved in the following ways: increasing pressure, changing the feeding position, and using low shrinkage or no shrinkage resin.

Problem 9: sink marks

*The depressed deformation on the surface, ribs, raised part and/or the back side (shiny or dark).

Solutions: using low or no shrinkage resin in formulation; increasing the temperature of cavity or core and to bring the temperature difference between cavity and core to 5-6℃; increasing the pressure and shortening the length of fiber; improving the mold design, changing the feed position; narrowing gap between core and cavity.

Problem 10: abrasion of mold sheared edge

*Metal damage in the direction of applied force.

Solutions: precising mold orientation; reinforceding guide post; improving feeding position to minimize side thrust.

Problem 11: surface darkening

*The surface does not have enough luster.

Solutions: increasing pressure; raising mold temperature; chromium plating core and cavity.

*Ripple on partial surface

Solutions: improving design; raising mold temperature; increasing feeding area and shortening flowing; improving mold guidance.

Posted by Shine

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Taizhou Huangyan Aoxu Mould Technology Co., Ltd