Causes and Solutions for Sink Marks and Shrinkage Voids

(1) Epoxy casting curing is exothermic. Material temperature shall be lower than mold and casting‑pot temperature during casting. Sink marks tend to occur when pot and mold temperatures are lower than material temperature. Sufficient heating time shall be guaranteed after mold demolding. Measure mold temperature with infrared pyrometer before feeding into casting furnace. Accurate measurement is achieved by measuring cavity temperature via pouring gate of the largest‑volume mold in furnace. Mold temperature shall be about 10 ℃ higher than casting‑compound temperature. After molds are placed inside casting furnace, furnace temperature shall not drop below mold temperature to keep mold temperature consistently higher than material temperature.

(2) Unreasonable mold design leads to poor cooling effect at pouring gates; untimely cooling by water bags for gates, improper water‑bag size or incorrect placement. Scientifically arrange pouring‑gate positions and positions & sizes of cooling water tanks for gates during mold design, so that casting compound at gates can feed shrinkage into cavities. External water bags must be added for special‑shaped products which cannot be fully handled by mold‑mounted water tanks. Water‑bag size and placement can be adjusted in practical operation.