三河マルシェ【MARCHE】三河エリアのコミュニティポータルサイト

Differences Between Closed Molding vs Open Molding

Plastics encompass a wide array of materials and molding processes used to create finished parts. Typical injection molding involves heating thermoplastic or thermosetting plastic polymers and injecting them into a mold where it conforms to the mold cavity, cools and hardens. Other molding processes, like Resin Transfer Molding (RTM), involve injecting or spraying liquid thermosetting materials into a mold with reinforcing fibers, like fiberglass. Typical plastic molding can be done two ways: either by closed molding or open molding. In simple terms, plastic resin exposed to the atmosphere during curing is known as open molding, while that which is not exposed to air during curing is known as closed molding. Each type of molding has its place within the plastics industry, with advantages and disadvantages for each.Get more news about double deck compression forming machine,you can vist our website!

OPEN MOLDING PROCESS
The open molding process is generally less expensive since it doesn’t require the resin to be sealed off from the surrounding environment. The three main types of open molding processes are:

Hand lay-up molding is the least expensive and most common open molding method, with fiber reinforcement placed into a single mold cavity and resin applied via hand with rollers or brushes. It’s used for a variety of large and small products, including storage tanks, showers, tubs and boats.
Spray-up molding is similar to the hand lay-up method, though it uses a chopper gun and other special equipment to cut reinforcing material into shorter fibers before adding it to the resin mixture on the mold’s surface. As it involves automation, this method tends to be used for producing on large scales.
Filament winding molding involves applying fiber strands that are saturated with resin to reinforce it in a cylindrical mold that rotates. It’s less labor intensive than other types of open molding methods and is used in the manufacture of such things as piping, stacks, chemical storage tanks and rocket motor casings.
Because tooling costs for open molds tend to be lower, open molding is more widely used for short production runs. It’s typically used for larger products for which automated processes are unsuited or products made in such low volumes that the cost of automating the process isn’t justifiable. As only one side of a finished part created in an open mold is smooth, the process is not appropriate for parts that require a smooth finish across all surfaces.

CLOSED MOLDING PROCESS
For most larger scale plastic production, closed molding processes are more advantageous. With closed molding methods, dry reinforcing material can be put into the mold, which is then closed. The plastic resin is then put into this enclosed cavity, using either a vacuum or pressure pump to infuse it with resin. Once the material cures, the mold is opened and the plastic part or product is removed. Closed molding via processes like Reaction Injection Molding (RIM) often do not utilize a reinforcing material, as the materials used are often structurally sound without reinforcements. The following are types of closed molding processes: