tailieunhanh - Mold Selection P2

Selection of an Appropriate Mold Self-degating is somewhat more expensive than edge gating and while an insert for the gate area adds some cost, it may be necessary for long running molds to avoid expensive repairs later. The somewhat higher mold cost may be well worth it in the long run. There is a number of different designs for tunnel gates [5]. The size of the tunnel gate is determined the same way as the size for any other gate; however, there is a limit to the size that the can be sheared off cleanly. . | previous page Copyrighted Materials Copyright 2006 Hanser Publishers Retrieved from Selection of an Appropriate Mold------------------------------- 125 Self-degating is somewhat more expensive than edge gating and while an insert for the gate area adds some cost it may be necessary for long running molds to avoid expensive repairs later. The somewhat higher mold cost may be well worth it in the long run. There is a number of different designs for tunnel gates 5 . The size of the tunnel gate is determined the same way as the size for any other gate however there is a limit to the size that the can be sheared off cleanly. If the gate is too large hard and brittle plastics may shear poorly very rough and uneven and can easily damage the cavity wall where the gate is located. Submarine gating is another method of self-degating if the piece is shallow and no gate vestige is permitted either on top or on the sides 5 . Submarine gates are more difficult to build than tunnel gates and are therefore more expensive to manufacture the mold will also cycle slower. The vestige is similar to that of a 3-plate mold gate but is on the underside of the product. Note Dirt in the plastic can easily plug any cold runner gate but such dirt is molded into the plastic as it freezes it will be ejected with the runner so that the following cycle will see again a clean open gate. As the runner is ground up before reusing the plastic hopefully the dirt will also be ground up otherwise sometimes later it could again plug a gate. Inherently Self-Degating Molds 3-plate and hot runner molds are inherently self-degating . the gates break off as soon as the cavities and cores with the products held on them separate provided the product stays reliably on the core as the mold opens. Gates for 3-plate molds are usually very small pin point gates and often take advantage of the fact that the plastic will heat up due to shear as it passes through the gate. Gates as small .