The Injection Mold
--The design of Runner
1.The basic
The runner is a channel machined into the mod plate to connect the sprue with the entrance(gate) to the impression. In the basic two-plate mod the runner is positioned on the surface while on the more complex designs the runner may be positioned below the parting surface
The wall of the runner channel must be smooth to prevent any restriction to flow. Also, as the runner has to be removed with the molding, there must be no machine marks left, which would tend to retain the runner in the mod plate. To ensure that these points are met, it's desirable for the mod designer to specify that the runner(channel) is polished 'in line of draw'.
There are some other considerations for the designer to bear in mind: (i) the shape of the cross section of the runner, (ii) the size of the runner.
Runner cross-section shape The cross-sectional shape of the runner used in a mod is usually one of four forms (Figure 4.2): fully round (a), trapezoidal (b), modified trapezoidal (c) and hexagonal (d). The reason why these particular forms are used in preference to others are outlined below.
　　　

注塑模具設(shè)計(jì)--流道設(shè)計(jì) 

　　　流道基礎(chǔ)
　　　流道是在模板上加工出的連接主流道和進(jìn)入（澆口）型腔的一條溝槽。在兩板式基本模具中，流道設(shè)置在分型面上而在較復(fù)雜的設(shè)計(jì)中流道也許設(shè)置在分型面的下面。
　　　流道的壁必須光滑，防止料流受到阻礙。另外，由于流道廢料必須和塑件一起取出，所以流道壁上必須不留下任何加工痕跡，避免流道廢料滯留在模板上。為了確保這些要點(diǎn)得到滿足，要求模具設(shè)計(jì)者在圖紙中注明這條流道需要沿取出方向拋光。
　　　另外還有一些要求設(shè)計(jì)者用心考慮的：（1）流道的橫截面形狀，（2）流道的尺寸和（3）流道的布置。模具中用到的流道橫截面形狀，通常是四種形式之一（圖4.2）：整圓（a），梯形（b）,U型（c），和六角形（d）。為什么采用這些特殊的形狀而不采用其他形狀的理由說明如下。
　　　流道設(shè)計(jì)效率的評判標(biāo)準(zhǔn)從壓力傳遞的角度來看流道應(yīng)該具有最大的橫截面積，而從熱量傳遞的角度來看，應(yīng)該和周邊有最小的接觸面積。因此橫截面積和周長的比率將直接可以指示流道設(shè)計(jì)的效率。這個(gè)值較高時(shí)，效率也高。各種類型流道橫截面的比率如圖4.3所示。可見從這種角度考慮圓形和方形的流道是兩種最滿意的設(shè)計(jì)。而半圓和矩形的比率使得它們通常很少使用。