【正文】 runner Increase the runner system and gate size for the specific mold and Flow marks are sometimes caused by a restrictive runner system and gate size that freezeoff prematurely so that the material cannot be pensated during the packing 。Shorten the sprue length or use a hot runner design instead of a cold runner Adjust the molding conditionsIncrease the injection pressure and packing Increase the barrel and nozzle Increase the mold Hesitation 滯流What is hesitation? Hesitation (or a hesitation mark) is a surface defect that results from the stagnation of polymer melt flow over a thinsectioned area, or an area of abrupt thickness variation. Hesitation can be eliminated by changing the part thickness or moving the gate （或滯流痕）是滯流的熔體流經(jīng)薄壁部分或壁厚突變時形成的表面缺陷。滯流可以通過改變壁厚或移動澆口位置去除。FIGURE 1. Hesitation results from stagnation of polymer melt flow Problems caused by hesitation When polymer melt is injected into a cavity of variable thickness, it tends to fill the thick, less resistant areas. As a result, polymer melt may stagnate at thin sections until the rest of the part is filled and the stagnated polymer melt starts moving again (see Figure 1). However, if the duration of hesitation is significant, polymer will solidify prematurely at the stagnated point. When the solidified melt front is pushed to the part surface, a surface defect such as a hesitation mark occurs. 熔體沖入多壁厚變化的型腔時，趨向于向較厚且阻力小的方向流動。結果，熔體將在薄壁部分停留直到零件的其余部分被填滿，然后停留的熔體再次開始填充。但是，如果滯流時間較長，熔體將在滯流點過早凝固。當凝固的熔體前端被沖入零件表面時，就產(chǎn)生了滯流痕的表面缺陷。Remedies When troubleshooting the cause of hesitation in your part, you39。ll need to rethink both your part and mold design. You can also try finetuning your processing conditions. 當發(fā)現(xiàn)零件存在滯流問題時，可以考慮零件或模具的設計是否正確。也可以調整工藝條件來改善。Alter the part design改變零件設計Reduce part thickness Alter the mold design改變模具形狀Position the gate away from the thinsectioned areas, or regions of sudden thickness 。In this manner, hesitation will occur at a later time, and for a shorter duration. Figure 2 shows that in a poor design, hesitation results from stagnation of polymer melt flow。 moving the gate away from the thin section reduces hesitation. 這樣是使得滯流發(fā)生較遲且持續(xù)時間也較短。圖2顯示較差的澆口設計使得熔體停滯產(chǎn)生滯流現(xiàn)象，使?jié)部谶h離薄壁有助于減少滯流FIGURE 2. Hesitation resulting from improper gate position Adjust the molding conditions調整充型條件Increase the melt temperature and/or the injection Jetting 噴射What is jetting? Jetting occurs when polymer melt is pushed at a high velocity through restrictive areas, such as the nozzle, runner, or gate, into open, thicker areas, without forming contact with the mold wall. The buckled, snakelike jetting stream causes contact points to form between the folds of melt in the jet, creating smallscale welds (see Figure 1). 當熔體高速通過限制性的區(qū)域時會產(chǎn)生噴射。比如噴嘴、流道、澆口、進入開放性的厚壁區(qū)域，并與型腔壁分離?？坌位蛏咝蔚膰娚淞鲗е略谌垠w噴射折痕間形成接觸點，造成小范圍熔接。FIGURE 1. Jetting vs. normal filling pattern. Effects of jetting 噴射的影響Jetting leads to part weakness, surface blemishes, and a multiplicity of internal defects. Contrast this with a normal filling pattern, in which melt advances in a progressive pattern from the gate to the extremities of the cavity, as illustrated above. 噴射導致制品強度較弱，表面有污痕，以及各種各樣的內(nèi)部缺陷。與正常的充型形式相比，正常充填是熔體從澆口到型腔端面逐漸前進的過程，以上已作出圖解Remedies Alter the mold design 更改模具設計You39。ll often find that the trouble lies with the gate Direct the melt against a metal Use an overlap gate or a submarine gate as shown in Figure 2 ，如圖2所示FIGURE 2. Using an overlap gate to avoid jettingSlow down the melt with a gradually divergent flow A tab or fan gate provides a smooth transition from the gate to the cavity. This reduces the melt shear stress and shear ，減少了熔體的剪切應力和剪切速率。FIGURE 3. Using a tab gate (left) and a fan gate (right) to avoid jetting Enlarge the size of the gate and runner or reduce the gateland You can also relocate or redesign the gate in one of the following ways to reduce Adjust the molding conditionsAdjust the ramspeed Use an optimized ramspeed profile so that meltfront velocity is initially slow when the melt passes through the gate, then increases once a dispersed, tongue shaped material is formed near the gate. Figure 4 below illustrates this ，在分散區(qū)域時速度加快，并在澆口附近形成舌形布置。Adjust the barrel temperature to increase or decrease the melt temperature The explanation for this is not well understood, but might be related to the dieswell effect and the change of the melt properties (such as viscosity and surface tension). For example, for most polymers, die swell increases as temperature decreases, while some materials, such as rigid PVC, exhibit increasing die swell as temperature ，它是與粒子膨脹效應和熔體性能（比如粘度和表面張力）改變有關。例如，對于大多數(shù)塑料，隨著溫度的降低，粒子膨脹減少，然而有部分材料，比如PVC，粒子膨脹隨著溫度的降低而降低。FIGURE 4. Adjust ramspeed profile to avoid jetting.Ripples 水波紋What are ripples? Ripples are the wavelets or small fingerprintlike waves near the edge or at the end of the flow. 水波紋是邊緣附近或流動末端出現(xiàn)的波紋或類似于指紋樣的波紋FIGURE 1. Ripples Cause of ripples 原因According to a recent visual analysis using a glassinserted mold, the ripple defect is due to the flow front portion of the melt cooling on a cavity wall, and the repeated phenomena of the subsequent melt getting over and cooling, as shown in the below. Flowfront velocity and mold temperature have a stronger influence on the formation of ripples pared to the shape of the gates and the melt temperature. 根據(jù)可視化玻璃插件顯示，水波紋是由于流動前端在模具壁冷卻，后來的熔體越過并冷卻。與澆口形狀和熔體溫度相比，流動前端速度和模具溫度對水波紋的形成有更大的影響。FIGURE 2. (1) Normal filling with no ripples. (2) Generation of ripples with cold mold wall and low meltfront velocity. Remedies Actions that increase the meltfront velocity or mold/melt temperature will help to eliminate the ripples. 增加熔體前端速度或模具/熔體溫度可以幫助消除水波紋。Modify the part designIncrease the part Change the mold designMake sure the runner system, including the sprue, runners, and gates, is adequate for the specific ，包括主流道、分流道和澆口足夠。Place an adequate venting system throughout the