【正文】 Air traps 困氣What is an air trap? An air trap is air that is caught inside the mold cavity. It bees trapped by converging polymer melt fronts or because it failed to escape from the mold vents, or mold inserts, which also act as vents. Airtrap locations are usually in areas that fill last. Lack of vents or undersized vents in these lasttofill areas are a mon cause of air traps and the resulting defects. Another mon cause is racetracking (the tendency of polymer melt to flow preferentially in thicker sections), caused by a large thickness ratio. 困氣是氣體存在于模具型腔內(nèi)無法排出，困氣會形成氣孔是其聚集在熔體前端或未從模具排氣孔以及鑲件排出。困氣通常發(fā)生在最終填充位置。在填充末端缺少排氣孔或排氣孔太小都會引起空位造成制品缺陷。另一個(gè)較為普遍的原因是跑馬場效應(yīng)（聚合物熔體有優(yōu)先向肉厚方向流動(dòng)的趨勢），是由于壁厚突變引起的。FIGURE 1. Air trap locations indicated by the puterpredicted meltfront advancements. (To replay the animation, click Replay) Problems caused by air traps Entrapped air will result in voids and bubbles inside the molded part, a short shot (inplete fill), or surface defects such as blemishes or burn marks. To eliminate air traps, you can modify the filling pattern by reducing the injection speed, enlarging venting, or placing proper venting in the cavity. 困氣將引起成型制品內(nèi)部空位和氣泡，短射（澆不足），或表面缺陷如污痕或燒焦?？梢岳酶纳瞥尚蜅l件來解決困氣問題，如減少注射速度，擴(kuò)大排氣孔，或者適當(dāng)位置開設(shè)排氣孔。In the figure below, an air trap results from racetracking in a part with a large thickness ratio. In this case, the entrapped air can be vented by changing the thickness ratio or by placing a vent (., via an ejector pin) at the air trap ，困氣是由于壁厚突變產(chǎn)生的跑馬場效應(yīng)引起的。困氣可以由減小壁厚變化率或者適當(dāng)位置開設(shè)排氣孔消除。Remedies 補(bǔ)救措施Alter the part design改變零件的設(shè)計(jì)Reduce the thickness This will minimize the racetracking effect of polymer 。Alter the mold design改變模具的設(shè)計(jì)Pay close attention to the proper placement of your Place vents in the areas that fill Vents are typically positioned at discontinuities of mold material, such as at parting surfaces, between the insert and mold wall, at ejector pins, and at mold ，比如分型面、鑲件與模具間隙、頂針、滑塊等。Redesign the gate and delivery Changing the delivery system can alter the filling pattern in such a way that the lasttofill areas are located at the proper venting 。Make sure the vent size is large enough so that the air present in the cavity can escape during 。Be careful, however, that the vent is not so large that it causes flash at the edge of the molding. The remended vent size is mm ( inch) for crystalline polymers, and mm ( inch) for amorphous ，排氣槽不能太大防止制品產(chǎn)生飛邊。對于結(jié)晶型塑料。Adjust the molding conditions改善填充條件Reduce the injection High injection speeds can lead to jetting, which causes air to bee entrapped in the part. Lowering the injection speed will give the air displaced by the melt sufficient time to escape from the ，這會使氣體無法逃脫。較低的注射速度可以使氣體有充足的時(shí)間從排氣槽排出。Black specks/black streaks黑斑和黑痕What are black specks and black streaks? Black specks and black streaks are dark spots or dark streaks found on the surface or throughout a molded part. Brown specks or streaks refer to the same type of defect, except the burning or discoloration is not as 。它們都是同種形式的缺陷，是不太嚴(yán)重的燒焦或色變。Causes of black specks/black streaks Black specks and black streaks are caused by overheated (degraded, burned) material or by contamination of the resin. 黑斑和黑痕是由于材料過熱或樹脂被污染而引起的。Material degradation Overheated materials can degrade and lead to black streaks. Material that stays in the nicked rough surfaces of the barrel wall and screw surfaces for a prolonged period of time after heating will char and degrade, resulting in the defect. 材料過熱會降解導(dǎo)致黑痕，材料在加熱過程中停留在粗糙的料筒和螺桿表面的時(shí)間過長會燒焦并講解，導(dǎo)致產(chǎn)品缺陷。Material contamination Contaminants in the air or material, such as dirty regrind, foreign material, different color material, or a lower melttemperature material, are what most often lead to black specks and black streaks. Airborne dirt can also cause dark spots on the surface of a molded ，比如被污染的外來料，不同顏色的材料，低熔點(diǎn)材料，都通常引起黑斑和黑痕的原因。空氣中的粉塵也是會引起成型制品表面的黑斑。Other defects resulting from the same causes 相同原因引起的其他缺陷 Brittleness 脆化 Burn marks 燒焦 Discoloration 色變Remedies Handle the material carefully小心使用材料Make sure no contaminated materials, such as dirty regrind, are blended into the original ，比如臟的再生料加入到原材料當(dāng)中。Put the cover on the hopper and all bins of material. Airborne dirt can contaminate the original material, leading to black ，空氣中的灰塵會污染原料導(dǎo)致黑斑。Alter the mold design改變模具設(shè)計(jì)Clean the ejectors and slides. The streaks could be caused by the grease or lubricants on the slides or ，條紋可以由滑塊或頂針上的油脂或潤滑油引起。Improve the venting system. If the black specks are found at the end of flow paths or blind spots, they are likely caused by a poor venting system. Compressed air trapped in the cavity is sometimes ignited, leading to the ，如果在流動(dòng)末端或盲點(diǎn)發(fā)現(xiàn)有黑斑，有可能是由于排氣不良引起的。被壓縮的型腔內(nèi)的氣體有時(shí)會被點(diǎn)燃，造成產(chǎn)品缺陷。Clean or polish any nicked surface on the runner system to keep dirt from lodging in these areas.Clean the mold before ，使污垢遠(yuǎn)離這些區(qū)域。并在成型前進(jìn)行清潔。Select a proper machine 選用適合的機(jī)臺Size a proper injection machine for a specific mold.The typical shot size should be between 20 and 80 percent of machine injection capacity. For temperaturesensitive materials, the range should be narrowed down more. Plastics simulation software can help you select the right size injection machine for a specific mold. This will help avoid resin remaining in the heated barrel for prolonged periods of %～80%，對于溫度敏感型材料，變化范圍應(yīng)該更窄些，塑膠仿真軟件可以為成型模具選擇適合的注射機(jī)。有助于避免塑料在加熱料筒中停留時(shí)間過長。Check for scratched or dented barrel/screw surfaces that trap This could lead to the material being overheated or Check for local overheating by a runaway heater band or a malfunctioning temperature 。Adjust the molding conditions調(diào)節(jié)成型條件Lower the barrel and nozzle Material degradation can result from a high melt temperature. 材料講解會由熔體溫度過高引起Purge and clean the injection The black streaks might be caused by contamination from the barrel wall or the screw surface. When molding with two materials, after switching from one material to the other,