空洞Void.doc

空洞Void1） 何谓空洞（外观）Void is a phenomenon that hole is generated in mold piece.是指成型品内部产生空洞的一种现象。图1. 手柄型试样的厚壁处出现的空洞Figure.1 Void in handle type test piece (X-Ray photo.)上面的图片是软X射线拍摄的透射图片。在软X光图片表明成型品内部存在空穴，呈白色。在OK品（合格品）中，仅在轴的插入部分（浇口附近）呈现白色。而在NG品（废品）中，除此以外还有2处呈现白色，表明产生了空洞。Above pictures are taken by soft x-ray photograph. Void is white area in the photograph. Voidless product has only bearing hole. Otherwise, Void product has another two hole as shown white area.空洞的原因大致分为两种：一种是大量气体的混入，另一种则是厚壁处的的树脂收缩。前者称为“气体空洞”，后者称为“真空空洞”，以示区别。The causes of void are classified into two. One is by mixing of a considerable amount of gas, and the other is by shrinkage of resin in a thick part. The former is called void by gas, and the latter is called vacuum void for differentiation.图2. 气体空洞与真空空洞的区别Figure.2 Difference between void by gas and vacuum void（2）空洞的生成原因 (2) Causes of Void Formation(2-1) 气体空洞(2-1) Void by gas气体空洞有两种类型：一种是由机筒内部产生的气体引起的，另一种是在模腔填充中封入了气体所致。The void by gas has two patterns. One is the pattern caused by gas generated inside the cylinder, and the other is the one caused by gas trapped in cavity filling.前一种空洞的气体成分有3种：水分、树脂的分解气体和空气。预干燥不足时容易产生水分；机筒温度高且滞留时间长时容易产生树脂的分解气体；计量期间螺杆转速过快且背压不足时容易产生空气。The gas components in voids of the former include moisture, decomposed gas of resin, and air. Moisture is liable to be generated when predrying is not sufficient, decomposition gas of resin is when cylinder temperature is high and residence time is long, and air is when the screw rotation speed is too high in metering and when the back pressure is not sufficient.后一种空洞取决于树脂的流动样式，因此原因在于浇口设计。就成型条件而言，如果注射速度很快、没有排气口、或排气不充分，则容易产生空洞。The latter pattern comes from flow pattern of resin and the cause is in gate design. As molding conditions, it is liable to be generated when injection speed is fast, and when no or insufficient vent is given.(2-2) 真空空洞（保压不足）2) Vacuum void (Insufficient holding pressure)通常，注射成型中有一道保压工序，冷却固化收缩的树脂量将通过保压来得到补充。不过，如果因某种原因 使有效保压偏低树脂难以的到充补，当模温偏高时就容易形成凹痕，而在模温偏低时容易形成空洞。导致保压变小的主要原因如下：Usually injection molding has a pressure holding process in which the shrinkage by cooling and solidification is covered to some extent by intruding resin (compensation) by the holding pressure force. However, if the effective holding pressure is insufficient or the compensation of resin is hard by any reason, either sink or void is easily formed, the former for high mold temperature and the latter for low mold temperature. The factors for insufficient holding pressure are as follows:1） 保压设定值偏低(1) Low setting value of holding pressure,（2）保压时间偏短(2) Short pressure holding（3）浇口尺寸偏小(3) Small gate size,（4）分流道偏细(4) Narrow runner.此外，鉴于浇口位置的重要性，必须尽可能将其设置在厚壁处 time,Gate position is also important, and it is necessary to locate it at the thickest part as far as possible.。2）图3. 模温引发空洞或凹痕Sink or Void generation by mold temperature（3） 空洞的对策(3) Countermeasures against Void(3-1) 补充树脂(3-1) To compensate resin无论是气体形成的空洞还是收缩形成的空洞，共同之处都在于通过妥善地补充树脂使问题得到改善。例如，通过提高保压（延长保压时间）可使情况发生显著变化。就提高保压的方法而言，与简单地调高保压的设定值相比，采用多段保压 效果会更好。Void, whether by gas or by shrinkage, can be improved in common by compensating resin well. For instance, to increase holding pressure (to extend pressure holding time) can change the condition considerably. The way of increasing holding pressure is better to gradually increase holding pressure by multistage pressure holding than to simply raise the setting value.但是，在实际成型中，即使提高保压的设定值，施加在空洞出现部位的压力也未必能变得足够大。因此建议同时采用下列方法：In actual molding, to increase the holding pressure set value does not necessarily mean to sufficiently increase the pressure to the part of void formation. Thus, it is recommended to jointly use the following methods:增大浇口尺寸To increase gate size,增大主流道和分流道的口径To expand sprue and/or runner size,浇口应尽可能设在空洞产生部位（较厚部分）的附近?Locate gate as close as possible to the void forming place (thick part).3-2) 减慢表面固化3-2) To delay solidification of surface如果是真空空洞，则提高模具温度可以减少空洞。不过，这种方法很可能会诱发凹痕，而且 对有些产品来说,没有什么好的解决方法In vacuum void, void is reduced by raising mold temperature. This method, however, has a high possibility of inducing sink, and no appropriate point may be found, depending on the product.。(3-3) 抑制气体的产生3-3) To suppress gas generation如果是气体空洞，则可通过抑制气体的产生来减轻空洞。具体方法如下：Void by gas can be reduced by suppressing gas generation. Concretely, the following methods may be effective.强化预干燥条件To intensify predrying condition降低机筒设定温度To lower cylinder setting temperature,缩短成型周期Shorten molding cycle,降低螺杆转速To reduce screw rotation speed,提高背压?, ?To increase back pressure.3-4) 改善排气状况(3-4) To facilitate gas venting对于模腔填充中因封入气体而产生的空洞，可通过降低注射速度、或强化排气口以改善排气状况来减少空洞的产生。In the void of the type generated by entrapping gas during cavity filling, void can be reduced by decreasing injection speed or facilitating gas venting with intensified venting.3-5) 减小厚度由于厚壁处出现的真空空洞起因于树脂收缩，因此可能的话，应该考虑更改制品形状以减 少厚度。可能的话，最好在设计阶段就事先采取“掏空”等改变制品形状的措施Since vacuum void formed in a thick part is caused by resin shrinkage, shape change to reduce this thickness should be considered, if possible. It is desirable to take a shape countermeasure such as thinning