计量不良Unstable metering.doc

计量不良Unstable metering何谓计量不良What is Unstable metering ? (appearance) 1. 是指无法向机筒内供给树脂，或供给量不稳定的一种现象。This failure is phenomenon that pellet can not be carried forward or Metering value is unstable. 这些现象虽然统称为计量不良，但实际上有几种模式：Unstable metering has three pattern.（1）根本不计量Never to meter 2. （2）计量时间有时会延长Sometimes, metering time is extend （3）有时会出现填充不足Sometimes, Short shot is occurredThese failures are come from unstable pellet supply into cylinder between metering.这些都会造成计量不良，也就是计量时提供给机筒内的树脂量不稳定。图1. 计量值Figure.1 Metering value（2）计量不良的生成原因 Causes of Metering Failure (2-1) 螺杆转速不当Screw rotation speed is not suitable.通常，螺杆转速越高，粒料的输送力就越强。因此，如果螺杆转速偏慢，粒料的输送力就会减弱，从而导致粒料供给不稳并产生计量不良。相反，如果转速过快，粒料就会与螺杆一起运动，同样也不能前进。Normally, as the screw rotation speed increases, the conveying force of pellets increases. Therefore, when the screw rotation speed is too low, the conveying force is so weak that pellet feed becomes unstable to cause metering failure. On the other hand, if the screw rotation speed is too fast, pellets turn with the screw and do not move forward to cause metering failure again.2-2) 背压偏高Back pressure is too high.背压具有抑制气体卷入树脂内和稳定注射树脂量的作用，但同时也有减弱输送力的效果。因此，如果背压过高，计量就会变得不稳定。While back pressure has effects to reduce gas components caught in resin and to stabilize the resin quantity to be injected, it also has an effect to weaken the conveying force. Accordingly, too strong back pressure may lead to unstable metering.2-3) 机筒设定温度不当Set cylinder temperature is not suitable.机筒设定温度会对机筒内的粒料温度产生影响。也就是说，由于粒料的表面状态及刚性发生变化，因此对计量也有影响。特别是料斗下方及其相邻的设定温度会对计量带来很大影响。Set cylinder temperature affects the pellet temperature in the cylinder. In other words, changes of surface condition and rigidity of pellets affect metering. In particular, the set temperatures under the hopper and of the adjacent position greatly affect metering.一般来说，从喷嘴到料斗下方的温度设定由高到低，且料斗下方的设定温度低，计量便会保持稳定。这是因为温度升高后，粒料表面就会熔化，粒料之间的摩擦增大，从而导致互相交织缠绕，或粘着在螺杆或机筒上。In general, metering is stabilized by giving a temperature gradient from the nozzle temperature to the under-the-hopper temperature with a low under-the-hopper temperature. If the temperature is too high, pellet surface is melted to increase the interpellet friction.2-4) 等级固有的问题Problem proper to grade在滑动等级中，由于与金属之间的滑动过于良好，因此螺杆旋转力不能很好地转换成向前的输送力，从而容易造成计量不良。另外，在耐冲击等级中，粒料之间的摩擦容易增大，这也极易造成计量不良。Some sliding grades have so good sliding on metal that the conveying force in screw rotation is reduced to cause metering failure. Impact resistant grades tend to have large interpellet friction, which also leads to metering failure如果要用螺杆来输送粒料这样的颗粒，则应在外侧的机筒面上使粒料难以滑动，而在内侧的螺杆面上使粒料易于滑动。正是由于这种摩擦上的差异，旋转力才变成了把粒料向前输送的力。如果外侧面易于滑动，而内侧面不易滑动，粒料就不能被很好地向前输送。图2. 基于螺杆的固体输送的原理Its necessary to use slippy surface screw and frictional inner surface barrel to carry small grain like pellet with screw in cylinder. The carrying force is generated from these friction differ between screw and cylinder surface. If inside surface of cylinder is slippy or surface of screw has much friction, pellet is not carried. ( If you want to know more detail, please refer Particle Technology Guide book)2-5) 使用了回收材料Use of recycled material回收材料通常形状很不规整，因此与普通粒料相比，料粒之间的摩擦容易增大，从而容易引起计量不良。此外，粉末混入后会粘着在螺杆上，从而使输送力减弱。Recycled materials usually have fairly irregular shapes so that the interpellet friction tends to be larger compared with normal pellets, leading to metering failure. When powder is mixed, it sticks to the screw and may weaken the conveying force.图3. 普通粒料、回收材料的粒料Figure.3 Normal (Left), Recycled (Right) pellet3） 计量不良的对策Countermeasures against metering failure3-1) 调整螺杆转速To adjust screw rotation speed首先应调整螺杆转速At first, adjust the screw rotation speed.若想定期观察有无计量不良现象，应测量计量时间。通过 50 100 次连续成型，并分若干阶段改变转速、根据计量时间是否突然变长等情况来作出判断。螺杆转速一般为 80 120rpm 左右，请根据具体情况，选择最佳范围In order to quantitatively observe if the metering failure is present, measure the metering time. Continuous molding of 50-100 shots is carried out with varied rotation speeds in several steps, and observe if the metering time suddenly becomes longer.。 单凭调整螺杆转速不能解决问题时，则可采取同时更改背压或机筒温度的方法。The screw rotation speed is normally 80-120 rpm, but the best range changes depending on the condition.3-2) 降低背压To reduce back pressure背压越低，粒料的输送力就越强，计量也就越稳定。但降得过低会使气体的卷入增多并导致树脂量不稳，因此设为0并不可取。As the back pressure decreases, the pellet conveying force increases to stabilize metering. Too much reduction may lead to gas catching to cause unstable resin quantity. So, back pressure should not be set at zero.3-3) 机筒温度Cylinder temperature具体来说就是要一点一点逐渐降低料斗下方的温度。过度降低会使粒料不易熔化，甚至会堵塞机筒，因此要逐渐调整（每次10左右）。Concretely, lower the under-the-hopper temperature little by little. Too much lowering may cause insufficient melting of pellets, leading to plugging in the cylinder at worst. The change should be made little by little (by about 10?unit).3-4) 等级固有的问题Problem proper to grade由于掺入了油或润滑剂，因此滑动等级原本就具有容易滑动的性质。如果同时调整螺杆转速、背压和机筒温度也难以解决问题时，则应考虑更改等级或螺杆设计Since sliding grades are formulated with oil and lubricant, they originally have a property to easily slide. If the failure can not be solved even by the joint use of screw rotation speed, back pressure and cylinder temperature, changes of grade or screw design may be necessary.在耐冲击性等级中，粒料之间的粘合对计量构成了最大障碍。这时，尤其需要降低料斗下方的机筒温度。In impact resistant grades, interpellet fusion is the largest obstacle in metering. At that time, lowering of the under-the-hopper temperature of the cylinder is necessary.3-5) 回收材料Recycled material尽可能将回收粒料和初始粒料