【導(dǎo)讀】常州機(jī)電職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)說(shuō)明書(shū)

　　

【正文】 nseets, etc. How close it is safe to position in a flow way adjacent to another hole depends to a large extent on the depth of the flow way drilling required. When drilling deep flow ways there is a tendency for the up to 150mm deep the flow way should not be closer than 3mm to any other hole. For deeper flow ways this allowance is increased to 5mm. To obtain the best possible position for a circuit it is good practice to lay the circuit in at the earliest opportunity in the design. The other mould items such as ejector pins, guide bushes, etc, Can then be positioned accordingly. 常州機(jī)電職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 32 模具冷卻系統(tǒng) 注塑生產(chǎn)的基本原理是把高溫熔體注入模具型腔，熔體在型腔內(nèi)迅速冷卻到固化溫度并保持一定形狀。由于模具溫度在一定程度上控制塑件的整個(gè)成型周期，因此非常重要。熔體在高溫模具內(nèi)流動(dòng)順暢，但固化塑件推出前，一定的冷卻階段是必不可少的。寧一方面，熔體在溫度較低的模具中固化較快，但也有可能造成塑件末端填充不滿。因此必須在這兩種對(duì)立的條件中選擇一個(gè)平衡點(diǎn)，以獲得最佳的生產(chǎn)循環(huán)。 模具的動(dòng)作溫度與幾種因素有關(guān)，包括成型材料的等級(jí)與類(lèi)型、熔體在型腔內(nèi)的流動(dòng)路線、塑件壁厚以及澆注系統(tǒng)長(zhǎng)度得等。使用比充模要求稍高的溫度注塑比較有利，這樣生產(chǎn)的塑件熔接痕少、流痕不明顯，其他缺陷也比較少，因此，提高了塑件表面質(zhì)量。 為保持模具和塑料熔體之間所需的溫差，水在模具上的通道或通孔中循環(huán)。這些通道或通孔稱為流道或水道，整個(gè)水道系統(tǒng)稱為冷卻循環(huán)系統(tǒng)。 在充模階段，溫度最高的熔體位于進(jìn)入口，即澆口附近；溫度最低的熔體位于距進(jìn)入口最遠(yuǎn)的地方。冷卻介質(zhì)在模具內(nèi)循環(huán)時(shí)，介質(zhì)溫度將升高。因此，為使塑件表面獲得均勻的冷卻速率，冷卻通道的入口應(yīng)開(kāi)設(shè)在高溫塑件附近，受熱后冷 卻介質(zhì)溫度升高，出口開(kāi)設(shè)在低溫塑件附近。然而有下面討論可知，這種理想狀態(tài)并不總是可行的。為避免不必要的模具費(fèi)用，設(shè)計(jì)者往往憑借經(jīng)驗(yàn)設(shè)計(jì)冷卻通道。冷卻水回路所需的部件在市場(chǎng)上就可以買(mǎi)到。這些部件通過(guò)軟管與模具直常州機(jī)電職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 33 接連在一起，通過(guò)這些部件模具溫度便控制在要求的范圍內(nèi)。但是，使用這種直接與冷水相連的冷卻是不可能精確低控制模具溫度的。 為模具提供適合的冷卻系統(tǒng)是是記者的責(zé)任。通常，最簡(jiǎn)單的冷卻系統(tǒng)是在模板上縱向鉆出通孔。然而，對(duì)于精密模具，這不是最有效的冷卻方法。 然而，使用鉆孔的方式加工冷卻水道時(shí)，冷卻通道是塑件的 距離一定不能太近如果距離太近，有可能引起整個(gè)型腔的溫度發(fā)生顯著改變，使塑件出現(xiàn)問(wèn)題。 由于冷卻通道不能距離同一模板上任何其他的孔道太近，這使得冷卻回路的布局通常比較復(fù)雜?？梢韵氲侥０迳洗嬖诖罅康目椎阑虬枷?，用來(lái)安裝推桿、導(dǎo)柱、導(dǎo)套、澆口套以及鑲件等。冷卻通道與其他孔道之間的安全距離為多遠(yuǎn)，很大程度上取決于所需的冷卻通道的鉆入深度。流道深度較深時(shí)，鉆頭有偏離預(yù)定路線的趨勢(shì)。常用的規(guī)則是鉆入深度達(dá)到 150mm 的冷卻水道與其他孔道距離不小于 3mm，比這更深的流道所需的距離增加到 5mm。 為獲得最佳的冷卻回路，設(shè)計(jì) 初期就考慮冷卻回路的位置不失為一種好辦法。其他模具零件，如推桿、導(dǎo)套等，更具需要確定安裝位置。 常州機(jī)電職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 34 Runnerless Moulds Nozzle types The purpose of the nozzle is to provide a flow path for the plastic melted from the machine’s cylinder to the mould. In the simplest design the nozzle butts on to the sprue bush of the mould. There are two standard designs in mon use and they differ only with respect to the form of seating that is made with the sprue bush. One design incorporates a hemispherical end and the other design is flatended. The small length of reverse taper in the bore at the front end of the nozzle is such that the sprue is broken just inside the nozzle. This helps to keep the nozzle fface clean and assists in maintaining a leakfree sealing face. The nozzle types are as follows: extended nozzle, barb nozzle, antechamber design, internally heated sprue buch internally heated extension nozzle, multinozzle manifold. This is the name given to a mould which contains a heated runner manifold block within its structure. The block, suitably insulated from the rest of the mould, is maintained at a closely controlled elevated temperature to keep the runner permanently as a melt. The polymer material can thereby be directeted to the mould extremities without loss of the heat and without the pressure loss associated with tenperature variations. The hotrunner unit is mounted adjacent to the cavity plate and acmodated in a suitably design grid. The polymer material enters via a 常州機(jī)電職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 35 centrally positioned sprue bush, passes through the flowway and leaves the unit via a secondary nozzle in line with the impression. When the mould is opened the molding is pulled from the cavity, and the sprue is broken at the small diameter end. The remainder of the feed system remains heated within the unit, ready for the next shot. An insulated runner mould is one in which the melt flows through a largediameter runner machined in the butting surfaces of the cavity plate and thefeed plate of a threepart mould. The two plates are attached together by quickrelease swing laches during the normal molding operation. Polymer melt flows from a standard or extended nozzle into a largedimmeter runner, and finally into the impression via the reverse tapered sprue and gate. The mould is operated as a simple twopart mould in that the runner system is not removed during the normal cycle of operations. As the mould opens, the molding is extracted from the cavity and the gate is broken at its junction with the reverse tapered sprue. This technique is only practicable because thermoplastics have such good insulating properties. The outer layer of the melt solidifies against the code runner wall which forms an insulating shell, while the central core of the material remains in the melt state. Proided that the molding cycle permits the melt to pass intermittently through the runner system without extended holdups, the mould can operate continuously in this 常州機(jī)電職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì)說(shuō)明書(shū) 36 fashion. Naturally, solidification of the runner syetem will occur if the production cycle is interrupted for any reason. When this happens the laches are released, the respective plates are separated, the‘ solidified’ runner is removed. The insulated runner mould is similar in construction to the underfeed mould. Basically, the only differerence between the two is that the former design incorporates a largerdiameter runner, a largerdiameter reverse taaperd sprue, and a swing latch systen. The diameter adopted for the runner is in the range 13mm~25mm, and a correspondingly large diameter is chosen for the reverse tapered sprue. From the above ments it will be apparent that an underfeed mould can be readily modified to an insulated runner design, if required. The development of the insulated runner mould is credited to Philips