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中文English

超聲波焊接原理

“超聲波換能器”-夾心式壓電換能器的結構

在進行超聲波焊接的時候考慮到實用，在功率超聲中其振動頻率往往處在低頻的超聲範圍。爲了降低超聲波換能器的工作頻率，又能獲得較高的縱向振動電聲效率，在工程技術中常釆用一種複合式夾心壓電換能器結構。即采用片狀壓電體堆與前後端金屬塊組合而成。所謂改進就是考慮到壓電陶瓷體抗拉強度較差，通過金屬塊給壓電體施加足夠的預應力，使壓電換能器作大功率振動時，壓電效應始終處于受壓縮的周期變化之中，這種力學狀態確保壓電體不破裂，而最大限度地發揮換能的功能。這是壓電換能器能廣泛應用于功率超聲技術中關鍵之一。

其次，夾心式壓電換能器可以通過改變金屬塊的厚度來獲得不同的工作頻率(5kHz—100kHz),制作方便，它的典型結構如圖L18所示。圖中結構由PZT壓電陶瓷、電極片、預應力螺杆及前後金屬蓋板等組成。壓電陶瓷晶片以偶數疊台，相鄰兩片的極化方向相反，電極片間采用並聯的方法連接。

前蓋板通常是钛、鋁合金，後蓋板通常是鋼。所有這些材料的疲勞強度要高，材料的機械損耗要低。組合前的加工另件的光潔度和平行度均要足夠好，才能保證超聲波換能器有良好的机电耦合特性。预应力螺杆要采用高强度的螺栓钢制造,抗张强度要在80kg/mm2以上。对不同使用对象，前后盖板可做成不同形状。例如，在超声清洗应用中，为增大辐射阻，前盖板做成啦叭形，使辐射面适当增大。在超聲波塑料焊接等應用中，爲了要把超聲能量高度聚焦到一定的加工面積上，前蓋板可制作成各種λ/4聚能器形式。

夹心式换能器的压电晶片数量、形状、直径及厚度。是根据工作频率及需要给岀的声功率等条件设计计算岀来的。除了这些之外，还要根据振子谐振条件，计算出前后盖板厚度及振子节点 (即振幅为零的部位，用作固定点)。一般振子的长度为 λ/4、λ/2或3λ/2等。这个λ(波长)是等效波长，因为振子是不均匀的复合结构。

超聲波模具改短後還可以使用嗎？

“超聲波”除了焊接、清洗，你知道它的篩分功能嗎？

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