- 學位論文
超深冷設備改良及其在電鍍工件脫氫上之應用
The Improvement of the Cryogenic Equipment and the Application on the Dehydrogenation of Electroplated Carbon Steel
摘要
為了改善一般超深冷處理設備的缺點，本研究設計以浮力帶動工件的超深冷處理裝置和PID溫度控制裝置，來實施超深冷處理。將工件從室溫緩慢而穩定地冷卻至液態氮的溫度，保持適當的時間，使其內應力完全釋放，組織結構達到安定化，以提升其使用壽命。與一般工業上所用的超深冷處理設備比較，本計畫所開發的浮力式超深冷和PID溫度控制裝置之特點為:其所能達到的溫度較低，處理效果較好;而且降溫、升溫的速率較為穩定平滑，不會有溫度突升或突降的情形發生，故處理後的工件完全沒有熱應力;此外，也能顯著節省液態氮的消耗，降低超深冷處理的成本。 工業上有很多種方式，使金屬獲得鍍層，包括電鍍、物理氣相沈積、離子鍍、化學鍍、熱浸鍍等等，其中可沈積金屬應用最多最廣的為電鍍工業。電鍍為一種氧化還原反應，將所要被鍍鍍層的工件放在陰極，欲想鍍的金屬放在陽極，放入欲鍍層的金屬液，通以電源後表面即得到想要的鍍層。產品施以電鍍時，由於陰極會產生氫氣，而氫原子滲入產品表層及內部，導致產品韌性降低，受力時產生氫脆現象。一般在工業上解決的方法為將產品加熱到一定的溫度，使得固溶在產品中的氫原子擴散出來，以恢復韌性，但此種方法容易犧牲其硬度，使得產品強度降低。本研究擬採用氫的溶解度隨著溫度降低而減少的原理，將電鍍後的縫紉車針，以適當穩定的降溫速率冷至液態氮溫度(-196℃)，保持一段時間使其固溶在縫紉車針中的氫原子擴散出來，再以適當速率回升到室溫或室溫以上，而完成超深冷脫氫處理。實驗過程先在不同條件下將電鍍後的縫紉車針烘烤加熱，再實施適當的超低溫處理，並分別測試硬度、彎斷角度、氫含量，以了解其脫氫效果，進而尋求最佳脫氫處理條件。跟傳統比起來，除了改變不同加熱烘烤參數外，還對烘烤後的縫紉車針施以超低溫處理，以促進其脫氫效果。此外，超深冷處理對於縫紉車針的基材組織而言，也有安定化而延長其使用壽命的效果。
並列摘要
To improve the disadvantages of the apparatus in the cryogenic treatment, a design of buoyancy-drive and a PID temperature control apparatus were applied for cryogenic treatment in this research. With the purpose of extending the service life, workpieces were cooled down slowly and steadily from room temperature to the temperature of liquid nitrogen, kept for an appropriate period of time for the relaxation of inner stress and the stabilization of microstructures. Compared with the cryogenic equipment used in industries, the buoyancy-drive cryogenic apparatus designed in this research has the following features: lower temperatures could be reached, thus resulting in better effects of treatment; the temperature variation rates were steadier and smoother, without the occurrences of abrupt rises or falls in temperatures, thus, no thermal stress would be induced in the workpiece. Besides, the consumption rate of liquid nitrogen was relatively low, and the cost of cryogenic treatment could be reduced. There are many methods in industry for metals to attain coated layers, including electroplating, physical vapor deposition, ion coating, chemical coating, thermal immersed coating, etc. Among these the most widely used method is electroplating. Electroplating is an oxidation-reduction reaction, in which the workpiece needed for coating is placed at the cathode, with the desired coated metal layer at the anode, and then placed into the metallic liquid of the desired coating layer. When power source is applied, the surface will attain the desired coating layer. During electroplating process, hydrogen generated at the cathode will penetrate into the interiors of the products and decrease the toughness of products. This is the so-called hydrogen embrittlement. To solve this problem, the products are reheated to an appropriate temperature and kept for a period of time. Thus, the hydrogen atoms dissolved in the products will be released, and the toughness and ductility of the products will be recovered. But, this method tends to lower the hardness of the products. In this study, cryogenic dehydrogenation was accomplished by adapting the principle that the solubility of hydrogen in steels reduces with temperature. Electroplated sewing needles were cooled down to the temperature of liquid nitrogen (-196℃), and kept for a period of time to release the hydrogen atoms dissolved in them. Then, temperatures were raised back to or above the room temperature with appropriate rates. In the experimental process, electroplated sewing needles were baked under various conditions in advance to the cryogenic treatment. The hardness, bending angle, hydrogen amount of the specimens were then tested respectively to understand the effect of dehydrogenation. Thus, optimized dehydrogenation treatment conditions could be attained. Compared to traditional dehydrogenation treatment, in this research, besides altering different baking parameters, cryogenic treatments were also applied to the baked sewing needles in order to promote the effect of dehydrogenation. Moreover, cryogenic treatment also has the effect to stabilize the microstructure of the sewing needle and extend its service life.