Tantalum is often used to make capacitors because the anodized surface forms an amorphous oxide film with a high dielectric constant. Tantalum wire is used as the anode lead for capacitors. One of the key indicators of capacitors is the leakage current performance. The hardness characteristics of tantalum wire have a great influence on the leakage current. High hardness tantalum wire cannot be used to manufacture capacitors.
Tantalum wire can be divided into three types according to different tensile strength :(1) soft state (M), tensile strength σb = 300 ~ 600MPa; (2) Semi-hard (Y2), tensile strength σb = 600 ~ 1000MPa; (3) Hard (Y), tensile strength σb> 1000 MPa. The traditional tantalum wire manufacturing process is as follows:
Powder forming (bar making)→ sintering → rolling → surface oxidation film forming → large drawing → intermediate annealing → small drawing (straightening)→ cleaning → rewinding → packing and warehousing
Annealing of tantalum wire can eliminate the residual stress and improve the microstructure by recrystallization. At present, tantalum wire annealing is generally carried out in vacuum heat treatment furnace with the annealing temperature basically at 1400-1500℃. After annealing, the finished product is straightened by wire drawing machine. This method can be used to produce hard tantalum wire, but when producing semi-hard or soft tantalum wire, it is difficult to straighten the annealed tantalum wire and its flatness is low. The flatness of tantalum wire refers to the ratio of the distance between the center line of the two endpoints of 200mm tantalum wire and the center line of tantalum wire after the natural loosening and the length of tantalum wire. The flatness is a dimensionless value, and the smaller the value, the straighter the tantalum wire. There are strict requirements for the flatness of tantalum wire for preparing capacitors, so it is necessary to find a suitable annealing device and method.
The tantalum wire is threaded, and the tantalum wire is carried out by the wire releasing wheel. After winding through the upper guide wheel, the tantalum wire enters the insulation box through the inner conduit of the upper guide box vertically. Open the incubator, pass the tantalum wire through the opening on the heat insulation screen, and run it vertically into the guide post of the hanging cabinet heater; The tantalum wire goes down through the hatch heater and out through the opening below the heat shield. The tantalum wire is then inserted into the inner conduit in the lower guide box. After passing through the lower guide box, the tantalum wire is wound through the lower guide wheel and then collected by the receiving wheel.
Tantalum wire in wire finished, start the circulation water cooling device, argon shielding gas is piped in, start the monitoring oxygen content and oxygen monitoring system when the oxygen content is less than 50 PPM inside the heat shield, start the electric heating system for heating, when condole heater temperature reaches the specified temperature, the feeding wheel began to radiate, take-up wheel synchronous line, according to the specified speed for tantalum wire annealing. The tension on the wire pulley is less than 10N during annealing.
The annealing temperature is between 1150-1250℃, the tension on the wire pulley is less than 10N during annealing, and the diameter of tantalum wire remains unchanged after annealing. When the drawing speed is between 3.5m /min and 4.5m/min, the semi-hard tantalum wire is made. When the winding speed is between 2-2.5m/min, the soft tantalum wire is made.
