Refer to Section 4.4 for general quality control requirements.
Dry Room Conditions
The electrolyte and anode materials are very hygroscopic and react to moisture. Therefore, active cell components must be prepared in a very dry atmosphere. Batteries must also be assembled in a similar atmosphere. For some processes, a relative humidity level of 5% (at +27ºC) or less may be required.
Vacuum drying is an important step in ensuring proper battery performance. The reactivity of cell components with moisture makes vacuum drying of battery components a must. Manufacturers and thermal battery engineers have their own specific methods of vacuum drying certain components. Table 8-5 is a list of typical temperatures and times for vacuum drying battery components.
Due to the high internal temperature of a thermal battery, it is preferred that all metal-to-metal joints be made by the resistance welding process. Resistance welding is a very reliable process. Joints created by this process will withstand the thermal shock caused by rapidly raising the temperature of the joint from 55ºC to at least +330ºC. MIL-W-8939 or MIL-W-6858 specify the resistance welding to be used.
The thermal battery is enclosed in a hermetically sealed metal container. The header is welded to case by the fusion welding process as specified in NAVSEA Drawing No. 5257344.
All structural and external welding should be performed in accordance with the requirements of MIL-W-8611 or AMS 2681. With the cell stack in place, care must be exercised to prevent the pyrotechnic device in the cell stack from igniting. All spot welding should be performed in accordance with MIL-W-6858, Group 2, Class A.
The manufacturer should establish a suitable welding schedule for each type and size of weld joint and material for each model of battery. Welding should be performed only by qualified welders and welding operators.
All brazing performed on the thermal battery should be in accordance with MIL-B-007883.
Soldering & Solderability Specifications
Solderability of the battery output terminals should be verified by testing to the requirements of MIL-STD-202, Method 208. Either high temperature solder or spot welding should be used for electrical connections to the output terminals. DOD-STD-2000 requirements apply for soldering of external electrical connections.