AWS C37M/C37 pdf free download
AWS C37M/C37 pdf free download.Specification for Aluminum Brazing.
5. Process Requirements
5.1 Process I)escription. Aluminum and aluminum alloys are brazed using techniques that disrupt the surface oxides and limit their ability to re-fonn during the brazing process. These include brazing in a molten flux bath or molten metal bath, torch brazing with fluxes, induction brazing with fluxes, brazing in a controlled atmosphere furnace with special fluxes, and hrating in vacuum or controlled atmosphere furnaces. fluxless processes use elemental magnesium, magnesiumcontaining brazing filler metal, or magnesium-bearing base metals to getter available oxygen in the vacuum retort and to disrupt and penetrate the oxide film present on the aluminum surface.
The magnesium and other active elements can modify the wetting and alloying characteristics of the standard aluminum brazing filler metals, making them significantly more effective, as well as making the base metal more susceptible to brazing filler metal penetration. Because the melting ranges of the base metal and the brazing filler metal are usually close together, the temperature control requirements are more restrictive than those commonly used in the brazing of other metals.
5.2 General Heat Source Requirements. All furnaces and molten baths used in the brazing of aluminum shall have automatic temperature controlling and recording devices in good working order that are capable of controlling the temperature of the furnace or molten bath to the requirements of this specification. Furnaces and molten baths shall have adequate heating capacity to accomplish uniform heating of the workload at the rate required to prevent both thermal distortion of the assemblies and liquation of the brazing filler metal. They shall be properly maintained in good working order.
5.2.1 Temperature-Measurement and Control Instruments. In closed hatch-type furnaces and molten baths, suitable instruments and thermocouples shall be provided to measure and control the temperature of assemblies being brazed. The instrument shall be of the potentiometer type or equivalent and capable of measuring, recording, and providing a permanent record of the temperature throughout the entire brazing thermal cycle. In furnaces with multiple heating zones, similar instrumentation shall be provided for each zone.
All instruments used to measure the temperature of assemblies being brazed or to control furnace or bath temperature shall have an indicated temperature accuracy range of not more than ±O.57c of the maximum for which the furnace or bath is qualified over the entire operating range.
The indicated lemperature accuracy of the instrument shall he determined in accordance with the equipment manufacturer’s recommendations using a known electromotive force input traceable to the National Institute of Standards and Technology (NIST). All instruments shall be calibrated in accordance with SAE AMS 2750, Pyrometry, and ANSI Z540- I, General Requirements for Calibration Laboratories and Measuring and Test Equipment. Instruments shall be calibrated whenever repairs or modifications are made to them.
Instruments used exclusively to protect the furnace or bath from over-temperature accidents are not subject to the requirements of this subclausc.
5.2.1.1 Workload Thermocouples. Workload control thermocouples shall be of a type listed in ASTM E 230, Standard Specification and Temperature-Electromoti ic Force (EMF) Tables for Standardized Thermocouples. They shall be calibrated by comparison to a calibrated test instrument traceable to NIST.
The frequency of calibration shall he in accordance with ANSI Z540- 1.
5.2.1.2 Work-Zone Thermocouples. Work-zone control thermocouples shall be of a type listed in ASTM E 230. They shall be calibrated by comparison to a calibrated test instrument traceable to N 1ST.
The frequency of calibration shall he in accordance with ANSI Z540-l.AWS C37M/C37 pdf download.
