TASK 70-44-01-370-002
1 . General.
A.Localized heat treatment is a process used to stress relieve or age repair welds and cold-worked areas. The process is particularly suited to the heating of small localized areas on large parts that can be difficult or inconvenient to transport or process in a furnace. This section identifies the equipment and setup procedure, while TASK 70-44-02-370-003, Localized Heat Treatment Procedures, lists various heat treat cycles that apply, using this method. The repair procedure for a particular part, contained in the Engine/Shop Manual, specifies the required cycle by referring to the applicable cycle code number and TASK 70-44-02-370-003, Localized Heat Treatment Procedures.
NOTE:
Localized heat treatment is to be used only when specifically directed by repair instructions for a particular part.
2 . Equipment.
Subtask 70-44-01-370-021
A.Heaters.
Various heater types and heat sources are available and suited for this process.
(1)Quartz-halogen, tungsten-quartz, and infrared heating elements with directional or focused reflectors.
(2)Ceramic pad heaters.
(3)Induction heating with coils suited for the geometry of the repair area.
(4)Heated atmosphere delivery device (HADD) or torch whereas air or other atmosphere is flowed at a controlled rate across resistive heating elements. This hot gas is impinged or flowed onto the repair area.
(5)Wire coil resistive heating elements wrapped or positioned around or about the repair area.
B.Controls.
(1)The heat source selected for use shall have a controlling device that allows output adjustment in order to maintain the desired temperature set point.
(2)Each heat source used shall have a separate control device for over temperature protection.
C.Service Leads.
(1)Service leads for power, air (or other gasses), and/or water cooling are required for most heater types.
D.Recording Instrumentation and Thermocouples.
(1)Ensure that all temperature measuring instruments have an indicated temperature measuring accuracy of ±0.5 percent of the maximum temperature measured over the entire operating range.
(2)Thermocouples must be in accordance with ASTM E 220 and ASTM E 230. Gauge of thermocouple used can be varied to allow access and/or attachment to the various repaired areas and geometries of the parts.
(3)Test Method - Temperature sensors and recording devices will be calibrated to the requirements of AMS 2750 unless otherwise specified.
E.Setup.
Set up the equipment in the following manner.
(1)Heaters.
(a)Position the heat source to encompass the entire repaired area and any secondary affected areas such as heat-effected zones or cold-worked stressed areas.
(b)When using multiple heating devices on one side of the repair area, ensure there is no cold zone between the various heaters by overlapping or keeping heaters as close as possible.
(c)Heat can be applied to both sides of a repair, if accessible, or to one side only.
(d)Configuration of part and heating equipment usually determines which way the heat is applied. If heat is applied from one side only, a glass cloth blanket, batt or C06-022   ceramic fiber insulation or similar insulation should be used on the side opposite the heater. Surfaces surrounding the repaired area should be protected from heating by covering or shielding them with insulation blankets or batts. Only those surfaces requiring heat treatment are to be exposed to direct heating, within limits of part geometry.
(e)The heating elements shall extend beyond all parts of the repair as geometry allows, and shall be positioned as close as practical, approximately 0.50 inch (12.7 mm) from the surface of the part without allowing element contact to the part.
(2)Thermocouples.
(a)Generally, thermocouples should be attached to the back or reverse side of the repair area from the heating element. Enough thermocouples shall be used to ensure that the repair area reaches, and is held at, the specified temperature per the repair procedure. A minimum of 2 thermocouples will be used on all repairs.
(b)Excessive changes in material thickness, configuration, or the existence of accessory pads, ribs, brackets, etc. within the repair length to be heated by a specific heat source, must be considered independent sections within that length. These sections must have thermocouples attached to ensure uniform temperature within the repair requirement or have their own subsequent and separate local heat treatment at the necessary temperature, unless specified differently within the repair procedure.
CAUTION:
TACK-WELDED THERMOCOUPLES TO TITANIUM PARTS MUST HAVE ALL WELD-AFFECTED MATERIAL SUBSEQUENTLY MACHINED OFF.
(c)Thermocouples can be attached to the weld repaired area by the capacitance discharge weld method; this is the preferred method.
1Thermocouples can be attached to a consumable detail and clamped in a manner that allows intimate contact to the part; this method is typical for a finished surface.
2Thermocouples can be used in heat sinks where a chamber is devised around or about the repaired area provided a survey is performed to correlate the heat sink and part temperatures.
3Non-expendable thermocouples can be used as stand-alone where a chamber is devised around or about the repaired area provided a survey is performed to correlate the thermocouple and part temperatures.
aFor titanium parts, the weld can be built-up approximately 0.100 inch (2.54 mm) for thermocouple attachment. It is necessary to machine off the weld build-up.
bAfter the cycle, thermocouples are broken or ground off and the part blended to the initial contour.
(d)Thermocouples placed per paragraphs 2.E.(2)(c) and 2.E.(2)(c)1 must be spaced every 2.0 inches (50.8 mm) maximum along the area that is to be locally heat-treated.
1Thermocouples placed per paragraphs 2.E.(2)(c)2 and 2.E.(2)(c)3 must be spaced reflective of the survey performed along the area that is to be locally heat-treated.
aFor long welds of constant thickness (such as circumferential welds), it is permitted to use less than one thermocouple every 2 inches (50.8 mm) if there are sufficient thermocouples to monitor the weld and heat-affected zone temperature.
(e)For welds greater than 8 inches (20.3 cm) long and of constant thickness, a minimum of four thermocouples is necessary.
(f)The temperature profile must be monitored with thermocouples to give a correct readout for control during the heat treat cycle. Temperatures shall be monitored constantly using a chart recorder to record all monitoring thermocouple readings. At a minimum, thermocouple readings should be checked at regular (10 minute) intervals by the operator.
1Each thermocouple attached to the part shall be numbered, and a map of the thermocouple positions, preferably drawn to scale, recorded in a log or attached to the chart record.