Preliminary Requirements

Procedure

1. SUBTASK 70-37-03-370-001 Safety Precautions

   1. The health and safety data given are general guidelines in use at Rolls-Royce, it is the responsibility of the operator/user to obtain detailed health and safety data for the materials in use and to refer to local regulations to ensure safe working practice.

2. SUBTASK 70-37-03-370-002 Furnace and Oven Instrumentation Control and Routine Checks

   1. Heat Treatment Furnaces, Hot Working Furnaces and Ovens for non-critical applications shall be controlled in accordance with AMS 2750 (latest issue) with the exception of the parameters listed in Step. Additional exceptions for Ovens for non-critical applications are listed in Step.

   2. The use of AMS 2750 (latest issue) tolerances and control are subject to all the requirements of the relevant repair instructions being met.

3. SUBTASK 70-37-03-370-003 Exceptions to AMS 2750 (latest issue)

   1. This SUBTASK details all the requirements in addition to those listed in AMS 2750 (latest issue).

   2. The information list below must be recorded where applicable.

      Table 2. DATA CARD INFORMATION

      1.	Temperature
      2.	Time
      3.	Preparation
      4.	Atmosphere
      5.	Furnace Loading Plan
      6.	Cooling Method
      7.	Safety Instrument Setting
      8.	Time Delay between consecutive Heat Treatment Operations

   3. Daily Furnace Checks to be carried out and recorded.

      1. All instrumentation, when in use, shall be checked to make sure it is working accurately/correctly.

      2. Charge monitor thermocouples shall be checked for condition and servicibility before use.

      3. Furnace Condition inspection, for example no broken heat shields, bricks, seals.

   4. Weekly Furnace Checks to be carried out and recorded.

      1. Check that the over temperature system is working correctly.

   5. Rolls of thermocouple wire less than 305 m (1000 ft) long shall be sampled at each end for calibration. If the individual correction factors are within the limits of Table 1 of AMS 2750 (latest issue) then the correction factor used shall be the average calculated from both ends of the roll.

4. SUBTASK 70-37-03-370-004 Ovens used for Non-Critical Drying/Fitting Applications

   1. Ovens used for non-critical operations such as drying/fitting shall be controlled as follows.

      1. They shall be fitted with a temperature indicator and controller.

      2. They do not require a temperature recorder.

      3. They shall be fitted with an over-temperature system capable of taking over the control but not necessarily interrupting the power supply.

      4. An initial temperature survey must be carried out in line with Step. The maximum temperature variation around the set point shall be +/- 10 deg C unless otherwise specified. They do not require 6 monthly temperature surveys. However further surveys shall be required after any repair or modification to the oven.

      5. The temperature control system shall be calibrated at intervals of 12 months to an accuracy of +/- 10 deg C or better.

      6. They shall carry a notice defining the uses for which they may be applied.

5. SUBTASK 70-37-03-370-005 Furnace and Oven Setting

   1. The following guidelines are for the setting of the furnace controllers prior to use.

      1. If the Repair Scheme instruction details a furnace setting temperature and no tolerance then the furnace should be set to that temperature.

      2. If the Repair Scheme instruction details a temperature range then the furnace should be set to the mid temperature. (for example the repair scheme states 790 deg C - 810 deg C (1454 deg F - 1490 deg F) then the furnace should be set to 800 deg C (1472 deg F).

      3. If the Repair Scheme instruction details a temperature range greater than 20 deg C (for example a brazing operation) then it will be a requirement of the operation data card to detail the exact furnace temperature setting.

6. SUBTASK 70-37-03-370-006 Over-temperature System

   1. Furnace Over-temperature shall be controlled by:

      1. All thermal processing equipment shall be fitted with over-temperature safety instrumentation to protect the workload. Where possible this system should be capable of shutting down the heating source and it should not be possible for the heating power to be restored until the cut out device has been reset.

      2. The over-temperature instruments shall be fitted and coupled with an independent temperature sensor capable of operating an audible or visual alarm where there is a failure of the controller at the pre set temperature. The thermocouple of the over temperature system shall be independent of the control system but may be shared with the recorder.

      3. Over-temperature sensors and equipment should conform to AMS 2750 (latest issue) Table.

      4. The thermal processing safety instrument shall be set at a maximum of 20 deg C (36 deg F) above the furnace set point for all alloys except Aluminium and Magnesium where the maximum temperature is 10 deg C (18 deg F) above the furnace set point.