Improper tightening, jamming of tightening screw, or dirt on inner surface of clamp blocks will cause tubing to slip. The short inner flare is caused by inserting tubing too low in clamp blocks or by tubing slipping during flaring operation. A short inner flare should not be used because of short bearing surface for the fitting nipple. Incorrect double flares, as shown in figure 4-11, should be cut off and another flare made. Correct use of the flare tool will give a perfect flare. It will produce a double lap flare, conforming to Military Standard MS33583, on 3/16-inch through 3/4-inch mild aluminum tubing, and a single lap flare, conforming to Military Standard MS33584, on all grades of aircraft tubing including 1/8-inch through 3/4-inch, 1/4-hard, corrosion-resistant steel. The flaring tool shown In figure 4-10 is suitable for producing tubing flares having a 74- degree included angle.
Draw marks and scratches are likely to spread and split tubing when it is flared.
(e) Inspect tubing end to see if it is round, cut square, clean, and free from draw marks and scratches. (c) Remove all filings, chips, and grit from inside of tube. (b) Remove burrs from inside and outside of tubing with burring tool. (a) File end of tubing square with fine flat file. The tubing end is prepared using the following procedures (see figure 4-9). Acceptable and Unacceptable Tubing Bends (2) Preparing tubing end for flaring. The inner surface of clamping blocks should never be sandpapered, ground, or refinished, as this will render the tool unsatisfactory for use. This will remove the aluminum alloy particles. If tubing slips in the tool during the flaring operation and the cleaning procedure does not work, clamping blocks should be dipped in a 20 percent solution, by weight, of sodium hydroxide, Military Standard MS36037, or potassium hydroxide, Military Standard MS36035, in water. Clamping surfaces may be cleaned with naphtha, Federal Specification TT-N-95, or anhydrous ethyl alcohol, Federal Specification O-E-760, Class A, and a stiff fiber brush. Before using flaring tool, clamping surfaces should be free from oil, grease, or aluminum particles. See figures 4-7 and 4-8 for tube dimensions. Double flaring reduces cutting of flare by overtightening and failure of tube assembly under operating pressure. Double flared tubing is used for tubing joints on all sizes of 5052 aluminum alloy having an OD of 1/2 inch or less. Single flared tubing is used for tubing joints on all sizes of steel tubing, 6061 aluminum alloy tubing, MIL-T-7081, and all sizes of 5052 aluminum alloy tubing, Federal Specification WW-T-700/4, above 1/2- inch OD. As system pressures increase, tubing joints must be designed so as not to be adversely affected by increasing pressures. This measurement may be made with original measurements, but should be rechecked after final bending operation. Distance B is the distance from the last bend to the end of the tube.
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