Document Ev627aRqK7gjpN3nMY8Yy7qyj

January 17, 1951 MEMORANDUM TO: R. E. WING X CC: B, H, Reeves C, A* Berlepsch E.S. Blake H 0, Anderson R. B. Miniter J* F. McClelland, F. S. Bacon A. L. Bristol D.A. Charlotte H. S. Moore W. W. Gaylord L.E. Robb - File (2) SUBJECT: Engineering Project 507 - Final Report REF: Memo same subject dated November 28, 1950 The purpose of the final phase of this project was to check the suitability of the cable binder constructions for MSCA and S, T, D and FSGA sizes 5 through 9, type cables suggested in the Novem ber 88, 1950 memo* Conclusions: 1. As reported in the November 28, 1950 memo, the low insulation resistance found on MSCA type cables is caused by the attack of hydrochloric acid liberated in small quantities from the vinyl asbestos tapes previously used as a cable binder. It was further found that the PVC sheath liberates enough HCl to seriously lower the Insulation resistance of these cables, even in the absence of heating, except during the extrusion operation. 2. That silicone asbestos tapes suggested in the above reference memo as a cable binder do not provide protection for the singles and should not be used alone. 3. It is therefore suggested that one F.ockbestos Spec. B tape, applied 1/2 to 2/3 lap, be used directly over the cabled con ductors under a single silicone asbestos tape applied 1/4 lap. This construction gives good protection to the singles from the attack of BC1, it was found to be sufficiently watertight, and no difficulties were encountered from tape rupture in the tubing operation*) 4 c The Production Department found that it was possible to apply a synthetic sheath over a single silicone asbestos tape con struction without rupturing the tape on an MSCA-7 type cable. Previous experience has shown that this is not possible for larger size cables, and the single tape construction should not be specified* 50 The additional curing procedure recommended in the November 28th memo for silicone rubber singles must be used. The Hesearoh Department found that it was not possible to up-grade the IE of completed cables without removing the sheath cued both cable tapes ana then"curing the cable at 300F. for at least four hours. It has been necessary to subject some of our silicone rubber insulated RBB 01372 SC-ELEC-01775 X1 Page 2 RBB 01373 cables now In production to an additional curs of four hours at 300F. or eight hours at 250F. after the cable tape operation because of low IR. This treatment should be avoided where pos sible because the additional heating will lower the percent elongation to break of the singles which is now barely above the temporary minimum of 60fa allowable on most cables. If the addi tional cure is made because of low HI, the cable must be respooled twice and tipped with the die called for on the cable wrap opera tion in order to oheok for swell of the Scotch tape used In patch ing broken cable tapes. This should be done to prevent Jamming and resultant breaks during the tubing operation<> 6. It was suggested by the Dow Corning representative that the DC-181 would not be subject to the attack of HC1 were it com pletely cured. A 50-foot sample of MSCA-7 was made with singles having been cured at 480F. for 24 hours, a single silicone asbes tos tape applied V4 lap over the cabled conductors, and a regular Navy sheath applied overall. Two 25-foot samples were made from the above; the as made IR of each was measured, and the control sample was cured in a circulating air oven for 24 hours at 250F, Following this treatment, the IR test results showed that the ovenaged sample had been attacked to the extent that its IR was approximately 5% of the as made value. It was found that the high temperature cure made the rubber stiff and it adhered to the con ductor so firmly that it could not be removed for tensile and elongation tests. Procedure * Two 125-foot samples of M5CA-7 were made in accordance with W. W, Gaylord's memo of November 28, 1950, The following tests were run with the results shown: ' 1. Water Leakage Test - Standard water leakage tests were run on each of the above samples as outlined in Navy Spec. 15C1. Spec. & Construction Water Leakage Cu Inches A lISCA-7 - 1 Silicone asbes tos tape 1/4 lap 3.78 Col 4, 10# reduction B0 HSCA-7 - 1 Silicone asbes tos tape 1/4 lap over 1 B tape 1/2 to 2/3 lap 1.46 Col 3, 5% reduction All leakage on both samples was through the strand caused by in adequate plugging. Three singles in sample B were found without any sealing compound in the strand. Inspection tests made on DSGA-4 cables showed no leakage for three sables tested. A physical examination following the water leakage tests revealed the following: water followed the shingle in the silioone asbes tos tape for the entire length of one sample, 2/3 of another sample and the first 2 inches from gland end of the third sample, the leakage path evidently being along the overlapped portions of page S the silicone asbestos tapes. In only one sample w$s there any evidence of water having worked tinder the B tape, and this for only 2 inches from the glaiod end of the cable. There was no evi dence of water in any other components of the cable. These re sults are surprising because "the cable was subjected to an addi tional cure of four hours at 500P. after the cable tape operation and it was expected that B tape shrinkage and Duxseal expansion would cause separation of the tapes and resultant high water leakage. 2, Insulation Resistance Tests: Two 25-foot samples were cut from the 125-foot length of MSCA-7 made with 1-Silicone asbestos Tape over the cabled conductors. The IR of each conductor to all other conductors and armor was measured with the following results* Insulation .Resistance in Hegohms/Mf at 15.5C Sample Control Test Min. 400 416 Max. 675 693 Av. 7/C 526 553 The test .sample was then placed in a circulating air oven for 24 hours at 20QF.* removed and allowed to cool to room temperature and the IR of both samples was checked again. , Sample Control Test Insulation Resistance in % of Megohms/M1 at 15.5C As Made Value Min. Max, Av. 7/0 480 20,4 764 99.7 604 37.7 115 6.82 It was felt that the reduction in IR found on the test sample was caused by the attack of ECl liberated by the vinyl sheath. To show this, it was decided to cut the control sample in half, remove the sheath and armor from one length, and then cure both samples in the oven at 200?F for 24 hour periods, reading the IR after each heating cycle. . Heating Time Insulation Resistance in Megohms/M1 at 15o5F. With Sheath and Armor Intact Min, Max. A v. 7/C iaae With Sheath and Armor Removed Min. Max, AV. 7/C As Made 24 hr3. 48 hrs. 78 hrs. 526 903 688 510 878 668 16.5 80,3 30 .4 4.41 438 591 507 75,9 9.50 18.8 14 .0 2.04 739 923 788 118 .641 1.05 .900 131 768 1100 910 136 RBB 01374 page 4 This test conclusively showed that the sheath was liberating suf ficient quantities of HC1 to degrade the IR* It further shows that the silicone asbestos tape is not an adequate barrier alone to prevent the attack. The effectiveness of the B tape silicone asbestos tape construc tion was checked as follows: two 25-foot samples were cut from the 125-foot cable EP507E (as designated in W. W. Gaylord's memo dated Kovember 28* 1950) as made by the Production Department. The IR each conductor to all others and armor was eheoked for both samples.' One length* the test sample, was then subjected to cycles of heating at 200F* for 24 hours and cooling to room tem perature after which the IR of both samples was measured again. This procedure was repeated for a total of four cycles* at which time the test sample had been cured for 89 hours at 200F. The atiring temperature was then raised to 250F. and the test sample was subjected to an additional 24 hours of heating at this tem perature. The IR of both samples was checked again. The other 25-foot length* the oontrol sample* was aged at room temperature for the total test period. Summary of test results is shown below: IpMilfltlon Resistanoe In Megohms/M* at 155C Heating Time As made After 24 hrs at 200F, After 48 hrs at 200F. After 72 hrs at 200F. After 89 hrs at 200F. After 89 hrs at 200F. and 24 hrs at 250Fe> Min. 477 649 405 314 379 263 Test Sample Max , Av. 7/C fiaa4es 855 671 974 795 118 646 516 76*9 539 424 63.2 609 501 74.7 414 328 48.9 Control Sample Min. Max,o Av. 7/C 494 697 550 637 1160 575 1130 915 836 657 1390 m 974 - 646 1170 943 % as Made 166 152. 177 m 171 It is evident that same attack occurred during the curing. How-' ever, as the test sample final value-is well above the Navy mini mum of 100 Megohms/M*, it is felt that the B tape silicone asbestos tape construction provides adequate protection for the silicone rubber' o. Allen Hubbard III idj Approved: R. Wing1' RBB 01375