Document pBoYQ8rVzXVnqpRwxo4gGqm6E

January 17, 1951 MEMORANDUM TO: R. B. WING CC: B H* Reeves C, A Berlepsch E.S. H 0# Anderson R, B. Miniter J, F* F* S* Bacon A* L* Bristol D.A. K* S* Moore W* W. Gaylord, l.e. : File (2) SUBJECT: Engineering Project 507 - Final Report KEF: 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, X) and FSGA sizes 5 through 9, type cables suggested in the Novem ber 28, 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 HC1 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 HC1, it was found to be sufficiently watertight, and no difficulties were encountered from tape rupture in the tubing operatlon 4, 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 Kesearoh Department found that it was not possible to up-grade the IR of completed cables without removing the sheath and 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 Page 2 RBB 01373 oables now In production to an additional cure 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 60% allowable on most cables* If the addi tional oure is made because of low Ht, the cable must be respooled twioe and tipped with the die called for on the cable wrap opera tion in order to oheck 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 3/4 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 3% 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 s Two 125-foot samples of MSCA-7 were made in accordance with W* W. Gaylord*s memo of November 26, 1950* The following tests were run with the results shown: ' 1* Water De&kage 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* MSCA-7 - 1 Silicone asbes tos tape 1/4 lap 3*78 Col 4, 10% reduction Bo MSCA-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 5 were found without any sealing compound in the strand* Inspection tests made on DSGA-4 cables showed no leakage for three samples 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 frcm gland end of the third sample, the leakage path evidently being along the overlapped portions of Page 3 the silicone asbestos tapes* In only one sample w$s there any evidence of water having worked under the B tape, and this for only 2 inches from the gla&d 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 500F. 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 Testsj 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 Megohms/M * 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 200F*, 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 Max, Av* 7/C 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 EC1 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/M* at 15o5F* With Sheath and Armor Intact Min* Max. Av. 7/C iaai With Sheath and Azmor Removed Min. Max* AV. 7/C fatl As Made 24 hrs. 48 hrs* 78 hrs* 526 1903 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 November 28, 1950) as made by the Production Department* The IE each conductor to all others and armor was oheoked 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 curing temperature was then raised to 250F* and the test aample 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: Insulation Resistance in Megohma/M* at 155C Heating Time As made After 24 hrs at 200P. After 48 hrs at 200F After 72 hrs at 200F* After 89 hrs at 200F. After 89 hrs at 200F* and 24 hrs at 250F* Min* 477 649 405 314 379 263 Test Sample Max* AV. 7/C MaAa8e 853 671 974 795 118 646 516 76*9 539 424 63*2 609 501 74*7 414 328 48*9 Control Sample Min Max* AV. 7/C 494 697 550 637 1160 915 575 1130 836 657 1390 974 - 646 1170 943 % 88 Made 166 152. 177 m 171 It is evident that some 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 rUbb6r d Allen Hubbard in ldj Approved* R Winy RBB 01375