BS EN 681-4:2000 pdf free.Elastomeric seals —Materials requirements for pipe joint seals usedin water and drainagea pplications — Cast polyurethane sealingelements.
Test pieces prepared for the determination of hardness (see 4.2.3) shall be aged in air bythe normal oven method specified in lSO 188 for 7 days at 70 c.
The change in hardness shall comply with the requirement given in table 1.
The stress relaxation shall be determined at 23 C by method A of lSO 3384:1999, exceptthat the initial measurement shall be taken at 10 min, using the small cylindrical test pieceafter applying mechanical and thermal conditioning. Measurements shall then be takenafter 3 h,1,3,7 days for the 7 day test and after 3 h,1,3,7,30,100 days for the 100days test. The best fit straight line shall be determined by regression analysis using alogarithmic time scale and the correlation coefficients derived from these analyses shallnot be lower than 0,93 for the 7 day test and 0,83 for the 100 day test.The 7 and 100days requirements in table 1 are those derived from this straight line.
For continuous measurement using an apparatus described in the first paragraph of 5.2 ofISO 3384 the 7 days and 100 days requirements in table 1 are those derived from themeasurements at 7 and 100 days.
The stress relaxation in compression shall comply with the requirements given in table 1.
The test temperature shall be maintained within the specified tolerance during the wholeperiod of the test and verified by suitable recording equipment on a continuous basis.The 100 days test shall be considered as a type approval test.
lf the test piece is taken from a seal, then the measurement shall be carried out as far aspossible in the direction of compression of the seal in service.
Unless otherwise specified, test pieces shall be cut from the finished product by themethod specified in lSO 4661-1. lf satisfactory test pieces cannot be prepared in accordance with the instructions given for the appropriate test method, they shall be takenfrom test slabs or sheets, of suitable dimensions, made from the same batch of the elastomer mix used to make the seals and cast under conditions which are comparablewith those used in production.
For tests in which different sizes of test pieces are permissible, the same size of test pieceshall be used for each batch and for any comparative purposes.BS EN 681-4 pdf download.