PIPES FOR MIRAMAR

Evening Post, Volume CVII, Issue 55, 8 March 1929, Page 5

PIPES FOR MIRAMAR

INTERESTING INDUSTRY

A 32-TON TEST APPLIED

ENGINEERS IMPRESSED

'J^llE big work of remedying storm water drainage shortcomings at Miramar is to-day definitely under way, for the first of the great concrete pipes which will form the drainage mains have been delivered by the contractors, .the Wellington Concrete, Pipe Company, Ltd., to the City Council, and from now on delivery will continue steadily. The manufacture of concrete pipes of such large diameter—up to six feet, the largest pipes of-this nature so far used in the Dominion —is a particularly interesting business, and the testing of the finished job is very severe. The new pipe iompaiiy'B factory is the first

of the.industrial plants of the new Eastern Hutt area, and occupies about four acres of land immediately behind the new railway workshops. Thoroughly up-to-dato machinery is installed (some of tho units being specially manufactured to handle the unusually large diameters called for), and a railway siding is provided for the dispatch of pipe products beyond Wellington, Somewhat of a record was established in. plant erection, for the first work was clone on the ground on 12th November last, and tho first pipe was turned out one day under two months later, on 11th 'January. The-contract .with the council required a commencement of delivery on Ist March, but the company made it ono day earlier. ,- ' .; THROUGH AN ABNORMAL TEST. It is one thing to make a concrete, pipe and another altogether to make a pipe that will satisfy extreme requirements under test, but the sft flic pipe —actually the first made —which was subjected to an abnormally severe test in the presence of the City Engineer, Mr. G. A. Hart, and the Waterworks and Drainage Engineer, Mr. E.. R. M'Killop, and-the directors of the company, on Wednesday afternoon, came through with more than flying colours.

Each pipe is eight feet long, and the council's specifications provided for a pressure test of 16 tons, or two tons per foot of length. The pipe tested stood up to double that pressure, four tons per foot, a performance which the engineers readily admitted was most impressive.

The length of pipe was bedded down over one quarter of its circumference in rammed sand, and on the upper quarter was placed a heavy timbering to hold another deep sand pack, sand being used to bring about as exact a distribution of pressure as possible. A heavy, steel girder, so placed that the weight applied to its free end (by a heavy double screw) exerted a five-to-one downward pressure on the upper sand pack, was used to apply the pressures, the weight of timbering, sand, and girder, of course, being taken into account. At five, six, and up to ton tons nothing happened, but above that the heavy pressure commenced to squeeze water out of apparently dry sand; the pipe itself was not, as far as measurement could show it,- moved a fraction of an inch. The sixteen-ton, test was reached, and was held for five minutes. Not the slightest sign of weakness developed. " As far as fulfilling requirements we're concerned, the test could have ended

then and there, but Mr. J. E. Todd, in general control of the company's operations, and Mr. W. E. Fisher, the work 3 manager, were quite willing to carry on. Twenty tons were applied, and held; then twentyrfive tons. At this stage tiny hair cracks appeared at the ■ sides where the stress was greatest, but a hair crack does not signify failure. Thirty tons and then thirty-two tons— double the required test—were applied and hold, but the hair cracks remained unopened. Mr. Todd was confident that a forty-ton test would be passed without difficulty, and was inclined to put more weight on, but doubts were expressed of the safety of the application of such extreme weights a a the ■overhead gear might carry away. - It was therefore decided to let it go at that, and to be very well satisfied. Mr. Hart stated that, as far as he was concerned he was more: than satisfied. He heartily congratulated the directors and staff upon turning out pipes of such remarkably high quality. PIPES SPUN, NOT MOULDED. All these pipes, from-six feet down to eighteen inches in diameter,- are spun, not moulded. After 1 the test, demonstrations were given of the processes of manufacture. According to

the diameter of pipe various thicknesses of steel rod are u^cd for reinforcing. In the case of tho largest diameters threeeigtth inch rod is used, twenty hoops being held in position by twenty longitudinal rods. All arc . electrically; welded, and over the whole heavy gauge wire i 3 wound.

The next step is to place the reinforcing in an exactly circular steel mould, with heavy east steel collars at either end, which later determine the thickness of the pipe wall. The mould is then placed on four rollers which, under power, give the mould its spin. ■ Concrete, machine-mixed to a very definite proportion and consistency, is rapidly shovelled into the spinning mould and the centrifugal force due to the rapid spin holds the wet concrete with great force against the smooth mould. The centrifugal force also centres the reinforcing exactly, and as the spinning continues the excess water, being lighter than crushed metal, sand and cement, is separated out, but is also held round the inner wall of the pipe. After so many minutes the. spinning is stopped, the 'water falls from the sidfia and is swept off. Further spinning consolidates the still soft concrete, and trimming and "squeegeeing" give the inner wall a remarkably fine finish. Fifteen minutes from the time the

spinning commences the concrete is compact and set so hard that one cannot impress it with a finger, and the mould is rolled away to the .first curing shed. Here it is held in a moist, steamy atmosphere, at a temperature of about 100 degrees F., for fifteen or sixteen hours, and- is then taken to a second curing shed, where it remains for a fortnight or so in a.cool damp atmosphere, induced by fine water spraya. The spun pipe has several, advantages over a moulded pipe, the chief being the remarkably even . and ' extremely compact nature of the .concrete. A NEW JOINT. ."'. One of the features of the.pipe is the special self-centring and 'interlocking, dove-tail joint, which i 3 so designed that all jointing, after the pipe lengths are pressed together, is accurately centred, and that all work is carried out from the top of the pipe circumference. ■ It is a most ingenious principle, and will solve what would: otherwise be serious difficulties in such ground as that of the Miramar flats, where water and loose sand a few feet below the surface- would render collar jointing anexpensive and just about impossible business. . - .