The New Sand Spun Centrifugal Cast Iron Pipe
Latest Development in Pipe Manufacture Said to Have Many Advantages—Foundries to Use New Method—May Cast Any Thickness
AT the Convention of the American Water Works Association recently held in New York, there was displayed by a number of cast iron pipe manufacturers samples of the new sand-spun pipe, an interesting development in the manufacture of pipe to be used for water, gas, oil and many other purposes. Until very recently it had been almost a century since any practical commercial effort had been made toward revolutionizing the methods of manufacturing cast iron pipe. The previous improved departures from old established practice was when vertical casting in dry sand moulds was adopted the middle of the last century.
Prior to this time, pipe had been for many years cast on their side—or horizontally—in green sand or non-dried moulds with a core having a clay or loam coating. Under this operation, in spite of the core being firmly held at each end there was a tendency for it to float in the molten iron, making a casting which was uneven in thickness, and this movement of the core was difficult to prevent even with the use of chaplets or anchors.
Upright Casting Insures Equal Thickness
This vertical or upright casting, insuring an equal thickness in the pipe, was at once popular and the foundries using the old horizontal moulds rapidly went out of existence. Many mechanical improvements in the details of running the sand into the moulds and of handling the flasks have been developed, but these were only the ordinary and natural changes to be expected.
For more than one hundred years engineers throughout the world have been working to develop a machine which would produce cast iron pipe of all kinds centrifugally, but the difficulties they encountered were manifold. Centrifugal methods with chilled moulds have been developed but pipe cast in a chilled mould must undergo an annealing operation before the pipe is in condition for use. Furthermore, when chilled moulds are employed, they must be water cooled.
What New Process Accomplishes
The new sand-spun process just introduced employs the sand mould in a new way, overcoming the difficulties of chilling the casting, and avoids the objections surrounding the annealing process. In carrying out this new sand-spun method the metal, at pre-determined temperatures, is poured into a rapidly revolving sand-lined flask, against which the metal is cast without _any chilling action.
In addition to this the centrifugal action of the mould, together with further manipulations thereof serve to evenly distribute the molten metal throughout the length of the mould, thus securing a pipe of uniform thickness from end to end. The speed or revolution of the mould is such as to cause the metal to be exceedingly dense and solid, thus increasing its tensile strength by more than 50 per cent, and making it tough and hard to fracture, yet without interfering in the least with drilling or tapping for service pipe or turning down or threading the exterior for any desired purpose.
Pipe May Be Cast Any Thickness
An important feature of this new sand-spun process, employing the sand-lined flask, is that pipe may be cast of any thickness, heavy or light. Another very important feature is that not only the bell but the spigot or bead end can be formed by this new method just as easily as it has always been formed by the old sand cast method.
A refractory lining which is applied to the sand mould before casting, prevents the burning of the sand to the iron and avoids all scabbing. The sand in the flask is held in place by the centrifugal action. The refractory material which has been applied to the sand mould is of such a character that during the casting operation it becomes incorporated by a fusing action with the outer shell of the casting, thus forming a very desirable and attractive coating which prevents the formation of rust or corrosion, and acts as a protection to the pipe. The finished pipe may, if desired, be coated with the regular Angus Smith or other tar varnish or coating, and can be coated on the interior with a cement or other lining material to prevent the formation of tubercules which are sometimes formed by certain characters of water or other fluids, and this coating preserves the co-efficient of the flow of fluids through the pipe.
Strength of New Pipe
Cast iron pipe made by the new process in centrifugal sand lined moulds have been thoroughly tested in the usual way in hydraulic presses, individual pipe being tested to 2400 lbs. per square inch it is reported, without showing defects.
Bars made from the actual casting have shown over 30,000 lbs. in tensile strain, and proportionate results in transverse and breaking tests.
This new sand-spun pipe is now being regularly made and marketed. Enlarged and up-to-date foundries are being built and old plants are being reconstructed for the installation of the new method, all of which will supersede the methods now employed.
This new sand spun method is protected by patents of a fundamental character and which cover not only the process, but the machinery and the product.