The Asbestos cement pressure pipes are manufactured by the lamination process i.e. Manufacture of pipes layer by layer. The various stages in the manufacture of A.C. Pressure pipes are as under : 

The System of manufacture of pipes has been divided into the following stages:

A. Slurry Preparation Section

i. Kollargang

The fibre is milled in Kollargang having Granite Stone runner wheels (Approx. 3 tons weight), which move over a Granite base stone (Approx. 5 tons weight) for optimum opening of fibre, without damage to the strength and length of the fibre. A sprinkler system has been installed inside the Kollargang to ensure uniform water addition. Electronic timer arrangement for controlling the fibre milling time has been installed to avoid any human error that may cause damage to the fibre by increasing or reducing the milling time.

ii. Hydro Disintegrator / Turbo Mixer and Cement Mixer

Water is taken in the mixer with a high discharge circulation pump where fibre is added and is circulated for optimum opening of fibre in water for a preset time. Thereafter cement and fly ash (when required) is added for preparing a homogenous slurry. A vertical shaft having Turbo type impeller is installed to run at a slow speed by vertically mounted motor. Timings are set for both the above operations to eliminate any human error. 

iii. Storage Tank

The slurry prepared is transferred to the Storage Tank for feeding the slurry to the pipe forming machine. The slurry remains suspended due to slow agitating blades for maintaining uniform consistency for better ffibre orientation in the Lamination Process.

B. Pipe forming Section

i. The pipe is formed on a hollow steel mandrel by Lamination process. The slurry is fed from the storage

tank by a centrifugal pump to a traveling feeder system, which ensures uniform and un-interrupted supply

of slurry throughout the length of the pipe. The forming roller is laterally shifted to ensure thin layer formation

of thickness ranging between 0.20 mm to 0.30 mm by means of a gearing system and an electronically controlled,

 variable frequency drive. As the roller shifts laterally by the above arrangement, the pipe is formed layer by layer

(1 layer is formed for 1 rotation of the mandrel). In this way uniform thickness of layer is ensured.

Dewatering of the layers is done with the help of a high capacity vacuum system from inside the mandrel and formed pipe is further compressed by hydraulic pressure loading system wherein the pressure range from 20 Kg. to 60 Kg. / cm2., to ensure optimum binding of the formed layers and achieve the required strength and density.  

The pipe is then subjected to atmospheric drying and then final curing under water for a period ranging from 12 to 15 days so that the requisite strength is attained. It was witnessed that there is ample space for atmospheric drying to take care of the entire production in the facility of Kalani Industries Limited.

C. Pipe finishing Section

i. Lathe Machine

A fully automatic, hydraulically and electrically controlled pipe cutting, chamfering and turning lathe machine has been installed. The pipe is held by the jaws from the inside and a variable speed drive unit rotates it. All the 3 operations of cutting, turning and chamfering are done simultaneously with the tools attached at both ends. Limit switches and timers are provided for complete automation to adjust the tool movements to attain the required finish of the pipes and the required diameters at the ends.

ii. Hydraulic Pressure Testing machine

Pipe is tested for hydraulic pressure as per the requirement of each class of pipe. The pipe is held at both ends on the test heads and is subjected to water pressure from a reciprocating pump.

D. Pipe handling and loading Section

The handling and loading of pipes is done by an Electrically Operating Travelling (EOT) crane so that

no stress develops. Manual handling of pipes is totally eliminated. For loading on to the trucks, the

pipes are lifted with a tackle attached to the crane having hooks on both ends for holding the pipe

and then gently lowering them on the truck. Loading operation is thus mechanised to avoid damage

to the pipes because of manual loading.