What Is the Manufacturing Process for PVC Pipes?

Written by lee grayson Google
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Polyvinyl chloride (PVC) is created from a combination of vinyl and plastic. Experiments to create a vinyl chloride polymer were first done in the mid-1830s, but the solid product created in the lab was simply an oddity, without any apparent use at that time. Additional experimentation in the 1880s reproduced a solid that withstood high heat exposure, but it was ignored in commercial applications due to the inflexibility of the product. Not until the 1920s did scientists attempt to use copolymers of vinyl chloride. These were easier to produce and created an extremely durable substance. The first experimental pipes made from a copolymer of polyvinyl chloride were first produced in 1932. Three years later, commercial production began. The first commercial pipes were used in applications to transport water, sewage and waste water, and for the movement of chemicals.

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Preparing Ingredients

The first step in manufacturing PVC pipes is to prepare the ingredients. PVC is created in a chemical process that bonds the vinyl and chloride. The process involves the polymerisation of monomer vinyl chloride (VCM). Most manufacturers use suspended polymerisation that involves use of a polymerisation reactor to mix chemicals and a polymerisation initiator. The resulting PVC resin is suspended in water and then removed for degassing and water removal, which is accomplished by use of a centrifuge. The product is then dried and turned into a granulated dust for transportation to the manufacturing plant, where it will be heated to the melting point. Early manufacturing melted the dry powder as a sheet on a roll mill. Once this was done it was moulded into a solid product that was ready to be rolled.

Additives

Early PVC production created a rigid and stiff product. As a result of experimentation with other polymers and oil products during the 1950s and the subsequent decades, the PVC product improved dramatically. While formulas for PVC are patented by individual companies, most modern PVC ingredients include various types of stabilisers and lubricants to facilitate processing. Colours are also added during the manufacturing process to indicate the appropriate use of the piping. Dark grey pipe is used for industrial pressure applications, white and blue pipes indicate cold water uses, and green is used for sewer applications.

Extrusion

While rolled PVC was produced beginning in the 1930s, no extrusion process to form PVC pipe was perfected until the 1950s and 1960s. Modifications to such processes are still underway, but today there are two predominant types of PVC pipe--cellular core and solid wall. Three separate layers are extruded to create the cellular core pipe, with hard outer layer walls sandwiching a cellular core centre. All three layers are immediately incorporated into one pipe during the manufacturing process. Solid wall PVC pipes are formed in a single manufacturing step. PVC pipe is extruded to meet industry-standard 10 and 20 foot lengths. Pipes are tested for compliance with industry and government standards for durability and the ability to withstand pressure.

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