PE Pipe Extrusion Process (2)

Extrusion Basics

The function of the extruder is to heat, melt, mix, and convey the material to the die, where it is shaped into a pipe . The extruder screw design is critical to the performance of the extruder and the quality of the pipe. The mixing sections of the screw are important for producing a homogeneous mix when extruding blends. A typical extruder is shown in Figure 2.

There are many different types of screw designs , but they all have in common the features shown in Figure 3. Each screw is designed specifically for the type of material being extruded.

The extruder screw operates on the stick/slip principle. The polymer needs to stick

to the barrel so that, as the screw rotates, it forces the material in a forward direction.

In the course of doing this, the polymer is subjected to heat, pressure and shear (mechanical heating). The extent to which the material is subjected to these three conditions is the function of the screw speed, the barrel temperature settings and the screw design. The design of the screw is important for the production of high quality pipe.

If a natural resin and concentrate blend is used, the screw will also have to incorporate the colorant into the natural resin. Various mixing devices are used for this purpose as shown in Figure 4. They include mixing rings or pins, fluted or cavity transfer mixers, blister rings, and helix shaped mixers, which are an integral part of the screw.

The pipe extrusion line generally consists of the extruder, die, cooling systems, puller, printer, saw and take-off equipment. Each of these items will be addressed in the following section.

PE Pipe Extrusion Process (1)

Pipe Extrusion

The essential aspects of a solid wall PE pipe manufacturing facility are presented in Figure 1. This section will describe the production of solid wall pipe from raw material handling, extrusion, sizing, cooling, printing, and cutting, through finished product handling. Details concerning profile wall pipe are also discussed in the appropriate sections.

Raw Materials Description

The quality of the starting resin material is closely monitored at the resin manufacturing site. As discussed in the chapter on test methods and codes in this handbook, a battery of tests is used to ensure that the resin is of prime quality. A certification sheet is sent to the pipe and fitting manufacturer documenting important physical properties such as melt index, density, ESCR (environmental stress crack resistance), SCG (slow crack growth), stabilizer tests, amongst others.The resin supplier and pipe manufacturer may agree upon additional tests to be conducted.

Extrusion Line

The raw material, usually referred to as PE compound, is typically supplied to the pipe producer as non-pigmented pellets. PE pellets are stabilized for both heat and UV protection. Usually, color pigment is added to the pipe at the producer’s facility. In North America, the most common colors are black and yellow. The choice of color will depend upon the intended application and the requirements of the pipe purchaser. Carbon black is the most common pigment used for water, industrial, sewer and above-ground uses. Yellow is reserved exclusively for natural gas applications, although black with yellow stripes is also permitted for this application. Other colors are used for telecommunications and other specialty markets. All ASTM and many other industry standards specify that a PPI-listed compound shall be used to produce pipe and fittings for pressure pipe applications. A compound is defined as the blend of natural resin and color concentrate and the ingredients that make up each of those two materials. The pipe producer may not change any of the ingredients. In a listed compound, such as substituting a different color concentrate that could affect the long-term strength performance of the pipe. Any change to a listed formulation has to be pre-approved. These stringent requirements ensure that only previously tested and approved compounds are being used.

If the resin is supplied as a natural pellet, the pipe producer will blend a color concentrate with the resin prior to extrusion. In order to obtain a PPI Listing, each manufacturer producing pipe in this manner is required to submit data, according to ASTM 2837, to the PPI Hydrostatic Stress Board. A careful review of the data is made according to PPI Policy TR-3 (5) to assess the long-term strength characteristics of the in-plant blended compound. When those requirements are met, the compound qualifies for a Dependent listing and is listed as such in the PPI Publication TR-4 (6), which lists compounds that have satisfied the requirements of TR-3. Producers of potable water pipe are usually required to have the approval of the NSF International or an equivalent laboratory. NSF conducts un-announced visits during which time they verify that the correct compounds are being used to produce pipe that bears their seal.

Raw Materials Handling

After the material passes the resin manufacturer’s quality control tests, it is shipped to the pipe manufacturer’s facility in 180,000- to 200,000-pound capacity railcars, 40,000-pound bulk trucks, or 1000- to 1400-pound boxes. Each pipe producing plant establishes quality control procedures for testing incoming resin against specification requirements. The parameters that are typically tested include: melt flow rate, density, moisture content and checks for contamination. Many resin producers utilize statistical process control (SPC) on certain key physical properties to ensure consistency of the product. Resin is pneumatically conveyed from the bulk transporters to silos at the plant site. The resin is then transferred from the silos to the pipe extruder by a vacuum transfer system. Pre-colored materials can be moved directly into the hopper above the extruder. If a natural material is used, it must first be mixed homogeneously with a color concentrate. The resin may be mixed with the color concentrate in a central blender remote from the extruder or with an individual blender mounted above the extruder hopper. The blender’s efficiency is monitored on a regular basis to ensure that the correct amount of color concentrate is added to the raw material.

Advantages of HDPE Pipe

                    Advantages of HDPE Pipe

High Density Polyethylene Pipe (HDPE) is a thermoplastic pipe made from material that can be melted and reformed. It is rugged, flexible, and durable.  It has outstanding chemical and environmental stress crack resistance.

Relative to existing infrastructure, like ductile iron, concrete or PVC, HDPE seems like a new product. In reality, it has been successfully used in a wide variety of piping applications for over 50 years.

The outstanding physical and performance benefits of HDPE pipe make it the perfect choice for your piping systems.

Corrosion Resistance

Corrosion is one of the most costly problems associated with metal piping systems. It occurs both inside and outside the pipe and affects hydraulic efficiency. Many cities treat their water to help slow rust and pitting that is inevitable with metal pipes.  Others choose costly cathodic protection, plastic coating, or sleeving to try and extend the service life of the pipe.

Unlike traditional metal infrastructure products, HDPE pipe does not rust, rot or corrode.  It is resistant to biological growth. This means an extended service life and long term cost savings.

Fatigue Resistance

HDPE pipe is flexible and ductile, not rigid. It has outstanding resistance to fatigue.  Unlike other plastic pipes, it is designed and pressure rated to handle the kind of occasional and recurring surge events that are common in water distribution systems.

In many instances, this will enable you to utilize a thinner wall HDPE pipe as compared to other types of plastic piping.

Extended Service Life

HDPE pipe is a safe and durable product ideal for your piping infrastructure. The service life of HDPE is estimated to be between 50 to 100 years, depending on application, design and installation.

Leak-Free Joints

An independent study reports that municipalities in 43 states average a water loss of 16% due to leaking joints. Some report water losses as high as 50%.

Traditional infrastructure piping is joined with bell and spigot or mechanical type joints and all acknowledge a specified leakage factor. Not only is our most precious resource being lost, but leaking pipes are costing our cities money. HDPE piping systems can be joined with heat fusion to produce permanent leak free joints.

Fusion Joints

HDPE piping systems can be joined with heat fusion welds. Heat fusion involves the heating of two HDPE surfaces then bringing them together to form a permanent, monolithic, leak-free system.

Unlike the fusion process developed for other plastics pipes, the fusion process for HDPE is proven and has been used by the natural gas industry for over 40 years. Approximately 95% of all gas distribution piping in the United States is polyethylene pipe joined by heat fusion.

Fusing HDPE pipe is not difficult and personnel can be trained in the process.

Adaptability

In addition to joining HDPE with heat fusion, HDPE pipe can also be joined with Stab or Mechanical Fittings.

There are a wide range of these fittings available, specific to your pipe size and application.

HDPE pipe can easily be transitioned to and from non-HDPE piping systems utilizing Mechanical Joint adapters (MJ’s), Stab fittings and Mechanical and Flanged Connections.

Trenchless Installation

Traditional piping systems are installed by open cut (digging a ditch), resulting in traffic and environmental disruption. HDPE can be installed using this traditional open-cut method or by utilizing eco-friendly trenchless technology.

For trenchless installation, a horizontal directional machine bores a continuous hole beneath the ground. When the drilling head reaches the end of the bore, the pipe is attached and pulled back through the hole.

The flexibility of HDPE, combined with its outstanding tensile strength and abrasion resistance, make it the preferred and proven choice for trenchless installation technology.

HDPE pipe can be installed utilizing trenchless technology under creeks, rivers, lakes, roads, or right-of-ways with minimal environmental and public disruption.

When compared to a non-plastic pipe installed using the open-cut method, a leak-free HDPE system installed utilizing less invasive trenchless technology is more cost effective.

Pipeline Rehabilitation

Trenchless technologies are also used to rehabilitate old, failing pipelines with HDPE. There are several technologies to choose from when rehabilitating old pipelines.  These technologies include slip lining and pipe bursting.  Both are excellent techniques for cities to revitalize or replace and upsize older existing infrastructure.

Eco-Friendly

In addition to its outstanding physical characteristics, HDPE is recognized for its minimal impact on the environment:

• It takes less energy to manufacture HDPE than non-plastic pipes.

• HDPE is lightweight and is often more cost effective to transport than metal pipes.

• The flexibility of HDPE, combined with the use of heat fusion to join the pipe, means fewer fittings are required.

• In trenchless installations, the physical characteristics of HDPE pipe enables you to use a smaller pipe, resulting in less ground disruption than when installing other fusible products.

• HDPE pipe joined with heat fusion provides leak free connections.

• HDPE does not emit potentially hazardous levels of toxins into the air during production, during fusion or into the ground or water during use.

• HDPE pipe can be recycled back into non-pressure piping applications.

How to Connect Polyethylene Pipe to Water Supply Pipe

                    How to Connect Polyethylene Pipe to Water Supply Pipe

A polyethylene pipe is one of the most popular alternatives when it comes to water supply pipes. Water supply pipes are extremely important as they are used to carry water supply from the well or a water meter into your house for domestic use. Water supply pipes are connected with every home and each area has building codes that specify the kinds of water pipes that are required and how indoor plumbing should be managed.

Polyethylene pipes experience much less wear and tear and are better than metal pipes, which are not only expensive but also expand in warmer climates. If you want to connect polyethylene pipes to your main water supply line in order to direct the water to your lawn sprinklers or dishwashers, here’s how you can connect a polyethylene pipe to your water supply pipe.

Step 1 – Shutting off the Water Supply

First disconnect the water supply to the line that you will be working on. You will also have to remove part of the water supply to work and install additional fittings and pipes. Usually, this can be done by simply screwing on a connection; however in some cases, the pipes are soldered and you may need a hacksaw to remove the plumbing.

Step 2 – Attaching T-Fittings

Drain the line before you begin your work. Now, bring the T-fitting and align it with the water supply pipes. Mark the place on the water supply pipe where the T-fitting will be inserted. Now cut out the section that is marked for the insertion of the T-fitting. The output of the T-fitting should face you so that the polyethylene tubes can be inserted. Use the Teflon tape to secure the T-fitting into place.

Step 3 – Installing the Shut-off Valve

Remove the compression nut from the shut-off valve, inserting the valve into the pipe that has the threads facing the open end. Slide on the compression ring and wrap the newly inserted valve with Teflon tape. You can also use plumbing joint compounds and sealants, spreading them onto the end of the pipe before you insert the shut-off valve. Once the valve has been fixed, slide in the compression nut and tighten it. Attach the compression fittings to the other end of the valve and tighten them with your hand. Use the wrench to further tighten all the fittings. Copper shut-off valves have to be integrated with copper adapters. The adapters have to be attached with the use of threaded sealants. To attach the copper adapters, solder the copper union onto an already threaded adapter. When the union has been fixed completely, use the threaded sealants to seal the automatic shut-off valve.

Step 4 – Attaching the Polyethylene Pipe

Finally, attach the polyethylene pipe to the open end of the T-fitting. You can use threaded sealants to seal the fixture and then cover it with the Teflon tape to prevent leakages.

Advantages of conical twin screw extruder

          Advantages of conical twin screw extruder

 For users, it is important to the choose and buy of twin screw extruder, the different types of twin screw extruder with different properties and applications, therefore, must want to understand all kinds of performance and the application of the twin screw extruder.For example, the mesh type synthetic rotating twin screw extruder for its high speed, shear rate, combination of screw, it widely applies to the thermal decomposition of the polymer modification, blending, filling, fiber reinforcement and material of reactive extrusion.For example, the mesh type differential rotating twin screw extruder, because of its good mixing plasticization functions, its biggest characteristics is a direct forming PVC powder.Such as change the geometric structure of the screw, can also be used for other materials processing, but its strength is still the PVC processing.According to the size of the section, plastic extrusion, by extrusion amount again to choose the specifications of the twin screw extruder.In the plastic processing and molding process conditions under the condition of basically the same, conical double screw extrusion mechanism to adapt to the larger head pressure, parallel twin-screw extrusion function adapted to small head pressure.

Two root conical screw horizontal arrangement, two axis in an Angle into the barrel, the center distance of two axis from the small to the big end increases gradually, make the transmission gearbox output shaft have two larger center distance, the transmission system of gear and gear shaft and bearing of the gear shaft radial and thrust bearings have larger installation space, it can device of the radial and thrust bearings of large size, the shaft is enough to meet the diameter of axle torque, so big torque, load bearing ability is an important characteristic of conical twin screw extruder.This parallel twin-screw extruder is incomparable.

Conical double screw extruder with the arrangement of two screw Angle, so the transmission gearbox output shaft have two larger center distance, in the gear box unit before and after the two staggered larger thrust self-aligning ball bearings, enough to stop by the axial force formed by the pressure of the nose, the characteristics of bearing capacity is big, the gearbox manufacturing cost is low, maintenance is convenient.

Design of PVC pipe extrusion

       Design of PVC pipe extrusion 

1-Introduction

This article aims at giving a bird's eye view on PVC extrusion with particular emphasis on screw design.

PVC compounds are extruded in single as well as in twin screw extruders.

Whereas co rotating twin screws are mainly used for compounding operations, counter rotating screws are used for the extrusion of profiles, tubes and rods.

Twin screws are divided in parallel and conical configurations.

PVC is of low thermal stability and high melt viscosity. Therefore, it is combined with a number of additives to vary properties to suit different end-use applications. PVC formulation is key to processing success.

Extruded PVC can be 100% recycled. However hot spots in the extruder lead to burnt polymer which has to be rejected otherwise it will contribute to the degradation of the virgin polymer.

2-Twin screw extrusion

A co-rotating extruder with interchangeable elements is extremely versatile and can be used for most PVC compounds. Conical twins are best for rigid PVC. The production of rigid PVC pipes is dominated by counter-rotating twin screw extruders. This plasticizing system matches perfectly the demands of processing powder shaped, shear sensitive polymers. Compared to single screw extruders the twin screw extruders provide a constant feeding of powder as well as a gentle and uniform plasticizing at low screw speeds allowing for high output rates.
The counter-rotating twin screw extruders can be divided into two types with conical and parallel screw systems.

The lower the required output rate the more the conical twin screw extruder is preferred. The application range of this system goes up to 150 kg/h but as outputs increase so do the benefits of the parallel system. At output rates above 300 kg/h parallel twin screw extruders are dominant.

Conical extruders have been successful at the lower throughput end of the extruder market. In the feed zone, the surface area in contact with the material is large this improves the heat transfer to the material.

The conical shape of the screw and the continuous reduction of the channel volume result in very gentle plasticizing. Shear friction in the metering zone is very low, due to the very small screw diameter at this point.

Conical screw convey the melt smoothly and steadily even at high die resistance, although pellet rigid PVC compound can be run in twin screw extruders (starve feeding required to avoid high amps & torque), twins are ideally suited for powder dry blend.

Twin-screw extruders were designed to extrude powder by gravity feed. They normally have smaller horsepower motors, but are able to achieve higher production rates than an equivalent size single-screw extruder. The recipe should be designed to allow the powder to run flood feed. This takes advantage of the twin screw extruder's constant pump machine and achieves better dimensional control of the finished parts.

3-Single screw extrusion

Single screw extruders have been traditionally utilized for sheet extrusion because of their low initial cost.

A general-purpose screw design for rigid PVC extrusion consists of a constant flight and pitch (lead). The pitch is equal to the diameter, and the length is equal to 24D. It should be bored for screw cooling. Screw flights should be hardened. Regardless of the screw size, a 2.4:1 compression ratio is recommended for rigid PVC. Higher compression screws, such as those designed for flexible PVC, can cause over-heating and degradation of the material. (ref: PolyOne technical report). Around 14 metering flights and a metering depth of 0.3inches are required.

Four rows of pins in the metering zone at 3, 6, 9 and 12 flights from the screw tip contribute to the homogenization of the melt

Screw designs, such as double flighted screws, can also offer improved performance such as a higher rate at the same melt quality and temperature.

At recommended processing temperatures (190ºC to 216ºC for a smooth extruding), rigid PVC is typically higher in viscosity than many other materials. To prevent overloading the motor, a 150 to 250 horsepower motor for a 4 1/2" extruder is used. Screw speed ranges of 40 to 80 RPM are used. This means a gear ratio should be used to give a maximum speed of about 80 but not more than 100 RPM. Higher viscosities also mean higher temperatures are reached by shear heating or friction. Thus, screw cooling and efficient barrel cooling (i.e. water cooling), are critical to rigid PVC extrusion. An extruder length of 24 to 1 should be considered minimum while the longer 30 to 1 or 32 to 1 is desirable, especially if a vented barrel and two stage screw is used.

Typically pelletized compound is used with single screw extruders. Powder compounds are available for single screw machines but they require special handling and are more prone to air and moisture entrapment in the melt. One of two methods is used to address this issue. For pelletized or powder compounds, a two stage screw can be used with either an open vent or an applied vacuum at the vent. A two stage screw and vent combination must be carefully balanced for specific rates, dies and compounds.

A second technique used for powder extrusion is the vacuum hopper. This allows the use of single stage screws with a special vacuum seal at the screw shank. A two hopper system is used to maintain a uniform vacuum on the feed hopper. With either system, a crammer feed is recommended to assure uniform feed of the powder.

Screw cooling is mandatory for PVC sheet extrusion. The system should be set up so that the oil flows to the screw tip first so as to cool the tip and thus prevent hang up and burning on the tip. The oil should then return between the screw and the feed tube. The oil temperature should be controlled, with a recommended starting point of about 93-121°C.

The two popular methods of feeding an extruder are starve-feeding and force-feeding. During force-feeding, a reserve of material is maintained in the hopper of the extruder and material is forced in the extruder.

In starve-feeding the extruder is fed at a rate less than the capacity of the screw. The hopper remains empty and functions as a conduit to avoid material from spilling. Starve feeding is the more popular method for feeding.

Advantages of Single Screw Extruder

     Advantages of Single Screw Extruder

The significant advantages the Single Screw Extruder with barrier according to the present invention has the advantage that the pressure build-up capability is improved. Compared to the known Twin Screw Extruder it is not necessary any more to build up a very high pressure in the so-called feed zone as to enable a predetermined lower pressure at the end of thegravimetric feeder With the according to the present invention it is possible to substantially reduce the pressure between the feed zone and the melting zone. This in turn results in a reduction of wear of the gear pump in the transition area between the feed zone and the melting zone since it is operated with lower pressures.

(1)In a preferred embodiment the barrel comprises several grooves being equally spaced apart in circumferential direction which grooves extend preferably parallel to the longitudinal axis of the barrel. This has the advantage that the process of matching the grooves is simplified compared with the groove helically arranged.

(2)Due to the pressure reduction in the area of the feed zone it does not have to be constructed any more as complicated as in prior solutions and does not have to be provided with cooling means and a “heat separation” towards the heated melting zone. Advantageously, the feed zone and the melting zone may therefore be formed individually.

(3)In a further preferred embodiment the width and/or the depth of the groove varies in a longitudinal direction, preferably the grooves depth decreases towards the downstream end of the melting zone section, preferably to zero.

This has the advantage sheet production extruderthat the groove extends continuously without Single Screw Extruderany break along the feed zone and melting zone thereby further improving the output and the pressure build-up. 

In a further preferred embodiment of the invention at least one groove is provided also in the barrel inner surface (innerwall) in the area of the feed zone section, the groove extending parallel or helically relative to the longitudinal axis. Preferably, the groove in the area of the feed zone section leads into the groove in the area of the melting zone without transition. Preferably both grooves have the same lead angle.

What are the key differences between PVC and PE pipes and fittings?

      What are differences between PVC and PE pipes ?

PE  benefits

• Chemically inert, no off gassing or leaching.
• Flexible, can be pulled to around corners to eliminate fittings.  This give a better water flow, and saves time and money.
• Can freeze without bursting
• Is rated to last at least 200 years
• No glue to add poisonous vapors or soldering to reduce risk of fire.

Negatives

• Pipe and fittings are reduced in diameter, may need to up size for good flow.
• Pipe has no rigidity.  Must be supported it's entire length.
• Need special tools to install.

PVC and CPVC "for hot" benefits

• Any can do it, all you need is a cutter to assemble.
• Very cheap and you can get it anywhere.
• PVC is full bore, but only for cold water.

Negatives

• All sorts of leaching flavors and chemicals into water.
• Rated for 20 years, this is an over statement.
• Glue needs to cure for 24 hours before charging with pressure.  Most do not do this, but that is what is instructed.
• Freezes and bursts quite quickly.
• Some plumbers will not attach to it for it has a high failure rate.

How to Make Plastic Pipes

             How to Make Plastic Pipes

Plastic has largely become the material of choice for pipes. Its flexibility, ease of bonding, lighter weight than iron and steel and lower cost than copper has made it a common choice. Pipe is generally produced by an extrusion process. Although this process may vary in actual operating conditions (temperatures, pressures, extrusion rate) based on the type of plastic used, diameter of pipe and wall thickness, the fundamental process of extrusion is reasonably consistent throughout the industry. 

• Add the thermoplastic resin to the feed hopper. Although this can be done manually, it is generally transferred to the hopper via a vacuum feeder due to the steady state nature of the process. This helps minimize the chance of running out of resin during the process.
• Turn on machine screw and barrel heaters per specific resin requirements. The heaters add heat to the plastic while it is in the barrel to melt the plastic. The rotating screw adds shear heat to the plastic for melting as well as building up the pressure to force the plastic through the die.
• Extrude plastic through the die. The die is designed and built based on the dimensions desired in the pipe and the shrink rate of the type of plastic being used.

• Cut the pipe at the desired length. The extruded pipe will exit the die onto a roller system to allow the pipe to cool without deforming under its own weight. Once it has passed a certain length, it will trip a sensor (electric eye) triggering a cutting operation on the pipe. The cut is made by a cutter that moves forward at the rate of pipe extrusion to offset the motion of the pipe moving forward so that the end of the pipe will remain perpendicular to the pipe wall after it is cut.
• Continue the process in a steady-state environment until the desired quantity of plastic is produced.

     Ingredients of PVC Pipe Manufacturing

Polyvinyl Chloride (PVC) is a thermoplastic material that is used in a myriad of products including water pipe and electrical conduit. It is a polymer whose long chain molecules are made from the building blocks of vinyl chloride. Additives are used to enhance the properties of PVC for specific applications. Finished products come in a number of colors, are tolerant to ultraviolet light, and have various degrees of flexibility.

Raw Materials

• The two raw materials used in the manufacture of PVC are sea water and oil. Salt derived from sea water is used to make chlorine gas and petroleum oil is the original source for ethylene gas. Chlorine and ethylene are the two main ingredients needed to make PVC.

Chlorine

• Chlorine is produced from a saline solution by the process of electrolysis. A solution of sodium chlorine, or common table salt, is placed in a container with electrodes. When electric current is applied, the positive electrode attracts chloride ions in the solution where they combine to form chlorine gas.

Ethylene

• Ethylene is a colorless and odorless gas with the chemical formula C2H4. It is highly flammable and can cause explosions if mishandled. It is produced commercially from the refining of petroleum.

Making PVC

• The chlorine and ethylene gases are combined to produce ethylene dichloride which is converted at high temperatures to vinyl chloride (CH2=CHCl). The vinyl chloride molecules are then polymerized to form the PVC resin. Other compounds are added to improve its appearance and physical and chemical properties. The finished product is formed into pipe or other products where it hardens as it cools.

Additives

• A number of compounds can be added to raw PVC. The most common additives are pigments to add color, UV inhibitors to protect the material from being degraded by prolonged exposure to sunlight, and plasticizers to adjust the degree of flexibility of the specific product. Most plasticizers come from a chemical group called phthalates.

Toxicity of Materials

• Chlorine in the gaseous form is dangerous because it is a severe irritant to the skin, eyes, and respiratory system. Ethylene chloride compounds that are made in the manufacturing process and not converted into polymers are known to be carcinogenic. There are remnants of these compounds that are not combined in the finished PVC which makes water pipe and other products potentially hazardous as well. The phthalates that are used as to increase plasticity are also very toxic.

                  How is PVC Pipe Made?

Chemical Reaction

• PVC has its origins in the chemical gas referred to as vinyl chloride. When vinyl chloride is exposed to sunlight a chemical reaction occurs. The reaction is known as polymerization, which transmutes into a whitish solid material. To achieve the shape and solidity of a PVC pipe, a series of chemicals are introduced to one another. Natural gas is heated to create ethylene. The process is referred to as cracking. Later, sodium chloride (found in the form of rock salt) is spliced using electrolysis. As a result chlorine and lye (sodium hydroxide) is produced.

Molecular bonding

• Chlorine and ethylene (natural gas heated under pressure) are introduced to make vinyl chloride monomer (VCM). The molecules are bonded from each molecule's end. The result is a long chain of polyvinyl chloride polymer. In essence, plastic is created. The polymerized plastic, called thermoplastic PVC powder (which is compounded), melted and molded into piping. The result is a tube of PVC plastic. As a result of the chemical process (PVC becomes very solid and rigid), PVC is less likely to break during earthquakes. It can withstand pressures that many metals (such as copper piping) cannot tolerate. This is why PVC is the preferred material for plumbing and underground wiring.

Manufacturing

• As small as 16 mm and as large as 630 mm tubing/pipes are manufactured using a machine called an extruder. PVC plastic is routed through a double screw stem extruder (conical twin screw) or a parallel double screw extruder. Molding determines the wall thickness of the PVC hose. The diameter of the pipe is made by the PVC pipe extruder (The standard is 1/2 to 24 inches in diameter). The production speed of the standard PVC pipe extruder is about 20 meters per minute. The PVC hose runs through a vacuum pump. A ring cutting machine is employed at the end of the assembly line to divide the PVC tubing into sections of individual pipes. The individual pipes are cooled and racked. After inspection, the completed PVC pipes are sent to the warehouse for final inspection, labeling and shipping.

           The Plastic Manufacturing Process

Plastic Extrusion Molding Process

• Extrusion molding is another method of manufacturing plastic components. Extrusion molding is very similar to injection molding and is used to make pipes, tubes, straws, hoses and other hollow pieces. Plastic resin is fed into a barrel where it is liquefied. A rotating screw propels the liquefied plastic into a mold, which contains a tube-shaped orifice. The size and shape of the tube determines the size and shape of the plastic piece. The liquefied plastic then cools and is fed through an extruder, which flattens the plastic and forms the piece into its final shape.

Plastic Injection Molding Process

• Injection molding is one of the main methods by which parts are manufactured from plastic. The first step in the injection molding process is to feed plastic pellets into the hopper, which then feeds the pellets into the barrel. The barrel is heated and contains a reciprocating screw or a ram injector. A reciprocating screw is typically found in machines that produce smaller parts. The reciprocating screw crushes the pellets, making it easier for the plastic to be liquefied. Toward the front of the barrel, the reciprocating screw propels the liquefied plastic forward, thereby injecting the plastic through a nozzle and into the empty mold. Unlike the barrel, the mold is kept cool to harden the plastic into the correct shape. The mold plates are held closed by a large plate (referred to as a movable platen). The movable platen is attached to a hydraulic piston, which puts pressure on the mold. Clamping the mold shut prevents plastic from leaking out, which would create deformities in the finished pieces. 

The Differences Between UPVC & PVC Pipes

The Differences Between UPVC & PVC Pipes

To the casual observer, there's little difference between PVC pipe and uPVC pipe. Both are plastic pipe used extensively in building. Beyond the superficial similarities, the two types of pipe are manufactured differently and thus have different properties and slightly different applications in building and other industrial processes and most repair-work exposure to plastic pipe is to PVC rather than uPVC.

Manufacture

• PVC and uPVC are largely made of the same material. Polyvinylchloride is a polymer that can be heated and molded to create very hard, strong compounds such as piping. Because of its rigid properties once it's formed, manufacturers frequently blend additional plasticizing polymers into PVC. These polymers make PVC pipe more bendable and, generally, easier to work with than if it remains unplasticized. Those plasticizing agents are left out when uPVC is manufactured---the name is short for unplasticized polyvinylchloride---which is nearly as rigid as cast iron pipe.

Handling

• For installation purposes, PVC and uPVC pipe are generally handled in the same fashion. Both can be easily cut with plastic-cutting hack saw blades or power tools designed to cut PVC pipe and both are joined using gluing compounds rather than through soldering. Because uPVC pipe doesn't contain the plasticizing polymers that make PVC slightly flexible, it must be cut perfectly to size because it doesn't allow for give.

Applications

• PVC pipe is used as a replacement for copper and aluminum piping on non-potable water, replacing metal piping in waste lines, irrigation systems and pool circulation systems. Because it resists corrosion and degradation from biological sources, it's a durable product to use in plumbing systems. It's easily cut and its joints don't require soldering, fastening with glue instead, and offers a little amount of give when pipes aren't sized perfectly, so PVC pipe is frequently chosen by handymen as an easier-to-use alternative to metal piping.
  The use of uPVC isn't quite as widespread in plumbing in America, though its durability has helped it to become the material of choice for plumbing sewage lines, replacing cast-iron pipe. It's also frequently used in manufacturing exterior drainage systems such as rain gutter downspouts.
  The only type of plastic pipe that should be used for transmission of drinking water is cPVC pipe.

Types of PVC Pipes

                   Types of PVC Pipes

Polyvinyl chloride, or PVC, is a synthetic material that has been used to make pipes since the early 20th century. It has become an increasingly popular substance for builders and plumbers because of its resistance to corrosion. In addition to varying by size, thickness and chemical composition, PVC pipes can be color-coded by function (e.g., blue for water main, red for fire main)

Plain PVC

• Cheap, light and resistant to corrosion, PVC became an obvious solution to many of the problems faced by plumbers, builders and city planners. It gained popularity in the United States in the 1940s, and has since become a mainstay for many uses, including irrigation, sanitary sewer collection and electrical communications. Because it is a thermostatic plastic, PVC can only be melted and molded once. A second melting to re-shape PVC pipes will cause them to lose some of their integrity.

CPVC and UPVC

• CPVC stands for chlorinated PVC pipe. Suitable for a variety of applications, CPVC has a higher chlorine content than regular PVC, which means it can withstand a broad spectrum of temperatures. CPVC is ideal for use with hot water heaters. UPVC stands for unplasticized PVC pipe. This type of material is more rigid than traditional PVC material, and is commonly used for water waste transport. It can also be used to make siding materials for construction and remodel purposes.

PVC-U, PVC-M and PVC-O

• If you see PVC with a dash after it, the subsequent character has something to do with the thickness of the pipe walls. PVC-U pipes have thicker walls than regular PVC pipes. This modification enables them to withstand more internal pressure. PVC-M and PVC-O pipes are newer versions of the PVC-U. Though they have thinner walls than the traditional PVC-U, PVC-M and PVC-O pipes are specifically designed for high levels of internal pressure as well.

Lead Reinforcement

• Outside the United States, where the use of lead pipes for potable water has been banned since 1986, PVC pipes are often reinforced with lead, a process that makes the pipes stronger and less susceptible to bursting under pressure. In China, more than 90 percent of PVC pipes are manufactured with lead reinforcement. The Environmental Protection Agency has advised that exposure to lead can cause sundry adverse health effects. Globally, other governments have succumbed to public pressure and are in the process of phasing out lead in drinking water pipe manufacture