PE Pipe Extrusion Process (6)

Pullers

The puller must provide the necessary force to pull the pipe through the entire cooling operation. It also maintains the proper wall thickness control by providing a constant pulling rate. The rate at which the pipe is pulled, in combination with the extruder screw speed, determines the wall thickness of the finished pipe. Increasing the puller speed at a constant screw speed reduces the wall thickness, while reducing the puller speed at the same screw speed increases the wall thickness.

Standards of ASTM International and other specifications require that the pipe be marked at frequent intervals. The markings include nominal pipe size, type of plastic, SDR and/or pressure rating, and manufacturer’s name or trademark and manufacturing code. The marking is usually ink, applied to the pipe surface by an offset roller. Other marking techniques include hot stamp, ink jet and indent printing. If indent printing is used, the mark should not reduce the wall thickness to less than the minimum value for the pipe or tubing, and the long-term strength of the pipe or tubing must not be affected. The mark should also not allow leakage channels when gasket or compression fittings are used to join the pipe or tubing.

Take-off Equipment

Most pipe four inches or smaller can be coiled for handling and shipping convenience. Some manufacturers have coiled pipe as large as 6 inch. Equipment allows the pipe to be coiled in various lengths. Depending upon the pipe diameter, lengths of up to 10,000 feet are possible. This is advantageous when long uninterrupted lengths of pipe are required - for example, when installing gas and water pipes.

Saw Equipment and Bundling

Pipe four inches or more in diameter is usually cut into specified lengths for storage and shipping. Typical lengths are 40 to 50 feet, which can be shipped easily by rail or truck. The pipe is usually bundled before it is placed on the truck or railcar. Bundling provides ease of handling and safety during loading and unloading.

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.

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.