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 (5)

Pipe Sizing

The dimensions and tolerances of the pipe are determined and set during the sizing and cooling operation. The sizing operation holds the pipe in its proper dimensions during the cooling of the molten material. For solid wall pipe, the process is accomplished by drawing the hot material from the die through a sizing sleeve and into a cooling tank. Sizing may be accomplished by using either vacuum or pressure techniques. Vacuum sizing is generally the preferred method.

In the vacuum sizing system, molten extrudate is drawn through a sizing tube or rings while its surface is cooled enough to maintain proper dimensions and a circular form. The outside surface of the pipe is held against the sizing sleeve by vacuum. After the pipe exits the vacuum sizing tank, it is moved through a second vacuum tank or a series of spray or immersion cooling tanks.

In the pressure sizing system, a positive pressure is maintained on the inside of the pipe by the use of a plug attached to the die face by a cable or, on very small bore pipe, by closing or pinching off the end of the pipe. The pressure on the outside of the pipe remains at ambient and the melt is forced against the inside of the calibration sleeve with the same results as in the vacuum system.

The production of very large diameter profile pipe, up to 10 feet in diameter, uses mandrel sizing. In one form of this process, the extruded profile is wrapped around a mandrel. As the mandrel rotates, the extruded profile is wrapped such that each turn overlaps the previous turn. In some other techniques, the turns are not overlapped. A typical profile wall PE pipe is shown in Figure 7.

Cooling

For either the vacuum or pressure sizing technique, the pipe must be cool enough so that it maintains its circularity before it exits the cooling tank. Various methods of cooling are utilized to remove the residual heat out of the PE pipe. Depending upon the pipe size, the system may use either total immersion or spray cooling. Spray cooling is usually applied to large diameter pipe where total immersion would be inconvenient. Smaller diameter pipe is usually immersed in a water bath. Cooling water temperatures are typically in the optimum range of 40° to 50°F (4° to 10°C). The total length of the cooling baths must be adequate to cool the pipe below 160°F (71°C) in order to withstand subsequent handling operations.

Residual stresses generated by the cooling process within the pipe wall are minimized by providing annealing zones.(4) These zones are spaces between the cooling baths which allow the heat contained within the inner pipe wall to radiate outward and anneal the entire pipe wall. Proper cooling bath spacing is important in controlling pipe wall stresses. Long-term pipe performance is improved when the internal pipe wall stresses are minimized.

PE Pipe Extrusion Process (4)

Die Design

The pipe extrusion die supports and distributes the homogeneous polymer melt around a solid mandrel, which forms it into an annular shape for solid wall pipe . The production of a profile wall pipe involves extruding the molten polymer through a die which has a certain shaped profile.

The die head is mounted directly behind and downstream of the screen changer unless the extruder splits and serves two offset dies.

There are two common types of die designs for solid wall pipe; the spider die design and the basket die design. They are illustrated in Figure 5. These designs refer to the manner in which the melt is broken and distributed into an annular shape and also the means by which the mandrel is supported.

In the spider die (Figure 5.1), the melt stream is distributed around the mandrel by a cone which is supported by a ring of spokes. Since the melt has been split by the spider legs, the flow must be rejoined.

Flow lines caused by mandrel supports should be avoided. This is done by reducing the annular area of the flow channel just after the spider legs to cause a buildup in die pressure and force the melt streams to converge, minimizing weld or spider lines. After the melt is rejoined, the melt moves into the last section of the die, called the land.

The land is the part of the die that has a constant cross-sectional area. It reestablishes a uniform flow and allows the final shaping of the melt and also allows the resin a certain amount of relaxation time. The land can adversely affect the surface finish of the pipe if it is too short in length. Typical land lengths are 15 to 20 times the annular spacing.

The basket design (Figure 5.2) has an advantage over the spider die concerning melt convergence. The molten polymer is forced through a perforated sleeve or plate, which contains hundreds of small holes. Polymer is then rejoined under pressure as a round profile. The perforated sleeve, which is also called a screen basket,eliminates spider leg lines.

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.

           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. 

Did you know how many different types of extrusion processes ?

                     Did you know how many different types of extrusion processes ?

There are different types of extrusion processes

Cold extrusion is used to gently mix and shape dough, without direct heating or cooking within the extruder. In food processing, it is used mainly for producing pasta and dough. These products can then be subsequently processed: dried, baked, vacuum-packed, frozen, etc.

Hot extrusion consists of thermomechanically transform raw materials in short time and high temperature conditions under pressure. In food processing, it is used mainly to cook biopolymer-based raw materials to produce textured food and feed products, such as ready-to-eat breakfast cereals, snacks (savory and sweet), pet foods, feed pellets, etc.

Steam-induced expansion, means melt expansion at the die exit due to water flashing off, hence leading to highly expanded products. Subsequent processing then determines the textural attributes of extruded products such as crispness, crunchiness, hardness, etc. This process is used to produce directly expanded breakfast cereals, snacks and crispy breads.

Expanded co-extrusion combines steam-induced expansion and filling injection, hence leading to expanded products with dual textures. It is mainly used in breakfast cereals and snacks.

The advantages of twin screw extrusion

      The advantages of twin screw extrusion

Twin screw extrusion has become the standard over time in several industries because it offers numerous advantages over single screw extrusion:

1.More consistency in production and control of product quality

2.Increased productivity due to continuous processing, faster start up and shut down between product changes, quick changeover and advanced automation

3.Greater flexibility, with the capability to process a wide range of raw materials

4.Optimized footprint thanks to energy and water savings

5.Simple and easy to maintain and clean

Twin Screw 

How does extrusion work?

                  How does extrusion work?

Extrusion processing aims to physico-chemically transform continuously viscous polymeric media and produce high quality structured products thanks to the accurate control of processing conditions.

Twin screw extruders consist of two intermeshing, co-rotating screws mounted on splined shafts in a closed barrel. Due to a wide range of screw and barrel designs, various screw profiles and process functions can be set up according to process requirements. Hence, a twin screw extruder is able to ensure transporting, compressing, mixing, cooking, shearing, heating, cooling, pumping, shaping, etc. with high level of flexibility. The major advantage of intermeshing co-rotating twin screw extruders is their remarkable mixing capability which confers exceptional characteristics to extruded products and adds significant value to processing units.

In twin screw extrusion processing, the raw materials may be solids (powders, granulates, flours), liquids, slurries, and possibly gases. Extruded products are plastics compounds, chemically modified polymers, textured food and feed products, cellulose pulps, etc.

Overview of Double Screew Extruder

     Overview of Double Screew Extruder 

Overview

Twin screw extrusion is used extensively for mixing, compounding, or reacting polymeric materials. The flexibility of twin screw extrusion equipment allows this operation to be designed specifically for the formulation being processed. For example, the two screws may be corotating or counterrotating, intermeshing or nonintermeshing. In addition, the configurations of the screws themselves may be varied using forward conveying elements, reverse conveying elements, kneading blocks, and other designs in order to achieve particular mixing characteristics.

Process Schematic

Maintenance Method Of Plastic Extruder in Daily

Today we know the plastic extrusion machine maintenance method!

Ventilation points • plastic extrusion equipment should be placed to ensure motor heat and prolong its life; maintain good grounding of the machine.

• Regularly check tool screws, new machine using 1 hours Hou, with tool tight solid moving knife, set knife of screws, strengthening blade and turret between of fixed sex; should regularly on bearing raises lubricants, guarantee bearing between of lubrication sex; for guarantee tool incision of sharp degrees, should often check tool, guarantee its sharp degrees, reduced due to blade blunt deficiency and caused other parts of not necessary damaged; regularly check belt whether relaxation, timely adjustable tight.

• Restart-the second start, should clear the remaining scrap, reduce the starting resistance. should periodically turn inertia cover and belt pulley cover, remove flange bottom ash, Crusher discharge powder into the axle bearing.

• Replacement parts-when replacing the cutters, knives and the gap between the fixed knife: 20HP Crusher 0.8MM, 20HP Crusher 0.5MM. recycled material is thinner, the clearance can be adjusted.

Extrusion System For Plastics Extrusion Machine

Extrusion system consists of screw and barrel, Hopper, die, and die, plastics by squeezing the system plastics melt evenly, and, in the process of establishing, under pressure from continuous by screw extruder.

1, screw: is the most important parts of extruder, it is directly related to applications and productivity of extruders, made from high-strength corrosion-resistant alloy steel.

2, barrel: is a metal cylinder, generally with higher heat resistance, compressive strength, strong wear-resistant, corrosion-resistant alloy steel composite pipe made of or lined with alloy steel. Barrel and screw fit, realize the plastic pieces, softening, melting and plasticizing, vent and compaction, and uniform conveyor rubber molding system. Barrel length is 15~30 times the diameter, so that the plastic is fully heated and fully plastic into principles.

3, Hopper: hopper with cut-off device at the bottom, so you can adjust and cut off the flow, side of the hopper with sight and calibration of metering devices.

4, die and mold: head made of alloy steel and carbon steel coat, and head is equipped with mold, heads are used to rotate the plastic melts into parallel straight line movement, steady import model Kit, and endows plastics with the necessary pressure. Plastic plastic in the barrel of the compaction, porous plate along a certain flow through head neck into head mold, die mandrel set appropriate, formation cross section decreases of the annular space, plastic melt around the wire to form a continuous solid tube coating. In the guarantees head plastic reasonable channel, elimination of accumulated plastic corner, often placed with split sleeves, for elimination of plastic extrusion pressure fluctuations, there is set of grading rings. Head is also equipped with mould correction and adjustment device, easy to adjust and align core and mould sleeve of concentricity.