Wednesday, May 24, 2017

Tube Plastic Extrusion Machine Process

Plastic extrusion of tube, hose and pipe is a steady-state process for converting a thermoplastic raw material to a finished or near-finished annular product. The raw material is usually in the form of plastic pellets or powder. The conversion takes place by forming a homogeneous molten mass in the extruder and forcing it under pressure through an extrusion die orifice that defines the shape of the product's cross section. The formed material, or extrudate, is cooled and drawn away from the die exit at a controlled rate. The extrudate can then be wound on a spool, cut to a specified length, or directed into another in-line process.
Plastic Extrusion Machine Process
By contrast with injection molding or blow molding, which are cyclic processes, extrusion is a steady-state process. This steady-state characteristic produces some unique benefits and challenges as a manufacturing process. Extruded products are very long and continuous, and have a cross section that is usually constant with respect to the axis or direction of production. Injection-molded products are discrete items with varying cross sections in each axis. The fact that the extrusion of tube, hose and pipe is a steady-state process will be discussed in many areas of this article.The terminology used for describing tube, hose and pipe varies from industry to industry.
The major components of a tube, hose, or pipe extrusion system are often divided into components that are upstream of the extruder, the extruder itself, and those that are downstream of the extruder. Upstream components include resin handling equipment for conveying the raw materials to the extruder, and resin conditioning equipment that will pre-heat the resin, or control the moisture content of the resin before it enters the extruder feed throat. The downstream components include a molten resin filter or screen changer, the extrusion die assembly, the quench or vacuum sizing tank, any product measurement instruments, the extrusion line speed controller in the form of a belt puller or nip roll set, and finally a product cut-off device or winding equipment. There are additional extrusion process methods that will take the extruded product directly into another in-line process for the addition of a reinforcement braiding or for the addition of other coatings or resin layers. 
Extrusion techniques can be used to process most thermoplastics and some thermoset plastics. The resins most commonly extruded for tube, hose and pipe products include high and low density polyethylene, polypropylene, polyurethane, polystyrene, fluoropolymers, PTFE, polyester, and flexible and rigid PVC. A characteristic that often differentiates extruded resins from injection-molded resins is the melt viscosity of the plastic at normal processing temperatures. Extruded plastics often have a higher melt viscosity, which allows the extrudate to retain the shape imparted to it by the die while the extrudate is in the quenching stages.
Combinations of various resins can be used to gain special physical, biological, or chemical properties. Many additives can be used during the extrusion process to enhance processing characteristics of the polymer or to alter product properties. Such additives include lubricants, thermal stabilizers, antioxidants, radiopacifying agents, and colorants. 
Processing Parameters
The parameters important to extrusion processing are similar to those of injection molding processes. Resin temperature, resin pressure, resin moisture content, screw speed, and screw motor amperage are usually controlled or monitored to provide a homogeneous melt at a controlled volumetric rate. Quenching temperature and the rate at which the extrudate is drawn are controlled or monitored to provide a controlled product size. Dimension measurements, using a variety of gauging methods, can be taken of the extrudate as it is produced. In contrast to injection molding, extrusion can vary the size of the final product without changing the die tooling. Common extrusion production tolerances or process consistency are held to within 1% of the nominal measured value. As these manufacturing processes involve steady state conditions, any action that can stabilize any parameter or condition is beneficial to the process. 

Monday, May 22, 2017

Extrusion Process

Extrusion is the process which is used to manufacture long as well as straight metal parts. In other words, extrusion process is used for the development of such objects that have a cross-sectional profile, which is fixed. With the use of extrusion process, the cross-sections can be made in a number of shapes such as solid round, T shapes, rectangular, Tubes, L shapes, etc. Basically, in the extrusion process the metal is squeezed in a die with the use of hydraulic or mechanical press. 

A Brief History
First extrusion process was patented in 1797 by Joseph Bramah, for the development of lead pipe. This process involved two steps, first in which metal was preheated and the second step was to force the heated metal through a die through a plunger that was hand driven. In the year 1820, Thomas Burr acquired success in constructing the hydraulic powered press, which was first of its type. Till this time, extrusion process was known as squirting. In the year 1894, Alexander Dick gained success in expanding the extrusion process to the brass and copper alloys. 

Features And Benefits of Extrusion Process
Extrusion process provides a number of benefits over the other production processes. One of these benefits is the ability of extrusion to create extremely complex cross-sections as well as work materials, which are frangible as the material encounters only the shear and compressive stresses. Its another benefit is that with the use of best Extrusion Equipments or Extrusion Machines, such parts can be created that have an exceptional surface finish. 

Till date, many Extrusion Machines have been developed and used to create objects having cross-sectional profile. The features of the Extrusion Process are tabulated below: 

Cost EffectiveMinimizes the requirement of secondary machining process
Cross SectionWide variety of cross-sections can be made
Surface FinishFor Steel is 3 µm; (125 µ in)
For Aluminum and Magnesium -0.8 µm (30 µ in)
Minimum ThicknessFor Steel 3 mm (0.120 in)
For Aluminum and Magnesium 1mm (0.040 in)
Minimum Cross SectionFor Steel 250 mm (0.4 in)
Corner And Fillet RadiiFor Aluminum and Magnesium 0.4 mm (0.015 in)
For Steel the minimum corner radius is 0.8mm (0.030 in) and fillet radius is 4 mm (0.120 in)

Some General Points Of Extrusion Process
  • Extrusion can be semi-continuous (creating a number of pieces) or continuous (theoretically creating indefinitely long material)
  • Extrusion process can be done with the hot material or cold material
  • Metals, concrete, polymers, ceramics and foodstuffs are the material that can be commonly extruded
  • Extrusion ratio may be extremely large along with the development of qualitative parts
  • Extrusion process is of three types:
    • Hot Extrusion
    • Cold Extrusion
    • Warm Extrusion
    • Extrusion Defects

Surface crackingIt occurs when the surface of an extrusion splits. This is generally caused by the high values of extrusion temperature, speed or friction. The cracking may also occur at lower temperatures, in case the extruded product temporarily sticks to the die.
PipeA flow pattern that draws the surface oxides and impurities to the center of the product. Such a pattern is normally caused by high friction or cooling of the outer regions of billet.
Internal crackingIt occurs when the center of extrusion develops cracks or voids. These cracks are directly attributed to a state of hydrostatic tensile stress at the centerline in the deformation zone in the die.

Sunday, May 21, 2017

Plastic Extrusion

Plastic ExtrusionPlastic extrusion is defined as a manufacturing process (high-volume), in which the raw plastic / raw plastic material is melted and then formed in a continuous profile. With this process various products can be manufactured such as pipe/tubing, window frames, weather stripping, wire insulation, and adhesive tape. In general, the plastic materials that are used in the process of extrusion are Polyethylene, Polypropylene, Nylon (Polyamides), Polystyrene, Polycarbonate, Acetal, Acrylic, and Acrylonitrile Butadiene Styrene (ABS). These are just the primary plastic materials that are extruded. Apart from these, there are many other plastic materials that can be / are extruded all around.

Plastic Extrusion Process
In the processing of plastic raw materials through the extrusion process, the raw thermoplastic material is gravity fed from a hopper (top mounted) into the barrel, which is a part of extruder. The raw material is in the form of small beads and is generally called resin, in industrial terms. Before the material arrives at the hopper, it can be (& often is) mixed with various additives like colorants & UV inhibitors (in pellet or liquid form). The further steps of the process of plastic extrusions are as follows:

Through the feed throat, the material enters and comes in contact with screw. The feed throat is an opening near the rear side of barrel.
The rotating screw, which is generally turning at 120 rpm (max.) forces the plastic beads ahead in the barrel. At this time, the barrel is heated to the required melt temperature of the molten plastic. This temperature can be within the range of 200 °C (392 °F) to 275 °C (527 °F), which depends on the polymer being extruded.
In most of the plastic extrusion processes, a specific heating profile is set for the barrel. Inside the barrel, three or more individual / separated PID controlled heater zones slowly enhance the barrels' temperature from the rear side (from where the entry of plastic takes place) to the front side.

This permits the plastic beads to slowly melt as these are forced through the barrel, lowering the risk of overheating that may result in polymer's degradation. Additional heat is contributed from the intense friction and pressure that takes place in the barrel. Actually, if a specific extrusion line is operating on a fast-enough material, the heaters can be switched off & the melt temperature can be maintained by the effect of friction and pressure alone in the barrel. In a large number of extruders, there are cooling fans for keeping the temperature less than a set value, in case there is too much heat generation. In case the forced air cooling seems to be incommensurate, then cast-in heater jackets are used. These commonly use a closed loop of distilled water during the exchange of heat with the city water or tower. Further steps of plastic extrusions are as follows:
Plastic Extrusion
In the barrels' front, molten plastic leaves the screw & moves through a screen pack for the removal of contaminants present in the melt.
Then, a breaker plate is used to reinforce the screens as at this point the pressure may exceed 5000 psi (34 Mpa). Breaker plate is a thick metal puck that has many holes drilled in it.

The assembly of screen pack / breaker plate also serves the purpose of creating a back pressure inside the barrel, which is needed for proper mixing and uniform melting of the polymer. The amount of generated pressure can be easily 'tweaked' by changing the screen pack composition i.e., number of screens, wire weave size of the screens, & various other parameters. The combination of breaker plate & screen pack also serves the purpose of converting the "rotational memory" of molten plastic into the "longitudinal memory".

After the molten plastic passes through the breaker plate, it enters the die. The die provides a specific profile to the final product and it must be designed in such a way that the flow of molten plastic is uniform from a cylindrical profile to the product's profile shape. Until, it is a continuous profile any imaginable shape can be developed.

At this stage, the product is now cooled by pulling the extrudate by way of water bath. It is well known fact that plastics are extremely good thermal insulators & hence are difficult to cool swiftly. In a pipe or tube extrusion line, a carefully controlled vacuum is used to act on the sealed water bath. This is done for avoiding the collapse of newly formed and still molten pipe or tube. For products like plastic sheeting, the required cooling is acquired by pulling through a definite set of cooling rolls.

Friday, May 19, 2017

Drives And Motors

Drives system is an important part of the extrusion machine. It is very important to have the right kind of motor and drive combination that will help in saving energy and enable in improving the efficiency of the extrusion machine. Nearly 40% of the fuel consumption goes for generating electricity so as to convert the the energy into mechanical energy. 

Types of Drives 
The main types of drives that are commonly available are:
Drives And Motors
AC drive system: AC drive refers to the device used to control the speed of an AC motor. The AC drive system consist of a converter, a regulator and an inverter. In an AC driver the electrons alternates in direction as the voltage force alternates between pushing and pulling of electrons.

DC drive system: A basic DC drive controller consist of a drive controller and DC motor. In DC systems, electrons flow continually in one direction. The drive controller converts AC power to DC power. DC drive is the speed control system of the DC motors. 

Hydraulic drive system: It consist of a constant speed AC motor driving a hydraulic pump which in turn drives a hydraulic motor and the associated controls. The entire package is often referred as the hydrostatic drive.

Qualities of Drive
In the drive system alternating current or the direct current is converted into the required energy form. The main work of a drive is to maintain a constant speed of the screw throughout because the fluctuation of the screw will cause changes in the dimension of the extrudate. Thus, constancy of speed is a very important requirement of an extruder drive. The drive must supply the required amount of torque and must be able to continuously adjust from zero to maximum screw speed.

Today's motor design and construction are highly refined. A wide range of machines are available in the market that allows the operator to start, stop, and change direction and speed of the motor. Industrial drives are available in a variety of configurations and combinations. When one selects a motor one mus t ensure that the drive suits the requirement in terms of the the motor type, horse power, input voltage , etc.

Thursday, May 18, 2017

Types Of Plastic Extruders

Plastic extruders are used to create a wide range of items, including plastic tubing, trims, seals, plastic sheets and rods. Extruder is the machine for producing more or less continuous lengths of plastic sections out of a selected type Types Of Plastic Extrudersof plastic resin. There are a number of extrusion techniques available such as co-extrusion, offset extrusion, oriented extrusion, overcoat extrusion, cold extrusion, ram extrusion and much more. 

The essential elements for a thermoplastic extruder are a tubular barrel, usually electrically heated; a revolving screw, ram or plunger within the barrel; a hopper at one end from which the material to be extruded is fed to the screw, ram or plunger; a die at the opposite end for shaping the extruded mass. Extruders may be divided into three general types :
  • Single Screw Extruder
  • Twin or Multiple Screw Extruder
  • Ram Extruder
Single screw extruders and twin screw extuders are the most widely used extruders. The screw that is used to push the resin out of the die is the important component of a screw extruder. In the earlier days rubber screw were used but the rubber screw was not able to give enough amount of shear into the polymer. Therefore, screws were designed that would start deeper in the feed and gradually taper shallower in the metering section to apply more work on the polymer as it was going from the feed to the discharge. 

Basic screw design: The screw is usually contained inside a tight fitting barrel driven by a variable speed motor and gearbox. It is a highly efficient device capable of processing several tons of plastic per hour, even in modestly sized extruders. The screw is divided into three division the feed section, the compressor and the metering section. 

The feed section of the screw mechanism stores and delivers resin pellets from a gravity fed hopper into the jacketed screw to begin the plastic longitudinal movement. Screw threads move the plastic using axial rotation. Within the barrel, heaters help the plastic develop a tack to increase its friction against the barrel wall. Without this friction the plastic could not be conveyed forward and would merely rotate inside the screw. 

In the transition or melt stage, the root diameter of the screw increases while the height of the flight decreases. The Types Of Plastic Extrudersresin is melted here because of compression, shearing and heating produced in the barrel. Now the melt moves to the metering section, where the screw diameter remains constant. The melted plastic which is under high pressure now is pumped into the extruder die. 

Barrier Screws: The resin is sometimes not completely melted in the basic extrusion screw. The barrier screw in designed to counter this problem. Additional flights are attached to the transition section so as to separate molten and solid plastic to different channels. As the solid pellet moves forward it melts due to shear against the wall and thus melts and flows into the liquid channel. Thus the solid channel narrow gradually and the liquid channel widens. 

Mixing Screws: When mixing two different additives, a more efficient way is to mix extrusion materials with twin screw extruder. In this method two screw rotate with or against each other and have special mixing features, such as kneading blocks and forward and reverse capabilities. Some single screw systems can, however, be used for mixing. 

Though general-purpose screws are available, different plastics require differently calibrated extrusion screws. The length-to-diameter ratio, pitch, length of each zone and helix angles of a screw must all be matched to the plastic type being used. The screw must also be designed to suit a specific type of die. 

Extrusion screw design has been improving over the years, with new innovations and ideas that help in perpetually adjusting the process so as to meet the needs of specific applications. 

Wednesday, May 17, 2017

Plastic Extrusion Machines

Plastic Extrusion MachinesWith technical knowledge and engineering skills plastic resin can be converted into any desired shape. Plastic is one such material which in its variety of designs and colours find widespread application in homes and industries. Industries largely use the plastic extrusion process to shape the products, for which a variety of sophisticated extrusion machines with unique features are available in the market. 

An extrusion machine consist of various component for the various stage of the extrusion process. The entire process can be fully automated. Plastic can be extruded in the continuous and semi-continuous manner and in various shapes like round, rectangular, tubes etc. The resin that is introduced into the machine, get melted and eventually forced out through the die. The design of the die decides the ultimate shape of the product. Plastic solidifies on cooling. After which the plaster is cut in section according to the required size. 

Types of extrusion machines: Basically, an extruder machine consist of a feed screw, barrel and temperature controller. But the design and features of the machine depend of several other factors like the type of material to be extruded and the design of the product. A profusion of plastic extrusion machines are available in the market, some of them being:
  • HDPE pipe Extrusion line
  • Plastic Sheet Extrusion Machine
  • Blown Film Plant
  • PP TQ Film Plant
  • Multi layer Blown Film Plant
  • Cast Film Line
  • Raffia Tape Stretching Line
  • Plastic Extrusion MachinesAir Bubble Sheet Plant
  • PP/HDPE Box Strapping Plant
  • PET Box Strapping Plant
  • Extrusion Coating Lamination Plant
  • PP/HDPE/PET Monofilament plant
  • Synthetic String Plant (Sutli Plant)
  • PET Recycling Plant
  • HDPE/RPVC/PPR Pipe Plant
Features of machines
Plastic extrusion machines can be either standardized or custom made. In either of the case some of the feature of the machines are to paid special attention so as to get optimum productivity and quality.

Design characteristicDesign of a extruder machine can be optimized by using durable head. Robust and sophisticated construction methods must be used for fabricating a extruder machine. At the same time the maintenance and operations of the machines should be easy.
Flow channelFlow channel should be able to handle the material The length of the flow path should be kept in proportion to the requirement of the material.
ToolingScrew design greatly influences the machines output.

The application of plastic is highly relevant both in industrial, commercial and domestic sector. Some of the commonly used plastic extruded products are release paper, soft food packaging, medical packaging, paper packaging, industrial packaging, pipe, blown film, coated paper, plastic filaments for brush bristles, carpet fibers, vinyl siding, and many more. 

Tuesday, May 16, 2017

Extrusion Materials

Extrusion MaterialsExtrusion is the most important process where a billet is pushed and / or drawn by way of die for creating rod, or pipe in a specific shape. This process is also used to develop vinyl (PVC), aluminum & other profiles / components that are used to produce windows and doors. The extrusion process is carried out with the assistance of various Extrusions Machinery such as Extruder, PP / TQ Film Plant, Extrusion Lamination Plant, Synthetic String Plant, and others. There are mainly two types of extrusions processes, hot extrusion and cold extrusion. 

In the Hot Extrusion Process, different products are manufactured using various materials that are also called Extrusion Materials. Mainly, the extrusion materials that are used include Aluminium, and Copper along with their alloys. Some of the other quality extrusion materials that are extruded using hot extrusion process are as follows:
  • Magnesium
  • Steel
  • Titanium
  • Nickel
  • Refractory Alloys
Similarly, in the Cold Extrusion Process various products are developed from a range of materials. Some of the major Extrusion Materials include:
  • Copper
  • Lead
  • Tin
  • Aluminum Alloys
  • Titanium
  • Molybdenum
  • Vanadium
  • Steel
  • Zirconium
  • Niobium.
Depending on your requirements, you can choose different extrusion materials for developing an array of products. The selected material must have the capability of being extruded into the designed profile. The extrusion material specifications may or may not match the design requirements as desired by you, but if the material has low melt strength and low melt stiffness, then it may be possible to extrude it in the design geometry. Hence, it is very important to select the proper extrusion materials. Some of the good extrusion materials are as follows:
  • Acrylic
  • Acrylonitrile Butadiene Styrene (ABS)
  • Polycarbonate (PC)
  • Polyester (PETG)
  • Polyethylene (High Density-HDPE, Low Density-LDPE)
  • Polypropylene (PP)
  • Polystyrene (General Purpose-GPPS, High Impact-HIPS)
  • Polyvinyl Chloride (Rigid-RPVC, Flexible-FPVC)
During the selection of the extrusion materials, you must consider some of the important attributes related to them such as: 
Additives and Co-polymerFlexibility
AestheticsHeat Stability
Chemical ResistanceImpact Strength
Comparative Material ChartRigidity
Flame RetardancySmell
UV Stability