How to control quality of Teflon tapes under processing ? (1)

Some people have one question, how to control quality of Teflon tapes under processing ? What's factors on the quality of PTFE tapes ?

Now PTFE tape supplier will tell you the truth  about how to control quality of Teflon thread seal tapes.

Teflon tapes products quality depends on many factors, such as raw material quality, heating time, straightness of roller for calendar, stretch ratio, temperature of slitting machine, blade quality, worker’s skills and so on.

First most important factor is PTFE raw powder quality, now PTFE material suppliers always offer different classes material, if PTFE tape manufacturer use lowest class material, the strenching ratio and quality of PTFE tapes must not be good. Most of Teflon tape manufacturers are mixing middle class material with low class together. Their cost can be saved about USD 600/ Ton. 

Sure, some good manufacturer like http://ptfe-tape.com using top class and middle class material for mixing, this product be with high performance and good quality , it is not easy to broken when you using it.

Next time, Teflon  tape supplier will tell you another factor that how to stretch ratio impact the quality of thread seal tapes.

The above information is from Teflon tape manufacturer Amstar Seal Tape Co.,Ltd. and Magstar Machinery Technology Co.,Ltd.

Source from : http://ptfe-tape.com
http://ptfemachinery.com

PTFE Plumber’s Tape

Thread seal tape is a polytetrafluoroethylene (PTFE) film used in sealing pipe threads. It is also known by the trade name Teflon tape. thread seal tape lubricates allowing for a deeper seating and tightening of the threads, helping to prevent the threads from seizing when being unscrewed. The tape also works as a deformable filler and thread lubricant, helping to seal the joint without hardening or making it more difficult to tighten, and making it easier to tighten. The tape is typically wrapped around a pipe’s thread three times before it is screwed into place and is commonly used commercially in applications including pressurized water systems, central heating systems, and air compression equipment.

AMSTAR PTFE thread seal tapes meet MIL spec 27730A and are 3.5 mils thick. They are composed of white sintered PTFE and are wound on a blue spool with a white snap-on shell cover. Can-Do stocks PTFE thread seal tapes that are manufactured and imported from the Far East, but domestic products are also popular. These PTFE film products are recommended for use on all threaded fittings for passage of water, gas, oxygen, chemicals, and other fluids or gases.

The above information is from PTFE tape machine manufacturer. 

PTFE tapes price depends on its quality

In recent years, with the development of economy, the sealing industry such as Teflon tape has developed rapidly. However, unlike other industries, although the sealing industry has developed rapidly, changes in the sealing company is slow. The price of PTFE thread seal tape determines the anticorrosion performance is superior, and the overall adhesion is better, the service life is relatively longer.

The overall performance of good quality PTFE plumbers tape is very superior during construction, . It can be cured at normal temperature as the conventional anticorrosive paint. It is relatively simple in construction. For some unfamiliar people, the same can be done. In our opinion, the sealing of the PTFE thread seal tape is also very perfect, and its performance is also very perfect, it can withstand high temperatures, even in more than 200 degree above the high temperature can be used.

In addition, the PTFE tape is also resistant to low temperature, even in the state of one hundred degrees below zero, can also maintain a soft state. At the same time is also resistant to corrosion, whether those organic solvents, will not have any effect on it. In a large number of plastic materials, its aging life is very long. The effect is also very good, there is enough lubrication, and non stick performance is perfect.

Amstar seal tape co.,ltd not only adopts advanced teflon tape machine with high technology, but aslo using top grade high density of ptfe raw material it ensures good quality of products. 

Characteristics of Teflon thread seal tape

   Characteristics of Teflon thread seal tape

Teflon Thread Seal Tape has excellent practicability and can be used in many occasions because of its various advantages.

Corrosion resistance - for most chemicals and solvents, exhibits inertia, resistance to strong acids, alkalis, water, and various organic solvents.

High temperature resistance -  using operating temperature of 250 degrees.

Low temperature resistance -  good mechanical toughness. Even if the temperature drops to -196 degrees, 5% elongation can be maintained.

No toxicity - it has physiological inertia. As an artificial vessel and organ, it is implanted into the body for a long time without any adverse reaction.

Weather resistance - the best aging life in plastic.

High lubrication - the lowest friction coefficient in solid materials.

Non adhesion-  the smallest surface tension in solid material and does not adhere to any substance.

Amstar Seal Tape Co., Ltd. is a professional PTFE tape manufacture with advanced technology, equipment and experienced staff, we are not only offer good products but also good service, sincerely look forward to meeting with you, hope we can bring you a different experience. 

PTFE Tapes Making Process

Process of PTFE Tape Making Machine 

PTFE Tapes making machines are component of series continuted machines, such as shaking machine, mixing machine, heating oven machine, calendar machine, deoiling machine, streching machine, sliiting machine, rewinding machines, packing machine, injection machine, printing machine and so on. 

The PTFE tapes main making process as following :

Mixing PTFE material with kerosene for half hour at least–––Oven heating baking mixed material for six hours at least–––Pressing material into round shape first and then press round shape into rope shape by special mould––– Using calender machine for making rope shape into to fixed film you requires–––Sittling to the width you need after kerosene out and high stretching ratio–––Wrapping request length to reel–––Packing.

The above is PTFE machine information . Hope it can help you understand how to make PTFE tapes. 

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 (3)

Extruder 

An extruder is usually described by its bore size and barrel length. Pipe extruders typically have an inside diameter of 2 to 6 inches with barrel lengths of 20 to 32 times the bore diameter. The barrel length divided by the inside diameter is referred to as the L/D ratio. An extruder with an L/D ratio of 24:1 or greater provides adequate residence time to produce a homogeneous mixture.

The extruder is used to heat the raw material and then force the resulting melted polymer through the pipe extrusion die. The barrel of the machine has a series of four to six heater bands. The temperature of each band is individually controlled by an instrumented thermocouple. During the manufacturing process, the major portion of the heat supplied to the polymer is the shear energy generated by the screw and motor drive system. This supply of heat can be further controlled by applying cooling or heating to the various barrel zones on the extruder by a series of air or water cooling systems. This is important since the amount of heat that is absorbed by the polymer needs to be closely monitored. The temperature of the extruder melted polymer is usually between 390˚F and 450˚F, and it is also under high pressure (2000 to 4000 psi).

Breaker Plate/Screen Pack

The molten polymer leaves the extruder in the form of two ribbons. It then goes through a screen pack which consists of one or more wire mesh screens, positioned against the breaker plate. The breaker plate is a perforated solid steel plate. Screen packs prevent foreign contaminants from entering the pipe wall and assist in the development of a pressure gradient along the screw. This helps to homogenize the polymer. To assist in the changing of dirty screen packs, many extruders are equipped with an automatic screen changer device. It removes the old pack while it inserts the new pack without removing the die head from the extruder.

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.