extrusion of plastics

In the extrusion of plastics,raw thermoplastic material in the form of small beads (often called resin in the industry) is gravity fed from a top mounted hopper into the barrel of the extruder.
Additives such as colorants and UV inhibitors (in either liquid or pellet form) are often used and can be mixed into the resin prior to arriving at the hopper.

Polymer resin pellets used in plastics extrusion.
The material enters through the feed throat (an opening near the rear of the barrel) and comes into contact with the screw.
The rotating screw (normally turning at up to 120 rpm) forces the plastic beads forward into the barrel which is heated to the desired melt temperature of the molten plastic (usually around 200 °C/400 °F).
In most processes,a heating profile is set for the barrel in which three or more independently controlled heaters. gradually increase the temperature of the barrel from the rear (where the plastic enters) to the front.
This allows the plastic beads to melt gradually as they are pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer.
Extra heat is contributed by the intense pressure and friction taking place inside the barrel.
In fact,if an extrusion line is running a certain material fast enough,the heaters can be shut off and the melt temperature maintained by pressure and friction alone inside the barrel.
In most extruders,cooling fans are present to keep the temperature below a set value if too much heat is generated.
Plastic extruder cut in half to show the components.
At the front of the barrel,the molten plastic leaves the screw and travels through a screen pack to remove any contaminants in the melt.
The screens are reinforced by a breaker plate (a thick metal puck with many holes drilled through it) since the pressure at this point can exceed 5000 psi (34 MPa).
The screen pack/breaker plate assembly also serves to create back pressure in the barrel.
Back pressure is required for uniform melting and proper mixing of the polymer.
After passing through the breaker plate, the molten plastic enters the die.
The die is what gives the final product its profile and must be designed so that the molten plastic evenly flows from a cylindrical profile,to the product's profile shape.
Uneven flow at this stage would produce a product with unwanted stresses at certain points in the profile.
These stresses can cause warping upon cooling.
Almost any shape imaginable can be created so long as it is a continuous profile.
The product must now be cooled and this is usually achieved by pulling the extrudate through a water bath.
Plastics are very good
thermal insulators and are therefore difficult to cool quickly.
Compared with steel,plastic conducts its heat away 2000 times more slowly.
In a tube or pipe extrusion line,a sealed water bath is acted upon by a carefully controlled vacuum to keep the newly formed and still molten tube or pipe from collapsing.
For products such as plastic sheeting,the cooling is achieved by pulling through a set of cooling rolls.
Sometimes on the same line a secondary process may occur before the product has finished its run.
In the manufacture of adhesive tape,a second extruder melts 

thermo forming processes(Plastic Extrusion)

Extrusion is a manufacturing process used to create long objects of a fixed cross-sectional profile.
A material is pushed and/or drawn through a die of the desired profile shape.
Hollow sections are usually extruded by placing a pin or piercing mandrel inside of the die,and in some cases positive pressure is applied to the internal cavities through the pin. Extrusion may be continuous (producing indefinitely long material) or semi-continuous (producing many short pieces). Some materials arehot drawn while others may be cold drawn.
The feedstock may be forced through the die by various methods.
A single or twin screw auger,powered by an electric motor,or a ram,driven by hydraulic pressure),oil pressure,or in other specialized processes such as rollers inside a perforated drum for the production of many simultaneous streams of material.Extrusion simulation tools help to understand the extrusion process and to optimize development of tools and product
Commonly extruded materials include metals,polymers, ceramics,and foodstuffs.
We will show extrusion of plastic material.
Plastic Extrusion

Plastics extrusion is a high volume manufacturing process in which raw plastic material is melted and formed into a continuous profile.
Extrusion produces items such as pipe/tubing,weather stripping,window frames,plastic sheeting and wire insulation.
Plastic extrusion commonly uses plastic chips or pellets, which are usually dried in a hopper before going to the feed screw.
The polymer resin is heated to molten state by a combination of heating elements and shear heating from the extrusion screw.
The screw forces the resin through a die,forming the resin into the desired shape.
The extrudate is cooled and solidified as it is pulled through the die or water tank.
A multitude of polymers are used in the production of plastic tubing pipes,rods,rails,seals and sheets or films. 

every thing about PPr raw material

Traditionally,three manufacturing process are the most representative ways to produce polypropylene.
Hydrocarbon slurry or suspension:
Uses a liquid inert hydrocarbon diluent in the reactor to facilitate transfer of propylene to the catalyst,the removal of heat from the system,the deactivation/removal of the catalyst as well as dissolving the atactic polymer.
The range of grades that could be produced was very limited. (The technology has fallen into disuse).

Bulk (or bulk slurry):
Uses liquid propylene instead of liquid inert hydrocarbon diluent.
The polymer does not dissolve into a diluent,but rather rides on the liquid propylene.
The formed polymer is withdrawn and any unreacted monomer is flashed off.
Gas phase:
Uses gaseous propylene in contact with the solid catalyst, resulting in a fluidized-bed medium.
products MFG

The most common shaping technique is injection molding, which is used for parts such as cups, cutlery,vials,caps, containers,housewares,and automotive parts such as batteries. The related techniques of blow molding and injection-stretch blow molding are also used,which involve both extrusion and molding.
The large number of end-use applications for polypropylene are often possible because of the ability to tailor grades with specific molecular properties and additives during its manufacture. For example, antistatic additives can be added to help polypropylene surfaces resist dust and dirt. Many physical finishing techniques can also be used on polypropylene, such as machining. Surface treatments can be applied to polypropylene parts in order to promote adhesion of printing ink and paints.
devleopments

With the increase in the level of performance required for polypropylene quality in recent years,a variety of ideas and contrivances have been integrated into the production process for polypropylene.

There are roughly two directions for the specific methods. One is improvement of uniformity of the polymer particles produced using a circulation type reactor,and the other is improvement in the uniformity among polymer particles produced by using a reactor with a narrow retention time distribution.
applications

PP-R pipes mainly used:-

1-PP-R pipes are used to build hot and cold water systems, including central heating systems;
2-PP-R pipes are a part of building heating system, including floor,wall and radiant heating systems;
3-PP-R pipes can be directly purified water drinking water supply systems;
4-In the central (concentration) air conditioning systems,PP-R pipes always also play an important part;
5-PP-R pipes are used to transfer or discharge of chemical media, such as industrial piping system.
PPR pipes have good heat resistance.
PP-R pipes vicat softening point of 131.5 ℃.
Maximum working temperature of PPR is 95 ℃.
while at water supply and drainage,PPR pipes meet the require of construction specifications of hot water system.
PPR cold water pipes are generally used as water pipes,and PPR hot water pipes usually used to connect tubes,but it can also be used as the cold pipes.
PPR pipes are non-toxic and healthy.
The elements of PPR pipes are only carbon and hydrogen,and there is no harmful toxic elements.Therefore,PPR pipes can be used to clean drinking water systems.
After broken and cleaned,PPR pipes can be recycled and used again,but the condition is that the recycled materials does not exceed the total amount of 10%,it will do not affect product quality

History of Propylene

Propylene was first polymerized to a crystalline isotactic polymer by Giulio Natta as well as by the German chemist Karl Rehn in March 1954.
This pioneering discovery led to large-scale commercial production of isotactic polypropylene by the Italian firm Montecatini from 1957 onwards.
Syndiotactic polypropylene was also first synthesized by Natta and his coworkers.
Polypropylene is the second most important plastic with revenues expected to exceed US$145 billion by 2019.
The demand for this material was growing at a rate of 4.4% per year between 2004 and 2012.
An important concept in understanding the link between the structure of polypropylene and its properties istacticity. The relative orientation of each methyl group relative to the methyl groups in neighboring monomer units has a strong effect on the polymer's ability to form crystals.
A Ziegler-Natta catalyst is able to restrict linking of monomer molecules to a specific regular orientation,either isotactic,when all methyl groups are positioned at the same side with respect to the backbone of the polymer chain,or syndiotactic,when the positions of the methyl groups alternate.
Commercially available isotactic polypropylene is made with two types of Ziegler-Natta catalysts. The first group of the catalysts encompases solid (mostly supported) catalysts and certain types of soluble metallocene catalysts.
Such isotactic macromolecules coil into a helical shape; these helices then line up next to one another to form the crystals that give commercial isotactic polypropylene many of its desirable properties.

Polypropylene (PPr)

Polypropylene(PPr)is a thermoplastic polymer used in a wide variety of applications including packaging and labeling, textiles (e.g.,ropes,thermal underwear and carpets), stationery,plastic parts and reusable containers of various types,laboratory equipment,loudspeakers,automotive components,and polymer banknotes.
An addition polymer made from the monomer propylene,it is rugged and unusually resistant to many chemical solvents, bases and acids.
In 2008, the global market for polypropylene had a volume of 45.1 million metric tons,which led to a turnover of about $65 billion (~ €47.4 billion).
chemical and physical properties
Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low-density polyethylene (LDPE) and high-density polyethylene (HDPE).
Polypropylene is normally tough and flexible, especially when copolymerized with ethylene.
This allows polypropylene to be used as an engineering plastic,competing with materials such as ABS.
Polypropylene is reasonably economical,and can be made translucent when  uncolored but is not as readily made transparent as polystyrene,acrylic,or certain other plastics. It is often opaque or colored using pigments.
Polypropylene has good resistance to fatigue.

The melting point of polypropylene occurs at a range,so a melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. Perfectly isotactic PP has a melting point of 171 °C (340 °F).
Commercial isotactic PP has a melting point that ranges from 160 to 166 °C (320 to 331 °F),depending on atactic material and crystallinity.
Syndiotactic PP with a crystallinity of 30% has a melting point of 130 °C(266 °F).

The melt flow rate (MFR) or melt flow index (MFI) is a measure of molecular weight of polypropylene.
The measure helps to determine how easily the molten raw material will flow during processing.
Polypropylene with higher MFR will fill the plastic mold more easily during the injection or blow-molding production process.
As the melt flow increases,however,some physical properties, like impact strength,will decrease.

There are three general types of polypropylene:
homopolymer,random copolymer,and block copolymer.
The comonomer is typically used with ethylene.
Ethylene-propylene rubber or EPDMadded to polypropylene homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to polypropylene homopolymer decreases the polymer crystallinity and makes the polymer more transparent.

Causes of Variation in Quality

Perhaps the major barrier to perfecting quality in a manufacturing environment is variability.
Variability is inherent in every product—no two products are ever identical.
For example,the dimensions of two thin films used for interconnect will vary according to the precise conditions and equipment used to deposit and pattern the films.
Small variations might have negligible impact on the final product,but large variations can lead to final products that are unacceptable.
Quality improvement may be defined as the reduction of such variability in processes and products.
The variation in the quality of product in any manufacturing process is broadly classified as:
(a)Chance causes
(b)Assignable causes.

(A)CHANCE CAUSES
The chance causes are those causes which are inherit in manufacturing process by virtue of operational and constructional features of the equipments involved in a manufacturing process.
This is because of:
1.Machine vibrations
2.Voltage variations
3.Composition variation of material,etc.
They are difficult to trace and difficult to control,even under best condition of production.
Even though,it is possible to trace out,it is not economical to eliminate.
The chance causes results in only a minute amount of variation in process.
Variation in chance causes is due to internal factors only the general pattern of variation under chance causes will follow a stable statistical distribution (normal distribution).
Variation within the control limits means only random causes are present.
(B) ASSIGNABLE CAUSES

These are the causes which creates ordinary variation in the production quality.
Assignable cause’s variation can always be traced to a specific quality.
They occur due to:
1.Lack of skill in operation
2.Wrong maintenance practice
3.New vendors
4.Error in setting jigs and fixtures
5.Raw material defects
Variation due to these causes can be controlled before the defective items are produced.
Any one assignable cause can result in a large amount of variation in process.
If the assignable causes are present,the system will not follow a stable statistical distribution.
When the actual variation exceeds the control limits,it is a signal that assignable causes extend the process and process should be investigated.

Types of Quality Control

QC is not a function of any single department or a person. It is the primary responsibility of any supervisor to turn out work of acceptable quality.
1. Off-line quality control
2. Statistical process control
3. Acceptance sampling plans.

1. Off-line quality control:
Its procedure deal with measures to select and choose controllable product and process parameters in such a way that the deviation between the product or process output and the standard will be minimized.
Much of this task is accomplished through product and process design.
Example:Taguchi method,principles of experimental design etc.
2.Statistical process control:
SPC involves comparing the output of a process or a service with a standard and taking remedial actions in case of a discrepancy between the two.
It also involves determining whether a process can produce a product that meets desired specification or requirements. On-line SPC means that information is gathered about the product,process,or service while it is functional.
The corrective action is taken in that operational phase. This is real-time basis.

3.Acceptance sampling plans:
A plan that determines the number of items to sample and the acceptance criteria of the lot,based on meeting certain stipulated conditions (such as the risk of rejecting a good lot or accepting a bad lot) is known as an acceptance sampling plan.

Quality Control (QC)

Quality Control (QC) may be defined as a system that is used to maintain a desired level of quality in a product or service.
It is a systematic control of various factors that affect the quality of the product.
It depends on materials,tools,machines,type of labor,working conditions etc.
QC is a broad term,it involves inspection at particular stage but mere inspection does not mean QC.
As opposed to inspection,in quality control activity emphasis is placed on the quality future production.
Quality control aims at prevention of defects at the source, relies on effective feedback system and corrective action procedure.
Quality control uses inspection as a valuable tool.
According to Juran “Quality control is the regulatory process through which we measure actual quality performance, compare it with standards,and act on the difference”.
Another definition of quality control is from ANSI/ASQC standard (1978) quality control is defined as “The operational techniques and the activities which sustain a quality of product or service that will satisfy given needs; also the use of such techniques and activities”.
Alford and Beatty define QC as “In the broad sense,quality control is the mechanism by which products are made to measure up to specifications determined from customers, demands and transformed into sales engineering and manufacturing requirements,it is concerned with making things right rather than discovering and rejecting those made wrong”.

Methods of Inspection

Methods of inspection
There are two methods of inspection.
100% inspection and sampling inspection.

1-100% inspection
This type will involve careful inspection in detail of quality at each strategic point or stage of manufacture where the test is involved is non-destructive and every piece is separately inspected.
It requires more number of inspectors and hence it is a costly method. There is no sampling error.
This is subjected to inspection error arising out of fatigue, negligence,difficulty of supervision etc.
Hence,completer accuracy of influence is seldom attained. It is suitable only when a small number of pieces are there or a very high degree of quality is required for Example:
Jet engines,aircraft,medical and scientific equipment.

2-sampling inspection
In this method randomly selected samples are inspected. Samples taken from different patches of products are representatives.
If the sample proves defective,the entire concerned is to be rejected or recovered.
Sampling inspection is cheaper and quicker.It requires less number of Inspectors.
It is subjected to sampling errors but the magnitude of sampling error can be estimated.
In the case of destructive test,random or sampling inspection is desirable.
This type of inspection governs wide currency due to the introduction of automatic machines or equipments which are less susceptible to chance variable and hence require less inspection,suitable for inspection of products which have less precision importance and are less costly.
Example: Electrical bulbs,radio bulbs,washing machine etc.

Objectives and Purpose of inspection

objectives of inspection:
1.To detect and remove the faulty raw materials before it undergoes production.
2.To detect the faulty products in production whenever it is detected.
3.To bring facts to the notice of managers before they become serous to enable them discover weaknesses and over the problem.
4.To prevent the substandard reaching the customer and reducing complaints.
5.To promote reputation for quality and reliability of product.
Purpose of inspection:
1.To distinguish good lots from bad lots.
2.To distinguish good pieces from bad pieces.
3.To determine if the process is changing.
4.To determine if the process is approaching the specification limits.
5.To rate quality of product.
6.To rate accuracy of inspectors.
7.To measure the precision of the measuring instrument.
8.To secure products-design information.
9.To measure process capability.

What do we need for qualityControl

control:
The process through which the standards are established and met with standards is called control.
This process consists of observing our activity performance, comparing the performance with some standard and then taking action if the observed performance is significantly too different from the standards.
The control process involves a universal sequence of steps as follows:
1.Choose the control object
2.Choose a unit of measure
3.Set the standard value
4.Choose a sensing device which can measure
5.Measure actual performance
6.Interpret the difference between actual and standard
7.Taking action.
what do we need for controling quality
In the absence of quality,the following will result:
1.No yardstick for comparing the quality of goods/services.
2.Difficulty in maintaining consistency in quality.
3.Dissatisfied customers due to increased maintenance and operating costs of products/services.
4.Increased rework cost while manufacturing products/providing services.
5.Reduced life time of the products/services.
6.Reduced flexibility with respect to usage of standard spare parts.
7. Hence, controlling quality is an essential activity.

Inspection

Inspection is an important tool to achieve quality concept. It is necessary to assure confidence to manufacturer and aims satisfaction to customer.
Inspection is an indispensable tool of modern manufacturing process.
It helps to control quality,reduces manufacturing costs, eliminate scrap losses and assignable causes of defective work.
The inspection and test unit is responsible for appraising the quality of incoming raw materials and components as well as the quality of the manufactured product or service.
It checks the components at various stages with reference to certain predetermined factors and detecting and sorting out the faulty or defective items.
It also specified the types of inspection devices to use and the procedures to follow to measure the quality characteristics.
Inspection only measures the degree of conformance to a standard in the case of variables. In the case of attributes inspection merely separates the nonconforming from the conforming.
Inspection does not show why the nonconforming units are being produced.
Inspection is the most common method of attaining standardization,uniformity and quality of workmanship.
It is the cost art of controlling the production quality after comparison with the established standards and specifications.
It is the function of quality control.
If the said item does not fall within the zone of acceptability it will be rejected and corrective measure will be applied to see that the items in future conform to specified standards

fundamental factors affecting the quality of products

The nine fundamental factors(9 M’s),which are affecting the quality of products and services,are: markets,money,management,men,motivation,materials,machines and mechanization.
Modern information methods and mounting product requirements:

1.Market: Because of technology advancement,we could see many new products to satisfy customer wants.
At the same time,the customer wants are also changing dynamically.
So,it is the role of companies to identify needs and then meet it with existing technologies or by developing new technologies.
2.Money:The increased global competition necessitates huge outlays for new equipments and process.
This should be rewarded by improved productivity. This is possible by minimizing quality costs associated with the maintenance and improvements of quality level.
3.Management: Because of the increased complex structure of business organization, the quality related responsibilities lie with persons at different levels in the organization.
4.Men:The rapid growth in technical knowledge leads to development of human resource with different specialization. This necessitates some groups like,system engineering group to integrate the idea of full specialization.
5.Motivation:If we fix the responsibility of achieving quality with each individual in the organization with proper motivation techniques,there will not be any problem in producing the designed quality products.
6.Materials:Selection of proper materials to meet the desired tolerance limit is also an important consideration.Quality attributes like,surface finish,strength,diameter etc.
can be obtained by proper selection of material.
7.Machines and mechanization: In order to have quality products which will lead to higher productivity of any organization, we need to use advanced machines and mechanize various operations.
8.Modern information methods: The modern information methods help in storing and retrieving needed data for manufacturing, marketing and servicing.
9.Mounting product requirements:Product diversification to meet customers taste leads to intricacy in design, manufacturing and quality standards.
Hence,companies should plan adequate system to tackle all these requirements.

introduction

Quality has become the single most important force leading to organizational success and company growth in national and international markets .strong and effective quality programs result in substantial increase in market penetration, improvements in total productivity, much lower costs of quality, and stronger competitive leadership.Successful businesses inevitably place great emphasis on managing quality control  carefully planned steps taken to ensure that the products and services offered to their customers are consistent and reliable and truly meet their customer’s needs.Product quality is becoming the most important factor in customer decision. It is very important for the customer and for organization.Quality control (QC) is the responsibility of all workers and all divisions, people at all levels are the essence of an organization and their full involvement enables their abilities to be used for organization’s benefit.This project uses some statistical methods, specifically Statistical Process Control (SPC), to construct control charts for some polypropylene (PPR) pipes produced at plastic factory located in 10th Ramadan City. For more information about the history and the products of this factory refer to about Alamal plastic pipes ( Elsharif ).
Essentially, quality control requires that materials and products be tested at all stages to ensure that:
1-The purchased scrap are fit for specifications
2- Non conforming materials at each stages of manufacturingneed a corrective action to achieve the required quality level
3-The final product should be made and inspected according to the international specification
In any business organization, profit is the ultimate goal. To achieve this, there are several approaches. Profit may be maximized by cutting costs for the same selling price per unit. If it is a monopolistic business, without giving much of importance to the cost reduction programs, the price may be fixed suitably to earn sufficient profit. But, to survive in a competitive business environment, goods and services produced by a firm should have the minimum required quality. Extra quality means extra cost. So, the level of quality should be decided in relation to other factors such that the product is well absorbed in the market. In all these cases, to have repeated sales and thereby increased sales revenue, basic quality is considered to be one of the supportive factors. Quality is a measure of how closely a good or service conforms to specified standard.
Quality standards may be any one or a combination of attributes and variables of the product being manufactured. The attributes will include performance, reliability, appearance, commitment to delivery time, etc., variables may be some measurement variables like, length, width, height, diameter, surface finish, etc.
Most of the above characteristics are related to products. Similarly, some of the quality characteristics of services are meeting promised due dates, safety, comfort, security, less waiting time and so forth. So, the various dimensions of quality are performance, features, reliability, conformance, durability, serviceability, aesthetics, perceived quality, safety, comfort, security, commitment to due dates, less waiting time, etc.