Extrusion Process

Cast film: Less Toughness, Less Stiffer, More Costlier Process, Requires less space, not so easy, excellent gloss & clarity.

Tabular-Quench (TQ): In invade the down word extrusion of a tubular extrudes Forman annular die. Followed by overching on water coverd Conving bloods. It is windy recommenened for pp files. The tobes is inflated with an to give.

Extrusion coating: The plastic is coated over a substrate like paper, by extruding through a slot die downward between two rolls. Substrate is fed between the molten plastic and the roll and is joined with the plastic by pressure between rolls without the use of an adhesive. Material used LDPE & PVC, PP, HDPE, Ionomer etc. are also used. Equipment compresses of Pre treatment unit, Coating unit, Take off & winding.

Wire Coating Extrusion: Diagram of a production line for the coating of wire or cable with plastic. The conductor to be covered unwinds at the left, is preheated, and passes into the crosshead die (center). The extruder is behind the die, and feeds it with molten plastic, which coats the conductor. The finished product is cooled, tested and wound up at the right. 

Tube/Pipe Extrusion: Wall thickness & flexibility/Rigidity differentiates between tube/pipe, Pipes are produced by horizontally extruding molten polymer through an annular opening into several sizing, cooling devices that stabilizes the final dimension. Comprises of Extruder, Die, and Sizing device.. Sizing in pipe: Sleeve sizing, cooling water tank, Cutting section.

Calendering: Dough-consistent thermoplastic mass is formed into a sheet of uniform thickness by passing it through and over a series of heated or cooled rolls. Calendars are also utilized to apply plastic covering to the backs of other materials. Low cost, and sheet materials are virtually free of moulded-in stresses. Limited to sheet materials and very thin films are not possible.

War page: is the dimensional distortion of the product and it can be considered as one kind of product effect. Variation in shrinkage is the driving foes war page. Normally war page is due to non uniform distribution of temperation on the mould surface.

Casting: Liquid plastic which is generally thermoset except for acrylics is poured into a mould without pressure, cured, and taken from the mould. Cast thermoplastic films are produced via building up the material (either in solution or hot-melt form) against a highly polished supporting surface. Low mould cost, capability to form large parts with thick cross sections, good surface finish, and convenient for low-volume production. Limited to relatively simple shapes. Most thermoplastics are not suitable for this method. Except for cast films, method becomes uneconomical at high volume production rates.

Centrifugal casting: Reinforcement is placed in mould and is rotated. Resin distributed through pipe; impregnates reinforcement through centrifugal action. Utilized for round objects, particularly pipe.

Coating: Process methods vary. Both thermoplastics and thermosets widely used in coating of numerous materials. Roller coating similar to calendaring process. Spread coating employs blade in front of roller to position resin on material. Coatings also applied via brushings, spraying, and dipping. Economics generally depends on close tolerance control.

Filament winding: Excellent strength-to-weight. Continuous, reinforced filaments, usually glass, in the form of roving are saturated with resin and machine-wound onto mandrels having shape of desired finished part. Once winding completed, part and mandrel are cured; mandrel can then be removed through porthole at end of wound part. High-strength reinforcements can be oriented precisely in direction where strength is required. Good uniformity of resin distribution in finished part; mainly circular objects such as pressure vessels, pipes, and rocket cases.

Clamping Force required: FC=APf, A-Projected Area.  P-Blow Pressure (Usually in the range of 0.5to1.5MPa). F-Safety factor (25% extra)

Plastic material used: LDPE us used for more flexible items. HDPE is used for Rigid Bottles, Chemical Drums, and gasoline tanks. PP is used because of high stiffness, good chemical resistance, clarity and good glass and good resistance to high temperature. PVC & PS for general purpose articles requiring transparency at modest cost. RPVC – Can be bi axially oriented in extrusion stretch blow moulding. PC is used for containers which show good transparency, excellent impact strength, good heat resistance, good printability. PET is used in basically oriented stretch blow moulding & commonly used for carbonated beverages, packaging of drinks pharmacy products & water bottles. EVAL (Ethylene Vinyl Alcohol) is used as barrier layer in Multilayer containers.   

Hydraulic screw drive system: Low 60-75%, relief value will prevent screw damage, Small and light weight good weight short weight control, Consist ant output, infinitely adjustable, must have max. Torque.

Electrical screw driver system: High 95%, overload protection with small diameter screw, heavy poorer weight control, more stress in the system, various with screw spend, Excellent starting speed, teristies and at low screw spends.

Venting: is the mechanism, which is used to permit the displacement of air and gass from the cavity so that the incoming plastic martial will form a solid part free from included gas pockets. Venting is also used in barrel when recycled platic materials are used for processing to remove the gas from the melt.

Melting zone: The final portion of the metering screw that builds pressure to force the melt through screws and die. The metering section usually has a constant lead and shallower channel then the processing section of the screw.

Back pressure: When screw rotated push the melt at steady rate through non-return is sprue a head of screw tip then it makes space for it self by pushing the screw assembly backword is called back pressure. It is generated in front of screw tip which while screw is rotated.

Shutt off nozzle value: is used to prevent melt from drooling out of the nozzle. It is one of the controles required for function of injection.

Compresion ratio: the ratio B/w the channel both is the feed zone to that of the material zone usually form 1:5 to 4:1.

Drag flow: takes placed vista of adhesion of the melt the slip.   QD=π²/2 D² N H sinΦ cosΦ.

Silver streak: In presence of mixture in the resin, the product may contain some shining line on its surface called silver streak.

Thermocouple: is to give the information of temperature of the particular zone where it is situation. It is used to get the temperature feedback on the display unit.

Plasticizing capacity: It is defend as the amount of material that machine cam bring per hour to moulding temperature. Plasticizing rate=weight of moulding X no. of importation.

Predrying neoin: is the most important process before processing to get quality product. Moisture content result in poor surface quality and loss of physical properties. Thus to overcome the defects on the finished product proper drying of neoin is very important and only by this we can get quality product.

Microprocessor controlled: To regular the injection speed profile in multistage, to regular screw rpm in three on more stages, to regulate the follow up pressure in multitudes, To regulate injection pressure, Freely programmable hydeulic are pulling and air ejection sequences. Fault diagnostics by clear text, Temperature control by feed throat, storage of process parameters for blow mould.

Reciprocating screw: have two motion rotary & reciprocating motions. Reciprocating screw is combination of injection and plasticizing unit in which an extrusion devil with a reciprocating screw is used to plasticized the material. During part of the injection cycle, the screw plate’s rapid, moving backward as it accumulates or change short of melt in forward end of the cylinder. The ram are with draw screw rotation recommences, the mould open to eject the part’s the mould close and a new cycle begins.

Crystalline plastic: The molecular are an adored, which took up much less space than the amorphous state. Crystallisation indicated by a sharp decrease in volume, thus crystalline polymer show greater shrinkage an amorphous.

Hydrometer: is a device which is use to convert huid energy to mechanical energy. This is use in various speration of injection moulding.

Heater: Depending upon the heating capacity in know wall, Diameter and size of heater.

Injection pressure: It’s is the pressure required to inject the melt into the mould cavity through sprue bush, runner and gate syatem. The unit of injection pressure is Ton.

Injection rate: It is the amount of the melt which keeps following at the set injection speed into the mould cavity in unit time, unit of injection rate is cc/sec.

Semi automatic injection machine: The moulding performs & complete cycle of programmed moulding functions automatically and then stops. Then it required an operation to normally start another complete cycle. Clamp opening after one cycle and then starting another cycle is done normally. The operation need to be consent with checking product quality ensuring an adequate supply of granular plastics material to desirable station. The operation need to perform auxiliary operation.

Automatic injection moulding: The m/c perform a computer cycle of programmed moulding function repetitively and stops only if there is m/c on moulding melt functions is manually in term pled. The stop limit switch for the clamp ram initiate the clamp open times the cycle while the gat stays closed. Moulds that have been design and tested for automatic operate require only intermittent do ovation by the operator to ensure that everything is working in an approved manner.

Straight hydraulic: This design uses hydraulic fluids and pressure to open and close the clamp and to develop the force required to hold the mould closed during the injection of plastic. The straight hydraulic has proved over the year to have reliability, excellent control of low pressure exact control of tonnage prevents clamp from overstress due to high injection force.

Toggle: This concept used the machinal advantage of a linkage to dew lop the force required to hold the closed. The toggle clamping has two closing and opening action, lower cost. The energy required hold the developed tonnage is less than the straight higher hydraulic.

Toggle clamping: this concept uses the mechanical advantage of a linkage to develop the force required to mould closed during the plastic injection portion of the cycle. Normally, the linkage design is done in such a way that slowdowns are built in. A small hydraulic is  used to close the clamp. The cylinder travels at a constant speed with the slow down for mould close built into the linkage. The machinal advantage of the linkage is extremely high, so a relatively small closing cylinder can develop high tonnage. Double toggle system are currently the most widely used them single toggle clamping for machine having high clamping force, because this system offers higher moving platen speeds, shortening mould clamping md opening time and reducing the total moulding cycle time. Power consumption is also reached.

Lower original cost, Positive clamp, limited stroke, No-direct read out, more difficult, more involved mould setup, frequent maintenance.

Hydraulic clamping: Higher mould original cost, higher hones power needed therefore more expensive to rum, Non positive clamp, unlimited stroke potential, Direct read out of clamping force, easy adjustment of clamping force, easy mould setup, less maintenance.

Co-extrusion process: Process of combining two or more layers of extrudes produre a multiple-layer product in a single step. Co-extrusion is employed in film blowing, shut and flat-film extrusion, blow moulding and extrusion coating. The advantage of co-extrusion is that each ply imparts a desired characteristic property, such as stiffness, heat-scalability, impermeability or resistance to all of which properties would be impossible obtain with any single material. Laqers of poorly compatible plastics can be co-extruded by including a their adhesive laqer b/w them.

Sink mark: is a depression or the surface of an injection moulding part’s due to collapsing of the surface following local internal shrinkage after the gate seal.

Nozzle: Four types

1. Standard type injection nozzle

2. Reverse tapered nozzle 

3. Face flow nozzle

4. Ball check nozzle

Screw helix angle: The helix angle is the angle of a screw flight relative to a plane perpendicular to the screw axis.

Drooling: The melt which come out from the nozzle without the application of injection pressure is called drooling.

Plasticization: The conversion of plastic solid granular into homogeneous melt is known as plasticization.

Plasticization rate: The amount of homogeneous melt produced by the screw per unit time (Productivity of screw) is known as plasticization rate. It unit is Kg/hr.

Annealing: Operation consists of heating the steel or melts to a certain predetermined temperation holding at that temperature for a sufficient time to allow the necessary changes to occur and then cooling slowly at pre determent rate.

Screen pack: Its main function is to eliminate the particulate contaminants. Wire mesh 40, 60, 80, Arrests the unmelted particles and contamination, helps in developing back pressure

Draw down ratio: is a measure of the extent of thinning of the web without rupturing it. It is defined as a ratio of the die orifice gap to the film thickness at the nominal blow ratio BR = 1, given by the product of the measured film thickness and blow ratio: Die gap / Film thickness x blow ratio.

Flat film-extrusion: The Melt emerging out of the die lips strikes the chrome plated chill roll where it solidifies. Subsequently the film is pulled through nip rolls. Trimming blades trims-off the thicker edges. Then the film is wound on the winder.

Sheet Extrusion: Sheet is produced by forcing molten thermoplastic through a long horizontal slit die. The extruded hot web passes around metal cooling rolls and is then cut up or rolled up.

Material used: HIPS is the most important sheet material. HDPE, PVC, ABS are also used. Sheet grades usually have high melt viscosity. 

Shrinkage: Length wise shrinkage. Horizontal shrinkage occurs in wall thickness. May be reduced by raising the blowing pressure & lowering the temperature of the mould. High shrinkage is observed in HDPE (Due to crystalline) & thicker-walled products (due to slower cooling rate).

Pinch-off flash: The pinch-off is the section of the mould where the prisons is squeezed & welded together. Its design: Should be structurally sound to with stand pressure. Should push a small amount of plastic material into the interior of the part. Should leave a thin pinch line to provide a clean break point for flash removal.

Blow moulding cycle: is made off:  Blowing time + mould closing time + blow pin insert time + cooling time + ejection or removal time.

Blow Ratio: The blow ratio is the ratio of the outer diameter of the blown container divided by the outer diameter of the person. The required die gap can be approximately calculated multiplying the desired wall thickness of a blown bottle by the blow ratio. 

Die shaping: used to improve well distribution of a blow moulding part. Irregularity parts such as gas (fuel tank) used need die shaping.

L/D ratio: Screw is specified by oviler diameter D and it’s length “L” i.e. L/D ratio where L ia the length from feed throat to the beginning of first flight when screw is fully forwarded. length to normal dia of screw usually 20 to 22:1. 

Shot capacity: Short capacity is the maximum amount of plastic melt to be injected in one complete stroke of the machine screw or plunger. The unit of shot capacity is gram/cc.

Weld line: are created when two flow fronts from opposite direction ducts. There are significant because the property in weld line negion differ significantly from those in the rest of the part. There lines are generally weaker and likely points of past failure.

Breaker plate: Support for Screen pack, Converts the Spiral flow of melt in to stream lined laminar flow, and Holds back contamination and unmelted particles. Perforated circular metallic disc of about 4-5 mm thick.

Functions:

- Support for Screen pack

- Converts the Spiral flow of melt in to stream lined laminar flow

- Holds back contamination and unmelted particles.

Back pressure: When screw rotated push the melt at steady rate through non-return is sprue a head of screw tip then it makes space for itself by pushing the screw assembly backword is called back pressure. It is generated in front of screw tip which while screw is rotated.