Plastic Extrusion Machines
Suppliers of plastic extrusion machines, extrusion lines, plastic extrusion machines,
extruders, plastic extruders,profile extruder, foam sheet extrusion lines,
cable extrusion,pipe extrusion line, profile extrusionline,film extrusion
line pelletisers, pipe extrusion lines, plastic pipe extrusion machines and profile extrusion machines, PVC pipe extruders, pelletizers, blown film extrusion machines, extruders, PE foam sheet extruder,EPE foam sheet extrusion line, PS foam sheet extrusion lines, cutting machines for extrusion, cable extrusion machines and extrusion equipment
PMS
Plastics
Specialists in Service, Sales and Repair of a diverse range of plastic
injection moulding machines and blow moulding machines. Incl : BOY Injection
Moulding machines, FKI Extrusion Machines, Hesta Blow Moulding, Stretch
Blow Moulding machines, Wanner Granulators, Industrial Robots.
Technimac
(Pty) Ltd
Manufacturer of hi-tech servo driven automatic winding and bagmaking
machinery for flexible film conversion. These products are used in
the food packaging, consumer goods and allied fields. Bag Making Machinery,
GAPA Bottom Seal Bagmaking machine,Bottom Welding Machine.
Cabletech
Marketing
For over 30 years Cabletech has been providing technical advice and providing
customised solutions for a full range of plastics processing applications
from individual machine supply to complete turnkey plants for plastic
pipes and fittings, profiles, recycling applications, compounding and
a wide range of moulding processes.
Nissei ASB South Africa
One-Step Injection Stretch Blow Molding
Machines machines and molds are able to produce PET containers with advanced features such as
Heat Resistance, Heat & Pressure Resistance, containers with Barrier
Properties, and more. Equally important
Krauss Maffei Berstoff
Pipe extrusion Machines, Pipe Lines, Complete Pipe lines, Pipe extruders, Twin Screw Pipe Extruders, Single Screw Pipe Extruders, Polyolefin Pipe Heads , PVC Pipe Heads
Profile Extrusion Machine
Sheet Extrusion, Cast Film extrusion , PVC Sheet extrusion, Thermoplastic Sheet extrusion, Thin sheet Extrusion, Thick Sheet Extrusion
PET Film and Sheet Extrusion Machine
Maritime Marketing
Rigids Division : Injection Moulding Machines, Extrusion and Injection
Blow Moulding Machines, PET Blow Moulding Machines, Pipe and Profile Extrusion
Machines, Extrusion Equipment. Flexible Plastics Division: Film Extrusion
Machines, Flexographic Printing Presses, Slitting and Rewinding Machines
Hans von der Heyde
Hans von der Heyde - custom machine & tooling development specializing
in "cutting edge technology", services include design &
manufacture of customized machine building & tooling, CNC machining,
wire cutting facilities & job lots.
SES cc
Seidel Electronic Systems cc - SES are specialists in the supply of plastic
injection moulding machines and ancillary equipment We supply a range
of Haitai Plastic Injection Moulding Machines, Plastic Ancillary Equipment
including : Hopper Dryers, Autoloaders, Material Mixers, Chillers, Crushers,
etc; and In-Mould Labelling Machines.
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.
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 (which can range from 200 °C/400
°F to 275 °C/530 °F depending on the polymer). In most processes,
a heating profile is set for the barrel in which three or more independent
PID controlled heater zones 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. If forced
air cooling proves insufficient then cast-in heater jackets are employed,
and they generally use a closed loop of distilled water in heat exchange
with tower or city water.
Plastic extruder cut in half to show the componentsAt 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, and how much pressure is generated can be 'tweaked'
by varying screen pack composition (the number of screens, their wire
weave size, and other parameters). This breaker plate and screen pack
combination also does the function of converting "rotational memory"
of the molten plastic into "longitudinal memory".
After passing through the breaker plate
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.
Sheet / film extrusion
For products such as plastic sheet or film, the cooling is achieved by
pulling through a set of cooling rolls (calender or "chill"
rolls), usually 3 or 4 in number. Running too fast creates an undesirable
condition called "nerve"- basically, inadequate contact time
is allowed to dissipate the heat present in the extruded plastic. In sheet
extrusion, these rolls not only deliver the necessary cooling but also
determine sheet thickness and surface texture (in case of structured rolls;
i.e. smooth, levant, haircell, etc.).
Often co-extrusion is used to apply one or more layers to obtain specific properties
such as UV-absorption, soft touch or "grip", matte surface,
or energy reflection.
A common post-extrusion process for plastic
sheet stock is thermoforming, where the sheet is heated until soft (plastic),
and formed via a mold into a new shape. When vacuum is used, this is often
described as vacuum forming. Orientation (i.e. ability/ available density
of the sheet to be drawn to the mold which can vary in depths from 1 to
36 inches typically) is highly important and greatly affects forming cycle
times.
Thermoforming can go from line bended
pieces (e.g. displays) to complex shapes (computer housings), which often
look like being injection moulded, thanks to the various possibilities
in thermoforming, such as inserts, undercuts, divided moulds.
Plastic extrusion onto paper is the basis
of the liquid packaging industry (juice cartons, wine boxes...); usually
an aluminum layer is present as well. In food packaging plastic film is
sometimes metallised, see metallised film.
Blown film extrusion
The manufacture of plastic film for products such as shopping bags is
achieved using a blown film line.
This process is the same as a regular
extrusion process up until the die. The die is an upright cylinder with
a circular opening similar to a pipe die. The diameter can be a few centimetres
to more than three metres across. The molten plastic is pulled upwards
from the die by a pair of nip rolls high above the die (4 metres to 20
metres or more depending on the amount of cooling required). Changing
the speed of these nip rollers will change the gauge (wall thickness)
of the film. Around the die sits an air-ring. The air-ring cools the film
as it travels upwards. In the centre of the die is an air outlet from
which compressed air can be forced into the centre of the extruded circular
profile, creating a bubble.This expands the extruded circular cross section
by some ratio (a multiple of the die diameter). This ratio, called the
“blow-up ratio” can be just a few percent to more than 200
percent of the original diameter. The nip rolls flatten the bubble into
a double layer of film whose width (called the “layflat”)
is equal to ½ the circumference of the bubble. This film can then
be spooled or printed on, cut into shapes, and heat sealed into bags or
other items.
Tubing extrusion
Plastic tubing, such as drinking straws and medical tubing, is manufactured
by extruding molten polymer through a die of the desired profile shape
(square, round, triangular). Hollow sections are usually extruded by placing
a pin or mandrel inside of the die, and in most cases positive pressure
is applied to the internal cavities through the pin.
Sometimes tubing with multiple lumens
(holes) must be made for specialty applications. For these applications,
the tooling is made by placing more than one pin in the center of the
die, to produce the number of lumens necessary. In most cases, these pins
are supplied with air pressure from different sources. In this way, the
individual lumen sizes can be adjusted by adjusting the pressure to the
individual pins.
Coextrusion
Coextrusion refers to the extrusion of multiple layers of material simultaneously.
This type of extrusion utilizes two or more extruders to melt and deliver
a steady volumetric throughput of different viscous plastics to a single
extrusion head (die) which will extrude the materials in the desired form.
This technology is used on any of the processes described above (Blown
Film, Overjacketing, Tubing, Sheet). The layer thicknesses are controlled
by the relative speeds and sizes of the individual extruders delivering
the materials.
There are a variety of reasons a manufacturer
may choose coextrusion over single layer extrusion. One example is in
the vinyl fencing industry, where coextrusion is used to tailor the layers
based on whether they are exposed to the weather or not. Usually a thin
layer of compound that contains expensive weather resistant additives
are extruded on the outside while the inside has an additive package that
is more suited for impact resistance and structural performance.
Extrusion coating
Extrusion coating is using a blown or cast film process to coat an additional
layer onto an existing rollstock of paper, foil or film. For example,
this process can be used to improve the characteristics of paper by coating
it with polyethylene to make it more resistant to water. The extruded
layer can also be used as an adhesive to bring two other materials together.
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Contact the companies above for your plastic machine requirements including:
plastic injection moulding machines, blow moulding machines, film blowing
machines, bag making machines, cable extrusion machines, pipe extrusion
machines, slitting and rewinding machines, printing machines, labelling
machines, plastic recycling machines, twine and rope making machines,
vacuum forming machines, extrusion machines.
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