18-12-2010, 05:32 PM
This article is presented by:
Suryanarayana K.Y
Sharik Khan
Vinyas Rai M.V
Amit J Rao
Visvesvaraya Technological University
BELGAUM - 590 018
DESIGN AND FABRICATION OF PLASTIC COATING MACHINE
Introduction
Plastic products play a very important role in the modern world. The uses of plastic coated products are increasing day by day. Polyethylene, polystyrene, poly vinyl chloride are largely used in the manufacture of plastic products.
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, adhesive tape and wire insulation [1].
1.1 Extrusion Process
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section [1]. An extruder is a plastics manufacturing unit operation that is used to produce thermoplastic polymers with a uniform cross section, such as pipe, sheet, film and profiles. Since extruders also produce the polymer pellets that are used by other polymer processing operations (such as film blowing, injection moulding and blow moulding), almost all plastic material produced worldwide has passed through an extruder at least once.
The extrusion process basically is continuously shaping a fluid polymer through the orifice of a suitable tool (die), and subsequently solidifying it into a product (extrudate of constant cross section). In the case of thermoplastics, the feed material, in powder or pellet form, is most commonly heated to a fluid state and pumped into the die, through a screw extruder; it is then solidified by cooling after exiting from the die [1], [2].
1.2 Plastic Coating Using Extrusion Process
A barrel and screw extruder, the most widely used type, is employed in this designed project. The extruder consists of an rotating screw that closely fits within a heated barrel. Extruders can be fed with solid plastic pellets, chips, beads or powder. The functions of an extruder are to convey the solid polymer from the hopper, compact and melt the pellets, mix the resulting highly viscous polymer melt, pressurize and pump it through a die that produces the shape of the plastic product [2].
1.3 Types of Plastics and Their Properties
The term plastic is used to describe a wide Varity of resins or polymers with different characteristics and uses. Polymers are long chains of molecules, a group of many units, taking its name from the Greek poly (meaning many) and meros (meaning parts or units).
The term polymer is often used synonym for plastic, but many other types of molecules biological and inorganic are also polymeric. While all plastics are polymers, not all polymers are plastic. Polymers are rarely useful in them and are most often modified or compounded with additives (including colors) to form useful materials. The compounded product is generally termed a plastic. Most people have little contact “polymer” because most articles that they come across are actually modified and colored and therefore are actually plastics. Polymers can be classified in many ways, based on how they are developed and perform [2].
1.3.1 Types of Plastics
Thermoplastic polymers can be heated and formed, then heated and formed again and again. The shapes of the polymer molecules are generally linear or slightly branched this means that the molecules can flow under pressure when heated above their melting point.
Thermoset polymers undergo a chemical change when they are heated, creating a three-dimensional network. After they are heated and formed, this molecule cannot be re-heated or re-formed.
1.3.2 Classification of Plastics
Many items made out of plastic have a code or letters on to tell you what type of plastic they are. The most commonly recycled plastics are HDTE (high density polyethylene). The table below shows different types of plastic and what can be made from that type of plastic when it is been recycled.
1.3.3 Properties of Plastics
Plastic are classified based on their chemical composition, structure and density. Following classification shows the most commonly used classification [2], [3].
High Density Polyethylene (HDPE)
A linear polymer, High Density Polyethylene (HDPE) is prepared from ethylene by a catalytic process. The absence of branching results in a more closely packed structure with a higher density and somewhat higher chemical resistance than LDPE.HDPE is also somewhat harder and more opaque and it can withstand rather higher temperatures (120 Celsius for short periods, 110 Celsius continuously).
High density polyethylene leads itself particularly well to moulding, e.g. for bottles, cutting boards, dipping baskets, trays and containers.
Properties:
Excellent resistance (no attack) to dilute and concentrated Acids,Alcohols and Bases.
Good resistance (mirror attack) to Aldehydes, Esteres, Aliphatic and Aromatic Hydrocarbons, Ketones and Minerals and Vegetables Oils.
Limited resistance (moderate attack and suitable for short term use only) to Halogenated Hydrocarbons and Oxidizing Agents.
Maximum temperature : 248 0F/ 120 0C
Minimum temperature : -148 0F/ 100 0C
Density : 0.946 – 0.96 gram/cc
Melting Point : 266 0F/ 130 0C
Tensile Strength : 4550 psi
Hardness :SD65
Rigid
Specific Gravity : 0.95
Low Density Polyethylene (LDPE)
A plastic used predominantly in film applications due to its toughness. Flexibility and relative transparency. LDPE has a low melting point, making it popular for use in applications where heat sealing is necessary. Typically LDPE is used to manufacture flexible films such as those used for plastic retail bags and garment dry cleaning and grocery bags LDPE is also used to manufacture some flexible lids and bottles, and it is widely used in wire cable and bush applications for its stable electrical properties and processing characteristics.
Properties:
Excellent resistance to dilute and concentrated Acids, Alcohols, Bases and Esters.
Good resistance (minor attack) to Aldehydes, Ketones and Vegetable Oils.
Limited resistance (moderate attack suitable for short term use only) to Aliphatic Hydrocarbons, Mineral Oils and Oxidizing Agents.
Poor resistance and not recommended for use with Halogenated Hydrocarbons.
Maximum Temperature: 176 0F/ 80 0C
Minimum Temperature: -58 0F/ 50 0C
Density: -0.92gram/cc
Melting Point: 248 0F/ 120 0C
Tensile strength: 1700 psi
Hardness: SD55
Excellent flexibility
Specific Gravity: 0.92
Polypropylene
Polypropylene has excellent chemical resistance, is strong and has the lowest density of the plastic used in packing. It has a melting point, making it ideal for hot-fill liquids. In film form it may not be oriented (stretched). PP is found in everything from flexible and rigid packaging to fibers and large molded parts for automotive and consumer products.
Properties:
Excellent resistance to dilute and concentrated Acids, Alcohols, Bases & Mineral oils.
Good resistance (minor attack) to Aldehydes, Esters, Aliphatic Hydrocarbons, Ketones and Vegetable Oils.
Limited resistance (moderate attack and suitable for short term use only) to Aromatic and Halogenated Hydrocarbons and Oxidizing Agents
Great chemical resistance makes Polypropylene a popular choice for plating and chemical tanks, as well as laboratory cabinetry and semi-conductor bench tops.
This material machines well and is available in many profiles.
Other uses include fittings and connectors, storage containers, sinks and hoods.
The best joining method is hot air or nitrogen welding can be mechanically joined with screws or rivets.
Maximum temperature: 135 0C
Minimum temperature: 0 0C
Melting point: 170 0C
Tensile strength: 4500psi
Hardness: R95
Rigid
Specific gravity: 0.90
Chapter-2
Literature Survey
2.1 History
In 1868 Jhon Wesley Hyatt developed a plastic material he named celluloid which had been invented in 1851 by Alexander parks. Hyatt improved it so that it could be processed into finished form In 1872 Jhon, with his brother Isaiah, patented the first injection moulding machine. This machine was relatively simple compared to the machines we used today. It basically worked like a large hypodermic needle injecting plastic through a heated cylinder into a mould. The industry progressed to slowly over a year producing a product such as a collar stay, buttons, and hair combs until it exploded in the 1940s because the World War 2 created a huge demand for inexpensive, mass produced products. In 1946 James Hendry built the first screw injection machine. This machine allowed material to be mixed before injection, which meant colored plastic or recycled plastic could be added to the virgin material and mixed thoroughly before being injected. Today screw injection machine account for 95% of all injection machines. The has evolved over the years from producing combs and buttons to producing a vast array of products for many industries including automotive,medical,aerospace,consumer,toys, plumbing ,packaging and construction [3].
2.2 History of Plastic
In today’s world life without plastic is unimaginable the first man made plastic was unveiled by Alexander parks at the 1862 great international exhibition in London. This material dubbed by the public ad ‘parkesine’, was an organic material derived from cellulose that once heated could be moulded but that retained its shape when cooled. Parkes claimed that this new material could anything that rubber was capable of, but at lower price he had discovered a material that could be transparent as well as covered into thousands of different shapes. But Parkesine soon lost its luster when investor pulled the plug on the product due to high cost of raw materials needed in its production. The first completely synthetic man made substance was discovered in 1907 by a New York chemist Leo Baekeland created a liquid resin named bakelite [2].
2.3 Types of Coating
Traditional types of coating are Painting, Powder coating, enamel coating, Plasma coating, Galvanized coating, Electro plating etc [4].
Painting: Painting is a coating technique where a device sprays a coating material through the air onto a surface. The most common types employ compressed gas—usually air—to atomize and direct the paint particles. Spray guns evolved from airbrushes, and the two are usually distinguished by their size and the size of the spray pattern they produce. Airbrushes are hand-held and used instead of a brush for detailed work such as photo retouching, painting nails or fine art. Air gun spraying uses equipment that is generally larger. It is typically used for covering large surfaces with an even coating of liquid. Spray guns can be either automated or hand-held and have interchangeable heads to allow for different spray patterns. Single color aerosol paint cans are portable and easy to store.
