Unit 5 | unit 5 plastic processing

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WMP

Unit - 5

Plastic Moulding, Glass Cutting

5.1 Plastic Moulding

Plastic and non-metallic materials in the form of natural and synthetic resins and their compounds.

Plastic can be easily malted and fabricated to any shape

Plastic are superior to metals in many ways:

Plastic has good insulating properties against heat and electricity.

They have good corrosion resistance.

They can be easily moulded and fabricated to different shapes.

They have good surface finish and don't need machining.

Plastics are very light.

They have good sound absorption properties.

They have good coloring properties.

Limitations of plastics:

Low impact strength to with stand fracture.

Unstable to with stand distortions and shrinkage.

High thermal expansions.

Plastic can seize in bearings.

Plastics have made applications in the following areas:

Structural components.

Adhesives.

Heat and sound insulations.

Surface protection material.

Glazing insulations.

Lightning and electrical accessories.

Paper, fittings and sanitary.

Building components.

Classification of plastics:

All the plastics are broadly classified into two main groups as under.

Thermosetting plastics: Plastics which are hardened by heat, effecting a non-reversible chemical change, are called thermosetting plastics. In other words, these plastics acquire a permanent shape when heated and pressed and cannot be softened by the reheating. They are also known as heat setting thermosets.

Thermoplastics: Those plastics which can be soft in again and again by heating are called thermoplastics. Thursday can be heated and reshaped by pressing many times. On cooling they become hard. They are also known as cold setting materials. They can be shaped into birds, tubes, films and many other shapes.

Fabrication of plastics:

Plastics are available in industry in the forms:

Powder or granules.

Sheets, rod or tube.

Liquid reins and adhesives.

Commonly used method for fabrication:

Injection moulding, compression moulding, blog moulding, thermoforming, lamination, spreading, calendering etc.

Compressing moulding: Most of thermosetting plastics and few thermoplastics plastics can be moulded through this process. A correct amount of plastic compound is placed in a heated mould. A punch called force compressors the compound from top into the required shape and density. The mould is kept closed for sufficient time to allow the chemical change to complete, so that the product is sufficiently hardened.

Operating parameter:

Hydraulic pressure: 35Mpa to 40 MPa.

Moulding temperature:110c to 220c.

Cycling time: 10 sec to 10 min.

Injection moulding: It is very commonly used for thermoplastic plastics .the Powder plastic compound is first heated to drive of moisture and then fit into the pauper. When the RAM is drawn back, some of the Powder drops down into the chamber. After closing the Mount, the RAM is moved forward. Applying pressure behind the Powder. during heating in the chamber, the temperature of the material rises to between and .After the plastic has been cooled and sufficiently hardened in the mould, the mould is opened and the produced part is not out. It is a faster process and suites best for large quantity production.

Blow moulding: It is used for producing narrow neck plastic containers, like bottles in this process a heated closed and thermoplastic tube is placed in the mould and air pressure is applied to inflate it for acquire the shape of mould cavity. After the plastic is cooled the mould is open and the product taken out.

5.2 Glass Cutting

Glass cutting:

Glass is non crystalline amorphous solid and is often transparent to light.

Silicate glass is most common and contain silica. It can transmit, reflect and refract light.

Types of silicate glasses and their application

Fused quartz or fused silica glass or vitreous-silica glass: Used for high temperature applications such as tubes, lightning tubes etc.

Soda- lime -slicer glass or window glass: Used for windows, tableware and light bulbs.

Sodium borosilicate glass or Pyrex: Used for chemical glassware, cooking class, core head lamps etc.

Lead-oxide glass or Pyrex: It is used in factories and can be easily cut.

Aluminosilicate glass: It is used for fibre glass, glass reinforced plastics, boats and fishing rods.

Germanium -oxide glass: It is used for fibre optic waveguides in communication network.

Properties of glass:

Glass has the ability to reflect refract and transmitted light.

Silicate glass can be poured, formed, extruded and moulded into various form.

It is extremely durable under most conditions.

It is erosion resistant.

It is fairly insert substance.

It is resistant to chemical attack.

It does not react with food.

It is corrosion resistant.

Glass cutting:

Steps:

Marking on the glass: It requires proper tools and study hand.

Select proper work area.

Use clean area.

Do not work on carpet.

Keep pets and children away.

Clean the glass surface by wiping with a soft cloth.

Use proper glass cutters and cutting oil.

Marking the line of cutting using a marker and straight edge.

Scoring the glass:

Dip the cutter in the oil to create a smooth score line.
Layout a straight edge by using a thick yardstick or desk ruler.
Apply pressure tooth class, pull the cutter along the surface by rolling the small carbide wheel.
Run the cutter smoothly from one h to the other. Do not run back and forth.
Wipe the oil, the score should look like a small scratch.

Bracking and smoothing:

Grasp each side of the cut carefully.

Apply small pressure from the rest to break the glass along the score.

Remove the sharp edge along the breaking line.

Cutting a curve:

Mark lines on the glass with a marker or set the glass over the paper with pattern.

Use several straight lines to cut a sharp curve.

Flip the glass over and gently press on the center of the score from the back side.

Make some relief cuts to remove small pieces at a time instead of all at once.

Smoothen the Curved edges using a glass router. Polish the curve with the fine sandpaper

References:

1. Hajra Choudhury S.K., Hajra Choudhury A.K. And Nirjhar Roy S.K., “Elements of Workshop Technology”, Vol. I 2008 And Vol. Ii 2010, Media Promoters and Publishers Private Limited, Mumbai.

2. Kalpakjian S. And Steven S. Schmid, “Manufacturing Engineering and Technology”, 4th Edition, Pearson Education India Edition, 2002.

3. Gowri P. Hariharan and A. Suresh Babu,” Manufacturing Technology – I” Pearson Education, 2008.

4. Roy A. Lindberg, “Processes and Materials Of Manufacture”, 4th Edition, Prentice Hall India, 1998.

5. Rao P.N., “Manufacturing Technology”, Vol. I And Vol. Ii, Tata Mcgrawhill House, 2017.

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