Polymer Revision

Here is a clip on polymers and how the monomers join together
might help to understand the concept

Notes & Summer Exam

Any one needing notes e mail me or leave a comment, Project to be handed up last day before exams. The exam itself will cover all topic since September, you must complete question 1 and 4 other questions, you can find examples in your exam papers

• Materials
• Structure of materials
• Question1 short question
• Welding
• Mechanisms
• Thermal Equilibrum Diagrams
• Polymers

Example question

The polymer question for the Leaving Cert is always Q.6 split into 3 parts a,b & c

go to the following link to see an example of question 6

Example from Leaving Cert 2012

Rotational moulding and more

Rotational moulding.  A measured amount of  polymer powder is placed in a mould. The mould is then rotated in a complex motion  in an furnace or oven until the polymer lines the mould cavity. Polymer home heating tanks are made by this method.

4.    Heat forming, (Vacuum Forming).

This uses sheets of polymer, which are clamped and heated. The heat is then removed and the mould is forced up through the polymer sheet, a vacuum is applied which pulls the polymer against the mould. The polymer is allowed to cool and the polymer sheet then removed.

5.    Foaming.

Polymers, which are converted into sponge like materials, are formed or expanded.  A foaming agent is mixed with the resin. The combination is heated during moulding. The products, which are produced, have a very low density. Both rigid and flexible foams can be produced.

6.     Lamination.

Impregnating sheets of paper or cloth with a resin can produce high strength polymers. Layers of this material are bonded, by allowing the resin to set into a solid structure. Heat and pressure are often used in this process.

7.    Machining.

Polymers supplied in rods, tube or sheet can be machined into their final shape. These materials can be machined by both hand tools and machines but can require different cutting speeds.

8.    Welding.

Polymers are used to make variety of components for example in cars the bumpers, grill etc. But these can crack due to light impact, using a hot air welding tool can repair these cracks. The welding tool provides heat to make the polymer molten. A filler rod of the same polymer is fed in through a special nozzle.

Polymer Manufacturing

Manufacture of Polymers

This area of polymers deals with how we turn polymers into articles we can use, polymers can be drilled cut and file as we can do to metals but the ease and ability for polymers to be moulded is a key reason why polymers are so widly used.

Manufacturing of polymers.

Here is a slideshow dealing with polymers and manufacturing processes, in the exam you will be expected to identify manufacturing processes, describe how they work and what can be made by the process shown in the exam question. you will also need to be able to name the main parts of the equipement used to mould polymers. Save and print the slideshow when printing put 6 slides per page to cut down on the amount of pages you have to print. 

Slideshow of polymers & polymer manufacturing 

When manufacturing objects from polymers it is important to take into consideration – the type of polymer thermoplastic or thermosetting, the final shape of the product and the purpose of the product.

Processing of polymers.

There are many methods to convert polymers into a finished article, these include:

1.    Calendering

This is where continuous lengths of sheet are made from a thermoplastic. The material passes through heated rollers. the rollers soften the polymer and reducesthe tickness as it is forced between rollers, this method is used to produce rubber mats and floor covering.

1.    Extrusion

This is used to made continuous lengths of tubing or rods are extruded; thermoplastic in the form of grains is fed into the hopper through a heated chamber. The polymer is softened in the chamber and is force along the chamber by a screw and finally forced through a die. The shape of the die gives the product its final shape.

1.    Moulding.

As the name implies this method involves using a mould to form the final shape, there are several types of moulding methods these include:

Compression moulding. A measured amount of polymer in the form of powder is put into the die cavity. Internal heaters heat both the die and the punch. The mould closes forcing the polymer into the die shape, the mould then opens and the moulded polymer is removed and allowed to cool. This is used for thermosetting plastics as this allows the quick removal of the article as the cross lining prevents the piece from deforming.

Transfer moulding. This is similar to compression moulding but the polymer is placed in a separate compartment that the mould cavity. A plunger then forces the polymer through a small hole into the mould cavity; this allows the polymer to be moulded into more intricate shapes. This method also uses thermosetting plastic.

Blow moulding. This process is used to manufacture plastic bottles. The first stage involves a thick walled tube called a parison being extruded between a split moulds. While the parison is still soft the mould closes and clamps one end of the parison at the other end air is blown in and the parison expands until it is fully expanded. as the polymer touches the mould it cools and the mould then opens and the moulded bottle falls out.

Injection moulding

Used for thermoplastics and is very similiar to extrusion but the main difference is that it uses a hydraylic ram to force the polymer into the mould giving allowing more complicates moulds to be quickly manufactured. Polymer is fed from the hopper along the barrel by a screw thread, a hydraylic ram forces the polymer into the mould.