R2 Working properties of materials.
Initial skills rating**
September 2011
I know a little about the properties of some materials.
I know that glass and ceramics have excellent compressive strength but poor tensile strength which is why they break when they are dropped. That is to say the molecular structure is weak when a tensile force is placed upon it. They are also poor conductors.
I could make a similar stab at woods, metals and plastics but maybe a better approach would be to establish exactly what is meant by the ‘working properties’ first.
I know a little about the properties of some materials.
I know that glass and ceramics have excellent compressive strength but poor tensile strength which is why they break when they are dropped. That is to say the molecular structure is weak when a tensile force is placed upon it. They are also poor conductors.
I could make a similar stab at woods, metals and plastics but maybe a better approach would be to establish exactly what is meant by the ‘working properties’ first.
Whilst making a bedside cabinet I started to realise although I know how to design to take into account the effects of forces such as tension, compression and tensile, I had never done this for wood before. I needed to consider the weaknesses posed by the grain and the effect any applied forces will have on it. Not to mention the effects cutting and screwing into the wood will have. Some of this can be resolved with a logical approach but some can only be learned through experience or from a more knowledgeable other.
When joining my planks of wood I placed them with the growth rings that are visible on the end grain so that the curves alternative in opposite directions. By doing this when the wood moves i.e. expands, contracts and twists due to changes in temperature and moisture the natural forces within the wood will counterbalance each other out and provide a more stable structure.
12th February 2012
A quick glance at BBC bite size tells me I know a lot more about this topic than I realised. I need to find the time to revisit and digest!
Working Properties
Different materials exhibit different working properties. It is the characteristics of these working properties materials that materials are selected for different products and purposes. For example copper is a very good conductor. It is used to conduct electricity through electrical cables. However electricty is harmful to humans. So by covering the copper with plastic, a material that is naturally non conductive, the electricity is contained or as we know it, insulated
Listed below are the key properties which determine how materials behave.
Listed below are the key properties which determine how materials behave.
- conductivity is the ability of a material to conduct heat or electrical energy
- strength is the ability of a material to withstand a force without breaking or bending
- elasticity is the ability of a material to bend and then to return to its original shape and size
- plasticity is the ability of a material to permanently change in shape
- malleability is the ability of a material to permanently deform in all directions without cracking
- ductility is the ability of a material to deform, usually by stretching along its length
- hardness is the ability of a material to resist wear, scratching and indentation
- toughness is the ability of a material to withstand blows or sudden shocks without breaking
- durability is the ability of a material to withstand wear, especially as a result of weathering
- fusibility is the ability of a material to change into a liquid or molten state when heated to its melting point
Felt making
16th March 2012
Today a member of our course gave a lesson on felt making. I had had ago at this once before at home after I was given some wool tops and a book for Christmas but like all these things you can learn a lot from a book but you can learn even more from someone that has been doing it for years. I found this was true when I taught the stained glass. When everyone was working in the workshop I was able to help them out with the difficulties they were having by drawing on my own experiences and offering many of the solutions I had devised over a period of time. I think the same applied to the taught session we were given today. There were lots of little tips that did not appear in the book I had been given.
Although the method I had previously used to make felt used slightly different equipment the basic principles remained the same. The type of equipment can be easily sourced from any reference book but here are the bits you are less likely to find in a book:
Today a member of our course gave a lesson on felt making. I had had ago at this once before at home after I was given some wool tops and a book for Christmas but like all these things you can learn a lot from a book but you can learn even more from someone that has been doing it for years. I found this was true when I taught the stained glass. When everyone was working in the workshop I was able to help them out with the difficulties they were having by drawing on my own experiences and offering many of the solutions I had devised over a period of time. I think the same applied to the taught session we were given today. There were lots of little tips that did not appear in the book I had been given.
Although the method I had previously used to make felt used slightly different equipment the basic principles remained the same. The type of equipment can be easily sourced from any reference book but here are the bits you are less likely to find in a book:
- The felt is made by pulling small, thin bunches of wool from the wool tops which are lain on top of each other but with the strands laid at right angles to each other. It is this change of direction in the weave that will increase the strength of the finished fabric.
- The rubbing action of the felt slowly causes the fibres to knit together. The finished felt is about a third smaller after matting and shrinking takes place. It can be difficult to work out how many layers wool will make the desired thickness of felt but I guess that comes with experience.
- Inclusions such as embroidery thread used for decorative effects need to be fine for them to be held by the felt fibres.
- Bubble wrap between the fibres enables you to make a sealed shape. I used this method to make a stocking to hang on my Christmas tree but I could have made something like a purse or pencil case.
- The fibres shrink by about a third when they are worked together to make felt.
- Felt is a very strong fabric. Believed to have originated when our ancestors put sheep's wool in their shoes to keep their feet warm. The sweat and friction from walking working the fibres together.
- Patterns need to be loose rather than geometric. The fibres slip out of place during the felt making process.
- Different colours can be lain on top of each other especially if you want different colours on the inside and outside of things like bags.
- The netting should be lifted away from the felt if the fibres start to come through the net. It can then just be lain back down and the rubbing process continued.