Week 4

For today, we split 2 tasks amongst ourselves: One group proceeded to do the post-practical questions while the other group studied the COWS matrix and utilized Materials for Design (MFD) to choose the best material for a teat and cover of a milk bottle respectively.

 

For the post-practical questions, we were assigned a list of questions that investigated the experiment we did the week before in further detail. Questions 1-2 required us to understand the working principles and mechanism of the coffee maker; Question 3 contained our tabulated results; Questions 4-5 required calculations on the energy usage of the coffee machine; and Questions 6-8 asked on how we could improve on the coffee machine and our assumptions and errors. Everything went relatively smoothly, and we finished answering the questions within an hour. 

These are the COWS matrix for the teat. 

For the teat: 

Function	The baby will drink the milk from the teat.
Constraints	Non-reactive to milk ingredients  Flexible  Non-toxic  Soft
Objective	Maximizing softness and flexibility.

 

We had to find these 3 pieces of information first to narrow down our search of the suitable material, if not we would have a lot of random materials that would not work like stainless steel for a teat. 

 

Material candidates: Natural rubber latex, Silicone and ethylene propylene rubber 

Criteria	Weightage (%)	Options
		Nitrile Rubber	Silicone Rubber	ethylene propylene rubber
Hardness (Shore A)	30	30-90  Score:4  4x30%=120%	1-95  Score:5  5x30%=150%	30-95  Score:4  4x30%=120%
Flexibility	30	0.004 GPa  Score:5  5x30%=150%	0.001-0.05 GPa  Score:5  5x30%=150%	0.006 GPa  Score:5  5x30%=150%
Non-reactive to milk ingredients	20	5=Excellent  20%x5=100%	5=Excellent  20%x5=100%	4=Very good  20%x5=100%
Non-toxic	20	3=Good  3x20%=60%	5=Excellent  20%x5=100	5= Excellent  20%x5=100
Total	100	430%	500%	470%

 

These conditions favoured polyesters, so our options were all polyesters, these ratings are based on a 1 to 5 scale and the weightage is decided based on how important this factor is for the material to complete its task and it must total up to 100%. The score then gets multiplied by the weightage for that section and each section is added up to achieve the total score of each material. The cost and ease of manufacturing is then considered. 

 

Criteria	Weightage (%)	Options
		Nitrile Rubber	Silicone Rubber	ethylene propylene rubber
Cost of material	70	Expensive  Score: 1  1x70%=70%	Cheapest  Score:5  5x70%=350%	Cheap  Score:4  4x70%=280%
Ease of handling/ manufacturing	30	Very good  Score:4  30x30%=90%	Very good  Score:4  30x30%=90%	Very good  Score:4  30x30%=90%
Total	100%	160%	440%	370%

 

The same methodology is used and the score is decided. Based on these 2 tables we have decided the most suitable material is the silicone rubber. 

We were also tasked to find a material for the cover of the baby bottle. These are the tables we have come up with. 

 

For the cover: 

Function	To hold the teat and screw onto the top of the bottle to keep liquids inside
Constraints	Non-corrosive  Non-reactive  Hard   Non-toxic
Objective	Hold liquids in and be resistant to drops

 

Based on the description above, the material should be hard and tough with the requirement of being able to handle temperatures above 37°C. Ceramics will be discarded as a choice here as they are easy to break. Material candidates: Stainless steel, Makrolon WB1239 polycarbonate, Polypropylene. 

Criteria	Weightage (%)	Options
		Stainless steel 304	Makrolon WB1239 polycarbonate	Polypropylene
Hardness	60	215MPa  Score:5	64.0MPa  Score: 4	31.6MPa  Score: 3
Non-reactive to milk ingredients	20	5 = Excellent	5 = Excellent	5 = Excellent
Non-corrosive	20	5 = Excellent	5 = Excellent	5 = Excellent
Total	100	500	440	380

 

Criteria	Weightage (%)	Options
		Stainless steel 304	Makrolon WB1239 polycarbonate
Cost of material	70	More expensive: 4	Less expensive: 5
Ease of handling/ manufacturing	30	Easier to manufacture: 5	Harder to manufacture: 3
Total	100	430	440

 

With the scores we have decided that stainless steel 304 is the best material for a cover of the baby bottle.