Materials - Insulation & Transfer Surface
Ruishi Shen
Zack Foggetti
Background
Development zone will be made of aluminum plates (according to John and
Dr.Esterman; aluminum plates are cheap and easy to carry), and outside the development
zone, insulation materials are needed to ensure particles are only attracted/repelled to the area
of development zone. A sketch is shown below.
Another pure materials we need to consider the the materials used to make the transfer
surface. The transfer surface is the main part of the incline on our ECDA. It’s primary purpose is
to serve as a structural flat plane that can withstand the forces acting on it (lever arm, hopper,
bending moment, etc). It also needs to be smooth so that the granular particles used in testing
will fall down easily. The secondary purpose of the transfer surface is to be an electrically
grounded component. Thus, we needed to make the surface out of a material that had a
sufficient strength-to-weight ratio, could be machined easily and made smooth, and was
electrically conductive. A meeting with Dr. Esterman and subject matter expert John provided us
with the suggestion to use Aluminum in our construction.
Design Decisions & Research
For insulation materials, please see Pugh Chart below (Alternatives are selected if they
are common in market)
Based on the results shown in the Pugh Chart above, plastic is chosen as the insulation
materials that will be used to separate the plates of development zone. It is relatively robust
while still fairly easy to cut, and it is not too expensive. The team is also able to get it on time
after purchasing it (it does not have long of a lead time as ceramic does). There were also other
criteria during the concept selection process such as “the insulation material should be
guaranteed to be non-conductive under 0.4kV”, which is the highest voltage our power supply
can go. However when doing the Pugh Chart, the team realized that that is a fairly low standard
that all the alternatives selected will meet. For example, vinyl electrical tape is guaranteed to be
non-conductive under 0.6kV (reference website:
http://multimedia.3m.com/mws/media/765027O/iatd-product-info.pdf). Also, even low-voltage
insulating paper can deal with at least 35kV of voltage (reference website:
http://www.ndpaper.com/eng/business/insulating.htm) Therefore the criteria is not included in
the Pugh Chart.
For materials of transfer surface, more research into Aluminum was done to validate why
it would be a suitable solution. Firstly, Aluminum (specifically 6061-T6) has a yield strength of
276 MPa, which should be sufficiently strong for our use, as well as keep the thickness of the
transfer surface minimized. It has a density of around 2,700 kg/m3, making it one of the lightest
metals to choose from, and thereby keeping the weight of our unit minimized. Aluminum is
readily available, inexpensive, and relatively easy to machine. Finally, it has an electrical
conductivity of 3.5 x 107 S/m, making it at least 5 times more conductive than steel. Below is a
table of the design options we have.
Material
Description
Yield Strength (psi)
Cost (12x12x.125 in.)
6061
Multipurpose
35,000
$28
2024
High Strength
41,000
$44
7075
Hard High Strength
61,000
$48
Prices are approximate and are quoted from: http://www.mcmaster.com/#standardaluminum-sheets/=ubtq97.
The cost per square foot is given only as a reference for comparison. Final selection of
the material and dimensions will be largely determined by the final weight and design of the
hopper, as well as overall budget constraints.
Flow Down Explanation
Even though this is not one of the customer requirements, however, after talking with Dr.
Chang, she stated that it would be better to use some insulation materials to surround the
development zone to better collect charged particles.
Materials Chosen
Plastic sheets can be purchased from the website below:
http://www.professionalplastics.com/PLASTICSHEETS?&search_id=1745921
Prices need to be quoted from the website. Getting the exact price is part of the project
plan for the next three weeks. The price range for plastic sheeting is from $3.00 to $50.00.
Estimated Budget
$30.00 -- Insulation Materials
Risk Assessment Plan
References
http://multimedia.3m.com/mws/mediawebserver?mwsId=XXXXXZz15hKxQaYyTBkEQakhJ_zVJ
hz14_8XJ_8XJXXXXXX-www.professionalplastics.com
http://materias.fi.uba.ar/6209/download/insulate.pdf
http://www.mcmaster.com/#standard-aluminum-sheets/=ubtq97
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity
http://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html
http://www.matweb.com/search/datasheet_print.aspx?matguid=1b8c06d0ca7c456694c7777d9e
10be5b