Epoxy Composite Experiments

An epoxy composite is simply an epoxy resin which has other stuff mixed or laid into it before it hardens. The most familiar composite material made with epoxy is carbon fiber. Though we call the end product a 'carbon fiber' item it is more technically a 'carbon fiber reinforced polymer' item with the polymer in this case referring to the epoxy resin. Parts made this way are very light for the strength they offer but are expensive.

Reinforcements for polymers are typically cut fiber strands or whole fabric sheets. These relatively large reinforcements are typically 'laid up' into a mold and then saturated with resin. I wanted to use other less conventional (and less expensive) materials with epoxy resin as a filler to see what I could create with a specific focus on castable materials. A castable resin mix would need a viscosity low enough to run into and fill the parts of the mold. In addition the filler material would need to address some of the thermal problems encountered when creating thicker parts in epoxy.

As epoxy cures it releases heat. The hotter the epoxy is the faster it cures. These two aspects of thermosetting polymers (including epoxy) limit the thickness which can be cast. If the part is too thick it will not be able to dissipate the heat generated during the curing process resulting in a thermal runaway. In a thermal runaway the heat from curing speeds the curing generating more heat causing a rapid spike in the temperature of the curing resin. The addition of a filler will increase the volume of the epoxy and function as a heat sink to regulate the speed of the reaction.

Aluminium Filler Epoxy Composite

Samples created for this experiment were of two sizes. The smaller is approximately 40mL in volume while the larger (such as the above pictured) are approximately 90mL in volume. This first sample is about 50% aluminum powder by volume. When working with fillers it is important to consider how much space the filler will consume as compared to the resin. Since it is troublesome to measure these materials by volume their densities are consulted and the mass to be mixed in is determined which allows the appropriate amount to be scaled out.

Reducing resin volume to less than 60% when using aluminum as a filler significantly increases the viscosity of the mixture making it both more difficult to mix as well as pour.  

Iron Filing Epoxy Composite

This 90mL sample is 30% iron filings. The iron filings using in this sample came from a set intended for science demonstrations and as such are not particularly fine or cheap. I found sources of powdered iron on ebay later but not in time for this first batch of samples. Air pockets are clearly visible throughout the sample. While none of the samples examined here were vacuumed after mixing the effects of air entrainment are most visible on this sample.

Because of the iron present this sample has ferromagnetic properties though the resin's presence greatly diminishes them.  

Iron - Aluminium Epoxy Composite

This 90mL sample is 20% aluminum, 30% iron. The addition of the aluminum seemed to decrease the viscosity of the resultant mix compared to the previous iron sample. Otherwise it is exactly what one would expect compared to the previous iron or aluminum only samples.

Marble Powder Epoxy Composite

This 40mL sample is the first of the marble powder samples. Powdered marble makes up 40% of the volume of all the marble samples. All individuals presented with these samples determine them to be some type of stone with a minority guessing them to be marble. None supposed them to be a composite.

After this experiment I discovered cultured marble used in bathroom vanities and many other solid surface countertops are created using a similar process. These samples are different in their use of an epoxy resin as compared to the more conventional polyester resins used in commercial products.  

Marble Powder Epoxy Composite - Black Colorant

This sample had a black ink added after the mixing of the resin with the marble powder. The contrast is more pronounced in other samples. It is key the colorant not be added until after the resin has been completely mixed. Excessive mixing of the ink into the resin would create a uniform distribution of the colorant removing the striated effect seen.

Marble Powder Epoxy Composite - Blue and Black Colorant

Blue and black colorants were used in this sample. Various effects are possible via the manner in which the colorant is added and mixed into the resin as well as how it is poured into its mould.

Powdered Marble / Marble Chip Epoxy Composite

This sample was filled with both marble powder and whole pieces of marble in ratios similar to those used for course and fine aggregates in concrete. Both items (the epoxy sample and concrete) are similar as they are both composites of a large aggregate (to take up most of the volume), a fine aggregate (to fill the smaller spaces), and a binder to hold everything together (cement in the case of concrete and epoxy in the case of the sample). The red spots on the sample are the uncleaned remnants of the polishing compound used to polish the marble chips. The marble powder and resin matrix does not seem to respond well to polishing compound though it can be sanded to a relatively fine grit.

For a comparison of how a 'clear' resin (one without reinforcements or modifiers) cures compared to a resin with filler consider the following. The 90mL samples discussed above are just over an inch in depth and did not exceed 80F during their curing process. A 90mL block of clear resin cast into the same mould as the above samples exceeded 240F during its curing process. The high temperature experienced during curing caused the piece to deform in its mould. This might be correctable with a rigid mould (the mould used for these samples was a flexible silicon cookie bar mould) but this would likely lead to problematic stresses in the sample.

In conclusion these fillers seem to be capable of allowing epoxy to be used to cast larger parts than normally possible with clear resin. General appearance seems to be highly mutable based on added colorants and fillers. Further tests will be necessary to determine the machinability and general strength of these samples.

Consider using scalpels instead of X-ACTO knives

For working in soft materials such as paper, softwoods, or plastic you may want to consider a scalpel instead of an X-ACTO knife.

#11 scalpel blade installed on a #3 handle

The classic #11 X-ACTO blade has a thickness of 0.02” whereas the comparable #11 scalpel has a thickness of 0.015” making it easier to move though the material it has cut. This narrower blade also makes the scalpel a bit more flexible than the X-ACTO. My experience so far has shown the scalpel to be easier to use when making tight and detailed cuts. They also seem to last as long as my X-ACTOs in similar applications.

The attachment method for an X-ACTO normally involves using a screw to apply compression to the blade to hold it in place. If the user gets an X-ACTO stuck in a piece of material and pulls back with enough force to overcome this compression the blade will leave the handle.

#11 blade installed on #3 handle

 A scalpel attaches differently. It slides down a grove in the handle and snaps over the end ensuring it is not possible for the blade to come off of the handle without lifting the tab at the back.

blade installation track on a #3 handle

Somewhat surprisingly scalpels can be had for cheaper than X-ACTOs. From Amazon a pack of #11 X-ACTOs with 5 blades can be bought for $4.05. The equivalent scalpel, also a #11, can be had in a 100 pack for $17. That works out to an X-ACTO costing $0.81/blade compared to a scalpel at $0.17/blade.

X-ACTO knifes have a numbering scheme similar to but not totally comparable to that used for scalpels. In both systems the blade number indicates the shape of the blade and not its size. Some blades in both systems refer to a similar profile.

Left: #11 X-ACTO Right: #11 scalpel. Notice the  different attachment cutouts.

The #10, #11, and #22 blades of both systems are comparably shaped. Some blade numbers do not match such as the #15 (which in X-ACTO is actually a saw) so be careful when acquiring direct replacements for your X-ACTOs.

Scalpels will come individually packaged in a sealed sterilized film. The sealed film alleviates the need for an oil film to protect the blade in storage (which is common with X-ACTOs) so there is nothing to clean off of a new scalpel before use.

If you want to give a scalpel a try go out and buy a #3 handle and some #10 (round point) or #11 (angled point) blades. There are many different profiles but most of the ones you will likely use in a crafting scenario will fit the #3 handle.  

The micrometer goes to Barnes and Noble

There are many stories whose plot involves an object compelling its owner to use it. If the object were something like a sword you would likely have either a horror story or murder mystery. I often think this is very true for tools. Once you have a hammer everything starts to look like a nail and nails exist to be hammered. As I own a variety of tools I occasionally find novel uses for them. This weekend it was the micrometer I heard calling. As this is a measuring instrument I needed something to measure. I decided this would be paper.

There is much paper at the Barnes and Noble so there I headed early on a Saturday morning to measure their great stocks of it. The looks from both patrons and clerks was interesting. I enjoyed trying to imaging what they thought I was doing especially as they likely had never seen a micrometer before.

I had thought there would be a great variety in the thicknesses of the paper between volumes but was surprised to discover there was not. Conventional paperback novels are basically low resolution ink holders made of natural fiber paper and came in at 4 thou (four thousandths of an inch or .004”) with exceptional examples as low as 3.5 thou or as high as 5 thou. Black and white graphic novels are thicker with an average thickness of 6 thou. Color content seems to be mostly printed on glossier paper using synthetic fibers to achieve a higher resolution with better color fidelity and averaged around 3 thou. Black and white content printed on synthetic media also tended to average around 3 thou.

Larger format items such as color how to guides or coffee table books were more varied. Almost all are full color and ranged from 3 thou to 5.8 thou in thickness.

In hindsight I suppose this is not surprising to find the thickness of the paper tied to its application. Keeping standards for paper thickness also allows manufacturers of printing equipment to make reasonable assumptions about what their systems must accept.  

Cooking tools from the world of heavy industry

I do not cook, or bake, or execute any other from of food preparation beyond pouring cereal into a bowl milk. For this reason I am deficient in the realm of cooking implements. Thus when my sister arrived at my house with the intention of baking cookies in my oven I scrambled to find substitutes for the needed tools. The impending adventure led to some alternatives which I believed demonstrated greater usefulness than their traditional counterparts.

In the two years I had owned my house I had never used the gas oven. Little trust was placed in the oven's metered dial indicating temperature and as there was no display of current temperature we would be unable to judge when preheating was complete.

My IR temperature gauge filled the role of thermometer admirably. In addition to the simple ability to register a temperature the meter may be aimed at different segments of the oven's interior. This allows the user to find hot spots in the oven without laborious experimentation.

After the cookies were placed within the oven, whose preheating had been empirically confirmed, it occurred to us I was not in possession of any form of oven mitt. Various inferior and unimaginative alternatives were offered before I derived the ultimate solution.

Welding gloves being designed to protect their user from molten metal proved most effective. So great is the insulation of these gloves the user may maneuver hot surfaces at a leisurely pace. There is no haste necessary to drop a hot item before the heat becomes unbearable. As quality gloves may be had for $25 I cannot imagine a case in which a conventional oven mitt would excel them.