MOLDING AND CASTING¶
Assignment¶
The group assignment was to:
- Review the Safety Data Sheets (SDS) for each of our molding and casting materials.
- Make and compare test casts with each material.
- Compare different mold-making processes.
Materials Selected¶
For this group assignment, we selected two materials for testing:
| Material | Product | Application | Mixing Ratio |
|---|---|---|---|
| Silicone Rubber | RTV-820 | Mold making | 100:3 by weight |
| Epoxy Resin | Crystal Clear Epoxy Resin | Casting | 1:1 |
1. Silicone Rubber — RTV-820¶
The silicone rubber used for the molding process was purchased from Silicone Molds Kenya.
The supplier operates in Nairobi and provides silicone, resin, and other crafting materials. Their website also provides material support through WhatsApp.
Product Information¶
The information available on the actual RTV-820 container was:
| Property | Specification |
|---|---|
| Product | Silicone Rubber |
| Item No. | RTV-820 |
| Mix Ratio | 100:3 by weight |
| Part A | White |
| Part B | Clear Yellow |
| Cured Colour | White |
| Pot Life | 30–40 minutes at 25°C / 77°F |
| Cure Time | 8–10 hours at 25°C / 77°F |
| Hardness | 20 ± 2 Shore A |
SDS Availability¶
As part of the assignment, we attempted to obtain the Safety Data Sheet for the RTV-820 silicone rubber from the supplier.
Silicone Molds Kenya did not have an SDS available for the specific RTV-820 product we purchased.
Therefore, we did not substitute an SDS from another silicone product because different silicone formulations can have different chemical compositions, hazards, and handling requirements.
Instead, we documented the safety information available from the product packaging and used it together with the manufacturer’s/product technical information available online.
Note: The SDS for the exact RTV-820 product was not available from the supplier at the time of this assignment.
Available Product Information¶
The actual product label provided information about:
- Mixing ratio
- Pot life
- Cure time
- Hardness
- Part A and Part B identification
- Cured colour
The 100:3 ratio means that the silicone base and hardener must be measured accurately by weight.
For example, during my individual test:
Silicone base = 156.02 g
Hardener = 156.02 × 3 / 100
Hardener = 4.68 g
2. Epoxy Resin — 1:1¶
The second material selected for the group assignment was Crystal Clear Epoxy Resin 1:1, which is listed by Silicone Molds Kenya. Their current product catalogue lists the product as Crystal clear Epoxy Resin 1:1.
Product Information¶
| Property | Specification |
|---|---|
| Material | Crystal Clear Epoxy Resin |
| Type | Two-part epoxy |
| Components | Resin + Hardener |
| Mix Ratio | 1:1 |
| Application | Casting |
SDS Availability¶
We also checked with the supplier for the SDS for the epoxy resin.
At the time of documentation, the supplier did not provide an SDS for the specific 1:1 epoxy resin.
The supplier’s website confirms that the 1:1 epoxy resin is one of their products, but an SDS was not publicly available on the product listing we accessed.
Therefore, we documented the available product information rather than using an SDS from a different epoxy manufacturer.
Note: The SDS for the exact 1:1 epoxy product was not available from the supplier at the time of this assignment.
SDS Review Summary¶
| Material | Supplier | SDS Available? | Information Available |
|---|---|---|---|
| RTV-820 Silicone Rubber | Silicone Molds Kenya | No | Product label, mixing ratio, pot life, cure time, hardness |
| Crystal Clear Epoxy Resin 1:1 | Silicone Molds Kenya | No | Product listing and 1:1 mixing ratio |
Supplier¶
Silicone Molds Kenya — Official Website
The supplier’s website currently lists silicone rubber and Crystal Clear Epoxy Resin 1:1 among its products.
Safety Considerations¶
Although the specific SDS documents were unavailable, we still followed basic chemical-handling precautions during the experiments.
We used:
- Protective gloves
- Face mask
- Suitable mixing containers
- Accurate weighing equipment
- A ventilated working environment
- Careful handling of the resin and hardener components
The materials were measured according to their specified mixing ratios before mixing.
Test Casts¶
The next part of the group assignment was to make test casts using the selected materials.
Test 1 — Silicone Rubber¶
The RTV-820 silicone rubber was mixed at the specified 100:3 by weight ratio and used to produce a mold.
Test 2 — Epoxy Resin¶
The two-part epoxy resin was selected as the casting material and was mixed at the specified 1:1 ratio.
Photos of the epoxy preparation, mixing, casting, curing and final result will be added here.
Comparison of Test Casts¶
After completing the tests, we compared the materials based on their practical performance.
| Property | RTV-820 Silicone Rubber | 1:1 Epoxy Resin |
|---|---|---|
| Primary use | Mold making | Casting |
| Mixing ratio | 100:3 by weight | 1:1 |
| Flexibility | Flexible | Rigid after curing |
| Surface detail | ||
| Ease of mixing | ||
| Bubble formation | ||
| Curing time | 8–10 hours according to product label | |
| Demolding | ||
| Surface finish | ||
| Final result |
The empty cells will be completed using our actual observations from the test casts.
Comparison of Mold-Making Processes¶
We also compared different approaches that can be used to create molds.
| Mold-Making Process | Advantages | Disadvantages |
|---|---|---|
| 3D Printed Mold | Fast to produce and easy to modify | Visible layer lines and limited by printer size |
| Silicone Mold | Flexible and capable of reproducing detailed shapes | Requires mixing and curing time |
| One-Part Mold | Simple construction and easy to make | Not suitable for every geometry |
| Two-Part Mold | Can accommodate more complex shapes | More complicated to design and assemble |
| CNC Machined Mold | Accurate and suitable for repeated production | Requires CNC equipment and additional material |
Mold-Making Process Comparison¶
For our practical work, we compared the process of producing a mold using a 3D-printed mold structure and producing a flexible silicone mold.
3D-Printed Mold¶
CAD Design
↓
Export STL
↓
3D Printing
↓
Post-processing
↓
Ready for Casting
Silicone Mold¶
Prepare Model/Mold
↓
Measure Silicone
↓
Calculate Hardener
↓
Mix
↓
Remove Air Bubbles
↓
Pour
↓
Cure
↓
Demold
The 3D-printed approach allowed the mold structure to be produced directly from the digital design, while silicone provided a flexible mold that could reproduce the shape and be removed more easily from detailed geometries.
Group Assignment Conclusion¶
The group assignment allowed us to compare molding and casting materials through practical experimentation.
We worked with:
- RTV-820 silicone rubber at a 100:3 by-weight ratio
- Crystal Clear Epoxy Resin at a 1:1 ratio
We also investigated different mold-making approaches and compared their advantages and limitations.
A limitation of the assignment was the availability of formal Safety Data Sheets (SDS). Silicone Molds Kenya was identified as the supplier, but the supplier did not have the SDS documents for the specific RTV-820 silicone rubber and 1:1 epoxy resin available to us. Therefore, we documented the product information available from the packaging and supplier rather than presenting unrelated SDS documents as if they belonged to our materials.
This limitation was recorded as part of the documentation rather than omitted.