Molding and Casting

Group members

This week we were supposed to review the safety data sheets for each of our molding and casting materials, then we were supposed to make and compare test casts with each of them

Work description

We started to learn about molding and casting at 23.3.2018 with our local instructor Iván Sánchez Milara. We studied the basics of mold making, milling of the mold and different types of mold and cast materials. After we had learned the basics, we read the safety data sheets for each material and also read the instructions for their use.

Projection viewSafety first!!

Some interesting information we got from the different Safety Data Sheets

In Smooth-Cast 305 Safety Data Sheet we could read:

About respiratory Protection regulation, it mainly says (from OSHA respirator regulations 29 CFR 1910.134 ) " shall be accomplished as far as feasible by accepted engineering control measures (for example, enclosure or confinement of the operation, general and local ventilation, and substitution of less toxic materials) " and " A respirator shall be provided to each employee when such equipment is necessary"

In Ooomo 25 Safety Data Sheet we could read:

In Smooth-Sil 940 Safety Data Sheet we could read:

To follow the instructions given, we are working in a properly ventilated room. We are using nitril gloves and safety glasses.

Smooth-Cast® 305

First, we experienced casting a Smooth-Cast® 305 liguid plastic, which is ultra-low viscosity casting resin that yield castings that are bright white and virtually bubble free, so there is no need for vacuum degassing.

We put nitril gloves and safety glasses on and we started the work with Smooth-Cast 305. We and pre-mixed both Part A and Part B thoroughly, weighted them separately using a gram scale, and mixed them together (mixture was 10 parts of A and 9 parts of B. Total weight of the mixture was 40 g. Then, we stirred them by horizontal movements trying to avoid adding bubbles into the mixture.

The other part of the group worked on preparing the mold by taping the front and backside of the mold tightly together. However, the tape didn't stick too well, and we finished preparing the mold too late for pouring the material into a silicone mold, and Smooth-Cast was already started to harden so it didn't went well. Moreover, because the air bubbles were coming out the same way that the liquid plastic was poured, it was hard to know if the mold was full or if the material was just sticking on the neck of the mold.

Projection viewPreparing the material and pouring it with the help of a thin stick

We allowed the liquid plastic to cure on the mold at room temperature for 30-40 minutes. When it was time to check the result we noticed, that only a little bit of material had went in the mold, and the casting failed miserably.

Projection viewChecking the results

Projection view Pouring plastic failed: the air coudn't come out from the small hole for casting

Here is the product and Kati's result on casting (and coloring) Smooth-Cast® 305.

Projection viewResults on using Smooth-Cast® 305/legend>

OOMOO™ 25 Liguid Rubber

OOMOO™ 25 is an easy to use silicone rubber compound that features a convenient one-to-one by volume mix ratio. It has a low viscosity for easy mixing and pouring.

We had bad luck with OOMOO™ 25, because it had all gone bad (5 new packages) and the material itself was only 2 months old and sealed in the bottles. The whole shipment had gone bad and the material provider promised to send a new batch, but we were not sure, if it would get here in time. In the end it arrived 29.3.2018.

Projection viewPlanning and starting to work

This time we had prepared everything really well for the group work casting, but since the whole batch had gone bad, we couldn't work with it and we wasted a lot of time.

Projection viewAll of the OOMOO™ 25 Part A were bad

However, afterward Marta, used OOMOO™ 25 on her project. Here is the product and the result:

Projection viewResults on using OOMOO™ 25

OOMOO™ 30 Silicone Rubber

Moreover, Kati experieced using OOMOO™ 30 on her project. The main differences between OOMOO 25 and OOMOO™ 30 is the pot life and cure time of the materials, which the former has way more shorter. Here is the product and the result:

Projection viewResults on using OOMOO™ 30

Smooth-Sil™ 940

We had Smooth-Sil™ 940 in the shelf, but didn't make the casting with that one. The other group worked with it, but we used it in our own projects.

It was easy material to use. The pot life of the Smooth-Sil 940 is 30 min and cure time 24 h, so there is no hurry to cast it in the mold. The silicone part A was very viscous and required part B to make it more like fluid and less like rubber. The mixture according to instructions is 10 parts of part A and 1 part of part B.

Here is the product and Kati's result on experiencing Smooth-Sil™ 940.

Projection viewResults on using Smooth-Sil™ 940

Technical Overview of Materials

Material A:B Mix Ratio by Volume A:B Mix Ratio by Weight Pot Life Cure Time
Smooth-Cast® 305 1A:1B 100A:90B 7 min 30 min
OOMOO™ 25 Liguid Rubber 1A:1B 100A:130B 15 min 75 min
OOMOO™ 30 Silicone Rubber 1A:1B 100A:130B 30 min 6 hours
Smooth-Sil™ 940 100A:10B 100A:10B 30 min 24 hours