Mold Making & Casting Seminar & Workshop: October 2014

October 23rd, 2014

Last week, we held our fall Mold Making & Casting Workshop (see a recap of our March 2014 workshop here). Workshops are two days long and include the following:

 

  • Make your own molds and castings
  • One-on-one guidance from Polytek staff members
  • Work with a wide variety of mold rubbers and resins
  • Learn a variety of mold making and casting techniques
  • Meet others with similar interests
  • Buy material at low trial unit prices during the seminar

 

Attendees are invited to bring their own project to the workshop or choose from our large supply of in-house models.

For more details, visit the Polytek website.

 

Here are some photos from the workshop:

Mold Making and Casting Workshop

 

Demonstrations from Polytek staff members:

Polytek Workshop 1

Polytek Workshop 2

Polytek Workshop 3

Polytek Workshop 4

Polytek Workshop 11

Polytek Workshop 6

Mold making and casting photos:

Polytek Workshop 5

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Polytek Workshop 91

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Polytek Workshop 100

 

Check the Polytek website for upcoming workshop dates or get in touch with us:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Tutorial: How to Make a Silicone Rubber Candle Mold

October 15th, 2014

The following tutorial details the process of making a silicone rubber mold for casting wax to make candles.

 

Supplies Needed for Project:

Rubber Molds for Candle Making

 
 

Step 1: Select a Model

Select or create a model to replicate. The final wax candle will be a copy of this original model. Many candle makers sculpt their original models with clay, wood or wax or utilize computer-based options like 3-D printers and CNC routers to produce their designs.

The model that we selected for this particular project is made of glass:

 

Glass Object for Making Mold

 

This glass model is hollow; however, we would like the final candle to be solid, so we fill the model with wood and clay:

 

Inserting Wood

Wood Inserts

Fill Model with Clay

 

The mold rubber will pick up every detail of the model, so the clay is carefully smoothed out:

 

Even out Clay

Smooth Clay in Model

 

Step 2: Construct a Mold Box & Secure the Model

To make a one-piece poured block mold, construct a mold box or select a suitable container to place your model in. Make sure that there is enough space between the model and the mold box walls to create mold walls with an appropriate thickness.

We leave approximately 1″ of space for mold walls and the mold bottom in this example.

Plywood is being used to construct the mold box. Porous materials like this must be sealed prior to pouring liquid mold rubber. The plywood will be sealed in Step 3.

Some other possible options for mold boxes or mold containers: Plexiglas®, plastic pails, PVC pipe, Sonotubes®, melamine-laminated particle board (you can purchase a 24″ H mold box directly from Polytek).

 

Cutting Plywood for Mold Box Walls

 

Using a hole saw, we create a hole in the bottom board of the mold box to hide this part of the model (we do not want this protrusion on the final candle):

 

Protrusion in Glass

Cutout

Cutting Hole in Wood

Hole in Plywood

 

Securely adhere the model to the bottom board so it does not float when the mold rubber is poured around it.

Using PolyPoxy®  Quick Stick Adhesive, a two-part, fast-setting epoxy adhesive, we adhere the model to the bottom board:

 

Epoxy Adhesive for Mold Making

 

PolyPoxy® Quick Stick Adhesive has a 1:1 mix ratio and sets in 3-5 minutes.

 

Apply Epoxy Adhesive

Adhere Model in Bottom Board with Epoxy

Model on Baseboard (2)

 

While the epoxy is curing, construct the walls of the mold box:

 

Construct Mold Box

Construct Plywood Mold Box

Finished Mold Box

 

Step 3: Apply Sealer & Release Agents as Necessary & Finish Preparing the Model

Apply appropriate sealers and/or release agents to the mold box.

As mentioned previously, the plywood used for this mold box is not sealed. We coat it with Pol-Ease® 2350, a white petrolatum dissolved in mineral spirits, which serves as both a sealer and release agent. No additional release agent is necessary.

When using a non-porous mold box, consider applying Pol-Ease® 2500 Release Agent instead (Use this option when working with silicone rubber. Use Pol-Ease 2300 Release Agent when working with polyurethane rubbers).

Not sure which release agent to use for your particular project? Our Sealer & Release Agent Selection Guide may be helpful.

 

Pol-Ease 2350 Sealer and Release Agent

Apply Sealer to Mold Box

 

Apply a release agent to the model.

We also apply Pol-Ease 2350 Sealer & Release Agent to the model itself. Pol-Ease® 2500 Release Agent (an aerosol spray) is another option that could be used in this case (for use with silicone mold rubbers).

 

Polytek Sealer and Release Agent

 

Allow sufficient time for the solvent in Pol-Ease 2350 to evaporate (~1 hour, depending on temperature and humidity) before moving on to the next steps.

Seal any areas around the model where rubber may leak. There are small gaps at the base of this model, so we seal that area with plasticine clay (warmed up for easier application). Other options for sealing include caulk and hot glue.

 

Clay Snakes

 

Smooth and flatten the clay as best as possible:

 

Smooth Clay

Clay Caulking

 

Place the model in the mold box and secure the bottom board to the mold box walls:

 

Assemble Mold Box

Secure Mold Box

 

Place the mold box and model in the proper position for pouring the liquid rubber:

 

DSC06980 - Copy

 

Seal the edges of the mold box with plasticine clay to help prevent rubber from leaking outside of the box:

 

Clay Snakes - Caulk Box

Mold Box Sealed with Clay

 

Step 4: Measure, Mix & Pour Silicone Rubber

The mold rubber selected for this particular project is PlatSil® 73-15 Silicone Rubber.

Basic Specifications for this Rubber:

  • Type of Silicone: Platinum-Cured
  • Mix Ratio: 1A:1B
  • Shore Hardness: A15
  • Pour Time: 20 minutes
  • Demold Time: 4-5 hours
  • Color: White Translucent
  • Mixed Viscosity: 2,500 CP

 

NOTE ABOUT CURE INHIBITION: Contamination from amines, sulfur, tin compounds, polyester resins, some 3D-printed plastics, and some other materials can cause cure inhibition in platinum-cured silicone rubbers, so ensure that your model and other materials coming into contact with the silicone do not contain these inhibitors. It is best to perform a small test cure on your model before pouring a large mold.

This particular mold requires approximately 10 lb of PlatSil 73-15 rubber (5 lb of Part A & 5 lb of Part B).

PlatSil 73-15 Silicone Rubber for Candle Making - Polytek

 
Weigh out Part B on a digital scale – we recommend pouring Part B first because it is lower in viscosity than Part A and is less likely to cling to the sides of the mixing container:
 
Part A of PlatSil 73-15 Silicone Rubber

 
Tare the scale and weigh out Part A into the same mixing container.
 
Part B of PlatSil 73-15 Silicone Rubber

 
Thoroughly mix Part A and Part B together, scraping the sides and bottom of the mixing container several times:
 
Mix Silicone Rubber Thoroughly

 
Carefully pour the mixed rubber into the mold box. Pour into one corner and allow the rubber to rise. Do not pour rubber directly onto the model:
 
Pour Silicone Rubber into Mold Box

Soft Silicone Rubber

Allow Silicone Rubber to Cure

 
PlatSil 73-15 can be demolded in 4 to 5 hours at room temperature. If a different rubber is being used, make sure to check the demold time of that particular rubber. Demolding too soon can cause permanent warping of the mold.
 

Step 5: Demold & Cut Mold (if necessary)

Carefully remove the mold box bottom board and walls. A putty knife may be helpful in this process:
 

Remove Mold Box

Remove Mold Box Bottom Board

Carefully Remove Mold Box

Remove Wood and Clay

 
Depending on the shape of the model, the mold may have to be cut to remove the model and subsequent castings. We use a scalpel to cut an irregular pattern on one side of the mold (irregular patterns realign better for casting than straight cuts):
 
How to make a cut in Silicone Mold

Make Irregular Cut in Mold

 
Carefully remove the model from the mold:

 

Polytek Silicone Mold

Finished PlatSil 73-15 Silicone Candle Mold

 
Make a small hole in the bottom of the mold to later accommodate a wick:
 
Make Hole in Rubber Mold for Wick

 
This next step is completely optional. Before we move on to casting wax, we make a plastic copy of the original model just in case we need to make more molds at a later date (we broke the original glass model when demolding).
 
Wooden boards and duct tape are used to support the mold when casting (you could also use the original mold box for support):
 
Prepare Mold for Casting Plastic

 
EasyFlo 60, a fast-setting polyurethane plastic, is poured into the mold to make the copy:
 
Casting EasyFlo 60 Liquid Plastic

 
This plastic can be demolded in 15-30 minutes:
 
Plastic Copy of Candle

EasyFlo 60 Decorative Element

 

Step 6: Pour Wax into Mold

Feed a wick through the hole created earlier:

 

Place Wick in Silicone Mold

Candle Making with Silicone Mold

 
Temporarily tie a knot in the wick:
 
Knot in Wick

Wick in Silicone Mold

 
Secure the wick above the pour hole of the mold. Make sure it is centered:
 
Suspend Wick for Wax Casting

Secure Wick with Clip

 
Melt wax with the appropriate equipment and add dyes and fragrances if desired:
 
Wax in Parrafin Bath

DSC07282

 
Carefully pour the wax into the mold:
 
Casting Wax in Polytek Silicone Mold

Allow Wax to Cool in Silicone Mold

 
Allow the wax to completely cool:
 
Demold with Wax is Cooled

 

Step 7: Remove Candle from Mold

Carefully remove the candle from the mold:
 

Remove Candle from Mold

DSC07399

 
Trim the wick as necessary:
 
Trim Wick on Both Ends

 
Hundreds of candles can be made in this single mold. A finished candle is pictured below:
 
Decorative Candle from Silicone Mold

Close-Up of Candle Detail from Mold

Candle Making Tutorial

 

We utilized a soft, silicone rubber for this tutorial; however, polyurethane rubbers are also a viable option for candle making. Some waxes perform better in silicone molds vs. polyurethane molds. Please get in touch with us to discuss your specific candle-making project:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Warping Decorative Concrete Elements in Rubber Molds

September 30th, 2014

Last week, we posted a video tutorial on making a rubber mold to cast “warped” side-by-side concrete tables. Our latest tutorial (below) focuses on casting “warped” decorative concrete elements in Poly 74-20 polyurethane molds. The original model was constructed through a series of steps involving wood, silicone rubber (PlatSil® 71-10), and polyurethane casting resin (EasyFlo 60).

The finished concrete elements can be used for a variety of purposes: tables, light housing, planters, garden decor or trellis, decorative panels (when cast flat), and much more.

 

For more information on liquid rubbers that can be used to make molds for warping concrete:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Making Rubber Molds to Cast & “Warp” GFRC Tables

September 25th, 2014

Our latest video tutorial is now posted on our YouTube Channel and can also be viewed below. It features the making of a Poly 74-45 rubber mold designed to cast side-by-side “warped” concrete tables.

The original model is constructed from MDF and coated in primer paint. The mold is made from Poly 74-45, a two-part, mid-range hardness, polyurethane rubber. Shark-Tooth Inserts (patent pending: 62/045.228) are used to control the size and location of the bend in the mold.

 

Do you have questions about the liquid mold rubber used for this process?

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Polygel® Spray-On Mold of 19-Foot Tall Mastodon Sculpture

September 15th, 2014

Kent Ullberg is a highly acclaimed wildlife sculptor whose work spans the globe and can be found in numerous museums, municipalities, corporate offices, and private collections. Ullberg is well-known for his monumental works, which include a 23-foot-tall elephant (installed at the St. Louis Zoo) and an 18-foot mako shark (installed at NOVA Southeastern University), among many others [www.kentullberg.net].

According to the Reporter-Herald, Ullberg’s most recent monumental sculpture, a 19-foot-tall, 24-foot-long mastodon, is a scientific reconstruction based on findings by scientists from the Denver Museum of Nature and Science, the Smithsonian Institution (Washington, DC), and a Michigan university [www.reporterherald.com].
 

The Molding Process

The bronze casting process was completed by Art Castings in Loveland, CO. Spray Solutions, also located in Loveland, stepped in to create the rubber mold of the sculpture (one of the early steps in the casting process).

Spray Solutions utilized Polygel® Spray 35, a self-thickening, two-part (1A:1B mix ratio) polyurethane rubber, to make the mold. Because the sculpture was to be cast in 100 separate pieces, aluminum and plastic shims were strategically placed in order to construct the mold in 100 separate sections.

Polygel Spray 35 was applied to the clay sculpture with meter-mix spray equipment.

Some of the behind-the-scenes work can be seen below [photos courtesy of Sculpture Depot]:

Mastodon Sculpture - Shims
 

Kent Ullberg Mastodon Sculpture Mold
 

Monumental Mastodon Sculpture
 

Polygel Spray On Rubber - Mastodon Sculpture
 

Polygel Spray Polyurethane Rubber
 

Ullberg’s mastodon will arrive at the Denver Museum of Nature and Science at the end of September and the dedication date is late in October.

Visit Kent Ullberg’s website for biographical information and more examples of his work.

 

www.polytek.com  |  610.559.8620  |  sales@polytek.com  |  online contact form

Adding Fillers to Polyurethane Casting Resin

September 11th, 2014

There are a few common reasons that fillers are added to polyurethane casting resins (e.g., EasyFlo Series Liquid Plastics, Poly 15-Series Liquid Plastics):

  • to reduce cost
  • to help dissipate exotherm (exotherm can cause shrinkage in castings)
  • to achieve a different look or weight

 

NOTE: Other additives, like thickeners (Cabosil & PolyFiber II are dry fillers), softeners, retarders, and color dyes are often added to liquid plastics, but these types of additives will not be covered in this blog entry. Only dry fillers, used for the purposes above, will be discussed.

Dry Fillers-01

 

Things to Consider Before Adding Fillers

Moisture Sensitivity

Liquid polyurethane plastics are moisture sensitive, so it is important to only add dry fillers to these resins. Even some fillers that appear dry (e.g., wood powder, nut shell flours) may contain moisture and cause foaming of the plastic, so ensure that fillers are completely dry before using (baking may be necessary).

Moisture Sensitive Resin

[an example of foaming that can occur when water is introduced to EasyFlo 60 casting resin]

 

Change in Viscosity

Large amounts of filler can affect the flow characteristics of resin, so make sure to experiment before attempting a large project. Adding too much filler can increase viscosity which may result in air entrapment and bubbles in the finished casting.

 

Sinking & Floating

Heavy fillers tend to sink in resin and light fillers tend to float; therefore, it’s very important to mix the combination thoroughly before casting. Also, a fast-setting resin is generally a better option as it will begin to cure before fillers have the chance to settle or float to one side. A popular option is EasyFlo 60 Liquid Plastic, which has a 2 to 2.5-minute working time and a 15-30-minute demold time.

 

Weight & Appearance of Fillers

Fillers are often added to change the look or feel of a casting (see the “Adding Fillers to Change Look or Weight of Castings” section); however, it’s important to consider these physical changes when selecting a filler for other purposes, like cost reduction and to dissipate exotherm. For instance, heavy fillers absorb more exothermic heat, but they result in heavy castings, which may not be appropriate for the application at hand. Also consider that the color of the filler may affect the color of the finished casting.

 

Neutral-Density Option

For a neutral-density filler that will not affect the density of the casting, consider PolyFil ND. This filler can be used to reduce the cost of castings as well as dissipate exotherm.

p-3542-product_detailed_image_30128_312.jpg

 

Adding Fillers to Reduce Cost

Adding an equal volume of low-cost filler to a Polytek liquid plastic can potentially cut the cost of the casting in half.

Popular fillers for reducing cost are dry sand and limestone. As a reminder, these fillers will affect the viscosity of the casting resins.

Typical costs per cubic inch of these fillers are shown below, along with a few other fillers:

Filler $/lb Density (g/cc) $/in³ Typical Use
Dry Sand 0.05 2.7 0.01 Reduce Cost
Ground Limestone 0.15 2.7 0.01 Reduce Cost
Extendospheres CG 0.50 0.7 0.01 Make Lightweight Castings
Q-Cel 6014 or 3M K1 6.00 0.1 0.02 Make Lightweight Castings
Bronze Powder 15.00 8.8 4.79 Make Cold Cast Bronze Parts

 

Adding Fillers to Dissipate Exotherm

Exotherm is the heat of the reaction produced as the resin cures. In large castings, it can sometimes cause thermal shrinkage or distortion.

Large Plastic Casting-01

[shrinkage can occur in large castings, such as this EasyFlo 60 casting of a long, wood panel]

 

In our experience, Alumina Trihydrate performs well as a filler to disperse exothermic reaction and reduce shrinkage. Calcium carbonate and PolyFil ND are other options, but do not perform as well as Alumina Trihydrate.

 

Adding Fillers to Change the Look or Weight of Castings

Fillers are often added to resin to achieve a certain look or feel. For instance, bronze powder and other metal powders are used to create castings with a metal-like finish. In this example, castings are removed from the mold and then burnished with steel wool to expose the metal particles [see a cold cast bronze tutorial here]. Not only does the appearance change, but the weight increases.

The photo below features three EasyFlo 60 plastic castings with varying fillers. EasyFlo 60 naturally cures to a white color [the figurine on the right does not have any fillers]:

[left: Bronze Powder & Brown PolyColor Dye  |  center: Sand  |  right: No Fillers]

Polyurethane-Plastic-with-Fillers
 

Other dry fillers that are often used to create a distinct look include marble dust and glitter, which are more often featured in clear casting resins, like the Poly-Optic® 14-Series resins.

When added at the proper ratio, Extendospheres CG, Q-Cel 6014 or 3M K1 can make castings float or carve more easily.
 
 
Dry fillers can be a useful addition to resin for many reasons, but not all fillers will perform well. If you have questions about adding fillers to Polytek polyurethane casting resins, please get in touch with us:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Foaming Additive for Poly 15-6 Polyurethane Liquid Plastic

September 3rd, 2014

Poly 15 Part F Foamer can be added to Poly 15-6 Liquid Plastic (a two-part polyurethane plastic in the Polytek Poly 15-Series) to create a rigid, open-cell foam with densities as low as 6 lb/ft³.

 

Liquid Plastic with Foam Additive

 [Poly 15-6 Liquid Plastic and 1-ounce Poly 15 Part F Foamer]

 

Without foamer, Poly 15-6 Liquid Plastic cures to a rigid, Shore D72, tan/off-white plastic. It has a 1A:1B mix ratio, 5-minute pour time, and 1 to 3-hour demold time.

 

How to Use Poly 15 Part F Foamer

Stir Part F Foamer into Part B of Poly 15-6 before adding Part A. Experiment to determine the best amount of Part F Foamer for the application at hand, but never use more than 3% (of the total weight of the mix) of this additive or the final physical properties may be affected.

Poly 15 Part F Foamer

 

Uses for Poly 15-6 Liquid Plastic & Part F Foamer

One way to create durable, lightweight castings is to make a thin, hollow casting with a two-part casting resin (e.g., EasyFlo 60 Liquid Plastic) and then backfill the hollow piece with a two-part rigid or flexible foam (e.g., PolyFoam R-5 Casting Foam).

This casting technique is used widely for decor, props, displays, and more.

As noted, this process typically requires two different products: a two-part casting resin and a two-part casting foam. By using Poly 15-6 and Part F Foamer, the benefit is that you only have to stock one two-part casting resin and the one-part foaming additive (available in 1 oz, 1 pt, 1 gal, and 5 gal sizes) to make this type of casting.

 

Product Demonstration

The following demonstration shows the process of making a decorative architectural element with a rigid, plastic exterior and rigid foam interior using Poly 15-6 Liquid Plastic & Part F Foamer.

 

Step One: Make a Hollow Poly 15-6 Casting with Rotational Casting Machine

Spray Pol-Ease® 2300 Release Agent into the mold cavity and brush out with a dry brush. This step is only necessary when working with polyurethane rubber molds; a silicone mold would not require release agent.

Pol-Ease 2300 Release Agent
 

Apply Release Agent to Mold
 
 
Carefully weigh appropriate amounts of Poly 15-6 Part A & Part B on a scale.
 
Weigh Plastic on Scale

 
Combine Part A & Part B and mix thoroughly.
 
Combine Parts A & B

 
Stir Casting Resin

 
Pour the Poly 15-6 plastic mixture into the mold cavity.
 
Pour Plastic into Mold Cavity

 
Only a small amount of resin is necessary for rotocasting or slush casting (read more about slush casting here).
 
Resin for Rotocasting

 
Before attaching the lid to the mold shell, spray and brush out Pol-Ease 2300 Release Agent onto the areas of the lid that will contact the plastic.
 
Lid and Plug for Rotocasting

 
Insert a plug to prevent plastic from leaking out of the mold while on the rotational casting machine.
 
Lid for Rotocasting

 
Securely attach the mold to the rotational casting machine and rotate for about one hour.
 
Rotocast Hollow Part

 
Rotocasting Polyurethane Mold

 
Remove the mold from the rotational casting machine and set aside the plug.
 
Remove Plug

 
Step Two: Backfill the Hollow Poly 15-6 Casting with Foam

Carefully weigh an appropriate amount of Poly 15-6 Part B and then add the desired amount of Poly 15 Part F Foamer (we added 3%). Mix Part B and the foamer additive thoroughly and then add the appropriate amount of Poly 15-6 Part A. Mix all ingredients together; the foam will begin to rise quickly, so make sure that the mold is nearby.
 

Add Foamer to Plastic

 
Pour the mixture into the mold cavity. The demold time of Poly 15-6 without foamer is 1 to 3 hours; however, the demold time of Poly 15-6 with foamer is about 10 minutes.
 
Pour Foam into Mold Cavity

 
Foaming Additive

 
Resin and Foam Part

 
Excess foam that comes out of the pour hole can be easily trimmed off.
 
Remove Mold from Mold Shell

 
Remove Casting from Mold Shell
 
 
The finished casting:
 
Poly 15-6 Architectural Element
 

For more information on casting material options for your next project:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Customer Project: Decorated Venus Figurine – EasyFlo Liquid Plastic

August 28th, 2014

At the March 2014 Mold Making & Casting Workshop, attendee Ro-Z Esposito (more info. on this artist at the end of the blog) brought the plaster Venus figurine pictured below. She wanted to make a rubber mold of the figure and then cast plastic copies.

Plaster Venus Model
 

Ro-Z would later decorate the plastic casting by gluing intricate beading to the surface (pictures of the finished piece are at the end of this blog entry).

After a discussion with Polytek staff members at the workshop, a strategy was decided for the making of the mold:

  • Mold Making Method: Two-Part Poured Block Mold
  • Mold Product: PlatSil® 73-40 Silicone Rubber
  • Casting Material: EasyFlo Series Liquid Plastics

 

The following steps were taken to complete the mold and make the plastic castings:

 

Step 1: Test the Model Material for Cure Inhibition

Platinum silicone mold rubbers, like PlatSil 73-40, can suffer from cure inhibition when in contact with certain materials (e.g., sulfur, tin compounds), so a small amount of a fast-setting platinum silicone rubber was applied to the model surface to ensure that it would cure properly against the plaster. You can read more about cure inhibition and “test cures” here.

Testing Platinum Silicone for Inhibition-01
 

Step 2: Embed Half of the Model in Clay

As mentioned previously, the two-part poured block mold method was selected for this model. To begin, a parting line (i.e., the line where sections of the mold divide) was determined and then the process of embedding half of the model in plasticine clay was started. The selected parting line essentially split the front and the back of the model in half.

Begin to Build Clay Base
 

Meanwhile, the platinum silicone test sample was removed and we found that it cured properly.

Cured Silicone
 

The “pour hole” (i.e., where the casting material will later be poured) was built in at the “feet” of the model.

Embed Model in Clay-01
 

The surface of the exposed clay was smoothed and a mold box, tall enough to accommodate an appropriate mold wall thickness, was constructed. Melamine-laminated particle board and C-Clamps were used to make and secure the mold box.

Two-Part Block Mold - First Half Embedded
 

Marbles were partially embedded in the clay to create “keys” that would align the two halves of the mold when complete. The interior corners of the mold box were then sealed with clay to help prevent rubber from leaking out of the mold box.

Marbles Keys in Clay
 

Step 3: Apply Release Agent

A few sealer/release agent options could have been used in this case (e.g., Vaseline, Pol-Ease® 2500 Release Agent), but Pol-Ease 2350® Sealer & Release Agent was ultimately selected. Pol-Ease 2350 is white petrolatum dissolved in mineral spirits and can be used when working with liquid silicone or polyurethane mold rubber. It was sprayed on to the model, clay, and mold box walls with a Sure Shot Atomizer and then brushed out with a dry brush.

Apply Release Agent to Plaster
 

When working with Pol-Ease 2350, it is important to make sure that it has sufficiently evaporated before applying any rubber (evaporation takes ~1 hour and varies depending on temperature, porosity of the model, and thickness of the layer) – if the Pol-Ease 2350 has not evaporated sufficiently, it can interfere with the cure of the rubber.

 

Step 4: Measure, Mix & Pour the Mold Rubber

The mold rubber selected for this project was PlatSil® 73-40 Silicone Rubber. It is a 1A:10B mix (by weight), platinum-cured silicone rubber with a 45-minute pour time and a 16-hour demold time.

One of the reasons that a platinum silicone rubber was recommended as the mold material for this project is because release agent is not required when casting polyurethane plastic. Glue (used later in the process to apply items directly to the surface of the casting) does not adhere well to plastic coated in release agent and many release agents are difficult to wash off of plastic, so we eliminated the need for release agent entirely.

Parts A & B of PlatSil 73-40 were individually weighed using a digital scale and then combined and mixed thoroughly.

Mix PlatSil 73-40
 

The silicone rubber was poured into one corner of the mold box and allowed to flow across the model until it reached the top of the mold box walls.

Pouring PlatSil 73-40 Silicone Rubber
 

Pouring Platinum Silicone Rubber
 

Allow Rubber to Cure
 

The rubber was allowed to cure, undisturbed, for 16 hours. Heat (e.g., heat lamps) or PlatSil® 71/73 Part X Accelerator can be used to speed the cure.

 

Step 5: Make the Second Half of the Mold

To begin the process of making the second half of the mold, the mold box was temporarily set aside and all of the clay and marbles were removed.

Remove from Mold Box and Flip Over
 

Then the first half of the mold was turned over and the model was kept in the same position.

Remove Marbles
 

The mold box was repositioned around the first half of the mold and model and the interior corners of the mold box were sealed with clay. Silicone will bond to silicone if there is no release agent applied, so Pol-Ease® 2500 Release Agent was sprayed on to the model and exposed silicone and then brushed out with a dry brush to ensure even coverage.

Put into Mold Box
 

Pol-Ease 2500 Release Agent
 

Again, the rubber was carefully measured, mixed, and poured to the create the second half of the mold.

Pour Rubber to Make Second Half of Mold
 

Pour Second Half of Mold

 

Step 6: Demold

Upon cure of the second half of the mold (~16 hours), the mold box was removed and two halves were parted.

Finished Platinum Silicone Mold-01

 

Step 7: Casting EasyFlo Series Liquid Plastic

EasyFlo Series Liquid Plastics are fast-setting, two-part polyurethane plastics. All options within the series have simple 1A:1B mix ratios by volume.

Release agent is not necessary when casting EasyFlo Series liquid plastics in platinum silicone molds, so once the two halves of the mold are properly aligned (we used large rubber bands to further stabilize the mold), casting material can easily be poured into the pour hole, which is indicated by arrows in the pictures above and below.

The first casting that Ro-Z made was a solid pour of EasyFlo 60 Liquid Plastic, but she opted to slush cast the second time around to produce a lightweight, hollow part.

Casting in Two-Part Mold-01
 

For slush casting, a small amount of EasyFlo 120 was poured into the pour hole and the mold was manually rotated in all directions for about 5 minutes [you can learn more about slush casting in this blog entry].

EasyFlo 120 Casting Resin
 

Slush Cast EasyFlo Resin-01
 

Slush Cast EasyFlo 120 Part
 

EasyFlo 120 Liquid Plastic
 

In the picture below, the original model is displayed on the left, while the slush-cast, hollow EasyFlo 120 part is on the right.

EasyFlo Casting Resin
 

Ro-Z took this casting home and completed her design with intricate beading:

You can view Ro-Z Esposito’s work at www.ro-zesposito.com and can contact her at mypaintbrush@gmail.com.

Ro-Z has provided the following photos of her finished piece: 

Venus1
 

Venus2
 

Venus3
 

Do you have a mold making or casting project you would like to discuss with a Polytek Technical Support staff member?

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Blending Liquid Rubber & Plastic: Poly-Optic® Series

August 20th, 2014

Poly-Optic 14-Series Casting Resins are two-part, room temperature curing, polyurethane systems that result in water-clear castings. They can be colored with PolyColor Dyes to achieve transparent, colored castings.

Polytek Poly-Optic Clear Casting Resin
 

There are six individual product options within this series, most of which result in a rigid, Shore D80-D85 plastic. One option; however, is a firm rubber that cures to a Shore A70 hardness. As points of reference, Shore D80-D85 is comparable to the hardness of a hard hat, while Shore A70 is similar to that of a car tire [more examples of Shore hardness are below].

 

Shore Hardness Scale_Polytek
 

Blending Poly-Optic Products to Achieve Varying Hardness

If you require a clear polyurethane plastic that has a hardness between Shore A70 and Shore D80, Poly-Optic 1410 (a hard, Shore A80 plastic) and Poly-Optic 14-70 (a firm, A70 rubber) can be blended at different ratios to achieve varying hardness.

 

PlasticRubberMix

 [Samples of blended Poly-Optic cast in a slate tile mold:

25% 1410/75% 14-70, 75% 1410/25% 14-70, 50% of each]

 

In the table below, you will find what ratios (by weight) these two Poly-Optic products should be mixed at to achieve varying Shore hardness.

Ratios for Blending Poly-Optic Plastic & Rubber
NOTE: Poly-Optic 1410 is a non-yellowing formula (note: it is not recommended for long-term exterior use); however, Poly-Optic 14-70 is not a non-yellowing formula, so the addition of any amount of Poly-Optic 14-70 added to Poly-Optic 1410 will cause the entire casting to yellow more quickly when exposed to UV light than a casting without any Poly-Optic 14-70.

 

Do you have questions about blending rubber and plastics?

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!

Plasticine Clay: Multiple Uses in Mold Making

August 13th, 2014

Poly Plasticine is a non-hardening, sulfur-free modeling clay. It is non-toxic, odorless, and has a smooth, firm consistency.

Plasticene Clay - Polytek Development
 

It’s great for sculpting, which might be what most people think of when they hear modeling clay; however, we use this clay for varied purposes in our mold shop. You may be able to incorporate some of these uses into your everyday mold making routine.

We mentioned earlier that the clay that we use is sulfur-free. This is important because sulfur can cause cure inhibition in platinum-cured silicone rubber (you can read more about cure inhibition here). It is best to use an oil-based, sulfur-free clay, especially when working with platinum silicones.
 

Clay as Caulking

For the purposes of sealing, clay can often be easier to work with than hot glue or silicone caulking (and clay is recyclable!), especially when it’s warmed for easier application. We always keep of batch of clay in our oven, set at 140°F, so it’s ready to go at any time.

The photo below shows the edges of this stepping stone sealed with clay. This is a common practice that helps prevent rubber from leaking beneath the stone once the mold box is constructed around the stone and rubber is poured over it to make the mold (shown in the second picture below).

Seal Mold Box Edges with Clay

 [see this full project tutorial here]

DSC05270

 

In a similar scenario, pictured below, clay is used to seal the interior edges of the mold box to help prevent rubber from leaking outside of the mold box [see this project tutorial here].

Seal Mold Box with Clay
 

Below, clay is used to seal the exterior edges of a mold box that’s being used to make a two-part baluster mold [see the full tutorial here].

Seal Mold Box for Baluster
 

Plasticine clay can also be used to the seal the edges of mold shells. The mold shell below is constructed from Poly 1512X polyurethane plastic; the clay seals the edges as well as the areas around the hardware that is securing the mold shell to the base board.

Clay - Sealing Edges of Mold Shell-01
 

The plastic tubing pictured below is being used to create a through-hole in the mold. Clay is applied around the tube to help prevent leaks while the mold is being made.

Using Clay as Caulk
 

In the picture below, clay is being used to partition off an area of the mold that needs to be repaired with PolyBond adhesive [see the full tutorial here].

Position Clay in Corner-01

Apply PolyBond to Corner - Plug with Clay

 

Clay as Mold Boxes & Containment Areas

Not only is plasticine clay great at sealing mold boxes, it can can actually serve as a “mold box”, or containment area, itself. An example is pictured below.

Building a Clay Mold Box-01
 

In the picture below, we use clay to create a small containment area on the model to test for cure inhibition against the model material.

Clay for Test Cure

 

Two-Part Block Molds

Clay is an integral part in the making of two-part block molds, which are constructed by pouring one piece of the mold, allowing it to cure, and then pouring the second piece.

Before pouring rubber to make the first half of the mold, one portion of the model is embedded in clay, up to the desired parting line (example below).

Two-Piece Block Mold - Using Clay
 

Polytek Silicone Rubber

Once the rubber has cured, the clay is removed and the second half of the mold is made – you can see the full tutorial for this project here.
 

Poured Blanket Molds

Clay also plays a very important role when making poured blanket molds. In this process, the model is covered in a layer of clay (plastic wrap is often placed over the model before doing this) and then a mold shell is constructed around it (pictures below).

Following construction and cure of the mold shell, the shell and clay are removed and then the shell is re-positioned back over the model. Mold rubber is then poured into the mold shell, covering the model and filling the space that the clay once occupied. Read more about the basics of blanket molds here or view this poured blanket mold tutorial.

Clay for Blanket Mold

Plasticine Clay for Blanket Mold
 

DSC04030 

 

Keying

Keys are tongue-and-groove or button-like impressions that align molds or mold shell sections. The brush-on silicone mold pictured below is ready for mold shell construction. Before brushing on the first half of the mold shell, a cardboard shim is constructed to establish a parting line for the two halves of the mold shell and then two clay keys are positioned on the shim. The first half of the mold shell is brushed over the shim, clay keys, and mold. When the second half of the mold shell is constructed, the keys will provide an area of impression where the two halves will align nicely.

 

Clay Keys for Mold Shell-01

 [view this full tutorial on YouTube - Part I & Part II]

Clay Keys on Mold Shell-01 

 

Shims to Make Parting Lines for Mold Shells

While cardboard was used to make a shim in the example above, clay is used in the example below. The finished mold shell is also pictured.

Plasticine Clay Parting Lines-01
 

Two-Part Polytek Plastic Mold Shell

 

Modifying Models

Clay can be used to modify models before the mold making process. For instance, the person making a mold of this medallion wanted the final concrete castings to be thicker, so, prior to making the mold, he increased the height of the piece by adding a uniform layer of clay beneath the medallion.

Increase Height of Model with Clay-01
 

In this example, the holes in the model below were filled with clay prior to mold making because the holes were not wanted in the final castings.

Plugging Holes with Clay

What else do you use clay for around your shop?

Would you like to discuss your next mold making or casting project with a Polytek Technical Support staff member?
Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Or leave a comment right here on the blog!