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The Guide to Silicone Rubber Mould Making: Step-by-step

by Nice Rapid | Sep 08,2022 | Silicone Molding

Mould making is a process that involves creating a negative impression of the desired shape in a mouldable medium. Mouldable media can be made of metals, plastics, or rubber. In this blog post, we will focus on silicone rubber mould making.

Silicone rubber is often used for mould making because it is durable and can withstand high temperatures. The process of silicone rubber mould making is simple. It can be done at home with a few tools and materials.

Silicone oil bottle brush molds

The Basics of Silicone Rubber Mould Making: What Materials Do You Need?

Stretchy silicone rubber has permeated every aspect of our lives and is used extensively in industrial and domestic applications. Everyday items we all use include clear elastic in our clothing, potholders, muffin tins, and sealants for our bathroom showers.

Silicone rubber is frequently used to create moulds for various materials, including food, theatrical makeup, medical devices, and even polymer clay and jewelry components. Its wide use is due to its flexible nature and the way it faithfully conforms to the contours of whatever it touches when it cures.

RTV silicone is typically used to produce silicone moulds (for Room Temperature Vulcanizing). RTV silicone is made up of two components that, when combined, facilitate a chemical reaction that changes rubber from a sticky, flowable material to a non-stick, pliable, and resilient material.

RTV silicone rubber mould materials come in various forms and formulations. Still, for craft and hobby applications, they are most often found as silicone putty and pourable silicone rubber.

Silicone rubber is an artificial rubber created chemically by combining elastomers and polymers. Since it is not made of natural rubber, it lacks the proteins found in that material, which can cause allergies. Therefore, if you are allergic to latex, silicone rubber won't cause you any problems.

Step-by-step Procedure for Silicone Rubber Mould Making

If you're looking for a comprehensive guide to making silicone rubber moulds, you've come to the right place. This guide will walk you through the entire process, from start to finish. We'll cover everything you need to know, from choosing the right silicone rubber to creating the perfect mould.

With our step-by-step guide, you'll be an expert mould maker in no time. So, let's get started!

Creating the Master Pattern

Creating the master pattern is the first step in the duplication process. In the past, clay, wood, or plastic pattern shops were used to create the masters. Rapid prototyping (RP) technologies can now be added to aid in the creation of masters. These techniques include CNC machined masters, fused deposition modeling from Stratasys, stereolithography, and selective laser sintering from 3D Systems.

Rapid prototyping technologies, except for CNC machining are built using a layering technique. In most situations, post-processing finishing is necessary to ensure a high-quality polyurethane cast part. To apply this finish, sanding, filing, and painting create the desired texture or uniform smoothness.

Designing the Mould

Venting and gating need to be considered before creating mould. To regulate the flow of urethane into the mould, vents and gates must be made. The volume and shape of the master determine the size and placement of the gate needed for a particular mould (i.e., the greater the volume, the larger the gate area). Additional considerations include the master's wall thickness, viscosity, and pot life of the casting compound.

Mould locators are essential for the precise alignment of the mould halves to achieve an accurate component and prevent mould shift. Several methods can be used to add locators to the mould. Making a notch on the mould's first side is an easy technique. As the opposite side of the mould is cast, this depression reverses itself. For example, mould locators may be added during the first half of the mould construction setup. After curing, remove these locators and pour in the mould's second side.

Choosing Silicone

To ensure precise parts and inhibit mould shift, mould locators are essential to accurately align the mould halves. There are several methods for inserting locators in the mould. Making a tier in the mould's first side is a straightforward procedure.

The opposite side of the mould is cast, creating a reversal of this depression. When setting up the first side of the mould construction, mould locators can be added. After the locators have dried, take them out and pour the mould's second side.

Modeling clay with sulfur, natural rubber, neoprene, unsealed wood, and even wax from paper cups have all been found to inhibit reactions. Therefore, patch tests are advised whenever possible. Inhibition occurs after the recommended cure time has passed and the rubber is still gummy or completely uncured.

A customary practice is to apply a barrier coating to help prevent inhibition. A barrier coating is a substance that is applied to the master to stop the inhibiting property from meeting the uncured rubber. Polyvinyl alcohol, acrylic sprays, or paint primers are all acceptable coatings.

Making the Mould

When the master is completed, a silicone rubber mould can be created. The accuracy of reproduction is silicone rubber's most crucial feature. Silicones are renowned for duplicating excellent details.

It takes a few minutes to complete this crucial step in creating a mould, but it is time well spent. Start pouring material into the mould frame after removing the material from the chamber. Pour from the bottom up, letting the silicone flow around the master. Never pour over the master directly. A wave effect and air entrapment could result from this.

Pouring should continue until the silicone is at least 1 inch above the master or reaches the top of the mould box. Then, following the manufacturer's instructions, set the mould aside to cure. After the mould has dried, cut the book mould open or separate the mould halves (creating a parting line), then take out the master.

For more information about silicone rubber mould making or for help getting started with your own project, contact Nice Rapid. We would be happy to walk you through the process and answer any questions you may have. Thanks for reading!

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