Crafty Corner FAQ
What is Vulcanization or vulcanisation
It is a chemical process for converting natural rubber or related polymers into more durable materials by the addition of sulfur[1] or other equivalent curatives or accelerators. These additives modify the polymer by forming cross-links (bridges) between individual polymer chains.[2][3] Vulcanized materials are less sticky and have superior mechanical properties. The term vulcanized fiber refers to cellulose that has been treated in a zinc chloride solution to cross-link the cellulose fibers.
Although curing of rubber has been carried out since prehistoric times, the modern process of vulcanization, named after Vulcan, the Roman god of fire, was not developed until the 19th century, mainly by Charles Goodyear. Today, a vast array of products are made with vulcanized rubber, including tires, shoe soles, hoses, and conveyor belts. Hard vulcanized rubber is sometimes sold under the brand name Ebonite or the genericized former brand term "vulcanite", and is used in making articles such as clarinet and saxophone mouth pieces, bowling balls, and hockey pucks.
Why is the surface of my silicone mould tacky?
Extremely low humidity level can cause some issues but most can be solved by simply waiting another day, or simply put some baby powder or talc on the tacky surface and it will all but go away almost instantly. Sometimes users will scrap unmixed Base from the walls of their mixing container after pouring, which is then deposited on top of the mould where it remains tacky.
What kind of detail can I expect from RTV silicones?
Silicones pick up the exact detail of the original including flaws and imperfections. So make sure your master is exactly how you'd like it prior to pouring. Fingerprints and debris are examples of very fine detail that are captured using our silicone mould making products.
How long will a silicone mould last?
Many factors need to be taken into consideration, so this is difficult to answer. What is the mould used for and with what casting medium? How large is the mould, the severity of undercuts in the mould? How is it stored? As well as the type of silicone used. Yields can vary from 10 parts to hundreds of parts. Average mould life expectancy for urethane cast pieces average between 30-70 pulls depending on all the factors involved.
Is there something I can do to make my RTV silicone thinner and softer?
Silicone oil acts as a thinner of viscosity for unmixed silicone making it easier to pour. It will also slightly lower the hardness of your cured silicone system. The silicone oil can bleed from the cured RTV rubber if too much is added to the silicone; therefore we do not recommend ever going over 10%.
Why will can some silicone molds be reused only for a few times?
It can be due to the following reasons:a. Adding too much silicone oil in to silicon rubber. Silicon oil is an additive which can destroy the molecular weight of silicone rubber and reduce the tension and tear strength.
b. Using the silicon rubber with a high hardness to make molds for small sized products with delicate and intricate designs or the silicon rubber with a low hardness to makes molds for large sized products with simple designs.
(Notes: we should choose the silicon rubber specifically according to the requirements of our products to avoid this problem.)
I need a silicone that I can paint on to a vertical surface to capture a relief, is there such a thing?
Thixo is an additive that can be put into silicone RTV’s to increase the viscosity (consistency) of the mixed silicone rubber which allows the user to paint on and build up the wall thickness onto large moulds or vertical surfaces. Initial coats should be fairly thin to prevent air entrapment against the mould surface and secondary coats should be thicker and used to increase the overall thickness of your mould.
Can I do anything to minimize/eliminate bubbles when making my mould without using vacuum equipment?
You will need an artist brush (natural) to paint a thin/skin coat onto the original. It is not the idea to cover the object with this first layer, but to push the silicone into the nooks and crannies filling in all the fine detail.
This first layer or skin coat helps insure that no air bubbles will be trapped in the narrow recesses on the surface of the original.
After the skin coat is applied, you will then embed your piece with silicone, taking it 6mm above the highest point of the original.
The silicone should be poured in one spot in the corner of a mould box from a height of about 300mm. This method is often called a "string pour". This allows the material to come down in a steady, semi slow stream as it falls into the corner of the mould box. This lets the material flow freely up and over the original, pushing some air pockets out of the way.
The string pouring technique helps eliminate air that was incorporated into the silicone when it was mixed.
How do I release silicone from silicone?
To release silicone rubber from silicone rubber, use a release agent that does not contain a significant amount of silicone oil. You can use petroleum jelly thinned with a solvent such as mineral spirits. Make sure you don’t leave brush strokes on the cured rubber’s surface as they will be reflected in the mould
Can a rubber mould that has torn in production be repaired?
Although a repair may not be permanent, you can repair a silicone mould so that you can at least get a few more castings. You can then use that a casting to make a new mould.
For repairing a silicone mould – you can use a silicone sealant. Important; all surfaces to be bonded must be clean. Use acetone or other solvent to clean the area to be bonded before applying the sealant.
How do I increase the general strength of my mould?
Once you have de-moulded your mould and the mould is small enough you can submerge the mould overnight in a bucket of water. This will help remove any excess catalyst left in the silicone. A further step to this, size permitting is to place the mould within an oven and heating it to 90deg c for 30 min. This also further drives off any residue catalysts and oils in the silicone.
The self same method is used by many people in the confectionary industry to render the mould safer for use in making icing based items. It is important for us to note that this is by no means to be considered to render the silicone “certified food safe”.
Can you use standard tin sure silicone for pewter?
Pewter is an ALLOY which means it is composed of more than one metal. Most modern pewter is composed of 96 percent tin and 4 percent copper although there are many variations. It is a soft metal and can be shaped easily by hand tools and machine tools. Due to its low melting point (approximately 230 degrees centigrade) it is suitable for casting. It is a bright material, which makes it popular for the manufacture of ‘silverware’ such as tankards, candlesticks and even jewellery.
All that information aside yes you can the standard tin cure silicone can withstand up to 230 degree c for a short period and 180 for a sustained period. With any metal they will drop in temperature rapidly on entering the mould as the material is room temp brining the pewter to safe levels. The high temps will age the mould faster than normal but you will still be able to get 20 -30 castings from a mould.