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Technological

FAQs of RTV mold silicone

1. Why should the silicone mold 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 destroies the molecular weight of silicone rubber and reduce the tension and tear strength.

b. Adding too much catalyst(curing agent).Too much catalyst can make the silicone cure very fast and and reduce the mold life.

C. Using the silicon rubber with a high hardness to make molds for small sized products with delicate and intricate designs and 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.)

2. Why does the silicone mold get burnt out?
This consequence happens only because you have left out the important notes when using unsaturated resin materials to produce your products. The unsaturated resin produces great heat when added the curing agent. So you must demould the product within 3 minutes to avoid this problem.

3. Why does the silicone mould appear to be dry outside but wet inside?
Because molding silicone rubber is a kind of condensation silicone rubber, which get solidified after absorbing moisture from the air. In order to provide a significant shelf-life for the silicon rubber, we will dry out the water in the silicon rubber.
Solution: Add 0.05% water into the silicon rubber and Stir over a low speed briefly when you use it.

4. Why is the tear strength of the silicone mold weak?
In order to reduce the viscosity of silicone rubber and pursue a good quality, you may add a lot of silicone oil into the silicon rubber when making molds. In fact, it might have just the opposite effect. The tension and the tear strength will be reduced badly with the addition of silicon oil. And the silicon molds will be in a weak and flimsy manner.

5. Why is the silicon mold oily?
The molding silicone rubber itself doesn’t contain any oil, so it won’t be oily. If the mold is oily, it may be because you add the compound silicone oil( the compound of silicon oil and white oil). The white oil is not silicon oil but a kind of petrochemicals.

6. Why isn’t the silicon mold acid & alkali and aging resistant?
It is due to the addition of the silicon oil. Normally we do not advise our customers to add any silicon oil into the silicon rubber. If it is necessary, the ratio must be 5%-10%.

7. Why is the appearance of the finished mold striate and unsmooth?
It is because the appearance of the product or the model itself is not perfect, and it has not been polished before the further operation. So when you make silicon molds, firstly you should polish the product, spray the mold spray evenly on the product. In this case, the problem can be avoided.

8. How to deal with the bubbles during the mixing process?
It depends on your practical situation. Firstly you can deal the mixture with a vacuumizer if you have one; If no such machine, you can reduce the mixing ratio of the hardener from 5% to 2%-3%.Then in the prior period of the reaction of the mixture will be slower, then the air in the mixture will exhaust by itself for a longer curing time to release the bubble.

9. what should you do for imcomplete curing after the mold is finished?
Two causes lead to this problem:

a. Inexact mixing ratio, not to weigh following the standard ;

b. The mixture of the silicone and catalyst is not mixed evenly.

You should avoid this kind of problem ,otherwise there will be a waste of silicone mold.

10. What’s the solutions for the sticky of the silicone mold?
The main reason for this problem is that you do not handle the products or original molds well, then you should deal with the original mold or products carefully before molding. Such as for the products with a complicated

pattern or a unsmoothed surface, you should polish and clean the products after which it will be molded ,then spray the release agent. Normally, the release agent can be Vaseline , detergent. liquid wax Etc. In practical process, you can bush different release agent according to different material.

The second reason is that the operator pour the silicone into the mold when the mixture is mixed evenly, then the finish silicone mold will not cure and dry entirely..

11. What should you do for deformation of the silicone mold ?
It should deal apart according to the size of the products, In principle, the hardness of the silicone should be according to the size of the products. If the products features small size and detailed patterns on it, the soft silicone can be applicable which the shore A should be 15-20 for easy demoulding and not damage of the patterns. Other wise harder silicone should be needed for large size products, such as products with size 1meter will need harder silicone with 35-40 shore A , then no-deformation. If Large products but features detailed patterns then 30 shore A silicone will be workable.(The process should be a layer silicone add a layer fiber glass or cloth..).The outer of mold can be plaster, glass fiber reinforced plastic(unsaturated resin and fiber glass) to protect the products from deformation.

12.What’s the operation procedures for making Pouring or perfusion mold?
pouring or perfusion mold is always used for simple or smooth products, but it will cost more time and labour than mold line. Enclose the products with plastic plate or glass plate, pour the vacuumized silicone onto the products, after the silicone cured, you can take out your products, then a mold is formed.(note: Generally, in this pouring way,

you should use low-hardness silicone rubber to make molds, so it will be easier to demould and will not destroy the products.)

13. How to make an outer mold?
One is to enclose the mold by a plastic plate or wooden plate , then pour into the liquid plaster to fill the mold frame. Another is brushing or coating  a layer of resin and  then pasting a fiber glass, then repeatedly brushing and pasting one more time, then a outer mold will be finished for 3 layer same process

14.What’s the operation Procedure of making Multi-pieces mold?
For multiple piece instructions , you can use the vacuumized silicone to make molds in a brushing or pouring way.

If you want to do a multi-pieces mold in a brushing way, it’s necessary to coat a layer of release agent or dusting agent on the original mold before brushing, then brush a layer of silicone rubber to the surface of the products ( note: it should be brushed evenly), then after 30 minutes spread a layer of gauze or fiber glass cloth to improve the tear strength, then coat the second layer of silicone rubber, after the second layer silicone cured, you can make

a outer mold, which can be made of plaster or resin material.

15. How to distinguish the pure silicone oil and ungraded silicone oil?
(1)  Check by your observation: pure silicone oil is a transparent liquid without any smell, but ungraded silicone oil smells bad and in a turbid liquid form.

(2)  To test it by fire. take the pontil or glass rod to dip some liquid , if it can be lighted and fumed when burning, so the liquid is the ungraded silicone oil ,which is a kind of petrochemicals. And, Pure silicone oil can not be fired, which is colorless, odorless, clear, nontoxic. The burning point of pure silicone oil is 320C,but ungraded silicone oil is 100C.

(3)  Freezing point Method: Take 100g of two kinds of silicone oil into refrigerator at the same time. Under temperature of-5 to -10 C for 2 hours, ungraded silicone oil will turn to turbid or frozen ,while pure silicone oil is still clear and transparent as before, and it will not freeze until -5 0 0C.

16.What’s the limitations of silicone?
a.    When the hardness of silicon rubber is lower than 15 shore A, the tension, the tear strength, the ageing resistance, acid and alkali-resistance of silicon rubber will reduce respectively.

b.    When the hardness of silicon rubber is higher than 50 shore A, the tension and the tear strength of silicon rubber will reduce, and the solidified silicon mold will be easily broken.

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