Silicone rubber mold is a silicone room temperature two-component mold rubber (Room Temperature Vulcanization), referred to as RTV, commonly known as Silicone. This is a two-component compound. Wherein component A contains a crosslinking agent and component B contains a catalyst. During the packaging process, the crosslinking agent and catalyst must be separated. Its vulcanization is performed at room temperature. As long as the two components are mixed in a certain ratio (the specific ratio can be determined according to the operating time and product performance), the two component compounds undergo a cross-linking reaction to form a flexible and elastic colloid. Suitable for POLYSTER epoxy resin (EPOXY), Pu foam resin, gypsum, cement, candle, electronics and other craft factories, toy factories, electronics factories, lighting factories, silk screen factories, candle factories, decorative crafts and Copy products and make molds.
2 properties of mold silicone rubber
(1) Good chemical stability, non-toxic and non-corrosive;
(2) Good fluidity, can fill the mold automatically;
(3) The vulcanization speed can be controlled, and vulcanization at room temperature and atmospheric pressure is convenient for operation;
(4) Good demoldability;
(5) Strong simulation and realistic decoration;
(6) The mold making speed is fast. Generally, the mold can be made within 20 hours.
3 mold silicone rubber mold making process
(1) Raw materials
Mold silicone rubber is generally composed of a base rubber, a cross-linking agent, a catalyst, and a filler.
The base glue is 107 silicone rubber, called hydroxy-terminated polydimethylsiloxane.
This mold silicone rubber can be cured at room temperature, has good fluidity, no deformation, and only slight linear shrinkage.
The cross-linking agent was ethyl orthosilicate. The amount of crosslinking agent has a significant effect on the curing time, tear strength and elongation of silicone rubber. Practice has proven that the amount of crosslinking agent is preferably 5% (mass fraction) of the base rubber.
The catalyst was dibutyltin dilaurate. The amount of catalyst added has a direct relationship with the curing time. It should not be too much, generally 1% ~ 2% (mass fraction).
Fillers are talcum powder, quartz powder, and white carbon black. Talc powder is generally used as a filler. When white carbon black is used as a filler, the mechanical strength, tear strength and uniformity are significantly improved.
(2) Molding process
Take the manufacture and reproduction of Maitreya mold as an example to explain the manufacturing process of rubber mold.
(1) Select the bottom opening as the positioning part, and inject gypsum into the cavity with a height of about 30mm higher than the bottom, and dig out a pit for later positioning.
(2) Stick plasticine. Stick a layer of rice paper on the surface of the utensil, and then evenly paste 5mm thick plasticine on the surface.
(3) Gypsum master. In order to support and fix the RTV mold and prevent its elastic deformation, a plaster mold is first made outside the mud layer. Make plaster images one by one according to its approximate parting surface. Pay attention to the positioning between the plaster molds. The plaster slurry is plaster: water = 1: 1.
(4) Manufacturing of RTV mould. The gypsum is lifted in the reverse order of production, the plasticine is removed, cleaned, and the mold release agent is coated on the utensil and the gypsum mold, and then the mold is closed.
At the same time, the components of the RTV are weighed according to proportions, and then fully stirred after mixing. During the stirring process, the reaction between RTV and ethyl orthosilicate under the action of the organotin promoter will produce low-molecular-weight alcohols. During the casting of silicone rubber, pores will be generated in the mold body, so it must be removed under reduced pressure Foaming is performed in a closed container with a vacuum of 100 mmHg for about 5 minutes.
Inject the bubble-free silicone rubber into the cavity of the closed mold, and cure at room temperature for about 24 hours.
Take off the plaster mold, cut it with a razor according to the expected parting line, carefully peel off the silicone rubber from the utensil, remove the utensil, and then fit the silicone rubber mold with the plaster mold as it is. Done.
4 mold silicone rubber mold application
Columbia's Rand Co., Ltd. is an industrial company that does not use metal molds to make wax patterns in investment casting production. The company used silicone rubber molds to produce solid copper buckles and metal accessories for luggage and handbags in only two days. The cost of each mold is usually only 5 ~ 30 US dollars, and the processing cost of metal molds Usually between $ 1,000 and $ 10,000.
With a history of more than 50 years, the American Finite foundry company has been using silicone rubber molds in the jewelry industry for many years to make jewelry. The company has standardized the mold size of small parts according to the specifications of 63.5m × 88.9mm, making parts as large as 50.8mm × 25.4mm × 12.7mm, and the small wall thickness of the parts is 3.2mm.
New York State Texcaster Industrial Co., Ltd. combines the manufacture of silicone rubber molds with centrifugal casting and centrifugal casting, which greatly improves the production capacity of centrifugal casting. The material of parts can be wax, plastic and even low melting point alloy.
In recent years, China's application of RTV has made great progress in mold manufacturing and the reproduction of ancient bronzes. For example, the Hunan Machinery Research Institute has copied the Elephant Statue, Pig Statue, and Human Ding from the Shang Dynasty, Tilianglu from the Spring and Autumn Period, and Song Dynasty. Copper cymbals, etc., have achieved the effect of being real. Wuhan Mechanical Technology Research Institute copied Zenghou Yibian Bell to reproduce the sound of the ancient clock. In addition, the Shanghai Leather Industry Research Institute uses RTV as a mold for high-frequency molding, which is a new process developed in China in recent years in shoemaking and manufacturing operations.
5 mold silicone rubber operation method
1. The silica gel and the curing agent are stirred uniformly. The appearance of the mold silica gel is a flowing liquid, the component A is the silica gel, and the component B is the curing agent. Example: Take 100 grams of silica gel and add 2 grams of curing agent (Note: The silica gel and curing agent must be stirred evenly. If the silica gel and curing agent are not stirred evenly, one piece of the mold will be cured, and the other one will not be cured. The silica gel will appear uneven and dry. Will affect the life of the silicone mold and the number of mold turnover, and even cause the mold scrap.
2. Vacuum extraction and air bubble treatment: After the silica gel and the curing agent are evenly mixed, vacuum extraction and air bubble removal should be performed. The vacuum time should not be too long. Under normal circumstances, it should not exceed ten minutes. The vacuum time is too long, and the silicone will immediately solidify. A cross-linking reaction occurred, making the silica gel piece by piece, unable to be painted or poured. This wastes the silica gel. You can only put the silica gel in a trash can and take it again.
3． Brushing or operation process: Brush or pour the silica gel evacuated through air bubbles. Pour on the product (Note: the product or model to be copied before pouring the silicone must be release agent or release agent). Then apply the silica gel to the product. Be sure to apply it evenly. After 30 minutes, paste a layer of gauze and weft cloth to increase the strength and tensile strength of the silica gel. Then apply a layer of silicone, and then stick a layer of gauze, weft cloth, so that it can be done after two times. Only by doing so, the service life and the number of turning molds of the opened silicone mold are relatively increased, which can save costs and improve the rate.
4． Production of outer molds: Generally, the method and materials used are to surround the mold with plastic boards or wooden boards. Once the mold cabinet is filled with gypsum, another method is to paint with resin. Resin is pasted with a layer of glass fiber cloth, and then brushed and then pasted. Repeating two or three layers can complete the mold outer mold.
5. The operation method of the filling mold or filling mold: The filling mold or filling mold is used for relatively smooth or simple products. There is no mold line to save labor and time, which is to use plastic plates or glass for the product or model you want to copy Surround the board, pour the evacuated silica gel directly onto the product. After the silica gel is dried and formed, take out the product, and the mold is formed. (Note: The soft mold is generally used for the injection mold. It is easier to release the mold. , Will not damage the product inside the silicone mold)
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