Molding in silicone form: equipment. Vacuum molding in silicone molds

For the manufacture of a small number of plastic blanks, vacuum molding in silicone molds is most often used. This method is quite economical (making a metal mold requires more time and money). In addition, silicone molds are used many times, and this also significantly reduces the cost of production.

Casting of plastics

The essence of the method of casting plastic masses is as follows. The molten material is in the aggregate screw (special equipment for molding into silicone molds). Under the action of the piston, the mass moves through the sprue channels, then fills the space of the mold. Thus, it is possible to obtain a casting. When the plastic is heated, the atoms from which it is composed begin to move randomly and randomly. However, upon cooling, crystallization centers begin to form. The walls of the mold grow crystals, then this process takes place inside the casting. At this stage it is very important to comply with the temperature regime, to choose the right time for aging. Otherwise, plastic injection into silicone molds will be substandard, with visible signs of rejection. But, first of all, it is necessary to make the forms themselves, into which the mass for crystallization will be poured.

Technology for creating molds for casting

There are several ways to create silicone molds. The first of these is a solid fill. This method is suitable for simple designs: reliefs, souvenir products, two-dimensional parts. The model is placed in a formwork, filled with silicone. Plug-in forms are made like the previous ones, they are used for more complex shapes. Two-part forms are produced in several stages. First, the first half of the workpiece is poured, after the hardening of the silicone, the shape is inverted and the second part is similarly made. It is very important for this method to designate special locks on the basis (casting in silicone form of this type should occur without its displacement). Most accurately repeats all the details of the workpiece form "in namazku." A viscous silicone is applied to the part with a brush. The process takes place in several stages, this is necessary for a complete repetition of all the small nuances of the product. In this case, the form itself is rather thin - from 3 mm. To keep it in shape, an outer hard shell is created at the final stage.

Silicone for the manufacture of molds

Vacuum molding in silicone molds involves the use of different materials to create matrices. One of them is a silicone like Mold Star. It is used for continuous pouring, quite durable and flexible. The solidification takes place at room temperature. For the technique "in namazku" often use the series Rebount. This silicone has a high viscosity, which can be controlled with a thickener. Casting in a silicone form of this kind makes it possible to obtain a high-quality, solid matrix, and, accordingly, an extremely precise part. There are also translucent silicones, which are ideal for split shapes.

Materials for casting

As a rule, polyurethane is used for manufacturing the parts themselves. The material has high impact strength, hardness, elasticity. The polyurethane rubber has a higher tensile strength and tensile strength. They are used in the manufacture of various tapes, cylinders, dies, gaskets, bushings. Still for casting apply also a transparent plastic. It is quite resistant to ultraviolet rays and retains its transparency even when staining. The field of application is lenses for various tests, prototypes in medicine, the production of souvenirs, etc. Generally, molding in silicone form involves the use of two-component mixtures, which include directly plastic and a catalyst.

Plastic molding in silicone molds. Equipment

Small-scale production of cast billets is a technological process that allows obtaining a batch of exact copies of a detail of any complexity. Very often, the technique is used to obtain prototypes that are tested before launching mass production, testing the appearance, design.

Industrial molding of plastic in silicone mold equipment provides the following: a vacuum chamber (injection molding machine), a thermo cabinet, a vacuum mixer (mixer). Silicone is first prepared in a vacuum chamber, where the process of degassing the material takes place. This is necessary to prevent the formation of bubbles on the mold. After the casting mold has been made and preheated, the polyurethanes (or resins for the final part) are mixed directly. This process takes place in a vacuum chamber. Through the gate the mixture is poured into the mold. For final processing, the workpiece must be placed in a special oven, where the final hardening of the product occurs at a temperature of 70 ° C.

Vacuum chamber. Main characteristics

As a rule, in the scale of production, automatic molding into silicone molds is used. The equipment, namely the vacuum chamber, allows controlling both temperature and casting speed. The operator does not require special skills and knowledge, since all control comes from an operating system that has both automatic and manual switching. There is also the possibility of editing the specified program. Various modifications of the chambers are able to produce blanks up to 5 kg (for example, camera CT-02). The unit is equipped with a lift for lifting silicone molds. It should be noted that the CT-02 system allows the use of both small and rather heavy matrices.

Another option is the MCP camera. This silicone molding equipment makes it possible to manufacture parts with thin walls and a complex configuration. This process is carried out due to differential pressure. Then the obtained castings are extracted, and subsequently it solidifies in the air. Vacuum molding in silicone molds for some types of plastics is completed in thermo cabinets, which ensure a uniform heating of the air, and, accordingly, the workpiece.

Final processing of cast billets

After the plastic mass has completely hardened, it is carefully removed from the mold. There is a mechanical treatment of the surface, removed and cleaned out the protrusions, grinded irregularities. If necessary, the blank is covered with either paint or other protective material. It is necessary to clean and silicone form, remove the remnants of plastic. Then it is washed, ready for later use. It is worth noting that the molding of plastic into silicone molds provides for the repeated use of matrices (from 20 to 80 times).

The main advantages of the method

Small-scale production dynamically develops, it allows to qualitatively estimate the sales market, to test products, to create unique author's works in a small amount. Silicone molds, which are used in the molding of plastics, make it possible to completely copy the texture, shape, and construction of the workpiece. The part is easily released from the matrix, which can also be used repeatedly. Castings have a minimum number of surface defects, optimal physical and mechanical properties. In addition, in some cases, even metal can be poured into silicone molds.

But the main advantage that molding has in silicone molds is the price. The suppliers of this service indicate that the final cost of the workpiece will depend on the plastic material and on the volume parameters of the part (for example, a 10 * 10 * 10 cm billet can cost 1,500 rubles). Silicone itself can be purchased from 500 rubles per kilogram, plastic - from 700 rubles. The cost of metal forms is quite high, sometimes their use is simply inefficient (if the circulation is several units). And silicone matrices are also suitable for domestic use, it is not necessary to buy expensive equipment. It is only necessary to make a layout yourself, to take into account the lifetime of polyurethanes (the period when they remain liquid and suitable for pouring), to observe all technological nuances - and molding in silicone form can be carried out even at home. According to calculations, the cost of one billet in this case is about 70-140 rubles.