Custom rubber products will be the simplest, most affordable, and possibly the most extensive of the three basic moulding techniques.
Among the secrets to successful moulding is acceptable elimination of atmosphere while the mould hole is filling up with rubber. Compound put in the mould’s uncured bits are identified variously as preforms, billets or weight weights. For a ball, an elliptically shaped extrusion, cut to a suitable span might be used by one. This contour is important and intentionally chosen when the mould starts to close so that air in the mould hole is going to have free route of escape.
Typically this preform’s weight may be picked to be a few percentage (from 2 to) above the weight of the custom rubber products, to ensure a product that is fully-formed and to give an additional ‘drive’ for expulsion of any residual air that is trapped. The preform is put into the bottom hole and the top form section put on it.
Yourself. In case a substantial amount of custom rubber products must be made, it is frequently beneficial to mend the two halves of the mould for their respective press platens, hence decreasing manual handling and therefore labor costs.
The mould is continuously warmed to some temperature, commonly between 120 degC and 180 degC. A treatment period for an inferior part might be 20 minutes, at 150 degC, for slim cross-sections (6 mm). In this instance, temperatures degC could reduce the cure period.
At independent custom rubber products, the chemist plays his component by trying to control the uncured substance viscosity, in realizing a smooth flow of stuff in the mould. This must be high enough to create the back-pressure required to eliminate air efficiently as the form closes, and low enough to allow end of flow into all areas of the cavity before vulcanization begins. If we all appear at a low healed-hardness rubber, it generally contains no or little product (NR & CR), or instead fillers plus a big quantity of oil. This can commonly make its viscosity too low for successful compression mouldings as well as the compounder might try to increase its viscosity, by choosing a chewing gum elastomer level that is raw with a high Mooney viscosity.
At the other end of the scale, high vulcanized-hardness compounds with lots of fillers that are exceptionally reinforcing will require specific process aids and reduced Mooney viscosity raw chewing gum elastomers, as a way to boost the ingredient in the mould’s flow to reduce viscosity.
As the form is closed by the press platens, excessive substance begins to squeeze away in to the expensive grooves, taking atmosphere. Frequently, remaining air stays and various procedures are devised to eliminate it. One strategy is always to create the form strain back to zero after which return to full strain by rapidly reducing and lifting the press platens a quantity of times. This ‘shock’ therapy is called ‘colliding’. Yet another line of attack is to discover where atmosphere will be caught in the ultimate cured product and drill a small-diameter hole through the mould cavity in the identical area; these are called holes. They allow an alternate escape route for the air that is trapped (as well as some rubber). The preform’s contour and also its positioning in the mould is significant. The uncured rubber, put in the hole, may be one item or numerous bits. This method is quite definitely an art for the custom rubber products that are independent.
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