Generally speaking, rubber O-ringswith ID of above 500 mm are classified as large-diameter O-rings. This categorization is sensible considering that the largest ID of ISO 3601 Metric Size O-Rings is 658.88 mm.
Rubber O-rings (or gaskets) with above 500 mm ID pose significant challenges for processing. This is not because of the cost of moulding tool as we need to build a larger iron plate to accommodate the O-ring size.After all we can anyway make the moulding tool into doughnut shape to save costs. Rather, it is due to the size-limitation of the equipment (i.e., flat vulcanizing machine). It would be difficult for the vulcanization platform to cover the whole moulding of the ID of above 500 mm , let alone to exert adequate pressure on it. And you could imagine how things become trickier when the ID is 1 m, 2 m, or even 10 m.
In general there are three ways to address the above challenge.
One is to use rubber cord to make O-rings. Specifically, we first produce rubber cords by extrusion, then join the two ends of the cord by glue. The problem is, obviously, how well the joint is handled. The visible “scar” shows its weakness, and the swell indicates the problem of precision, even though we can apply force of compression or scratching to make the lump less notable. As a result, O-rings joint by rubber cords usually find their use only in less demanding application.
The second is still resorting to moulding process, but by designing the moulding tool into flower- or labyrinth-shape. In essence, the tool folds or squeezes the O-ring in a much smaller arena so as to be covered by the equipment platform. The problem is, however, that the O-rings will lose sphere (i.e., not perfectly round) when unfolded. Moreover, the moulding tool for these particular shapes will be significantly more expensive than the normal ones.
The third method, which is currently used in Yoda Rubber, represents a comparatively optimal approach, i.e., the technique of sectional vulcanization. Specifically, we first make rubber short cords by moulding/vulcanization, and then join the cords into an O-ring by the second moulding/vulcanization. The two steps are successive, meaning that the second vulcanization will take place before the first vulcanization fully takes effect. This ensures that the joining will be as seamless as possible. No scar, swell, or weakness will be present at the joining point.
The following video showcases our sectional vulcanization technique and how our large-size O-rings look as if they were moulded at one stroke of compression.
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