Manufacture and QC of Inflatable Seals
Iso-Flate® inflatable seals are manufactured in the UK in ISO accredited facilities. Whilst most are manufactured using a combination of extrusion and injection moulding, we do have the ability to fully mould endless inflatable seals in one piece (usually for small diameter inward inflating seals). Below is an outline of how we manufacture the seals, forgive us however for keeping some of what we do differently a secret…..
Extrusion and Compression Moulding of inflatable seals
Un cured elastomeric compounds have a consistency similar to that of putty or play dough, and have little or no use pre vulcanisation. Various fillers are added to the base polymer for the desired property (for eg carbon for electrical conductivity) as well as whats known as a catalyst which aids the vulcanisation when the compound is exposed to heat.
In the case of extrusion, the desired shape (or a very similar shape allowing for tolerances of contraction during manufacture etc) is cut into a plate usually made of steel, which is then securely fixed at the head of the extruder. This is usually known as a “die” or “die tool”
The compound (still in a putty like state) is then loaded into an opening atop a mechanically driven screw, which when activated forces the compound towards the plate building up pressure until the material is forced through the die. The size of the screw extruder therefore dictates the minimum run that can be produced as a certain amount of compound must be loaded in order to generate sufficient pressure.
The extrusion is then forced onto a “conveyor belt” made of a high temperature resistant material and is subjected to high temperatures (differing from compound to compound). With the aid of the catalyst/accelerator, the individual polymer chains cross link as they heat up, bringing about an irreversible change and turning the raw putty like compound into a flexible, durable material with both elasticity and recovery.
The cure times, belt speed and temperature will vary for different materials but also for the same base compound with different types and amounts of fillers. This means unless working with a commonly used stringently controlled compound , a trial run is often needed to ensure all settings and the size of the die are correct to produce the desired shape within tolerance.
It is worth noting that the belt is usually horizontal, however for certain profiles (for example top heavy and large shapes) extrusion vertically through the centre of a long oven is required in order to avoid collapse of the raw profile prior to it developing the ability to support its own weight by vulcanisation.
Also, in the case of inflatable seals, it is sometimes necessary to cure extrusion around a radius, in order to negotiate a sharp bend in a seal groove for example.
Once the extrusion is cured, in the case of making a circular seal (or endless) the desired “developed length” is cut and the two ends are placed in a “compression mould, along with raw compound of the same material). The compression mould mimics the shape of the seal, and comprises of an upper plate , lower plate and a core. The assembled unit is then placed under a heated platen and pressure is applied to ensure the raw compound flows into all cavities of the tool. The heat applied initiates cross linking between both ends of the seal to effect a join.
The core is extracted and inflation stems or valves are applied in order to allow the input of air (or in some cases water ) .
The seals are then entered in an oven and “post cured” in order to finish the cross linking process and “bleed out” any unwanted excess catalyst etc. This process is particularly important for FDA compliance.
Testing and QC
Upon completion of the manufacture, the seals are checked dimensionally against profile drawings using digital measuring equipment. They are then subject to pressure tests (which can be in free air or supported by a groove dependent upon client requirement) to ensure they are leak tight. This test may be carried out under water, or in some extremely stringent environments are subject to helium leak testing inside application. New inflatable seal profile designs are subject to accelerated cycle fatigue tests using our custom made equipment, and repeatedly inflated and deflated in order to asses suitability for application. This can be done to specific cycle life requirement of the client, and we have been known to achieve 60,000 cycles with no visible damage or loss of performance. These tests can also be made more application specific for example they can be carried out inside an oven to assess performance for high temperature use. No inflatable seal will leave our premises without first being subject to pressure testing.
What we do differently:
- Extremely stringent tolerances on extrusion and precision machined tooling ensure flush joins with no detriment to “seal ability”
- Unique ident number can be applied to inflatable seals which gives traceability data such as compound used, date of manufacture , operator etc
- Precision machined steel and rubber moulded valves/stems (some of which have been helium leak tested for containment environments)
For further details please see our Inflatable Seals page.