The Curing Equipment

Most UV lamps do not respond well to being switched on/off repeatedly as this can reduce the life of the UV bulb, but light-emitting-diode (LED) curing systems are now available and these can offer a much longer bulb life. 

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Erequendy, the curing equipment available, ie, presses, autoclaves, LCM lines, etc, do not allow the curing conditions to be varied as desired, so the compounder must design a cure system compatible with the existing equipment while also meeting the compound performance requirements. 

The curing equipment will operate at the sufficient efficiency if a minimum UV dose (mj/cm ) or a minimum exposure time can be applied to obtain the desired degree of cure. This requires fhat the reactive binders and photoinitiator system match closely the emission spectrum of fhe UV source. 

Hazards due to exposure can be minimized by sound basic engineering, and by administrative and hygiene controls. The curing equipment should be properly shielded to prevent escape of UV light into the workplace. Personnel working in the UV curing area should wear special protective eyewear. 

Adhesion tests of rubber to metal or rubber to fabric is to be done in counter samples kept along with the products in the curing equipment. 

Vulcanization is a chemical process where sulfur or other materials form crosslinks in the elastomer and thereby improve the polymer s mechanical properties. In many instances, not all of the desired properties reach an optimum level simultaneously. The task is to achieve a balance of the most important property requirements through design of the cure system and time-temperature cure cycle so as to attain the necessary compound mechanical properties. Frequently, the curing equipment available, such as presses or autoclaves, do not allow the curing conditions to be varied as desired, and so a cure system compatible with the existing equipment must be designed and also meet the compoimd performance requirements. 

The metallurgy of the cyclone equipment has in recent years focused primarily on type 304 H stainless steel. The 304 H material is durable and easy to fabricate and repair, withstands the high regenerator temperatures, and is oxidation- and corrosion-resistant. Essentially all internal surfaces of the cyclone that are subject to erosion are protected with a 2 cm layer of erosion-resistant lining. When installed and cured, most refractory linings are highly resistant to erosion. 

It is claimed that the cured materials may be used continuously in air up to 300°C and in oxygen-free environments to 400°C. The materials are of interest as heat- and corrosion-resistant coatings, for example in geothermal wells, high-temperature sodium and lithium batteries and high-temperature polymer- and metal-processing equipment. 

The ebonite compound before cure is a rather soft plastic mass which may be extruded, calendered and moulded on the simple equipment of the type that has been in use in the rubber industry for the last century. In the case of extruded and calendered products vulcanisation is carried out in an air or steam pan. There has been a progressive reduction in the cure times for ebonite mixes over the years from 4-5 hours down to 7-8 minutes. This has been brought about by considerable dilution of the reactive rubber and sulphur by inert fillers, by use of accelerators and an increase in cure temperatures up to 170-180°C. The valuable effect of ebonite dust in reducing the exotherm is shown graphically in Figure 30.3. 

Euran Furan resins are thermosetting polymers derived from furfuryl alcohol and Furfural. The cure must be carefully controlled to avoid the formation of blisters and delaminations. To obtain optimum strength and corrosion resistance, furan composites must undergo a postcure schedule at carefully selected temperatures depending upon the laminate thickness. Equipment made with furan resins exhibits excellent resistance to solvents and combinations of acids and solvents. These resins are not for use in strong oxidizing environments. 

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