Cold cure moulding

The polyether triols are the most important class of polyether polyols and they are used in flexible PU foam fabrication. The majority of polyether triols used in flexible foams are copolymers of PO-EO. Random copolymers are used in continuous slabstock flexible foams and block copolymers (PO-EO), with terminal poly[EO] block, are used in moulded foams (hot moulding and cold cure moulding processes). 

PIPA polyols, in spite of some disadvantages (tendency to foam shrinkage, and scorching), are used successfully for continuous slabstock flexible PU foams and high resilience foams (cold cure moulding process). 

Moulded cushions tend to have slightly better fire retardancy and better resilience properties than slab-stock products. Hot-cure and, more recently, cold-cure moulding techniques have allowed better control of the side reactions (such as formation of isocyanurate and allophanate cross-links). One-shot processing with low-pressure dual-component dispensing equip-... 

Cold-curing foams use polyethers of somewhat higher molecular weight (-4500-6000) and which have a higher proportion of primary hydroxyls than are used for hot moulding. In addition the isocyanates used have a functionality greater than 2, this being achieved by the use of modified isocyanates. 

Cold cure silicone rubbers and available as pastes. These pastes are mixed with an organometallic catalyst and silicate and cured at room temperature. These are used as adhesives, and as encapsulating materials for electronic components. They are also used for textile coating and in moulds. 

Most of the silicone rubbers used in the food industry are based on polydimethyl vinyl silicone and these materials have very good high- and low-temperature properties. It is their high-temperature resistance that enables them to be used for seals and tubing, for example, in drinks vending machines up to 100 °C. Cold cured silicones are used as release coatings on items such as food transportation belts and for sweet moulds. 

PHD polyols are successfully used for high resilience flexible PU foams (made by the cold cure process), for continuous slabstock flexible PU foams and for elastomers obtained especially by reaction injection moulding (RIM) technology. 

The finished dry rubber and latex based rubber products can be vulcanized by several techniques depending on the type of rubber compound (dry rubber compound/latex compound), size of the finished product, and its shape and structure. Moulded rubber products are vulcanized by press curing using compression, transfer, or injection moulding presses. The vulcanization techniques other than moulding may be grouped into batch and continuous methods. The batch methods include the use of autoclaves, hot air/gas oven, and hot liquid/ water bath. Rubber products may be vulcanized at room temperature by cold curing either by immersion of rubber products in a carbon disulphide solution of sulphur chloride (SjCy, or by exposure to its vapour. 

Cold Press Moulding—A low pressure, low temperature process in which fibres are impregnated with a cold cure resin and then pressed between matched dies. 

Resin systems are generally, but not essentially, cold cure. They are mixed and then injected into the mould generally within seconds but injection may take 5-10 minutes for large complex shapes. They can be extremely reactive and consequently have very short gel and cure times. Low visccsity/high reactivity versions of polyester, phenolic resin and epoxy resin are the most commonly used. 

A low viscosity, fast cure, modified acrylic resin for RTM and cold-press moulding application. 

A filled, medium reactive, general purpose, thixotropic, orthophthalic resin offering a fast cure rate and good filler stability and designed for cold press moulding and RIM. 

Unaccelerated. Medium fire retardant. Also suitable for cold-press moulding when the cure... 

Manufacture was achieved by resin transfer moulding using cold cure catalyst. 

Figure 24.9. Effect of cure time on some properties of M-F mouldings. Cure temperature cellulose filled 295-308°F mineral filled 300-320°F O glass-filled material, asbestos-filled material, A cellulose-filled material (a) Cross-breaking strength (b) tensile strength (c) impact strength (d) impact strength (e) water absorption (rag), boiling water 30 min (f) cold water 24 h, 23°C ...

Retreading of tyres may be undertaken in a variety of ways. Unvulcanised material can be applied and then cured at 150-180 °C ( hot retreading), or prevulcanised tread can be applied at temperatures of around 100 °C ( cold retreading). Vulcanisation may take place with or without moulds, or in an autoclave. 

A pre-cured tread with pattern is prepared by moulding. A thin strip of unvulcanised cushion rubber compound is inserted between the casing and the tread rubber to form the bonding agent between the new and old components. The tread is then applied to the casing and consolidated by pressure. The cushion rubber is then vulcanised. This is also known as cold retreading . 

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