Hot air resistance

Oil, fuel and grease resistance Good processing characteristics Variety of curing systems Good hot air resistance Long term 90°C 40 days 120°C 3 days 150°C Low permanent set Good abrasion resistance Low gas permeability... 

As its C-C doubie bond content increases, its hot-air resistance decreases. Figure 5.241. The foiiowing order of increasing aging resistance can be proposed semi-hydrated grade, sulfur crosslinked < semi-hydrated grade, peroxide crosslinked < fully hydrated grade, peroxide crosslinked [697],... 

Creating EVM with optimum hot-air resistance requires either carbon black or light-colored, non-active fillers. The best resistance is obtained using acetylene carbon black. Powdery talc, chalk, or kaolin grades are appropriate for light-colored mixtures [697]. 

Silicone rubber exhibits excellent hot-air resistance. At 180 °C, it can be used in long-term operation and with the appropriate formulation, its rubber elasticity can be maintained over several 1000 h even at 250 °C. In the short term, e.g., under the influence of heat shock, silicone rubber withstands temperatures of 300 to 400 C [13]. 

Sulfur crosslinking produces relatively unstable polysulfidic crosslinking points that facilitate elasticity loss. Quinone dioxime crosslinking produces more stable networks. However, crosslinking created by resin-vulcanization is extremely resistant it achieves the best hot-air resistance. Resin-vulcanized IIR grades are indispensable for applications involving continuous use in air at 150 °C [697]. 

Ethylene-propylene diene rubber exhibits very good hot-air resistance. If the temperature peaks do not exceed 135 °C, a sulfur/acceleration system can be used in most cases. Above 135 °C, peroxide crosslinking is required. The relatively best hot-air resistance is achieved by using a low-molecular type (so that no or very little free oil has to be added) and by using high ethylene content [697]. 

Complete saturation of the polymer backbone as shown above imparts much better resistance to ozone attack, extended service temperature range, and improved hot air resistance, compared to compounds based on conventional NBR. In other words, compounds based on HNBR are much more resistant to heat than those based on regular NBR elastomers. HNBR compounds have better thermo-oxidative aging resistance, qualifying them for automotive under the hood applications. 

Good quality steel is used and electrozinc is preferred for washing machines. Steel is pretreated with iron phosphate for economy electrozinc with a fine crystal zinc phosphate. No primer is normally used 25-40/im of finish is applied direct to metal. The required properties are best obtained with a thermosetting acrylic or polyester/melamine-formaldehyde finish. Self-reactive acrylics are usually preferred these resins contain about 15 Vo 7V-butoxymethyl acrylamide (CH2=CH —CO —NH —CHj—O —C4H,) monomer and cure in a manner similar to butylated melamine-formaldehyde resins. Resistance or anti-corrosive properties may be upgraded by the inclusion of small amounts of epoxy resin. Application is usually by electrostatic spray application from disc or bell. Shapes are complex enough to require convected hot-air curing. Schedules of 20 min at 150-175°C are... 

Thermal enhancement of volatilization.19 21 Volatility of contaminants increases greatly with temperature, so several techniques have been developed to raise soil temperature, including the injection of hot air or steam, electrical resistance heating, and radio frequency heating. 

In the production of wet process hardboards and serai-hardboards the press-dried boards are usually tempered or "cured" in hot air to increase their water resistance, dimensional stability, strenght and stiffness. A curing for 5 hours or more in hot air of 165°C is common. Higher curing temperatures reduce the period needed for each batch and thus increase the capacity of the heat treatment chamber, but they increase the auto-ignition risks. 

A molecular sieve bed was used to purify continuously the fire-resistant hydraulic fluid (a triaryl phosphate) in a large hydraulic press. Periodically the sieve bed was regenerated by treatment with steam, and then purified air at 205°C. After 9 years of uneventful operation, the bed ignited on admission of hot air. The fuel source was traced to the accumulation of organic residues (phenols or cresols ) on the sieve which were not removed by the steam/air treatment. 

The most suitable wires for this purpose are pure lead, indium and gold. The Pb and In wires should be between 0.1 and 0.4 mm thick, the Au ca. 0.05 to 0.1 mm. Under presure, these metals are deformed plastically and adapt themselves to the contour of the joint. There will momentarily be the greatest pressure at the point at which the ends cross over and thus the greatest deformation will occur there until a uniform thickness is attained. If such a joint resists dismantling, it can usually be freed by heating it gently with a brush flame or hot air gun. 

The sidewall compound is compounded to protect the ply and must possess resistance to weathering, ozone, abrasion, and tearing while providing excellent flex fatigue resistance. The innerliner compound must provide good air-permeation resistance and resist moist/hot air aging. The inside of a hot... 

There are six ways to heat materials in the lab open flame, steam, thermal radiation, electromagnetic bombardment (microwave ovens) passive electrical resistance (such as hot air guns), and direct electrical resistance (such as hot plates). All of these heating methods (except thermal radiation) use conduction to heat the container holding the material to make the material hot. 

The interface between the hot air and the dry layer of fabric provides negligible resistance to the water vapor leaving the interior of the fabric. 

Flame-retardant additives are often used to make polymers more fire resistant. Already in ancient times flame-retardants were applied during the siege of Piraeus in 83BC wooden assault towers were treated with an alum solution in 1638 Sabatini s book "The risk of fire in theatres" was published, where the preparation of flame-retardant coulisses is described and Montgolfier impregnated his hot-air balloons with alum ("Technische Winkler Prins Encyclopedic", Deel 2, Elsevier, Amsterdam, 1976, in Dutch). 

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