FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1943
1943 - 1860.PDF
IOO FLIGHT JULY 22ND, 1943 PLYWOOD AND PLASTICS and relatively high pressures, the resulting bond being stable and permanent. Heat and pressure required with the thermo-plastic resins, however, are not of the same magnitude. Thermo-setting resins experience a "chemical change under heat in which water is given off. It may be compared for analogy to cement, inasmuch as once it has set by the condensation of this water, it can never be made to liquefy or flux again. Thermo-plastic resins do not experience any chemical change, and a plywood panel fabricated in its flat form can later be treated by a source of heat and bent to a desired shape over a form or mould, and when reset will retain its new shape. Phenol-formaldehyde and urea-formaldehyde resins are of the thermo-setting variety. Thermo-plastic materials may be formed and then reformed many ti^aes into definite shapes by the simultaneous application of heat and pres- sure, providing sufficient plasticising materials be incor- porated to impart the proper flow, and the material remains plastic so long as the requisite temperature is main- tained. Vinylite resins belong to this class, and have been TABLE I.—PLYWOOD ADHESIVES AND CHARACTERISTICS 1 Adhesive Source Form supplied ... ' Cold or hot press... Added ingredients of mix. Preparations for use LHe of mixture — Spreading andhandling equip- ment. Spread, pounds per1,000 sq. ft—dry basis. Pressing temp. •-• Pressing time Moisture contentallowed in veneers. Ury bond strength. Wet bond strength. Water resistance ... Mould resistance ... Heat and fire resist-ance. Moisture trans-mission. Exterior durability. Relative cost Special features ... 2 Blood Albumen Dried beef blood. Powder, flake. Hot press. Water, alkalis, para-formaldehyde, hy- drated lime, albu-minous adhesives, etc Mixed cold. 2 hours to severaldays. Roller spreader. 10-33. 180-250° F. 3 min. for hot press;varies with thick- ness of panel. Over-night cold press. 2-3% for faces, 6%"or less for cores and crossbands. Medium. Medium. Medium. Poor to good. Poor. Marked. Fair to good. Medium to high. Especially suitablefor low temp. Hot pressing, most dur-able of adhesives except resins. 3 Animal Hides and bonesof animals cooked in water, evapo-rated, jellied, dried. Powder, pearlflake, shreds. Cold. Water, some pre-servatives. Soaked in cold orwarm water fol- lowed by cooking. Extended if pre-served. Heater, rollerspreader. 25-35. Cold, with warmcauls. 2-18 hours. As Col. 2. Very high. None. Poor. Poor. Poor. Marked. None. High. Relatively expen-sive. Easy to use. 4 Vegetable Starch Vegetable carbo-hydrate. Base mainly cassava(tapioca) also po- tato flour. Flour. Cold. Water, and alkalis(sodium hydrox- ide). Generally mixedhot. Many days. Roller spreader. 20-30. Ordinary room temp. 4-18 hours. As Ool. 2. Medium. None. Poor. Poor. Poor. Marked. None. Very tow. Inexpensive ad-hesive. 5 Casein Precipitated frommilk. Powder. Mainly cold, somehot. Water, CH2O, pre-servatives, and alkalis (lime andsodinm salt). Mixed cold. 2 hours to 2 days(preferably short). Roller spreader. 12-35. Ordinary roomtemp, for cold press,180-250° F.hot press. 2-18 hours forcold press. 3 min. fee thin panelshot press. As CoL 2. Medium. Poor to medium. Poor to good. Generally poor. Poor. Marked. Poor. AsCeJ.2. Superior to vege-table gtae for wet strength. 6 Urea- Formaldehyde Restns Urea—CH2O con-densation. Powder and liquid. Mainly hot, somecold. Water accelera-tors, wheat and rye flours. Some mixed withwater only; others accelera-tor ar.d flour added. Up to 1 day. Roller spreader. 16-25. 210-240° F. 3 min. for thinpanels hot press. 8 hours for coldpress. Wide range—2 to100% under special conditions. High. Medium to high. Cold water : good.Hot water : poor. High. Moderate. Medium. Good. Resin a!one high,•with fiHers low. Very economicalwhen mixed with Soar. Provides ahighly water re- sistant bond sethot or cold. 7 Phenol- Formaldehyde Resins Phenol—CH20 con-densation. Lumps, powder,liquid and film. Mainly hot, somecold. Alcohol and water,flour fillers. Dry film — nil.Liquid resin—nil. Solid resin dis-solved in alcohol and water. Cata-lyst added for cold pressing, warmsetting and fast hot pressing. Extended periodfor hot press mate- rial. Several hoursfor cold press resin. Liquids in rollerspreader film used as nixn. 25-40 for cold pressresin. 10-14 for hot press liquid.11-12 or film. Room temp, to320° F. 3-6 min. for thinpanels hot press. Overnight for coldpress. 2-14% for liquidresin. For film, cores and cross-band s 5-10%. faces 2-6%. Medium to high. Excellent in bothhot and cold water. Excellent. Excellent. High. Low. Excellent. High. By far the mostdurable bond: re- sists all forms o£deterioration. 8 ThermoptasSc Resins f Chiefly plasticised poH-vinyl butyr-aldehyde. Resin solution inorganic solvent. Hot press. None, thin -withsolvent if neces- sary. None. Indefinite. Not re-active. Roller spreader. 6-14. 230-300° F. Few minutes toseveral hours— must be cooled inpress or j&onld. 3-12%- Low to medmm. Medium. Medtom. HSgh--iM]* affected. Pocc. Low. Poor to good. High. Flows at elevatedtemp., must be coaled in press.AVffl reseal. Plies retain flexibility.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
