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Hardv/ood Record — Veneer & Panel Section 



August 10, 1922 



British Standards for Aeroplane Plywood 



The standards which the British government insists upon in 

 plywood for aeroplane construction are described in the following 

 article, which appeared recently in The Timber Trades Journal 

 of London, England: 



"In view of the fact that only the most reliable plywood can 

 be used for aeroplane construction, the standard quality and tests 

 of the plywood used for this purpose should be a matter of general 

 interest to plywood merchants and manufacturers, the question 

 of the right composition of a reliable board being one of the first 

 to be considered in this connection. 



"It has been found that in order to obtain the maximum factor 

 of safety, the face veneers of boards used in aircraft construction 

 should be either birch, ash, mahogany, or American gum. In some 

 cases, as, for example, in the construction of sea-plane floats, all 

 three plies must be of these materials, though for general air- 

 craft construction purposes the centre ply of a three-ply board 

 may be made of either poplar, American whitewood, or alder. 



"With regard to the quality of the individual veneers, no 

 specially hard and fast rules are applied, it being understood that 

 only veneers falling under the generally accepted grading as be- 

 ing free from sap, dote, loose knots, and other serious defects, 

 should be used in the manufacture of first-class plywood. How- 

 ever, special and careful attention should be paid to this process 

 of manufacturing the boards, and any board w^hich is either 'not 

 flat,' or shows any bumps or blisters (that is, parts where the 

 cement has not properly connected the plies) cannot be accepted, 

 not even for the lowest quality, and overlaps, either in the inside 

 or outside veneers are equally considered as not permissible in 

 any plywood of higher grades. Gaps between joints or shakes in 

 the w^ood would also condemn a board. The finished board, suit- 

 able for aeroplane construction, and generally termed as being 

 of the first quality, after drying under the following atmospheric 

 conditions: — Temperature, 95 degs. to 1 I degs. C, and humidity 



40 per cent, to 60 per cent. should show a moisture content of 



from 1 8 per cent, to 8 per cent. 



"As regards the cement shearing strength, it is generally ac- 

 cepted that a board should withstand from 150 to 200 lbs. per 

 sq. in. 



"The most important tests, however, are those of the cement, 

 and it is here w^here great difficulties are generally experienced 

 by the manufacturers, A certain cement may be extremely suit- 

 able for a particular kind of wood, but may be thoroughly un- 

 reliable with a different kind, and tests have therefore to be 

 made, not only at the factory before producing the boards, but 

 also after a certain time when the boards have had a chance of 

 drying properly. In view of the importance and the difficulties 

 of testing the cementing of the boards, various experiments are 

 generally made, so as to test not only the properties of the cement 

 itself but also its effectiveness in the particular board. The ordi- 

 nary cement test may be either an exposure of a sample for 

 one month of saturated air at a temperature from 20 to 25 degs., 

 at the end of which period no sign of separation of the plies 

 should be apparent; or secondly, an exposure of the sample to 

 alternating dry and w^et air for one month, whereby a careful 

 record of the effect of this test is to be kept; or thirdly, an ex- 

 posure of the sample for two months to atmospheric influence, 

 w^hereby it has to be protected from the direct influence of rain. 

 In these latter cases only a very slight separation of the plies is 

 allowed at the end of the period. The most ordinary cement test 

 is, however, the stripping of the plies apart by means of a knife, 

 and observing as to whether the fibres of the separate plies adhere 

 to each other, or whether the plies separate easily without leaving 

 any trace of adhesion. This test, however, is only a layman s 

 test, and certainly does not enable the examiner to pass any opin- 

 ion on the merits or the deficiencies of any particular cement 

 under examination. 



"A very effective test is the peeling test. This is generally ef- 



fected w^ith a sample of about 6 in. square, which is boiled for 

 a period varying in accordance with its thickness — it being ac- 

 cepted that for boards made of veneer of a thickness of ^2 in. 

 three hours of boiling should be required, and for each additional 

 sV in. thickness of veneer two hours should be added. After hav- 

 ing boiled the sample all this time, it should be dried at 70 degs. 

 Cel., and should then show no appreciable signs of separation. 



"In order to appreciate the wonderful strength of a reliable 

 cement, the foUow^ing bending test explains the property of a 

 well-built plywood board better than any lengthy details. A 

 sample of plywood 1 2 in. x 2 ft. should bend cold at a thickness 

 of 116 in. to a 3 in. radius: one of rh in. to a 4 in. radius; one of 

 J/g in. to a 6 in. radius; one of li'j in. to an 8 in. radius; one of 

 jr: in. to a I in. radius; and one of I/4 in. to a I 2 in. radius; and 

 at that not show on either side any signs of splits, cracks, or other 

 fractures, and no separation of the plies. 



"The severity of these tests, and the fact that plywood coming 

 up to the quality of these tests can, and is being manufactured, 

 justifies the great belief that plywood manufacturers place in 

 the future of plywood. 



"These extraordinary high properties of plywood prove once 

 more that, provided suitable and good wood is being supplied for 

 the manufacture of the boards, no limit has yet been found to 

 the development and application of this wonderful material, both 

 iu the construction of aeroplanes as also in the domain of general 

 engineering." 



New Courses to Be Given at Forest Products 

 Laboratory 



Plans are being made by the U. S. Forest Service to expand the 

 instructional work of the Forest Products Laboratory at Madison, 

 Wisconsin, so as to benefit other w^ood using industries besides 

 those interested in kiln drying and boxing and crating. Beginning 

 September I 1, a new course in the Gluing of Wood w^ill be given, 

 and courses along other lines of w^ood utilization will probably be 

 added during the next 1 2 months. 



Three short courses will be given in September as follows: 

 The Kiln-drying of Wood September 1 1 to 22 



The Gluing of Wood September II to !6 



Boxing and Crating September 11 to 16 



The course in Kiln Drying has been given 27 times with a total 

 attendance of 292 men. The course in Boxing and Crating has 

 been given 16 times with a total attendance of 143 men. The 

 men who have taken these courses represented a large variety of 

 interests and came from all parts of the country and even foreign 

 countries. 



In the new course in gluing, which lasts one week, the follow- 

 ing subjects w^ill be covered: structure of various woods and how 

 i: affects gluing; prevention of shrinking, swelling, warping, and 

 cupping in boards or panels; effect of moisture in wood on glue 

 joint; selection and use of animal glues, vegetable glues, and 

 w^ater- resistant glues; principles of laying veneer and plyw^ood 

 construction; control of temperature, pressure, and assembly time 

 iti gluing; testing strength of glued joints; and analysis of defects 

 common in gluing. 



These courses are of a practical nature; they are for industrial 

 representatives and do not call for any educational requirements. 

 The purpose of the Forest Service in offering them is to help the 

 industries to get better results with more of the lumber they 

 manufacture or buy. in this way not only will less timber need 

 tc be cut but the profits resulting from efficient production will 

 b'; greater than those derived from present wasteful methods. 



Many firms who have sent representatives to the Forest Prod- 

 ucts Laboratory for a week or two of study have stated that they 

 were able to effect savings and improve the quality of their goods 

 to the value of thousands of dollars annually. 



