1、MILITARY SPECIFICATION SANDWICH CONSTRUCTION CORE MATERIAL, BALSA WOOD This specification is mandatory for use by all Depart- ments and Agencies of the Department of Defense. 1. SCOPE 1.1 Scope - This specification covers one grade of balsa for use as a core material in the preparation of sandwich s
2、heets and shapes for aircraft. 2. APPLICABLE DOCUMENTS * 2.1 for bids or request for proposal, form a part of the specification to the extent specified he rein. The following documents of the issue in effect on date of invitation SPECIFICATION Miiitary MIL-W-6 110 Wood, Determination of Moisture Con
3、tent of STANDARDS Military MILSTD-105 Sampling Procedures and Tables for inspection by Attributes MIL-STD-129 Marking for Shipment and Storage (Copies of specifications, standards, drawings, and publications required by suppliers in connection with specific procurement functions should be obtained f
4、rom the procuring activity or as directed by the contracting officer.) * 2.2 Other publications - The following document forms a part of this specification to the extent specified herein. Unless otherwise indicated, the issue in effect on date of invitation for bids or request for proposal shall app
5、ly. U Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I MIL-S-7998A 55 m 9999906 0209983 9 m MlLS-7998A U. S. Department of Agriculture Agricultural Handbook No. 188 (Applications for copies should be addressed to: Superintendent of Documents, U. S,
6、Government Printing Office, Washington, D. C. 20360.) 3. REQUIREMEPUTS 3.1 Maerial - 3.1.1 Only balsa (ochroma lagopus) is acceptable material. * 3.1.2 The baisa furnished under this specification shall have been kiln- dried at the source in accordance with Agricultural Handbook No, 188, to safeguar
7、d against infection and decay. 3.1.3 Condition - The balsa may be rough-cut, except that both ends shall be, smooth enough to permit classification of the transverse area. The condition of the lateral faces of the baisa shall be such that the grain direction may be ascer- tained. * 3.2 Dimensions -
8、When dimensions are not specified, the following shall apply: (a) Length may be random but not less than 2 feet. (b) Width may be random but not less than 2 inches. (c) Thickness may be random but not less than 1.5 inches. Basis of measurement - The basis of measurement shall be in 3.2.1 board-foot
9、units. 3.3 Moisture content - Balsa shall have been kiln-dried to contain not more than 15 nor less than 5 percent moisture (based on oven-dry weight) in any one piece. Any lot of balsa submitted for inspection in accordance with this speci- fication shall have an average moisture content of not mor
10、e than 12 percent, and shaii be stored subsequently under conditions suitable for maintaining this moisture content. * 3.4 Density - The density of each piece shall be not less than 7 nor more than 14 pounds per cubic foot, oven-dry weight, and shall be within the density range specified in the cont
11、ract or order. 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-L MIL-S-777BA 55 W 777770b 020998Lt O M MI L- S- 7 59 8A 1:9 and 1:20 1:lO and 1:16 1:li and 1:14 1:12 and 1:12 l 3 I Local grain deviations greater than 1 in 8, caused by permissible d
12、efects, are accept- able when not over 1 inch in length. * 3.7 Defects - Balsa shall show no evidence of inferior quality, including damage caused by external agents, which is not removable in the ordinary process of smooth finishing. This includes kiln-drying defects, decay, excessive brashness, co
13、mpression failures, oil or grease, partial or included pith, water heart, unsound or loose knots, worm holes, and wane in the form of bark or lack of wood and bark. However, the following are acceptable: (a) Scattered pinworm holes, burls, twig-specs, birdsf-eye and p inknot clusters. (b) Occasional
14、 mineral stains and mild blue stain not associated with decay. (c) Checksor splits nowiderthan 1/32 inchoneachlateral surface. Length shall be no greater than 40 percent of the thickness of the board. (d) Sound, tight knots will be permitted provided the average diameter of individual knots does not
15、 exceed 1/2 inch and adjacent knots are not doser than 2 inches. 3.8 Workmanship - The workmanship, including kiln-drying shall be in accordance with high-grade manufacturing practice for balsa. 4. QUALITY ASSURANCE PROVISIONS * 4.1 Responsibility for inspection - Unless otherwise specified in the c
16、ontract or purchase order, the supplier is responsible for the performance of all I /- 0 _-. . Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-* MIL-S-777A 55 m 777770b 0207785 2 m MILS-199 8A inspection requirements as specified herein. Except as ot
17、herwise specified in the contract or order, the supplier may use his-own or any other facilities suitable for the performance of the inspection requirements specified herein, unless disapproved by the Government. The Government reserves the right to perform any of the inspec- tions set forth in the
18、specification where such inspections are deemed necessary to assure supplies and services conform to prescribed requirements. 4.1.1 Classification of tests - All the tests required for the testing of balsa material are classified as quality conformance tests. 4.2 Sampling - 4.2.1 - Lot - The unit fo
19、r sampling is a bundle. Unless otherwise speci- fied in the contract or order, for purposes of sampling, the lot shall consist of all the bundles of balsa of the same finish offered for delivery at one time. 4.2.2 Sampling plans - Unless otherwise specified, sampling plans and procedures in the dete
20、rmination of the acceptability of products submitted by a supplier shall be in accordance with the provisions set forth in MILSTD-105. 4.2.2.1 Visual and dimensional examination - A random sample of balsa wood shall be selected from each lot in accordance with the requirements of MILSTD-105, Inspect
21、ion Level If and Acceptance Quality Level 2.5 percent defec- tive for visual and dimensional examination and packaging and packing requirements. 4.2.2.2 Sampling for individual tests - Each piece of balsa wood shall be examined to determine conformance with this specification. 4.3 Moisture content -
22、 The moisture content shall be determined in accordance with MIL-W-6 110. 4.3.1 Density - The average density of each plank shall be determined by weight, moisture content (4.3) and volume measurements. Accuracy within reasonable limits commensurate with the rough condition of the balsa shall be ob
23、serve d. 4.3.2 Presence of low-density (corcho) material - Determination of the presence of low-density (corcho) material shall be made by visual observation of the smooth transverse cut ends. The end fibers shall be ruptured with a narrow, thin, flat, blunt instrument as, for example, the point of
24、a dull knife blade, held in a position approximately perpendicular to the cut section and dragged across the section in a radial direction. Low-density balsa will rupture easily under slight pressure, resulting in the abrupt tearing out of small chunks of wood, with a con- sequent “pithy1? or ?cork-
25、like“ appearance of the ruptured surface. Balsa of accept- able density will resist rupture when tested as indicated. If subjected to sufficient U 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-S-777A 55 W 777770b 02077b 4 MIL-S-799 8A pressur
26、e, fibers in the higher density material will bend or possibly tear loose, but will present a characteristically different appearance than in the case of low-density wood. 4.3.3 Grain - The slope of the grain shall be determined by drawing a sharply pointed steel scribe in the direction in which the
27、 grain runs, and measuring the slope of the grain as compared with the edges of the piece. The slope of grain is usually expressed by the ratio between a 1-inch deviation of the grain from the edge or axis of a piece and the distance within which this deviation occurs. 4.4 Acceptance stamp - Each pi
28、ece of balsa accepted shall be marked with the number of this specification. 4.5 Rejection - Balsa wood that fails to meet any of the requirements of this specification shall be rejected. 5. PREPARATION FOR DELIVERY 5.1 Packing - Unless otherwise specified, the balsa shall be bundled with a minimum
29、of two flat steel straps for lengths of 2 to 5 feet, and a minimum of three flat steel straps for lengths over 5 feet, to prevent breaking of the bundles during shipment. Steel strapping shall be O. 500 inch by O. 020 inch or heavier. The edges of the bundles shall be protected against cutting by th
30、e strapping, by the use of adequate edge protectors or by wooden slats placed across the top and bottom of the bundle beneath the strapping. Exposed faces of dressed balsa must be adequately protected by layers of rough lumber placed on the top and bottom of the bundle. The gross weight shall not ex
31、ceed approximately 200 pounds. Bundles shall consist of pieces of the same standard thickness and lengths as specified under the particular contract or order. 5.1.1 Protection - The balsa shall be protected against condensation drip during shipment, if shipment is made under such conditions that con
32、densation is probable, Nails shall not be driven into any of the material comprising the shipment. 5.1.2 Storage - Before processing, balsa wood shall be stored under conditions suitable for maintaining an average moisture content of not less than 8 nor more than 12 percent in each piece. 5.2 Markin
33、g and labeling - 5.2.1 Bundle - Each bundle shall be marked with the following information: BALSA (FOR SANDWICH CONSTRUCTION CORE) Density range Spec if icat ion MILS- 79 9 8A 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-S-7778A 55 m 77777Ob
34、 0207787 b m MI L- S- 7 9 9 8A Stock No. Contract or Order No. . Quantity Kame of Manufac tuer Name of Contractor (if different from manufacturer) CAUTION: Store balsa under condit ions suitable for maintaining an average moisture content of not more than 12 percent in the wood. 5.2.2 In addition to
35、 the above, marking shali conform to the applicable requirements as specified in MILSTD-129. 6. NOTES 6.1 Intended use - This material is intended for use as the core com- ponent of composite sandwich constructions used in aircraft. * 6.2 Ordering data - Requisitions, contracts, and orders should st
36、ate the length, width, and thickness desired, and the acceptable density range. 6.3 Definitions - (a) Birds-eye: A grain irregularity consisting of a small central spot with wood fibers arranged about it in the form of an ellipse so as to give the appearance of an eye. (b) Decay: A disintegration of
37、 wood substance caused by wood- destroying fungi. (c) Pinworm hole: Hole not over 1/16 inch in diameter. (d) Corcho or low-density balsa: Balsa wood having a density of less than O. 08 (based on weight and volume when oven-dry) as applied to any portion of the wood, rather than to the average or bul
38、k density of a piece. Such low-density wood is charac- terized by a relatively large number of short, large-diameter, thin-walled fibers, and comparatively few long, thick-walled, small-diameter fibers. (e) Stain: Discoloration of fiber caused by fungi, bacteria, min- erals, or mold not appreciably
39、weakening the wood, if) Kiln-drying defects: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-S-7978A 55 7779906 0209988 8 = MI LS- 799 8A (1) Collapse: Collapse of cellular structure in wood caused by poor kiln-drying practice. Extensive areas ma
40、y be affected giving appearance of great dimensional shrinkage. (2) Honeycombing: Internal checking of wood structure caused by poor kiln-drying practice. (3) Casehardening: A condition in lumber in which unequal stresses are set up by improper moisture gradient caused by poor kiln-drying practice.
41、(4) Kiln burn: Usually discernible in balsa by presence of light brown surface stain which is caused by use of exces- sively high temperatures during kiln-drying. (5) Crook, warp, and twist: Condition in which the faces of lumber deviate from a relatively flat, planar surface. Check: Void caused by
42、separation of fibers in a radial plane along the grain. Shake: Void caused by partial or complete separation of fibers along the grain within or between two growth rings. Compression failure: Walked buckling or creases across the grain produced by endwise compression of fibers beyond their elastic l
43、imit. They are discernible as fine, wavy lines at right angles to grain direction. Blue stain: Stain produced by fungi that feed on contents of cells and do not cause appreciable cell wall destruction or breakdown of wood structure. Mineral stain: Stain produced by deposition of mineral sub- stances
44、 in cellular structure. (m) Water heart: Water heart is a wet zone of pyramidal or conical shape, usually limited to the lower 5 to 8 feet of butt logs. (n) Brashness: A brittle wood which breaks with a clean instead of a splintery fracture and without warning. This is sometimes caused by too severe
45、 temperatures and is associated with a darkening in color. I U 7 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- MIL-S-799A 55 M 9999906 0209989 T M MILS-7998A 6.4 Changes from previous issue - The margins of this specification are marked with an as
46、terisk to indicate wheye changes (additions, modifications, corrections, deletions) from the previous issue were made. This was done as a convenience only and the mlernment assumes no liability whatsoever for any inac- curacies in these notations. Bidders and codractors are cautioned to evaluate the
47、 requirements of this document based on the entire content irrespective of the mar- ginal notations and relationship to the last previous issue. Custodians : Army - ME Navy - AS Air Force - 11 Review activities: Navy - AS Air Force - 11 DSA - CS Preparing activity: (Project No. 5680-0045) Navy - AS
48、Review/user information is current as of the date of this document. For future coordination of changes to this document, draft circulation should be based on the information in the current Federal Supply Classification Listing of DOD Standardiza- tion Documents. 8 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
