" " wisno wood furniture finishing: Swelling and shrinking of the wood

Friday, August 12, 2011

Swelling and shrinking of the wood

 sunken joint caused by wood movement

Wood is a hygroscopic material, he will absorb or release his moisture content according to the environment condition. In the open condition the wood moisture content will change to reach the equilibrium with its environment air humidity. You can see the graph of the wood m.c. vs the humidity in : moisture content of the wood
When he release his moisture the wood will shrink, while when he absorbs water from the air, and his moisture content is rising then he will swell. The swelling and shrinkage of the wood can cause problems in the wood products such as: crack, warp, uneven surfaces and other construction problems. 


 wood swelling and shrinking varies depend to the grain direction

The shrinkage and swelling of timber is more complicated since it varies from one wood to another. The wood behavior, is dependent on the structure of molecules and cells in the wood. While the cell structure depends on the type of wood and how the wood grew. Therefore the shrinkage and the swelling is depend on the type of wood, the origin of wood and also the grain direction. The amount of shrinkage and swelling changes with a given moisture content is about twice as great as the flat-grain surface surface the edge grain. A wet piece of wood will of wood shrinks more on one direction the another to distort itself.
This different in shrinkage tendencies mean when lumber of different moisture content, species or different grain direction is glued together side by side, some pieces has risk to swell or shrink more then the other. This phenomenon is resulting on some wood construction problems such as: crack, swell, open joints, warping, defects, etc.. In the bare core for the plywood, the wood pieces with uneven volume will result on the "sunken cores" or "wash board" appearance that all the make uneven surface for the plywood veneer.
Although there may be some variation upon the origin of wood, but the shrinkage and swelling of some wood species record is already recode. The amount of volume changes will help us to understand the wood behavior and find the best way to handle it. 


The amount of wood shrinkage of some species from green to dry condition ( mc 12%)
                                               

Wood species                               Volume   Edge grain (radial)      Flat grain ( tangential)
Alder, red                                         12,6                4,4                               7,3
Ash, black                                        15,2                 5,0                              7,8
Ash, white                                        12,5                 4,6                              7,1
Ash, white, 2nd grow                      14,0                 5,3                             8,7
Bassswood                                     15,8                 6,6                             9,3
Beech                                              16,2                 4,8                            10,6
Birch, sweet, black, cherry            15,0                 6,3                              7,6
Birch, yellow, gray, silver                 16,8                7,4                              9,0
Buckeye                                            12,0               3,5                              7,8
Butternut                                           10,2                3,3                              6,1
Cherry, black                                    11,5                 3,7                              7,1
Cherry, wild red                                  12,8               2,8                            10,3
Chesnut                                               11,6               3,4                              6,7
Cottonwood                                         14,1              3,9                              9,2
Cucumber                                           13,6              5,2                              8,8
Elm, rock                                             14,1              4,8                              8,1
Elm, slippery                                       13,8              4,9                              8,9
Elm, white or Ameican                       14,4              4,2                              9,5
Gum, black                                          13,9              4,4                              7,7
Gum, blue                                            22,5              7,6                            15,3
Gum, cotton,                                       12,5               4,2                              7,6
Gum, red, sweet                                 15,0               5,2                              9,9
Gum, sap (sapwood or redgum)      15,0               5,2                               9,9
Hickory, shelbaark, shagbark, pignut 17,9            7,4                             11,4
Hickory, pecan                                   13,6               4,9                               8,9
Holly, American                                   16,2              4,5                               9,5
Locust, black                                          9,8              4,4                               6,9
Locust, honey                                        10,8            4,2                               6,6
Maple, oregon, bigleaf,boradleaf          11,6          3,7                               7,1
Maple, red, swamp, scarlet, soft           12,0          3,0                               7,2
Maple, sugar rock, hard,                        14,5          4,8                               9,2
Mahogany, true, Central America              -            3,4                               4,9
Mahogany, African                                       -            4,1                               5,8
Oak, ref, yellow, Spanish, California    14,2           4,2                               8,5
Oak, white,bur, chesnut, post                15,3           5,1                               9,3
Pecan                                                     13,6            4,9                               8,9
Poplar, yellow                                    11,4                 4,1                               6,9
Sassafras                                          10,3                 4,0                               6,2
Sycamore                                          14,2                 5,1                               7,6
Walnut, clack, American                   11,3                 5,2                              7,1
Willow, black                                      13,8                 2,6                             7,8
Willow, western black                        13,8                2,9                              9,0
Softwood, western red                        8,1                 2,5                              5,1
Cedar, white                                        7,0                  2,1                              4,9
Cypress,                                             10,7                3,8                              6,0
Cypress, yellow                                 7,9                   1,9                              5,0
Fir, balsam                                         10,8                2,8                              6,6
Fir, Douglas                                       11,6                4,3                              7,0
Fir, white                                            10,2                 3,4                              7,0
Hemlock, eastern                              10,4                3,0                             6,4
Hemlock, western                             11,6                 4,5                              7,9
Larch, western                                   13,2                4,2                             8,1
Pine, Cubar, longleaf, western white   11,9            5,0                             7,4
Pine, shortleaf                                         12,6           5,1                             5,7
Pine, sugar                                        8,1                   2,5                            5,7
Spruce, Engelman                           10,4                 3,4                            6,6
Spruce, red                                       11,8                 3,8                            7,8
Spruce, Sitka                                    11,2                 4,5                            7,4
Spruce, white                                   14,8                  3,7                           7,3

                                   

0 comments:

Post a Comment