Blackhawk Millworks, Inc.

Transcription

1 Blackhawk Millworks, Inc. From the Forest To Your Home 14-Steps To Manufactured Lumber 2780 Dreibrodt Road San Marcos, TX Page 1

2 The use of wood as a construction material predates written history. The earliest evidence of wood construction comes from a site near Nice, France, where a series of post holes seems to indicate that a hut 20 ft. wide by 50 ft. long was built there 400,000 years ago using wood posts for support. The oldest wood construction found intact is located in northwest Germany, and was built about 7,300 years ago. By 500 B.C. iron axes, saws, and chisels were commonly used to cut and shape wood. The first reference to cutting wood in a saw mill, rather than using hand tools, comes from northern Europe and dates from about 375. The saw mill was powered by the flow of water. In North America, European colonists found vast forests of trees, and wood became the principal building material. The circular saw, which had been developed in England, was introduced in the United States in 1814 and was widely used in sawmills. A large-scale band saw was developed and patented by Jacob R. Hoffman in 1869 and replaced the circular saw for many sawmill operations. Lumber produced in early sawmills had varying dimensions depending on the customer's specific order or the mill's standard practice. Today, lumber pieces used in construction have standard dimensions and are divided into three categories, depending on the thickness of the piece. Lumber with nominal thicknesses of less than 2 inches are classified as boards. Those with nominal thicknesses of 2 inches but less than 5 inches are classified as dimension. Those with nominal thicknesses of 5 inches and greater are classified as timbers. The nominal widths of these pieces vary from 2-16 inches in 1 inch increments. Most rough-cut lumber pieces are dried and then finished, or surfaced, by running them through a planer to smooth all four sides. As a result, the actual dimensions are smaller than the nominal dimensions. For example, a standard two-by-four piece of dried, surfaced dimension lumber actually measures 1.5 inches by 3.5 inches. Pieces of lumber are not only surfaced, but also machined to produce a specific cross sectional shape and are classified as worked lumber or pattern lumber. Decorative molding, tongue-and-groove flooring, and shiplap siding are examples of pattern lumber. Today, processing wood products is a billion-dollar, worldwide industry. It not only produces construction lumber, but also plywood, fiberboard, paper, cardboard, turpentine, rosin, textiles, and a wide variety of industrial chemicals. Here are the 14 steps to manufacturing lumber: Felling 1. Selected trees in an area are visually inspected and marked as being ready to be cut down, or felled. If a road does not already exist in the area, one is cut and graded using bulldozers. If operations are expected to extend into the rainy season, the road may be graveled, and culverts may be installed across streams to prevent washouts. Page 2

3 2. Select tree felling is done with gasoline-powered chain saws. Two cuts are made near the base, one on each side, to control the direction the tree will fall. Once the tree is down, the limbs are trimmed off with chain saws, and the tree is cut into convenient lengths for transportation. 3. If the terrain is relatively level, diesel-powered tractors, called skidders, are used to drag the fallen tree sections to a cleared area for loading. If the terrain is steep, a self-propelled yarder is used. The yarder has a telescoping hydraulic tower that can be raised to a height of 110 ft. Guy wires support the tower, and cables are run from the top of the tower down the steep slopes to retrieve the felled trees. The tree sections, or logs, are then loaded on trucks using wheeled log loaders. 4. The trucks make their way down the graded road and onto public highways on their way to the lumber mill. Once at the mill, giant mobile unloaders grab the entire truck load in one bite and stack it in long piles, known as log decks. The decks are periodically sprayed with water to prevent the wood from drying out and shrinking. Debarking and Bucking 5. Logs are picked up from the log deck with rubber-tired loaders and are placed on a chain conveyor that brings them into the mill. In some cases, the outer bark of the log is removed, either with sharptoothed grinding wheels or with a jet of high-pressure water, while the log is slowly rotated about its long axis. The removed bark is pulverized and may be used as a fuel for the mill's furnaces or may be sold as decorative garden mulch. 6. The logs are carried into the mill on the chain conveyor, where they stop momentarily as a huge circular saw cuts them into predetermined lengths. This process is called bucking, and the saw is called a bucking saw. Headrig Sawing Large Logs 7. If the log has a diameter larger than 2-3 ft., it is tipped off the conveyor and clamped onto a moveable carriage that slides lengthwise on a set of rails. The carriage can position the log transversely relative to the rails and can also rotate the log 90 or 180 degrees about its length. Optical sensors scan the log and determine its diameter at each end, its length, and any visible defects. Based on this information, a computer then calculates a suggested cutting pattern to maximize the number of pieces of lumber obtainable from the log. 8. The headrig sawyer sits in an enclosed booth next to a large vertical band saw called the headrig saw. He reviews the suggested cutting pattern displayed on a television monitor, but relies more on his experience to make the series of cuts. The log is fed lengthwise through the vertical band saw. The first cut is made along the side closest to the operator and removes a piece of wood called a slab. The outer surface of the slab has the curvature of the original tree trunk, and this piece is usually discarded and ground to chips for use in paper pulp. Page 3

4 9. The carriage is returned to its original position, and the log is shifted sideways or rotated to make subsequent cuts. The headrig sawyer must constantly review the log for internal defects and modify the cutting pattern accordingly as each successive cut opens the log further. In general, thinner pieces destined to be made into boards are cut from the outer portion of the log where there are fewer knots. Thicker pieces for dimension lumber are cut next, while the center of the log yields stock for heavy timber pie. Bandsawing Small Logs 10. Smaller diameter logs are fed through a series of band saws that cut them into nominal 1 inch, 2 inch, or 4 inch thick pieces in one pass. Resawing 11. The large cut pieces from the headrig saw, called cants, are laid flat and moved by chain conveyor to multiple-blade band saws, where they are cut into the required widths and the outside edges are trimmed square. The pieces that were cut from smaller logs may also pass through multiple-blade band saws to cut them to width. If the pieces are small enough that they do not need further cutting, they may pass through a chipper, which grinds the uneven edges square. Drying or Seasoning 12. The cut and trimmed pieces of lumber are then moved to an area to be dried, or "seasoned." This is necessary to prevent decay and to permit the wood to shrink as it dries out. Timbers, because of their large dimensions, are difficult to thoroughly dry and are generally sold wet, or "green." Other lumber may be air dried or kiln dried, depending on the required moisture content of the finished piece. Air-dried lumber is stacked in a covered area with spacers between each piece to allow air to circulate. Air-dried woods generally contain about 20% moisture. Kiln-dried lumber is stacked in an enclosed area while F heated air is circulated through the stack. Kiln-dried woods generally contain less than 15% moisture and are often specified for interior floors, molding, and doors where minimal shrinkage is required. Planing 13. The dried pieces of lumber are passed through planers, where rotating cutting heads trim the pieces to their final dimensions, smooth all four surfaces, and round the edges. Grade Stamping and Banding 14. Each piece of lumber is visually or mechanically inspected and graded according to the amount of defects present. The grade is stamped on each piece, along with information about the moisture content, and a mill identification number. The lumber is then bundled according to the type of wood, Page 4

5 grade, and moisture content, and the bundle is secured with steel bands. The bundle is loaded on a truck or train and shipped to a lumber yard for resale to customers. This document was excerpted from How Products Are made ( 3/Lumber.html). You may want to read the complete article. Blackhawk Millworks, Inc Dreibrodt Road San Marcos, TX Website: doug@blackhawkmetalworks.com Phone: Page 5