Parallam Strand Lumber
Making big ones out of little ones occupies an important share of the wood products industry’s interest these days and is stirring waves with Parallam structural product for beams, headers and columns in lengths to 66ft. The product is produced from low grade fur veneers. Experiments are on to make use of pine veneer, aspen and even bamboo.
Parallam ? PSL ? is the name given to the process of Parallel Strand Lumber. It is the proprietary process of Mac Millan Bordell of Canada.
Parallam is made from narrow resin?coated veneer strips, upto 102 inches long, metered into a trough where they move into a continuous microwave? heated press. The 12inches x 15 inches pressed billet is then resawn, cross cut into desired dimensions and sanded. It sounds simple, but Mac Millan Bloedel has taken around twenty years to develop it and spent over $ 50 million .
Lower grades ? fishtals, veneer with large knots or holes, badly split sheets ? make good raw material. The roundup is the finest fibre in an old tree, much better than juvenile wood. The fishtail, castaways by the plywood mills are fully utilized here. Infact about 95% of the fibre from low quality veneer that is used in making Parallam is thrown away by other wood based mills. It benefits the ecology, as there is absolutely no waste. The plywood industry is benefited, because they can sell off their castaways and get a good price for it.
Bacock type jet dryers, such as are used for high value furniture grade veneers, take the veneer down to 3?4% moisture content. The veneer is held flat between 1 inch steel mesh. Both types of dryers are used : direct gas? fired and heated thermal fluid transfers from wood waste burning.
Low grade veneer is difficult to dry in conventional roller type dryers where it can clog the dryer and damage the veneer. Veneer is automatically marked in a moisture sort as it emerges from the dryers and then is pulled and stacked. Up to this point, the process is strictly plywood technology. From hereon its new.
The dry veneer is clipped into 1/2 inch wide strips by rotary clippers developed and engineered specially. All knots, sawdust and short strands are automatically eliminated. Plywood phenol formaldehyde resin, modified only slightly for the specialized cure rate, is applied in a proprietary system to faces, edges and ends of strips. The glued strips meter down into the trough across width of the forming line, as close to one at a time as possible, onto a continuous steel belt. The strips are parallel, lengthwise, to the mat. Metering continues the full length of the 70 ft forming through, building upto full depth where the mat enters the press.
The matte is squeezed down through the Kusters continuous belt press which compresses the mat on all four sides down to its 12 inches x 15 inches in size. The pressure is difficult to measure, but is somewhere in the 600 PSI neighbourhood. Microwave ports, formed by ceramic blocks, come in to the side of the press. Microwave power operating at 915 megahertz cures the resin. A conventional kitchen microwave oven operates at 2,450 megahertz.
The uniform heating ? in the 120o C range at the core ? is one of the reasons for the product’s good dimensional properties with low springbok. The uniform complete curing also explains the product’s lack of formaldehyde emissions. The system creates about 10% compression, working to a final density of 41 lb. per cu.ft. shipping weight. Small variations in raw wood density are adjusted for in the control system.
A 12 inch x 15 inches billet has an average of 3600 elements in cross section. Comparing with the much fewer elements in cross?section of conventional glued?panel, Parallam gains tremendously in product properties. The homogenizing properties of the material is being done thoroughly.
The billet is cross?cut and resawn through a 5 feet CAE linebar single?saw resawn into desired dimensions for the market or stock. A twin resaw is also installed. Each piece is tested for density after resawing. All four faces are smoothed on a 16 inch AEM sander and the edges are beveled in one pass. The product can be manufactured in thicknesses of 1 3/4, 3 1/2, 5 1/4, and 7 inches. Depths are : 7 1/4, 9 1/2, 11 1/4, 11 1/2, 11 7/8, 12, 12 1/4 and 14 inches. Depths of 16 and 18 inches are also possible. The standard maximum length of Parallam is 66 feet. Bigger lengths are also possible.
The entire process is automatic and computer controlled. At the maximum the workforce required is around 107 persons. In manufacturing Parallam, wood is the most expensive ingredient trailed by labour and resin. Sensors and feedback controls are installed throughout the system so that critical process judgment can be made and quality control be achieved.
Parallam can be used anywhere that highly engineered products are required. The co?efficient variation of less than 10% comparing this with good stress graded lumber where one is lucky if one gets 25 % to 30%. Lumber suffers badly in large sizes. You can’t get the reliability of the strength, therefore, you must degrade the strength of every beam one uses.
Garage door headers, picture window headers. cantilevered structures, balcony overhangs and vaulted ceiling beams are some of the other uses recommended. Beams or purloins in warehouses are other candidates.
Parallam design stresses, in PSL, are :
Flexural stress : 2900
Tension Parallel to Grain : 2400
Compression Parallel to Grain : 2900
Compression Perpendicular to grain : 600
Horizontal Sheer : 290
Modulus of Elasticity : 200000
- Parallam is also ideally suited for out-houses, exhibition pavilions and for interiors.
- Parallam is perhaps the most important invention in the timber trade ever since Mason discovered Masonite (Hardboard or Fibreboard as it is internationally known) over three decades ago.
The two individuals most closely connected with its invention are Mark Churchland and Derek Barnes, who have already been honoured by Sweden’s King Carl XVI Gustav. They have been awarded a cash prize of One million Swedish Kronor with citations. Barnes was born in Manchester, England and worked with MacMillan Bodell.
© 2012, AIDEC World. All rights reserved.