Articles containing the keyword 'sahaus'

A material of 478 birch logs were measured. The horizontal diameter was on average larger than the vertical one, the difference increasing with the increasing diameter. The reason was supposed to be the effect of sweep and out-of-roundness of logs. The difference between the actual and nominal length increased with the increasing lengths, but decreased with increasing diameter.

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• Kärkkäinen, E-mail: mk@mm.unknown

The present paper presents studies on the influence of some relatively common defects of Scots pine logs in Northern Finland on both the sawing yield and on the quality of the sawn goods. The study was based on test sawing of 25 logs for each of the defects (upright limb, heart shake and various kinds of wounds and scars) at Karihaara sawmill. The yield was graded into grades used for export timber according to the system of the sawmill. The proportion of the different export grades (U/S), fifths, sixths and culls) were used as characteristics together with the ratio of raw-wood consumption expressed as cu.ft/std.

Upright limbs occurring in a piece of sawn timber was shown to lower its quality to fifth grade in 43.5%, to sixth grade in 46.8% and to the category of culls in 6.5% of all cases. Only 3.2% of the cases the piece remained in U/S-grades. The size of the upright limb was the most important factor lowering the quality and affecting the ratio of raw-wood consumption.

Heart shakes are relatively common defects in pine logs deriving from over-mature trees. The quality-decreasing influence on the sawing yield depends clearly on the length of the shake in the cross-section. The same characteristics also decreases the ratio of raw-wood consumption. In addition, twisting and star shakes are considerably more harmful than straight ones. If rot occurs in connection with shakes, the places marred by the shakes are only capable of yielding sixth-grade sawn goods or culls.

Scar encountered in logs affect the sawn yield and its quality to quite a varying degree, but these defects themselves may also vary considerably both in size and quality. The length of the scar is highly significant as a quality-decreasing factor. If, in addition, rot is encountered, the defect is of a severe nature.

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• Heiskanen, E-mail: vh@mm.unknown

The objectives of the paper were to find out structure of the sawing time when using field circular saws, influence of the different factors on the sawing time and its structure, average sawing time per unit of raw material and sawn goods, and the fundamentals for the creation of an equitable system for the determination of the basis of payment in sawing work. The observations of the time study were made on both a single log and a work period basis. The material was collected using four saws of different brands.

The results showed that the season when the work was done, and top diameter of the logs to be sawn affected the constant times included in the total sawing time and the time used for sawing of center pieces. While the tree species did not affect the constant times, the grade of the logs of different tree species did have effect, especially in winter sawing. The factors affecting the different phases of the work are described in detail. The length of sawing time was longer in the winter than in the summer. The preparatory jobs in sawing required in average 82 cmin per log, and the time increased with increasing top diameter. The actual sawing is the most time-consuming part of the work, it took in average 132 cmin. 

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• Granvik, E-mail: bg@mm.unknown

The investigation concerns with the strength of the eccentric growth accompanying formation of tension wood in silver birch  (Betula pendula Roth.) and downy birch (Betula pubescens Ehrh.), behaviour of wood in wood-working machines and its macroscopic characteristics, its microscopic and sub-microscopic structure, chemical composition, resistance against certain chemicals, physical properties, and the strength characteristics of wood.

The most detrimental properties of tension wood used in wood working industry are high longitudinal shrinkage, warping, twisting and checking. The wooliness of the cut is unwanted, for instance, in plywood and furniture. In pulp industry tension wood is better raw material than normal wood because it yields more and purer cellulose than normal wood. However, it has poorer strength properties.

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• Ollinmaa, E-mail: po@mm.unknown

The aim of the study was to find out the ratio of raw wood consumption and the quantity and quality of the sawing yield using circular saws. The unit of study was one single log, the Norway spruce logs were divided into two grades and Scots pine logs in three grades. The principal material of the study was collected in 1950-51 using four types of saws of type EKA-50. The data consisted of 1,690 logs.

On the basis of the material, the efficiency of centre-piece sawing was 63.9% of the technical volume. On the average, 32.1% was unsorted goods, 11.5% fifths, 19.1% sixths and 1.2% culls. For spruce, the efficiency was superior to pine, which means that the consumption of raw wood for preparation of one standard of sawn goods is smaller in spruce than in pine. The volume of side boards trimmed reached about 2% of the total log volume. The efficiency of sawing and the ratio of raw-wood consumption were calculated both on the basis of the estimated and actual volume of trimmed goods. The raw-wood consumption is particularly good in logs of small and large top-diameter.

Goods sawn with circular saw have a characteristic shape. They are thinner at the ends than in the middle parts, and the deviation from the correct measure is larger in the first than in the last end of the pieces. They are also wedge-shaped because of the first piece sawn is thinner than the second one. The deviation from the correct measure exceeded the allowance for shrinking in seasoning. The goods are often under sized even if surplus measure occurs. In goods sawn using frame saws, however, it was difficult to discover any deviation from the correct measure.

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• Granvik, E-mail: bg@mm.unknown