DEVICE FOR COMPARING THE SHARPENABILITY OF PENCILS

V. V. Komin, I. I. Chashchin

(Presented by the scientific seminar of the Department of General Chemical Technology)

According to the existing standards, complex and diverse requirements are imposed on wood intended for the manufacture of pencils [1]. Various methods of upgrading make it possible to obtain wood of different softness, and this, in turn, requires the search for some methods of comparing samples by resistance to cutting.

No devices have yet been created that would make it possible to carry out such a comparison. The fixture proposed by N. F. Gusev [2], in our opinion, does not meet the necessary requirements, since with its aid it is possible to determine the forces of planing wood only along the fiber, which is, of course, insufficient for evaluating pencil quality.

The device proposed by us, the schematic of which is shown in Fig. 1, makes it possible to compare the sharpenability of pencils made from wood prepared in different ways and thereby to characterize qualitatively the various methods of treating cedar wood.

The device for comparing the sharpenability of pencils consists of the following:

Fig. 1. Schematic of the device for carrying out a comparison of the sharpenability properties of pencils: 1 — pencil, 2 — feed mechanism, 3 — weight, 4 — sharpening head, 5 — large gear, 6 — small gear, 7 — revolution counter, 8 — flexible shaft, 9 — stop, 10 — adjusting screw, 11 — capron thread, 12 — handle, 13 — pulley, 14 — knife.

Fig. 2. Graph comparing the sharpenability of pencils made from heartwood of Siberian cedar with Czechoslovak pencils. (The number of revolutions of the sharpening head when sharpening Czechoslovak pencils is indicated by the dashed line.)

Pencil 1, by means of the feed mechanism 2 and weight 3, is fed with a constant force into the sharpening head 4, which is set into rotary motion by the system of gears 5 and 6. The number of revolutions of the sharpening head is determined by the revolution counter 7, connected by the flexible shaft 8 to the large gear 5. The sharpening depth is set by stop 9 and adjusting screw 10. As soon as the pencil is sharpened to the specified depth, the stop (9) stops gear 5 by means of a ratchet mechanism.

The number of revolutions required for sharpening is determined three times for each pencil. The pencil is sharpened from both end faces, and then cut in the middle and one of the halves is sharpened. From the values obtained in this way, the arithmetic mean is taken, which makes it possible to somewhat reduce the influence of the nonuniformity of the wood on the results of the determination.

The acid treatment method consists of the following: heartwood pencil slats of Siberian cedar are placed in an aqueous solution containing 0.2% nitric and 0.5% tartaric acids, held for varying times under a vacuum of 85–90%, heated in the solution at atmospheric pressure for four hours at a temperature of 80°C and, finally, subjected to heat treatment at a temperature of 150°C for three hours. From slats treated in this way, graphite pencils are made, which are then used to determine sharpenability.

On the basis of the determinations carried out, it may be concluded that pencils approaching Czechoslovak pencils in sharpenability are obtained from heartwood slats treated under vacuum for four hours.

Conclusions

1. The proposed device makes it possible to compare the sharpenability of pencils made from wood treated by various methods.

2. The accuracy of the method can be varied by changing the magnitude of the load.

Literature

1. N. N. Chashin, V. V. Kobyan, L. M. Kovaleva. Treatment of wood in pencil manufacture. (This collection.)

2. N. F. Gusev. A new method of treating wood for pencils. Woodworking Industry, 11, p. 16, 1957.