УДК 811.11 + 674.05

О.И. Костюк, аспирант (БГТУ), А.А. Гришкевич, кандидат технических наук, доцент (БГТУ); А. М. Романова, кандидат педагогических наук, старший преподаватель (БГТУ)

TECHOLOGY OF MECHANICAL MACHINING FOR WOOD GRINDING

The article is dedicated to wood and slabby material grinding. Theoretical base of wood grinding and polishing instrument is described. Also the authors give some peculiarities of grinding with flat zone of the contact, with band wheel (cylindrical), with free tape, and with pressed (narrow and broad) ironing. In work one can find explanation of nature of the construction of polishing instrument, material abrasive, and ways of abrasive grain building.

Introduction. The most important problems of woodworking industry are the electric power economy, using rational power-saving mode of the cutting; increasing capacity, quality and accuracy processed to product; rational use of wood and wood slabby materials.

At present for practical furniture and joiner's-building production a big amount of various tools and ways milling and grinding is broadly. The main attention is paid to constructive improvement of the tool models, building rational technological flow on their base providing mode of their application. Annually enterprises of woodworking industry increase output of wood slabby materials.

The Main Part. Grinding means abrasive processing focusing on cutting detail surface to obtain flat detail with high smoothness. In woodworking industry they distinguish band, cylinder and disc grinding for giving veneered details high smoothness and calibration.

The polishing sandpaper is considered to be a multiplied instrument with a large number cutting elements, like abrasive grains with cutting edge. Such abrasive materials as fused alumina and carbide silicon, best suitable for graining, are bounded with each other and with base of paper, fabrics, fibres or combinations these material by means of bestial ligament gluing, car amide or resin phenol.

There are grinding process grade parameters for sandpaper of the chosen granularity: grinded surface pressure, direction of grinding powder concerning the grain flow, the cutting speed, feed fade, and wood contact length.

Figure 1 – The cutting pattern by abrasive grain

Each abrasive grain acts upon wood with elementary tangent and normal power (see Formula 1). The amount of these elementary powers forms total tangent power Fxi and normal power Fzi (see Figure 1).

As such grinding process has no stable conditions of cutting, tangent power Fx is considered to be a functional power of friction:

(1)

where A stands for an the contact area: A=blk, m²; and l_k stands for the contact length of the polishing sandpaper; b stands for a width of the processed stocking up; and C stands for a the traction factor of abrasives with wood [1].

The q pressure in the contact zone of the polishing instrument with the processed material influences the amount of active cutting grains and the instrument capacity.

The increase of pressure affects little the average thickness of cut shaving and roughness of the polishing surface. Up to test data, increasing pressure 50 times causes increase of the jaggies depth as much as 5-14 per cent. As practice and additional study show, at finishing grinding the best surface quality is reached under grinding along filaments (the rake corner being φс = 0º). The rake corner 15º is normal at final grinding of surfaces for a high-quality decorating. At φс= 15º, as while processing shield recoated in fir tree or in rhombus, grinding up to reception of the surfaces with microroughnesses by height not more than 6-8 micrometers is required, that helps to make grain traces imperceptible. Rough grinding of frame joiner's-building articles with longitudinal and transverse bars is recommended at φс= 45º. Grinding with the rake angle 90º i.e. across filaments (processing the parquet boards) is possible.

At band grinding there is optimum length contact of the sandpaper with wood, measured on direction. The sandpaper grain can cut and carry away from the product surface only that amount of the shaving, which fits in intergrading space. At overweening length of the contact shaving filles all free space between grains and forces the sandpaper back from product. This process causes slowing down of wood removal with its further stopping. The optimum length of the contact does not depend on grinding velocity, little depends on pressure and wood type, but depends on the sandpaper grain [2].The correlation of domestic and foreign polishing materials State standards is given in the table.

The correlation of domestic and foreign polishing materials State standards

(grain-oxide of black silicon)

Standard FEPA	State Standard 3647-1980	Grain size, micrometers	Standard FEPA	State Standard 3647-1980	Grain size, micrometers
R 12	№ 160	1815	R 220	№ 6	68
R 16	№ 125	1324	R 240	№ 5 и 4	58,5
R 20	№ 100	1000	R 260	№ М 63	52,2
R 22	№ 80	800	R 280	№М 50	46,2
R 24	№ 63	764	R 320	№ М 40	40,5
R 30	-	642	R 360	№ М 28	35,0
R 36	№ 50	538	R 400	№ М 20	18,3
R 40	№ 40	425	R 500	№ М 14	15,3
R 50	№ 32	336	R 600	№ М 10	12,6
R 60	№ 25	269	R 800	№ М 7	8,4
R 80	№ 20	201	R 1200	№ М 5	-
R 100	№ 16	162	R 1500	№ М 3	-
R 120	№ 12	125	R 2000	№ М 2	-
R 150	№ 10	100	R 2500	№ М 1	-
R 180	№ 8	82

As for grinding, it is difficult to foresee the polishing surface geometry as abrasive grains distribution is irregular and occasional in the instrument. In practice, the expected jaggies depth at the polished surfaces, micrometers, is formula (2) evaluated:

mkm (2)

where stand for grains size of the main granularity fraction (mm); stand for wood density (g/sm³); plus stand for strong sandpaper, and minus stand for soft sandpaper.

On the wide belts machine tool for surface leveling and clean processing local jaggies are deleted and its roughness is reduce (figure 2).

Figure 2 - the functional scheme of wide belts polishing tool for leveling final grinding [4].

The greater successe in mechanical processing of wood and grinding wood slabby material has been achieved by different Belarusian and foreign scientists V. V .Amalickiy, N.V. Makovskiy, V. A. Lyubchenko, A.A. Pizhurin, and etc.

The Conclusion. In the XXI century, community expansion plans are more fully developed and include the engineering of utility service so that careful consideration is given to meeting future projected Timber supply needs. Advanced planning provides the opportunity to design the pipe network as a grid with a series of loops to avoid dead ends. The objective is to produce a circulating system capable of supplying high quality Timber to all areas while at the same time permitting any section to be isolated for maintenance, repair, or decontamination without interrupting service to all other areas. There is need in qualification of physico-mechanical regularities of the power system expense for surface grinding and providing high capacity of abrasive instrument working.

List of references

1. Bershadskiy, A.L. The cutting wood/ A.L. Bershadskiy, A.I. Flowering. Minsk : - Minsk, High school, 1975;

2. Amalickiy, V.V. Equipment to branches: textbook/ V.V. Amalickiy, Vit. V. Amalickiy. - M. : GOU VPO MGUL, 2006. - 584 s. : silt

3. V.I. Lyubchenko.The cutting wood and wood material/ V.I. Lyubchenko: -. Moscow, Timber industry, 1986.

4. Rough A.E. Derevorezhuschie instruments/ A.E. Grube. -M.: Timber prom-ti,1971.