20 



HARDWOOD RECORD 



December 25, 1920 \ 



ment that in by far the majority of cases it will pay to erect an 

 isolated power plant, unless capital is limited or the plant be very 

 small. The power plant of any industrial institution is deserving of 

 the most careful thought and study on the part of the designing en- 

 gineer. Tlie almost uniform practice in the past, and in fact the too 

 prevalent custom today, is to treat the power plant as sort of a neces- 

 sary evil and install the cheapest equipment that money can buy. 

 The only excuse for such a procedure is the fact that most furniture 

 factories supply the large part of the fuel from waste and consequently 

 the owners feel that it is not economy to purchase good efficient 

 machinery. Witli the increasing cost of coal, however, this excuse, 

 if it may rightly be termed one, is disappearing and a well-designed 

 plant for the production of light, heat and power is coming to be 

 recognized as decidedly a paying investment. 



32. The first decision to be made in starting the power plant 

 design is the method of transmitting power to the various machines 

 in the factory. In by far the majority of cases, the most efficient 

 method of transmitting power from the prime mover to the princi- 

 pal machines in small and medium-sized plants is by means of shaft- 

 ing, pulleys, and belts. The principal machinery in a furniture fac- 

 tory is almost always in one department, the mill or machine room, 

 and consequently the larger portion of the machinery can be driven 

 by belts from one, or at most two, lines of shafting. Electric indi- 

 vidual or group driving of machinery is unquestionably the best 

 and most eocnomical where machinery is widely scattered, or where 

 some of the machinery is operated only part time, but where most 

 of the machinery may be arranged in one department and the ma- 

 jority of it is operated at all times, the initial expense and overall 

 efficiency of driving from line shafting take precedence over the elec- 

 tric drive. 



33. The location of the main lineshaft will depend on the arrange- 

 ment of the machine room or rooms. Where practically aU machin- 

 ery can be located on the main floor an excellent design is obtained 

 by incorporating a low basement in the building and placing the 

 main line shaft or shafts on concrete piers in this space. By using 

 wedge and lateral-adjustment bearings the shafting can be main- 

 tained in perfect alignment and many of the breakdowns incident to 

 poorly supported shafting will be avoided. This arrangement has 

 the additional advantage of removing all overhead shafting from the 

 machine room, the individual drives to machines coming up through 

 the floor, and it also admits of easy access to all bearings, pulleys, 

 and belts without the use of ladders, thus materially assisting in 

 proper attention being given to maintenance. Where it is necessary 

 to use ladders or scaffolding to make repairs to shafting and equip- 

 ment, it is but human nature to neglect this work until it becomes 

 unavoidable, consequently any arrangement which will make such 

 repairs and adjustments easy will be found profitable. 



34. If due to the arrangement and location of machinery it is 

 necessary to place machine rooms on two floors, the most logical 

 position for lineehafting is on the ceiling of the lower floor, for this 

 permits of driving machinery on both floors from the same lineshaft- 

 ing. In this case additional headroom .should be allowed on the lower 

 floor, 13 to 14 ft. in the clear being usually sufficient. Provision 

 should also be made in the design of the building for supporting the 

 main lineshafting, the joists being increased in size to not only carry 

 the additional load, but also to provide a structure as rigid and as 

 free from vibration as possible. A good method of designing the floor 

 structure of the building is to place the main girders or beams longi- 

 tudinally and the joists transversely, about 4 ft. apart. Every other 

 joist may then be increased in size to carry the lineshafting drop 

 hangers. This arrangement of joists also has the advantage that 

 when cutting holes for belt ways through the floor it will be unneces- 

 sary to cut the joists and thus weaken the floor structure. The only 

 objection to this arrangement of girders and joists is that it throws 

 the floor loads into the curtain walls between pilasters and thus 

 necessitates heavier lintels over window and door openings than 

 would be the case vrith girders running transversely and joists longi- 

 tudinally, as is the usual practice. 



35. In large plants with widely distributed machine rooms, or 

 where there are several isolated machines to be driven, the electric 



individual or group drive is practically the only means of transmit- 

 ting power efficiently and economically. In some plants a combina- 

 tion of lineshaft and electric drive may prove advantageous, but 

 each plant is a problem in itself, the decision being made upon 

 proper consideration of the various factors involved and no general 

 rules caji be laid down to govern such decision. In driving wood- 

 working machinery electrically it will generally be found the best 

 plan to arrange the machinery for driving purposes in groups, all of 

 each group operating for about the same period of each day. In this 

 way the initial expense for motors is kept to a minimum and also 

 each motor driving a group of machines is kept more uniformly loaded 

 to near its rating. Where certain machines are operated but inter- 

 mittently or require a comparatively large amount of power for 

 driving, then the individual motor driv.e will undoubtedly be found 

 the most satisfactory and economical. 



36. Upon deciding on the method of transmitting power to the 

 various machines the next step will be to select the proper type and 

 capacity of prime mover. The capacity may be determined by taking 

 a total of the power required to o))erate each machine, as furnished 

 by the manufacturers, assuming that there- will be periods during 

 \vhich all machinery will be in operation. This total will give the 

 "connected load," making no allowance for power lost in trans- 

 mission. 



37. The load factor in most furniture plants will average from 

 7.5 to 80 per cent of the connected load. An estimate must then be 

 made of the power consumed by power-transmission equipment, con- 

 sisting of shafting and belts or electric drives, and by adding the 

 connected load, corrected for load factor, plus an allowance for 

 mechanical efficiency of the prime mover, the indicated horsepower 

 capacity required to furnish the plant with power may be determined. 

 The electric load and lineshaft load should, of course, be kept sepa- 

 rate in order to determine the generating capacity required, also the 

 electric lighting should be laid out and proper, allowance be made 

 both in the generator and prime mover. Unless it is expected that 

 extensions to the plant will be made in a short time, the engine 

 should be so chosen that it will deliver the required indicated horse- 

 power when loaded to about 7.5 per cent of its rating. This will 

 allow a fair margin of growth to the plant before an additional power 

 unit is required, and at the same time the engine will be operating 

 under an economical load from the beginning. Having determined 

 the capacity the type of prime mover must next be decided upon, and 

 if part of the machinery is to be driven from lineshafting, then the 

 choice will be with some type of reciprocating engine. 



38. In all but the very largest woodworking plants the demand 

 for low-pressure steam for heating and drying purposes forms such 

 a considerable portion of the exhaust steam- available from the en- 

 gine and the waste from the plant makes up such a large part of the 

 full supply that it is uneconomical to operate condensing, at least 

 during the larger part of the year. As the scope of this paper is not 

 sufficiently broad to discuss all the factors effecting a decision to oper- 

 ate condensing at all periods of the year, it will be assumed that we 

 are treating of the small or medium-sized plant where it is seldom if 

 ever found economical to operate condensing, at least during the 

 heating season. 



39. The low-pressure steam requirements for dry kilns, heating, 

 etc., should be determined and a curve drawn showing the average 

 demand for low-pressure steam throughout the year. It is apparent 

 tliat the largest demand will be during the winter months at the 

 height of the heating season and will gradually taper off to a mini- 

 mum during the summer months. Assuming a steam consumption 

 of 26 or 27 lb. of steam per indicated horsepower per hour for the 

 ordinary Corliss type of engine and that 85 per cent of the exhaust 

 will be available for heating and drying purposes, a curve should 

 next be drawn showing the average available exhaust steam for the 

 various months of the year, and upon compai'ing the two curves it 

 will be seen at a glance during which periods of the year the heating 

 and drying demands exceed the exhaust from the engine, or vice 

 versa. 



(Covthiiteil in Jan. 10 issue) 



