Tuesday, February 28, 2012

Chemical Process Simplification: Improving Productivity and Sustainability - Book Information


Author Girish Malhotra

Published by John Wiley, 2010

282 pages

____________________

Table of Contents

Preface xiii 
1 Process Simplification: Basic Guidelines 1 
2 Process Solutions 9 
3 Commonalities of Businesses 53 
4 Laboratory Process Development 77 
5 Mass and Heat Balance 95 
6 Reaction Kinetics 111 
7 Physical Properties 123 
8 Combination of Heat, Mass Balance, and Physical Properties 135 
9 Cross-Fertilization of Technologies 159 
10 Scale-up to Commercialization 171 
Appendix A: Ideas and Observations from the Author 189 
Appendix B: Related Articles by the Author 231 
Index 279 



_____________________


Read the first Chapter

Monday, February 27, 2012

PLIBEL - A Method for Identification of Ergonomic Hazards

 
PLIBEL is a questionairre developed by Kristina Kemmlert for identification of musculoskeletal stress factors which may have injurious effects on operators or workmen. The check list examines issues related to five body regions.
 
1. Neck, shoulders, upper part of the back
2. Elbows, forearms, hands
3. Feet
4. Knees and hips
5. Low back
 
The questionairre has 17 items with some items having sub-items.
 
For some more details and references of Kemmlert's articles
 
 
For a filled checklist (Table B-6 and Table B-11) along with other types of evaluations for shear Operators)
 

Product Performance Improvement Technology Developments



LG Appliance Technology Improvements in products

Saturday, February 25, 2012

Motion-Economy Device Design - Important Devices



These devices improve the efficiency of manual operations.

Important Motion-Economy Devices


Watson and Wise, industrial engineers of Mine Safety Appliances Company mentioned the following as worthy of mention in a list of important motion-economy devices.

1. Holding, positioning, and assembly fixtures

Stops
Quick-acting clamps
Ball-joint or swivel fixtures
Hinged joints
Air-cylinder devices
Rotary fixture

2. Hoppers and motion-economy bins

3. Chutes and other drop-delivery methods

4. Removable table tops for planned workplaces

5. Foot pedals for

Holding
Release
Assembly

6. Special devices for indirect–labor operations.




Stops

A stop is a device for locating material at some predetermined position so that work can be performed while it is so located.

Quick-acting Clamps

These clams provide an efficient method of holding parts in positions for a wide variety of operations.

Ball-joint or Swivel Fixtures

This has a work table attached to a ball joint. In many assembly operations, work needs to be performed on the sub assemblies and main assembly at various angles and positions. A swivel or ball-joint may be used by the fitter or assembler to mount the assembly on it and enable the operator turn the fixture at will at any position at any time and use his both hands for working.

Hinged Fixtures


This fixture allows the operator to work one side of the part for some time and then turn over the part using the hinge and then work on the other side.

Air-Cylinder Devices


Air cylinders are used in machining, forming, and assembly operations. They are available in a wide range of sizes and types, and engineers can use them ingeniously for many applications.

Air cylinders are also used instead of arbor presses, foot presses, or bench-type punch presses for performing a wide variety of operations such holding, swaging, upsetting, riveting, and forming.

Rotary-Assembly Fixtures


In these fixtures there is a rotating table on which number of work pieces are mounted and each turn of the table brings a work piece to the operator. The operator completes his job and turns the table so that the next work piece comes to him. Another helper can now remove the finished work piece and load a new job.

Hopper and Motion-Economy Bins


A hopper is a storage device for either raw material or a component of an assembly, so designed that it delivers the material t be used at a selected point within the normal grasp area of the operator.

Chutes and Other Drop Delivery Methods


Chutes and drop delivery methods facilitate deliver of the finished work piece to the next conveyor belt or a storage bin.

Removable Table Tops


They provide specially fitted assembly table tops for two or three different assemblies that an operator may be working in a day. They can be removed and kept in a rack and the different top can be put on the work bench.

Foot Pedals


The use of foot-operated mechanisms provides an economical method of holding, releasing, or assembling in various types of operations.



References


J.P. Watson and D.N. Wise, “Motion-Economy-Device Design”, in Industrial Engineering Handbook, Second Edition, H.B. Maynard (Editor-in-Chief), McGraw-Hill, pp. 2-87  to 2-103.
__________________________________________________________________________



Originally posted in http://knol.google.com/k/ motion-economy-device-design-important-devices Knol No. 68

Energy Efficiency - An International Movement - Are IEs Participating?




International Energy Agency


Energy efficiency offers a powerful and cost-effective tool for achieving a sustainable energy future. Improvements in energy efficiency can reduce the need for investment in energy infrastructure, cut fuel costs, increase competitiveness and improve consumer welfare. Environmental benefits can also be achieved by the reduction of greenhouse gases emissions and local air pollution. Energy security can also profit from improved energy efficiency by decreasing the reliance on imported fossil fuels. For these reasons, energy efficiency was one of six broad focus areas of IEA's G8 Gleneagles Programme. The IEA has published 25 policy recommendations for promoting energy efficiency that were updated and endorsed by IEA ministers in 2011. If implemented globally it is estimated that global CO2 emissions could be reduced by 7.6 gigatonnes by 2030.

The IEA promotes energy efficiency policy and technology in buildings, appliances, transport and industry, as well as end-use applications such as lighting. Our analysis identifies best-practice, highlighting the possibilities for energy efficiency improvements and policy approaches to realise the full potential of energy efficiency for our Member countries.

http://www.iea.org/subjectqueries/keyresult.asp?keyword_id=4122 (Accessed on 26.2.2012)
IEA Energy Efficiency Home Page: http://www.iea.org/efficiency/index.asp


European Commission

Reducing energy consumption and eliminating energy wastage are among the main goals of the European Union (EU). EU support for improving energy efficiency will prove decisive for competitiveness, security of supply and for meeting the commitments on climate change made under the Kyoto Protocol. There is significant potential for reducing consumption, especially in energy-intensive sectors such as construction, manufacturing, energy conversion and transport. At the end of 2006, the EU pledged to cut its annual consumption of primary energy by 20% by 2020. To achieve this goal, it is working to mobilise public opinion, decision-makers and market operators and to set minimum energy efficiency standards and rules on labelling for products, services and infrastructure.

http://ec.europa.eu/energy/efficiency/index_en.htm (Accessed on 26.2.2012)


US Department of Energy - Energy Efficiency and Renewable Energy - Web page

India - Bureau of Energy Efficiency

Design a crankshaft for a vehicle Tavera Cheverolet engine and elaborate manufacturing process for same

 

Engine specifications of Chevrolet Tavera Car  

Engine Type

2.5L Direct Injection Turbo Diesel

Displacement (cc)

2499

Max. Output Ps/rpm

80 / 3900 (Approx.60KW@3900rpm )

Max. Torque kgm/rpm

19 / 1800

Bore Diameter(D)

93mm

Stroke length(L)

92mm

Compression Ratio(r)

18.5 : 1

Fuel Tank Capacity (liter)

55

No. of Valves/OHC

8

 

Table-1 Specifications of Engine


Source: www.chevrolet.co.इन

Crankshaft Nomenclature

 


1.  


DESIGN CONSIDERATIONS


Parameter

Theoretical Relation

Dimension in mm

Cylinder bore diameter

D

93.00

Cylinder centre distance

1.20 D

111.6

Big-end journals diameter

0.65 D

60.45

Main-end journal diameter

0.75D

69.75≈70

Big-end journal width

0.35 D

32.55

Main-end journal width

0.40 D

37.20

Web thickness

0.25 D

23.25

Fillet radius of journal and webs

0.04 D

3.72

Table-2 Theoretical relations

 

 

 Materials

              Crankshafts materials should be readily shaped, machined and heat-treated, and have adequate strength, toughness, hardness, and high fatigue strength. The crankshaft is manufactured from steel either by forging or casting. The main bearing and connecting rod bearing liners are made of Babbitt, a tin and lead alloy.

               Forged crankshafts are stronger than the cast crankshafts, but are more expensive. Forged crankshafts are made from SAE 1045 or similar type steel. Forging makes a very dense, tough shaft with a grain running parallel to the principal stress direction. Crankshafts are cast in steel, modular iron or malleable iron. The major advantage of the casting process is that crankshaft material and machining costs are reduced because the crankshaft may be made close to the required shape and size including counterweights. Cast crankshafts can handle loads from all directions as the metal grain structure is uniform and random throughout.

            Counterweights on cast crankshafts are slightly larger than counterweights on a forged crankshafts because the cast metal is less dense therefore somewhat lighter. Generally automobile crankshafts were forged in past to have all the desirable properties. However, with the evolution of the nodular cast irons and improvements in foundry techniques, cast crankshafts are now preferred for moderate loads. Only for heavy duty applications forged shafts are favored. The selection of crankshaft materials and heat treatments for various applications are as follows.

The crankshafts are subjected to shock and fatigue loads. Thus material of the crankshaft should be tough and fatigue resistant. The crankshafts are generally made of carbon steel, special steel or special cast iron.

Industrial engines: Crankshafts are commonly made from carbon steel such as 40 C 8, 55 C 8 and 60 C 4

Transport engines: Manganese steel such as 20 Mn 2, 27 Mn 2 and 37 Mn 2 are generally used for the making of crankshaft.

Aero engines: Nickel chromium steel such as 35 Ni 1 Cr 60 and 40 Ni 2 Cr 1 Mo 28 are extensively used for the crankshaft.

The crankshaft is subjected to shock and fatigue loads. So, the material should be tough and fatigue resistant. Commonly used materials for crankshaft are alloy steels, special steels or special cast iron. SAE 1541, 1548, 4340, 4310, VANARD 925 are some of the materials generally used.

Material Selection

 

Material chosen for crankshaft manufacturing is SAE 1045

Chemical proportion

C

Si

Mn

S

P

Fe

0.45

0.21

0.74

Max. 0.05

Max. 0.4

Balance

Table-3 Chemical composition of Material

Mechanical Properties

Yield Strength

(Mpa)

430

Tensile Strength (Mpa)

781

Elongation

17%

Reduction of Area

37%

Density

7.85 g/cc

Poisson Ratio

0.29                                       0.29

Hardness

179BHN

Shear Modulas

80Gpa

Youngs modulas

205Gpa

Table-4 Mechanical properties of Material

 


DESIGN CALCULATIONS

Assumption: Let us assume,

mech = Mechanical efficiency = 0.80

mech =        

BP=Brake power (KW) i.e. Maximum power

IP= Indicated power in KW

IP = 60/0.8 = 75KW

IP =P(i)\times L\times A\times n\times K\div 60000  

 

Where,

Pi=Indicated mean effective pressure

L=Stroke length

D=Bore diameter

K= No. of cylinders

n = N/2 for 4-stroke

N=Speed in rpm

Pi =  IP\times 60000\div L\times n\times K\times A

Pi =      (75000 x 60000) / [ 92 x ᴨ/4 x 93²  x  (3900/2) x 4 ]

Pi =      0.93 Mpa

 

At the TDC of the piston, the volume will be reduced by the compression. At this moment, the maximum pressure inside the cylinder will be,

                        Max. Pressure = B.M.E.P x Compression ratio

                                                 = 0.93 x 18.5

                                                 = 17.205 MPa

 

Now, this value of B.M.E.P acts on the piston head, and the whole force is transmitted to the crankpin through the connecting rod. This force is the most critical in the design of the crankshaft and the design in done on the basis of the above mentioned force.

To find the force exerted on the crankpin by the piston:

Piston force, F (kN)    =   cylinder bore area (mm2) x B.M.E.P

                        F          = 116.87 kN

Piston force will act at the middle of the crankpin, and it will be balanced by the reactions from the bearings at either side of the crankpin. Let the reactions be R1 and R2.

Considering the crankpin as a simply supported beam, we will see that



R1 + R2 = F     and     R1 = R2

Therefore, we get that             R1 = R2 = F/2 = 58.435 kN

Maximum bending moment (M) on the crank pin is given by M = R1 × b

            Where, b is the distance from the centre of the bearing to the centre of connecting rod

Assuming b = 1.2 x D = 111.6 i.e. b = 112mm.

Also, we know that 


From the above equation, we get that

 


Where,

                        d = diameter of the crankpin

 = max. bending stress of the material of the crankshaft with suitable factor of safety (350Mpa )

Equating the values of M in the above equations, we can get the value of the crankpin diameter d.

                                   

                                            d  = 58 mm

 

Length of the crankpin ( Lc)   = F* D/p

  

            Where, P = maximum permissible stress on the bearing, 50MPa,

                                    Lc         =  116870/58*60

                                           Lc = 40 mm

 

Crank web thickness is given by 0.25D, i.e. = 0.25 x 93 = 23.25 mm

 

 

Design of the main journal

The main journal diameter is usually given by 0.75D, where D is the bore diameter. In this case the value of main journal diameter will be 69.75

Now, we have to check if this diameter is sufficient to withstand the torque on the main journal due to the crank. For this, we need to find the thrust (FQ) on the connecting rod at the time of maximum torque.

Assuming that the torque is maximum when the connecting rod is at 35o (ɵ) with the line of stroke, and the pressure inside the cylinder at this point is 5MPa,

 

           

 

=          33.965 kN

 

The tangential component of this force will cause the torque on the main journal. This tangential component    FT                = FQ x cos 35o,

 

                                                = 27.822kN

 

Now, the torque acting will be given by FT  x r, where r is the crank radius, and is taken as 0.5 times the stroke.

Torque, Ts         = 27.822 x 0.045

                                                = 1252 Nm.

 

Now, we know that to design the diameter for a given torque, we use

d = 36.45mm

Where  is the maximum shear stress acting, which is taken as 175 MPa.

So, as per the above equation, the diameter of the main journal is obtained as 36.45 mm, which is much lesser than 5 mm, i.e. the design is safe and we can use the main journal diameter as 69.75 mm.

 

DIMENSIONS CALCUALTED:

Required design parameter

Dimension

Crank pin diameter (d)

58mm

Length of crank pin (Lc)

40mm

Table-5 Required dimensions

Manufacturing Process Chart


Manufacturing of Crankshaft

Usually, there are two kinds of process to produce large-scale crankshafts. One method is to cast crankshafts with nodular cast iron, which has advantages of short production cycle and low cost. The weak point using this process is low intensity and bad toughness of the materials. So this process is only suitable for the low load engines. Another process is to forge the crankshaft with the low alloy steel, which has advantages of high intensity and good toughness. We will use forging for this particular crankshaft.

 

Forging:

It is manufacturing process where metal is pressed, pounded or squeezed under great pressure into high strength parts known as forgings. Heated metal to be shaped is placed on a mold. Pressure is applied to the metal with the help of a press or hammer and due to this impact the malleable metal conforms to the die cavity shape.

 

·         Crankshaft is locally heated where web to be formed. Then axial press is used for formation of webs.                                                               

·         Sets of hydraulic presses are used for the formation crankpin journals and webs.

·         This method of forging gives continuous and parallel grain flow. This kind of grain flow increases the fatigue strength of crankshaft.


A)  Heat Treatment Of Crankshaft:

 Heat treatment is done to improve the machinability and to reduce the residual stresses. The typical heat-treating process for carbon-steel alloys is first to transform the structure of the rough-machined part into the face-centered-cubic austenite crystalline structure (‘austenite’) by heating the part in an oven until the temperature throughout the part stabilizes in the neighborhood of 1550°F to 1650°F (depending on the specific material). Next, the part is removed from the heating oven and rapidly cooled ("quenched") to extract heat from the part at a rate sufficient to transform a large percentage of the austenitic structure into fine-grained martensite.                                                                                                       

 

 

 

Crankshaft Machining:

Crankshaft machining contains operations like Turning, Facing, Centering, trimming, Web milling , crankpin milling , drilling of holes, deburring , rough grinding, finished grinding, threading ,super finishing etc.

1) Modern CNCs are used for the crankshaft machining if they produced in mass.

2) Some of the machines used for different operations are listed below

a)  SPM (Special Purpose Machines) :

 Facing, Centering, Crank web milling, journal milling, crankpin milling

Crank Journal Lapping, Crankpin Lapping, Super finishing

b) HMC (Horizontal machining Centre):

Journal Grinding, Main Journal Grinding, Threading

 

Heat Treatment Nitriding:

There are three common types of hardening processes used on steel crankshafts, and they are induction hardening, tuftriding, and nitriding.

Nitriding is a chemical hardening process in which the part is heated in a furnace, the oxygen is vacuumed out, and nitrogen is introduced which penetrates the entire surface. The depth of hardness is dependent upon the time the crankshaft is exposed to the gas. Typically, a nitrided crankshaft will have a hardness depth of about .010 - .030. The part gains a high-strength, high hardness surface with high wear resistance, and greatly improved fatigue performance due to both the high strength of the case and the residual compressive stress. Nitriding is a low heat process compared to Tuftriding, but it shares the advantage of avoiding the introduction of localized stress zones as in induction hardening.

 

REFERENCES

www.chevrolet.co.in

www.autoindia.com

www.steel-tube.com

www.the-crankshaft.info

Textbook “Design of Machine Elements” By Gupta and R.S. Khurmi

Team Members:

  1. Gajanan Gambhire (35)

  2. Anoop Singh Rajput (18)

  3. Ankit Jain (16)

  4. Adarsh Malu (05)

  5. Deepak Dhanotiya (32)



Originally published in Knol under creative commons license http://knol.google.com/k/anoop-singh-rajput/design-a-crankshaft-for-a-vehicle/3ddjl5ukgxdn4/3 by Anoop Singh Rajput as an assignment in my class

M.S. in Industrial Engineering - Online Course - LTU IE Online

Lawrence Technological University Michigan

MSIE Online course page

Online Master of Engineering Management Course Page

Saturday, February 18, 2012

Online Articles, presentations and Videos - Introduction to IE



Articles
Motion and Time Study - A Paper (1954)
Work measurement

Ergonomic Aspects of Biomechanics, Erwin R. Tichauer

Underground Workstation Design Principles - NIOSH Guidebook

Safety Instructions
Preventing Injuries and Deaths of Workers Who Operate or Work Near Forklifts



Reports

REPAIR TIME STANDARDS FOR TRANSIT VEHICLES, 2002 has a detailed flow process chart

Reducing Flow Time in Aircraft Manufacturing, 1990-91 project, MIT, Jackson Chao, Stephen C. Graves

Presentations

IE Methods (A presentation by JPC - PDF format)

Method Study (pdf format)




Videos
Easier way (General Motors Video clip 12.4 minutes)

Thesis

HUMAN FACTORS IN THE DESIGN AND OPERATION OF HANDWHEEL CONTROLS USED IN A DYNAMIC MANUAL TASK
by LARRY BERNARD JORDAN, B. E. S., A  MS THESIS IN  INDUSTRIAL ENGINEERING, 1969
http://etd.lib.ttu.edu/theses/available/etd-05122009-31295004438676/unrestricted/31295004438676.pdf

Originally posted in Knol

http://knol.google.com/k/narayana-rao/online-articles-presentations-and/2utb2lsm2k7a/ 2291

Variables of Motion Related to the Operator - Description by Frank Gilbreth

Frank Gilbreth in his book Motion Study (1911) discussed variable that are to be studied in motion study. He identified a group of variable as variables related to motion.

VARIABLES OF THE MOTION


Gilrbreth commented that discussion of variables of the motion by him only shows that each vari-
able is a necessary factor in making motions standard.  He left  to the universities and to properly created and  equipped bureaus of the national government the task of  reducing motion study to an exact science.

ACCELERATION

In considering acceleration of a motion as a variable, issues of interest are: 
1. The amount of acceleration that it is possible or economical to obtain.
2. The means by which the acceleration can be obtained.
3. The effect of the acceleration on
a. Economy in time required to make the motion.
b. Economy in time required for rest to overcome the fatigue of having made the motion.
Examples. i. Laying brick on a wall from a floor, from the height of the floor level up to three feet eight
inches high above the floor, can be done with greatest speed  when the brick to be picked up are each maintained at a height of one foot three inches, plus two-thirds the height that the wall is higher than the level of t he floor on which the bricklayer stands. The brick to be picked up should never be higher than three feet eight inches under any circumstances.
By maintaining the height of the brick to be laid in this relative position to the height of the wall, the brick will always be in a position that permits the bricklayer to accelerate the speed of transportation of the brick by using the path of the quickest speed.  Greater outputs will be noticeable as an immediate result of maintaining the brick as nearly as possible at the heights above stated. 
2. In laying the filling tiers in any one course, it is most economical to lay the farthest filling tier first and the next farthest tier second, and so on. This enables the brick- layer to accelerate the speed of transportation of the brick up to the instant that it is deposited in the mortar. The above practice is, of course, much more important on shove-joint work than on brick-and-brick construction.
3. The possible benefits from acceleration should be taken into consideration when determining the sequence in which the tiers shall be laid. The position of the feet of the bricklayer is an important factor in obtaining the acceleration desired. For the best results the feet should be on separate springy planks, so that the transportation of the brick can be speeded up, in addition to the speed of the arms by simply throwing the body by the aid of the spring of the plank. 

AUTOMATICITY

Nearly all often-repeated motions become automatic. This is especially true of motions that require no careful supervision of mind or eye.
The automaticity of motions is of great assistance to the worker whose training and methods conform to standardized motions. This fact makes it necessary to have the apprentice taught the right motions first, last, and always. 
When work is done by both hands simultaneously, it can be done quickest and with least mental effort if the work is done by both hands in a similar manner; that is to say, when one hand makes the same motions to the right as the other does to the left. Most work is accomplished when both hands start work
at the same time, and when the motions can be made at the same relative position on each side of a central fore and aft vertical plane dividing the worker's body symmetrically.
Even if motions cannot be planned to be similar for each hand and performed simultaneously, the plane in
which the work is to be done should be carefully located. If motions are so arranged as to be balanced, as sug- gested, it is possible not only to take advantage of automa- ticity, but also to cut down jar to the body. It is on this well-known principle that the shockless jarring machine is built. Balanced motions counteract each other. The result is, less bracing of the body is necessary, and less fatigue ensues. 

COMBINATION WITH OTHER MOTIONS, AND SEQUENCE

A motion may be combined with motions that are (a) similar to it, and (b) dissimilar to it.
(a) If the motions combined are similar to it, advantage must be taken of the automaticity. Care must also be taken that all the motions made in a series of similar motions are necessary. Sometimes one effective motion is preferable to several not so effective.
Examples. i . When tapping a brick down to grade with a trowel, one brisk tap will do the work as well as
several light taps, and with much less time and effort.
2. If it is necessary to spread mortar on a face tier, one stroke of the trowel will do the work as well as several.
(b) If the motions combined are dissimilar, two motions may often be transformed into one.
Example. - - The motion used to spread mortar may be combined with the motion used to butter the end of the brick laid just before the mortar was thrown. Thus, the two operations may be transformed into one, and a saving of time and motions will result. In fact, so doing may have other distinct advantages, such as leaving better keying for plastering direct upon the wall.
This subject of combinations of motions is barely touched here. Its full treatment involves all other vari- ables, and it can never be considered standardized till each separate motion is a standard. 
DIRECTION
In most cases, the direction of a motion that is most economical is the one that utilizes gravitation the most. Oftentimes delivering material to a high-priced workman by leaving the material in a high position also makes easy unloading for the low-priced workman.
Example. Stacking up packs 2 feet high saves motions, and saves stooping when the laborer unloads his trucket.
" Direction" admirably serves as an illustration of the close interrelation of the variables. It is closely con-
nscted with "path." It involves discussions of anatomy, acceleration, and speed. It demands consideration of all variables of surroundings, equipment, and tools. The best ''direction of motion" is not only important
in itself for increase of output; it must also be kept constantly in mind in standardizing the placing of both
materials and men.

EFFECTIVENESS

Effectiveness has been touched upon in discussing " combination with other motions."  An effective motion is one that produces the desired result. Oftentimes whole processes, methods, and operations can be so changed as to make the succeeding motions much more effective.
Example. The introduction of the fountain trowel, used in connection with an ordinary trowel, made each
motion in handling mortar much more effective.

FOOT-POUNDS OF WORK ACCOMPLISHED


After all, a human being or a work animal is a power plant, and is subject to nearly all the laws that govern
and limit the power plant. It is a law of motion study that, other things being equal, the less number of foot- pounds of work done by the workman, the smaller percentage of working hours he must devote to rest to overcome fatigue.
It is therefore of great importance in obtaining the largest possible output that the work shall be so arranged and the workman so placed that he can do his work with the least possible amount of foot-pounds of work done per unit of output accomplished. This is where the philanthropic employer has often been rewarded without knowing it. In his desire to make conditions such that the workman was most confortable while working, he reduced the number of foot-pounds of work to that which was absolutely necessary to do the work. He surrounded the workman with conditions that enabled him to have no
fatigue, except that which was acquired from the motions of the work itself. He made conditions such that the workman was enabled to overcome the fatigue from his motions in the quickest possible time. 

INERTIA AND MOMENTUM OVERCOME

There are two ways by which the amount of inertia and momentum may be reduced.
i. By standardizing surroundings and equipment so
that the inertia and the momentum are limited to practi-
cally that of the materials, and not the materials plus
arms and body.
Example. Picking up ninety pounds of brick at one lifting.
2. By so standardizing motions that as few starts and stops as possible occur from the time the material leaves the stock pile till the time it is in its final resting place in the work.
Example. In laying brick by the " pick-and-dip " method on face tiers, a brick is lifted in one hand and a
trowel full of mortar in the other. The brick must come to a full stop in the bricklayer's hand while the mortar is being laid and the bed prepared, and then move to its final resting place, unless brick and mortar are dropped in two different places.
In laying brick by the " stringing-mortar " method, the mortar is laid and the bed prepared before the bricks are lifted. The brick are conveyed from the pack to the wall without interruption or delay.
Standard methods of performing work may enable the worker to utilize the momentum.
Example. If the bricks are conveyed from the stock platform or pack to the wall with no stops, the momentum can be made to do valuable work by assisting to shove the joints full of mortar. If, instead of being utilized, the momentum must be overcome by the muscles of the bricklayer fatigue, not full joints, will result. The ideal case is to move the brick in a straight path and make the contact with the wall overcome the momentum. 

LENGTH

A general rule of motion economy is to make the shortest motions possible.
Eliminating unnecessary distances that workers' hands and arms must travel, will eliminate miles of motions that operators make everyday. 
Example. Put the wheelbarrow body as close as possible to the pile that is to be put into it, so that the distance the packets are carried from the pile to the barrow, or the sand from the pile to the barrow, will be the shortest distance possible.
Standard tools, equipment, and surroundings are essential if length of motions is to be made standard.
As already said when discussing clothes, the workman of the present should have even his overalls, belt, and clothes so designed that they will hold the different kinds of tools that are oftenest used, so that they may be picked up in the shortest time that is, with pockets for nails, clips, clamps, etc. The tools should be so placed that the least and shortest motions can be used after they are picked up, as cartridges are placed in a cartridge belt. 

PATH

The determination of the path which will result in the greatest economy of motion and the greatest increase of  output is a subject for the closest investigation and the most scientific determination.  The laws underlying physics, physiology, and psychology must be considered and followed. The path most desirable is usually that which permits gravitation to assist in carrying the material to place.
Example. We have found that the most economical height for laying brick is twenty-four inches above where the bricklayer stands, while it is most economical to pick the brick from a height about three feet above where the bricklayer stands; that is, about one foot higher than the top of the wall where the brick is to be laid. The path is affected by the direction that the material is to be shoved as it moves into its final resting place.
Examples. When the packet is placed on the wall it should be placed so that the brick can be picked up and moved in a comparatively straight line with the direction that the brick will be shoved for filling a joint.
In theory the ideal path would be in a line of quickest speed from the stock platform to the wall.
In practice it is seldom that the most economical path for carrying a brick or mortar from the stock platform to the wall is exactly a straight line from one to the other. It will generally be most economical to move the brick in the path that will bend the arms the least and that will permit almost a swing from the shoulder.

PLAYING FOR POSITION

Each motion should be made so as to be most economically combined with the next motion, like the bil-
liard player who plays for position. The direction in which a motion is made may affect the time required for a subsequent motion.
Example. In laying brick the motion of placing the mortar for the end joint can be done quickest if it is done in the direction of the next motion, such, for example, as the next motion that puts the trowel in the position to cut off the hanging mortar.
The sequence of motions in bricklaying, that determines when the particular motion is to be made that puts the mortar in the end joint, depends upon whether the "pick-and-dip" or the " stringing-mortar " method is used. When the motions are made in the correct sequence, many of them can be combined so that two, and in some cases three, motions can be made as one motion, in but little more time than is required for one motion.
Example. Cutting off mortar, buttering the end of the laid brick, and reaching for more mortar all as one motion, in the " pick-and-dip " method.

SPEED

Usually, the faster the motions, the more output. There are other advantages to speed of motions besides the fact that they require less time. Speed increases momentum, and this momentum may be utilized to do work.
Example. The momentum of the brick helps to shove the mortar better into the joint.
Again, high outputs are generally the result of the habit of speed in motions. Habits of speed are hard to
form, and they are hard to break. Next to fewest motions, speed of motions is the most important factor of high record of outputs.
The list of variables here given makes no claim to being complete. The field of study is so immense that it is impossible as yet to give a complete and detailed method of attack.
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Source:
Motion study : a method for increasing the efficiency of the workman (1911)
Download from
http://www.archive.org/details/motionstudymetho00gilbrich
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Originally posted be me in http://knol.google.com/k/narayana-rao/variables-of-motion-related-to-the/ 2utb2lsm2k7a/ 2366