ORTHOGRAPHIC PROJECTIONS

IT IS A TECHNICAL DRAWING IN WHICH DIFFERENT VIEWS OF AN OBJECT ARE PROJECTED ON DIFFERENT REFERENCE PLANES  OBSERVING PERPENDICULAR TO RESPECTIVE REFERENCE PLANE

    

Different Reference planes are

    

  Horizontal Plane (HP),                                                                                                                           Vertical Frontal Plane ( VP )                                                                                                                         Profile Plane ( PP)

                                                       And

                                                         

                                     Different Views are Front View (FV), Top View (TV) and  Side View (SV)

                                   FV is a view projected on VP.
                                    TV is a view projected on HP.
                                       SV is a view projected on PP.

IMPORTANT TERMS OF ORTHOGRAPHIC PROJECTIONS:

(1) Planes                                                                                                                                                        (2) Pattern of planes & Pattern of views.

          (3) Methods of drawing Orthographic Projections

                                                                 

                                           Pattern of planes & Pattern of views.     

Name of the experiment

Determination of moment of inertia of a flywheel about its axis of rotation

            Theory

                          The flywheel is a big sized wheel. Most of its mass is distributed over the peripheral region. A thick cylindrical rod, called the axle, passes through the centre of mass of the wheel. The axis of the axle is perpendicular to the circular surface of the flywheel. The axle is kept horizontally by means of a holder hung on the wall. The wheel with the axle can rotate about the axis of the axle. There is a peg joined with axle. Objective of this experiment is to deturmine the moment of inertia of the flywheel about the axis of rotation, i.e., the axis of the axle.

 (a) Flywheel when the rope and load is about to be detached from the axle.                                        (b) The same flywheel after rotating it for nl number of times (here n₁ is 6) There is a small peg on the axle, as shown in figure 1. We make a loop on one end of a rope round this peg. A load of mass, M, is connected to the other end of the rope. We hold the flywheel in such a way that the.

load is about to be detached from the axle (figure 1 b). Then we keep a straight meter scale at The bottom surface of the load, see where on the wall the end of the meter scale touches and put a mark over there. Next, we rotate the flywheel for n₁ times. Consequently the load moves  upward. Again, we keep the straight meter scale at the bottom surface of the load; we see where on the wall the end of the meter scale touches and put a mark over there. The separation between the two marks is h.

Now, if the flywheel is made free to rotate, then its angular velocity increases uniformly and the linear velocity of the load also increases uniformly. The flywheel completes n₁ revolutions after the release of the load and the load traverses a distance h vertically.

The work done by gravity on the load = M g h A part of this work is used to increase rotational kinetic energy of the flywheel, and part of it supplies the linear kinetic energy to the load and the rest is used to work against the friction between the flywheel and the holder.

Let, I is the moment of inertia of the flywheel about its axis of rotation..                                                 When the load is just detached from the axle, the angular velocity of the flywheel be ω and the linear velocity of the load is v.                                                                                                                              So the rotational kinetic energy of the flywheel      

and the kinetic energy of the load    

                                                        

  

 Let, the work done against friction to complete a single revolution = W_f , therefore, the work done against friction to complete n₁ revolutions = n₁W_f                                                                               So, we can write, 

Let, t is the time between the moment of detachment of the load from the axle and the moment when the flywheel comes into rest. In time t the flywheel completes n₂

                                                               revolutions.

During this second part of the motion of the flywheel, all of the rotational kinetic energy will be used to work against the friction which is n₂wf, and hence

        Since in one complete revolution the angular displacement is π2radian, in n2 revolutions, total angular displacement is 2n2π radian. The average angular velocity,

Now,

during this second part of the motion, the angular velocity decreases uniformly form 

                                                       

 By using equations (4) and (5) we can determine the moment of inertia of the flywheel about its axis of rotation by measuring M, h, r, n₁ and n₂

BINARY EUTECTIC SYSTEMS

Another type of common and relatively simple phase diagram found for binary alloys is shown in Figure for the copper silver system; this is known as a binary eutectic phase diagram. A number of features of this phase diagram are important and worth noting. First, three single-phase regions are found on the diagram: and liquid. The  α phase is a solid solution rich in copper; it has silver as the solute component and an FCC crystal structure.

                              The copper–silver phase diagram

Other Maintenance Improvement Methods

Over the past 10 years, a variety of management methods, such as total productive maintenance (TPM) and reliability-centered maintenance (RCM), have been devel- oped and touted as the panacea for ineffective maintenance. Many domestic plants have partially adopted one of these quick-fix methods in an attempt to compensate for perceived maintenance shortcomings.

Total Productive Maintenance

Touted as the Japanese approach to effective maintenance management, the TPM
concept was developed by Deming in the late 1950s. His concepts, as adapted by the Japanese, stress absolute adherence to the basics, such as lubrication, visual inspec-tions, and universal use of best practices in all aspects of maintenance.

TPM is not a maintenance management program. Most of the activities associated with the Japanese management approach are directed at the production function and assume that maintenance will provide the basic tasks required to maintain critical pro- duction assets. All of the quantifiable benefits of TPM are couched in terms of capac- ity, product quality, and total production cost. Unfortunately, domestic advocates of TPM have tried to implement its concepts as maintenance-only activities. As a result, few of these attempts have been successful.

At the core of TPM is a new partnership among the manufacturing or production people, maintenance, engineering, and technical services to improve what is called overall equipment effectiveness (OEE). It is a program of zero breakdowns and zero

defects aimed at improving or eliminating the following six crippling shop-floor losses:
•  Equipment breakdowns
•  Setup and adjustment slowdowns
•  Idling and short-term stoppages
•  Reduced capacity
•  Quality-related losses
•  Startup/restart losses

A concise definition of TPM is elusive, but improving equipment effectiveness comes close. The partnership idea is what makes it work. In the Japanese model for TPM are five pillars that help define how people work together in this partnership. Five Pillars of TPM. Total productive maintenance stresses the basics of good busi-ness practices as they relate to the maintenance function. The five fundamentals of this approach include the following:
1. Improving equipment effectiveness In other words, looking for the six big losses, finding out what causes your equipment to be ineffective, and making improvements.
2. Involving operators in daily maintenance This does not necessarily mean actually performing maintenance. In many successful TPM programs, oper-ators do not have to actively perform maintenance. They are involved in the maintenance activity—in the plan, in the program, and in the partner-ship—but not necessarily in the physical act of maintaining equipment.
3. Improving maintenance efficiency and effectiveness.In most TPM plans, though, the operator is directly involved in some level of maintenance. This effort involves better planning and scheduling better preventive mainte-nance, predictive maintenance, reliability-centered maintenance, spare parts equipment stores, and tool locations—the collective domain of the maintenance department and the maintenance technologies.
4. Educating and training personnel. This task is perhaps the most important in the TPM approach. It involves everyone in the company: Operators are taught how to operate their machines properly and maintenance personnel to maintain them properly. Because operators will be performing some of the inspections, routine machine adjustments, and other preventive tasks, training involves teaching operators how to do those inspections and how to work with maintenance in a partnership. Also involved is training super-visors on how to supervise in a TPM-type team environment.
5. Designing and managing equipment for maintenance prevention. Equip-ment is costly and should be viewed as a productive asset for its entire life. Designing equipment that is easier to operate and maintain than previous designs is a fundamental part of TPM. Suggestions from operators and maintenance technicians help engineers design, specify, and procure more effective equipment. By evaluating the costs of operating and maintaining Impact of Maintenance

Preventive Maintenance

There are many definitions of preventive maintenance, but all preventive maintenance management programs are time-driven. In other words, maintenance tasks are based on elapsed time or hours of operation. Figure 1–1 illustrates an example of the sta-tistical life of a machinetrain. The mean-time-to-failure (MTTF) or bathtub curve indicates that a new machine has a high probability of failure because of installation problems during the first few weeks of operation. After this initial period, the proba- bility of failure is relatively low for an extended period. After this normal machine life period, the probability of failure increases sharply with elapsed time. In preven- tive maintenance management, machine repairs or rebuilds are scheduled based on the MTTF statistic.

The actual implementation of preventive maintenance varies greatly. Some programs are extremely limited and consist of only lubrication and minor adjustments. Comprehensive preventive maintenance programs schedule repairs, lubrication, adjustments, and machine rebuilds for all critical plant machinery. The common denominator for all of these preventive maintenance programs is the scheduling  guideline—time.

All preventive maintenance management programs assume that machines will degrade within a time frame typical of their particular classification. For example, a single- stage, horizontal split-case centrifugal pump will normally run 18 months before it must be rebuilt. Using preventive management techniques, the pump would be removed from service and rebuilt after 17 months of operation. The problem with this  An Introduction to Predictive Maintenance

approach is that the mode of operation and system or plant-specific variables directly affect the normal operating life of machinery. The mean-time-between-failures (MTBF) is not the same for a pump that handles water and one that handles abrasive slurries.

The normal result of using MTBF statistics to schedule maintenance is either unnec essary repairs or catastrophic failure. In the example, the pump may not need to be rebuilt after 17 months. Therefore, the labor and material used to make the repair was wasted. The second option using preventive maintenance is even more costly. If the pump fails before 17 months, it must be repaired using run-to-failure techniques. Analysis of maintenance costs has shown that repairs made in a reactive (i.e., after failure) mode are normally three times greater than the same repairs made on a scheduled basis

approach is that the mode of operation and system or plant-specific variables directly affect the normal operating life of machinery. The mean-time-between-failures (MTBF) is not the same for a pump that handles water and one that handles abrasive slurries.

The normal result of using MTBF statistics to schedule maintenance is either unnec- essary repairs or catastrophic failure. In the example, the pump may not need to be rebuilt after 17 months. Therefore, the labor and material used to make the repair was wasted. The second option using preventive maintenance is even more costly. If the pump fails before 17 months, it must be repaired using run-to-failure techniques. Analysis of maintenance costs has shown that repairs made in a reactive (i.e., after failure) mode are normally three times greater than the same repairs made on a scheduled basis

Run-to-Failure Management

The logic of run-to-failure management is simple and straightforward: When a machine breaks down, fix it. The “If it ain’t broke, don’t fix it” method of maintain-ing plant machinery has been a major part of plant maintenance operations since the first manufacturing plant was built, and on the surface it sounds reasonable. A plant using run-to-failure management does not spend any money on maintenance until a machine or system fails to operate.

Run-to-failure is a reactive management technique that waits for machine or equip-ment failure before any maintenance action is taken; however, it is actually a “no- maintenance” approach of management. It is also the most expensive method of maintenance management. Few plants use a true run-to-failure management philoso- phy. In almost all instances, plants perform basic preventive tasks (i.e., lubrication, machine adjustments, and other adjustments), even in a run-to-failure environment. In this type of management, however, machines and other plant equipment are not rebuilt, nor are any major repairs made until the equipment fails to operate. The major expenses associated with this type of maintenance management are high spare parts An Introduction to Predictive Maintenance inventory cost, high overtime labor costs, high machine downtime, and low produc-tion availability.

Because no attempt is made to anticipate maintenance requirements, a plant that uses true run-to-failure management must be able to react to all possible failures within the plant. This reactive method of management forces the maintenance department to maintain extensive spare parts inventories that include spare machines or at least all
major components for all critical equipment in the plant. The alternative is to rely on equip ent vendors that can provide immediate delivery of all required spare parts.

Even if the latter option is possible, premiums for expedited delivery substantially increase the costs of repair parts and downtime required to correct machine failures. To minimize the impact on production created by unexpected machine failures, main- tenance personnel must also be able to react immediately to all machine failures. The net result of this reactive type of maintenance management is higher maintenance cost and lower availability of process machinery. Analysis of maintenance costs indicates that a repair performed in the reactive or run-to-failure mode will average about three times higher than the same repair made within a scheduled or preventive mode. Sched- uling the repair minimizes the repair time and associated labor costs. It also reduces the negative impact of expedited shipments and lost production.

IMPACT OF MAINTENANCE

Maintenance costs are a major part of the total operating costs of all manufacturing or production plants. Depending on the specific industry, maintenance costs can rep- resent between 15 and 60 percent of the cost of goods produced. For example, in food-related industries, average maintenance costs represent about 15 percent of the cost of goods produced, whereas maintenance costs for iron and steel, pulp and paper, and other heavy industries represent up to 60 percent of the total production costs.

These percentages may be misleading. In most American plants, reported maintenance costs include many nonmaintenance-related expenditures. For example, many plants include modifications to existing capital systems that are driven by market-related factors, such as new products. These expenses are not truly maintenance and should be allocated to nonmaintenance cost centers; however, true maintenance costs are  substantial and do represent a short-term improvement that can directly impact plant profitability.

Recent surveys of maintenance management effectiveness indicate that one-third—33 cents out of every dollar—of all maintenance costs is wasted as the result of unnec- essary or improperly carried out maintenance. When you consider that U.S. industry spends more than $200 billion each year on maintenance of plant equipment and facil-

ities, the impact on productivity and profit that is represented by the maintenance oper- ation becomes clear.

The result of ineffective maintenance management represents a loss of more than $60 billion each year. Perhaps more important is the fact that ineffective maintenance management significantly affects the ability to manufacture quality products that  are competitive in the world market. The losses of production time and product  quality that result from poor or inadequate maintenance management have had a 

dramatic impact on U.S. industries’ ability to compete with Japan and other countries