STRATIGIES FOR MAINTENANCE OF CONSTRUCTION EQUIPMENT

MAINTENANCE COST

In latest years, there is a rising concern on the subject of higher maintenance cost and productivity of maintenance. According to some company, maintenance is the largest single manageable expenditure in the plant: in many companies, exceed their annual net profit. Although many agree that maintenance strategies such as preventative and predictive maintenance policy have been shown to produce a saving of up to 25%, a study has shown that still 1/3 of this maintenance cost can be saved. Basically, maintenance cost can be categorized into two main groups. The first one referred as direct costs are easy to justify and to report. These direct costs consist of items such as labor, services, material, and maintenance overhead cost are the cost tabulated and shown as maintenance costs. The other Type of maintenance costs is hidden costs or indirect costs which are difficult to measure. This hidden cost of maintenance are classified as the six big losses:-

1. Losses due to breakdowns and unplanned plant shutdown
2. Idling and minor stoppages
3. Excessive set-up, changeovers and adjustments losses
4. Running at reduced speed
5. Quality defects and
6. Startup losses

INVENTORY CONTROL

Inventory can help organizations in various ways. The basic types of inventories include raw materials inventory, finished goods inventory, work-in-process inventory, supplies inventory, transportation inventory, and replacement parts inventory.

In the case of raw materials inventory, items are purchased from suppliers for use in production processes. Finished goods inventory is concerned with finished product items not yet delivered to customers. The supplies inventory is concerned with parts/materials used to support the production process. Usually, these items are not an element of the product.

1. ABC Classification Approach for Maintenance Inventory Control

The ABC classification approach gives information for routine and non-routine maintenance. Consequently, it allows different levels of control based on the item’s relative importance. The ABC approach is based on the reasoning that a small percentage of items usually dictates the results achieved under any condition. This reasoning is often referred to as Pareto principle, named after Vilfredo Pareto (1848 –1923), an Italian economist and sociologist.

The ABC approach classifies in-house inventory into three classes(i.e., A, B, and C) based on annual dollar volume. The following approximate relationship between the percentage of inventory items and the percentage of annual dollar usage is observed:

• A: Of the items, 20% are responsible for 80% of the money usage.
• B: Of the items, 30% are responsible for 15% of the money usage.
• C: Of the items, 50% are responsible for 5% of the money usage.

The following three steps are associated with the ABC classification approach:

1. Determine the item characteristics that can influence inventory management results. Often, this is the annual dollar usage.
2. Group items based on the criteria established above.
3. Practice control relative to the group importance.

After the classification of inventory items, control policies can be established. Some of these policies associated with each classification are as follows:

• Classification A items: These are high-priority items. Practice tight control including frequent review of demand forecasts, complete accurate records, periodic and frequent review by management, close follow-up, and expediting to minimize lead time.
• Classification B items: These are medium priority items. Practice regular controls including good records, regular processing, and normal attention.
• Classification C items: These are low-priority items. Practice simple controls, but ensure they are sufficient to meet demand.

Keep plenty of low-cost items, and use the money and control effort saved to minimize inventory of high-cost items.

Economic Order Quantity Model

The economic order quantity model may be traced back to 1915 and is one of the most widely known inventory control methods. Some assumptions associated with the model are as follows:

• Constant and known demand
• Instantaneous receipt of inventory
• Constant and known time between order placement and receipt of the order
• Infeasible quantity discounts
• Stock-outs can be avoided by placing orders at the right time
• Two variable costs: holding cost and ordering or setup cost

Other Inventory control Models

1. VED – analysis: It is based on the criticality of items.

V- Vital items: without which production come to halt

E – Essential items: without which dislocation of production works occurs

D – Desirable items: without which no immediate loss in production

2. SDE analysis: Analysis is based on availability position of each items.

S – Scare items: short supplies: imported good

D – Difficult items: cannot be procured easily

E – Easily available items

3. MNG analysis:

M – Moving items: more consumable items

N - Non-moving items: in consumed in last 1 year

G – Ghost items: no transaction of items during year- nonexisting item

4. FSN (fast, slow, non-moving)

Basis: Issue from stores:

Application: obsolescence control

5. HML (High, Medium, Low)

Basis: unit price of material

Application: to delegate purchasing power

6. VEIN (Vital, Essential, Important, Normal)

Basis: equipment criticality;

Application- Maintenance

8. FAN (Failure analysis):

Basis: design and issue of material

Application: reliability engineering

9. GOLF (Government, Ordinary, Local, Foreign):

Basis: Source of origin of material;

Application: purchase strategy

Spare Parts policy

Spare parts policy must be based on the characteristics of spares demands and cover six main types of decision such as form, source, when to stock, standardization, ordering method and budget

1. Forms :

• Spare machine or equipment: in case of critical machine, ratio of spare parts prices to machine prices, lead time for getting spares
• Spare assemblies: quick replacing method for protection against stop cost: engine, gearbox, electric motor, pumps, filters
• A Recent development is a unit exchange: overhauled engine, gearbox etc.
• Spares parts: lowest protection against stop cost however the cheapest form of proving spares.

2. Source :

• Repair: welding, brazing, metal spraying, electroplating of worn metallic surfaces by regrinding.
• Make: simple components can be made: Copper pipes, rubber hose, electrical components, paper gaskets
• Buy: buy parts from the supplier or from his agent: the cheapest source of supply spares.
• Borrow : borrow or buy from the other users of the same machine : aeroplanes

3. Whether to stock : to decide which items to stock and which to order on demand

4. Standardization: standardize some machines assemblies and parts to use them in different models of machines to reduce spare provisioning cost and stop cost: pumps, motors, gears, bearings, nuts, bolts etc.

5. Ordering methods: it affects the both the cost of spares and the investment or capital tie-up in stocks:

• Stock controlling order: fixed order quantities of different parts in medium quantities with a low total cost per year.
• Schedule ordering or maximum: many times orders or periodically revised delivery schedule for high annual value item required in large numbers.
• Base stock control: A base stock is fixed for every items .An order is placed just after items are issued from store.
• Order on demand: spare parts are ordered on demand for short lead times items and predictable items.

6. The spares budget: effective spare parts policy reduces budget spent of spares. If we store more items than needed then money will be blocked and if we have less stock then more money will spend due more stop time.

• More budget: stock more, stock equipment, assembled unit etc.
• Less budget: more items can store than equipment and assembled unit

A Model for Estimating Spare Part Quantity

There are a number of factors that tend to increase the amount of maintenance-related inventory and, ultimately, the cost of maintenance. Careful consideration of these factors can help reduce inventory costs and, in turn, the cost of maintenance. Some of the factors are as follows:

• Cost of production downtime
• Lack of parts standardization
• Poor attention to inventory or order quantities
• Maintenance scheduling requirements
• Existence of multiple storage depots
• Inadequate attention paid to the economics of quantity purchasing
• Undependable suppliers
• Nature and condition of facilities

The factors that tend to decrease maintenance-related inventory include good service from suppliers, infrequent equipment breakdown, availability of cash, and the cost associated with storeroom activity.

Safety inspection special care and precautions required for repair and maintenance of components of construction equipment

Safety inspections:

1. Park construction equipment safely
   
   
2. Perform daily and periodic physical checkup:

1. Engine cooling and lubrication system
2. Leakage and top up hydraulic system (breakage of hoses, oil seal, loose nut etc.
3. Leakage of transmission oil (if manual transmission system)
4. Check brake and clutch fluid
5. Inspect hydro -drive system
6. Inspect steering system
7. check steering fluidInspect wheel: tire pressure, tyre tread, wheel nuts
8. Undercarriage: cleanliness, breakage, greasing etc.

3. Daily operational or functional inspection:

1. Operation of engine and transmission system
2. Operation of undercarriage system
3. Operation of steering and brake system
4. Operation of boom, stick, bucket, stabilizer, blade, ripper etc before performing jobs.
5. Operation of lighting system etc.

Special care and precautions

1. Provide safety education and training to technical team or skilled or semi-skilled mechanics
2. Wear proper clothing and protective devices
3. Use proper tools for checking pressurized hydraulic system
4. Always park the equipment on a level solid ground firmly and support it from rolling off.
5. Put down the bucket, moldboard, boom etc. for inspections when park or retract all arms and lower the attachments to the ground.
6. Carry out servicing, adjustment or repairs when equipment is in stop condition
7. Use strong strut or bar to support raised arm, bucket etc. during maintenance if you needed to work with raised arm.
8. Be care of falling from boom, stick, and bucket.
9. Engage boom lock and slew lock before traveling on the road while running equipment for testing
10. Before testing the park brake makes sure the area around the equipment is clear of people.
11. Do not test equipment with damaged hoses.
12. Removed the starter key to prevent any one starting the engine.
13. Disconnect the battery.

References

1. Technical book, “Construction Machinery Training”, Instate, Imlambad
2. Harris, F. and McCaffer, “Management of Construction Equipment”, Macmillan Education Ltd. London, UK.
3. Erich J. Schulz, “Diesel Equipment I and II”, Mcgraw-Hill book co.
4. Frank Harries, Ronald McCaffer, “Construction of Plant Excavating and Material Handling”, Granda Publishing.
5. SAE Handbook Volume 4
6. “Caterpillar performance Handbook”, Edition 33, Caterpillar Inc, Peoria, Illinois, USA.