Excavator Boom Design Essay Example

relevant calculations. In our research for the Mini-excavator there were many useful sources that helped in our design and understanding of the Mini-Excavator as they directly pertained to our project.

These sources gave a brief history of the excavator as well as how it operates and functions. There were also sources pertaining to Hydraulic systems and the different types of steels used to construct the excavator itself. The first source used was an excerpt from the book, “Tall Buildings: From Engineering to Sustainability. ” This was used to attain a basic knowledge of the workings and the history of the hydraulic excavator. This was utilised in tandem with other sources to provide a coherent amount of background knowledge on the hydraulic excavator.

The design of the excavator goes way back to the year 1839 by inventor William Smith Otis, starting with the Otis Steam Shovel. This machine was powered by steam and for many years after, most inventions that were created used the same steam principle. As the age of steam powered excavators died off, new excavator inventions were created. These new excavators were powered by fuel such as diesel and the movements of the machine itself as well as the arms were run using a hydraulic system.

Prior to this, there were even excavators whose arms and its mechanism for digging were run by cables, running along pulley systems. Excavators have a wide variety of uses and can be customized to fit the desired job. The customization of an excavator involves changing of the bucket or adding hydraulic attachments. The standard bucket can be changed with various sizes of different types of buckets and other attachments include

augers, hammers, vibratory compactors, dozers, breakers, grapples, thumbs, clamshells, wood clippers, brush cutters and concrete crushers.

Excavators are used in digging of trenches, holes for foundations beams, general construction or even demolition of old buildings, sewage works, road widening works, pipe laying and rock breaking and dragging; resources mining which include overburden, removal in coal mining, gravel collection; forestry works which entails timber handling and prune off work; metal recycling which involves slag handling and scrap handling; brush cutting with hydraulic attachments, general grading and landscaping. To assist in understanding the basis of operation of the excavator, an article on hydraulics was used.

This article gave a general understanding of the principles governing the transmission of pressure due to hydraulics and its widespread application. The basic idea behind any hydraulic system is very simple: Force that is applied at one point is transmitted to another point using an incompressible fluid. The fluid is almost always an oil of some sort. The force is almost always multiplied in the process. 2 The arm of the excavator is attached to the lower part of the frame chassis. This arm has three hydraulic pistons with chromed steel piston arms to reduce corrosion. The arm has two main sections and a bucket loader.

The two main sections are jointed with a hinge. One piston is attached to the underneath side of the first section and one on the top side of the second section. When the first piston extends, the rod pushes against the arm and raises it, extending the section. The second arm contracts or expands, raising and lowering the second section for more reach. An additional hydraulic piston moves the

bucket loader forward and backward so the bucket can dig or scoop up material. Articles on interaction with soil were also used to obtain some background information on the material that the excavator would be designed to work with.

Soil type is extremely important when considering the type of excavator to be selected for design for an application. When choosing an excavator, soil density, drainage and ability to withstand differing weights must be on the criteria list determining the selection of the excavator. Fine sands are found in the coastal areas where the use of the mini excavator is limited. Clay soil particles are the smallest of all soil particles being approximately 0. 002mm in size. The bulk density of the soil is defined as the mass per unit volume including the pore space of the soil.

Since clay soils have the smallest particles they can be held together most compact and a high bulk density is directly related to being more compact. Further compaction of the clay soil can be done however with use of the plate compactor attachment to the excavator. Soil Porosity refers to the amount of pore or open space between particles. Clay soils hold the least amount of water as they are the least porous in nature. If a highly porous soil was considered for being excavated like when digging, holes will have to be present at the sides of the bucket to make ure that excess water is removed from the material and not adding to the weight to be carried therefore decreasing stability. Tracks are ideally suited for use when working in areas when the material is clay soil as

it has a high stability and manoeuvrability in this type of condition. For the purpose of this design, the working material is assumed to be a loamy soil of density 1360kg/m3. This influenced our choice of maximum digging force which was chosen to be 25kN. The excavator final design included rubber tracks since the excavator is designed to work at small construction sites and around the home.

Rubber tracks will decrease the amount of damage done to the ground and hence would be much more suitable than steel tracks. A fixed boom was used for simplicity in the design and also for the advantage of producing a much larger digging force than a swing boom. To aid in our design, a few patents and previous mini-excavator designs were looked at. The first patent looked at was from the United States Patent Publication, Patent number US 2002/0174573, published on November 28th, 2002. This patent was a design of a mini excavator, which made it relevant to my design.

However, the main aim of their design was to solve the problem of the hydraulic hoses obscuring the view of the operator. The patent was helpful in that 3 it provided some information on the design of the hydraulic system. My design differed in that my aim was to design a mini-excavator to be used on a small construction site. Therefore, when compared to the referred patent, the excavator I designed had a smaller total weight. This was due to the fact that the excavator would be used around the home and on small construction sites and therefore the weight was minimized to reduce damage to the surface on which

the excavator is operating.

Another patent was used for this literature review to aid in determining the final design of the excavator. The patent used was a United States Patent, Patent number Des. 406152, dated February 23rd 1999. This patent is an ornamental design of an excavator. This patent was different to my final design in that their design had greater manoeuvrability of the boom and stick. The boom was designed in two parts, allowing the second part to rotate with respect to the first part. This was also the case for the stick, in that it could rotate in two planes with respect to the boom. My design however, was more conventional in hat the stick could only move with respect to the boom in one plane. Although the design put forward in this patent can prove to be a great innovation, it significantly reduces the magnitude of both the applied digging force and the payload capacity. Also, my design is much simply to manufacture and will contain less points of stress concentration. This is due to each connecting point in the design from the patent providing a point of stress concentration and making the overall machine weaker. Thus, my design would be stronger overall and can also be said to be more durable.

The sources used for this literature provided sufficient background information to allow for accurate completion of the project. Patents were used for comparison so that there would be certainty that my design is actually an improvement to existing designs of its type in terms of performance and customer satisfaction. Large excavators are generally needed for heavy duty construction projects, but these excavators

have proven to be too cumbersome for smaller size projects. To design a Mini-Multipurpose excavator for the use on small light duty projects. The payload capacity = 0. 5 tonnes Diesel powered Standard bucket size = 0. 3m3 Attachments : A trench/ditch cleaning bucket An Auger for digging deep narrow holes A Hydraulic hammer A Compactor

DESIGN SPECIFICATIONS

1. Since excavator will not be needed to make large movements across ground, the top speed is limited to 5km/h.

2. Excavator will be working with soil hence a max digging force of 25kN.

3. The standard bucket size is 0. 3m3

4. Diesel engine chosen for power.

5. Excavator total weight limited to 5. 5 tonnes.

6. The payload capacity of the excavator is limited to 0. 5 tonnes.

This combination was used as the datum and the other combinations were compared with reference to this one. Combination 2 consisted of motion by hovering with air, using cables for both manipulation of the arm and for dumping and scooping, and swivelling by using hydraulics directly. When compared to combination 1, this combination was seen to be inferior in that its evaluation produced a total of -62. Combination 3 consisted of motion using tracks, using hydraulics for both manipulation of the arm and for dumping and scooping. The rack and pinion method was used for swivelling.

Although a swing boom presents obvious advantages, the fixed boom was chosen to allow for a greater digging force to be obtained. The material chosen for the structural components was AISI 4340 steel. This material was chosen mainly because of its high tensile strength 830 MN/m2 and its resistance to corrosion. This type of steel is alloyed with nickel, chromium

and molybdenum making it extremely corrosion resistant in a variety of environments. Also, this material has good forming and machining characteristics, making it ideal for structural parts.

This material was therefore used for the boom, stick, bucket and the pins at the connecting joints. The hydraulic pistons were made using AISI 6150 steel which has a yield strength of 745MN/m2. As in any design, an appropriate factor of safety must be chosen. The factor of safety is used to account for effects of temperature, uncertainties in the material and also uncertainties in the loading of the component. Where nS represents the strength based factor of safety.

1.Hydraulic Setup Failure mode Failure cause Effects Safeguards Actions Seizure Improper Lubrication Piston sticks and pump would not work causing a total shut down Corrosion of metal fittings Exposure to Moisture It can cause a leakage Design hydraulic setup such that lubrication is made simple and does not need a significant halt in work progress. Use more corrosion resistance materials Use a good lubricant Ensure enough lubricant is used within reasonable ime intervals Replacement of the rings. Have regular check up to ensure everything is in order Replacement of piston rings Wearing of pistons rings Constant in an out movement Reduction in pump efficiency due to oil leakage and reduction in output pressure Use Stronger materials 13

2. Tracks Failure mode Crack Failure cause Environment in which equipment is working in Effects Equipment would not be able to move properly Equipment would not be able to move properly Safeguards Use a very strong material which can withstand shocks, impacts etc Install a lubrication system.

Use stronger materials in making gears Install a lubrication

system Actions Replacement of tracks Wearing of gears Constant turning the tracks movement cause gears to wear Replacement of gears Seizure of tracks Not lubricating the gears Equipment would not be able to move Lubricate gears within reasonable time intervals

3. Cabin Failure Modes Surge Failure Cause Faulty alternator overcharging Effects Injury to operator due to electrical shock and also loss of control of the machine. Safeguards / Backups Contacts made with non corrosive materials.

Wires are made off material that allows it to be flexible. Also, use of PCB? s for hydraulic controls. Actions 14

4. Engine Failure Modes Corrosion Failure Cause Exposure to water flowing through water lines in engine block Effects Damage to water lines in engine block. Also, engine may overheat, malfunction, an eventually fail Safeguards / Backups Actions Use of anticorrosion engine coolant in the radiator Fracture Overheating Design of smoothed shaped water lines in block.

Also, the use of some corrosion resistant metal in casting of engine block Hair line cracks Introduction of an may develop on onboard engine head due to instrument panel stress with a temperature concentrations. gauge so that the This causes the temperature can engine to lose be monitored. power and eventually fail and overheat again Engine may not start due to lack of current to the starter and/or diesel pump. Electrical hydraulics controls may also malfunction and light may also fail. Starter can? t turn flywheel so therefore engine won? t start Electrical short

Corrosion at electrical contacts, broken or burnt electrical wires, or even a faulty battery To prevent fracture, use engine coolant, and check the level of coolant regularly. Also, check the oil level to make sure

it is adequate. Contacts made When electrical with non corrosive fault indicator materials. Wires are made off comes on, stop material that usage and get allows it to be electrical system flexible. Also, use checked of PCB? s for hydraulic controls Have onboard water and oil check lights to indicate low level of fluid. Before starting engine, always check oil and water levels.

Seizure Corrosion, oil starvation 15 Wear Happens over time with usage. Also, may be cause by lack of oil. Leaking Damaged or faulty seals, gaskets and/or hoses. Loose fitting Vibration, wear Surge Faulty alternator, battery or fuses Oil starvation Oil leakage, bad seals, gaskets, hoses. Wear of rings may lead to engine smoking, back pressuring and eventually failure. Wear on cylinder may cause ridges and this may damage rings. Could lead to lack of oil, which implies loss in performance, overheating and eventually engine failure. Lack of water could lead to overheating, cracking nd then engine failure Can leak fluids, exhaust gas, lose compression. Can overheat and/or starve for oil due to lack of fluid. Could damage electrical controls, and render it and therefore boom and bucket operation, useless. Could damage other electrical systems, like lights, air conditioning, etc, Engine may overheat, begin to lose power and eventually fail. Main bearings may burn and seize. Make replacement parts readily available. Have onboard oil check light to monitor level of oil in engine. Check oil regularly, and change oil when required. To fix wear, the engine would need to be overhauled, or rebuilt.

Check oil and water levels before starting engine, and monitor if fluid is being lost from the fluid reservoirs. Use of appropriate,

high quality materials for manufacture of hoses, seals and gaskets. Also, having the onboard oil and water temperature and level check lights. Implement vibration dampers on the engine in the design. Proper sizing and usage of fuses, and voltage, current regulators and filters. Equip cabin with an onboard electrical check light. Observe onboard electrical light and replace any faulty parts. Equip with an onboard oil check light in a very visible location

Check oil levels regularly and change oil when required. If oil starvation occurs, engine may need to be rebuilt or overhauled 16 5. Arm Failure Mode Failure Cause Mechanical Component Crack or fracture exposed to excessive stress. Component exposed to impact loading exceeding maximum force it can withstand. Corrode The component may rust or corrode upon exposure to rain or corrosive chemicals Effects Causes an immediate halt in work progress. May cause load to fall to ground, damaging other equipment as well as injuring personnel.

Actions Carry out check after selected time periods to ensure no cracking or yielding develops. Do not subject component to loads beyond its rated load. Causes a Consider working Do not weakening of the environment when operate component, choosing a material machine in making it more for component. Also environment vulnerable to carry out proper for which it mechanical treatment to make was not failure. component more designed. corrosion resistant. Periodically ensure paint is fully applied for protection. Causes a Consider a suitable Carry out complete material and diameter routine checks dissembling of for bolts and rivets to ensure no arm.

May cause based on force cracks workload falling analysis. Reinforce develop at to the ground joints to account for joints

or bolts. resulting in stress concentrating Ensure joints injury to effect. are well personnel. greased at all Damage to joints times. may transfer to damage to hydraulic system and hoses. Safeguards/Backups Ensure thorough force analysis is done to ensure suitable material as well as dimensions are chosen. Include appropriate F. O. S. Include a range of loads to be used in operation. Failure of Connecting Joints Cracks developed in bolts or rivets at joints.

Also, due to stress concentration at joints. 17 6. Electronic Control System Failure Mode Damage to connecting wires Failure Cause General wear of wires or being subjected to excessive current. Effects Causes operator to have no control of machine. Can result in fire or electrical shock, injuring operator. This can cause a total shutdown of the excavator due to the fact that operator cannot perform any processes. Safeguards/Backups Ensure a means of disconnecting or shutting off power in case of malfunction. Design electrical system so that wires and other components are easy to replace.

Contacts made with non corrosive materials. Wires are made off material that allows it to be flexible. Also, use of PCB for hydraulic controls. Actions Carry out periodic inspections of battery and wires to ensure no deterioration is occurring. Electrical short Faulty alternator, fuses, contacts, short circuiting, corrosion Monitor the electrical fault indicator, and get it checked by an electrical when it comes on. Swivel Mechanism Failure mode Wear of Gear teeth Failure cause Direct contact of pinion and internally meshing gear from rotating cabin can cause the gear teeth to gradually wear.

Hazards Can cause user to lose control of the rotation of the cabin. Can cause over swing

where arm can swing out of control and can damage buildings, nearby equipment and injure individuals Not lubricated Can cause an Overheating properly with instant halt in between oil and rotation of the bearings and grease. cabin or eventual sticking. failure. Effects Can cause the swivel movement of the cabin to stick or even halt when rotating Safeguards Use stronger material which is more resistant to fatigue and creep. Use material with high hardness As this would be better against deformation.

This made use of the basic buckling equation to obtain a critical buckling load, and then compare this to the largest force in any hydraulic piston. It was clearly seen that the pistons would not buckle since the actual load carried was less than the buckling load. To ensure that the excavator would not tip, calculations were carried out to determine the position of the equivalent concentrated normal reaction when the bucket was filled to capacity at maximum reach. This involved taking moments about the centre of gravity and it was found that the reaction lay within the span of the tracks and hence the unit would not tip.

To determine the hydraulic pump capacity, the pressure required by them pump was calculated using the largest force and the area of application of the pressure to exert this force. To account for the pump not being 100% efficient, an extra 20% of pressure was added to give the final pump capacity in terms of pressure. The engine capacity was found by using the velocity at which the piston under the maximum force would be required to move. Similarly to the pump calculations, inefficiency of the engine

was accounted for. To attain a maximum speed of 5km/hr as chosen in the design specifications, the angular velocity of the gear riving the tracks was calculated. Jackhammer – Gerard Mohammed The hydraulic hammer is used to break up concrete, asphalt or rock by producing repeating impacts to the surface. The mechanism behind the hydraulic hammer consists of two valves, which alternate to apply pressure to opposite ends of the piston. This causes reciprocation of the piston which transfers this motion to the tool and hence destructive blows are applied to the desired surface. A tool length of 525mm was chosen. The material chosen for the tool was AISI 1080 steel which is a high carbon steel known for hardness and resistance to wear.

Augers usually consists of two major pieces, the auger bit, which does the actual cutting into of materials, and the hydraulic head, which is the hydraulic gerator motor that drives the auger bit. The workings of the hydraulic auger head obey the principles put forward by Blaise Pascal. Pascal said that the pressure is transmitted everywhere undiminished in an enclosed static fluid this just means that if there were two pistons, of different sizes, in a sealed completely filled hydraulic system, a large movement in the smaller piston would induce a small movement in the larger piston.

This also follows the Law of conservation of energy as what is put into the system is equal to what comes out of the system. This multiplication of force is a very useful property as now it wouldn? t be required to use such a large initial force, but instead have a very small initial force

that would be multiplied by the use of hydraulics and then have a relatively huge output force. The auger works on this hydraulic principle which allows it to possess lots of power and torque required for the task it is required and also allows for the variation of speed and direction of motion.

Augers are used for drilling holes for footings, signs, fencings etc, in construction applications and for trees and shrubs in agricultural and landscaping applications. In this design project, it was required to design a mini excavator that could be used for small domestic applications. One additional requirement was the design of an auger attachment for the excavator. The addition of the auger to the excavator? s already existing features greatly improves the versatility of the excavator especially in terms of domestic uses.

Augers are used domestically for drilling holes for footings, fencings and in construction of foundations, etc, in construction applications and for planting of trees and shrubs in agricultural and landscaping applications. In this design, the auger was designed with the right amount of power, speed and torque for maximum productivity in the various soil types. It is desirable to have the proper amount of torque for the application so that when the auger bit enters the material it does not stick or stall or strain.