design-and-construction-of-a-hydraulically-powered-scissors-lift (1).docx

TITLE PAGE

DESIGN AND CONSTRUCTION OF HYDRAULIC SCISSORS LIFT BY OKOLIE IZUNNA JUDE FPI/HND/MEC/010/001 BEN DAVID IDOKO FPI/HND/MEC/010/002 OKECHUKWU NNAMDI FPI/HND/MEC/010/004 ENEJIYON ABDULMALEEQ FPI/HND/MEC/010/009 AGONOR WILLIAMS FPI/HND/MEC/010/019

BEING A REPORT SUBMITTED TO THE DEPARTMENT OF MECHANICAL ENGINEERING, SCHOOL OF ENGINEERING, FEDERAL POLYTECHNIC IDAH, KOGI STATE IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF HIGHER NATIONAL DIPLOMA (HND) IN MECHANICAL ENGINEERING

2011/2012 SESSION 1

CERTIFICATION We the undersigned hereby certify that this project was carried out by the under listed students.

OKOLO IZUNNA JUDE FPI/HND/MEC/010/001

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BEN DAVID IDOKO FPI/HND/MEC/010/002

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OKECHUKWU NNAMDI FPI/HND/MEC/010/004

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ENEJIYON ABDULMALEEQ FPI/HND/MEC/010/009

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AGONOR WILLIAMS FPI/HND/MEC/010/019

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Mechanical Engineering Department under the supervision of Mr. Bingfa Bongfa.

I certify that the work is adequate in scope and quality for the partial fulfillment for the award of Higher National Diploma (HND) in Mechanical Engineering.

___________________________ ENGR. O. Y. USMAN Head of Department

_______________________ MR. BINGFA BONGFA Supervisor

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APPROVAL PAGE

This project work titled design and construction of hydraulic scissors lift has been read and approved as meeting the requirement of the national Board for Technical Education (NBTE) for the award of Higher National Diploma (HND) in the department of Mechanical Engineering, Federal Polytechnic Idah, Kogi State.

__________________________ MR. BINGFA BONGFA Project Supervisor

________________________ External Examiner

Date ______________________

Date ____________________

_________________________ ENGR. O.Y. USMAN Head of Department

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DEDICATION

We dedicated this project to the Almighty God who spare our lives to this day and make this project a reality.

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ACKNOWLEDGEMENT

All praises, magnification and adoration is due to Almighty God alone who guide, direct and sustain us throughout our programme. I acknowledge the effort of my supervisor Mr. Bingfa Bongfa, who work relentlessly to see the success of this project. The head of Department, Engr. O.Y. Usman for all his support, Engr. A.M. Aboh and all other lecturers and students in the department of Mechanical Engineering.

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ABSTRACT

The conventional method of using rope, ladder, scaffold and even mechanical scissors lift in getting to a height encounter a lot of limitation (time and energy consumption, comfortability, amount of load that can be carried etc), which hydraulic scissors lift is set out to achieve. In this project a mobile scissors lift has been designed that will be powered by hydraulic to a height of 3m carrying a maximum load of 300kg. the project has been tested and it work successfully.

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TABLE OF CONTENT

Title Page -

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Certification -

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Approval page -

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Dedication -

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Acknowledgement - -

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Abstract - -

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Table of content-

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1.2 Statement of the Problem

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1.3 Scope of the Study -

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1.4 Importance / Significance of the Study

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1.5 Aims/Objectives of the Study

CHAPTER ONE 1.0 Introduction -

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2.0 Review of Related Literature

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2.1 Upright Scissors Lift

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2.2 Scaffold -

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2.3 Boom Lift

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2.3.1 The Straight Boom Lift -

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CHAPTER TWO

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2.3.2 Articulated Boom Lift

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2.4 Mechanical Scissors Lift -

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2.5 Hydraulic Lift -

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2.5.1 Hydraulic Scissors Lift -

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2.5.2 Principle of Operation of Hydraulic Lift CHAPTER THREE 3.0 Design Theory and Calculation -

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3.1 Design Theory

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3.1.1.2 Double Acting Cylinders - -

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3.2 Buckling Action on Cylinder -

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3.2.1 Stresses of Cylinder - -

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3.2 Design Calculations -

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3.1.1 Cylinder Selection -

3.1.1.1 Single Acting Cylinders -

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CHAPTER FOUR 4.0 Material Selection, Construction Procedures, Cost Analysis and Maintenance

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4.1 Material Selection --

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4.2 Construction Operation and Tools

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4.3 Cost Analysis of Materials

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CHAPTER FIVE 5.0 Conclusion and Recommendation - -

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5.1 Conclusion - -

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Reference -

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CHAPTER ONE

1.0

INTRODUCTION A scissor lift or mechanism is a device used to extend or position a

platform by mechanical means. The term “scissor” comes from the mechanic which has folding supports in criss cross “X” pattern. The extension or displacement motion is achieved by the application of force to one or more supports, resulting in an elongation of the cross pattern. The force applied to extend the scissors mechanism may by hydraulic, pneumatic or mechanical (via a lead screw or rack and pinion system). The need for the use of lift is very paramount and it runs across labs, workshops, factories, residential/commercial buildings to repair street lights, fixing of bill boards, electric bulbs etc. expanded and lessefficient, the engineers may run into one or more problems when in use. [http://ritchikmikie.com/work/index.php/arial-platform] The name scissors lift originated from the ability of the device to open (expand) and close (contract) just like a scissors. Considering the need for this kind of mechanism, estimating as well the cost of expanding energy more that result gotten as well the maintenance etc. it is better to adopt this design concept to the production of the machine. The initial idea of design considered was the design of a single hydraulic ram for heavy duty vehicles and putting it underneath, but this has 10

limitations as to the height and stability, and someone will be beneath controlling it. It was rather found out that; there is a possibility of the individual ascending/descending, to be controlling the device himself. Therefore further research was made to see how to achieve this aim. Before this time scissors lift existing use mechanical or hydraulic system powered by batteries for its operations. Several challenges were encountered in this very design. Some amongst many include; low efficiency, risk of having the batteries discharged during an emergency, extended time of operation, dependent operation, as well as maintenance cost. It is the consideration of these factors that initiated the idea of producing this hydraulically powered scissors lift with independent operator. The idea is geared towards producing a scissors lift using one hydraulic ram placed across flat, in between two cross frames and powered by a pump connected to a motor wheel may be powered by a pump generator. Also, the individual ascending / descending is still the same person controlling it. I.e. the control station will be located on the top frame. A scissors lift is attached to a piece of equipment having a work station known as scissors lift table that houses the pump, the reservoir, the generator, control valves and connections and the motor. A scissors lift does not go as high as a boom lift; it sacrifices heights for a large work

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station. Where more height is needed, a boom lift can be used. [http://en.wikipedia.org/wiki/aerial-work-platform] 1.2

STATEMENT OF THE PROBLEM

A problem remains a problem until a solution is proffered. With the limitations encountered in the use of ropes, ladders, scaffold and mechanical scissors lifts in getting to elevated height such as the amount of load to be carried, conformability, time consumption, much energy expended etc. the idea of a hydraulically powered scissors lift which will overcome the above stated limitations is used. 1.3

SCOPE OF THE STUDY

The design and construction of the hydraulic scissors lift is to lift up to a height of 3.2m and carrying capacity of less than 500kg (500 kilograms) with the available engineering materials. However, there is for academic purpose, a similar project for general carrying – capacity with a selection of better engineering materials. 1.4

IMPORTANCE / SIGNIFICANCE OF THE STUDY

The design and construction of a hydraulic scissors lift is to lift a worker together with the working equipment comfortably and safely to a required working height not easily accessible. It may be used without a necessary external assistance or assistance from a second party due to the concept of the design. This project will be an important engineering tool 12

or device used in maintenance jobs. Changing of street lights, painting of high buildings and walls around the school environment. 1.5

AIMS/OBJECTIVES OF THE STUDY

The project is aimed at designing and constructing a hydraulically powered scissors lift to lift and lowers worker and his working equipment with ease and in the most economical way. The lift is expected to work with minimal technical challenges and greater comfort due to its wide range of application. The device can easily be handled to the site to be used with a tow-van and then powered by a generator. Between the heights of lift (i.e. the maximum height) the device can be used in any height within this range and can be descend immediately in case of emergency, and can be operated independent of a second party.

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CHAPTER TWO

2.0

REVIEW OF RELATED LITERATURE

Mans quest for improvement has never been satisfied. The drive towards better and greater scientific and technological outcome has made the world dynamic. Before now, several scientist and engineers have done a lot of work as regards the scissors lift in general. A review of some of that work gives the design and construction of a hydraulic scissors lift a platform. 2.1

UPRIGHT’S SCISSORS LIFT

In Selma California, there is a manufacturer of aerial platforms by name “UPRIGHT”, this world – wide company was founded in 1946, and now it manufactures and distributes its product. According to Wikipedia article, upright was founded by an engineer, Walkce Johnson who created and sold the first platform which was called a “scissors lift” due to the steel cross bricking that supported the platform giving it the product name “magic carpet”. The magic carpet was able to provide instant revenue for the young company due to its quick popularity among its companies. Wikipedia further explained that the company constructed innovating and by early 1930s their product included the X – series scissors lift. By

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1986, they had introduced their first sigma arm lift, model SL20. In 1990, they improved upon their product line by introducing the sigma arm speed level. This feature continued to be unique to be upright product and allow self-leveling of the platform on rough terrains Upright introduced an equal innovative family of boom lift in 1990s. In 1995 they produced their first trailer mounted boom. The 8P37 (known as AS38) in 1996. This truly innovated company has left their mark with the other products including compact scissors design and modular alloy bridging, as well as expanding the versatility of instant span towers with aircraft docking and faced system, you will find upright products, especially the scissors lift, as standard equipment for a variety of application it is now a visual application in numerous fields and locations. [www.carliftequipment.ca/inventory/upright] 2.2

SCAFFOLD

Scaffold allows workers to transport themselves and their materials to elevated heights, usually up and down in an unfinished building. Scaffolds are designed to allow workers get to elevated heights; they are used in building sites and construction sites but used mainly in building sites. According to Google internet search machine, scaffold is cross section of pipes, irons or woods which are arranged in such a way that

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workers or operators can climb on the arranged pipes to get to elevated heights. Scaffolds cannot be adjusted automatically and they only can remain fixed the way it is arranged unless rearranged. The tubes are either steel or aluminum, although composite scaffolding using filament wound tubes of glass fiber in a nylon or polyester matrix. If steel, they are either “black” or galvanized. The tubes come in a variety of length and a standard diameter of 48.3mm. The basic difference between the two types of tubes is the lower weight of aluminum tubes (1.7kg/m as opposed to 4.4kg/m) and also a greater flexibility and so less resistance to force. Tubes are generally bought in 6.3m length and can be cut down to certain typical sizes. Boards provide a working surface for users of the scaffold. They are seasoned wood and are very strong. Scaffolds for increased height are preferably made of hardened materials like metal pipes. After arranging the pipes, a flat materials usually made of wood is placed on top so that the

worker

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comfortable

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top.

[http://en.m.wikipedia.org/wiki/scaffold] 2.3

BOOM LIFT

Boom lifts are used for lifting materials especially on construction sites, they are designed to carry heavy equipment and materials from one

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place to another. They are usually connected to cars or trucks that move from one place to another. Boom lifts can lift materials and equipment high to height so great that carrying this equipment by other means will almost be impossible. According to material handling equipment from ask search engine, Boom lifts can move vertically, horizontally and sideways and some can even rotate depending on the circumstance. Boom lifts are very complex iron design and the jointed parts should be lubricated to reduce friction and improve efficiency. Boom lifts are formed mainly in construction sites and building sites. They are also utilized by Electrical companies and firms such as PHCN (Power Holding Company of Nigeria) Plc. They are very expensive and are not available in crude or semi mechanized type of production. Boom lift possess advantage over other types of lifts because it can lift heavy materials, keep them at elevated heights for a long period of time; rotate and the lift span of the equipment is long. Boom lift can fold together to become compressed and portable. There are two basic types of boom lifts: straight boom lift and articulated boom lift. These units are often hydraulically powered. 2.3.1 THE STRAIGHT BOOM LIFTS Straight boom lifts are generally used for jobs that required a high reach without obstruction. The machines turntable can rotate 360 o with an

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extensible boom that can be raised vertically to below horizontally. The operator can maneuver and steer the vehicle while the boom is fully extended. It is available in gas, propane or diesel-powered models with two or four wheel drive. 2.3.2 ARTICULATED BOOM LIFT: Articulated boom lifts are used for jobs that require reaching up and over obstacles to gain access to a job not easily achieved by a straight telescopic boom. This lift is nearly identical to the straight boom lift in every aspect; except in the boom’s ability to articulate. Articulation points on the boom allow it to bend in any number of different directions enabling it to maneuver around various obstacles on a job site. Boom lifts can be equipped with out riggers to stabilize the unit while the boom is fully extended. [http://ritchienikit.com/wiki/index.php/aerialplatform] 2.4

MECHANICAL SCISSORS LIFT

The mechanical scissors lift is used for lifting materials especially on construction sites. This is one of the most recent advancement on scissors lift. There, the lift utilizes a belt drive system connected to a load screw which constructs the “X” pattern on tightening and expands it on loosening. The lead screw actually does the work, since the applied force from the wheel is converted to linear motion of the lift by help of the 18

lead screw. This can be used to lift the working and equipment to a height. A general knowledge however, regarding screws will reveal the loss due to friction in the screw threats. Therefore, the efficiency of this device is low due to losses in friction. Also, the power needed to drive the machine is manual, and much energy is expanded to achieve a desired result. Its suitability however, cannot be overemphasized as it can be used in almost every part of the country whether there is availability of electricity or not. 2.5

HYDRAULIC LIFT:

Hydraulic lift is a device for carrying persons and loads from one floor to another, in a multi-storey building. The hydraulic lifts are of the following types. 1.

Direct acting hydraulic lift and

2.

Suspended hydraulic lift.

The direct acting hydraulic lift consist of a ram sliding in a cylinder. A platform or a cage is fitted to the top end of ram on which goods may be placed or the persons may stand. As the liquid under pressure is admitted to the cylinder, the ram moves up and the cage is lifted. The lift of the cage is equal to the stroke of the ram. The cage moves in the downward direction when the liquid from the fixed cylinder is removed.

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The suspended hydraulic lift is a modified form of the direct acting hydraulic lift. It is fitted with a jigger which is exactly, same as in the case of a hydraulic crane. The cage is suspended by ropes. It runs between guides of hard wood round steel. In order to balance the weight of the cage sliding balance weights are provided. [Gupta, 2006] 2.5.1 HYDRAULIC SCISSORS LIFT Scissors lifts has developed overtime, and at each stage of its development, critical problems are solved. The hydraulic type, but this time, the load screw is replaced by a hydraulic ram powered by a pump and on electric motor and generator. One outstanding feature about this design however. Is its independent operation and increased efficiency. Fluid power is one of the greater form of power where small input results in a very large output. This scissors lift can be handled by one person to a place of use, and power the generator. The lift does not lifting immediately, the operators climbs on the platform and switches open the hydraulic circuit thereby leading to an upward extension. When the required height is reached the circuit is closed, and lifting stops the control panel or station is located on the top frame. When work is done, the scissors lift is folded by hydraulic means and handled back to the point of collection.

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2.5.2 PRINCIPLE

OF

OPERATION

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HYDRAULIC

LIFT

(EXTENSION AND CONTRACTION) A scissors lift is a type of platform that can usually only move vertically. The mechanism to achieve this is the use of linked, folding supports in a criss-cross “X” pattern, known as a scissors mechanism. The upward motion is achieved by the application of pressure to the outer side of the lowest set of supports, elongating the crossing pattern and prepelling the work platform vertically. The platform may also have extending “bridge” to allow closer access to the work area, because of the inherent limits of vertical – only movement. The contraction of the scissor action can be hydrdaulic, pneumatic or mechanical (via a leadscrew or rack and pinion system), but in this case, it is hydraulic. Depending on the power system employed on the lift; it may require no power to enter “desert” mode, but rather a simple release of hydraulic or pneumatic pressure. This is the main reason that these methods of powering the lift (hydraulic) is preferred, as it allows a fail – safe option of returning the platform to the ground by release of a manual valve [http://en.wikipedia.org/wiki/aerial_work_platform scissors_lift]

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DEFLECTIONS IN SCISSORS LIFT Deflection Defined Deflection in scissors lifts can be defined as the resulting change in elevation of all or part of a scissors lift assembly, typically measured from the floor to the top of platform deck, whenever loads are applied to or removed from the lift. ANSI MH29.1 - Safety Requirements for Industrial Scissors Lifts states that “. . . all industrial scissors lifts will deflect under load”. The industry standard goes on to outline the maximum allowable deflection based on platform size and number of scissors mechanisms within the lift design. What Causes Deflection? Before attempting to discuss how to limit scissors lift deflection, it is important to understand the contributing factors to a lift’s total deflection. An open, or raised, scissors lift acts very much like a spring would – apply a load and it compresses, remove a load and it expands. Each component within the scissors lift has the potential to store or release energy when loaded and unloaded (and therefore deflect). There are also application-specific characteristics that may promote deflection. Understanding these Top 10 root causes helps to pinpoint and apply effective measures to limit deflection.

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Scissors Legs Leg deflection due to bending is a result of stress, which is driven by total weight supported by the legs, scissors leg length, and available leg cross section. The longer the scissors legs are, the more difficult it is to control bending under load. Increased leg strength via increased leg material height does improve resistance to deflection, but can create a potentially undesirable increased collapsed height of the lift. Platform Structure Platform bending will increase as the load’s center of gravity moves from the center (evenly distributed) to any edge (eccentrically loaded) of the platform. Also, as the scissors open during raising of the lift, the rollers roll back towards the platform hinges and create an increasingly unsupported, overhung portion of the platform assembly. Eccentric loads applied to this unsupported end of the platform can greatly impact bending of the platform. Increased platform strength via increased support structure material height does improve resistance to deflection, but also contributes to an increased collapsed height of the lift. Base Frame Normally, the lift’s base frame is mounted to the floor and should not experience deflection. For those cases where the scissors lift is mounted to an elevated or portable frame, the potential for deflection increases. To effectively resist deflection, the base frame must be rigidly supported 23

from beneath to support the point loading created by the two scissors leg rollers and the two scissors leg hinges. Pinned Joints Scissors lifts are pinned at all hinge points, and each pin has a running clearance between the O.D. of the pin and the I.D. of its clearance hole or bushing. The more scissors pairs, or pantographs, that are stacked on top of each other, the more pinned connections there are to accumulate movement, or deflection, when compressing these running clearances under load. Hydraulic Circuit – Air Entrapment All entrapped air must be removed from the hydraulic circuit through approved “bleeding” procedures – air is very compressible and is often the culprit when a scissors lift over-compresses under load, or otherwise bounces (like a spring) during operation. Hydraulic Circuit – Fluid Compressibility Oil or hydraulic fluid will compress slightly under pressure. And because there is an approximate 5:1 ratio of lift travel to cylinder stroke for most scissors lift designs (with the cylinders mounted horizontally in the legs), there is a resulting 5:1 ratio of scissors lift compression to cylinder compression. For example: 1/16” of fluid compressibility in the cylinder(s) translates into 5/16” of vertical lift movement.

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Hydraulic Circuit – Hose Swell All high pressure, flexible hosing is susceptible to a degree of hose swell when the system pressure is increased. System pressure drops slightly because of this increased hose volume, and the scissors table compresses under load until the maximum system pressure is reestablished. And, as with compressibility, the resulting lift movement (deflection) is 5 times the change in oil column height in the hosing. Cylinder Thrust Resistance Cylinders lay nearly flat inside the scissors legs when the lift is fully lowered and must generate initial horizontal forces up to 10 times the amount of the load on the scissors lift due to the mechanical disadvantage of their lifting geometry. As a result, there are tremendous stresses (and resulting deflection) placed on the scissors inner leg member(s) that are designed to resist these cylinder forces. And, as already mentioned above with any changes in column length along the line of the lifting actuator(s)/cylinder(s), the resulting vertical lift movement is 5 times the amount of deflection or movement of cylinder hinge points mounted to leg cross members. Load Placement Load placement also plays a large part in scissors lift deflection. Offcentered loads cause the scissors lift to deflect differently than with centered or evenly distributed, loads. End loads (in-line with the 25

scissors) are usually shared well between the two scissors leg pairs. Side loads (perpendicular to the scissors), however, are not shared as well between the scissors leg pairs and must be kept within acceptable design limits to prevent leg twist (unequal scissors leg pair deflection) – which, in addition to platform movement due to deflection, often results in poor roller tracking, unequal axle pin wear, and misalignment of cylinder mounts. Lift Elevation During Transfer As mentioned above, degree of deflection is directly related to change in system pressure and change in component stress as a result of loading and unloading. Scissors lifts typically experience their highest system pressure and highest stresses (and therefore the highest potential for deflection) within the first 20% of total available vertical travel (from the fully lowered position). What can be done to Limit Deflection? There are a variety of proven methods to reduce scissors lift deflection, with varying design and cost impacts to accomplish each. Listed below are the most common of these methods, in no particular order, to provide the reader an understanding of where to begin when attempting to reduce or eliminate deflection during load transfer (i.e. applying a load, or removing a load).

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Select a Lift with a Design Capacity Greater Than Required for the Application Most scissors lifts designed for duty at higher capacities will experience less stress in all structural components, as well as lower system pressures, at lower, or de-rated, working capacities. Reduced stresses & pressures always result in reduced deflection. The amount of this reduction varies depending on the lift’s design, so consult the manufacturer to obtain a more specific estimate of reduction in deflection. Minimize Potential for Air Entrapment Scissors lift manufacturers provide an approved method of “bleeding” entrapped air from a new or repaired hydraulic system which may have had air introduced. This usually involves operating an empty lift through multiple cycles, and then safely cracking open fittings near high spots in the system where air accumulates. Refer to the O&M manual for this procedure. Limit or Eliminate Hosing Flexible hose lengths should be limited wherever possible and replaced with pipe or mechanical tubing as practicable to minimize or eliminate swell as the system pressure fluctuates. Use Mechanical Actuators in lieu of Hydraulic Actuators

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Although it is more difficult, and more expensive, to achieve high vertical lifting forces with mechanical actuators, they do eliminate the issue of fluid compressibility and provide a more accurate and repeatable means of achieving – and holding – a desired transfer elevation. Avoid Transfer of Loads Within First 20% of Lift’s Travel To minimize stresses and deflection at transfer elevations, it is critical to design the conveyor or transfer system to ensure that these elevations are above the scissors lift’s “critical zone” of the first 20% of the lift’s available travel. Transfer Loads Over Fixed End of the Platform First, if possible, loads should not be transferred over the sides of a raised scissors lift. It is much more difficult to control deflection when the load is not shared equally between the two scissors leg pairs. Make it rule to only transfer over the ends of the lift – in line with the scissors legs. Second, load transfer should be made over the hinged, or fixed, end of the lift platform to avoid placing concentrated loads on the less supported, overhung end of the platform – provided the platform is equipped with “trapped” rollers, or is otherwise capable of withstanding this edge loading without risk of the platform tipping up or losing contact with the rollers.

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Ensure that the Base Frame is Lagged Down and Fully Supported First, base frames should be adequately attached to the surface on which they are mounted. Base frames that are not bolted, welded, or otherwise attached to withstand the upward forces created by eccentric loading of the platform will contribute to deflection by bending or moving while resisting such forces. Next, bases must be rigidly supported beneath the entire perimeter of the frame in order to withstand without deflection the four point loads imposed upon the frame from above by the four scissors legs – (2) moving roller points and (2) fixed hinge points. Platform Locking Pins When there is no alternative to transferring loads over the sides of a lift, or whenever lift deflection must be held to near zero in any transfer orientation, consider using platform locking pins. These pins can be manual or powered, and mounted beneath the scissors lift deck or an adjoining fixed landing. The pins are extended into receivers located in the mating elevated structure during load transfer, and then retracted before the lift can be operated again. Use Vertical Acting Actuators in lieu of Horizontal Mounts Some permanent installations may accommodate actuators which are mounted vertically beneath the lift instead of horizontally inside the lift structure. Vertical orientation of the actuators provide a 1:1 ratio of lift 29

travel to actuator stroke instead of the 5:1 ratio normal with horizontal mounting of the actuators inside the scissors. This means a 1:1 ratio of lift deflection to actuator compression, 80% less than the 5:1 ratio experienced normally. Vertical mounting and pushing upward against underneath side of the platform to raise the lift also eliminates the high stresses usually exerted at the actuator thrust inner leg member(s). Summary on Deflection Deflection is a normal and expected characteristic of industrial scissors lifts. And though odds are that most scissors lift users have not had to concern themselves with this issue because their lifting application is fairly immune to the effects of deflection, there is always a chance that it matters greatly. ANSI MH29.1accurately points out that “It is the responsibility of the user/purchaser to advise the manufacturer where deflection may be critical to the application.” Though deflection is easier to qualify than it is to quantify, there are industry best practices which can be applied to reduce the impact or amount of deflection being experienced.

(Michael, 2008)

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CHAPTER THREE

3.0

DESIGN THEORY AND CALCULATION In this section all design concepts developed are discussed and

based on evaluation criteria and process developed, and a final here modified to further enhance the functionality of the design. Considerations made during the design and fabrication of a acting cylinder is as follows: a Functionality of the design b Manufacturability c Economic availability. i.e. General cost of materials and fabrication techniques employed. 3.1

DESIGN THEORY In this chapter, mathematical relationships are developed for the

various parameters necessary for the implementation of this design and arranged in sections below corresponding to the sequence of their implementation. Hydraulic systems are used to control and transmit power. A pump driven by a prime mover such as an electric motor creates a flow of fluid, in which the pressure, direction and rate of flow are controlled by values. An actuator is used to convert the energy of the fluid back into mechanical power. The amount of output power developed depends

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upon the flow rate, the pressure drop a cross the actuator and its overall efficiency. Most lifting devices are powered by either electricity, pneumatic or mechanical

means. Although

these

methods

are

efficient

and

satisfactory, they exist lots of limitations and complexity of design of such lifts as well as high cost of electricity, maintenance and repairs does not allow these lifts to exist in common places. The idea of a hydraulically powered scissors lift is based on Pascal’s law employed in car jacks and hydraulic rams which states that “pressure exerted anywhere in a conformed incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio remains the same”

(Michael and John, 1989).

3.1.1 CYLINDER SELECTION The hydraulic cylinder (or the hydraulic actuator) is a mechanical actuator that is used to give a unidirectional stroke. It has many applications, notably in engineering. 3.1.1.1

Single Acting Cylinders

Single acting cylinders use hydraulic oil for a power stroke in one direction only. The return stroke is affected by a mechanical in one direction only. The return stroke is affected by a mechanical spring

32

located inside the cylinder. For single acting cylinders with no spring, some external actin force on the piston rod causes its return. 3.1.1.2

Double Acting Cylinders

Double acting cylinder uses compressed air or hydraulic fluid to pour both the forward and return strokes. This makes them ideal for bushing and pulling and pulling within the same application they are suitable for full stroke working only at slow speed which results in gentle contact at the ends of stroke. PRESSURE SUPPLIED TO THE HYDRAULIC CYLINDER Pressure (P) = Force (P) Area (A) Where

P=F A

F = [W + (WA)] 2_ tan

 = angle between the scissors and the horizontal F = force needed to hold the scissors lift W = the weight of the payload and platform WA = combine weight of the two scissors arms. Weight of the arm = mass of the scissors arm × acceleration due to gravity 3.2

Buckling Action on Cylinder

In the selection of cylinder, two primary concerns were noted:

33

a The strength of the rod. i.e its ability to support a specified load without experiencing excessive stresses b The ability of the piston to support a specified load without undergoing unacceptable deformations. PE

=

2EI L2

Where E = Young Modulus of elasticity I = Moment of Inertia L = Unsupported Length

I

= d4 64

(Rajput, 2010)

= AK2

To avoid buckling (bending) of the strut, the compressive stress E must not exceed the yield stress Y. (E < Y) Because of the large deflection caused by buckling, the least moment of inertia I can be expressed as I=AK2 Where A is the cross sectional area and K is the radius of gyration of the cross sectional area. i.e K

=

I_ A

Note that the smallest radius of gyration of the column, i.e the least moment of inertia I must be taken in order to find the CRITICAL STESS OR BUCKLING STRESS OR CRIPPLING STRESS. 34

Dividing the buckling equation by A, gives E

= PE A

= 2E_ (L/k)2

Where E = is the compressive stress in the column and must not exceed the yield stress Y of the material i.e E < Y L/K is called the SLENDERNESS RATIO; it is a measure of the column’s flexibility. CASE END CONDITIONS

EQUIVALENT

BUCKLING

1

Both ends hinged or pin

LENGTH Le L

LOAD (EULER) 2EI

2

jointed or rounded or free One end fixed, alter end

2L

L2 2EI

3

free One end fixed other end

L/ 2

4L2 22EI

4

pin jointed Both ends fixed or

L/2

L2 42EI

encastered

L2 (Rajput, 2010)

3.2.1 STRESSES IN CYLINDERS When cylinders are subjected to internal fluid pressure, the following types of stresses are developed. 1 Hoop or circumferential stress. 2 Longitudinal stress. Hoop stress is produced as a result of forces applied from inside the cylindrical pipe pushing against the pipe walls. Hoop stress is the result 35

of forces pushing against the circumferential cylinder walls. While, longitudinal stress is as a result of forces pushing against the top ends of a cylinder. These forces are derived using Newton’s first law. Let

d = internal diameter of cylinder T = thickness of cylinder P = internal pressure (gauge) in the cylinder C = circumferential or hoop stress L = longitudinal stress L = length of cylinder or pipe

Hoop stress C = pd/2t Longitudinal stress L = pd/4t = C - L 2

Maximum Shear Stress Tmax = pd 8t Bursting force (pressure) = pdL Resisting strength = 2LtC

Busting force = resisting strength ( pdL = 2LtC ) Note: the maximum stress developed must not exceed the permissible tensile stress (t) of the material.

(Rajput, 2010)

BASIC DIMENSIONS OF COMPONENT MEMBER. Lift Extension - At maximum extension, an “X” arrangement of the lift moves 0.9m = 900mm. - Total number of tiers of scissors (combined) = 3 36

-

Thus, total height of extension = 3 × 0.9 = 2.7m. Length of base = 1400mm Width of base = 800mm Height of base from ground = 500mm At maximum extension, Angle of inclination = 50 At maximum extension, distance between two scissors feet = 800mm Distance moved by sliding foot to full extension = 400mm

Bearings -

Number of ball bearings = 4 Number of shell bearings = 36 Internal diameter of ball bearings = 30mm Internal diameter of shell bearings = 11mm External diameter of ball bearings = 50mm External diameter of shell bearings = 15mm Pivot pin diameter = 14.6mm

Platform -

Total height of platform = 1400mm. Total width of plat form = 800mm Total height of platform = 800mm Permissible load on plat form + platform weight = 300kg = 2.94kn.

Jointed Members - Thickness of rectangular pipe = 3mm - Thickness of angle bar = 3mm. Scissors Arm The material used for the scissors arms (members), is stainless steel. With the density and the dimensions of the scissors arms known, the mass can be calculated using the relationship. Density (p) = Mass (M) Volume Mass = p.v

kg/m3

Density of stainless steel (type 304) = 7900kg/m3 37

Area (cross sectional area) = A1 – A2 A1 = Outer cross sectional area A2 = Inner cross sectional area A1 = Height × breadth = h × b A2 = (h – t)(b – t) Where h = scissors arm height b = breadth t = thickness of material. Volume (v) = area × length V = AL (m3)

X

L

X t

h

Section X - . - - X

b

38

Scissors Arm Cross Section

DESIGN OF SCISSOR LIFT WITH FORCE APPLIED FROM THE SIDE

W

Actuator F

W + Wf 2

W + Wf 2

F = W + Wa 2tan Where 39

F = force provide by the hydraulic Ram W = combined weight of the pay load and plat form Wa = combined weight of two scissors arms themselves  = Angle between the scissors arm and the horizontal.

Psin = (W+WF) 2 P = [(W+WF)/2sin]

where WF = Frame weight.

F = Pcos F = cos [(W+WF)/2sin] F = (W+WF)/2tan

40

3.2 DESIGN CALCULATIONS Input h =50MM b = 25MM t = 3mm

A = 216MM2 L = 1200MM

ᵨ

stainless steel

Processing A1 = b × h = 25 × 50 A2 = (b – t)(h – t) = (25 – 3)(50 – 3) = 22 × 47

Output A1 = 1250m2

A = A1 – A2 = 1250 – 1034

A = 216mm2

V =A× L = 216 × 10-6 × 1200×10-3

V = 2.59×10-4m3

A2 = 1034M2

=

7900Kg/M3 M = PV V = 2,59 × 10-4 M3 = 7900 × 2.54 × 10-4 M = 2.05Kg Mass of one tier = M × 4 = 2.05 × 4

M = 2.05kg

8.2kg

Ms = 8.2Kg g = 9.81M/s2

Mp = 300Kg g = 9.81M/s2 WA = 80.4N θ = 500

Wa = Msg = 8.2 × 9.81

W = 80.4N

41

F=

[

WA 2 tanθ

W+

W = 2943

]

F 2503.1N

W= Mpg = 300 × 9.81 F

80.4 2 ¿ 2943+ tan 50

¿ 2943+

Foverall = 7509N = 7.5kN

40.2 1.1918

Foverall = 2503.1 × 3 HYDRAULIC CYLINDER CALCULATION Selected cylinder diameter from standard cylinder sizes D=36 D=50

A1=πD 2/4 =π 502/4

A1 =1963.5mm2

A2=π/4[D2-d2] =π/4[502-362]

A2=945.6mm2

F=7.5KN Supplied pressure A=1.9635×10-3m2 P=F/A =7.5×103/1.9635×10-3 DESIGN OF CYLINDER FOR BUCKLING For both ends pinned, Buckling load PE =π2EI/L2

42

P=38.20bar

L=0.8m E=210GN/m2 (for mild steel) D = 0.036m

I=πd4/64 I=π(0.036)4/64

I=8.24×10-8m4

PE =π2×210×109×8.24×10-8/0.82

A=

PE = 267004.7N D = 0.036

π d2 4 2

0.036 ¿ ¿ π¿ ¿¿

Buckling stress ᵟE ¿

267004.7 −3 10 1.02

Since the load required 43

PE=267KN

A = 1.02×10-3m2

(7.5kN) is less than the Buckling load (PE) = 267kN, the cylinder is safe in operation

d = 0.036 L = 0.8m

SLENDERNESS RATIO Radius of gyration d K ¿4 ¿

K = 0.009

0.036 4

Slenderness Ratio = ¿

3.5.2.2

P = 38.2 bar D = 50mm t = 5mm

ᵟE = 262Mn/m2

L K

ᶋ = 89 long column

0.8 0.009

DESIGN OF CYLINDER FOR STRESSES Hoop stress ᵟc = 6

Pd 2t

ᵟc=19.1MN/M2

−3

¿ 3.83× 1 0 × 50× 1 0 −3

¿ 2× 5× 1 0

P = 38.2 bar D = 50mm t = 5mm

Longitudinal stress Pd ᵟL ¿ 4 t

44

ᵟL = 9.55mn/m2

10−3 ¿ 3.82× 10 × 50 × ×5 ×10−3 4 6

L = 450mm D = 50mm P = 38.2 bar

Bursting force (pressure) = PdL 3.82 × 106 × 50 × 10-3 0.45 Therefore Bursting force = Resisting force. Since the Hoop stress is less than the tensile stress of the material of the cylinder, the cylinder will not burst. ᵟc = 19.1MN/M2 < 410MN/M2 = ᵟt DESIGN OF PINS FOR SHEARING AND CRUSHING F

F

16

9 60mm

Head

body

thread

F = 750 d = 9mm

Area of pin Ap = πdp2/4 π(9 × 10-3)2 / 4

π = 22/7 r = 0.045m h = 0.06m

total surface area of pin As = 2πr (r + h) = 2π × 0.045 (0.045 + 0.06)

45

Ap = 6.36×10-5m2 As = 2.969 × 10-2

ᵟ = 118mn/m2

Shear stress =shear load/share Area crushng stress=shear ¿ F/ As

¿

ᵟcr = 253kn/m2

load sruface area total

7509 ×10 x 2 2.969

DESIGN OF MEMNERS FOR BUCKLING

D

d

b B

B = 50mm D = 25mm T = 3mm

b = B – t = 50 – 3 d = D – t = 25 – 3 I =B D3 −

b = 47mm d = 22mm

b d3 12

I = 2.34 × 10-8m2

22 ¿3 /12 25 ¿3−47 ¿ ¿50 ¿

Π = 22/7 E = 193 × 109 I = 2.34 × 10-8 L = 1.2m A = 216mm2

Buckling load for the members PE =

π 2 EI L2

¿ π 2 ×193 ∪109 ×

PE = 37.144kN −8

2.341 o 1.2

Critical stress бE = 172MN/M2 46

бE

l 2 ¿ k ¿ π 2 E /¿

P ¿ E A

1.2 2 ¿ k π 2 ×193 × 109 /¿

3

¿ 37.144 ×

10 × 10−6 216

Since the critical stress (бE = 172MN/M2) is less than the yield stress of stainless steel (415MN/M2), therefore the material is safe I operation.

DESIGN OF MEMBERS FOR BENDING W/ 2 θ F 0.6m 0.6m

θ O

F

θ 47

W+WF/2

Where WF = Weight of frame W = weight of platform + payload Θ = angle of inclination of scissors arm=

W=2943N WF=20.111N

10, 20, 30,40, 500

+

Σ M = force × perpendicular 0

distance. For θ = 100 , Bending moment =(W+WF/2)cosθ×0.6 +W/2cosθ×0.6 =0.6cosθ(W+WF/2 + W/2) = 0.6 cos10(2943+20.111/2 +2943/2) =0.6×0.9848(2953.06). =1744Nm

FOR θ =200 Bending moment= 0.6cosθ(W+WF/2 +W/2) =0.6cos20(2943+20.111/2 +2943/2) =835.331 +829.661 =1664.99Nm

FOR θ=300 Bending moment= 0.6cosθ(W+WF/2 +w/2) 48

=0.6cos30(2943+20.111/2 +2943/2) =769.84 + 764.59

FOR θ=400

=1534.43Nm

Bending moment= 0.6cosθ(W+WF/2 +W/2) = 0.6cos40(2943+20.111/2 +2943/2) =0.4596(2953.06)

FOR θ=500 =1357.23Nm Bending moment = 0.6cosθ(W+WF/2 +W/2) = 0.6cos50 (2943+20.111/2 +2943/2) =0.3857×2953.06

M/I=б/Y=E/R Therefore from the analysis of the bending moment above, the Maximum bending moment = 1744.92Nm occurs at the point when θ=100 Therefore, the smaller the angle, the higher the bending moment and vis-visa.

49

=1138.91Nm

CHAPTER FOUR

4.0 MATERIAL SELECTION, CONSTRUCTION PROCEDURES, COST ANALYSIS AND MAINTENANCE 4.1: MATERIAL SELECTION Material selection plays a very important role in machine design. For example, the cost of materials in any machine is a good determinant of the cost of the machi8ne. more than the cost is the fact that materials are always a very decisive factor for a good design. The choice of the particular material for the machine depends on the particular purpose 50

and the material for the machine depends on the particular purpose and the mode of operation of the machine components. Also, it depends on the expected mode of failure of the components. Engineering materials are mainly classified as: 1 Metal and their alloys, such as iron, steel, copper, aluminum etc. 2 Non-metals such as glass, rubber, plastic etc. metals are further classified as ferrous metals and non-ferrous metals. Ferrous metals are those metals which have iron as their main constituent, such as cast iron, wrought iron and steels. Non-ferrous metals are those which have a metal other than iron as there main constituent, such as copper, aluminum, brass, tin, zinc etc. For the purpose of this project, based on the particular working conditions machine component were designed for only the ferrous metals have been considered. Also, certain mechanical properties of metals have greatly influenced our decisions. These properties include: 1 Strength: it is the ability of a material to resist the externally applied force without break down or yielding the internal resistance offered without break down or yielding the internally applied force is called stress. 2 Stiffness: it is the ability of a material to resist deformation under stress. 3 Elasticity: it is the property of a material to regain its original shape after deformation when the external force are removed. 51

4.

Plasticity: it is property of a material which retains the deformation

produced under load, permanently. 4 Ductility: a very important property of the material enabling it to be drawn into wire with the application of a tensile force. A ductile material is both strong and plastic. Ductile materials commonly used in engineering practical (in order of diminishing ductility) are mold steel, copper, aluminum, nickel, zinc tin and lead. 5 Malleability: it is a special case of ductility which permit materials to be rolled or hammered into thin sheets. A malleable material is plastic but not 80 essentially strong. Examples include; lead soft steel, wrought iron, wrought iron, copper and aluminum in order of diminishing malleability. 6 Toughness: it is the property of a material to resist fracture due to high impact loads like hammer blows, when heated. This property decreases. 7 Brittleness: it is the properties of a material opposite to ductility, it is the property of breaking of a material with little permanent deformation when subjected to tensile load, brittle materials snap off without giving any sensible elongation. Cast iron is a brittle material. 8 Hardness it embraces difference properties such as resistance to water, scratching, deformation and machinability etc. it also measure of the ability of a metal to cut another metal. ANALYSIS OF MECHANICAL PROPERTY REQUIREMENT OF ESSENTIAL MACHINE COMPONENTS.

52

It is necessary to evaluate the particular type of forces imposed on components with a view to determining the exact mechanical properties and necessary material for each equipment. A very brief analysis of each component follows thus: I II III IV V

Scissors arms Hydraulic cylinder Top plat form Base plat form Wheels

Scissors Arms: this component is subjected to buckling load and bending load tending to break or cause bending of the components. Hence based on strength, stiffness, plasticity an hardness. A recommended material is stainless steel. Hydraulic Cylinder: this component is considered as a strut with both ends pinned. It is subjected to direct compressive force which imposes a bending stress which may cause buckling of the component. It is also subjected

to

internal

compressive

pressure

which

generates

circumferential and longitudinal stresses all around the wall thickness. Hence necessary material property must include strength, ductility, toughness and hardness. The recommended material is mild steel. Top Platform: this component is subjected to the weight of the workman and his equipment, hence strength is required, the frame of the plat form is mild steel and the base is wood.

53

Base Platform: this component is subjected to the weight of the top plat form and the scissors arms. It is also responsible for the stability of the whole assembly, therefore strength. Hardness and stiffness are needed mechanical properties. Mild steel is used. Wheels: the wheels are position at the base part of the scissors lift and enable the lift to move from one place to the other without necessary employment of external equipment like car. Choice of stainless and mild steel 1

Mild Steel contains 0.05 to 0.3 percent carbons it has for almost all purpose replaced wrought iron, its greater strength giving it under viable advantages. Mild steel can be rolled, wielded and down. It can even be cast, though not very successfully. Among its application are plates for ship building, bicycle frame tubes, mesh work, bolts, nuts, studs etc. solid and hollow constructional sections, sheet metal parts and steel

2

castings such as flywheels and locomotive wheel centers. Stainless Steel: these are steel with high rust and corrosion resistance to meet specific application requirements. They also have high strength and toughness. It is an alloy of iron with about 11% chromium and other metals like nickel, molybdenum etc. the properties of rust and corrosion resistance, toughness and strength, aesthetics and how coefficient of friction were

54

considered to meet all requirements and the choice of stainless steel for the scissors members.

4.2 CONSTRUCTION OPERATION AND TOOLS In the design and construction of the hydraulic scissors lift, the procedures followed to achieve a positive result are laid down in the preceding text. But first, a look at the operations and tools involved. Operations 1 2 3 4

Marking out Cutting Drilling Joining (welding and bolt and nut)

Tools 1 Engineers rule 2 Scriber 3 Hack saw 4 Hand file 5 Drilling machine 6 Welding machine 7 Pliers 8 spanner 9 Try square 10 Electric grinder

Construction Procedure 1 Base Platform the material used for this purpose is mild steel angle bar. (3×3 inch) thickness 3mm. this is used because the base frame is 55

responsible for the stability of the platform. The basic dimensions were marked out using on Engr’s rule and scriber and then cut with the use of hack saw after being welded firmly clamped to the vice. They are then joined together by welding to give the base frame. 2 Scissors Arms these include the members that are arranged in a crosscross ‘X’ pattern and whose construction is responsible for lifting the platform and extension and lowering of the platform. It is usually made up of pipes with rectangular cross-section and have high resistance to bending. The material is stainless steel for corrosion and rust resistance to give high strength. After marking out, they were cut to the required sizes holes of appropriate diameter were drilled at both ends and the middle of each member. Hollow pins of external diameter corresponding to the drilled holes we then fit into holes and welded in order to strengthen the position then joined together to give the “X” pattern using bolts and nuts. The scissors arms were brazed to increase the strength and bending resistance.

Top Platform The material used for the construction of this component is mild steel angle bar for the frame and timber for the base of the platform. The 56

angle bar is cut into the required sizes and welded to form a rigid platform. The timber was equally into the required dimensions, drilled at the edges and fastened using bolt and nut to secures it in position at the base of the platform. Assembling of various components of the hydraulic scissors lift. The scissors assemblage was mounted on the base frame with one end hinged and the other fitted with roller (bearing) to produce the needed motion of rolling along the rail to cause lifting and lowering of the scissors lift. The scissors arm connected to the platform is also connected with one end hinged and the other fitted with roller to effect extension and contraction of the lit. The hydraulic cylinder is connected to the first arm of the scissors lift with both ends hinged. This cylinder provides the force needed to lift the load on the platform. The force is as a result of the pressure of the hydraulic supplied to the cylinder by the pump from the reservoir. The lift is fitted with wheels to aid mobility from one location to another. Painting of the entire unit is done to improve it aesthetics and increase the corrosion and resistance to rust. COST ANALYSIS OF MATERIAL The table below shows the cost of material used in constructing the hydraulic scissors lift 57

NO.

OF MATERIAL

QUANTITY

UNIT COST

TOTAL COST

ITEM 1

DESCRIPTION REQUIRED 3 x 3 lnch Angular 3

2400

7200

2 3

bar 1 x 1 Inch Angle bar 8 1 x 2 inch stainless 8

1000 3000

300 30, 400

4 5

steel pipe Mild steel bushins 20 Stainless steel 13

50 100

1000 1500

6 7

electrode Mild steel electrode 20 Drilling of stainless 12

25 250

500 3000

8

steel pipe Stainless steel drive 2

250

500

9 10 11 12

bit Bolt and nut Wood timber Roller bearing Hydraulic cylinder

25 650 100 6500

1000 1300 400 6500

13

(Ram) Electric motor and 1

20, 000

20, 000

14

pump Directional

control 1

5000

5000

4

2500

10, 000 6000 2000 96, 600

15 16 17

valve Wheel Transportation Miscellaneous TOTAL

40 3 4 1

CHAPTER 5

CONCLUSIONS AND RECOMMENDATION 5.1

CONCLUSION The design and fabrication of a portable work platform elevated by

a hydraulic cylinder was carried out meeting the required design standards. The portable work platform is operated by hydraulic cylinder 58

which is operated by a motor. The scissor lift can be design for high load also if a suitable high capacity hydraulic cylinder is used. The hydraulic scissor lift is simple in use and does not required routine maintenance. It can also lift heavier loads. The main constraint of this device is its high initial cost, but has a low operating cost. The shearing tool should be heat treated to have high strength. Savings resulting from the use of this device will make it pay for itself with in short period of time and it can be a great companion in any engineering industry dealing with rusted and unused metals. 5.2

RECOMMENDATION This device affords plenty of scope for modifications for further

improvements and operational efficiency, which should make it commercially available and attractive. Hence, its wide application in industries, hydraulic pressure system, for lifting of vehicle in garages, maintenance of huge machines, and for staking purpose. Thus, it is recommended for the engineering industry and for commercial production.

59

REFERENCE

GUPTA S.C (2006). Fluid mechanics and hydraulic machines. Pearson Education India, 2006. P.p 1296 RAJPUT R.K (2010). Strength of materials (mechanics of solids). S.Chand and Company LTD; 2010. P.p (928-941, 2-3, 590-592, 264-265).

60

HENRY W. SASLACH JR. and ROWLAND W. ARMSTRONG (2005). Deformatble bodies and their material behaviour. John Wiley and Sons inc. P.p (105-212). KHURMI R.S and GUPTA J.K (2006). Machine design. Fourteenth edition. P.p (40-45). DR. SADHU SINGH (2000) Applied stress analysis (fourth edition) P.p (35-42). KHURMI R.S and J.K GUPTA (2005). Theory of machines (second edition). Eurasia publishing house LTD. P.p(99-117). MICHAEL .A. (2008). Understanding scissors lift deflection. Autoquip corporation. (2008. PDF book). P.p (1-4).

Aerial platform: Retrieved online from http://ritchiewiki.com/wiki/index.php/Aerial-platform. Upright lifts: Retrieved online from www.canliftequipment.ca/inventory/upright. Scaffolding: http://en.m.wikipedia.org/wiki/scaffolding.

61