Clevis Pin Types

Having chosen Clevis Pins as the type of beam pins, it is now important to decide on a type of pin. It would be of benefit if all pins and bolts in the kit were the same, thus reducing assembly time as any bolt would fit any hole.

The image below shows a selection of pin types. The most appropriate for this crane would be either the SAE pin or the Bent pin. Once the stress analysis on the legs has been completed I shall use that information to select an appropriate standard pin for this crane.


http://www.huyett.com/catalog/index.php?cPath=21_30&gclid=CLWA-cbKgaECFSEulAod7wabuA

Preliminary Research on Potential Beam Pins

Introduction
In this post I will examine the potential of Hex bolts, Clevis pins, and U bolts for the application of becoming the crane pin component. I will use preliminary research to identify strengths and weaknesses of each type, and attempt to draw a conclusion of which one to investigate in more detail.

HEX Bolts
The bolts used for the crane must be a standard dimension and strong enough to withstand the forces applied when the crane is loaded. The first image is of the standard bolt measurement system and the second is of a table of standard dimensions and strengths. Note that the dimensions shown are all prior to coating and thus slightly undersized, and that all images were obtained from the same article which is referenced at the end.





This article also dealt with nuts and washers. The information is shown in the images below and will be used as a start point in finding the ideal bolt/washer/nut combination should the group decide to use HEX bolts for the crane pins.





http://www.mbw.co.uk/documents/factsheets/Non-Preload.pdf

The material that the bolts are made from also contributes considerably to their yield strengths. The following table was taken from a manufacturers website and applies to M16 HEX bolts. Further research will be conducted to assist the group in deciding the type and size of crane pin to use.



http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

In conclusion, this preliminary research shows that HEX bolts do have potential for use as our crane pins. Depending on the type they have yield strengths of approximately of the order of 100MPa, have many optional standard dimensions, and are cheap to purchase (~£1 per unit referenced below). There may be an issue with the numbers of small washers and nuts that would be required however, as these may easily be lost in a disaster relief environment.

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Ne=4294957938&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&N=4294962569+4294955562+4294905479&Ns=stockPolicy_uk%7c1%7c%7cnew_uk%7c1&binCount=85&multiselectParam=4294962569%204294955562&selectAttribute=M20#breadCrumb

Clevis Pins
Clevis pins are ideal for fast assembly situations such as with this emergency crane. The pin slots in the hole and is fastened by a split pin or similar. The table below, sourced from a manufacturers website, details the dimensions of some standard Clevis pins.



http://www.automotioncomponents.co.uk/purchase.php?p_no=P1242

The pins may be fixed in a variety of ways such as split pins, hitch pins, and linch pins. The image below shows a section of different connection types for Clevis pins.



http://www.automotioncomponents.co.uk/purchase.php?p_no=P1242

In conclusion, Clevis pins are a better option than HEX bolts. The cost and yield strengths of the Clevis pins are approximately the same as for the HEX bolts, though they are considerable quicker to assemble and do not require washers.

U Bolts
U bolts are slightly stronger than Hex bolts or Clevis pins as they fit two holes connected in pairs. They have a slight advantage over the HEX bolts as their washers may also be doubled up, as depicted below.



www.sea-sure.co.uk/ubolt2.htm

There are many different designs of U bolt, the two main types of which are shown below, though for the application of the emergency crane the square bend U bolt is most appropriate.



http://www.clampsinc.com/guidelines%20for%20ubolts.htm#COLD%20DRAWING%20AND%20BOLT%20STRENGTH

In conclusion, U bolts would be better than HEX bolts as they require fewer washers. They also cost only slightly more than Hex bolts or Clevis pins, meaning that overall they are the cheapest option as one would only require half as many of them for the crane as a whole.

Summary
HEX Bolts:
Strength - Acceptable
Price - Moderate
Speed of Assembly - Slow
Number of Parts - High

Clevis Pins:
Strength - Acceptable
Price - Moderate
Speed of Assembly - Fast
Number of Parts - Low

U Bolts:
Strength - High
Price - Low
Speed of Assembly - Slow
Number of Parts - Moderate

Conclusion
The HEX bolts are not appropriate for this crane. They have too many small parts and a system using them would require too much time to assemble in an emergency situation. The U bolts are the cheapest and strongest, though the number of small parts which may be lost and the speed of assembly mean they would not be appropriate either.

Therefore I conclude that Clevis pins are the most appropriate pins for this emergency crane. They are reasonably priced, they are fast to assemble, and they have the least number of components of the crane pin types considered.

Mark Hawkins - General Formula for Beam Dimensions

In order to assist with the stress analysis and beam design, I have created this general formula to calculate the beam dimensions in relation to each other for different materials.

List of alloys that can be used for legs / boom is too thick!!! - Jarrett D

LEGS
we have estimated that the maximum amount of stress any part of the legs are exposed to is around 8mpa. Although our calculations need to be refined it is unlikely that this value will not be greatly affected. Therefore i have put together a list of aluminium alloys that can be used.

alloy....................... ...compression yield stregnth (mpa)
Aluminum 2014-O .................................................185
Aluminum 2014-T4; 2014-T451 ............................425

Aluminum 2014-T6; 2014-T651 ...........................470

Aluminum 2048-T851 Plate .................................420

Aluminum 2618-T61.............................................370

Aluminum 5086-H112 ..........................................270

Aluminum 5086-H116; 5086-H32 .......................290

Aluminum 5086-H34 ..........................................325

Aluminum 5086-O ..............................................160

Aluminum 7039-T61 ..........................................390

Aluminum 7039-T64 ..........................................410

Aluminum 7178-T6; 7178-T651 ........................530

Aluminum 7178-T76; 7178-T7651 ...................460

Aluminum 7475-T7351 ...................................380

Aluminum A206.0-T7 Casting Alloy ..............372

Aluminum 206.0-T7 Casting Alloy ................372

Aluminum 208.0-F, Sand Cast .....................105

Aluminum 242.0-T21, Sand Cast ..................125

Aluminum 242.0-T571, Permanent Mold Cast .235

Aluminum 242.0-T571, Sand Cast ....................235

Aluminum 242.0-T61, Permanent Mold Cast ....305

Aluminum 242.0-T77, Sand Cast .....................165

Aluminum 295.0-T4, Sand Cast ......................115

Aluminum 295.0-T6, Sand Cast .....................170

Aluminum 295.0-T62, Sand Cast ...................235

Aluminum 296.0-T4, Cast ...............................140

Aluminum 296.0-T6, Permanent Mold Cast .180

Aluminum 296.0-T7, Cast ..............................140

Aluminum 319.0-F, Permanent Mold Cast .....130

Aluminum 319.0-F, Sand Cast ........................130

Aluminum 319.0-T6, Sand Cast ......................170

Aluminum 336.0-T551, Permanent Mold Cast 193

Aluminum 336.0-T65, Permanent Mold Cast ...296

Aluminum 354.0-T61, Permanent Mold Cast ....250

Aluminum 355.0-T71, Permanent Mold Cast .....215

Aluminum 355.0-T71, Sand Cast ........................205

Aluminum 355.0-T51, Permanent Mold Cast ....165

Aluminum 355.0-T51, Sand Cast .......................165

Aluminum 355.0-T61, Cast ................................215

Aluminum 355.0-T62, Permanent Mold Cast .....275

Aluminum 355.0-T6, Permanent Mold Cast ........185

Aluminum 355.0-T6, Sand Cast ..........................180

STEEL WIRE
I have calculted that if we use steel wire with a thickness of 1cm to lift the objects, it will be exposed to a maximum tension of 124.9 mpa. Therefore a medium carbon steel should be used to create the wire as it typically has a tensile strength much higher than this.

mass estimation of the legs and boom
using the dimensions given on the cad drawings i calculated a rough estimate of the mass of the crane legs and boom.

legs
given that all of the aforementioned alloys have a density between 2800 - 2650 kg/m^3

mass of the crane foot extender= 3.69-3.50kg
'' '' crane foot = 1.76- 1.67kg
'' ''crane leg = 3.25-3.08kg
'' ''crane shoulder = 5.00 - 4.74kg

Boom
when estimating the boom i came across something very worrying. i will show my calculations so someone can spot a mistake if i have made one.

density of carbon steel = 7800kg/m^3

cross sectional area of boom = (0.05x0.06)+2(0.02x0.07)= 5.8x10^-3 m^2
volume of boom = 5.1 x 5.8x10^-3 = 0.02958 m^3
mass of boom = 7800 x 0.02958 = 230.724 kg

here you can see that the boom is very heavy, therefore i suggest we make it thinner or shorter unless my calculations are wrong.

all facts and figures were obtained from http://www.matweb.com/

Ideas for the crane design and safety - Sandra Donohoe

Source:
Strength of materials by Nicholas Willems, John T. Easley, Stanley T. Rolfe, New York ; London : McGraw-Hill, c1981.

Materials

The table from the listed source highlights typical properties of some materials commonly used in construction.

The materials which have the greatest probability in being used as part of the crane structure include: steels, high carbon steel, aluminium alloys.

Steels have the possibility to be used in areas where high strength is required (high Young’s Modulus and a high yield stress) e.g the glide beam (I beam design). However it can pose carrying issues for the workers over long and uneven ground, due to its high mass/weight density.

A design that could be looked into for the glide rail according to BS5950-1:2000 (structural use of steelwork in building - part 1: code of practice for design- rolled and welded sections), include the use of castellated beams of the following dimensions (stresses would need to be calculated however it can reduce the weight issues but would be more expensive than a standard I beam ):



On the other hand as the region is currently susceptible to aftershocks, collapse of infrastructures… rescuers will be working in potentially dangerous conditions, to avoid toppling over of the structure the extra weight (e.g. of the steel) could provide some stability if such events were to occur.

Aluminium alloys possess a low mass/weight density and a relatively high yield stress but also have noticeably lower E value (than steels) proving strength per weight and less brittleness than steel. Aluminium however has the disadvantage of being more costly than steels as it requires more specialised manufacturing and repair processes, however due to their chemical properties are generally more resistant to corrosion.

Once the rescues has been completed and most of the rubble removed, if there are no further uses for some of these cranes, having produced them using these types of materials would allow them to be recycled and be considered environmentally friendly.