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.
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