Wednesday, July 18, 2012

Carbon Steel Bolts and Fasteners, Truths and myths

An Engineer Rambles
Is it possible to write an essay about bolts? If you are a Engineer, and your livelihood depends on machine design, then its possible to write a book about bolts.
There are three grades of bolt in common use in most locations. Most bolts which you will come across will only deviate slightly from these three grades. The lowest grade is 4.6, commonly known as commercial grade. Next comes grade 8.8, known as structural grade, and finally, the highest grade is 12.9, known as high tensile bolts. The first number represents the ultimate tensile strength of the bolt, 400 MPa, 800 MPa or 1200 MPa respectively. The second number represents the point at which the bolt will permanently stretch. (Officially, the 0.2% proof load stress).  A 4.6 bolt permanently stretches at 60% of its ultimate, an 8.8 at 80% and a 12.9 at 90 %.
Grade 12.9 bolts
Grade 12.9 bolts are most often supplied as socket head bolts or socket head cap screws with hexagon socket (Allen Key) drives.  Grade 12.9 bolts can also be obtained with hexagon heads. Popular brands of grade 12.9 bolts are Bufab Bulten and Umbrako. It is possible to obtain zinc or chrome plated versions, but not galvanised. Galvanising destroys the heat treatment of the steel. Beware! it is not possible to source 12.9 grade stainless steel bolts but it is possiable to get BUMAX Stainless in some cases for 8.8 and 10.9 replacements. 316 and 304 stainless steel will only be equivalent to grade 4.6, but BUMAX is  They may look cute in an engine bay, but they do not meet the grade. Grade 12.9 nuts are not made.
Grade 8.8 bolts are usually supplied as hexagon head bolts, often galvanised, sometimes zinc plated, but usually black. They are distinguished by the three radial lines on the head, or these day, by the numerals 8.8 stamped on the head. Grade 8.8 nuts are taller than grade 4.6, but do not have any distinguishing marks
Grade 4.6 bolts come in a vast array of configurations. Hexagon head, countersunk slot drive, galvanised, zinc plated, oxy-sealed (ie gold zinc plating), chrome plated. On a motor vehicle, grade 4.6 bolts are used to hold on trim parts and light objects. Grade If you need to replace a bolt, and the grade is doubtful, use grade 8.8 and be safe. The head of a grade 4.6 bolts is easily scratched with a file, not so a 8.8 bolt.
BUMAX 88 M2 and M36 Bolt same tensile strength as class 8.8

Correct design of a bolted joint is quite involved. Serious joints are designed on the basis of maximum stretch in the bolt, with minimum cyclical fluctuation of stresses in the bolt under working conditions. In order to achieve this aim, high tensile bolts are pre-tensioned, bolts are made as long as possible, and the minimum size bolt is used. Often the shank of a bolt (ie a cylinder head stud) is reduced in area to assist. Bolted joint design too complex to delve into here. The average Corvette enthusiast will be replacing bolts in an existing designed joint and need not worry to much about the design of joints.

How do you tighten a bolt?Grade 12.9 bolts are tightened with a torque wrench, right up to their 90% proof load. There is no other effective way to tighten a grade 12.9 bolt. Automotive manuals will give the tightening torque required. Grade 12.9 bolts do not work effectively with spring washers or shakeproof washers. These don't bite into the hardened surface of the bolt. There are only two ways of adding extra security to grade 12.9 bolts. Use Loctite on the threads or drill the heads and wire the bolts. It is possible to buy pre-drilled cap screws. Mating surfaces of a 12.9 bolted joint are not painted. For serious work, never re-use a fully tensioned 12.9 bolt.
Grade 8.8 bolts are tightened by the part turn method, torque wrench, or by using load indicating washers. In the part turn method, the bolt is done up to snug tight, and then advanced one, two or three flats of the hexagon, depending on the size, length etc. The torque wrench method is used commonly, often in the form of an air operated rattle gun. Special load indicating washers, such as Coronet washers can be used. These have dimples which indent the mating surface. A feeler gauge is used to determine the pre-load. Grade 8.8 Bolts are used in High Strength Friction Grip applications. If this is the case, the mating surfaces must not be painted or galvanised. For added security of the joint , use any one of the plethora of systems such as spring washers, shakeproof washers, Loctite, wired heads, split pins and castle nuts, locking tabs, lock nut or patented nut systems (Nyloc is common). For serious work, use castle nuts, either with split pins or wired together in groups. Also for serious work, do not re-use fully tensioned grade 8.8 bolts, Nylocs, split pins etc.
Grade 4.6 bolts are not pre-tensioned in the joint. They are tightened to snug tight only. For all intents, this means a reasonable hand effort on a spanner. Use good springy chrome-moly spanners, and never put an extension bar on the spanner. All of the security systems available for 8.8 bolts are available on 4.6 bolts. If you need much more than a spring washer, question whether the joint really requires an 8.8 bolt. Mating surfaces of a grade 4.6 bolted joint are usually painted prior to assembly.

16 comments:

  1. Super Engineers is the best leading manufacturing company in india exports a wide range of all type of fasteners high tensile fastener, long tensile fastener and many more at best industrial price.

    Long Tensile Fasteners Manufacturers

    ReplyDelete
  2. Pankaj International is committed to developing, manufacturing, delivering and servicing quality products. Our goal is to continuously improve our products and services in order to satisfy the needs of our customers before, during and after sales.

    In each of our product Category our quality is amongst the best in the world. We use the best quality of raw materials that are tested and subjected to stringent standards as per required specifications. Process capability studies & other statistical tools are employed to check all critical parameters during production. Every batch of finished product undergoes strict down the line process control monitoring which guarantees superior quality products. As a result, Pankaj International is synonymous with technology, quality and service.

    Fasteners exporter




    ReplyDelete
  3. thanks admin for providing very useful trick for make a wonderful website or blog, here you can find top alerts:
    tools and dies manufacturers in india

    ReplyDelete

  4. Thanks for providing this information was of great help for my needs, Keep posting content related to
    Stainless steel bolts

    ReplyDelete
  5. pee vee fastener is the best leading manufacturing company in india exports a wide range of all type of hex socket screw supplier india ,

    ReplyDelete
  6. Thank you for sharing great information about Stainless Fasteners Suppliers. For more details check out this website.

    ReplyDelete
  7. Thanks for providing such a great information really helpful blog
    Spring Washer Manufacturers In Delhi

    ReplyDelete
  8. Nice Blog. Thanx For Sharing. Kova Fasteners is an IATF 16949:2009 & CE 15048 certified leading manufacturer of high tensile hot and cold forged fasteners in India. EN 14399 manufacturer Supplier in India, Automotive fasteners, superior fasteners.

    KOVA
    Cold Forged Components
    Cold Forged Fasteners
    Bolts And Nuts Manufacturers
    Fastener Manufacturers
    Fasteners Exporters
    Fasteners
    Steel Fasteners Manufacturer
    High Tensile Fasteners
    Din 931 Bolts Supplier

    ReplyDelete
  9. Nice Blog, Thanx For Sharing. We Rachna Fasteners is an ISO 9001:2008 certified & CE Approved Fasteners manufacturer As Per EN-15048 Part-1 and 2 from TUV Nord leading manufacturer of high tensile hot and cold forged fasteners in India. EN 14399 manufacturer Supplier in India, Automotive fasteners, superior fasteners.

    Din 933 Screw Supplier Ludhiana
    ISO 4014 Manufacturer Ludhiana
    ISO 4017 Manufacturer India
    Hexagon Bolts Manufacturer In India
    Automotive Fasteners Manufacturer In India
    ISO Certified Fasteners
    Ce Certified Fasteners India
    15048 Assembled Bolting
    Non Preloaded Assembly 15048
    Preloaded Assembled Bolting 14399

    ReplyDelete
  10. Great post. Strongest stainless steel are going faster in the world,These plates are manufactured by the vendors using superior grade mild steel so as to ensure their longer service life and high tensile strength. ms plate price in Chennai will offer you an affordable price.

    ReplyDelete
  11. Nice Blog, Thanx For Sharing. We Rachna Fasteners is an IATF 16949:2016 certified & CE Approved Fasteners manufacturer As Per EN-15048 Part-1 and 2 from TUV Nord leading manufacturer of high tensile hot and cold forged fasteners in India. EN 14399 manufacturer Supplier in India, Automotive fasteners, superior fasteners.

    Fastener Manufacturers In India
    Fasteners Exporters In India
    Fasteners In Ludhiana
    Steel Fasteners Manufacturer Ludhiana
    High Tensile Fasteners Ludhiana
    Din 931 Bolts Supplier India
    Din 933 screw Supplier India
    ISO 4014 Manufacturer India
    ISO 4017 Manufacturer India
    Hexagon Bolt Manufacturer In India

    ReplyDelete
  12. Nice blog bost how we can find the best manufacturer for fastener itemes that provide strongest stainless steel nut bolts items. visit here to find professional Nut bolt manufacturers

    ReplyDelete
  13. Nice Blog Thanx For Sharing The Detail We Are At Nishant Steel Industries is ISO certified leading Fasteners manufacturer of high tensile hot and cold forged fasteners made in India.

    Fasteners
    Automotive Fasteners
    Industrial Fasteners
    Structural Bolting
    Agricultural Fasteners
    Road Crash Barriers
    Threaded Rods & Stud Bolts
    Button Head Bolts
    Hex Bolts & Screws
    Hex Nuts

    ReplyDelete