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Clean HolesA must in Chemical AnchoringRAMIL CRISOLO B. Eng, AEFAC Technical Committee Member

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Hobson Engineering Volume 31

HOBSON NEWS

On LocationEngineering Product Application

Engineering

Mechanical and chemical anchors need some form of hole cleaning before they are installed in drilled holes. Mechanical anchors are less sensitive to un-cleaned holes because of the mechanisms that make them work. However, chemical anchor performance largely depends on how well the holes were prepared. Tests show that if holes are not properly cleaned prior to chemical application,

pull-out strength reduction can be as high as 60%.

As shown in Figure 1, there are two main mechanisms at play in chemical anchoring, bonding and keying. Relatively, drilled holes are not perfectly smooth, even diamond cored holes. The hole’s rough surface enables the creation of micro-interlocks with the hardened adhesive. Supplementing these

micro-interlocks is the bonding of the chemical to the hole surface. The combination of micro-interlocking and bonding defines a chemical anchor’s pullout strength.

‘Hammer drilling’ produces dust while ‘wet diamond drilling’ produces slurry. These are by-products of drilling that need to be cleaned out prior to chemical injection. Figure 2 illustrates what happens when a hole

Continued …

Clean Holes �������������������� 1-2High-Tensile and Stainless Steel Head Markings ������������������������� 2-3

On Location ����������������������� 4

HobSpec Guides ��������������� 5

On Location ����������������������� 6

Squirter Washers �������������� 7

In this issueFigure 1. Chemical anchors working through a combination of keying and bonding.

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Engineering

is properly cleaned and when drilling by-products are not cleaned out. The uncleaned hole has a noticeable layer of material that prevents the chemical from creating the required

micro-interlocking and bonding with the hole surface. This is the reason why there is a significant drop in pullout strength when holes are not properly cleaned. It is therefore

imperative that hole preparation be done strictly in accordance with the MII (manufacturer’s installation instructions).

Figure 2. The difference between well cleaned and un-cleaned holes.

Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.

Yield Strength: The maximum load at which a material exhibits a specific permanent deformation.

Proof Load: An axial tensile load which the product must withstand without evidence of any permanent set.1MPa = 1N/mm² = 145 pounds/inch²

Application

Imperial

Head Marking Grade and Material

Nominal Size Range

(inches)

Mechanical Properties

Proof Load (psi)

Min� Yield Strength (psi)

Min� Tensile Strength (psi)

No markingsGrade 2

Low or medium Carbon Steel

1/4 through 3/4 55,000 57,000 74,000

Over 3/4 through 1-1/2 33,000 36,000 60,000

3 radial linesGrade 5

Medium Carbon Steel, quenched and tempered

1/4 through 1 85,000 92,000 120,000

Over 1 through 1-1/2 74,000 81,000 105,000

High-Tensile and Stainless Steel Head Markings

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Where A2 and A4 are used without property class, assume it is Class 50 unless supplied with a certificate.

A2 may be replaced with 304. A4 may be replaced with 316.

We stock A4-80 strength product in both Neptune® and Bumax® categories.

Corrosion PropertiesThe three most common and most severe types of corrosion in falling severeness are Pitting, Crevise and General Corrosion.

The chemical composition of the steel has an important influence on how well it can combat the different types of corrosion. The most important elements for this ability are Chromium (Cr), Molybdeunum

(Mo) and Nickel (Ni). Also, the Carbon content (C) has influence, especially at elevated temperatures.

The seemingly small differences of these alloying elements has a great influence on the properties of the steel.

A number of laboratory tests have proved that the 316 L Hi Mo (SS2343) the grade used in BUMAX®88 and BUMAX®109, is superior to normal trade standard A4 for all different media and all types of corrosion.

6 radial linesGrade 8

Medium Carbon Alloy quenched and tempered

1/4 through 1-1/2 120,000 130,000 150,000

Metric Bolts

Head Marking Class and Material Nominal Size Range

Mechanical Properties

Proof Load (MPa)

Min� Yield Strength (MPa)

Min� Tensile Strength (MPa)

8�8

Class 8�8 Medium Carbon Steel,

quenched and tempered

All sizes below M16 580 640 800

M16 - M72 600 660 830

10�9

Class 10�9 Alloy Steel, quenched

and temperedM6 - M48 830 940 1040

12�9

Class 12�9 Alloy Steel, quenched

and temperedM6 - M48 970 1100 1220

A4

Class 50 Austenitic Steel with 16-18.5% Chromium and 10-15% Nickel

M20 - M48 – 210 500

A4-70

Class 70 Austenitic Steel with 16-18.5% Chromium and 10-15% Nickel

M6 - M20 – 450 700

A4-80

Class 80 Austenitic Steel with 16-18.5% Chromium and 10-15% Nickel

M6 - M36 – 600 800

Bumax® Neptune®

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On Location

Flying foxGUNGAHLIN ACT

Look what we found while out and about in Yerrabi Ponds, Gungahlin ACT.Hobson Bolts!

From the playground to the oil rig.

The gas pipeline to the timber deck.

People rely on Hobson.

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Log onto the Hobson Portal » Click Guides

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Product

» Hobson Website Portal Help How to create, manage and use favourite lists on the portal.

» Your Website Setup How to set up your website with Hobson product, images, lists and guides.

» Hobson Logos Instructions and downloads.

What’s here:

Did you know you can display all of Hobson’s Products on your website?Here is your handy guide for using the Hobson Portal, Hobson Logos and setting up your website with Hobson Products.

*Any use of the logo needs to be pre-approved by Hobson Engineering.

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I recently spotted on Sydney Harbour my father’s racing yacht “Joanne Brodie”, fully restored and the sexiest yacht I have ever seen on the harbour. I have written a number of articles for this newsletter over the years on this yacht, and I must say it has brought back some memories. It is now 21 years since my father passed away, and he came third in this yacht in the 1964 Sydney to Hobart (the year I was born). He of course won the race in 1953 in “Ripple”.

The sight of the Joanne Brodie looking as good as she does, is almost enough to sell up and leave the fastener Industry, buy her back and retire … almost … But then I remember an old addidge “True happiness is achieved by admiring without desiring” – so lots yet to be achieved at Hobson Engineering. We have a very exciting 2016 planned with lots of improvements to make. To stop and rest is to surrender!

The things you seePETER HOBSON

On Location

HOBSONTHE

Goodbye old friendHobson Engineering’s Newsletter now has a new look!

It will still be full of the interesting articles and useful information that you are used to, with the addition of more user friendly sections and a modern, new look.

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Product

Application

Squirter WashersDirect Tension Indicator (DTI)STEVEN ZENOS

Two recent failures of high strength bolts continue to demonstrate that using Torque (Nm) to measure bolt tension (Nm) is inaccurate.

Bolt over-tensioning is the likely cause of fracture in two critical fastener applications, where M36 10.9 and M22 8.8 Property Class bolts were installed.

Hobson Engineering recommended Direct Tension Indicator (DTI) compression Squirter Washers, manufactured to ASTM F969, in both applications.

Investigation revealed installation Torque (Nm) varied by 50% (+/- 25%) depending upon how much or

how little lubrication was used.

It is the variation in friction when bolting a joint that causes the variation in Torque (Nm). The relationship between Torque (Nm) and tension (kN) uses the formula:

T = P x k x D

‘k’ means friction and it is not constant, (as the symbol ‘k’ is typically represented in most equations), in most real world applications.

The new draft of AS1252, High strength steel bolt assemblies comprising bolts, nuts and washers for structural engineering, reminds readers that critical k-class K1 and

K2 “… bolt assemblies cannot be tensioned by torque controlled methods but may be tensioned by the part turn method or direct tension indicator (DTI) method detailed in AS 4100 and NZS 3404.”

Only 10% of Torque (Nm) goes towards tensioning (kN) and stretching the bolt, which is required to satisfactorily clamp and tighten the joint.

ASTM F959 Type 8.8 and 10.9 compression Squirter washers measure direct tension to an accuracy better than +/10%.

Contact Hobson if you would like to see a demonstration of the accuracy of Squirter Washers, over using torque or part turn methods to install bolt assemblies.

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