Requirement for Holes - Holes for Hanging
In order for items to progress through the series of pretreatment and galvanizing baths at our facility, they must
be suspended in a suitable manner to ensure all liquids
are able to clean and galvanize all surfaces. If items are
small enough, they can be out sourced and centrifuged in
perforated baskets (spinning). This process is ideal for large
numbers of nuts, bolts etc. Touch marks are often an issue
with centrifuged items where they make contact whilst
being processed.
In house, some products are processed in specialized
dipping frames or racks and allow large quantities of
straight lengths to be galvanized at the same time. Minimal
areas of the surface of each section will be in contact with
parts of the dipping racks resulting in small touch marks
which, subject to quantity and end use of the items, may or
may not be touched up with repair paint.
Large assemblies are supported by chain slings or lifting
fixtures. To enable safe handling, lifting points should be
incorporated into the fabrication’s design distributing the
weight equally over 4 points. Lifting lugs and heavy duty
washers can be welded at the required points and then
removed after galvanizing. These are preferable to chain or
wire marks remaining after galvanizing. The coating can be
repaired with appropriate zinc enriched paint if aesthetics is
an issue after removing unwanted lifting points.
Most general fabrications are suspended by wire on
apparatus referred to as headframes and hung vertically
or on an angle to maximise drainage of pre-treatment
chemicals and molten zinc. Additional holes or lifting lugs
may be required after fabrication to enable successful
galvanizing of items.
In order to understand where to place a hole for
galvanizing, the function of each hole must be understood.
The various functions of holes can be categorized into
four requirements: hanging, prevention of pooling and
entrapment, venting and draining and to relieve pressure
from overlapping surfaces.
Reference here-on is made to the high end (air exit point)
and low end (zinc entry point).
Holes for Hanging
The shape and dimensions of an item will determine how it
is suspended during the hot dip galvanizing process. Where
possible holes located in cleats, flanges or base plates will
be utilised to suspend general fabricated items. Should holes
not be available, they will be required to be added to enable
the item to be hung in the correct plane, allow processing
liquids to drain and to minimize distortion.
Hunter Galvanizing prefers external lifting lugs to be fitted to long or
heavy items.
General Guidelines
•Subject to weight; items less than 2m require a hole or
lifting lug placed at one end. Longer and heavy items will
require holes or lifting lugs at both ends. Holes should be a
minimum of 10mm diameter, large enough for jigging wire
to be passed through.
•Larger fabrications will require numerous wire strands to
be used and hole sizes should be adjusted accordingly.
Further information should be sought from Hunter
Galvanizing staff regarding size and location of holes
specific to each item.
Holes in end plates, cleats and gussets are utilised to suspend items.
•Wire, Chain or Other Touch Marks
All items are processed either in dipping frames, held by chains or suspended by wire.
Items supported in dipping frames may have small touch marks evident where they have
been in contact with the frame structure.
Chains are utilised for heavy items and will leave touch marks in their immediate area as will
wire if required to be wrapped around an item or through hanging holes. The wire sticks to
the surface of the galvanized coating as the item is withdrawn from the galvanizing bath.
Touch marks or chain marks are usually completely galvanized affecting only the outer free
zinc layer of the coating and therefore not a reason for rejection.
Requirement for Holes - Holes to Prevent Entrapment
In order for items to progress through the series of pretreatment and galvanizing baths at our facility, they must
be suspended in a suitable manner to ensure all liquids
are able to clean and galvanize all surfaces. If items are
small enough, they can be out sourced and centrifuged in
perforated baskets (spinning). This process is ideal for large
numbers of nuts, bolts etc. Touch marks are often an issue
with centrifuged items where they make contact whilst
being processed.
In house, some product ranges are processed in specialized
dipping frames or racks and allow large quantities of
straight lengths to be processed at the same time. Minimal
areas of the surface of each section will be in contact with
parts of the dipping racks resulting in small touch marks
which, subject to quantity and end use of the items, may be
touched up with repair paint.
Large assemblies are supported by chain slings or lifting
fixtures. To enable safe handling, lifting points should be
incorporated into the fabrication’s design distributing the
weight equally over 4 points. Lifting lugs and heavy duty
washers can be welded at the required points and then
removed after galvanizing. These are preferable to chain or
wire marks remaining after galvanizing. The coating can be
repaired with appropriate zinc enriched paint if aesthetics is
an issue after removing unwanted lifting points.
Most general fabrications are suspended by wire on
apparatus referred to as headframes and hung vertically
or on an angle to maximise drainage of pre-treatment
chemicals and molten zinc. Additional holes or lifting lugs
may be required after fabrication to enable successful
galvanizing of items.
In order to understand where to place a hole for
galvanizing, the function of each hole must be understood.
The various functions of holes can be categorized into
four requirements: hanging, prevention of pooling and
entrapment, venting and draining and to relieve pressure
from overlapping surfaces.
Reference here-on is made to the high end (air exit point)
and low end (zinc entry point).
Holes to Prevent Entrapment
When an item is suspended on a headframe, it remains
in the same hanging position throughout the hot dip
galvanizing process. Holes are required to be in the
appropriate location to ensure pre-treatment acids, molten
zinc and zinc ash can flow freely from all item surfaces as it
is submerged and withdrawn from each processing bath.
General Guidelines:
•A hole, gap or mitre in the corners of gussets or stiffeners
will assist processing products to drain.
•Holes through end plates or web plates will also provide
suitable access for zinc and zinc ash to drain and means of
air to escape.
•By adopting a “hole in every corner” principle, the
majority of issues relating to draining can be eliminated
and the best possible hot dip galvanized finish can
be achieved.
•We recommend holes should not be less than 12mm in
diameter, (larger if the design permits) to enable zinc and
zinc ash to escape freely as items are withdrawn from the
galvanizing bath.
The following aesthetic issues are generally deemed
acceptable under the governing standards for hot dip
galvanizing. Simple allowances whilst fabricating can
minimise these effects.
Recommended holes or mitres for general fabrications, universal beams and columns.
By placing a ‘HOLE IN EVERY CORNER’ of general fabrications, most issues relating to
entrapment of air, zinc and zinc ash will be minimised.
Recommended location of holes, mitres or cropped corners
•Air Locks
Pre-treatment acids are critical in preparing the steel surface for galvanizing.
The acids remove contaminants including surface rust, soluble oils and water
based paint coatings. When an item is suspended on a headframe, air can
become trapped in corners at the high points. An air pocket prevents cleaning
solutions from preparing the steel surface and the zinc coating will
not form in these areas.
An airlock will form if pre-treatment chemicals
are unable to escape from corner areas.
•Zinc Pooling
Molten zinc is very dense and solidifies immediately upon withdrawal from the
galvanizing bath. Excess zinc will collect in corners of fabrications subject to the
item’s hanging position. Zinc pooling will increase the overall weight of an item
and may affect the cost and end use application.
Zinc collects in corners of items if holes are not correctly positioned.
•Ash Formation
Zinc ash is a bi-product of the zinc iron alloying process.
Ash forms on the surface of the molten zinc and is
skimmed away from items as they are withdrawn through
the zinc’s surface. Subject to the number of items
processed in the galvanizing bath at one time, some
surfaces may not be reached by operating staff and ash
may adhere to the steel as it is withdrawn. A light skin
or film may form in isolated areas on the surface of an
item. Heavier deposits of ash may remain trapped within
a fabricated item or hollow section. Upon drying the ash
appears as a yellow-brown powder or in clumps. As ash is
relatively pure zinc it does not represent any concern to the
coating properties other than aesthetics and can be easily
brushed from the surface.
Light film of ash.
Ash can become trapped on surfaces within structural
steel sections.
Ash will be caught in long lengths of
hollow sections.
Requirement for Holes - Overlapping Surfaces
In order for items to progress through the series of pretreatment and galvanizing baths at our facility, they must
be suspended in a suitable manner to ensure all liquids
are able to clean and galvanize all surfaces. If items are
small enough, they can be out sourced and centrifuged in
perforated baskets (spinning). This process is ideal for large
numbers of nuts, bolts etc. Touch marks are often an issue
with centrifuged items where they make contact whilst
being processed.
In house, some product ranges are processed in specialized
dipping frames or racks and allow large quantities of
straight lengths to be processed at the same time. Minimal
areas of the surface of each section will be in contact with
parts of the dipping racks resulting in small touch marks
which, subject to quantity and end use of the items, may be
touched up with repair paint.
Large assemblies are supported by chain slings or lifting
fixtures. To enable safe handling, lifting points should be
incorporated into the fabrication’s design distributing the
weight equally over 4 points. Lifting lugs and heavy duty
washers can be welded at the required points and then
removed after galvanizing. These are preferable to chain or
wire marks remaining after galvanizing. The coating can be
repaired with appropriate zinc enriched paint if aesthetics is
an issue after removing unwanted lifting points.
Galvanizing staff are at risk as this force may cause steel
fragments or molten zinc to be blown from the galvanizing
bath causing injury and rendering processing equipment
inoperable. In order for items to be processed safely, holes
are required to enable air and moisture to escape and
pressure to be relieved. The following rules must apply
regarding size and location of relief holes.
General Guidelines:
•Overlapping areas 10cm² or greater must have one hole
every 100mm.
•Thin, long overlapping areas require one hole every
300mm in length.
•Where possible avoid designing items with back to back
channels and angles unless a gap of 2.5mm or greater is
allowed.
•Overlapping areas greater than 40cm² should be avoided
at all times.
•Holes may be placed through one or both steel surfaces
and must be greater than 10mm in diameter.
•Alternatively, staggered welding can provide sufficient
means for air to escape.
•In some instances, it may be suitable to leave one edge
free of weld.
•A s detailed in Welding pre-treatment chemicals become
trapped between overlapping surfaces and may result in
aesthetic issues.
Most general fabrications are suspended by wire on
apparatus referred to as headframes and hung vertically
or on an angle to maximise drainage of pre-treatment
chemicals and molten zinc. Additional holes or lifting lugs
may be required after fabrication to enable successful
galvanizing of items.
In order to understand where to place a hole for
galvanizing, the function of each hole must be understood.
The various functions of holes can be categorized into
four requirements: hanging, prevention of pooling and
entrapment, venting and draining and to relieve pressure
from overlapping surfaces.
Reference here-on is made to the high end (air exit point)
and low end (zinc entry point).
Holes for Venting Overlapping Surfaces
When steel sections are welded together, air is trapped
between the overlapping surfaces. At galvanizing
temperatures, the entrapped air converts to super heated
steam with pressure sufficient to force weak areas within
a fabrication (either in steel thickness or weld) to expand,
distort or tear.
The overhanging edge remains free of weld to allow air to escape.
Overlapping areas will require suitable venting
holes in place.
Holes can be through one or both surfaces.
Gaps should be provided between back to back
channels and plates.
Entrapped acid causes issues in weld pin holes
and overlapping surfaces.
Recommended location of holes, mitres or cropped corners
Requirement for Holes - Holes for Hollow Sections
In order for items to progress through the series of pretreatment and galvanizing baths at our facility, they must
be suspended in a suitable manner to ensure all liquids
are able to clean and galvanize all surfaces. If items are
small enough, they can be out sourced and centrifuged in
perforated baskets (spinning). This process is ideal for large
numbers of nuts, bolts etc. Touch marks are often an issue
with centrifuged items where they make contact whilst
being processed.
In house, some product ranges are processed in specialized
dipping frames or racks and allow large quantities of
straight lengths to be processed at the same time. Minimal
areas of the surface of each section will be in contact with
parts of the dipping racks resulting in small touch marks
which, subject to quantity and end use of the items, may be
touched up with repair paint.
Large assemblies are supported by chain slings or lifting
fixtures. To enable safe handling, lifting points should be
incorporated into the fabrication’s design distributing the
weight equally over 4 points. Lifting lugs and heavy duty
washers can be welded at the required points and then
removed after galvanizing. These are preferable to chain or
wire marks remaining after galvanizing. The coating can be
repaired with appropriate zinc enriched paint if aesthetics is
an issue after removing unwanted lifting points.
Most general fabrications are suspended by wire on
apparatus referred to as headframes and hung vertically
or on an angle to maximise drainage of pre-treatment
chemicals and molten zinc. Additional holes or lifting lugs
may be required after fabrication to enable successful
galvanizing of items.
In order to understand where to place a hole for
galvanizing, the function of each hole must be understood.
The various functions of holes can be categorized into
four requirements: hanging, prevention of pooling and
entrapment, venting and draining and to relieve pressure
from overlapping surfaces.
Reference here-on is made to the high end (air exit point)
and low end (zinc entry point).
Holes for Venting & Draining Hollow Sections
Molten zinc is extremely dense. Consideration of
venting and draining requirements is mandatory when
fabricating items for hot dip galvanizing to eliminate
potential hazards:
– items may float on top of the molten zinc
– air may become trapped or is slow to escape
Sealed hollow sections will float on the surface until such
time they are either pushed or dragged below the zinc’s
surface. As discussed in Holes for Venting Overlapping
Surfaces; at galvanizing temperatures trapped air or
moisture will very quickly convert to super heated steam.
The resultant pressure can expand, distort or tear weaker
areas within a fabrication (either in steel thickness or weld)
with explosive force. Galvanizing staff are at risk as this
force may cause steel fragments or molten zinc to be blown
from the galvanizing bath causing injury and rendering
processing equipment inoperable.
In order for items to be processed safely, vent holes are
required to enable the item to be submerged and allow air
and moisture to escape at the same rate as the zinc enters.
The following rules must apply regarding size and location
of holes for hollow sections to permit hot dip galvanizing in
a controlled and safe manner.
General Guidelines:
•All capped hollow sections must have a minimum of one
hole or cropped corner diagonally placed at each end to
permit zinc entry at the low end and air escape at the high
end when suspended on a headframe.
•Hollow sections open one end (low end) require a
minimum of one hole or cropped corner at the capped end
(high end).
•Hollow sections welded within a fabrication must have
holes placed at both ends of each hollow section.
•Holes or cropped areas should be as large as the design or
end use will allow for expanding air, processing liquids, zinc
and zinc ash to escape from within.
•The total area of holes must be equal to or no less than
25% of the diameter of cross section of the hollow
piece. Numerous holes can be placed in order to meet
this venting requirement. Holes less than 10mm are not
functional as they can easily become blocked; Hunter
Galvanizing recommends 12mm diameter holes minimum.
Holes must be located in diagonally opposite corners of SHS and RHS.
Holes or V notches must be present in all hollow sections within
a fabrication.
The overall dimensions of an item and hanging
method must be considered when fabricating items
which include hollow sections.
Small holes may result in floating or
drainage issues. Holes should be as
large as possible to facilitate ease of
galvanizing and to allow the best possible
coating to be achieved.
•External Holes SHS, RHS, CHS & Pipe Sections
In open-ended SHS, RHS and pipe sections, a hanging
hole each end is required to allow hanging wire to pass
through. If the hollow section is capped, additional holes
for venting are required. For SHS and RHS sections, holes
should be placed in the corners. In pipe sections holes are
required to be as close to the outside diameter as possible.
Holes placed in the centre of end caps will allow air
pockets to form or zinc to pool.
The minimum acceptable number of venting holes is one
each end placed diagonally opposite. If there are no means
of holding the item two holes each end are required, with
holes located diagonally opposite each other.
The size of the venting holes is critical for processing
hollow sections. Sufficient air must escape at the same rate
zinc is entering the section. Holes should be no less than
25% of the cross section of the hollow section.
*The minimum hole size acceptable on any item is 10mm,
however as holes this size can prove ineffective we
recommend
holes sizes of 12mm or greater.
Hole Placement Options for RHS & SHS Sections
•A section of 100 x 100 SHS or 100 x 50 RHS must have
holes at each end equivalent to approximately 25mm either
as:
1 x 25mm hole each end OR 2 x 12mm holes each end
OR 4 x 6mm holes each end
•A section of 50mm diameter pipe must have holes at each
end equivalent to approximately 12mm either as:
1 x 12mm hole each end OR 2 x 10mm* holes each end
Fabricated items, gates, handrails and fencing require
thought regarding placement of holes. Ideally holes should
be placed externally to allow quick visual inspection by the
galvanizer. Unwanted holes can later be filled with epoxy
filler, lead or threaded plugs.
Hole Placement Options for CHS & Pipe Sections
Preferred Option
Preferred Option
No end
plate
Correct Holes
Examples
Holes for
hanging
No end
plate
Holes for
hanging
•Internal Holes SHS, RHS, CHS & Pipe Sections
Where internal holes are utilised, sections should be interconnected using
mitred joints or interconnecting holes. Internal holes should be as close
as possible in size to the cross section of the hollow section (minimum
of 50%) to eliminate air pockets and zinc pooling inside the fabrication.
Internal holes are not recommended due to inherent safety concerns.
Hunter Galvanizing requires signed documentation to guarantee holes
have been correctly placed.
Air and zinc must flow freely within the hollow sections.
1. External Holes
2. Internal Holes
3. M
andatory - Holes
in Bends
4. M
andatory - Ends
Remain Open
Holes for Venting
•Tanks and Hollow Vessels
Specific attention to venting and draining is required
when preparing large hollow items such as tanks, pods
or vessels for galvanizing. The design of tanks and closed
vessels must allow for pre-treatment chemicals, air and
zinc to enter, fill and flow out of the enclosed space. A
large filling hole (minimum of 50mm diameter for each 0.5
cubic metres) is required at the low end when suspended
for galvanizing. A vent hole of equal dimensions will be
needed diagonally opposite the filling hole to allow air
to escape.
Internal baffles in tanks must have their corners cropped
prior to installation or with large drainage holes to permit
free flow of the air and zinc within. Access ports, bosses
and openings should be finished flush inside and should be
positioned so that all processing fluids can be drained out
during the galvanizing process.
Whilst processing tanks, a large volume of zinc will
pass through the vessel. As a safety precaution, we
require heavy duty lifting lugs attached to each item.
We recommend discussing this requirement with Hunter
Galvanizing staff prior to fabrication.
General Guidelines
•Venting holes are required to be diametrically opposite.
•Minimum acceptable hole size is 50mm in diameter.
Subject to tank size additional holes may be required.
•Internal baffles should be cropped top and bottom.
•Lifting lugs will be required to facilitate handling.
•Design should incorporate an inspection hole to enable
internal surfaces to be viewed.
Vent
Drain
Internal baffles of tanks must be cropped