safety helmet (hard hat) is a type of helmet predominantly used in workplace
environments such as industrial and construction sites. The helmet is used to shield
the head from injury due to falling objects, collision other items, electrocution
and rainwater. Suspension cushion inside the helmet surround the helmet’s mass and
the pressure of an impact over the top of the skull. A suspension gives space
of roughly 30 mm between the helmet’s shell and the person’s head. The force of the object is less likely to be
transferred straight to the skull If an object hits the shell. Some hardhat
shells hold a mid-line reinforcement backbone to enhance impact protection.
study among USA workers shows that although 20 million people use safety helmet
while working. 1500 of accidents are fatal among the 120,000 on-the-job head
injuries to happen each year. The American National Standards Institute (ANSI)
developed its performance standards to maintain safety helmet quality. Moreover, safety helmets must be properly
cared for to guarantee their lasting effectiveness to satisfy manufacturing
specifications. One essential for ANSI approval is that a guidance booklet is
provided with each safety helmet, describing how to care for the helmet, how to
examine it for indications of damage, and how to make certain it matches
perfectly. A safety helmet should be replaced after five years of use even
though there are no damages in the helmet.
safety helmet needs to fit ANSI Z89.1 is OSHA compliant. 29 CFR 1910.135(b)(1)
and 29 CFR 1926.100(b)(1) state that head protection must reach 1997, 2003, or
2009 editions of ANSI Z89.1, or be shown to offer similar or better protection.
Use of Safety Helmet
helmet should be used when falling object hazards may occur from activities
with closeness to:
persons or operations where accidental
dropping of tools and equipment could drive to a head wound
a blocked destruction or construction
area where head hazards exist.
things stocked on shelves or
platforms that may fall and cause a head
overhead bare energized electric conductors
Construction of a
– shell, 2 – harness, 3 – harness fixing, 4 – headband, 5 – sweatband, 6 –
peak, 7 – chinstrap.
Types and Classes
Ø Type 1
– Helmets designed to diminish the force of impact resulting in a hit only to
the top of the head (United States)
Ø Type 2
– Helmets intended to lessen the force of impact resulting in a hit to the top
and the side of the head (Europe)
v Class E
(Formerly Class B): Helmets for
use where electrical dangers are present and intended to guard against dropping
objects and decrease the threat of exposure to high voltage electrical shocks
and blisters. Allows the highest security against high-voltage shock and burn
protection up to 20,000 volts.
v Class G
(Formerly Class A): Intended to protect against falling objects and reduce the
hazard of exposure to moderate voltage electrical wirings. They give shock and
penetration cover and protection from up to 2,200 volts.
v Class C : Safety helmets designed for
lightweight comfort and collision protection and are not planned to give
protection from electrical conductors.
Safety helmet shells can be constructed from a
variety of materials. Most are made of a thermoplastic like polycarbonate and polyethene
(HDPE). These materials are lightweight, durable, and easily formed. Besides,
materials such as resin-soaked textiles, fibreglass and aluminium are used in
most industrial safety helmet. This is due to the materials have tough, nonconductive
to electricity and light mass. Safety helmet suspensions will usually consists
of sheets of woven nylon webbing and rings of moulded HDPE, fabric or vinyl.
Type II safety helmet regularly have an extra polystyrene foam included into
the hole around the suspension.
The helmet shell’s headband enhance comfort for the
user by adding brow sponge to the front of the helmet. Many materials are
utilized for brow pads, including foam-backed vinyl, foam-backed cotton terry
cloth, and speciality fibres such as Sportek or Coolmax created for sweat
absorption in sports outfit and adornment.
The upcoming method of the
production of Type I industrial safety helmet is based generally on the
manufacturing methods of particular major producer. Nonetheless, some feature have
been developed helmet modifications used by other companies.
1. The manufacturer select a proper shell
mould for the model that to be created. The mould is placed in an injection
moulding press. Electric cords are attached to the mould and pipe carry chilled
water that will cool the mould.
2. High-density polyethene (HDPE) pellets are
dragged from a supply tank by a vacuum operation. Colourant pellets are moved
from the different supply tank and blended with the HDPE pellets in a ratio of
4% to 96%. The vacuum operation transports the pellet mixture into the
injection moulding press.
3. The pellets are melted within the press. The
molten plastic is injected into the mould to create the safety helmet shell.
The press frees the mould and dumps the shell onto a conveyor belt.
4. An operator collects the shell and cuts off
the sprue. The worker sticks a label inside the shell; the label identifies the
manufacturer and the appropriate ANSI type and class designations.
Figure 1: Different types of safety helmet
suspension systems help to lessen the consequences of a blow to the head by
distributing the force of it over a broader area
Injection Molding Process
Injection moulding process is the proper
way to build the safety helmet. Injection moulding is the most regularly used
manufacturing process for the fabrication of plastic parts. A broad category of
products is fabricated utilizing injection moulding. This may range hugely in
their volume, complexity, and application. The injection moulding method needs
the use of an injection moulding machine, raw plastic material, and a mould.
The plastic is heated to melt in the injection moulding machine and then
inserted into the mould, where it chills and hardens into the final part.
The process cycle for injection molding is very short and consists of
the following four stages:
Clamping – First, the mould needs to be
securely fastened by the clamping unit before the material injection into
the mould. There are two sections of the mould. One half of the mould is
connected to the injection moulding machine and another half is enabled to
slide. The 2 section moulds pushed by hydraulically powered clamping unit
and exert enough force to hold the mould securely locked. Then, the
material is inserted. The time needed to close and clamp the mould is
dependent upon the machine. Larger machines will need more time due to the
larger clamping force. This time can be measured from the dry cycle time
of the machine..
Injection – The unprepared plastic material
normally in the form of pellets. Later, the material is filled into the
injection moulding machine and proceeded towards the mould by the
injection unit. The plastic material
is melted by pressure and heat during this method. The development of
pressure compresses and keeps the material after the molten plastic is
injected into the mould instantly. Shot indicated as is the amount of
material that is injected. Due to complicated and varying the flow of the
molten plastic in the mould, the injection time is difficult to determine
precisely. Nevertheless, the injection rate can be evaluated by the shot
volume, injection power and injection pressure.
Cooling -The molten plastic that is inside the
mould starts to cool quickly it makes contact with the inner mould
surfaces. It will harden into the appearance of the wanted component as
the plastic chills. Though, some part will contract during the cooling
process. Extra material to pass
into the mould when the packing of material in the injection stage and
decrease the volume of noticeable shrinkage. The mould will be opened
after the necessary cooling interval has elapsed. Thermodynamic properties of the plastic
and the maximum wall thickness of the part are main factors that affected
Ejection – The cooled part may be removed
from the mould by the removal system after adequate time has passed. The
part is appended to the rear half of the mould. A device is used to shift
the part out of the mould after the mould is opened. Force need be applied
to dismiss the part because of the part contracts and sticks to the mould
during the cooling process. In
addition, a mould release tool can be sprayed onto the surfaces of the mould
hole earlier to injection of the material in order to promote the removal
of the part. The time needed to open the mould and remove the part can be
measured from the dry cycle time of the machine. The dry cycle time must
include time for the part to come free of the mould. The mould can be
clamped shut for the next shot to be inserted after the part is removed.
Post-processing is typically needed
after the injection moulding cycle. The material in the channels of the mould
will thicken joined to the part during cooling. If there are excess material or
any flash, it must be trimmed from the part using cutters. The scrap material
such as thermoplastics that formed from trimming process can be recycled. The
excessive plastics deposited into a plastic grinder called regrind granulators
to regrinds the scrap material into pellets.
The regrind process must be combined with raw material in the correct
regrind ratio so it can be reused in the injection moulding process. This is
due to some degradation of the material properties,
There are several advantages
of using injection moulding process in producing the safety helmet. Injection
moulding process creates a product that has a high-grade surface finish. This
is one of the main measures of a safety helmet. The top and bottom of the safety
helmet have to be a smooth surface. Therefore, that when any objects fall on
the safety helmet will easily slight down because even surfaces have little
friction. Moreover, injection moulding method is able to produce a complicated
geometry products. Besides, injection moulding process has huge production
scale. This indicates that it can deliver a product immediately and does not
slow the process of producing the shell. The injection moulding method is
completely automated and limited labour is needed to control the machine.
The main limitations of the
injection moulding process are that special tooling and machinery expense is
needed. This is because the machine runs with extraordinary accuracy and
accuracy without the aid of workers. On the other hand, part with a big
undercut cannot be created.
Structural Foam Molding
method to produce safety helmets is by using Structural Foam Moulding which is
a low-pressure injection moulding process. It is utilized to prepare
thermoplastics such as high-density polyethene (HDPE) in a low-pressure
environment. Structural foam moulding
relies on the foaming operation caused by an inert gas diffused in the plastic
substance to promote the flow rather than applying high pressures to push the
melted polymer to fill up the hole of the mould. Alternatively, foaming can
also be produced by the gasses released by the breakdown of a chemical blowing
agent combined with the resin.
components commonly have thicker wall segments due to the absence of large
pressures during the moulding process. Moreover, structural foams have a vital
density cut as large as 40% from its base material. The parts generally present
superior strength-to-weight ratio, upgraded thermal and acoustic protecting
characteristics but suffer from moderate tensile strengths.
structural foam moulding may utilize inexpensive and thinner moulds and it may
be applied to fabricate bigger components compared with injection moulding. The
disadvantage of structural foam moulding is its lower production rate. The
settings expense of structural foam moulding is lower and giving it a viable
choice to injection moulding for moderate-volume applications.
In additional to HDPE, other
polymers commonly used in structural foam moulding are:
Butadiene Styrene (ABS)
The design studies of
structural foam moulding are quite alike to those of injection moulding. Hence,
it is by far the closest technique to produce safety helmet shell rather than
the injection moulding method.
Figure 3: Schematic of the advanced structural foam molding machine
In conclusion, this report
describes the importance of safety helmet in the working atmosphere. The
characteristics of the safety helmet are also described and the variety of
materials used to make the safety helmet shell. This is to show a proper way of
how the properties of the hard hats are accomplished. Furthermore, the main
objective of this report has been accomplished. The common and proper
manufacturing method for the safety helmet shell, injection moulding process is
explained. The goods and limitations of the method were found. Some other
method to produce safety helmet shell has been discussed. The hard hat can be
also constructed by utilizing the structural foam moulding process. Finally, it
is discovered that injection moulding method is by far the most efficient
method and the most suitable substance is High-density polyethene (HDPE) to
create safety helmet shell.