IntroductionAsafety helmet (hard hat) is a type of helmet predominantly used in workplaceenvironments such as industrial and construction sites. The helmet is used to shieldthe head from injury due to falling objects, collision other items, electrocutionand rainwater.
Suspension cushion inside the helmet surround the helmet’s mass andthe pressure of an impact over the top of the skull. A suspension gives spaceof roughly 30 mm between the helmet’s shell and the person’s head. The force of the object is less likely to betransferred straight to the skull If an object hits the shell. Some hardhatshells hold a mid-line reinforcement backbone to enhance impact protection. Astudy among USA workers shows that although 20 million people use safety helmetwhile working.
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1500 of accidents are fatal among the 120,000 on-the-job headinjuries to happen each year. The American National Standards Institute (ANSI)developed its performance standards to maintain safety helmet quality. Moreover, safety helmets must be properlycared for to guarantee their lasting effectiveness to satisfy manufacturingspecifications. One essential for ANSI approval is that a guidance booklet isprovided with each safety helmet, describing how to care for the helmet, how toexamine it for indications of damage, and how to make certain it matchesperfectly. A safety helmet should be replaced after five years of use eventhough there are no damages in the helmet.Asafety 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, or2009 editions of ANSI Z89.1, or be shown to offer similar or better protection. Use of Safety HelmetSafetyhelmet should be used when falling object hazards may occur from activitieswith closeness to:· persons or operations where accidentaldropping of tools and equipment could drive to a head wound· a blocked destruction or constructionarea where head hazards exist.
· things stocked on shelves orplatforms that may fall and cause a headinjury.· overhead bare energized electric conductorsadjacent. Construction of asafety helmet 1– shell, 2 – harness, 3 – harness fixing, 4 – headband, 5 – sweatband, 6 –peak, 7 – chinstrap.
Types and ClassesØ Type 1- Helmets designed to diminish the force of impact resulting in a hit only tothe top of the head (United States) Ø Type 2- Helmets intended to lessen the force of impact resulting in a hit to the topand the side of the head (Europe) v Class E(Formerly Class B): Helmets foruse where electrical dangers are present and intended to guard against droppingobjects and decrease the threat of exposure to high voltage electrical shocksand blisters. Allows the highest security against high-voltage shock and burnprotection up to 20,000 volts. v Class G(Formerly Class A): Intended to protect against falling objects and reduce thehazard of exposure to moderate voltage electrical wirings. They give shock andpenetration cover and protection from up to 2,200 volts. v Class C : Safety helmets designed forlightweight comfort and collision protection and are not planned to giveprotection from electrical conductors. Manufacturing Method 1.
2Material Safety helmet shells can be constructed from avariety 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 inmost industrial safety helmet.
This is due to the materials have tough, nonconductiveto electricity and light mass. Safety helmet suspensions will usually consistsof sheets of woven nylon webbing and rings of moulded HDPE, fabric or vinyl.Type II safety helmet regularly have an extra polystyrene foam included intothe hole around the suspension.The helmet shell’s headband enhance comfort for theuser by adding brow sponge to the front of the helmet. Many materials areutilized for brow pads, including foam-backed vinyl, foam-backed cotton terrycloth, and speciality fibres such as Sportek or Coolmax created for sweatabsorption in sports outfit and adornment. TheManufacturing Process The upcoming method of theproduction of Type I industrial safety helmet is based generally on themanufacturing methods of particular major producer. Nonetheless, some feature havebeen developed helmet modifications used by other companies. TheShell1.
The manufacturer select a proper shellmould for the model that to be created. The mould is placed in an injectionmoulding press. Electric cords are attached to the mould and pipe carry chilledwater that will cool the mould.
2. High-density polyethene (HDPE) pellets aredragged from a supply tank by a vacuum operation. Colourant pellets are movedfrom the different supply tank and blended with the HDPE pellets in a ratio of4% to 96%. The vacuum operation transports the pellet mixture into theinjection moulding press.3. The pellets are melted within the press.
Themolten 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 offthe sprue. The worker sticks a label inside the shell; the label identifies themanufacturer and the appropriate ANSI type and class designations.
Figure 1: Different types of safety helmetsuspension systems help to lessen the consequences of a blow to the head bydistributing the force of it over a broader area Injection Molding Process Injection moulding process is the properway to build the safety helmet. Injection moulding is the most regularly usedmanufacturing process for the fabrication of plastic parts. A broad category ofproducts is fabricated utilizing injection moulding. This may range hugely intheir volume, complexity, and application. The injection moulding method needsthe use of an injection moulding machine, raw plastic material, and a mould.The plastic is heated to melt in the injection moulding machine and theninserted into the mould, where it chills and hardens into the final part. Process CycleThe process cycle for injection molding is very short and consists ofthe 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 cooling time. 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 neededafter the injection moulding cycle. The material in the channels of the mouldwill thicken joined to the part during cooling. If there are excess material orany flash, it must be trimmed from the part using cutters.
The scrap materialsuch as thermoplastics that formed from trimming process can be recycled. Theexcessive plastics deposited into a plastic grinder called regrind granulatorsto regrinds the scrap material into pellets. The regrind process must be combined with raw material in the correctregrind ratio so it can be reused in the injection moulding process. This isdue to some degradation of the material properties, 2.
2.1AdvantagesThere are several advantagesof using injection moulding process in producing the safety helmet. Injectionmoulding process creates a product that has a high-grade surface finish. Thisis one of the main measures of a safety helmet. The top and bottom of the safetyhelmet have to be a smooth surface.
Therefore, that when any objects fall onthe safety helmet will easily slight down because even surfaces have littlefriction. Moreover, injection moulding method is able to produce a complicatedgeometry products. Besides, injection moulding process has huge productionscale. This indicates that it can deliver a product immediately and does notslow the process of producing the shell. The injection moulding method iscompletely automated and limited labour is needed to control the machine.
2.2.2DisadvantagesThe main limitations of theinjection moulding process are that special tooling and machinery expense isneeded. This is because the machine runs with extraordinary accuracy andaccuracy without the aid of workers. On the other hand, part with a bigundercut cannot be created.
2.3Structural Foam Molding Different propermethod to produce safety helmets is by using Structural Foam Moulding which isa low-pressure injection moulding process. It is utilized to preparethermoplastics such as high-density polyethene (HDPE) in a low-pressureenvironment. Structural foam mouldingrelies on the foaming operation caused by an inert gas diffused in the plasticsubstance to promote the flow rather than applying high pressures to push themelted polymer to fill up the hole of the mould. Alternatively, foaming canalso be produced by the gasses released by the breakdown of a chemical blowingagent combined with the resin.Structural foamcomponents commonly have thicker wall segments due to the absence of largepressures during the moulding process. Moreover, structural foams have a vitaldensity cut as large as 40% from its base material.
The parts generally presentsuperior strength-to-weight ratio, upgraded thermal and acoustic protectingcharacteristics but suffer from moderate tensile strengths.Furthermore,structural foam moulding may utilize inexpensive and thinner moulds and it maybe applied to fabricate bigger components compared with injection moulding. Thedisadvantage of structural foam moulding is its lower production rate. Thesettings expense of structural foam moulding is lower and giving it a viablechoice to injection moulding for moderate-volume applications.In additional to HDPE, otherpolymers commonly used in structural foam moulding are: Acrylonitrile Butadiene Styrene (ABS) Polypropylene (PP) Polyethylene (PE)The design studies ofstructural foam moulding are quite alike to those of injection moulding. Hence,it is by far the closest technique to produce safety helmet shell rather thanthe injection moulding method.Figure 3: Schematic of the advanced structural foam molding machine 1.
0 Conclusion In conclusion, this reportdescribes the importance of safety helmet in the working atmosphere. Thecharacteristics of the safety helmet are also described and the variety ofmaterials used to make the safety helmet shell. This is to show a proper way ofhow the properties of the hard hats are accomplished.
Furthermore, the mainobjective of this report has been accomplished. The common and propermanufacturing method for the safety helmet shell, injection moulding process isexplained. The goods and limitations of the method were found. Some othermethod to produce safety helmet shell has been discussed. The hard hat can bealso constructed by utilizing the structural foam moulding process. Finally, itis discovered that injection moulding method is by far the most efficientmethod and the most suitable substance is High-density polyethene (HDPE) tocreate safety helmet shell.