Production and testing technology of helmets at home and abroad
Time：2019-04-30 16:40:12 / Popularity： / Source：
- Common materials and performance of helmets
1.1 ABS helmet
Full name of ABS is acrylonitrile-butadiene-styrene resin, which is abbreviation of Acrylonitrile Butadiene Styrene. This engineering plastic has heat resistance, high surface hardness, dimensional stability and chemical resistance. At the same time, electrical insulation performance is good, rarely affected by temperature and humidity, and remains constant over a wide range of frequency variations. In addition, its chemical properties are also very good, with little effect on water, inorganic salts, alkalis and acids.
ABS materials have good impact strength and do not drop rapidly at low temperatures. Of course, materials suitable for production of helmets generally use ultra-high impact type ABS materials, otherwise impact test is unqualified. This material, except for a small number of countries such as North America, does not be used to produce helmets, which are widely used in other countries.
1.2 HDPE helmet
HDPE is High Density Polyethylene. This material has high surface hardness and good heat resistance, electrical insulation and dimensional stability. It is widely used in helmet production. However, compressive strength of this material is poor. If internal structure of cap and design of product wall thickness are not improved, lateral pressure test is often unqualified, so helmet cap of this material must be strengthened with anti-side pressure design, otherwise it will be difficult to pass in European, Australia, Japanese and Chinese standards. Because North American standards do not have side pressure, HDPE helmets are widely used in Americas, while in Japan, South Korea and other countries, HDPE is basically not used to produce helmets.
1.3 PC helmet
PC is polycarbonate (Polycarbonate), which is hard and tough, has high impact resistance, high dimensional stability, good electrical insulation and high temperature resistance. Due to high price of materials, this material is rarely used in other countries except Japan. Of course, because of high temperature resistance of some special materials in PCs, many metal smelting industries require such high temperature PC helmets.
1.4 FRP helmet
FRP is glass fiber reinforced plastic, referred to as Fiberglass Reinforced Plastics. This material has high fiber strength, excellent heat resistance and electrical insulation properties, and has excellent acid and water resistance, flame retardancy and small deformation. All countries in the world have helmets of this material. However, since composite material is a thermosetting resin, a large amount of waste, scraps is created in production process and garbage recycling after use of helmet is difficult to handle, which cause environmental pollution and fail to meet low carbon economy. Therefore, developed countries in Europe and United States are gradually reducing production of such materials.
- Helmet technology
2.1 Helmet mould material
Helmet mould materials used to produce helmets are mainly steel, and some are also made of non-ferrous or non-metallic materials. Thirty years ago, due to lack of scientific and technological development, hard hats and accessory molds were generally produced using carbon tool steel materials such as 45# steel and 40Cr at home and abroad. However, products produced using these steels have shortcomings such as poor brightness, low dimensional accuracy and mold life. With development of science and technology, some new steel products with high hardness performance, good sliding wear performance and strong corrosion resistance have emerged, which has greatly improved precision and smoothness of helmet products, improved entire industrial level. At present, Japan Green Safety, American JACKSON and other safety products companies generally use high-hardness, high-toughness alloy tool steels such as 718, 2738, 2316 to produce helmet mould, which make products more smooth and precise, extend service life of mold to reach more than 2 million times. In recent years, domestic helmet mould manufacturers, whether they are self-produced or commissioned mold manufacturers in China to make helmet mould, also gradually use P20, 718 steel from original medium carbon steel. Most helmet mould manufacturers requiring high quality use standard mold bases such as Hong Kong Longji to manufacture molds, which effectively ensure precision, high efficiency and long life of mold.
2.2 Moulding process technology
Traditional mold production, often based on designer's experience and existing design materials, from calculation of helmet to design of mold, relying on manual labor, in mold production, relying on skilled craftsmanship and heavy bench work, combined with ordinary lathes, planers, milling machines, grinding machines and other ordinary machine tools, precision of processing dimensions and product quality are far from meeting needs of production development. In past 20 years, plastic molding industry in the world has developed rapidly. With wide application of CAD/CAM/CAE, advanced CMM, CNC and CNC machine tools, machining centers, high-speed milling and other advanced machine tools are used to improve quality of mold and dimensional accuracy of helmet. After several years of development, because mold manufacturers in China can meet requirements of customers with high quality, short time and low price, many foreign helmet mould manufacturers have commissioned mold manufacturers in China to produce molds, such as JACKSON in US, Green Security in Japan, and SPERIAN in France.
2.3 Hot runner technology
In the early helmets, cold runner structure was generally used, and there was an injection gate mark on the outside of helmet shell, which affected appearance. With further development of injection molding technology, developed countries have begun to use hot runner structure to make molds, leaving injection gates inside caps, making appearance of helmet products more aesthetic. Production of parts such as caps can save gate waste and save energy.
2.4 Degree of automation
With advancement of technology, further development of injection moulding and mechanical automation, injection moulding machine manipulators and automatic shear gate devices, intelligent assembly line packaging, etc. have been applied to production of helmets in advanced countries such as Japan. Molded FRP helmet automation system has also made great progress, which has promoted progress of entire helmet industry. With development of society and increase of labor costs, automated production of helmet products will be development direction of this industry.
- Domestic and foreign helmet standard differences
In addition to national hard hat standards listed, there are also Singapore SS98, France NFS72-202, Germany DIN4840 and other standards. Looking at the world, European and African countries mainly adopt CE standards, South America and North America mainly adopt ANSI and CSA standards, Korea and Japan mainly adopt JIS standards.
- Hard Hat International Certification
4.1 CE certification
EU CE certification is mandatory in EU market. Whether it is produced in EU or in other countries, it must be CE-certified to be freely circulated in EU market. At present, authorized UN certification CE agencies include TUV Rheinland Group (EU Bulletin No. 0197) and UK INSPEC Testing Agency (EU Bulletin No. 0194).
4.2 GS Certification
German GS certification is a sign of German safety certification. GS certification has strict requirements for factory quality assurance system. Factory is subject to annual review and annual inspection. At the same time, PAHs (aromatic hydrocarbon) limit test is required for all parts of helmet product, and all parts are required to be free of cancer. At present, testing agency that can do safety helmet GS certification is only TUV Rheinland Group.
4.3 ANSI Certification
US ANSI helmet standards are basically the same as Canadian CSA standards and are mutually recognized in each other's country. Established in 1894, US safety testing laboratory UL Corporation is the main safety testing and certification body for ANSI and CSA standards. With UL certification, helmet products are highly recognized by consumers in United States and Canada, but UL certification requires a high level of quality assurance, and factory needs to be reviewed four times a year. Of course, SGS Group, which was founded in 1878 by Swiss General Public Notary, can also do ANSI helmet standard tests, but they can only do G and C grades, but not E grade electrical insulation tests.
4.4 AS/NZS Certification
Australia and New Zealand AS/NZS helmet standards are standards developed by the two countries' Occupational Protection Committees. Currently, organizations that can authorize AS/NZS helmet certification include British Standards Association BSI Group and Taiwan ICS Lab.
- Helmet testing equipment and requirements
Our standards stipulate that performance indicators of helmets mainly include basic indicators and special indicators, as follows:
Impact performance. ZKHW-101 helmet impact puncture test, test result force value can not be greater than 4900N, shell must not have debris falling off.
Puncture resistance. ZKHW-101 helmet impact puncture test, test results shall not touch surface of head mold, and shell must not fall off.
Strength of chin strap. ZKHW102 helmet is tested with a strength and lateral rigidity tester. Test results show that force of belt is between 150N and 250N.
Lateral rigidity. Test is carried out with ZKHW-102 helmet under belt strength and lateral rigidity tester. Maximum deformation of test results is not more than 40mm, residual deformation is not more than 15mm, and cap shell must not fall off.
Vertical spacing. Test was carried out with ZKHW-103 helmet under belt strength and lateral rigidity tester. Vertical spacing is not more than 50 mm.
Wearing height. Test was carried out with a ZKHW-103 helmet under belt strength and lateral rigidity tester. Wearing height is between 80-90 mm.
Anti-static properties. Tested with ZKHW-109 helmet anti-static performance tester, surface resistivity should not be greater than 109 Ω.
Electrical insulation properties. Tested with ZKHW-110 helmet electrical insulation performance tester, leakage current does not exceed 1.2mA.
Flame retardant properties. Tested with ZKHW-108 helmet flame retardant tester. Burning time should not exceed 5s, and cap must not be burnt through.
Before impact resistance and puncture performance of helmet are made, there are high temperature, low temperature, water immersion, and ultraviolet lamp pretreatment. Also there are also corresponding equipment for pretreatment test.
High temperature pretreatment. Use ZKHW-106 helmet high temperature pretreatment box. Test high temperature is 50 ± 2℃, placed for 3 h.
Low temperature pretreatment. Tested with ZKHW-107 low temperature/constant temperature water soaking pretreatment tank. Low temperature is -10 ± 2℃or -20 ± 2℃ placed for 3 h.
Soak pretreatment. Tested with ZKHW-107 low temperature/constant temperature water soaking pretreatment tank. Low temperature is 20 ± 2℃, placed for 3 h.
UV pretreatment. Use ZKHW-105 helmet UV aging box. Limited UV irradiation method, test time 400h.
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