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Material for children's slides and toddler slides
In the design and manufacture of children's playground equipment,the selection of materials has a direct impact on the final product's safety, longevity, cost, and applicability. Larger and more complex slides are usually rotational molded from linear low density polyethylene (LLDPE) and toddler slides are typically manufactured of high density polyethylene (HDPE) through blow molding and injection molding. This is due to a holistic consideration of material properties, production cost, and application scenario.
Material
LLDPE and HDPE have distinct performance due to their unique molecular structure. The molecular chain of LLDPE has short branches, low crystallinity (50%-65%), and elongation at break above 300%. This molecular structure confers it with good flexibility and impact resistance. The main chain of HDPE is more regular with almost no branches. Molecules are densely packed. It has high crystallinity (70%-85%). Compared with LLDPE, HD has good hardness. Hardness of HDPE is between 60-70 and has good rigidity and high hardness. It is relatively weak in impact resistance and brittle.
Process
Rotational molding is a process of melting and forming a material through a rotating mold. It is applicable in producing large, hollow and complex products. LLDPE has high melt viscosity and moderate fluidity. When rotating, it can evenly stick to the inner wall of the mold. The product casted through Roll moldinghas uniform wall thickness. Uniform wall thickness of the product is very important for ensuring strength in complex structure of curves and corners. Larger children's slides are heavier. The weight of one piece can reach hundreds kilograms and is designed in more complicated shapes. In addition to straight planes, it also has spiral and wave shapes. Rotomolding has certain advantages compared with blow molding. The cost of mold is approximately one third of that of injection mold. The production cycle of one piece is longer than that of injection molding (approximately 40-60 minutes). Therefore, it is more suitable for producing small batches of customized large children's playground slides.
HDPE toddler slides should be a mixture of blow molding and injection molding, because HDPE has very regular molecular chains and a high molten viscosity but a low flow rate. Blow molding uses high-pressure gas to force the molten material into the mold, preventing uneven wall thickness due to low fluidity. This method is used to produce small hollow components (slides, side panels, columns). Injection molding uses high pressure to inject molten material into a mold, allowing for precise control of details and a smooth surface. This method is used to produce small, structurally regular products (handrails, pedals). toddler slides should not have burrs or protrusions, injection-molded HDPE toddler slides have smooth surfaces and will not cause abrasions. In terms of production efficiency, both injection and blow molding have short cycle times, which is only a few minutes per molding cycle and is suitable for mass production of small-sized and high-demand toddler slides.
Costs
In terms of unit prices, the price of HDPE raw materials is generally 500-1000 CNY/ton higher than that of LLDPE. The difference in process costs is even more evident. The equipment for roto-molding requires large investment, complex molds and long heating times. Therefore, the unit cost of LLDPE children's slides is higher. On the contrary, the equipment for injection molding is mature and the mass production efficiency is high. Therefore, injection molding of HDPE toddler slides is more economical and can be produced on a large scale.
Use Scenario
Large toddler slides are often used in public playgrounds for children aged 3-12 to use repeatedly. The advantages of LLDPE fatigue resistance are shown in this scenario: impact strength can reach 50kJ/m², much higher than that of HDPE (15kJ/m²). More importantly, the environmental stress crack resistance (ESC) of LLDPE exceeds 1000 hours, that is, LLDPE toddler slides are not afraid of UV rays, corrosion and temperature changes, will not suddenly break because the material ages and corrodes.
Toddler slides (1-3 years old) are used in a different environment.Generally used in indoor, kindergarten and other semi-closed sunshade places, low intensity, gentle action, small impact force,HDPE children's slides are hard, smooth and not easily scratched, will not produce toxic odors in long-term storage.Of course, the disadvantages of HDPE children's slides are also very obvious. When the number of uses per day exceeds 200 times or the weight exceeds 40kg, the rigid structure will produce stress concentration at the joint and cause the micro-crack to develop. Therefore, HDPE slides are usually used only for children aged 1-3 years, and the structure should be checked regularly.