The weight error of plastic trash cans is not accidental, but a systematic problem that runs through multiple links such as raw materials, mold design, injection molding process, equipment status, and environmental factors. These factors work together to result in differences in final weight even for products of the same specification and batch.
Raw materials: the fundamental source of weight errors
The quality and condition of raw materials are the primary factors determining the weight of finished products.
Differences in raw material batches and grades
Plastic raw materials such as polyethylene (PE) or polypropylene (PP) from different manufacturers and batches have natural fluctuations in key indicators such as density and melt index. Even for the same brand, subtle differences between different batches can lead to inconsistent final product weight.
The impact of recycled materials and impurities
Recycled materials or impurities added to reduce costs are an important cause of weight instability. The density of these substances is different from that of pure raw materials, and their composition is complex, which can directly change the density and flowability of the melted material, causing weight deviation.
Artificial weight gain of fillers
Some dishonest manufacturers will deliberately add cheap fillers such as stone powder (calcium carbonate) to the raw materials to increase weight. This will cause the garbage bin to become "bloated", although the weight meets the standard, the material becomes brittle, the toughness is extremely poor, and the service life is greatly shortened.
Moisture in raw materials
If plastic particles become damp during storage, the moisture will vaporize during injection molding, forming defects such as bubbles or silver lines inside the finished product. This not only affects the appearance and strength, but also results in a lighter weight due to the less dense internal structure.
Mold: The "mold" that determines weight accuracy
Mold is the key to molding, and its design, processing accuracy, and usage status directly affect the weight of the product.
Gate design and filling
If the size of the gate (the channel for plastic melt to enter the mold) is too small, it will hinder the smooth filling of the mold cavity by the melt, which may lead to product "shortage" and insufficient weight.
Mold temperature control
Uneven or overall low temperatures in various areas of the mold can affect the fluidity and cooling rate of the melt, resulting in inconsistent shrinkage rates in different parts and ultimately affecting the final weight.
Mold wear
After long-term use, the mold cavity will wear due to the erosion of the melt, resulting in an increase in cavity volume and an increase in the weight of subsequent products produced.
The various process parameters during injection molding are the direct cause of weight fluctuations, and any small changes in parameters will be reflected in the weight of the finished product.
01
Temperature
The melt temperature and mold temperature are the main factors affecting the weight of the product. Temperature changes can cause changes in the density and viscosity of the melt, which in turn affect the filling amount and final weight.
02
Pressure
The magnitude of injection pressure and holding pressure directly affects the tightness of the mold cavity filling. Insufficient pressure can lead to a shortage of materials and a lighter product; Excessive pressure may cause the product to "flash" or become too dense and heavy.
03
Time and speed
The setting of parameters such as injection time, holding time, cooling time, as well as injection speed, will affect the state and final weight of the melt in the mold cavity.
04
Back pressure and feeding
Insufficient back pressure can cause gas to mix into the molten material, resulting in a decrease in density and a lighter weight. Unstable feeding from the hopper can result in varying amounts of material entering the hopper, leading to weight fluctuations.
Injection molding equipment: guarantee of performance
The state of the injection molding machine is the hardware foundation for stable production, and its performance fluctuations can directly lead to weight errors.
1
Wear of anti reverse ring:
If the anti reverse ring at the front end of the screw of the injection molding machine is worn, the molten material will reflux during injection, resulting in a decrease in the actual amount of material injected into the mold cavity, and the product weight will become lighter and unstable.
2
Measurement and mold locking:
Inaccurate measurement stroke can cause changes in the amount of molten material injected each time. Insufficient locking force may cause the mold to be slightly stretched during high-pressure injection, resulting in product burrs and an increase in weight.
Environmental factors: external influences that cannot be ignored
The environment of the production workshop, especially the temperature, can also have an impact on the production process and product weight.
Workshop temperature: Changes in ambient temperature can affect the oil temperature of injection molding machines, mold temperature, and cooling rate of raw materials. Products produced in different seasons or time periods may have weight differences due to environmental temperature differences
Summary
The weight error of outdoor plastic trash cans is a result of multiple coupled factors, from the quality of raw materials and the accuracy of molds, to the setting of injection molding process parameters, equipment status, and even subtle changes in the production environment. Every link may become a variable of weight fluctuations. Therefore, understanding and controlling these factors is the key to achieving stable product quality and reliable performance.
According to industry standards, there is a certain allowable error in the weight of plastic products, usually between 3% and 5%, depending on the size and requirements of the product. For the purchaser, while paying attention to weight, they should also be wary of inferior products that are falsely labeled as "weight gain" and actually "adulterated". Raw material purity, wall thickness uniformity, and structural design should be taken as the core indicators for measuring quality
