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Why thin wall cup mould so expensive?

Why thin wall cup mould price is so high? General speaking, thin wall cup mould are using better steel, hot runner, better cooling, better venting and better demolding effectiveness.

The thin wall cup mould runs on high speed machine which needs withstand high pressure during cup molding, so the mould moving plate and fixed plate thickness are thicker than common mould. There need many interlocks inside the thin wall mould to ensure accuracy and pillar support to avoid deform and eccentric. The plastic airline cup mould need use high hardness steel, high-wear and high-erosion with HRC 55 or above. This means thin wall mould steel cost is higher.

The hot runner design is larger than the common plastic moulds, and at the same time, need limit the melt residence tome to prevent the resin degradation. When the mould is mult-cavities, the gating balance is much higher than that of common molds. Which means thin wall cup mould hot runner cost is higher.

Thin-walled products do not withstand the large residual stresses due to heat transfer irregularities like traditional wall thickness parts. In order to ensure the dimensional stability of the product, and to control the shrinkage and warpage within an acceptable range, it is necessary to strengthen the cooling of the mold to ensure the cooling balance. Which means need better cooling design to enhance the cooling effect, adding high conductivity metal inserts where necessary to accelerate heat transfer, like BeCu beryllium copper. The cooling cost is higher than common moulds.

Due to the short filling time and high injection speed, it is very important to fully exhaust the mold, especially the exhaust in the flow front gathering area, to prevent air trap. The air is usually discharged through mould cores, rams, ribs, studs, and parting surfaces.

The airline cup walls and ribs are very thin, they are very easy to damage, and the shrinkage in the thickness direction is small, the ribs and other small structures are hard to separate, to avoid sticking, there need use more ejector pins when thin wall injection molding.

In a word, thin wall mould structure is more complicated than common moulds. That’s why the thin wall cup mould is so expensive.

Cutlery mould exhaust problem

In the process of producing cutlery mould, sometimes will have unfilled parts, air bubbles etc, this is caused by air exhaust.

1. The source of air in the injection cutlery mold.

(1) The air contained in the gating system and the mould cavity. (2) Some raw materials contain moisture that is not removed by drying, and they are vaporized into water vapor at a high temperature. (3) Air generated by decomposition of some unstable plastics due to excessive temperature during injection molding. (4) Air formed by volatilization or chemical reaction of certain additives in plastic raw materials.

Poor exhaust of the knife and fork mold will bring a series of hazards to the quality of the plastic parts. The main performance is as follows:

(1) In the injection molding process, the melt will replace the air in the cavity. If the air is not discharged in time, the melt filling will be difficult, resulting in insufficient injection volume to fill the cavity.

(2) Excluding the unsatisfactory air will form a high pressure in the cavity and penetrate into the plastic inside under a certain degree of compression, resulting in quality defects such as pores, voids, tissue sparseness, and silver streaks.

(3) Due to the high compression of the air, the temperature in the cavity rises sharply, which causes decomposition and burning of the surrounding melt, causing local carbonization and charring of the plastic part. It mainly occurs at the junction of the two melts at the gate flange.

(4) The air is not well removed, so that the melt velocity entering each cavity is different, so flow marks and fusion marks are easily formed, and the mechanical properties of the plastic parts are lowered.

(5) Due to the obstruction of air in the cavity, the filling speed will be reduced, the molding cycle will be affected, and the taxation efficiency will be reduced.

Distribution of bubbles in plastic parts

(1) The bubbles generated by the accumulation of air in the mould cavity of the cutlery spoon are often distributed on the opposite part of the gate.

(2) Bubbles generated by decomposition or chemical reaction in the plastic raw material are distributed along the thickness of the plastic part.

(3) The bubbles generated by the vaporization of residual water in the plastic raw material are irregularly distributed on the entire plastic part.

Injection molding is a process in which a molten plastic is injected into a closed mold having a relatively low temperature through a nozzle under high pressure. Both thermoplastics and thermosets can be injection molded. It can be used to make various box-type packaging buckets and pails, such as various pails boxes and small boxes mould. For box-type packaging containers, China bucket mold manufacturers will consider the following aspects in bucket mould structural design.
1. The wall thickness of the bucket mould
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