Why thin wall cup mould so expensive?
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
The design of the wall thickness mainly considers three aspects: one is thickness; the other is uniformity; the third is
gentle transition.
1 Thickness: The wall thickness of the bucket is mainly determined by its use, plastic type, structure and so on. For
thermoplastics, generally not less than 0. 6mm, often choose 2~4mm; for thermosetting plastics, because of its poor fluidity,
the thickness is larger, the small pieces are 1. 6~2. 5ram, the large pieces are 3. 2 ~ 8mm, the maximum is no more than
10mm.
2 Uniformity: The uniformity of wall thickness has a great influence on the quality of the bucket. If the thickness
difference of a bucket is too large, the shrinkage will be uneven, causing defects such as deformation and crack. Therefore,
the structure should be designed with an equal thickness structure.
3 Smooth transition: In some buckets, some parts must have different thicknesses due to structural requirements, such as
the bucket turning point. At this time, a gentle transition should be adopted to avoid the sudden change of the section.
2. Improve stiffness of the bucket
The plastic is relatively flexible, the bucket is made of poor rigidity, and the turnover box type container sometimes
has a large load capacity, so various measures for improving the rigidity should be adopted in the structure.
1 Add reinforcement: Reinforcement can enhance the strength and rigidity of the container. The basic requirements for the
ribs are: the number should be more, the wall thickness should be thin, the height should be short, and the slope should be
sufficient. The bottom of the rib should be a circular arc transition. The direction of the rib should be consistent with the
flow direction to improve the plastic. toughness;
2 Improve the shape: the box-shaped bucket is mostly rectangular thin-walled parts, which are easy to be deformed.
Various reinforcement measures should be taken to slightly extend the four side walls of the bucket to improve the rigidity;
it is a strip shape on the side wall to prevent distortion. Enhancement; edge reinforcement at the edge of the bucket to
prevent deformation of the mouth; bottom reinforcement at the bottom of the bucket designed in a corrugated, arched shape.
3 Reasonable support: The bottom area of the box-shaped bucket is large, but it is unreasonable to use the whole bottom
surface as the support. Because the bottom is slightly curved, it is not flat. Therefore, the surface support should be
changed into a line support or a point support, and the convex side support (ie, the line) Support); raised foot support (ie
point support); the height of the protrusion is generally 0. 3 ~ 0. 5mm.
4 Corner: The corner is the intersection of two faces or three faces. Regardless of the shape of the bucket, the
intersection of the faces must be rounded, which can greatly improve the rigidity of the bucket and improve the plastic
filling model. Sex, and can disperse stress and reduce deformation.
3. Demoulding slope
In order to facilitate the demolding of the molded part, a suitable draft angle must be considered when designing the
bucket. The draft is too small, the demoulding is difficult, and the surface of the bucket is damaged; if it is too large,
the dimensional accuracy is affected.
The draft angle varies depending on the shape of the plastic part, the type of plastic, the mold structure, the surface
roughness, the molding method, and the like. Generally speaking, the commonly used slope of the plastic part along the
demolding direction is 1o~1.5o, and the minimum is not less than 0.5o.
Household molds are a form of fungus. There are many different
types, and they can occur both indoors and outdoors.
Molds produce spores, which spread by floating around in the air. Mold spores are present in all indoor environments.
There is no way to prevent spores, and they can persist in conditions where mold itself cannot grow.
Mold spores thrive in environments that are moist and warm, so when they land on a damp spot, they begin to grow.
Molds can grow on a variety of different surfaces, including fabric, paper, wood, glass, and plastic. As they grow, they
may digest the material they are growing on.