Food Preservation Bucket Mould Design
The case of the food preservation bucket mould is a real case of a client of the company from last year. The drawings were provided by the customer. Our engineers worked out the following detailed design based on the customer’s requirements for this food preservation bucket mould. From the structural analysis to the analysis of the bucket moulding process.
As a professional plastic bucket mould manufacturer, YuanCheng Mold was able to provide the customer with a satisfactory design and mould.
Structural analysis of the food preservation bucket
Fig 1 shows a bucket for storing and transporting insured foodstuffs. From the customer’s drawing we can see that the three plastic parts that make up the food preservation bucket are: the bucket body, the bucket lid and the bucket ring.For food safety reasons, the structure of the container should be designed in such a way as to ensure that the food is not contaminated or split during storage, storage, delivery and use.
Fig 1: The 3 plastic parts that make up the food preservation bucket
Food preservation bucket mould requirements
Structural requirements for food preservation buckets
- The assembly process of the bucket lid and buckle after placing food in the bucket is shown in Figure 2.
- Food is placed in the bucket.
The bucket lid is rotated by 30° to cover it.
- After the lid has been put on, the lid is rotated by 60° and tightened with the 3 shoulders inside the bucket.
- After the lid has been tightened, the buckle is slowly pushed in from the side of the barrel where there is a small convex circle along the side (the handle is guided by a bevel).
- After the buckle is pushed into place, the two small convex circles on the inside are pressed into the inner holes of the handle to complete the assembly.
Fig 2: Assembly process after placing food in the bucket
The buckle is designed for single use and is made of hard polyethene (PS) plastic with a concave arc at the rear. If the receiving party finds that the ring is broken or missing, it is possible that the food has been split and contaminated. To access the food, the receiver simply cuts the ring and rotates the lid to remove the food.
Material requirements for food preservation buckets
The material used in injection moulded food containers is PP engineering plastic, which is commonly used in beverage and food packaging. PP plastic is a safe engineering plastic that is widely used for packaging, storage and repeated use. PP engineering plastics also have an excellent melt index and good melt flow and formability during injection moulding.
Wall thickness requirements for the finished food preservation bucket
The customer required a uniform wall thickness (all around 4mm) to meet the injection moulding process requirements.
Food preservation bucket mould
Analysis of the moulding process for food preservation buckets
The structure of the plastic part of the lid and the related dimensions are shown in Figure 3. In the view: the plastic part is a disc-shaped hollow shape with a handle design in the upper part and a large circular arc downwards in the centre for the main purpose of increasing the pulling strength of the handle. The inner bottom surface of the moulded part is designed with three 120° equal 45° interlocking structures with the shoulder surface of the food bucket, and two ϕ4mm venting holes on the lid surface.
Fig. 3 Food preservation bucket lid (PP)
Plastic moulding characteristics
1: Polypropylene PP is a non-toxic, odourless, colourless, white, waxy and transparent granule of acrylic. It is non-absorbent, has good gloss and is easily coloured.
However, colouring is not recommended for use in storage and packaging with foodstuffs. It is chemically stable except for strong oxidising agents; it is insoluble in water, hardly absorbs water and has good stability to water. The melting point of polypropylene plastic is between 164°C and 170°C.
It has good heat resistance, with a heat deflection temperature of 150°C, and can be used for a long time at 110°C or below.
2: The structure of the plastic part is crafty.
- Analysis of the dimensional accuracy of plastic parts. The dimensional accuracy of the shape and inner wall of the plastic part is not high, and the deviation of the allowed tolerance size varies widely and is easy to control in the actual production process. Free size can be checked according to MT7 tolerance value.
- Analysis of the surface quality of plastic parts. The inner and outer wall of the plastic part should have a smooth surface and no flying burrs, the parts of the plastic part diagram (see Figure 3) in the technical requirements of the plastic part are not high requirements for all surfaces, to achieve the surface roughness value Ra3.2μm can be.
- Structural process analysis of the plastic part. The shape of the plastic part and the inner wall dimensional accuracy requirements are not high, the allowable tolerance size of the wall thickness size is more uniform (about 2.5mm), in line with the injection molding requirements.
The design of the parting surface and pouring system for food bucket moulds
(1) The choice of parting surface.
When choosing the parting surface, according to the principles of parting surface selection, the maximum contour of the plastic part should be the parting interface of the moving and fixed moulds, which is also conducive to the exhaust of the mould cavity and makes the plastic part stay in the moving part as far as possible. In the design of this injection mould, the bottom side of the part is considered to be a circular plane.
Therefore, the bottom of the mould is chosen as the horizontal parting surface between the moving and fixed moulds, while the shape of the handle side of the mould with the grommet is partly partitioned laterally, as shown in Figure 4.
Fig 4: Schematic diagram of the selection and determination of the parting surface
(2) Design of the pouring system.
As the plastic parts are thin-walled and large in size, the pouring system should adopt a point gate feeding method. Because of the long flow of plastic material in the mould, the filling speed of the plastic melt in the mould is affected to a certain extent.
Therefore, a 3-point equivocal point gate feed is used to avoid melt traces or underfilling of the melt. A diagram of the pouring system is shown in Figure 5.
Fig 5: Schematic diagram of the evenly spaced parts of the 3-point gate
Design of the cavity and push-out mechanism of the mould forming part
The part of the mould to be moulded consists of two main parts.
A structure designed with three 120° equal 45° interlocking with the shoulder surface of the food drum on the inner bottom surface of the moulded part, which must be formed by means of an oblique guide forming slide bar.
A ϕ6 mm recess is formed laterally at one end of the handle to match the grommet. The form of the moulding of one of the three diagonal guide slides is shown in Fig 6.
Fig 6: Diagram of triple sliding rod core forming
The partial mould structure for lateral moulding is shown in section C-C (partial) in the general assembly drawing. Due to the shallow (1.5 mm) 2 – ϕ6 mm pit hole at one end of the handle, the moulded part exerts very little clamping force on the extractor core. Therefore a simple mould construction with a circular spring pushing off the mould was used instead of a slider with an inclined guide pillar pushing.
The lateral core extraction mechanism consists of an inclined wedge, a round spring, a slider and a laterally moulded ϕ6mm round core. In the design of the push-out mechanism after the moulding of the plastic part, the three connection blocks for the tilt-guided plastic part slider are fixed to the push rod fixing plate at the same time together with the reset rod. The reset mechanism consisting of the reset rod pushing the push rod fixing plate etc. Completes the restoration of the three inclined guide moulding sliders after the moulding of the moulded part.
In order to achieve the automatic separation of the pouring system after the mould has been opened, a release plate is set up between the fixed mould plate and the fixed mould base plate.
Structural design of the food bucket mould
Considering the large size of the overhanging part between the moving and fixed moulds (>290mm) after the mould is fully opened, the following measures and structural solutions were adopted to ensure continuous and safe injection production.
1: When the mould is opened, the self-weight of the fixed mould part is large. The four long reverse guide pillars that bear the gravity are designed as ϕ40mm second-order guide pillars.
This avoids the deformation of the guide pillars due to the excessive weight of the mould, which may cause the moulded part to have uneven wall thickness at the four rounded edges.
2:In order to achieve semi-automatic and automatic production of the mould, the automatic shedding of the pouring system is the key.
The mould consists of an open mould fixed distance sleeve, a fixed distance tie bar, a Z-type tie bar and a sprue popping top stripping column to form a set of automatic stripping mechanism for the pouring system.
3: The exhaust of the moving part of the mould is discharged from the parting plane with the gap between the large insert sleeve of the fixed mould forming and the large insert sleeve of the moving mould forming, and the exhaust is discharged at the end of the plastic flow.
The gap value is 0.03~0.05mm, which is in line with the molding exhaust conditions of PP plastics.
Conclusion-Food preservation bucket mould design
YuanCheng Mold successfully completed the food preservation bucket mould requested by the customer, and the customer was very satisfied with the moulded food bucket.
YC Mold, as a leader in plastic injection moulding in China, provides one-stop service for you, contact us now!