JPH0415732B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing plastic pallets for use in cargo handling machines such as forklifts and handlifts.

[Conventional technology and its problems]

For example, pallets made of synthetic resins such as high-density polyethylene and polypropylene are known to be lightweight, durable, and economically inexpensive. Pallets are divided into single-sided and double-sided types, but in either case, they consist of a deck board on which the cargo is placed and legs to support it, with space around the legs to insert a fork. It is something.

In the case of synthetic resin pallets, the deck board and the legs are either molded integrally or molded separately and then joined together, but in the former case, if you try to obtain something with a certain level of strength, the shape will change. Since it is quite complex, blow molding is often not possible, and even injection molding results in a complicated mold and high cost. On the other hand, in the method of building the deck board and legs separately and combining them,
Bolts and nuts are usually used for connection, but manufacturing is time-consuming as the heads must be processed to prevent them from protruding.Furthermore, there is a risk that the bolts and nuts may loosen during use, resulting in incomplete installation. .

Another option is to attach the legs to the deck board with adhesive or by welding them, but it is difficult to ensure sufficient joint strength at the joint, and it requires attaching a large number of legs one by one. It takes time and effort.

It is an object of the present invention to provide a method for manufacturing synthetic resin pallets that eliminates the disadvantages of the conventional method and can manufacture lightweight pallets with high rigidity using fewer steps and fewer members.

[Means for solving problems]

In order to achieve the above object, the present invention separately forms by blow molding a hollow deck board having a protrusion for coupling on the lower surface, and a hollow leg in the form of a flat plate that juxtaposes columnar parts and protrudes upward. The gist of this method is to attach the legs to the deck board by then heat-sealing the protrusion and the column body.

[Effect]

According to the present invention, since both the deck board and the legs are hollow bodies, they are lightweight, and the deck board and the legs can be easily connected by heat fusion without using other attachment members.
Furthermore, the legs are not individual pillars, but rather a flat plate with several pieces integrated, so they can be attached all at once and fixed securely.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Fig. 1 is a perspective view of a synthetic resin pallet manufactured by the method of the present invention, Fig. 2 is a view in the direction of the arrow B shown above, and Fig. 3 is a view in the direction of the arrow A of the above. In the figure, 1 is a deck board, 2 is a leg, Numeral 3 is a protrusion integrally formed on the lower surface of the deck board 1, and numeral 4 is a column protruding upward from the flat leg 2. A plurality of these are arranged in parallel at appropriate intervals.

First, to explain the materials forming the deck board 1 and the legs 2, they are both hollow bodies that are blow-molded separately, and are made of polyolefin resin that can be blow-molded into large sizes, such as high-density polyethylene, polypropylene, or any of these. A mixture is used.

For high density polyethylene, MI is 0.5 [g/
10min] or less homopolymer or butene-1
copolymers with α-olefins such as hexene-1 and hexene-1 are used.

For polypropylene, MFR1 [g/
10 min] or less, it is preferable to use an ethylene/propylene block copolymer in terms of cold resistance. Alternatively, various elastomers (such as EPM, EPDM, etc.) can be added to polypropylene (including homopolymers).
EVA, EEA, etc.) and low-density polyethylene are also used. In addition, various fillers (e.g. mica, talc, glass fiber,
Inorganic fillers such as whitebait balloon charcoal, wood flour, waste paper, etc.) may be mixed. As will be described later, it is preferable that the deck board 1 and the legs 2 are made of the same material because they are heat-sealed, but they may be made of different materials if they can be bonded well.

The deck board 1 is a flat plate with no unevenness on the upper surface, and on the lower surface, as shown in FIG. They are integrally formed at appropriate intervals such as in the middle. Similarly, as shown in FIG. 12, the lower surface of the deck board 1 is made up of a set of two walls c that are depressed from the back side during molding, and the bottom d is a wall on the upper surface side of the deck board 1. Longitudinal continuous ribs 5, 6, and 7 consisting of concave grooves fused to the deck are installed in a lattice pattern, while ribs 8 and 9 of a similar structure are arranged radially from the center of the deck board 1 between them. will be established.

In another embodiment, as shown in FIG.
It may be added.

These ribs 5 to 10 are arranged to pass through the protrusion 3 for forming the joint surface 3a, or to hang over a part of the protrusion 3, thereby maintaining the continuity of the ribs and also intersecting with other ribs. This ensures a strong connection.

In this way, many ribs are installed inside the pallet while maintaining continuity, and the ends of the ribs are placed on the joint surface 3.
Since they are connected at point a, they receive the stationary load of the pallet and the load during transportation by lift as a so-called continuous beam.

This means that the fulcrum reaction force that occurs locally when the pallet is in use (for example, around the contact surface of the fork or around the joint between the legs and the deck board when the pallet is left still) is absorbed by these continuous ribs. It helps in smoothly transmitting stress to the entire deck board, dispersing and averaging stress to various parts, and as a result, local deformation of the deck board is not caused, and therefore deformation can be suppressed to a small level as a whole.

On the other hand, as shown in FIGS. 4 to 9, the leg 2 consists of a flat plate-shaped girder 2a extending in the longitudinal direction.
A columnar portion 4 is integrally formed upward from a, and its upper surface becomes a joint surface 4a.

This column body portion 4 is a portion that bears the load due to the cargo as a compressive load, and in this case, the compressive load e (arrow in FIG. 5) is transmitted to the girder 2a or the ground plane via the side wall 4b. In particular, when the pallet is placed on the ground, the compressive buckling strength of the wall surface controls the load that can be mounted. Although increasing the wall thickness is effective in improving the buckling strength, it causes an increase in weight, which is not very desirable.

In addition, it is desirable for the side wall 4b to be parallel to the direction of the load e, that is, to stand upright, in terms of buckling resistance, but on the other hand, the taper θ ( However, within 5°) is required. However, this angle θ generates a bending moment on the wall surface when the load e is applied, and greatly reduces the buckling limit load. Therefore, in order to eliminate such restrictions, an embossing rib 11 is installed inside the column body 4.
A double wall structure was installed to improve buckling strength.

Furthermore, a rib 12 continuous in the longitudinal direction is provided on the ground surface side of the girder 2a, and if necessary, after the continuous rib 12 is installed, an auxiliary rib 13 may be provided in the remaining space.

On the other hand, girder 2a is made easier for forks to enter.
A chamfer 14 is formed to reduce damage to the girder 2a due to the fork coming in and going out.

Next, to explain the manufacturing method, the deck board 1 and the legs 2 are individually molded using a blow molding machine, and the protruding portion 3 of the deck board 1 and the column body portion 4 of the leg 2 are formed.
The legs 2 are attached to the deck board 1 by heat-sealing the joint surfaces 3a, 4a of each by hot plate welding, vibration friction welding, electromagnetic induction heating, or the like. Here, "separately" means to be manufactured separately, and includes both cases where the same mold is used and molded with different cavities, and cases where completely different molds are used.

The "height" of the column body 4 needs to be constant in order to form the opening b (Fig. 1), but since the blow ratio is different from that of the girder 2a, it is necessary to have a certain height, especially at the corner part 4c. Easy to make thin. For this reason, a protrusion 3 is also provided on the deck board 1 side to ensure the height and opening of the pallet while suppressing the height of the column body 4.

In this manner, the protruding portion 3 has the role of limiting and securing the welded portion and at the same time adjusting the height of the column portion 4 so that it does not become unduly high.

The pallet produced in this way is the first
Openings a and b in the figure are secured in the direction of arrow A and arrow B.
It is possible for forklifts (including hand lifters) to enter and handle cargo from any direction (so-called four-way type).

In addition, as another embodiment, the legs 2 are assembled in a grid pattern,
It can also be installed in the shape of a field.

Since the upper surface of the deck board 1 is flat, it is difficult for dust to accumulate and is easy to clean, making it sanitary.

Further, since the side wall 4b of the column body portion 4 is formed of a curved surface, the impact of the fork can be deflected laterally on the curved surface to prevent damage.

If the back side of deck board 1 is as shown in Figure 10,
If the fork enters from direction A, rib 5,
7, 8, and 9 act as bridges to suppress deflection during lift transportation. Furthermore, if the fork enters from direction B, the ribs 6, 8, and 9 will perform the same role.

If the back side of deck board 1 is as shown in Figure 11,
The ribs are placed mainly in the vertical direction, whereas the leg 2 is installed in the horizontal direction in the diagram, so this acts as a reinforcing material, so even if you reduce the number of ribs installed in the horizontal direction, there will be no problem. There isn't.

In addition, the ribs 12 provided on the beams 2a of the legs 2 contribute to improving the rigidity of the pallet against bending (the moment marked with a cross in Figure 5), and when the pallet is supported on both sides or lifted by a forklift. It is effective in preventing deformation when In particular, when the ribs 13 are provided, they mainly serve to strengthen the pressure receiving surface of the forklift.

Regarding actual examples and test results, a mold based on the design was attached to a blow molding machine IPB-200 manufactured by Ishikawajima Harima Heavy Industries, and molding was carried out. The molding material is
High-density polyethylene made by the Phillips method [homopolymer, density 0.952 or more, MI (high load method 21.6 kg)
After molding the deck board and the legs (3 pieces) at a molding temperature of 200° C., the two were fused together. The deck board size was 1100 x 900 mm, height 150 mm, deck board weight was 10 kg, and leg weight was 1.5 kg/piece.

When this pallet was subjected to a bending strength test based on JISZ0602, the strength was 15mm under a 1 ton load.
The deformation was 25 mm under a load of 1.5 tons, and it was ranked as a Class B pallet for a 1-ton load.

When we also conducted a compression test based on JISZ0602, it was 3 mm at a 4/3 ton load/(per leg).
Class A and B standards for pallets with a carrying capacity of 1 ton (4 mm
(within)

A drop test (dropping at a corner from a height of 1 m) based on JIS Z0602 was also carried out, and the dimensional change rate of the diagonal length of the pallet was 0%, passing the A and B standards (±1.5% or less).

In addition, we carried out a transportation test using a fork lifter carrying 1 ton of resin (25 kg paper bags, 40 bags).
The deformation when the fork goes up and down is 5mm at the end of the pallet.
within the limits, and no practical problems were observed.

〔Effect of the invention〕

As described above, in the method for manufacturing synthetic resin pallets of the present invention, the deck board and the legs can be easily joined by heat fusion without using other members such as bolts, and a relatively wide joint surface is ensured. Therefore, stress concentration at the joint can be avoided.

Furthermore, the deck board and legs are not integrally molded,
Since it is separated as a separate molded product,
This eliminates the uneven wall thickness distribution caused by uneven blow ratios, allows continuous ribs to be placed on the back of the deck board and the legs in any desired arrangement, and allows the wall thickness of the legs and deck board to be selected according to the required performance. Measures that are advantageous in terms of strength can be taken.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a synthetic resin pallet manufactured by the method of the present invention, Fig. 2 is a view taken in the direction of arrow B in Fig. 1, Fig. 3 is a view taken in the direction of arrow A in Fig. 1, and Fig. 4 is a view taken in the direction of arrow A in Fig. 1. A perspective view of the legs, FIG. 5 is a front view of the same as above, FIG. 6 is a plan view of the same as above, FIG. 7 is a bottom view of same as above, and FIG.
An X-ray cross-sectional view, Figure 9 is a Y-Y cross-sectional view of Figure 7,
FIG. 10 is a bottom view of the deck board, FIG. 11 is a bottom view of the deck board in another embodiment, and FIG. 12 is a sectional view of the main part showing the ribs. DESCRIPTION OF SYMBOLS 1...Deck board, 2...Legs, 2a...Girders, 3...Protrusions, 3a...Joint surfaces, 4...Column body parts, 4a...Joint surfaces, 4b...Side walls, 4c...Corner parts, 5, 6,
7, 8, 9, 10, 12, 13...rib, 11...embossed rib, 14...chamfer.

Claims (1)

[Claims] 1. A hollow deck board having a protrusion for coupling on the lower surface and a flat hollow leg protruding upward with columnar parts arranged in parallel are formed separately by blow molding, and then the protrusion and the columnar part are bonded together. A method for manufacturing a synthetic resin pallet characterized by attaching legs to a deck board by heat-sealing the legs.