Some domestic cold chain transportation equipment manufacturers adopt closed pouring foaming, polyurethane rigid foam chip resin adhesive bonding, structural adhesive bonding and other processes.

Polyurethane rigid foam is an effective thermal insulation material. Its use is to mix the black and white material into the cavity of the mold through the foaming machine, and the polyurethane rigid foam expands and fills the whole mold space. As a kind of heat insulation material, polyurethane rigid foam can meet the needs of special structure or shape of the plate, which is very flexible and convenient to use.

Principle of polyurethane foaming

The production of rigid polyurethane foam needs two main liquid components polyol and isocyanate, which are commonly known as white and black. Foaming agents are usually added to the polyols mixture with additives such as reaction catalysts, foam stabilizers and flame retardants. They are collectively referred to as white materials. Polyols react with isocyanates to generate heat and vaporize the foaming agent. Therefore, the liquid mixture expands into foam, and the vaporized foaming agent is wrapped in the polyurethane foam. After the reaction is completely cured, the foaming agent and polyurethane form stable, temperature retaining material with a certain degree of strength. In addition, in order to maintain the fluidity and control the density, a certain amount of water is usually added to the polyol.

In the process of polyurethane foam formation, the main reactions are as follows

1. Isocyanate reacts with hydroxyl, polyisocyanate reacts with polyol (polyether, polyester or other polyol) to produce polyurethane. The reaction principle is as follows.

"Introduction to reaction principle of closed and open casting and foaming process for refrigerated car compartment" 1618965458 (1). JPG polyurethane reaction equation

(2) Isocyanate reacts with water, and the compound with isocyanate group reacts with water to produce polyurea and emit carbon dioxide. The reaction principle is as follows.

Isocyanate water reaction equation

Introduction of closed pouring foaming process and open pouring foaming process

Closed pouring foaming process

The traditional closed pouring foaming process is as follows: the operator first makes a closed cavity with surface material on the mold, and reserves injection holes and exhaust holes on the side; The high pressure foaming machine is started, the mould is tilted, and the amount of foam material is injected into the cavity of the mold. After the foam expansion is filled, the mold is released for a certain time after curing, and the product is removed. When the plate length is more than 6m or the injection time is longer than the foaming time, the cavity injection method is often used: in the middle of the mold cavity, a stable isolation rib is used to divide the mold cavity, and the operator holds the injection gun head to inject material into the mold several times.

Schematic diagram of closed charging mode

Open casting foaming process

Open casting foaming process; The upper skin is placed on the service trolley 4 to calculate the total amount of polyurethane foaming material to be input, the starting position and the ending position. The above three parameters are input into the control system, and then the equipment is started. The service trolley 4 will carry the upper skin into the press 3 automatically, The upper skin is adsorbed on the surface of the upper template of the press, the trolley 1 automatically calculates the moving speed according to the parameters provided, enters the press at a uniform speed, and completes the injection of foaming material during operation.

Schematic diagram of open casting foaming equipment

After the casting is completed, the trolley 1 enters the position of 3 of the press completely, the press 3 is closed, the upper skin is covered on the mold, the foam expands and bubbles in the mold, and after a certain time, the product is removed. The foaming material is coated in the moving plate through the transverse porous tube, as shown in the figure below.

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