1. Core Scorching (Center temperature exceeding material's oxidation temperature)

A. Poor quality polyether polyols: excessive moisture, high peroxide content, high boiling point impurities, elevated metal ion concentration, improper use of antioxidants.

B. Formulation issues: high TDI index in low-density formulas, improper ratio of water to physical blowing agents, insufficient physical blowing agent, excessive water.

C. Climate impact: high summer temperatures, slow heat dissipation, high material temperatures, high humidity leading to center temperature surpassing oxidation temperature.

D. Improper storage: Increased TDI index leading to accumulation of heat during post-curing, resulting in elevated internal temperature and core scorching.

2. Large Compression Deformation

A. Polyether Polyol: Functionality less than 2.5, propylene oxide ratio greater than 8%, high proportion of low molecular weight components, unsaturation greater than 0.05 mol/kg.

B. Process Conditions: The reaction center temperature is too low or too high, poor post-curing, incomplete reaction, or partial scorching.

C. Process Formula: TDI index too low (controlled within 105-108), excess silicone oil stannous octoate and silicone oil, low foam air content, high closed-cell content.

3. Soft Foam (Decreased hardness at same density)

A. Polyether polyols: low functionality, low hydroxyl value, high molecular weight.

B. Process formulation: insufficient T9 octoate, slow gelation reaction, lower water content with the same amount of tin catalyst, higher amount of physical blowing agents, high dosage of highly active silicone oil, low TDI index.

4. Large Cell Size

A. Poor mixing: uneven mixing, short cream time; increase mixing head speed, reduce mixing head pressure, increase gas injection.

B. Process formulation: silicone oil below lower limit, insufficient or poor quality octoate tin, slow gelation speed.

5. Density Higher than Set Value

A. Polyether polyols: low activity, high molecular weight.

B. Process formulation: silicone oil below lower limit, low TDI index, low foam index.

C. Climate conditions: low temperature, high pressure. A 30% increase in atmospheric pressure increases density by 10-15%.

6. Collapsed Cells and Hollows (Gas evolution rate greater than gelation rate)

A. Polyether polyols: excessive acid value (affects reaction rate), high impurities, low activity, high molecular weight.

B. Process formulation: excess amine, low tin catalyst (rapid foaming and slow gelation), low TDI index, insufficient or ineffective silicone oil.

C. Low-pressure foaming machine: reduce gas injection and mixing head speed.

7. High Closed-Cell Ratio

A. Polyether polyols: high epoxy ethane ratio, high activity, often occurs when switching to polyether polyols with different activity levels.

B. Process formulation: excessive octoate tin, high isocyanate activity, high crosslinking degree, high crosslinking speed, excessive amine and physical blowing agents leading to low foam pressure, high foam elasticity resulting in poor cell opening, excessively high TDI index leading to high closed-cell ratio.

8. Shrinkage (Gelation rate greater than foaming rate)

A. High closed-cell ratio, shrinkage during cooling.

B. Process conditions: low air and material temperature.

C. Process formulation: excessive silicone oil, less amine, more tin, low TDI index.

D. Low-pressure foaming machine: increase mixing head speed, increase gas injection.

9. Cracking

A. "八" shaped cracks indicate excess amine, single line cracks indicate excess water.

B. Mid and bottom cracks: Excessive amine, fast foaming rate (excessive physical blowing agent, poor silicone oil and catalyst quality).

C. Top cracks: Unbalanced gas-evolution gelation rate (low temperature, low material temperature, insufficient catalyst, less amine, poor silicone oil quality).

D. Internal cracks: Low air temperature, high center temperature, low TDI index, excessive tin, high early foaming strength, highly active silicone oil in small quantities.

E. Side middle cracks: Increase tin dosage.

F. Cracking throughout the process may be due to discrepancies in dropping plate and foaming reaction, or premature foaming, or incorrect plates. Apart from formulation, it also relates to the smoothness of the base paper; if the base paper is wrinkled, it can divide the liquid into several parts, causing cracks.

10. Blurred Cell Structure

A. Excessive stirring speed.

B. High air injection volume.

C. Inaccurate metering pump flow.

D. Clogged material pipelines and filters.

11. Bottom Edge Cracks (Excessive amine, fast foaming rate)

Surface large pores: excessive physical blowing agent, poor silicone oil and catalyst quality.

12. Poor Low-Temperature Performance

Poor inherent quality of polyether polyols: low hydroxyl value, low functionality, high unsaturation, low TDI index with the same tin usage.

13. Poor Ventilation

A. Climate conditions: low temperature.

B. Raw materials: high polyether polyol content, highly active silicone oil.

C. Process formulation: excess tin, or low tin and amine content with the same tin usage, high TDI index.

PLC (Programmable Logic Controller)

It is an automatic control device with instruction memory, digital or analog I/O interfaces; primarily used for logical, sequential, timing, counting, and arithmetic operations with bit operations; used to control machines or production processes.

Variable Frequency Drive (VFD)

A VFD is a control device that transforms power frequency from one frequency to another using the on-off action of power semiconductor devices.

The main circuits of a VFD can generally be divided into two types:

- Voltage type: Converts DC voltage from a voltage source to AC in the VFD, with capacitor filtering in the DC circuit.

- Current type: Converts DC current from a current source to AC in the VFD, with inductor filtering in the DC circuit.

Photoelectric Switch

It utilizes the obstruction or reflection of an infrared light beam by a detected object, detected by the synchronous circuit, to determine the presence or absence of the object. It can detect any object that reflects light, not limited to metals.

A mirror-reflective photoelectric switch is used on the vacuum perforating machine.

Heat Exchanger System

Controls the temperature of raw materials in the system to meet requirements.

As the temperature of the raw material rises after passing through the heat exchanger, its viscosity increases. To ensure the normal operation of the high-pressure pump, a special feeding pump is required. Specific requirements are calculated based on flow rate and raw material viscosity.

The temperature control of the heat exchanger should be near the mixing head, correlating the raw material temperature with the switch of the cooling water to automatically control the flow of cooling water to cool the raw material.

Perforating Machine

There are roller perforating machines, vacuum perforating machines, and brush perforating machines, with roller machines having the best control effect, followed by vacuum perforating machines, and brush perforating machines being the worst. Currently, brush perforating machines are rarely used.

The purpose of perforating is to prevent product deformation.

The roller perforating machine controls the size of the gaps. If the gaps are too large, the perforating effect is not good; if the gaps are too small, there will be obvious pressure marks on the product.

There are two methods of perforating: 1. Chemical method - using perforating agents, 2. Mechanical method - using perforating machines.

Products must be perforated as soon as they come out of the mold. Some products may expand after being demolded, and at this time, they should be left for a period before perforating.

TPR

It can prevent product shrinkage and collapse of bubbles; its most basic function is effective perforating to facilitate demolding. However, it can also lead to fluctuations in ILD (Indentation Load Deflection); TPR directly affects the rise speed of the foam.

Loop Pressure Regulating Valve

It is crucial for balancing system pressure in the control system and should be placed as close to the nozzle as possible. If it is far from the nozzle, pressure fluctuations may occur, leading to system instability and unstable products.

Foam scorching is a common phenomenon encountered in actual foam production. Below are the reasons behind this issue along with potential solutions:

(1) Issues with the quality of polyether polyols: During production and transportation, the product's water content exceeds the standard, there is an excess of peroxides and low-boiling-point impurities, the concentration of metal ions is too high, and there is improper selection and concentration of antioxidants.

(2) Formulation: In low-density formulations, the TDI index is too high, the proportion of water to physical blowing agents in the foaming agent is improper, the amount of physical blowing agent is insufficient, and there is excessive water content.

(3) Climate impact: In summer, high temperatures lead to slow heat dissipation, high material temperatures, high air humidity, and the temperature at the reaction center exceeds the antioxidant temperature.

(4) Improper storage: When the TDI index increases, the accumulated heat energy during post-maturation causes an increase in internal temperature, leading to scorching.

I. Advantages of Polyurethane On-site Foaming Technology:

The method of on-site foaming, spraying (or pouring) polyurethane foam insulation layer, has the surface as a whole without seams, reducing heat loss, with high construction efficiency, easy to meet quality requirements, reducing construction procedures, and eliminating the need for anti-corrosive coatings on pipe surfaces.

II. Polyurethane On-site Foaming Construction Process Principle:

The principle of polyurethane foam plastic foaming and spraying, pouring process is that polyether isocyanate can undergo a polycondensation reaction to form amine methacrylate, which can generate the required polyaminomethyl ethyl, commonly known as polyurethane foam plastic. Catalysts, crosslinking agents, foaming agents, foam stabilizers, etc., are simultaneously added during the reaction to promote and perfect the chemical reaction.

These raw materials are divided into two groups, fully mixed, and then pumped into a special spray gun by metering pumps in proportion. They are fully mixed and sprayed on the surface of pipelines or equipment in the spray gun or pouring mixer, react, foam, and form foam plastic within 5-10 seconds, which then cures and solidifies.

III. Polyurethane On-site Foaming Construction Methods:

Spraying Method: According to this formula, two groups of solutions are stored in two barrels respectively. The materials are filtered to the metering pump, driven by a pneumatic motor, and input into the gun body through the material tube. Compressed air regulates the material into the mixing chamber, mixed, and then sprayed onto the pipeline or equipment to foam and form.

Pouring Method: The prepared two groups of solutions are stored in barrels, filtered to the metering pump, driven by a pneumatic motor, and input into the pouring mixer through the material tube. Compressed air is introduced into the pouring motor, driving the stirring shaft to mix the two groups of materials, which are then injected into the mold for foaming and forming.

Precautions for Polyurethane On-site Foaming Construction:

Stir the material at room temperature to mix and react, then quickly pour it into the space that needs to be formed. During construction, control the reaction foaming time so that the mixed material after stirring is in a liquid state when poured into the gap. During the foaming process, significant expansion forces will be generated, so proper reinforcement should be made to the pouring interlayer or mold.

1. Adjust Formulation:

Control the amount of water to not exceed 4.5 parts, and if necessary, use low-boiling-point liquid compounds as auxiliary foaming agents to replace some water. Pay attention to the amount of water in the formulation, which must not exceed 5 parts. The highest safe temperature rise point for low-density foam is 160°C, and it must not exceed 170°C.

2. Strictly Control the Accuracy of Component Measurement:

During continuous block foam production, adjust the discharge speed of the mixing head material and the conveyor belt speed to coordinate them. Avoid phenomena such as under-foaming materials flowing into the bottom of already foaming materials due to slow conveyor belt speed or excessive discharge, which can prevent normal foaming, resulting in collapse. Collapsed materials are not easily able to produce localized "gas species," leading to localized heat accumulation and increased risk of scorching. In actual production, poor process parameters may result in small yellow scorching lines appearing at the bottom of foam blocks.

3. Avoid Compressing the Newly Produced Foam:

This is because compressing the foam before it is fully cured affects the foam network and structure. It also prevents heat accumulation due to compression, increasing the risk of self-ignition of new foam. Especially during the most sensitive stage of foam rising, any operational errors and vibrations, such as sudden movements caused by tight conveyor belt chains or excessive folding of isolation paper and belt shaking, can cause compression of immature foam, leading to scorching.

4. Strictly Observe the Curing and Storage Process of Foam:

For the production of polyurethane soft block foam, the curing process of new foam is a high-risk period for fire accidents. Due to the high internal temperature and long duration of heat dissipation in large block foams, the time to reach the highest internal temperature is usually about 30 to 60 minutes, and it takes 3 to 4 hours or longer for it to slowly decrease. During this time, the new foams have left the production line and entered the curing and storage phase, which is easily overlooked. Without proper monitoring measures, it can easily lead to fires. There have been reports that when producing block soft foam with a density of 22kg/? using a polyol with a molecular weight of over 5000, 4.7 parts of water, and 8 parts of F-11 with a TDI index of 1.07, a small amount of light yellow smoke was observed 2 hours later. Although the external temperature of the foam was not high, the interior was in a very dangerous initial stage of decomposition, with a temperature of around 200-250°C, already beginning to self-ignite.

5. To Prevent Self-Ignition of Foam:

Newly produced foam should be cured and stored, not exceeding 3 layers when stacked, with a spacing of more than 100mm between layers, preferably placed separately. The curing and storage phase should have dedicated personnel for enhanced monitoring, such as measuring the internal temperature of the foam every 15 minutes for at least 12 hours, or even longer, before normal storage. For foams that may generate high temperatures, large foam blocks should be cut horizontally (e.g., with a thickness of 200mm) to facilitate heat dissipation. When smoke or self-ignition is detected, use water spray or fire extinguishers, and do not move the foam or open doors and windows indiscriminately to prevent increasing airflow and exacerbating the fire.