In September 2021, we received an inquiry from Mr. Abdullah in Saudi Arabia regarding a continuous foaming machine. The client was planning to establish a PU foam factory to produce products for the local and Yemeni markets. He had some basic knowledge about machine usage and selection.



The client had no prior experience in foam production before, so he was particularly concerned about after-sales support and technical assistance.



We began by analyzing the client's target market (specific industry) and understanding the local product requirements (such as foam density, hardness, etc.) to confirm the client's production needs.



Through video conferences, we guided the client through our PU foam production process, providing the client with a concrete understanding of foam production and highlighting the convenience and efficiency advantages of our machines compared to those of other manufacturers.



Drawing upon our more than 20 years of experience in foam foaming, we shared insights with the client about using the machine and common challenges in the foam foaming process, addressing any technical concerns the client may have had.



We also provided the client with factory layout plans to expedite the setup of the entire foam production line while maximizing production efficiency.

Due to the client's high level of trust in our professional service, he ultimately chose us as his supplier for foam machinery and later made repeat purchases for a rebonded foam production line and foam cutting machines.

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.

Functionality: Refers to the number of special groups (and reactivity) in the structure of an organic compound. For polyether or polyester polyols, functionality refers to the number of atoms containing active hydrogen.



Hydroxyl Value (OHV): From an analytical perspective, the hydroxyl value is defined as the milligrams of potassium hydroxide equivalent to the hydroxyl value in 1 gram of the sample. The weight percentage of hydroxyl value is represented as OH%. OHV = Weight percentage of hydroxyl value * 33.



Molecular Weight: The molecular weight refers to the relative weight of a single substance or compound molecule, equal to the sum of the atomic weights of the atoms in the molecule.

Molecular Weight = 56.1*Functionality *1000 / Hydroxyl Value

56.1 is the molecular weight of potassium hydroxide. For simple compounds, the molecular weight is the sum of the atomic weights of the atoms in the molecule.



Isocyanate Group Percentage Content: The isocyanate group percentage content is typically expressed as NCO%. For pure TDI/MDI, it can be calculated using the molecular formula:

NCO% for TDI = 42 * 2 / 174 = 48%

NCO% for MDI = 42 * 2 / 250 = 33.6%

42 is the molecular weight of NCO.

Sometimes NCO% is also represented using amine equivalents: the number of grams of isocyanate ester consumed per gram of molecule amine to form the corresponding urea.

Amine Equivalent and NCO% are related as follows:

Amine Equivalent = 4200 / NCO%



Equivalent Value and Equivalent Number: Equivalent value refers to the molecular weight corresponding to one unit functionality in each compound molecule.

Equivalent Value = Number average molecular weight / Functionality

For polyester and polyether products, the equivalent value is calculated directly from the hydroxyl value data.

Equivalent Value = 56100 / Hydroxyl Value

TDI Equivalent = Number average molecular weight / Functionality

= 174 / 2 = 87

= 42.02 * 100 / NCO%

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.

How to Solve the Issue of Thread Breakage or Dropping in a Quilting Machine?

First, check if the thread clamp is rusty or has debris. If such issues are found, clean the thread clamp with a cloth. Additionally, push up the optical axis of the quilting machine and check if the distance between the hook tip and the needle is around 2 millimeters. If there is a deviation, adjust the hook left, right, up, or down accordingly. Regular maintenance and cleaning of the equipment are also essential.



How to Maintain a Quilting Machine?

Clean the equipment at the start and end of each work shift to remove debris and dust, ensuring smooth operation of the needle and hook. Regularly lubricate areas with significant wear using machine oil or grease to facilitate smooth high-speed operation. Bearings with oil nozzles should be greased at least once a year to prevent excessive machine wear. Insufficient air pressure or unopened cylinders can cause temporary loss of some functions, so ensure the cylinders are activated before turning on the machine. When shutting down, do not turn off the machine power directly; first, turn off the computer, then the power.