How to deal with the deformation of plastic pallets - Knowledge

1. Resin

Since the resin is the root cause, we can improve the shrinkage of the resin itself. Because of the different reaction mechanisms of different systems, the shrinkage rate of resins is also very different. For example, the volume shrinkage rate of common unsaturated polyester resin is generally 7-10%, while the volume shrinkage rate of epoxy resin is generally 2%. about. Choose different resins, there is a very big gap in shrinkage.

The same is an unsaturated polyester resin, and the shrinkage rate can be fundamentally controlled by choosing different raw materials in the synthesis stage. The volume shrinkage of some new UP resins can be controlled at 2-3% or even lower.

2. Packing

The problem of resin shrinkage is that after curing, its space volume becomes larger, so some fillers can be added to reduce the shrinkage rate.

Commonly used inorganic fillers include calcium carbonate, talc, aluminum hydroxide, etc. These fillers generally do not participate in chemical reactions and are inert materials. Reduce the shrinkage rate by reducing the resin content per unit volume and the way of occupying pits.

In addition, the shrinkage rate can be controlled by adding a low shrinkage agent (LPA), the main component of which is some thermoplastic resins, elastomers or combined polymers. In addition to the pit, the thermoplastic resin will expand during the process of resin heat release, which can offset the volume shrinkage caused by the curing process of the thermosetting resin, thereby reducing the shrinkage rate more effectively.

3. Process

Control the curing speed. The curing speed is too fast and the reaction is violent, which will often cause the exothermic peak to be too high. Excessive temperature changes in the system are likely to cause thermal shrinkage. Therefore, under the premise of ensuring production efficiency, the curing speed must be controlled, not too fast.

Control the resin content. The main source of shrinkage lies in the resin, so controlling the resin content can also control the shrinkage rate. Especially in the hand lay-up process, workers often increase the amount of resin in order to rush to work, resulting in excessive resin content in the product, which is more prone to shrinkage and deformation.

Control the number of layers at a time. This is mainly reflected in the hand lay-up process. There is a very obvious difference in shrinkage between a single-layer paste and a single-pass five-layer paste. The more layers there are, the more concentrated the reaction exotherm, which is more likely to cause heat shrinkage. .

post-curing treatment. By curing after heating, the degree of curing of the product is improved, and the monomers continue to react after demolding to prevent shrinkage and deformation. This link is ignored in many room temperature processes (hand lay-up, vacuum introduction, RTM), and in order to improve production efficiency, often demoulding is too fast, so it is easy to cause the product to be placed for a period of time, and it will be deformed before it is out of the warehouse.

4. Laying design

The choice of different reinforcing materials has a certain influence on the content and distribution of the resin, so this issue needs to be considered when designing the ply.

Whether the product chooses the core material or not, it will also affect the resin content. For example, 20mm products, one solution is pure glass fiber reinforcement, and the other design solution is to use 10mm sandwich foam + 10mm skin, the shrinkage rate of the two is also different.

5. Partial strengthening

Shrinkage will cause internal stress, and the existence of internal stress will cause deformation of the product, thereby affecting the use. In order to restrain this kind of deformation, some local reinforcement can be made on the product to offset the internal stress and prevent the product from deforming.

In the glass fiber reinforced plastic mold, steel structure is basically used for post reinforcement. When the mold is subjected to external force or internal stress, it can prevent deformation. In products, ribs are often used to ensure the rigidity of the product.