General delivery conditions

Points for attention when using plastics

Over the years, plastics have often initially been developed as a solution for a specific situation. Often as an alternative to the more traditional materials. More durable, lighter in weight, better chemically resistant, more wear-resistant, cheaper, etc. Subsequently, such a material also appears to be a solution for many other applications and the market for the product in question is growing.

In addition to very favorable properties, every type of plastic naturally also has disadvantageous properties. In other words; where a property is beneficial in a specific situation, the same property may be detrimental in another situation. On this page we highlight a number of features that we think are good for customers to be aware of.

Dimensional tolerances semi-finished product

Lakwijk is a wholesaler of semi-finished products. We are the link between manufacturer and the market. Semi-finished product has the appearances; plate, rod and tube. Plates, rods and tubes are produced larger than the dimensions indicated on paper. The plate is slightly thicker, wider and longer. The staff is therefore slightly thicker and longer. The tube is slightly thicker on the outside and the hole is slightly smaller. The manufacturer does this in order to guarantee that the dimensions can be extracted from the material during processing. Manufacturers apply a plus tolerance and speak of “clean sizes”.
If a plate, rod or tube has to be exactly the right size, the customer must process the material himself or give Lakwijk the order. Of course we can take care of that for you.

Dimensional tolerances of processed product

If Lakwijk processes plastics according to specified dimensions or according to drawing, this is done extremely accurately. Our skilled colleagues and our machinery are of the highest quality level. However, it is not possible to demand the same dimensional accuracy in the application of the material as is usual in metal. This has nothing to do with the quality of the processing or the material, but with the intrinsic properties of plastic. Plastic is much more sensitive to temperature differences than metal. Expansion and contraction are comparatively greater. We take into account the temperature input during machining, but if the temperature during transport or in the final application, deviates significantly from the room temperature in our workshop, you have lost some of the accuracy. We are talking about one to a few tenths of a millimeter here. In most cases this is not a problem because the flexibility of plastic ensures a degree of forgiveness. It is important to take this into account. Within the most regular plastics, POM and above that PETP (Ertalyte) are the most dimensionally stable. In addition, there are a number of so-called “high performance” plastics such as PEEK and PEI that are even more dimensionally stable.

Gluing

Customers usually have to install Lakwijk products in an application. A product can be locked or clamped, a product can be mechanically attached, a product can be welded and it is also sometimes decided to glue a product. Gluing is very good with a number of plastics. However, there are also plastics that cannot be glued or cannot be glued properly. Your contact person will ask you if you want to glue, but it is also good if you are aware of this during a development process. Ask in time whether a material can be glued or which fastening technique we recommend.

UV resistance

There are situations where plastics are used outdoors. That is hardly ever a problem.
Many plastics are UV resistant and do not or hardly discolour or degrade.
However, there are also plastics, for example certain crystal-clear plastics, that are not UV resistant. Fortunately, this discoloration only proceeds very slowly and evenly, but in the long run the sun has an effect on that material. These materials are often also available with a UV-resistant top layer. Here too, your Lakwijk contact person will ask the question proactively, but you should also realize that this is a point of attention.

Food grade / Food Grade

Certain plastics are suitable for applications in which they come into contact with foodstuffs. If these materials come into contact with foodstuffs, no substances (plasticisers) migrate from the plastic to the food and therefore do not pose a threat to public health. That does not mean that these materials can be used indiscriminately in food applications. In order to comply with European legislation, a product must meet specific standards in order to receive the European label “Food Grade”.
A material is Food Grade if the material has been proven to be safe, but is also traceable in the chain up to the raw material in the event of calamities. In addition, a product must be accompanied by a certificate that indicates that everything was carried out safely during handling and processing (packaging, coolants, air, cleaning agents, etc.). Every plate, every staff, every tube therefore has a unique code and every delivery is accompanied by unique documents. Without that identity and documents, the material is therefore safe, but it does not meet the Food Grade standard. Sometimes customers still have insufficient knowledge or there are still misunderstandings on this point. Lakwijk is a specialist in the field of processing and delivery within the Food Grade provisions, and can provide you with excellent support in this.

Chemical resistance and cleaning

Specific plastics are used because of their chemical resistance. Think of PVC, PP and PE within the regular materials. These materials are also resistant to harsh cleaning agents that are necessary in certain applications.
However, there are also plastics that are not chemically resistant. In practice, this most often leads to problems in the crystal-clear plastics. If acrylic and polycarbonate are cleaned with more aggressive cleaning agents than simple soapy water (or rather just warm water), this can cause dull spots or hairline cracks and the sheet can even become brittle.

Stiffness

Full core plate is very stiff, and there are more plastic materials that have been specifically developed with stiffness in mind, usually by means of a channel structure. In general, however, plastic is much less rigid compared to glass, wood or metal. The flexibility of plastic is desirable in many situations, but of course also entails disadvantages. Acrylic mirror is a very safe and affordable alternative to glass, but if it is used for a larger surface, the plate remains less rigid and in the mirror you will get unwanted distortion. If a larger plastic sheet is used horizontally and is not supported at sufficient points, the sheet will sag. A thicker and therefore stiffer plate is not always a solution, because the weight of the plate in turn leads to more sagging. It is important in the application to take into account the limited stiffness of plastics when determining the design and dimensions.

Scratch sensitivity plastics

Glass, metal and wood are sensitive to scratches. Plastics are even more sensitive to scratches.
The virtually unbreakable polycarbonate is very strong, but nevertheless very sensitive to scratches. Polycarbonate is also available in a version with a scratch-resistant top layer. This top layer makes the record more resistant to scratches, but does not make it scratch-free.
The plastics that are usually used in visual applications where their appearance is important, are supplied with a protective film. Industrial plastics for which this does not apply or to a lesser extent, and whose surface is in most cases still being processed, do not have a protective film from the factory. There may therefore be slightly scratches as a result of shifting in the production process or during transport. This is almost never a problem, but it is an aspect to take into account for the customer, and also for us in the material advice.

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