Points to consider when using plastics

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

In addition to very favorable characteristics, every material also has disadvantageous characteristics. In other words; where a characteristic is favorable in one specific situation, the same characteristic may be disadvantageous in another situation. On this page we highlight a number of properties, which we think it is good that you as a customer and/or user are aware of them.

Dimensional tolerances semi-finished product

Lakwijk Kunststoffen BV is a wholesaler of semi-finished products. We are the link between manufacturer and the market. Semi-finished products have 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 to guarantee that the dimensions can be extracted from the material during processing. Manufacturers apply a plus tolerance and speak of “clean sizes”.

PVC, PE and PP pipes are manufactured in accordance with the DIN standard and then the external and internal dimensions are of the right size for a matching fitting. In other cases, when a plate, rod or tube has to be exactly the right size, the material must be processed. You can do this yourself, but you can also commission Lakwijk Kunststoffen BV.

Dimensional tolerances processed product

If Lakwijk Kunststoffen BV processes according to specified dimensions or according to drawing, this is done extremely accurately. Our skilled colleagues and our machinery are of the highest level.

However, the same dimensional accuracy cannot be demanded from the material in the application as is customary in metal. This has nothing to do with the quality of the processing or the material, but with the intrinsic characteristics of plastic.

Plastic is much more sensitive to temperature differences than metal. Expansion and contraction are proportionally greater. We take the introduction of temperature into account during processing, but if the temperature during transport or in the final application, differs significantly from the room temperature in our workshop, you lose part of the accuracy. We are talking about one to several tenths of a millimeter here.

Stress relaxation and with certain materials moisture absorption needs to be taken into consideration. In most cases this is not a problem because the flexibility of plastic provides a degree of deviation. However, 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 need to assemble Lakwijk products into an application. A product can be locked or clamped, a product can be mechanically attached, a product can be welded and it is sometimes decided to glue a product. Gluing can be done very well with a number of plastics. However, there are also plastics that cannot be bonded or cannot be bonded well.

Your contact person will ask you if you want to start gluing, but it is also good that you are aware of this during a development process. Ask us 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 almost never a problem. Many plastics are UV resistant and do not or hardly degrade or discolour.

However, there are also plastics, for example certain crystal-clear plastics, that are not UV resistant. Fortunately, that discoloration is very slow and even, but in the long run the sun has an effect on that material, causing the material to age faster than desired. This manifests itself in craquelure, hairline cracks and brittleness. However, these materials are often also available with a UV-resistant top layer. In that situation, too, your Lakwijk contact person will proactively ask the question, but it is wise for you to realize that this is a point for 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 (plasticizers) migrate from the plastic to the food, so these materials 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, specific standards must be met in order to receive the European “Food Grade” label, and that involves more than just the physical properties of the material.

A material is Food Grade if the material is proven to be safe, but is also traceable in the chain down to the raw material in the unlikely event of calamities. In addition, a product must be accompanied by a certificate that indicates that everything has been carried out safely during handling and processing (packaging, coolants, air, cleaning agents, etc.). Every plate, every rod, 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 guidance in this regard.

Chemical resistance and cleaning

Specific plastics are used because of their chemical resistance. Within the regular materials, think of PVC, PP and PE. These materials are also resistant to corrosive 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 crystal-clear plastics. If acrylic and polycarbonate are cleaned with agents that are more aggressive than simple soapy water (or better still, just warm water), dull spots or hairline cracks can occur and the sheet can even become brittle.

Stiffness

Solid core and other thermosetting plastics are very stiff, and there are more plastic materials that have been specifically developed with stiffness in mind, usually through a channel structure. In general, however, compared to glass, wood or metal, plastic is less rigid. The flexibility of plastic is desirable in many situations, but of course also has drawbacks.

Acrylic mirror is a very safe and affordable alternative to glass, but if it is used for a larger surface, the plate remains less tight and (certainly in the version as a mirror) you 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 then leads to more sagging. It is important to take into account the limited stiffness of plastics in the application when determining the design and dimensions.

Scratch sensitivity plastics

Glass, metal and wood are sensitive to scratches. Plastics are also prone to scratches.

The virtually unbreakable polycarbonate is very strong, but nevertheless very sensitive to scratches. A user of this material sometimes makes a mistake. Polycarbonate is also available in a version with a scratch-resistant top layer. This top layer makes the plate more resistant to scratches, but does not make it scratch-free.

The plastics that are usually used in visual applications where their appearance and aesthetics are important are supplied with a protective film. Industrial plastics for which this does not apply or to a lesser extent, and whose surface in most cases still needs to be processed, do not have a protective film from the factory. It may therefore be slightly scratched as a result of sliding in the production process or during transport. That 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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