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MDF is often a very misunderstood type of wood. When I first got into wood and woodworking I thought MDF was of poor quality and no good for us woodworkers. Only Ikea furniture used that stuff. But I could not be more wrong. MDF has many good uses, sometimes, it is better to use than solid wood. So let’s take a look into how MDF is made so we can better understand the product that is all around us.
MDF is made by breaking down solid wood into small wood fibers, the wood fibers are then mixed with resin which acts as a binder. The resin and wood fiber mix is evenly distributed into a thick layer and then pressed to form the dense MDF board. The boards are sanded, trimmed, and sawn into appropriate sizes.
Here is a quick overview of how MDF is made. If you want to know more in detail about the process of how MDF is made I would recommend reading through the article.
1. Wood is Sourced
The main ingredient of MDF is real wood. The MDF plants need a steady influx of wood to maintain their production. The wood used for MDF usually comes in the form of tree trunks from forests. Trees that are not suitable to use as lumber or other applications are sent to the MDF plant.
Wood for MDF can also be sourced from cut-offs from different types of lumber production and recycled materials. MDF is commonly referred to as a green wood industry because of this.
2. Wood gets Debarked
Wood is transported from the supplier or from storage at the manufacturing site, the logs are unloaded and are sent to a debarking machine which removes the bark from the logs. In the finished MDF product, bark constitutes less than 1% of the content.
3. Wood gets Churned to Woodchips
Debarked logs are processed in a chip mill. Entire trees are turned into woodchips in a matter of seconds and are extremely effective. Processing the trees is the first step to turning the logs into smaller wooden fibers. The wood chips are usually stored in a chip pile and then retrieved when needed for further processing.
4. The Woodchips Are Cleaned
Before further processing, the wood chips need to be cleaned. We do not want any impurities in the final product, the wood chips are washed to remove sand, dirt, and other impurities before being grounded into even smaller fibers where it will be harder to remove the impurities.
5. Metal Removed From Woodchips
The quality and consistency of the MDF product are important to the MDF manufacturer, and they do not want any pieces of metal in their MDF boards. Metal detectors and magnets are staged at key locations along the production line, removing any metal debris or larger pieces of metal.
Why is there metal in trees exactly? Trees grow and develop over 10s and 100s of years before being processed. If a nail, screw, or even a chain has been attached to the tree was growing, the tree would simply consume any kind of metal object. And the metal will be stuck inside. And it is actually quite normal to find metal inside trees.
6. Wood Chips are Made to Wood Fibers.
When the manufacturer is certain they can be that the woodchips are free from any kind of impurities, the wood chips are broken down into even smaller pieces to small wooden fibers, or pulp as we call it.
These fine wooden fibers are the product that will be used in the final MDF boards
7. Resin Are Mixed In With Wood FIbers
Resin is mixed in with the wood fibers to act as a binder. The resin literally holds the wood fibers together and makes a strong bond between the fibers and the resin.
Urea-formaldehyde is the resin that traditionally had been used as a binder. Recent studies show that Urea-formaldehyde is harmful to the environment and can cause negative health effects for humans and animals (cancer). Limits on allowed Urea-formaldehyde emissions have been put in place in several countries. And has become more costly to use.
Many MDF mills are switching over to polymeric methylene diphenyl diisocyanate (p-MDI) as a binder.
8. Resin and Wood Forms A Mat
With the wood fibers and resin mixed we have our MDF dough. Now it is ready to be formed and baked. The mixed MDF and resin are evenly distributed onto a conveyer belt as a thick mat at least twice as thick as it will be after being pressed.
Before being passed the density of the wood and resin mix has a low density compared to the final product.
The thickness of the mats is determined at this stage, by making a thicker MDF mat before pressing, the final product will be thicker. Standard thicknesses for MDF plates are 6mm, 9mm, 12mm, 15mm, 18mm, 22mm, 25mm.
9. The Mat is Pressed Into Boards
The mat is now either pressed in a hot press or a continuous press. The MDF boards are getting close to being finished now. After the pressing, the boards look more or less like a finished MDF plate. But there is still some processing needed to be done before the MDF plate can get to market.
10. Cooling of the Boards
After pressing, the boards are too hot to be sanded straight away. The board needs to be cooled off before going in the sander.
11. Sanding
The board is now at the right temperature and ready to be sanded. The boards go through an industrial sanding machine that sands the boards from both sides to make a silky smooth finish. The MDF is now close very close to being finished.
12. Cutting to size
The edges of the MDF are trimmed before packaging by quickly running the edges through a table saw. Then the MDF is cut to desired lengths and widths.
The great thing about MDF boards is that they can be cut in desired lengths and widths because of the uniform structure of the board. The most common size to get MDF from the manufacturers is 2440mm x 1220mm. But smaller pieces of MDF will be available at home centers.
13. Packaging
The final step of making MDF is packaging the MDF and sending it off to customers. MDF is heavy, it is actually heavier than most solid woods. So shipping MDF long distances can be expensive.
