Good surface quality is essential for those panel makers whose customer base is strongly focused on the furniture and decorative surface markets.
The sanding process is vital in achieving that finish, both in terms of the sanding machine itself and the abrasives used in it. But there is more to those abrasives than just grit stuck to a backing material.
Frauenfeld in Switzerland has been the home of a company specialising in the production of coated abrasives for 130 years.
The origin of the sia Abrasives name dates back to 1914 and the family business Swiss Industrial Abrasives. It continued as a family concern until a management buyout in 1997 and in 1999 it went public on the Swiss and German stock markets.
Today sia claims to be number three in the world in coated abrasives, with a 9% market share – and number one in Europe – with turnover almost doubling in the last 10 years, to reach CHF252.1m (€164m) in 2004. It has group companies in North and South America, all over Europe, and in Australia and China.
The general wood products industry accounts for 32.6% of total turnover, with the panel manufacturing industry accounting for another 15% and around US$40m.
“We are looking to grow two to three times faster than the market as a whole and that is what we have been doing in the wood based panels sector for the last few years,said Angelo DiNardo, marketing and sales manager for the panel sector.
There are two principal groupings of abrasives and these are coated and bonded, with sia Abrasives’ speciality – coated products – being more pliable, having low noise and vibration, little fine dust, conformability to the shape of the work piece and constant grain geometry.
Of particular interest to the panel makers are the segmented wide belts.
The manufacturing process for these belts has two main stages – production of the ‘jumbo rolls’ of abrasive material and then ‘conversion’ of it into endless belts.
The backing material can be paper, polyester, cloth, or a combination of paper and cloth.
Silicon carbide is the grit material normally used for sanding MDF and particleboard, while aluminium oxide would be the normal choice for plywood, with the choice being governed by the hardness and brittleness of the abrasive material.
Additionally, all products for the panel industry have an anti-static treatment.
In the production process, the backing is first printed with the sia Abrasives name and the  specification of the belt before the ‘make coat’ is applied as the adhesive base.
This backing is then electrostatically coated with the grit, which is first applied to a conveyor belt and then lifted on to the abrasive belt backing by means of a positive electrode above it. The belt is then hung in loops in an oven, which holds around 1.5km of belt.
The size coat is then applied over the abrasive. “We apply much more size coat than make coat and because it is water based, we have to dry it below the boiling point of water in a 230m long dryer – this one holds two to four kilometres of belt,explains Donat Frei, head of production and a member of the group management.
After three and a half hours the resin is pre-cured and the jumbo roll goes into another oven to complete the curing.
The next process is after-treatment and then ‘breaking’ over opposing-angled rollers to flex the belt before it is re-hydrated with water.
The company has recently invested a total of CHF35m in extending and modernizing its jumbo roll manufacturing and conversion facilities with CHF2.5m going to the fully automated glue mixing systems.
“We have also re-engineered the whole production process, putting everything into a linear and modular system as part of our five-year investment programme,said Mr Frei.
“We now produce for all markets in one grit size at one time by having all size formulations, types and colours prepared in one place and, together with other streamlining measures, we have reduced production time from nine weeks for batch production to three weeks for the whole assortment.”
Other investments included reorganizing the storage of backing and grit and a fully automated, robotic warehouse.
The next production stage is conversion. Here, a new facility for the panel industry, opened in October 2004, led to an increase of over 30% in capacity, with the potential to double the original output.
The belt is cut to length at an angle (to prevent chatter in the sander) and these lengths are actually the width of the wide belt which is to be produced.
These sections are then joined together, or lapped. In the lap preparation unit, diamond wheels remove the grit from the surface of the belt to expose the backing on the longitudinal edges and this is followed by automatic gluing of those edges in the same machine, with glue being applied to one edge and a splice tape to the other.
The edges are then lapped and a heated plate lowered on to the lap joint, which is roller-pressed.
When a sufficient number of segments have been joined in this way to form the desired length of belt, the ends are joined in a similar process to form a loop.
The final stage is visual inspection and the belt is then rolled with brown paper in between the layers and packed in a cardboard box. Some belts are packed with foil to protect against climatic influences.
One of sia Abrasive’s latest products, launched at Ligna in 2005, is a completely new approach to the sanding platen.
“The existing system, used for the last 30 or 40 years, involved sticking felt and an anti-slip surface to the platen and then covering it with graphite so that it slides on the back of the belt,explained Mr Frei. The graphite material was then clamped along both edges of the platen with many screws along each side.
“With that system and a change of platen once or twice a day on a six- or eighthead sander a lot of production time is lost, and if you tighten the screws unevenly you get bubbles in the graphite layer and consequent marks on the panel surface – or in the worst case, the graphite material can tear,said Mr Frei.
The new system, the sia-slide-pad, is based on a new metal platen beam with a swallow-tail cross-sectional profile. An MDF-based pad with the same surface components as a conventional platen is simply slid into the platen from one end and the end closed with a twist lock.
“Now, changing the pad takes 30 to 60 seconds instead of five to 10 minutes and it is not necessary to lift the heavy platen out of the sander – it can all be done in situ,said the production manager.
The newest product specifically aimed at the woodworking industry, and also launched at Ligna, is a wide belt called TopTec. This is said to offer greatly improved anti-static properties, thus avoiding dust problems on the work piece. The belt is paper-backed, with a special treatment to help it stay flat in humid conditions, while a special coating has given better performance, says sia Abrasives.
Readers may have realised by now that the whole sanding issue is a lot more complex than it looks, which is why sia Abrasives runs training seminars for its customers.
Considerable capital investment at Frauenfeld, and ongoing investment of 3% of turnover in its R&D department, which employs 30 scientists and engineers, suggests ‘true grit’ in this Swiss abrasives manufacturer’s approach to the market.