Professional training would be good for most of the Plywood QC/QA Parts 52: Oblique Sanding unit/ Parallel Sanding unit Surface sanding of plywood

Surface sanding problem of plywood

Plywood sanding, determines its final surface quality. The core platform sand paper needs 60 to 80 grit and the belt, or other.

For the sanding of the plywood top face and bottom back surface , generally at least 120 grit or 240 or 360.. Oblique 53” Two Head Wide Belt Sander

For the wood panels substrate platform of sanding, and some need to be fixed calibrated sanding and calibrated thickness , one single calibrated sanding ,two-side calibrated sanding , Some sanding machinery are two sanding heads, and some is one sand head.

The last two years in the country appears oblique sanding machine, meaning that the sanding belt sander and sanding machines are not directly vertical, but there is a certain angle of about 8 degrees 15 degree angle or some oblique angle. Such sanding function effectively avoided conventional sanding machine brings wavy or hourglass phenomenon. You can sand the surface of the platform is very smooth and credentials. Generally used for sanding sheet substrate melamine board substrate or other high-end requirements.

The conventional widebelt sanding machine by placing the workpieces slightly oblique to the feed direction ,oblique sanding machines are specially designed for users with high demands on quality and finish.

After a short period of time, even sanding belts of the best quality and when used correctly suffer from unavoidable, small damages, grit outbreaks and irregularities due to wear and clogging. Such small damages cause on conventional widebelt sanding machines with parallel units evident imperfections reducing the quality of the sanding image. This is an inherent flaw of the parallel sanding process which becomes visible especially with delicate surfaces such as lacquer, veneers of any kind and plastics. 

Oblique sanding provides better results

Brilliant intermediate lacquer sanding

Our Engineers found that such undesirable irregularities may be avoided if the sanding belt does not rotate parallel to the feed direction. Using a pivoted sanding head, the defects on the belt are shifted slightly sidewards with each rotation and do not show on the workpiece.

No oscillation traces

Even a new sanding belt has a grit structure which is not completely homogeneous. As a result the oscillation of the belt tracking causes tracks or traces along the length of the workpiece, which will impair a high quality surface. With oblique sanding such traces become blurred and are no longer visible.

Better sanding image

With traditional widebelt sanding the abrasive grits create a structure of parallel lines on the workpiece. Grit outbreaks show as unsanded areas. With oblique sanding, the sanding lines overlap to create a consistent sanding image making the grit outbreaks no longer visible.

Oblique sanding we call the sanding process developed  at which the sanding unit rotates slightly oblique to the feed belt. That way, especially in the highest quality range, considerably better results are achieved.

Parallel Sanding unit

A parallel sanding unit we call a traditional sanding unit as it is commonly used up until today in widebelt sanding machines. The axis of the sanding unit and of the feed belt are parallel.

Oblique Sanding unit

An oblique sanding unit we call the sanding unit invented and patented , which can be used either in the conventional parallel direction and can also be pivoted for oblique sanding.

because on a conventional widebelt sanding machine the sanding unit and the conveyor belt with the workpieces always run in exactly the same direction, hence parallel and in this way irregularities and clogging of the sanding belt are not shifted sidewards, but show up as oblique traces on the workpieces.

Oblique sanding units may be an economical alternative to cross belt sanding units. They are a recommendable up-grade to a cross belt sander if they are positioned at the machines exit and in this way produce a better finish than with the conventional sanding unit.

Today, more and more furniture manufacturers and craftsmen choose oblique sanding machines. This new and innovative process has been widely accepted and with great acclaim from many manufacturers throughout the world, who confirm the superiority of oblique sanding to conventional parallel sanding. Along with all the benefits already mentioned, many customers have also reported that the blemishes caused by irregularities on the sanding pad’s graphite cloth are no longer present.

All models of widebelt sanders can be fitted with oblique sanding units. On which position depends on the operation requirements. There are advantages even on single belt sanding machines, which can achieve the quality of surface finish normally only associated with large production companies. In addition, the oblique sanding units can be readily used according to the surface requirements in either the oblique or traditional sanding position.

So far, the most popular models are the single belt -1 widebelt sanding machines with oblique sanding head incorporating a contact roller and electronic segmental pad and the twin belt .In addition there are different variants which can include crossbelt sanding units. Also, along with all the afore mentioned benefits and reduced costs when oblique sanding, machines equipped for sanding lacquer i.e. with infinitely variable sanding belt speed, belt blowers and vacuum table, have shown that even the most difficult surfaces can be sanded to give a flawless finish.

We will be pleased to demonstrate the advantages of the new oblique sanding technique .Why not take one of your “problem workpieces” with you and ask for the advice of our technicians on how to perfectly sand even the most difficult of surfaces. 

Thanks for the info of www.kuendig.ch and http://www.pawprintuk.co.uk/news164.htm 

The advantages of oblique sanding with Kündig

Top, Fig. (a): above, Fig. (b).

ALL of us have seen them on photocopies and faxes: those lovely lines running the length of the page, across whatever it is you are trying to read. These arise from flaws in the rollers, which have often developed over time, and now appear on every page which is printed.

Something similar can occur when sanding. The manufacturer of the sanding belts will take every care to ensure that the belt is delivered to the end user in the best possible condition: however, tiny flaws that develop over time can result in track lines, known as oscillation marks, being transferred to the workpiece during sanding, this being one of the unavoidable and inherent flaws when sanding in a straight line. The resulting damage can be expensive both in time and materials, if new pieces need to be manufactured, especially where high-end products are being used. Kündig has addressed this issue with its oblique sanding technique, which uniquely offers an overlapping of the grit structure arising from passing the workpiece under the sanding head which is set at an oblique angle.

Figure (a) shows a traditionally mounted sanding head where sanding is in a straight line and where the abrasive has a full frontal attack angle, thus any defects on the sanding belt are exaggerated due to the speed of the abrasive which continually pounds this defect onto the surface of the workpiece: Figure (b) shows a sanding head mounted at an oblique angle which totally shifts the relationship between the travel of the workpiece and the way the surface is sanded.

As can be seen there is an overlap of the grit structure which produces a greater level of uniformity across the surface and eliminates defects from the sanding belt being transferred.

Oblique sanding is especially suited to those looking to achieve a totally flawless surface and in particular those using higher grade abrasives such as when looking to achieve a high gloss finish. The standard grit belts used in sanding are essentially cutting tools: the rougher the belt, the more material they can remove. The down side is that the rougher the belt, the deeper the scratch: and when the surface of a sanded material is magnified, it resembles a valley full of ‘peaks and troughs’. Hence the general rule on traditional sanding machines to skip a single grit size so, for example, on a two belt machine starting with a 100 grit belt, the operator would miss out 120 and the second head would be 150 grit. The finer grit structure enables the removal of grit scratches left by the 100 grit belt: however, since both heads operate in the same direction, grit from the second belt will naturally fall into the peaks and troughs left by of the first belt.

With oblique sanding, the second belt travels in a different direction to the first and is therefore a lot more effective in shearing off all the peaks and sanding evenly into the troughs, therefore enabling more flexibility on the selection of grit. It is possible to miss out two grit sizes instead of one so that, for example, on a two head machine with the second head oblique, starting with a 100 grit on the first head, the operator would miss out 120 and 150 to finish on a 180 grit. This saves time as well as reducing running costs in both the consumption of abrasives and the actual running costs of the machine.

Although Kündig produces bespoke sanding machines having multiple top and bottom sanding heads, one of the most popular configurations of the Oblique sander is simply in a two sanding head format, the first being a dedicated calibration roller, the second being a sanding pad which, depending on the specification, could be used for solid wood, veneer or lacquer sanding. A machine in this format is the perfect “all rounder” as it will offer accurate calibration for solid wood or boards prior to veneering or spraying, then offer all the advantages of oblique sanding to ensure a perfect finish.

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