DIRECT BOLTED JOINTS ON "SOLID SURFACE"

Solid surface (SS) manufacturers always indicate in their material handling manuals that direct screw fixing is CONTRAINDICATED and outside the manufacturer´s warranty. In spite of the manufacturers´ guidelines, we wanted to rule out all possible options of direct bolting before definitively ruling out this path.

After testing with screws with different threads, we found the ideal screw profile from the manufacturer CELO. This is the "REMFORM" thread, with a very low angle insertion profile that facilitates screw penetration and a high extraction angle, considerably increasing resistance to traction and loosening due to vibration. As if this wasn´t enough, CELO has a model with "REMFORM" profile and with a reduced pitch, the "REMFORM F" variant, which is exactly what we were looking for (here you have the link). This type of screw is specifically indicated for very hard plastic materials, which are very similar in their mechanical behaviour to the SS.

Krion specimen after breakage at 315 kg. Blind hole with screw D4

The tensile strength tests we have recently carried out with these screws in the CLAM Desarrollo laboratory have been very positive. With screws of 4 mm diameter and 8.5 mm depth in the SS, the breakage of the tensile joint is around 300 kg. The breakage is produced by resistant exhaustion of the SS, in this case krion (Solid Surfade by Porcelanosa Group), breaking the material through the surface of a resistant cone with an external diameter of about 40 - 50 mm. That is to say, the perfect break, showing that the resistant exhaustion is neither in the screw, nor in the screw/SS interface.

The tensile breaking load in the test we carried out with the "Remform F" screw D4x12 in a blind hole D3.25 and 8.5 mm of thread depth on 6 krion specimens 65x65x12 mm was 309, 279, 290, 294, 280 and 315 kg respectively with an average of 294 kg.

We can establish a safe resistance of 200 kg per screwed joint (blind) in krion of 12 mm.

Breakage with D5 blind screw

In the same test, we tested with the 5 millimetre diameter screw obtaining lower loads. We think this is due to 2 factors:

1º - As the thread pitch is larger, there are fewer support threads to distribute the load.
2º - The shallow depth of the drill together with the fact that the first 2 thread pitches are not effective as they serve to centre and start the thread. In this area, the diameter is smaller.

The geometry of the "Remform" thread allows greater penetration of the screw thread into the SS than with the plastic screws from our first tests. In the case of 4 mm diameter screws, the penetration in the SS is 3.5 tenths of a millimetre, 50% more than in the plastic thread screws tested previously.

D5 mm screw thread

With these results and with the subsequent support of the SS manufacturers (if their tests consolidate our experimentation) we are facing a substantial change in the prior art of fastening on SS elements.

The level of resistance that we have obtained is more than suitable for use in the fixing of SS ventilated facades on resistant metal support profiles. This environment is probably the most demanding and restrictive we can find. For these cases, the important thing will be the structural design and distribution of fixing points, so that in this design all the forces to which the SS will be subjected are contemplated, ensuring that the loads are adequately distributed to the structure and that the tensions in the fixings of the metal supporting elements to the SS, through these screws, are below the established resistance values.

From the technical department of "CELO Fixing technology", in its facilities in Barcelona, Xènia Dasquens and Narcís Morató have carried out several test sequences on the krion samples that we supplied, to find the best values of the different parameters for each diameter and type of screw as they are:

- Optimum torque.
- Drill diameter.
- Maximum admissible load
- Transfer screw length to the SS, depending on the screw diameter
- Etcetera.

Here are the results of the first CELO trial (in Spanish). 

INDUTEC SOLID technical team:

Guillermo Mollá. General Manager.

Carlos Vidal. Chief Operating Officer and Industrial Engineer.

Vicente Timoneda. Industrial Design Engineer.

Juan Micó. Industrial Design Engineer.

Crístian Martin. Industrial Design Engineer.