Embossing calenders – Dos & donts

In the previous issue [ITJ December] you have read about embossing calender and related running in instructions.

In the embossing calenders, instead of woollen paper bowl, if super elastic bowl is introduced, it will be more suitable for CREPES. As you know there are many designs of crepes, some are fine and a few are coarse. Basically, CREPE design is a shrunk design and these calenders too fall under the division of embossing and it will be interesting to know about its running in procedure.

You have to follow certain norms or operational instructions before starting of the machine after installation of new bowl. Not only that, you certainly will appreciate that it is essential for desired results to achieve.

Hence, here are some operational instructions pertaining to pre-creping calender.

In Running Design

When a new super-elastic bowl has got installed in an embossing calender, a perfect impression of the design on the steel bowl must be worked on the surface, prior to embossing the fabric. To do this, the top and the bottom bowls must be run for at least 30 minutes with temperature.

On design roll: The bowls should be slightly separated during this period. When the correct temperature has achieved say 160-180¦F, the working in process can be commenced. Thoroughly wet the surface of the super elastic bowl and then apply the load. Run the calender until the super elastic bowl is almost dry. Again wet the bowl and dry it. This should be repeated frequently.

During the running in operation the two bowls must be heated to a temperature of 160¦F. And this is the temperature required for creping. After running for a few hours allow the bottom bowl to dry and then examine the MATRIX to confirm/ascertain if it is perfect.

This can easily be judged in the dry state. If the design is perfectly worked in, the whole surface of the MATRIX will show a polished face. So to say, the running in must continue with wet super elastic bowl.

Remember, the water used for wetting should be hot. Cold water will not do. The object of heating both the bowls is to ensure equal expansion of both the bowls. If the top one only is heated then it will expand and the bottom one will not.

Accordingly, there will be increased pressure on one side of the matrix thus resulting bruising or tendering of the fabric. When the matrix appears to have evenly worked in then a short length of cloth should be tried and should be tested for strength. If the results are fine then bulk quantity can be produced.

If, however, the cloth shows the signs of tendering, even though matrix is polished all over, the super elastic bowl must be wetted again with hot water for further period say 2 or 3 hours.

The object of this is to make sure that the surface of the matrix is evenly hard both at the top and bottom of the design. Another piece can be tried again and judged. If the tendering is still there then it is almost certain that the engraving on steel bowl is at fault.

May be the engraving is too sharp or may be too vertical in places and this is something only an engraver can study and correct. If everything is correct then the super elastic bowl must be dried thoroughly before running the cloth in the machine.

To do this, run the machine for an hour with both bowls heated and without cloth. This procedure will ensure best impressions. In applying the water to the elastic bowl a cloth pad to be used and it must be held at the other side of the entry nip. Otherwise, there is a chance of cloth being carried through the nip. Otherwise there remains a possibility of cloth pad entering in to the nip and damaging the roll.

Further inspections that are required are:

Check wheels

The teeth of the check wheels on the bowl ends should never be separated. There are