Tension on Rollers

The tensions applied on the substrates are closely monitored . This is done with the help of a load cell. A load cell is able to convert a force exerted on it by means of deforming a strain gauge which in turns measures this deformation applied on it into an electrical signal. This electrical signal varies when different forces are applied because the strain gauge's electrical resistance varies by the degree it's deformed. A strain gauge is a length of conductor arranged in a zigzag pattern in a membrane whose electrical resistance increases the more it's stretched. The voltages are normally in the order of millivolts and require amplification before it can be used to measure anything.

Normal load cells consists of four strain gauges arranged in the Wheatstone configuration, but the one in this context utilises only two strain gauges arranged in a half bridge configuration as shown below and is calibrated as such to indicate the tension in terms of kilograms, as this is a more common unit that technicians are more accustomed to.

According to the machine operators, the normal operating tensions for the Aluminium foil are around 12 kilograms worth of pressure whereas the PET will require something in the order of 9. With the help of the load cell, it is much easier for operation as the right amount of tension is easier to be applied. With the right tension applied on the substrates, the chances of creasing or wrinkling occurring is reduced drastically.

An improvement to the existing system is the implementation of a Tension Roll Transducer. The Tension Roll Transducer is combined with a regular idler roll consisting of 2 load cells. The reasons as to this being recommended in all the machinery are as follows:

• Measures and displays the actual web tension and allows for the control of the tension too.
• Since they are all assembled into one unit, there no assembly required whatsoever.
• Costs less than an idler roll and a load cell bought separately.
• Easy to install and takes up the same space as an ider roll.
• Only one transducer cable hence no cables will cross the machine. 

In addition to that, the bearing on the nip roller were also replaced as it was observed to not have a stable rotation and it was believed to be one of the reasons for the formation of creases on the final laminate.