February 15 2018, Enhanced process control in spray-painting by Nitrotherm-technology

Executive summary

Nitrotherm replaces air by Conditioned Nitrogen as paint-carrier

Physical properties of Conditioned Nitrogen can result in paint-savings, quality improvements and productivity improvements

Applications occur in automotive, consumer electronics, furniture

Underrated aspect of Nitrotherm technology is improved process control.

Spray-painting systems basically consist of 3 elements: gun, paint and carrier medium. Over the past 20 – 30 years worldwide, paint consuming industries – such as automotive, consumer goods and equipment – emphasised the development of the gun and the paint performance. The paint carrier medium however received much less attention by process engineers and production line designers. As a result, the medium carrying the paint to the target usually still consists of compressed air at 5-7 bar and often of questionable quality.

Nitrotherm®technology was introduced and patented by Eurosider SAS in Italy about ten years ago.  Essentially this technology replaces compressed air by Conditioned Nitrogen as the carrier for the paint. This Conditioned Nitrogen is produced in Nitrotherm units making use of – among others – hollow fibre technology and can be supplied to painting gun with the required pressure and flow rates.

The technology has been applied mainly in Europe so far and hundreds of units were installed for manual-, automatic gun- and recently also rotary bell painting lines. The benefits of the technology result from the physical properties of Conditioned Nitrogen as a paint-carrier medium and have been proven in many painting applications in automotive, consumer electronics, furniture etc. and include significant paint savings (avg. 20%), cosmetic quality improvement and productivity improvement from shorter process cycles.

At present, we see Nitrotherm-technology making its way into the Asian markets, in particular China’s booming automotive industry but also in Korea.

One attribute of the Nitrotherm technology that is highly underrated is the significantly improved process control through Nitrotherm. In my personal experience this aspect is of critical importance for the performance of the spray-painting process. This aspect is discussed in more detail below.

When I was a young process engineer 30 years ago and working in Philips Electronics, I was specifically educated in (Statistical) Process Control which principles at that time became very popular in order to improve the yield of production processes and the quality of products. Huge improvements were realized in factories (for instance in the automotive industry) in the USA, Europe and Japan by applying these principles and techniques.

In manufacturing companies that I have been leading after that I always emphasized the importance of the principles of process control as a way of life. In my past 4 years leading a company in China however I also learned how poorly these principles in many Chinese factories are known and applied. This is well understandable because the Chinese industry has been growing incredibly fast over the past two decades and the entire focus was on volume and less on efficiency and quality. Process operators and –engineers were not educated and trained in the principles of process control and consequently many production processes perform poorly.

Each production process and consequently each product property is exposed to variation. This brings us to the definition of Process Control which is to Manage Process Variation. Each process is defined by its process settings formalizedin the Standard Operating Procedure (SOP). No operator is allowed to change settings and the SOP can only be changed after formal release by technical management and based on new insight. However the numeric value of each process parameter – like temperature, pressure, humidity etc. –  is subject to an intrinsic (or normal) variation around the numeric value of the setting due to variation in the process system that is not captured in the technical control loops. This intrinsic variation is called Process Capability and within this process capability the outcome (quality and yield) is fully predictable – see Chart I.

 Chart I

 Chart II

In the case a Process is ‘out-of-control’ it is not predictable and consequently the quality and yield performance cannot achieve good levels. Therefore it is mandatory that a process is brought technically ‘’ In-Control” . When that is achieved, Process Control is to manage the process variation within the boundaries of its process capability. This means that when an operator observes that a parameter is moving outside its boundaries (control limits) of normal variation , this is an indication that something went wrong (special cause) causing the system moving out-of-control. When this happens the reaction of the operator should never be to change the process settings. Instead the operator should sort out the root cause of the disturbance and solve the problem so the system can go back within its boundaries. These corrective actions are normally defined in a so called Out of Control Action Plan (OCAP)

If we are not satisfied with the current performance of the process in terms of yield and quality, this only can be improved by technical innovation resulting in improved process settings and/or better control systems that reduce the intrinsic variation within the system. This with other words brings an improved Process Capability- see chart 3 below.

Chart lll

Within the theory of process control as explained above, Nitrotherm technology should be seen as a technical innovation to better control the spray painting process. This besides the physical benefits of Nitrotherm as explained in the introduction. As explained with Nitrotherm the paint carrier is changed from compressed air into Conditioned Nitrogen. By doing this two important improvements are achieved:

The natural variation of the carrier parameters (Temperature, Pressure and Flow) is substantially reduced by the Nitrotherm unit. Moreover the Purity of the carrier is much higher (for example water and oil contamination is fully eliminated) and the carrier is provided with a pre-set Ionisation (or static electric charge).

Operator (Human) is reduced as the Nitrotherm unit takes over the full control of the paint carrier medium.

These two elements will result in an overall much better controlled spray painting process which consequently brings an intrinsic higher yield and product quality. For this reason I see Nitrotherm technology as a real technical innovation in spray-painting that will become a future standard as paint-carrier medium in the many industries where spray-painting performance is of critical importance.

C.M Saris

Former CEO of Perlos/Lite-On Mobile

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