Author: Bill Hood
Date Published: 2007-11-01

Productivity failings exposed

Bill Hood provides some practical advice on how to increase productivity and raise print quality through improvements to your exposure system…

Recently, I consulted with a very large textile company that operates several automatics. I had been hired as a consultant by the owners of the company to investigate two things: productivity and quality.

The owners had been in business for 32 years and despite their best efforts productivity seemed to be at a standstill. In an attempt to increase production, they added another automatic and the necessary personnel to operate it. However, while there was an increase in productivity, it was nowhere near what they had expected or what the new machine was capable of producing. The statistics were saying that they should be printing an additional 750 shirts an hour, but try as they might, the press seemed to add only 300 shirts an hour. This shouldn’t have come as too much of a surprise as each of the five automatics was producing only 300 shirts an hour on average!

Clearly, their cause for concern was well justified, therefore: there is a big difference between their actual output of 1500 shirts per hour and the anticipated output of 3750 shirts per hour.

Frames and tension control

The company had outgrown its space, and the capacity to add even more machines, and thus had moved to a 24-hour workday to keep up with the demand for their contract work. Faced with having to now work on weekends and pay overtime to their employees, it was looking for solutions.The shortfall meant a loss of 2250 shirts an hour or approximately 54,000 in the 24-hour workday at the shop. At approximately £0.25 a shirt the financial shortfall had surpassed £3.5 million a year. Of course this did not include the cost of labour that was needed to handle the, (what turned out to be), unnecessary extra 12-hours per day, the utilities and other associated costs.

While the company’s productivity had grown stagnant, the quality of its printing had declined to the point where clients had started complaining. A few of the company’s larger clients had even begun moving some of their work to another printer. Something had to be done.

The company owners’ first question was whether I was familiar with their particular brand of press. To their mind, the problem must be at the press. Experience told me that this was not the case and the problem would likely be found elsewhere in the shop. The most important tools in a printshop are most often those that are easily overlooked.

Productivity loss, which is easily quantified, is usually more valued than quality and thus it was noticed before the decline in quality, which actually came first and was most likely the real culprit. My decision, therefore, was to look first at the quality of the work being produced. You can tell a lot about a shop by the quality of its printing: the type of frames being used; the tension level of the screens; the exposure unit; the level of education attained by the employees; and much more.

These will all be manifested in the quality of the final product. The frame is often overlooked because of its seemingly simple and relatively inconsequential job of ‘just’ holding the mesh in place. In fact, holding the mesh in place and maintaining it at the correct tension is one of the most important tasks in the entire screen printing process. If the frame allows the tension level to drop, the mesh openings become smaller, allowing less ink transfer and thus the operators find themselves making two or more passes to get a sufficient ink deposit. In the meantime, because the mesh is loose, it will roll in front of the squeegee and produce a smear or double image. While this may be slight on newly stretched frames it will become more apparent as the mesh relaxes leading to a decline in quality.

In my opinion, the best way to hold and maintain mesh at the correct tension is by using retensionable frames. These allow the screen maker to quickly bring the mesh to the suggested tension level and hold it there while the job is printed. After the mesh relaxes it can be quickly and easily brought back to the required tension level again and again until the mesh becomes work hardened and the relaxation process has slowed significantly. No other frame can ‘hold the mesh in place’ better than a retensionable frame and thus it is the only frame that has a return on its investment. Retensionable frames are the first and most important investment a shop can make to improve both productivity and quality.

However, it is one thing to invest in retensionable frames, it is quite another to use them properly. While the shop in question had invested in Newman Roller Frames years before and was using them exclusively, I discovered that the screen makers had became complacent and were not retensioning the mesh to the manufacturer’s suggested tension levels. In fact, tension levels were in chaos and thus the set up times on the presses were so extreme that the presses were sitting idle for hours while the printers grappled with registration.

By improving tension levels the company was able to take a 2-hour set up and turn it into a 20-minute task, thus increasing productivity by approximately 16 man hours a day in the shop, a 13.3 percent overall increase in productivity. And this does not address the decrease in the frequency of double strokes on press, or the increase in quality, which were both significant.

Many screen printers start out in a small way, and this company was no exception. Thirty two years earlier it had started trading with a single manual press and a homemade mercury vapour lamp exposure unit. A bathtub served as the development booth and a garden hose was used for reclaiming screens, which were subsequently leaned against the outside of the building.

The fact is that my client had grown accustomed to the level of quality produced by such rudimentary equipment and techniques, and the fledgling company looked upon any increase in quality as a major development. However, the business had grown and the quality expectations of its most recent new clients now exceeded those of the company’s owners.

Exposure control

The largest shops might want to consider an exposure system with multi-screen frame capacity, such as the Helios T, which has the potential to significantly reduce man-hours and speed up production.

The printshop’s homemade exposure unit was on par with those found in many other screen printing shops that had not bothered to upgrade their exposure equipment as their business grew, customer expectations rose, and emulsion technology moved on. When funds are tight in the beginning,most owners will resort to common, inexpensive light sources, including fluorescent lamps, quartz halogen work lamps, mercury vapour lamps,and even metal-halide lights scrounged from the warehouse ceiling. And, since each of these lamps is capable of exposing a usable screen, the owners see no need to purchase a commercially manufactured exposure unit.

However, they are not getting a full picture of the total benefits that accompany such an investment. My client was a case in point – it was still using a single mercury vapour exposure unit to make screens for five automatic presses!

It is important to bear in mind that the exposure unit is where the emulsion and the image are married and the detail in the final product captured or lost. This makes the moment very special in the overall scheme of the screen printing process. The fact is that investing in a single point, UV rich light source exposure unit, with a proper vacuum system, and a light integrator can deliver significant improvement in the quality and consistency of the finished print. So let’s look at those four features.

Single point light source: The ideal light source is one where the light rays are perpendicular to the film surface. If the light approaches the film at an angle there is always the chance of the light getting under the edges of the image on the film resulting in a loss of detail and a degraded sharpness. A single lamp, by itself, cannot produce such a perpendicular light as the rays will only be perpendicular in the middle of the image and will meet the outer edges of the film at an angle. A fluorescent lamp unit will have a tendency to scatter light in all directions, risking undercutting throughout the image. Only by combining a single point light source with a well-designed reflector can this perpendicular result be achieved.

UV-rich light source: In order for emulsion to polymerize (harden) it must be exposed to UV rays in the 330-440 nanometre range. These rays cause the photosensitisers in the emulsion to react. However, not all UV light sources are the same. While some metal halide lamps can provide an effective source for exposing emulsion it is important to choose one that emits the required spectral energy. There is a vast difference in a metal halide lamp designed to expose emulsion and one used to light a work area. And, while some people use quartz halogen lamps, the fact is that these contain very little UV light and thus result in slow exposure times – a guaranteed productivity killer.

My client had chosen a mercury vapour lamp when the company first went into business in 1973. This type of lamp worked well at the time. However, my client was not aware that changes in emulsions over the years meant that this lamp now represented a poor exposure choice. Vacuum: Like many screen printers, my client was still using a sheet of plywood and buckets of ink to sandwich the film between the emulsion and glass of the homemade exposure unit. What they didn’t realise was that the heat of the lamps had caused the centre of the glass to drop in the centre of the unit and thus the contact in that area was non-existent.
The result was a very soft image in the middle of their four-colour process prints. By simply switching to a well-made exposure system with a vacuum system we were able to produce enough pressure to hold the film positive tightly against the emulsion and thus produce extremely sharp detail throughout the image.

Light Integrator: Second only to having a proper UV spectrum is the ability to control the exposure from screen to screen. The best device to ensure consistency is the light integrator. This unit measures the quantity of UV light and adjusts the exposure in order to compensate for minor voltage fluctuations. The unit also compensates for aging lamps, which will gradually decline in output levels.

Return on Investment

Prior to my visit, the shop produced an average of 50 screens a day on their single exposure unit. Acting upon my recommendations, the owners purchased an exposure unit capable of exposing two 23 x 31” OD screens at one time. The exposure unit has two metal halide lamps, one directly under each screen. The unit is equipped with a vacuum hold down and a light integrator. The exposures were cut from 105 seconds to 16 seconds,but now they are doing two screens at a time instead of one.

This equals a savings of 350 man-hours a year. The reduced handling amounted to another 300 man-hours per year. Not only did the improvement in tension help with faster setups, the owners found that the presses could be operated at a much higher speed:they are now running all five presses at 700 pieces per hour. The shop was able to cut back to just two shifts instead of three, which saved another 8,320 man-hours a year.

The owners have found that simple things, such as ensuring the mesh is correctly tensioned, and investing in a good quality metal halide exposure unit, have more than paid off for them in the long run – they have made savings equivalent to 13,130 man hours a year. However, the savings didn’t stop there. They noticed that the number of screens that had to be remade dropped significantly. Together with the increase in press production, the improvement in print quality and the reduction in reworking required led to a noticeable increase in employee moral. This in turn led to reduced absenteeism. People actually looked forward to coming to work because things were working well.

Client satisfaction increased too, and among the new clients that found their way to the company there were several past clients that returned once they became aware of the improvements in quality.

The bottom line is that there are many shops that are still working with low-tension screens and a poor quality exposure system. They are complacent when it comes to what they would consider to be ‘good’ screens. These shops are totally unaware of the savings that they are leaving on the table.

(This article has been condensed from the original text, which can be viewed on the author’s website: www.schoolofscreenprinting.com)

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