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That's A Mistake: Using Two Roll Grinding Providers

Posted by Robert Rourke on Jun 10, 2015 11:11:00 AM

Screen_Shot_2015-05-28_at_12.19.37_PMThe importance of precision roll grinding can’t be emphasized enough. Perfectly maintained rolls have an enormous impact on the quality of your product and the efficiency with which you produce it

Many manufacturers understand the significance of expert and timely roll grinding, but even so, a large portion of them only apply these concepts to their calender rolls.

This wayward thinking sometimes leads to the decision to use more than one roll grinding company: one precision grinding partner to handle the rolls used for finish, and another partner to service the other working rolls.

Why Is Using Multiple Roll Grinding Partners A Bad Idea?

With most services in life, you tend to get what you pay for. Precision grinding is no different.

Because the cost of a lesser roll grinding service is relatively cheap, many manufacturers with both working and finishing rolls choose to use the less expensive provider for the former set, and the more expensive and precise provider for the latter. Their line of thinking is that it would be best to spend more on the rolls that seem to make the biggest imprint on the quality of your sheet.

However, this mindset is flawed.

How Flawed Working Rolls Diminish Your Product Quality

The press section is the part of your machine that’s most likely to cause streaking. If you use a cheap grinding company for the rolls in your press section, you have a much greater  chance of producing a sheet with streaks, which typically needs to be corrected after it leaves your dryers.

Let’s take a typical paper manufacturer that produces packaging papers:

When your sheet leaves the table and reaches the first press, it’s usually 25% dry. It goes through a press (or multiple presses) to the point at which it reaches 42% to 50% dryness.

By the time it reaches the reel, there may be 5% moisture left in your sheet. If the level of moisture (or dryness) is evenly distributed on your sheet, you should be content that you’ve produced a high-quality product.

But, what if the rolls in your press section are miscrowned, carrot-shaped or both? Unfortunately, this is quite common.

Your sheet is going to have an uneven profile and non-uniform dryness across its surface area. It will have dry streaks in certain areas and moist streaks in others. In all likelihood, your sheet is going to miss its moisture target, and you’ll need to dry your paper excessively to meet your targets.

The traditional rule of thumb is that you must add 4% more steam to your dryer drums to remove every 1% of moisture from your sheet. While this reduces dryness to meet your moisture target, it also further dries areas that already met this specification.

These spots are still proportionally drier than the moister areas, often resulting in a sheet with tension variation, which likely creates issues in converting.

Not only are you forced to produce lower-quality paper that’s riddled with streaks, but you’ve also added the cost of steam in order to fix a problem from a previous step in the process.

Cheap, Imperfect Roll Grinding Hurts Your Customers

This issue is by no means common within the paper industry alone, but it is a great example of how uneven roll profiles and improperly positioned crowns cause streaks in a product.

The low-quality variability in your product then creates converter or end-user issues, the kind that damage your reputation.

If a magazine, newspaper, packaging or envelope-making company uses paper with the type of streaking outlined above, they could battle issues with variations in tension and how their ink is printed and dried.

If you leverage an expert precision roll grinding company for your finishing rolls, you’re in a good position to produce the high-quality product your customers need. If your working rolls are not treated with the same approach, though, the investment in your finishing rolls could be for naught.

Ensure the quality of your product and the profitability of your operation by utilizing precision grinding for every roll that’s used to produce your sheet.

Consult a precision grinding expert to learn how you could improve the quality of your product.

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Topics: Paper Industry, Roll Grinding, Best Practices

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