1. Outside Diameter
For specific recommendations on knife diameter to rubber diameter, please contact us.
2. Inside Diameter
Should match the OD size of your metal spacers. We will automagically adjust the fit to your requested type of fit (see box at right). We have to know the actual OD of your spacers in order to properly manufacture your rings.
3. Durometer Hardness
Choose from 60, 70 or 80 Shore A.
4. Color
You can choose any one of our vibrant colors.
5. Quantities of Each Thickness
Thickness should be the spacer widths. Please don’t add or subtract clearances.
OD: +0.010/-0.010″
ID: Snug fit (most common),
but we can make tight fit, slip fit or loose fit too
Thickness: +0.010/-0.030″
Nitrile is the more modern term for Buna N. They are different terms for the same material.
Neoprene is another type of elastomer, generally not recommended for slitting applications.
Neapolitan is a style of ice cream.
It’s ok if you don’t want to know. Just skip the rest of the answer. Otherwise, grab a cup of coffee.
There are various types of materials used to make elastomers. The term elastomer refers to any polymer with elastic properties, or “rubber-like” properties.
Rubber stripper rings are elastomers used to push back on the strip during slitting, like ejector pads or springs in dies. But, they have some unique requirements. Of the many types of materials which could be used, Nitrile has some very unique properties suited for stripper rings. Nitrile is resilient, has excellent oil resistance, and can be made in various colors.
But saying something is Nitrile is about as descriptive as saying something is steel. You know that steel has standard grades. However, Nitrile (and most elastomers and most plastics and polymers) do not have standardized grades like the metals industry.
Instead of a grade, Nitrile is made to a formula or recipe. Nordic Company has developed a proprietary formula (secret recipe) for rubber stripper rings which meets the demands of the metals processing industry. You can’t get our formula anywhere else.
Just because you got a quote for nitrile somewhere else, it doesn’t mean it is going to be a good rubber stripper ring.
That depends on how much work they are asked to do. If your referring to how long they stay snug, then that is a function of the number or cycles (basically revolutions) and the amount of compression (deflection, or strain) in each cycle. Rings can last 15 years or 15 minutes. For more information, click here.
Successful slitting requires that you to establish the correct OD relationship between the knives and the rubbers, and then maintain it. Best practices are to grind rubber rings every knife grind. Yes, it is expensive. Maybe you can do it less often, and save money, but you’ll be sacrificing the usable life of the rings by causing over-compression. Replacing rings is expensive too. It has been said “Grind me now, or replace me later.”
That depends on a number of factors, but the most important is the thickness of the material that you are cutting. But, here’s a hint. Harder durometer shouldn’t be used for hard to cut materials. We see that mistake a lot. Why don’t you email or call to discuss. Yes, we answer the phone.
Nope. Dual durometer isn’t doing what you think or what you’ve been told. We will make it for you if you really want it. We won’t even charge more for it. (Doesn’t seem right to charge more for something that doesn’t work, does it?) We have strong opinions about what type of construction is best. Why don’t you contact us?
Zero. Don’t use dual durometer. The reason it isn’t working is not because you don’t have enough. It is because you have too much.
Really? If dual durometer didn’t work, don’t conclude it is because you don’t have enough durometers. Give us a call.
Ok. We can make them. Send us a description.
There are really no standard solutions to anything involving slitting. Your equipment, your customer’s needs, and your tooling are all unique. It’s also why we don’t have these items sitting on a shelf. We are available to assist you with a unique solution. The lowest cost way to buy rubber rings is to get the rings that work in your plant, out of the box and right from the start.
If you are the person grinding rubber rings, call us and we can talk you through the solutions.
The diameter relationship between the OD of the knives and the rubber is by far the most important aspect for success. This is the primary way that you have to adjust the amount of push force ejecting the strip from between the knives.
This can get pretty detailed. You are welcome to call us to discuss it. Or read on.
Let’s discuss the male rubber rings first. Male rings need to be slightly larger than the diameter of the knives, because they just need to keep the non-cutting edge of the knife from contacting the strip and making knife marks. If you are getting knife marks, you need to adjust the diameter relationship and allow the male rings to be larger in diameter.
More importantly, the female rings need to be sized correctly to give enough just enough ejection force to keep the strip from sticking, but not a lot more. The diameter relationship of knives to rubbers is your key to control it.
To understand this, you need to think about the fact that rubber is a spring. Its easier to imagine if we think about metal springs. A metal coiled spring will push back with different amounts of force depending on how much it is compressed. If you need a little force, you compress the spring just a little. More compression gives more force. It’s the same way with a rubber rings, except that the dimension being compressed is the distance between the OD and the ID. If we have a bigger diameter on the rubber, we will compress it a longer distance, and the force will be greater.
Of course, you never want the strip to stick down between the knives, but there is a problem having the diameters larger than necessary. First, you will have more forces on your arbors. It is easy to underestimate the force required to compress all that rubber across the width of your arbors. Those forces contribute to arbor deflection, and changing horizontal clearances that you were so careful to set up. Your bearings are going to be subjected to increases pressures too.
Secondly, you are going to be overcompressing the rubbers, causing them to stretch out. Overcompressing rubber rings is the primary reason that unbonded rubber rings become loose.
We have strong opinions about the proper relationship of knives and rubbers. Contact us for more details.
Hopefully, you read the above section. First, let’s bust some myths.
MYTH Oil causes rubber to stretch.
BUSTED! Unless you are using rings made from an inappropriate formula, rubber doesn’t stretch due to oil. Nordic rings are specifically formulated to resist attack by oils.
MYTH I need a harder rubber to resist stretching.
BUSTED! Nope, that is really wrong thinking.
Let’s talk first about the mechanism causing rings to stretch on the ID. When rubber gets compressed, it doesn’t return to its original size. It gets very close, but not quite. That happens on the next compression cycle, and the next. Think about how many compression cycles (revolutions) your rings turn in a production shift. For very small compressions, you might get millions or hundreds of million cycles before you had a noticeable change. But, large compressions cause noticeable changes with fewer cycles. With a large enough compression, you might notice it after 1 cycle.
When rubber rings fail to return to their original size, they get longer in the circumference, which means larger in the diameter, which means that they will fit less snugly, or may become loose on the ID.
You can’t control the number of cycles (hey, you got to get thru that warehouse of coils, right?), but you can control the amount of compression by managing the diameter relationship of the knives and rubbers. Don’t over-compress the rubbers.
Shouldn’t dual durometer rings stop that from happening? Nope. (read the Common Question section.)
(We do manufacture a proprietary fiber reinforced ring which does help rings keep their snugness longer. Contact us directly for details)
Nordic can bond rubber to new or existing spacers in our facility. We’ve had great success with our technique and with the performance of our rings.
Rubber rings permanently bonded to steel spacers is a great way to improve a number of nagging problems. They will never get loose and go around like a hula hoop. Your regrinder will be able to hold better diameter accuracy and circularity because he won’t have your rings going around like a hula hoop either. Your personnel will be handing 1 piece rather than 2 (spacer and ring).
On the other hand, you’ve got to send spacers and the rubbers bonded out for grinding, so might need more tooling. And, when it comes time for new knives, you’ll have to send the spacers to Nordic to have the old rubber removed and new rubber applied. Either that has to be done during shut down maintenance, or you’ll need more tooling to cover things while they are in our shop.
We can help you to plan a conversion or to recover your existing spacers.
Nordic Company
Contact Information
TELEPHONE: 724-443-6840
TOLL FREE: 1-877-443-6840
FAX: 724-443-6933
E-MAIL: sales@nordiccompany.com
Nordic Company
