Steel plate rolling is not new but even today, despite the degree of sophistication of new rolling machines (sometimes called benders), the fact remains that the perfect roller does not exist and that A competent operator is often the key to success. However, the new 4-roller rolling machines equipped with digital controls (NC or CNC) can greatly help the cause.
We will take a few minutes in this communication to tell you a minimum of things to know when you are looking for a roller. Particularly in terms of capacities and design.
The plate rolling machines available on the current market are mainly manufactured in Europe. Given that the steel available in Canada is generally stiffer (“yield strength” or greater elastic limit), many buyers often find themselves biased by the specifications provided by the European manufacturer. It is therefore important to specify to your advisor the elastic limit or at least the material that you roll most of the time as well as the harder materials that you might be prone to rolling.
In the world of rolling, subcontractors who roll several part sizes and different thicknesses generally have to use two or three different rollers to be able to cover all needs. For example, a high capacity roller (say 10' x ½''), must have a camber (ovality) at the level of the upper roller to compensate for its bending. It's a bit like a crowning system on a press brake. Therefore, if you are rolling thin material using this same roller, this camber will look to roll more from the center otherwise rolling your piece to the middle of the roller. In addition, it is impossible to roll parts with a diameter smaller than the upper roller, just as it is impossible to roll thick plates with a low capacity roller. Hence the need to have rollers of different capacities.
Most rollers are defined by their ability to “roll” AND “pre-roll” a certain thickness. For example, a roll with a capacity of 10' x ½ generally means it can "roll ½" and "pre-roll 3/8". The pre-rolling capacity is always lower than that of rolling because pre-rolling requires offset use of one side of the roller and therefore all the force available at the hydraulic unit. From one manufacturer to another, this capacity may vary but it is important to know that if you want to minimize flat sections at the entry and exit of parts, a good pre-rolling capacity is important. In addition, some manufacturers set the rolling capacity at 3X (3 times) the diameter of the upper roller while others do it at 5X. Which means that the 5X manufacturer manufactures a roller that is less rigid (diameter and roller material, motorization, etc.) than the one that can roll the material at 3X. For example, a roller with a capacity of 10' x ½'' having a top roller of 11'' could roll, in one case a plate of 10' x ½'' in a diameter of 33'' and in the otherwise, he could not roll it in a diameter smaller than 55''. This is a significant gap and it is important to know this nuance.
General rule, if you want to roll less than 3X the upper diameter, you can do so but for thinner plates. But if the plates are too thin, the camber of the upper roller could harm the result. Some models of plate rolling machines offer the possibility of changing the upper roller. Although the variation in roller diameter is not major, it is possible to play with the camber and give your rolling machine a wider range of possibilities. Your advisor, assisted by the manufacturer, will be able to make certain recommendations on this subject with a list of your rolling parts.
If you are looking to roll cones or minimize the length of flat sections, it is also a good idea to specify this to your advisor. Typically flat sections can vary from 1.5 times to 3.5 times the thickness of the material, depending on the thickness and grade. Cone rolling requires considerable effort on the mechanics of the rolling machine. Therefore, the maximum cone forming capacity is greatly reduced. Certain types of rollers (particularly those with 4 rollers, double hook) will make this application easier, although it is not as easy as it may seem in the videos found on the web. A well-trained and competent operator will quickly become skilled after a while. It is important to clearly specify all the parameters required for cone rolling.
Rolling hard plates (stainless steel, Hardox, etc.) requires increased effort. Choosing a rolling machine of sufficient capacity is important. This should also be specified upfront since if you frequently roll these harder materials, there are two types of steel for making rollers, one being more suitable for these types of parts. Likewise, the hardness of the rollers and the level of polishing could have a short and long-term impact on the lifespan of your rollers but also on the finish of your parts.
In terms of design, there are several configurations on the market. 2, 3 and 4 rollers, single hook, double hook, variable geometry. All its configurations have their advantages, whether in terms of price, handling or results. Here you will find the main ones with a brief description:
This roller is the most common configuration due to its low purchase cost and the rolling principle, as you can see, is relatively simple. It is generally used for low capacity rolling machines.
This type of roller offers an interesting compromise by allowing even thick plates to be rolled without too much handling. However, it requires a good level operator since it is easy to lose hold of the plate and squaring is not so easy to carry out.
Unlike standard rollers, the top roller moves up and down. This type of roller is gaining popularity thanks to its ability to roll thicker plates than standard rollers. It is generally considered for rolling plates of 3″ and above. In addition, it offers an interesting overcapacity since with the side rollers opened to the maximum, it is possible to roll up to thicker 50%. Another interesting feature: the length of the plate at the start of rolling is shorter than on other types of rollers.
Most often recommended in a context of large production of relatively thin plates (3/16'' or less). Some can even roll up to 250 pieces per hour! In this system, roller A functions as a die, it determines the radius of the parts. So if you want to change the radius you need to change roller A with another roller or a suitable sleeve.
This type of roller offers several advantages when compared to the three pyramid type rollers:
The 4-reel is by far the most popular configuration on the market today.
Other aspects are important in terms of design to guarantee you better results. For example, the positioning of the crushing roller (the one which determines the rolling diameter) must be ensured precisely. There are significant differences in design on the market. The principle which ensures the greatest precision is the electronic balancing of the roller(s). When electronically balanced, it is a bit like a Synchro type press brake, each side of the roller is controlled independently and the position measured using a sensor or encoder which guarantees very precise positioning. Some roller models on the market with a simpler and less expensive design use a “torsion bar” type mechanism which is more prone to causing inaccuracies in positioning and parallelism. If you are looking for high precision, this design should be avoided. The electronic swing is therefore more precise and also offers more possibilities if you are rolling cones.
Make sure the rolling machine you are considering is equipped with adequate roller drive. For example, if you need to roll small diameter coins on a 3-roller, it is better that all three rollers are driven otherwise there is a good chance that your coin will slip between the rollers. On 4-rollers, typically the side rollers are not driven since the two in the center pinch the material. This pinch is another important aspect if you are considering purchasing a 4-reel. If the pinch is ensured only by pressure maintained by hydraulic cylinders, you may encounter deviations in your rolling because although the oil is only very slightly compressible, it is slightly compressible, which means that to adjust the rolling diameters according to the pressure exerted by the side rollers. A hydraulic-mechanical system will ensure uniform pinching and greater precision.
As for rolling machines equipped with digital control, there are several versions (NC, CNC) with somewhat different possibilities from one model to another. The elaboration of all these possibilities would require a complete article alone, so if you have any questions at this level, we invite you to contact us for more information. I hope this information is of interest to you, we are at your disposal for any questions relating to rollers but also for any other manufacturing equipment that may interest you.
SYLVAIN DAGUERRE
YAN DESCHENES
YVES GARANT