Choosing The Right Plate or Sheet Rolling Machine
We have compiled some general basic educational information regarding plate rolls and their use. It is our hope that this information will assist you in selecting and properly sizing a machine to fit a particular application. For further in-depth information and application engineering please contact us directly.
Plate or Sheet Bending Rolls are built in 2 main categories, single and double pinch and may have different geometries or styles. Matching the most appropriate machine style to the application is important. General machine styles are: 3 Roll Initial Pinch, 3 Roll Double Pinch, 4 Roll Double Pinch, 3 Roll Variable Translating, 3 Roll Pyramid and 2 Roll Systems. Plate rolls are also built in a vertical format for special applications.
Machine capacity is of equal or greater importance to style. Steel mills are producing materials with increasingly higher yields. Plate roll manufacturers commonly rate machines according to a baseline material yield strength between 36 to 38,000 psi. When choosing a machine you must refer to your mill certificates to verify the common yields of the plates being delivered. It is not uncommon to find that the material you are actually rolling will have yields in the 48,000 to 58,000 psi range if it is ‘mild steel’. Machine capacity must match your material type. Most manufacturers can provide detailed tables or graphs that allow you to match capacity to yields.
You will often see ratings for pre-bending and rolling given for any one size Plate Roll. Pre-bending is performed on the plate roll at the leading and trailing edge of the sheet (eventually the seam). Sheets cannot physically be bent completely to the edge and thus will leave what is referred to as the ‘un-bent flat’. The minimum you could expect for flat length is 1.5 x material thickness and often it will be from 2.5 to 3.5 times material thickness for heavier plate. It is the pre-bending operation attempting to reduce the unbent flat to the minimum possible that takes the most power. This is why pre-bending ratings are lower than rolling capacities for any given machine. You must be mindful when reviewing machine ratings since the maximum total rolling capacity is generally expressed with the intrinsic requirement of multiple rolling passes and very long un-bent flats. Un-bent flat lengths for any given sheet are a function of thickness, width, cylinder diameter, machine type, yield, top roll size, operator proficiency among other factors. NC and CNC Controls are ever more common in the workplace. Most all NC/CNC machines are 4 roll types. Automated controls are recommended for high volume cylinder or shell production or to roll complex shapes that are not easily reproduced by using manual machine controls. Multiple bends, variable radius bends, ovals and the like are some examples.
Three Roll Initial Pinch or Single Initial Pinch Plate Rolls are generally for lighter capacity applications and may be electro-mechanical or hydraulic. They work by "pinching" the flat sheet between two counter-opposed rolls while the third offset roll or ‘bending roll’ moves upward to contact and then bend the sheet. When rotation of the rollers is activated, the sheet exits at a given radius. With the sheet cut to the developed length and the bending roll properly positioned; the part is rolled into a cylindrical form, where it can then be welded at the seam to produce a cylinder. The upper roll is in a fixed position; the lower pinch roll can move up/down to pinch the material. The third roll (the forming roll) is also adjustable. To remove a rolled cylinder, it must be extracted from off of the top roll. Machines are generally equipped with some type of release mechanism on the top roll to allow extraction of the cylinder. Typical methods are either a forward tilting or releasing top roll or a removable end yoke. In most applications, these machines require removal and re-insertion of the sheet in order to pre-bend both ends. They are cost effective but in contrast may be more labor intensive in a production setting. There were many large mechanical initial pinch machines built during the 1930’s, 40’s & 50’s and can be found on the used market. All have cast frames as modern alloys and welding techniques had yet to be invented.
Double Pinch Plate Rolls are available from light to extremely heavy capacities and may have three or four rolls. The terminology can be confusing as these units may also be referred to as ‘double pinch pyramid plate rolls’ or ‘double initial pinch plate rolls’. Both three and four roll styles have fixed position top rolls and two offset rollers or ‘lateral rolls’, one on each sides. The 4 Roll styles have an additional roller underneath the top roll, which constantly pinches the plate during rolling. Double Pinch Rolls can pre-bend both ends of the plate without removal as is required with single pinch rolls. Three Roll machines generally require pre-bending the leading end, running the sheet through the machine to pre-bend the trailing end then switching roll rotation direction to roll the cylinder body. Four Roll Plate Rolls have a slight advantage in cycle time since the permit pre-bending of the leading edge, rolling the cylinder body and finishing off the trailing pre-bend all while rolling in the same direction. Smaller machines can be mechanical but most modern machines are hydraulic and include drop end yokes for easy extraction of the work-piece.
Automatic NC or CNC Controls and Four Roll Plate Rolls: Automatic cycle systems are generally used only on four roll plate rolls because there is minimal chance for slippage thanks to the constant pinching action of the forth roll. Automatic controls use an encoder to track movement of the plate through the machine. If the plate slips, the bending roll movements will be out of synch with the rolling movement..
Variable Geometry Three Roll Plate Rolls are not new but are gaining in popularity around the world. They are built for medium, heavy to extremely thick plate applications. The top roll moves up/down and the lower two rolls each move horizontally. This lower roll movement allows increasing the offset distance from the top roll and commensurately increasing mechanical advantage in bending. A machine of this type works well over a wide range of material thickness. By adjusting the geometry they can be used similar to single pinch, double pinch and pyramid style machines and require minimal sheet movement during the pre-bend operations. In the past these machines were commonly found in shipyards but now are being placed in general job shop and manufacturing applications.
True Pyramid Machines are rarely used in modern business. They may be found on the used market and are more common in third world or developing countries. The have three rolls, both lower rolls fixed in position and the top roll moves up/down. In general they leave a very long un-bent flat and have several other disadvantages.
Two Roll Machines are designed for thin gauge material rolled to reasonably small diameters. They use a large diameter urethane coated pinch roller which moves up with extreme pressure against a small diameter steel top roller. A mandrel or drum, very close in OD to the desired ID of the part is fitted over the top roll. Two roll sheet rolls are extremely fast and will roll a round part even if the blank has cutouts or holes. Since they require a mandrel for each different part diameter and material thickness they are not as versatile as some other machines. For dedicated high speed production however they are often the absolute best choice.
Optional Equipment can be found listed on most proposals for plate rolling machines: The most important items to consider are hardened roll surfaces and cone rolling devices. With today’s harder materials and laser/plasma cutting techniques it is ever more important to have very hard outer roll surfaces. Look for hardness rating from 50 to 55 Rockwell C Scale. Hardness in this range will have a reasonable penetration depth and provide long lasting protection against roll surface wear. Hardness exceeding 60 will have a shallow penetration and result in cracking or crazing of the roll surface. Cone rolling devices permit the operator to roll a conical shape and are standard on some machines. Lateral material supports and overhead supports are optional but less frequently requested. Overhead supports prevent lighter materials from collapsing when rolled to large diameters. A side support can also assist in this function to prevent light materials from re-curving toward the floor if the radius is very large. Some machines have extended roll shafts that protrude through the machine frame and section or pipe dies can be fitted on these ‘stub shafts’. It is not practical to roll angle iron on a plate roll since angle tends to twist when rolled. Plate rolls do not have outboard adjustable lateral material guides to prevent this twist. You should consider using a section rolling machine or angle roll. In general, section dies on plate rolls are good for bending flat bar the hard way, rods or small pipe.
General Note: Roll Bending Machines are very dangerous if used carelessly. It is the responsibility of the owner to ensure the installation and proper use of point of operation safety guards or devices. |
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All Fabricating Machinery and Equipment including bending machines of all types must only be operated by trained and authorized individuals and care must be taken to; follow all safety warnings, read all labels, use proper procedures, wear proper clothing, take all material handling precautions available, check machinery before and during each work shift, provide regular proper maintenance, operate well within rated maximum capacities and ENSURE that the owner installs and maintains primary point of operation safety guards or safety devices that are adequately adapted to the use in which the machine has been employed.
Carell Corporation or Carell Corp. is your single source provider of superior quality bending machines and metal fabricating equipment designed for dependability and versatility. Carell Corp. provides and stocks; angle rolls, section benders, profile bending machines, CNC angle rolls, CNC section benders, CNC benders, ring rollers, pyramid rolls, universal roll benders, coiling machines, plate rolls, slip rolls, initial pinch rolls, three roll plate rolls, 3 roll plate rolls, four roll plate rolls, 4 roll plate rolls, cone rolling machines, hydraulic plate rolls, mechanical plate rolls, plate bending machines, ornamental bending machines, Scroll benders,slip rolls, scrolling tools, bar twisters, picket twisting machines, ring forming machines, flange forming machines, fixed angle notchers, notching machines, corner notchers, variable angle notchers, rebar benders, rebar bending machines, rebar benders, rebar shears, rebar cutters, rebar fabricating machines, tube benders, pipe benders, CNC tube bending machines, mandrel benders, compression benders, rotary draw benders, bar working machines, horizontal presses, bulldozer presses, and manual benders. We manufacture and stock; tools for bending, tube rolls, pipe rolls, special tooling and custom tooling. We also carry the following brand names; Imcar, Famar, Simasv, Icaro, Sergi, CBC, FSB, Carell and others.
Manufacturer and Carell Corp reserve the right to revise design, construction and specifications without prior notice. Transcription and clerical errors subject to correction. All images and text on this page are the property of Carell Corporation. and may not be copied or used in any way without permission from Carell Corporation.
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