Guillotine vs. Swing Beam Shear
Guillotine Shear
A guillotine shear is a machine that can shear or cut various materials with a guillotine design. The word “guillotine” is associated with a blade that drops along a vertical track. This type of machine was primarily used in familiar history as a method of execution, particularly in the French Revolution, but the modern guillotine shear cutter is a tool used to form and shape products for a market. The principles of the guillotine shear were incorporated into the design of metal shears and have been the primary design for all of these years. Some of the shortcomings of a guillotine shear are that it must run in gibs and ways and therefore need a certain amount of clearance which has a direct effect on the thinnest sheet than can be cut (see figure 1).
Also, the ram moves down with approximately 1 degree of backward motion. This allows the cut sheet to clear the back gauge and drop, although sometimes even this is not enough and the cut part is wedged between the lower blade and the back gauge.
When a guillotine shear has a throat it must be heavily re-enforced to avoid the deflection that would normally result from a deep throat. The apron of the upper ram is heavily gusseted to keep the blades parallel to the bottom blades. This system has worked well for hundreds of years however times change and new engineering becomes available.
Swing Beam Shear
On a swing beam shear the ram moves on bearings so there is no play what so ever. This allows the swing beam shear to be able to cut paper as long as the blades are sharp. The ram moves from a fulcrum point in the rear of the side frames giving the shear a massive amount of plate between it and the cutting point (see figure 2). This means almost no detectable deflection.
The back gauge is attached to the bottom of the cutting column and moves up as the blade goes down. This means there will never be a possibility for the material to become stuck between the blade and the back gauge.
Rather than gussets on the apron a swing beam shear wraps the entire ram as one solid gusset making it much stronger than a similarly gusseted ram. It can have a deep throat with no possibility of deflection and can cut even the thickest piece of metal with a very low rake angle.
In my opinion the swing beam shear reviewed the short comings of the guillotine shear and fixed them; however, it is important to remember that before making a decision on purchasing any kind of a shearing machine factors such as the type of shear, required capacity, productivity options, and safety should be carefully evaluated.
One important consideration used in deciding what shear is the right one for any job is the capacity required to perform the job. Most of the shears on the market today list capacities for mild steel and stainless steel. It is advised to compare a fabricator's requirements to those of the actual machine.
Some shear capacities are rated on mild steel, which may have 60,000 pounds per square inch (PSI) tensile strength, while others are rated for A-36 steel or 80,000 PSI tensile strength. Capacities for stainless steel are almost always less than those for mild or A-36 steel. Surprisingly enough certain grades of aluminum require as much power to shear steel does. As always, when making a decision on any kind of metalworking machinery purchase, it is important to work with a reputable and knowledgeable company that can answer all the questions regarding the performance and capacity for the machine.
From the desk of Cary Marshall...
Rebar Cutting and Bending on the Job
Save time and money.
Steel used to reinforce concrete is known as rebar. It is usually made from carbon steel and the ridges on its surface are there to reinforce the anchoring into the concrete as well as help balancing the load between concrete and steel. Together, rebar and concrete, prevent the concrete from collapsing. A devastating example of incorrect usage of rebar is the 8.1 magnitude earthquake that struck Mexico City in 1985 leaving the capital in crumbles and killing thousands of people; most of the collapsed buildings’ rebar was either entirely too frail and thin to support the building—if the building had rebar at all.
Rebar is measured in fractions of 1/8 increments; it is available in different grades and ranges from #3 rebar up to #18 rebar. The grade designation is equal to the minimum yield strength of the bar. For example grade 40 rebar has minimum yield strength of 40 ksi, grade 60 has a minimum of 60 ksi, and grade 75 has a minimum of 75 ksi. The most common rebar used in concrete construction is grade 60; grade 75 is used in bridges and other heavy-duty construction and grade 40 can be found in low-stress concrete constructions such as sidewalks.
Picture to left: Building of Zampa-Memorial-Suspension-Bridge in California
Rebar comes most commonly in 20' long sticks, thus there is a need for machines to cut and form them so they fit the purpose they will be used for. Concrete contractors do not have many choices when they have to cut or bend rebar, no matter the thickness of the bar:
- outsourcing the rebar cutting/bending
- owning rebar cutting/bending machines
Using a rebar cutting/bending machine instead of a manual tool, in addition to making the work itself much easier, you will be able to cut 3 to 4 times more rebar which of course affects productivity positively. Another thing that speaks for the rebar/cutting machine is that they make it possible to make numerous identical pieces.
The entry-level price for rebar cutters and benders is not high. They run on electric power, either from wall sockets or generators. Also, the maintenance is easy, the blades last a long time and the machines are reliable and relatively easily to repair if needed.
As each job is unique it is very important to work with a good supplier in order to ensure that correct equipment is selected.
From the desk of Cary Marshall
Pictures below: using rebar in landscaping. Photos taken at the Getty Museum Gardens, Los Angeles, CA
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MG Plate Rolls vs the Need of Special Alloy Rolls
Special alloy rolls are necessary when there is a need to roll a relatively tight diameter on a machine where the standard roll is too large. The question is, however, should you really choose a special alloy roll or should you consider an option that gives you the benefits of the alloy roll but doesn't limit the usage of your machine? For an example, a 10’ X 3/8” roll should be used with a 10” roll diameter. Let’s say a person is looking for a roll of this size but has a requirement of rolling 13” diameters. He would have to by a smaller machine unless the power requirements called for the 10’ X 3/8” and in that case he would need a machine with a reduced diameter top roll. This roll would have to be a special alloy roll because it would be smaller yet still being able to do the work of a roll with more mass. Once you have made the decision to use a smaller special alloy roll you have turned your machine into a very narrow usage machine. A special alloy roll can take more deflection without taking a set (warping) and still go back to it original position. However, a special allow roll still has the same characteristics as any other roll. If it has less mass it will deflect more. So, having a smaller roll - even a special alloy roll - will mean you cannot do the range of work you could with the standard diameter roll. You will have severe barrel defects if you work anything beyond the mid-range of the machine. For this reason it is always better to bring the most massive roll to what ever job you are doing. MG rolls are capable of working to 1.1 times the top roll diameter at about 60% of its capacity by full length. Almost all other machines can only work to 1.4 or 1.5 times the top roll diameter by full length. Example: a MG plate roll and a competitor’s plate roll; both with 10” diameter top rolls. If a job requires a 13” diameter the competit
or would have to quote a smaller machine or a 10’ X 3/8” machine with a smaller special alloy roll. MG roll, however, would be able to roll the part with no problem even if the job called out for an 11” diameter. It does this with the full 10” diameter without having to reduce the roll to an 8.6” diameter and reducing the effectiveness of the roll.
The reason why MG rolls can work up to 1.1 times the top roll diameter is their exclusive geometry. It is not a matter of power at all. In fact, MG’s geometry allows it to use less power for any given job making it the most energy-efficient roll on the market. MG rolls also use less horse power than the competitor.
If you are looking for a bigger machine to make a smaller diameter you can always choose a special alloy roll; however, if you want to get a smaller diameter part without sacrificing a broader range of rolling, your best choice is the MG roll.
Cary Marshall, CMF...
Why is MG's Rolling Geometry Better than Competitors'
When comparing bending machines, the following items are critical:- Capacity of bending
- Accuracy of its products
- Ease of operation
- Customer references
- Other functions, such as maintenance and protection etc.
BENDING STAGE
Rolling is basically the same however we can state that MG machine keeps the material pinched constantly so a small radius can be reached in one or two passes according to the machine capacity. The competitor's system needs more passes as there is not as much dragging power as the upper roll is merely an idle roll.
L = Length of flat
As shown below, it becomes clear that on a plate roll the smaller the “X” value the better. In fact, it is the contact point between side rolls and top roll which is the point where the plate gets bent. Obviously, the shorter the “X” distance the better as the flat part of the plate gets shorter as well.
The situation is the opposite for the "Y" value as it becomes an advantage when it is longer. In fact, the longer the better as it effects only the bending. So, the more distance between the side rolls the less power is required.
Competitor: Scheme of a machine based on straight guides. The “X” distance is short but the “Y” distance is consequently short as well because of the geometry. See picture below.
Competitor: Scheme of a traditional swing arms machine is opposite to the above illustrated situation; the “Y” value is very large but the “X” gets large as well. So, the result is a great advantage on rolling but poor results on pre-bending. See picture below.
MG: Viewing the scheme of the MG machine with its exclusive technology you can see we achieve the best advantage of both "X" and "Y". Because of MG's swing arm technology the "Y" is much larger while achieving a tight "X". Having a larger "Y" means less power is required to make the same bend. See below.
Authors:
Mauro Roccia, MG s.r.l
Cary Marshall, CMF...
MG Swing Arms & Parallelism Control Compared to Other Systems
Below is an example of a machine using linear guides (left) and one using MG swing arm guides (right). Linear guides have been used for hundreds of years so most manufactures take it as a given to use them in their machine design. However, time marches on and so do designs. The MG machine is a engineered machine with no givens. There are several drawbacks to a linear system which we will show you below. We will show you why the MG system is superior to any other system available. It is apparent the Swing Guide System is more difficult and expensive to make; however, as we shall prove, it totally eliminates parallelism problems.
Let’s now analyze the different technology.
1) Linear side guide system is accurate when the machine is new and the bronze slides are tightly adjusted between the side rolls support and its guides (the yellow bars of the drawing below). It takes power though to move because of the friction generated; this is why usually all machines like this have a higher installed power requirement.
After a running in period the guides run well and smooth, however, the machine now doesn’t need the extra power needed at the beginning. The machine still absorbs the entire power output. This is a waste of power and money as you have to pay for the power whether you use it or not. After a certain period of time, the bronze slides get worn out and it’s here that the machine looses precision. If you look at the second picture (right) of linear side guides sketch above you can see how the support will soon start to move inside the guides and you’ll loose side rolls precision. At this point maintenance is needed to get back to the initial precision.
MG SWINGING ARMS
MG system use a pivot arm swinging around a center fixed by means of a bearing. It is a proven system working for years without LOSS OF PRECISION. The coupling with shaft and bearing is a very strong and precise fit. This has given MG a worldwide reputation of precision working for years.
2) Side rolls parallelism: The basics of electronic parallelism is that one piston - say the left one - moves while the second - the right one - follows it by means of a communication between two encoders (set on each hydraulic piston) and an electronic unit. It’s a continuous adjustment that is moving up and down following the left piston. You may not see it, but this is the way it works. One might think its like press brake system, but while the press brake has a very short stroke the plate roll has a large stroke. The electronic system could be ideal if the oil would not compress, it does though and it gets compressed by 2% every 100 bars. Look at the sketch below:
For this reason, the electronic or hydraulic parallelism control is continuously adjusting the system because one of the pistons, the one that gets more load (when the material is not perfectly on the center of the rolls) drops down because of the oil compression and there is no way to avoid it. This is why this system works on press brakes, which have less stroke, less quantity of oil, and therefore less compression. A plate roll, however, has a large stroke, a larger amount of oil involved and therefore more compression.
MG TORSION BARS
MG’s system is based on a massive round torsion bar that connects mechanically to the two hydraulic pistons of the side rolls from left to right. In this way the two pistons bec
ome actually one as they are firmly tied together by means of this torsion bar. Also, the oil compression doesn’t matter here because the amount of compression is always the result of the sum of the oil in both pistons. If something moves it is the couple of pistons and never ever one at a time. Due to the lever generated by the side rolls’ arms, we can install smaller pistons and have the same effect but with the great advantage of less oil traveling and so, again, less oil compression. That’s proved to be the most precise and reliable system worldwide and, in addition, it doesn’t need any kind of setting or adjustment for the life of the machine.
3) The lower roll parallelism control: Also in this case we see a design defect (pic.4). The lower roll of our competitors is directly driven by two hydraulic pistons. Again, because of the oil compression, there is no way to keep a constant pinch as one side of the rolls will always compress down a little bit making it very difficult to guarantee rolling precision (cone defect) as well as lack of dragging constancy.
Pic.4
MG TORSION BAR
The MG system is based on a roll set on two eccentric wheels driven by a torsion bar. See sketch below:
The eccentric is irreversible so there is no way to be compressed under loading. This is why MG can guarantee the best precision even when the machine is pushed to the limit.
4) Bearings. Below is a comparison between the MG system and the system adapted by some of our competitors:
MG OTHERS
If you look at the above sketches you understand how well every system can be adapted to the best geometry. The fact is that MG continuously researches and develops machines while others are still working with machines that have basically been designed 20 years ago.
Above is shown a slide guide system with a fixed geometry.
So it’s a pure matter of geometry? Remember, chose the right partner. MG never uses a given. MG is always trying to find a better way.
Authors:
Cary Marshall, CMF
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Comparing 4-rolls vs 3-rolls - Advantages & Disadvantages
COMPARING FOUR ROLLS VS THREE ROLLS – WHAT ARE THE ADVANTAGES & DISADVANTAGES
Four-roll technology has been around almost since the turn of the century: however, it was impractical, as the improved production did not justify the costs.
The single biggest advantage that four-roll machines have over the other two machines is simplicity.
In order to obtain a perfectly bent pipe with a three-roll double pinch, it is necessary to do three different operations:
- It is necessary to pre-bend the leading edge of material. This is done by pinching plate between one of the side rolls and top roll.
- You must also lower the opposing side roll to create the proper geometry for the pre-bend. Because of this it is impossible to load and roll material in the horizontal position. It also requires a much larger area in the shop as the material must pass all the way through the machine in its stretch-out condition for the pre-bending so it requires at least equal distance on both sides of the machine.
- It is necessary to completely change roll position and move plate back to center of machine and position side roll at correct position to achieve required diameter.
press brake. The only machine capable of bending a cone properly is a four-roll machine.
To roll cones on a three-roll machine is very difficult. First you must realize that a cone has to be developed by rolling a plate at two different speeds at the same time. This is a difficult situation to achieve. Both the three-roll and the four-roll machines are capable of inclining the side rolls in a positive attitude, and both have a hardened contrast die to control and slow down the speed of the small diameter. This is an equal comparison as far as it goes; but, by guiding the small diameter and inclining the roll (both of which are necessary to roll cones) you have still created an unnatural situation for rolling cones. Why? Because on three-roll double pinch machine all three-rolls are driven, which makes it very difficult for the contrast die to be able to retard the rotation on the small diameter while making the large diameter move faster. This causes lamination and scarring on plate and the roll.
So, why can a four-roll, which also has inclinable side rolls and a hardened contrast die do this difficult function better than three-roll? The answer is this: the four-roll (lower central pinch roll) can be inclined in a negative attitude and is also capable of adjusting the force at which it pinches which allows the roll to grip the cone only on the large diameter which needs to turn faster and only with enough force to turn the part. This allows the small diameter to be slowed down more easily.
To sum it up, rolling cones properly absolutely requires a lower central pinch roll (fourth roll) capable of a negative inclination and adjustable pinch pressure. Only four-roll machines have this capability but, be careful, not all four-roll machines have it. Be sure to ask the builder about this feature. Also, make sure when inquiring about four-roll machines that the side rolls move independently so that one can be used as a squaring gauge.
Handling the Plate:
Bending light sheet presents no particular handling problem to either type roll, although the three-roll must be lined up with a groove and then pressure applied to hold this position. On a four-roll, you merely bump the sheet off the back roll which acts as a positive stop and then pinches the plate to insure position.
The real problems start with the rolling of long plate. Because the three-roll pyramid has to lower one of the side rolls and pinch and pre-bend with the other, it is really not suited for long plates, as it would drag the ground. This leaves two options; the initial pinch and the four-roll.
The initial pinch can require as many as 2 or 3 people to help maintain control of the plate by using cranes, hoists, etc. Also remember, the plate has to be taken out of the machine and turned for the opposite pre-bend operation. Again, this sounds as a tough and time-consuming operation; companies doing this type of work will tell you it is tougher.
By contrast, once again, the four-roll is uniquely suited for this type of work. First, like the initial pinch, in a horizontal position allowing for conveyors or support stands, this is the safest, most controllable condition and does not require 2 or 3 men to control plate. Secondly, plate does not have to be turned around.
Speed:
Because the initial pinch must turn plate for second pre-bend and the three-roll double pyramid must make 6 positioning to roll a pipe, it is conservatively estimated that the floor-to-floor time on making a pipe is 50% faster in production situations on a four-roll with much less operator expertise required. Put simply, if a three-roll can roll a vessel in 20 minutes, a four-roll could do it in 10 minutes, or twice as fast. Even if a company is rolling only a few pipes a day, there is no reason not to do them a rapidly as possible so you can get on with your other work.
Automatic Squaring of Material:
On a three-roll machine, squaring of plate is a very difficult process and one of the most important. It is extremely difficult to control the squareness of plate over a 6'- 12' long piece with just one man.
Three-roll manufacturers usually put a small groove in the outboard rolls to help line plate up but even with this, it often requires two men to square plate properly. No matter how long it takes, there is no alternative; the plate has to be square or you cannot proceed. This process, on a three-roll, is time-consuming and can be very frustrating.
On a four-roll machine, the process is automatic and takes only a few seconds and, equally important, only one operator. This is done by lifting one of the independent outboard rolls and using it as a squaring gauge. Once the material is in contact all the way across, the operator simply drives the lower pinch roll up until it pinches material and, from that point, you can roll complete pipe in one pass.
Constantly Pinched Plate:
One advantage of maintaining a pinched condition is that the operator has total control of all plate motion. In this condition, it is possible for one operator to roll parabolic curves or boxes without leaving the control and with only one squaring of the plate.
This is impossible to do on a three-roll machine. It also isn’t possible to vary the pinch pressure so that you can supply strong force for big plate and less force for thin or soft material and because the plate is driven, it prevents it fro slipping out of position which happens with three-roll machines.
Another disadvantage of three-roll double pinch machine is rolling thin sheet (less than 30% capacity) because of the lack of resistance in the material. Again, this is not a problem for a four-roll which is pinching material and creating its own drive force, regardless of resistance in material.
Bottom line; a MG four-roll plate bending machine will improve your production dramatically.
Rotation Speed of Rolls:
Machines not using planetary drive system still rely on chains, gears, clutches and synchronization devices. These are items subject to maintenance. Studies have proven that most shop break-downs are due to lack of proper maintenance.
MG has for years used the Planetary Drive System that does not require synchronizing gears or any mechanical devices. It properly controls the different speeds. This is achieved by planetary drive systems which are much stronger than other drive systems and do not require synchronized gearing. More importantly it does not require any maintenance.
CNC Controls:
The four-roll machine is the only plate roll that truly utilizes a CNC control. On a three-roll machine, the CNC is basically used only to repeat side roll positioning. It cannot accurately control lateral movement. The three roll double pinch machine does not move the plate by driving it but rather by dragging it. There is no guarantee that the roll won't spin slightly during movement and lose part zero.
On a four-roll machine, because of the pinching of the fourth roll, you do have constant control of the material and, therefore, the CNC control can totally control an entire bend floor to floor.
The advantages of a CNC control can be justified in either large production applications, small production applications or in “just in time situations”.
The advantages in large production is that the computer will take care of most of the various rolling processes leaving the operator only responsible for putting the flat plate into the machine and taking the round cylinder off the machine. In cases where a vacuum feed, power feed table and parts ejector are part of the system, the control will even put the plate on the power feed table and then feed the plate in and eject the cylinder when finished.
The control also has very strong advantages when there are a lot of different parts to be rolled even in small quantities. The control gives the operator the ability to set up the machine from one part to another in literally seconds. In either one of these situations, the value of the CNC control can not be understated.
The MG Touch Command Control:
I believe this is the strongest control in the industry. If you have to make a parabolic shape, pentagons shape, hexagon shape or an elliptical shape you would not need test material. You would only require the one part you want to roll. The control will make the part one off.
MG is the largest roll manufacturer in the world selling more large machines than any other manufacturer. They do this while making 45 “bread and butter machines” a month. They are the most sold machine in Europe. Their machines have for many years been sold in the U.S. by a private label company. There are over 300 MG machines in the U.S., Canada and Mexico. We are now marketing the product under the trade name of MG. Europeans have known for years what Americans are about to find out.
MG is synonymous with quality.
From the desk of Cary Marshall
President and owner of CMF
Read more about the MG 3-rolls by clicking HERE
Read more about the MG 4-rolls by clicking HERE...
