Alliagtor shear or gantry shear ?

July 05 , 2022

Nowadays, there are many equipment manufacturers, and standard and non-standard products are constantly emerging. In addition to the quality and service of the scrap metal shearing machine, how to choose the suitable shearing equipment according to your own situation with the minimum investment for the maximum efficiency is always confuse our customers. Today TEYUN will compare the gantry shears and alligator shears to help our customers to choose the suitable machines.

gantry shear

Scrap metal shearing machine

In the scrap steel processing industry, the scrap metal shearing machine is mainly used to cut the raw scrap steel into qualified materials that meet the purchase requirements of the steel mill. There are roughly two common types: alligator shears and gantry shears (hereinafter referred to as alliagtpor/crocodile shears and gantry shears).

Alligator shears and gantry shears are composed of shearing mechanism, pressing mechanism and transmission device. It can also be divided into two parts: mechanical part and hydraulic part.

So alligator shears or gantry shears, how to choose?

Working principle:

The hydraulic transmission device is driven by the electric motor (the diesel engine can be used as power in the place without power supply), and the hydraulic transmission device drives the pressing mechanism and the shearing mechanism to achieve the purpose of cutting the steel plate.

Generally, the scrap metal shearing port of the steel plate shearing machine is composed of two upper and lower blades, the lower blade is mostly a fixed blade, and the upper blade is a movable blade. When the scrap enters the knife edge, the pressing device presses down to fix the scrap, and then the upper blade moves downward to cut the scrap. After cutting, the upper blade and the pressing mechanism return to the original position and wait for the next shearing process, and so on.

The main parameters:

Common data of steel plate shears are: shear force, blade size, shear frequency, and total mechanical power.

1. Shearing force: that is, the shearing pressure, generally marked with the maximum shearing force, and the units are slightly different from different manufacturers. For example, kn and t, kn is the international system unit of force, and it is also the legal unit of force in our country. 1t force=9.8kn≈10kn, that is to say, the shear force of 2000kn marked with kn is about 200t shear force. The greater the shear force, the greater the thickness of the metal that the device can cut.

2. The length of the blade: that is, the size of the blade, expressed in mm (mm), which is proportional to the maximum opening, that is, the longer the blade, the larger the blade, and the larger the metal size it can cut.

3. Cutting frequency: that is, the number of cuts per minute. The movement method of the alligator scissors is similar to a lever. The longer the blade, the larger the opening, and the longer the cutting process will take. Therefore, the machine with the higher shear force in the data will have a relatively lower shear frequency. The movement mode of the gantry scissors is straight up and down, and the size of the opening is not directly related to the length of the blade, so the shearing frequency of the gantry scissors with different shearing forces basically does not have much difference.

4. Total mechanical power: that is, the overall power consumption of the equipment. The greater the shear pressure, the greater the power of the equipment and the greater the power consumption. The unit is expressed in KW, which generally refers to KW/h, 1KW/h=1 degree, such as 7.5KW, which means 7.5 degrees of power consumption per hour.

There is a misunderstanding here: many people think that the greater the shearing force of the equipment purchased, the faster the processing efficiency, but in fact it is not so simple. The shear pressure determines the maximum thickness of the metal that can be sheared, the length of the blade determines the maximum size of the metal that can be sheared, and the shear frequency determines the processing speed. There is also an external important factor-feeding speed! If the equipment pressure is large, the shear frequency is low, the material thickness is large and the size is large, the weight is heavy, and the feeding speed is slow; the equipment pressure is small, the shear frequency is high, the material thickness is small, the size is small, the weight is light, and the feeding speed is fast.

In fact, the thickness of the shearing material on the market is mostly 2-6 thick. If the maximum processing size and thickness are not considered, how big is the gap between the crocodile shears and the gantry shears? The following takes 4mm scrap steel as an example to make a detailed calculation in terms of input and output.

Input and output calculation

  • Cost
The price of the alligator shears machine with a shearing force of 200 is about 8,500$. It can process about 4mm of material and can process about 1 ton per hour. The power of the motor is 22kw, and the electricity consumption per hour is about 22 kw. According to the price of 0.24$/kwh, the electricity cost for processing 1 ton of scrap steel is 5.28$. One labor daily salary is 40$/day, working time of 8 hours, equivalent to 5$/h, in theory, Electricity 5.28$ + labor$ = fixed cost 10.28$.

The gantry shearing machine with a shearing force of 630t is priced at about 136,000$. It can also process about 4mm of material and can process about 7 tons per hour. The power of the motor is 180kw, and the electricity consumption per hour is about 180 kWh. According to the price of 0.24$/kwh, the electricity cost for processing 7 tons of scrap steel is 41$, which is equivalent to 5.86$ per ton. Electricity 5.86$ + labor (5/7) = fixed cost 5.57$.

  • Profit

The gross material of scrap steel is about 4mm, 320$/ton, and after processing and shearing, it is about 3700$/ton, which is calculated according to the profit space of 50$.

Net profit of using crocodile shears: 50$ profit margin - 1$ fixed cost - freight 1$ = 48$.

Net profit of using gantry shears: 50$ profit margin - 6.25$ fixed cost - freight 1$ =42.75$.

8,500$ crocodile shears equipment, 10 tons a day profit of about 480$, 18 days can be recovered.

The 136,000$ gantry shearing equipment must be equipped with a steel grabbing machine (calculated at a market price of 22,700$), with a profit of 2,993$ per day for 70 tons, and the cost can be recovered in 54 days.

  • Material type and manpower constraints

In addition to the influence of the equipment itself, the processing efficiency is also affected by the type of materials to be processed and human factors.

For example, if all the processing materials are I-beams, take 16-gauge I-beam as an example: the theoretical weight of one meter of 16-gauge I-beam is 20.513 kg, a whole length is basically 6 meters, and the total weight is about 123 Kg, cut to 60cm size, need to cut 10 times. In the actual processing of crocodile shears, the frequency is basically set at 6-7 seconds per time. It takes 1 minute to cut a whole I-beam, and 60 pieces can be processed in one hour, that is, 7380 kg or 7.38 tons can be produced per hour. .

In fact, most of the workers are not young and strong men. Most of them are a little older. It is basically impossible to carry 123 kg of I-beams alone. Even if they can move it, no one is willing to do this every day. In addition, manpower cannot completely keep up with the rhythm of the machine (that is, feeding once every 6-7 seconds, feeding 10 times a minute, and not letting the machine cut empty).

  • Floor space
The size of crocodile scissors is generally 2-3 meters long, more than 1 meter wide, and more than 1.5 meters high, covering an area of about 2-3 square meters.

The gantry shearing box is 3-10 meters long, 1.2-2 meters wide, and the height of the feeding box is about 1.2 meters, and the cutting mechanism is up to 3 meters. Meters, in addition to the complex power transmission system, covers an area of about 50 square meters. In addition, due to the fast processing efficiency and the rapid accumulation of qualified materials after processing, a stacking pool is generally chosen to be dug under the discharge port, and the area is basically more than 10 square meters.

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