FAQs
To start with you must ensure that the density (t/m3) of the material to be handled is suitable for the equipment you have chosen.
Maximum density of the products to be handled is specified on the technical data sheets with a 15% margin
You must choose a grab that will cover the maximum density of the product to be handled.
A DENSITY TABLE of more than 700 products is available for you to consult.
After selecting a product, you will be told exactly which grab is most suitable for handling it.
When handling materials with a large particle size, it is necessary to fit penetration teeth
welded to the outside of the sealing lips.
In order to have a criteria of granulometries of materials for which they are necessary, we give a simple and informal idea:
If the granulometry is the size of an APPLE, it is convenient to place penetration teeth.
If the particle size ranges from sandy fine to walnut size, then it is not necessary to use them.
Sometimes the material is in a very compacted state at the bottom of ship holds or storage pits. In this case it is also necessary to fit penetration teeth.
Teeth allow a better penetration of the shells into the material to be handled, performing the SCRAPPING function and facilitating the dragging towards the interior of the grab and achieving optimal filling.
Crane power is indicated on the Technical Data Sheet
MAXIMUM LOAD taken and the WEIGHT of the grab are also shown.
The addition of both values determines the value of the CRANE POWER.
Maximum average load is indicated on the Technical Data Sheet.
The load data indicated in the table are real data taken from real experiences.
On the Technical Data Sheet, CLOSING and EMPTYING times are indicated.
The sum of both times gives the TOTAL OPERATING TIME.
There are other times to consider, such as the lifting and lowering of the hook, the movements of the trolley and the movements of the overhead crane inside the building.
Pause times before returning to the starting point to pick up a new load must also be considered.
All these times add up to the TOTAL TIME OF EACH CYCLE.
Production is a function of the number of TOTAL CYCLES carried out by the crane.
Multiplying the number of cycles carried out by the average maximum load that it takes in each operation, the TOTAL PRODUCTION is obtained.
The compaction factor is the ratio between the apparent density of the loose material and the resulting density after all the material has been collected inside the grab when the jaws are closed.
The volume of material picked up and dragged is a function of the kinematic design of the grabs and the compaction is a direct function of the penetration force of each grab jaw.
The degree of compaction also depends on the characteristics of the material, such as density, granulometry, moisture......
The usual degree of compaction in STEMM grabs is a factor varying between 1.9-2.5.
To calculate the load to be taken by a grab, the bulk density of the material is multiplied by the compaction factor.
The closing and opening orders are sent to a 3-position, 4-way solenoid valve which sends the oil from the pump to the hydraulic cylinders.
Standard coils of the solenoid valves are 24 VDC, the most common, but other voltages are available on request.
Optionally, the closing and opening manoeuvres of a grab can also be carried out by the REVERSAL OF THE DIRECTION OF ROTATION of the electric motor.
In these cases, the pumps installed are totally reversible and there are no solenoid valves.
The grab is always supplied with a COMPLETE SOCKET, Male + Female.
The multipolar electric cable coming from the reel, which is not included in the supply.is connected to the female part.
As for the reel, the supplier will define whether it is spring-loaded or electric motor-driven.
The following data must be provided to the supplier of the electric reel:
- Maximum vertical travel of the crane hook -Lifting and hoisting speeds
- Lifting and lowering speeds of the hook
- Power of the electric motor installed in the machine; column (5) on the Technical Data
- Characteristics of the electrical cables
STEMM supplies all kinds of details and electrical diagrams prior to the manufacturing of the electrical cabinet installed in the machine.
This information is transmitted to the customer or to the crane manufacturer, whose agreement and conformity is requested.
It is a question of perfectly coordinating the electrical installation in the crane cabin with all the manoeuvre controls that will be carried out inside the grab.
STEMM clamshell grabs have a very robust DOUBLE mechanical SYNCHRONISM installed on both sides of the shells, which ensures perfect synchronism and simultaneous, regular and uniform closing of both shells in the closing and opening manoeuvres.
Stemm grabs for amphibious conditions are designed, calculated and manufactured to work in marine environments up to a depth of 100m.
Watertightness is checked and certified after intensive tests with the intervention of external entities such as Lloyd's, TÜV, D.N.V. BUREAU VERITAS and similar.
The superficial treatment is very specific, with an initial shot blasting and subsequent priming and finishing coatings with thicknesses of 250 microns.
Electrical connection is made with IP-68 multipolar plugs with a DOUBLE SAFETY SYSTEM in case of snagging and breakage at the bottom of the sea.
This double safety consists on a MECHANICAL CLAMP that secures and prevents the female part of the plug, connected to the electrical cable, from loosening from its connection to the male part, placed on the machine.
There is a second safety feature which, in case of breakage of the plug due to impact or breakage and section of the electric cable, prevents the entry of water through the internal wires of the cable, which could reach the machine.
This is achieved by placing a SAFETY AND INSULATION CHAMBER between the plug itself and the inside of the machine, totally sealed with a BICOMPONENT SILICONE paste.
OUTCOME: WATER CAN NEVER ENTER INSIDE THE MACHINE.
All our machines are designed to guarantee maximum safety even in the event of a power cut.
Should this be the case, the grab is automatically locked in the position it was. The load inside it NEVER FALLS.
There are simple manual methods for unloading and emptying the contents.
On all STEMM grabs, all the claws and shells joints are grease-free and maintenance-free.
Optionally even the electric motors can be supplied with lifetime lubrication, maintenance-free.
Oil changes on STEMM machines can be done after very long periods of time, more than 4000 hours, thanks to a patented automatic system, which constantly performs a 3 micron filtering, which always keeps the oil in the tank clean.
The delivery times for all spare parts and commercial components are immediate, as we have them in stock in our warehouses.
If it is a machined component or non-commercial part, the maximum delivery time is 1 week.
Optionally, all the machines can be equipped with sensors that register data on PRESSURE and TEMPERATURE when the machine is working and performing operations.
These data are transmitted nonstop via BLUETOOTH when the machine is working or at rest, in neutral, but with the motor running.
This data can be read on a mobile phone at 50 meters from the machine, without physical contact and without having to access the interior of the hydraulic unit.
- All the equipment is calculated to fatigue by means of the ANSYS Finite Element Analysis
- Design and construction according to F.E.M. 100/98 category A8/M8 standards.
- ISO 9001:2015 quality assurance and quality management certification is in place
- All machines are tested and proven prior to shipment.
- A 2-year Warranty Certificate is issued for all machines.
STEMM's highly experienced engineers and project managers design and adapt the project to your needs, always offering the most suitable solution.
After each study, the project is shared with the customer and their approval is requested before manufacturing begins.
There are two assembly and manufacturing plants located in Spain and France, close to the border, but there is a third plant also located in Spain, in the BASQUE COUNTRY, where the FINAL ASSEMBLY, TESTING AND TESTS are carried out before shipment.
We have manufacturing licenses granted to companies in Turkey, India and Brazil.
STEMM grabs are used in all types of sectors, such as the iron and steel industry, the environment, incinerators, biomass plants, public works, ports, cement works, etc...
Thousands of machines have been built since 1986 in countries all over the world.
The main difference of the STEMM brand is the quality, the protocols of tests and trials, the 3 year guarantee and above all the constant and continuous 24/7 assistance service.
But there are other Differentiating Technical Features which can be examined by clicking on the link.
RENOVE service allows the replacement of hydraulic power units, hydraulic cylinders and joints.
The repaired machine is supplied completely refurbished with a perfect primed and painted finish, tested on our test benches, with a 2-year guarantee.
Yes, twice a year, training courses are given for groups of 20 people.
The duration of each course is 32 hours with a basic electrical, oil-hydraulic and mechanical content.
After many years of compiling the experiences of both our engineers and the personnel who participate in the courses, we have published ANALYSIS AND INCIDENT SOLUTION MANUALS which are distributed to the attendees.
Both the manuals and the courses are free of charge, but a financial contribution is requested for the Professional Schools of the Basque Country.
When there is an order in progress, STEMM can provide drawings on request of all the machines in STEP format to be integrated by the customer or engineering in the project assemblies.
All general dimensions and weights are indicated on the Technical Data Sheet.
For orange peel grab dimensions, please refer to dimensions A, C (length, width).
For dimensions of clamshell grabs refer to dimensions D, B, E (length, height, width).
All machines are shipped from our main workshops located in:
STEMM EQUIPOS INDUSTRIALES, S.L.
POLIGONO IBARLUZE, PAB. B-9
20.120 HERNANI (SPAIN)
Clamshell grabs are shipped open mounted on pallets or in closed boxes.
Orange peel grabs are shipped closed and lying down.
If the transport is by sea, STEMM carries out the appropriate protected packaging.
When the transport is to be carried out in a container, STEMM staff will take care of the positioning, adjustment, strapping and fastening inside the container.