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TECHNICAL INSPECTION OF JACKS
Each rack, screw and hydraulic jack must have a technical passport of the manufacturer and a plate indicating the lifting capacity.
Jacks in service are subject to technical examination and testing in accordance with clause 5.53 SNIP ΙΙΙ-Α.ΙΙ-62 at least after 12 months.
The test of jacks during the technical examination must be carried out for a static load exceeding the maximum rated carrying capacity by at least 10%. The jack must be under this load for 10 minutes, and the screw (rail, rod) must be extended to the uppermost position. Have hydraulic jacks by the end of the test, no more than 5% pressure drop is allowed. The test results are entered in the passport.
UNIVERSAL STAND FOR TESTING RIGGING EQUIPMENT
In fig. 5-7 shows a universal stand designed for testing blocks, hoists, jacks and mounting belts for a maximum load of 15 tons.
Figure: 5-7. Universal rig for testing rigging equipment,
The stand consists of a reinforced concrete foundation on which two supporting I-beams 1 are fixed. Two pipes 2 0 219X4.5 mm, 12 m high, are installed on the beams' consoles.
A crossbar 3 moves along the pipes, on which a dynamometer 4 is fixed, two rods 5 are also fixed to the crossbar for testing jacks. A fixed block is attached to the upper beam 6, a winch 7 is installed on the beams 1. A plate 8 is welded to the consoles of the beams 1, and plate 9 is welded to it, in which, as in the cross member 3, there is a hole for the thrust, with which they can be connected to each other with a friend.
When testing slings, blocks and hoists, this thrust must be installed, and when testing jacks it is removed.
The load on the tested slings, blocks and jacks is created by a winch through a chain hoist system; the load on the hoists can be created by the hoists themselves The load is indicated by a dynamometer.
TO Category:
Operation of installation equipment
Technical examination and tests
The technical examination of all accessories for all cranes and lifting mechanisms without exception, as well as cranes that are not subject to inspection by the Gosgortekhnadzor inspection, should be carried out by the technical administration of the enterprise that operates the accessories and lifting machines.
The technical survey aims to establish that:
1) a crane or a lifting mechanism is built and equipped in accordance with the rules of the Gosgortekhnadzor and its auxiliary devices correspond to their purpose and the documentation submitted for registration;
2) the crane or hoist is in good condition;
3) supervision and maintenance of the crane or lifting device, as well as its maintenance, is carried out by persons who have undergone special training and passed the test.
At each technical examination, the following should be checked:
1) the condition of metal structures and welded, riveted or bolted joints;
2) the condition of the hook and the details of its fastening in the holder or traverse;
3) the condition of the ropes and their fastenings;
4) the condition of the axles, their attachment parts, as well as the boom elements;
5) the state of grounding at electric cranes;
6) compliance of the weight of counterweights and ballast with the passport;
7) the condition of the crane runway and its compliance with current regulations.
Periodic partial technical inspections of cranes should be carried out at least every 12 months; full, once every three years.
Rarely used mechanisms undergo a full technical inspection once every five years.
Technical examination is also carried out in the following cases:
a) after transferring the lifting machine to a new place of work;
b) after reconstruction or major repairs;
c) after partial replacement of the main structures;
d) after changing the hoisting mechanism, hook or carrying ropes.
With a full technical examination, inspection, static and dynamic testing are performed; partial inspection only.
During the inspection, all mechanisms and electrical equipment, especially brakes, control equipment, safety and signaling devices, the condition of the metal structures of the machine and its welded and bolted joints, the condition of the hook and its fastening parts, the condition of the ropes, blocks, axles and parts should be inspected. fastening of pulley blocks, condition of grounding and crane runway.
Static testing of lifting machines during the initial test or after reconstruction or overhaul is carried out by lifting a load 25% higher than the rated load capacity (lifting by 200 mm); during periodic tests - with a load exceeding 10% of the lifting capacity, with a simultaneous inspection of the crane or lifting mechanism. With variable load capacities, the test is carried out in the position corresponding to the highest load capacity. During the test, the load remains suspended for 10 minutes.
Elastic deformation under the action of the ultimate working load should not exceed the permissible norms; permanent deformation is not allowed.
Dynamic testing consists in repeated lifting and lowering of the largest working load or a load exceeding its weight by 10%, while testing all moving mechanisms, automatic stops and limit switches.
The lift limiter must be tested when lifting a rated load and a load 10% heavier than the rated one, in the following order: lifting and lowering the load; lifting and lowering the boom with a load; rotation of the boom with a load by 360 °.
If the machine allows a combination of operations, it is tested during combined operations with verification of the correct operation of individual units. The results of the technical examination are recorded in the passport of the lifting machine.
Test of screw and rack jacks load optional. Their technical examination is carried out by inspection. A jack with screw or nut thread wear in excess of 20% is not allowed for use. Static testing of pneumatic and hydraulic jacks is carried out with a load exceeding their rated lifting capacity by 10%, with holding in the extreme upper position for 10 minutes:
Static testing of pneumatic lifting cylinders is carried out at the extreme upper position of the pistons by suspending a load weighing 10% higher than the rated lifting capacity.
Testing of ropes and chains of lifting mechanisms and cranes is carried out by the manufacturer with the recording of the results of this test in the certificate. In the absence of a rope or chain certificate, they must be tested in a laboratory. Untested ropes and chains are not allowed to work. The test of chains and ropes is carried out simultaneously with the test of the crane or mechanism once for the entire chain or coil of rope, each section of the rope being supplied with a certified copy of the laboratory test certificate. Ropes are not tested separately. Pull chains and ropes, as well as other removable accessories, are tested with a test load of 1.25 times the permissible working load, and, in addition, are periodically inspected. Periodic inspections are carried out at least every 6 months for traverse, after 1 month for other grips and every 10 days for slings. The inspection is carried out by the person in charge of the service. The results of the inspection are recorded in the register and inspection log of load gripping devices.
Responsibility for maintaining good health and safe action cranes, lifting mechanisms and removable accessories are carried by an engineer and technical worker, who is entrusted with this by order of the enterprise management. His surname and position are entered in the crane's passport. All tests and inspections of lifting devices are carried out by this person.
TO Category: - Operation of installation equipment
Jack (from the Dutch dommekracht) - a mechanism for lifting heavy piece loads when performing repair, installation or loading and unloading operations (Great Soviet Encyclopedia)
"BOTTLES"
Jack (from the Dutch dommekracht) - a mechanism for lifting heavy piece loads when performing repair, installation or loading and unloading operations (Great Soviet Encyclopedia). The range of application of modern jacks is wide and is limited, perhaps, only by your imagination. But you and I are motorists, and which motorist has never changed a punctured wheel of his car at least once? Naturally, the first assistant in this situation is the jack. And of course, many of you will object that, they say, is there to think: there is a standard device, set it up, raised it, changed the wheel and went? But is a regular lift so convenient and so safe? And how much effort should be applied to lift at least a passenger car? Let's try to figure it out a bit.
What are the jacks
Screw jack. This is the same jack that the VAZ family cars were equipped with. Its main drawback is that it is very high, and besides, it has a support platform for a special groove under the threshold of the Zhiguli, so there is no need to talk about universality. In addition, to install it, a certain skill is required, because even small deviations from a given axis are unacceptable here. The only advantage of this jack is the lifting height.
KING TOOLS Hydraulic Jack Test
Judging by the designation on the box, this strongman was produced in the Arab Emirates, but the inscription on the case Made in China betrays his true origin. The first impression is not very good, it is spoiled mainly by the packaging with simple printing. No plastic case provided. In the box lay the jack itself, two pipes connected by plastic holders, and an instruction in which there was not a word of Russian. Below is a diagram of the device with a cross-section and designation of the main elements, however, due to low-quality printing, it is very difficult to understand it.
The jack is covered with red paint, which, when checking the product in the store, began to fly around the return screw of the housing near it. There is a sticker on the body of the jack with the name, designation of the rated lifting capacity and a warning on english language... To return the jack to the downward position, there is a screw with a longitudinal hairpin, to which special grooves in the thicker handle cling. The same handle is used to raise the jack. The thinner tube serves as an extension for the lever. The rod of the jack has a screw that is unscrewed relative to the base by 6.5 cm. The stem itself extends 9.5cm. Jack body height 15cm. Thus, the total working height in the maximum raised position of the stem and screw is 31cm. The upper support platform has two criss-cross grooves and a fairly small size (its diameter is only 2 cm). The base of the jack has dimensions of 9.4 x 8.4 cm (area 78.96 cm2). During operation, the stem extends with noticeable dips.
Test results
During the tests, it was found that this sample requires maximum effort on the lever to overcome the load v2t as much as 60.3 kgf. The change in force over time for this jack was 5.7% of the initial value — an average result. Where this strongman surprised us was during the tests for the maximum breaking moment: the jack broke only under a load of 8.83 tons as a result of the large bending of the threaded extension. On the whole, this rather crude tool showed good results against the background of competitors, especially in maximum load. We must admit that we did not expect such records from this sample.
TOYA - Hydraulic Jack Test
At first glance, the Polish lift made a good impression. It is packed in a convenient plastic case, which, however, is made quite rough. Inside the package, we found the jack itself and two tubes, one of which is used to drive the elevator, and the other to open the operating valve. In addition, the package contains detailed instructions in 10 languages, including Russian and Ukrainian.
The jack is painted in metallic gray, the paint flies around only the working valve screw when the key tube is in contact. The decal on the body contains information about the manufacturer, model number, product name, rated load, as well as minimum and maximum lift. The serial number is glued to the bottom. On the base of the body, which has a rather rough rough surface, there is a screw for the drive of the working valve, the drive for the lift pump and the safety valve. The latter has a red plastic plug with the inscription Do not adjust. Adjustment of the safety valve is prohibited by the instruction. An extension screw is installed on the jack rod. It is unscrewed relative to the base of the stem by 5 cm. The rod itself extends 12.2 cm from the top base of the jack. The height of the case is 17cm. In total we get a maximum working height of 34.2 cm. This value falls short of only 3mm to the declared specifications of 34.5cm. The upper support platform has a diameter of 2.5 cm, and there are notches on its surface that prevent the load from slipping. The base of the jack has dimensions of 8.4 x 8.9 cm and a total area of \u200b\u200b74.76 cm2. The stem extends smoothly, without failures and fragments.
Test results
This sample at the first stage of testing yielded only to the jack from "Sorokinstrument". The maximum load on the handle for lifting a load weighing 2 tons was 52.2 kgf. The average load of the safety valve actuation is 22.7 kN. The change in strength over time is relatively small, 5.7% of the initial value. The result of loading before failure is not bad — 8.06 tons.
In all respects, this jack is a solid average. You can use it, especially considering the presence of a convenient case.
Big Red Hydraulic Jack Test
The commercial appearance, frankly, is nondescript: an ordinary white box with a jack pattern glued on and small logos. On a small store sticker in the corner of the box, the country of origin (USA) is indicated in the name of the product, but we could not find any further designations of the origin of the product. On the Internet, contradictory information was found: either China or the USA ... Inside the package we were waiting for the usual set: a jack, two pipes and instructions. The latter, albeit inconspicuous, on one crumpled sheet, but completely in Russian and contains the rules of use and maintenance, an explanatory diagram showing the designation of the main elements, technical data and a troubleshooting table.
The jack is coated with a fairly durable red paint, has a lift pump, a pilot valve drive screw and an oil reservoir plug. On the body there are two stickers, one with the manufacturer's logo, the other with warnings in English. The stem is topped with an extension screw with an extra-large bearing plate. The upper support has a fairly small diameter - only 2cm but, unlike King Tools, a deeper notch on the surface. The extension screw is unscrewed relative to the upper cut of the stem by 5 cm. The stem extends 12cm from the body. The body itself has a height of 17.3cm. Thus, the maximum working height is 34.3 cm. The jack support base measures 7.7 x 8.7 cm and an area of \u200b\u200b67 cm2. No jerks or dips were detected during the operation.
Test results
At the first stage of testing, the Big Red jack showed a good result: the load on the handle to overcome the weight of 2 tons was 53.2 kgf. When tested for the change in force over time, this sample won an honorable second place with a result of 4.8% of the initial value. On the other hand, Avot for maximum breaking load is the second result of the end. With a load of 7.66 tons, the extension thread was cut off, after which the rod simply fell out of the cylinder.
In terms of stability of characteristics, this jack seems to be not bad, but the result of the destruction test crossed out all the advantages.
MATRIX - Hydraulic jack test
The jack of the German company Matrix is \u200b\u200bmanufactured in Shanghai, which honestly says a small sticker on the package. This strong man is hidden away in a convenient black plastic case, on which high-quality printed labels flaunt with comprehensive information about the product in Russian. I was surprised only by the lack of instructions inside the suitcase. But in addition to the usual pipes for the pump drive and control valve, the kit contains a repair kit with four oil seals and gaskets.
The jack is painted in metallic gray, and for some reason the paint turned out to be on the plastic cap of the safety valve. In addition to the safety valve, in the lower part of the jack body there is a lift drive pump and a control valve screw. Above, on the cylindrical part of the body, there is an oil reservoir plug. The extension rod on the stem is unscrewed by 5cm. The stem rises by 12cm, the jack body has a height of 17cm. The total maximum working height is 34cm. The upper support platform with a diameter of 2.5 cm has a deep notch. The lower base is quite smooth and even, measures 7.7 x 9 cm and an area of \u200b\u200b69.3 cm2. Rise of the rod is even, without failures and fragments.
Test results
To lift a load weighing 2 tons, this sample required a tangible 54.6 kgf (not the best indicator). The safety valve worked at a load of 21.7 kN. The change in strength is also quite noticeable and amounts to 5.7% of the initial value. When tested for maximum destructive force, the Matrix jack turned out to be an outsider of the test: 7.36 tons, while, like a Big Red jack, the extension cut off and the rod fell out of the cylinder.
Good looks and neat execution cannot outweigh such poor results.
MEGA POWER - Hydraulic jack test
When we put two boxes next to each other: with this product from Big Red, we did not find any differences between them. The same packaging, the same stickers, only the names of the companies are different. Inside the nondescript box, instructions are absolutely identical to the sample from Big Red, printed, it seems, from a single file. There are still design differences between the samples. The Mega Power jack looks better. It is covered with a dark green and extremely resistant paint. There is a curved sticker on the body with the logo of the company, brief description products in Russian and a reminder that the jack was made in Germany. On the base of the body, in addition to the pump and the control valve screw, there is a safety valve with a red plastic plug and the Do Not Regulate warning label. On the case, there is also an oil reservoir plug. The jack rod rises from the upper cut of the body by 12 cm. The extension screw increases this value by another 5cm. The height of the case is 17.3cm. Total working height 34.3cm. The top pad is 2.5 cm in diameter and has a deep notch on the surface. The lower base of the jack is smooth and smooth, measures 7.7 x 8.7 cm and an area of \u200b\u200b67 cm2. No jerks or failures were observed during the lifting of the rod.
Test results
To overcome the weight of a 2-ton load with the help of this jack, it was necessary to put on the handle not at all small 54.7 kgf. The twin of the Big Red brand in the same test turned out to be more loyal to the coprator. The safety valve was triggered at 20.7 kN. The drop in strength is 6.7% of the initial value (the second end is the result). Well, apo the destructive force, this jack showed not the worst result: at a load of 77.8 kN, the threaded extension was cut.
Average test results, slightly lower than the "fellow", but not the lowest. You can work with this jack.
KAMASA-TOOLS - Hydraulic jack test
The tool from the renowned Swedish manufacturer is positioned as a professional one. It will be all the more interesting to find out whether this jack is so good in comparison with other samples. In addition, it was not so easy to find it for free sale, and the price is twice as high as that of the rest of the jacks.
The first thing we see when we pick up this splash jack is the box. It is the box, not the plastic case, which does not honor the well-known manufacturer. Step-by-step instructions for use are applied on the colorful packaging of the corporate green color, technical specifications, as well as a footnote according to which the jack can be used in any position (vertically, angled and horizontally). Inside the box were found a neatly laid jack, tube-levers in a separate package, an arduous instruction in several European languages. Unfortunately, there was no Russian.
Structurally, this jack is very similar to the King Tools model, but it has a more durable paint coating in comparison. However, the overall workmanship looks better than other samples. The pilot valve screw here, like the King Tools jack, has a transverse pin that engages the slots in the actuator lever. The thin tube fits snugly enough in the same groove on the lever and is used as an extension. On the cylindrical part of the jack body there is a sticker with the brand designation and recommendations for use in English. The lower housing contains the drive pump, pilot valve screw, and relief valve, which is fitted with a bright red plug with an English “Do Not Adjust” cap. According to the description, the maximum height of the jack is 33cm. What is in practice? The extension screw is unscrewed by 7cm, the stem extends to a height of 9.7cm from the upper edge of the jack body, the body has a height of 15cm. In total, we get 31.7 cm, which is slightly below the declared value. The upper support platform has a diameter of 2 cm and two cross-grooves. The lower surface is quite smooth and even, its dimensions are 8x 9.5 cm and an area of \u200b\u200b76 cm2. The process of lifting the rod is smooth, without failures and fragments.
Test results
We expected an unconditional victory in the test from a professional tool representative, but were disappointed. Already at the first stage, this sample showed only the penultimate result. To lift a load with a mass of 2 tons on the handle, it will be necessary to develop 59.8 kgf (whether this is a lot or a little - judge the consumer, we are just stating a fact). The force of the safety valve actuation is 24.4 kN (average value). The re-jack made us wonder when the force drop test was 6.9% (worst result!). The only thing in which the KAMASA-TOOLS jack managed to prove itself was its resistance to the maximum load: destruction occurred at 87.9 kN (bending of the threaded extension).
Comparison with other samples does not allow us to reproach us with excessive loyalty to global brands ...
Other jack tests:
WORKING WITH THE JACK
Order on the appointment of persons in charge when working with a jack
For the purpose of safe operation and organization of maintenance of the jacks available at the enterprise, in accordance with the requirements of regulatory and technical acts regulating work with devices, "Rules for working with tools and devices", approved. by order of the Ministry of Labor and Social Protection of the Russian Federation of August 18, 2013 N 552n,
I ORDER:
1. Appoint persons responsible for the organization and safe work with jacks, for the maintenance of jacks in good condition:
- Filatova A.A., mechanic of the transport department,
- Tulumbayev A.A., head of the boiler room.
2. Responsible persons appointed in clause 1. of this order:
2.1. Carry out maintenance, repair, technical inspection of jacks in accordance with the requirements technical documentation manufacturer;
2.2. Check the serviceability of the hydraulic jack before each use by conducting an inspection;
2.3. Ensure the presence of a plate on the body of the jack indicating the inventory number, carrying capacity, date of the next technical survey;
2.4. Carry out periodic technical inspection of jacks in operation at least once every 12 months, as well as after repair or replacement of critical parts. Technical examination of screw and rack-and-pinion jacks shall be carried out by inspecting them without static test... Technical examination of pneumatic and hydraulic jacks shall be carried out by inspection and carrying out a static test;
2.5. Do not allow faulty jacks or jacks that have not passed the technical examination;
2.6. The results of inspections, repairs, inspections, tests and technical examinations of jacks shall be entered in "";
3. The organization and performance of work with jacks in order to ensure the safety of workers performing them, and persons in the area of \u200b\u200btheir production, should be carried out in strict accordance with the normative documentation on labor protection (clause 43 of "Rules for labor protection when working with tools and devices" ).
4. Control over the execution of this order shall be entrusted to the chief engineer A.A. Vasiliev.
Director P.P. Pavlov
Testing of off-road rack and pinion jacks
Nowadays hi-jacks of two brands are on free sale: the American Hi-Lift and the Russian Sorokinstrument. Experienced jeepers will probably have Canadian Jack-All, but you won't find them on the shelves and in the price lists for a long time. And even at the time of its active presence in the Russian market, the area of \u200b\u200bdistribution of "Canadians" was not so wide as to take them into account in our test. Today they are rather collectible rarities, and not a tool of "off-road labor". As well as hi-jacks from other manufacturers, which were never officially supplied to us and came across in single copies. And this is despite the fact that among the latter there may be interesting models for research (for example, Tiger Jack from the American "Maasdam Pow'r-Pull Inc." - they are given a lifetime warranty). In general, today we decided to focus only on models that are available to the Russian buyer.
Hi-Lift Jack Company manufactures two types of rack and pinion jacks. According to the manufacturers, the "red series" is completely made of cast iron, with the exception of the steel handle, bolts and support pins. In the "black" part of the parts, including the support platform, the upper eyelet and some levers of the mechanism, are steel. Reiki, according to the manufacturer, is the same for both options. The prices are almost the same (the black model costs $ 5 cheaper than the red one of the same length). Despite this, each color has its own adherents and, according to the reviews of sellers, there are even regional preferences. So, Moscow mostly buys red high-elevators, but they almost stopped taking them to the Urals - only black ones ask. In short, both here and there they consider "their" color stronger.
Those who are trying to save money (regardless of geography) opt for the hi-jack offered by the Sorokinstrument chain of stores. Their jack, which was previously sold under the name "farm jack", and now has become just a "hi-jack", costs about one and a half times cheaper than the "lift". By design, it is similar to overseas competitors, except for the nuances. So, the handle here is made non-separable, and not bolts and nuts are used as the axes of the levers of the mechanism, but cotter pins. In this case, the rail is fastened to the sole, on the contrary, by a bolt. In addition, in this model, the end of the handle is covered with a rubber cover, and the role of its lock in the vertical position is played by two plates welded to it. By the way, as practice shows, over time they unbend and stop performing their function. The curly spring ring, designed for the same purpose in the "Americans", has proven to be more reliable.
Since we have touched on " national question", Let's dwell on it in more detail. The origin of Hi-Lift jacks is beyond doubt: Bloomfield, Illinois, USA. Their competitor's pedigree is not so clear. The passport, recently attached to the Sorokin hi-jacks, states: "Manufactured by Torin Jacks Inc., USA", and this despite the fact that these same instruments were previously sold as Dutch! And although evil tongues will claim that they are stamped in China, in order to avoid confusion in terminology, we will conventionally call the Sorokin jacks "ours", since they are sold under a domestic trademark.
For testing, we took the three longest versions of each model: HL-604, HL-605, and 5.8605. At first glance, jacks are very similar. Close overall dimensions, similar design, the same principle of operation, and the rails are completely interchangeable. Indeed, profile dimensions the subjects are very close, and the distance between the holes of the slats is the same in all three specimens. The only thing that is striking is the difference in the design of the handles of the representatives of competing brands and the stamped flat top eyelet of the HL-604 adapted exclusively for attaching the cable. "Red-skinned American" and "our", on the contrary, are able to work as presses (clamps) due to the fact that, being turned across the rail, their powerful upper eye becomes a reliable stop. But there are also nuances, so if Sorokin 
the lug is constantly in the "clamping" position (the configuration features do not allow turning it over in another way), then in the cast-iron Hi-Lift it rotates around its axis without any problems, which simplifies both transportation and work as a winch.
The first test was lifting a heavy Toyota LC on a country road ... All three jacks of course coped with this task. The wheel was suspended high enough to be changed, and the car remained stable. With the further rise of another thirty centimeters in all cases, the balance was disturbed and the car smoothly slid to the side. In general, everything is as it should be on an uneven surface. However, interesting moments have already emerged here. So, 
the mechanism of the "black American" we inherited refused to move freely up the rail, and it had to be "pumped" even without load, and the "sorokin" had an elastic band falling off the handle. However, we attributed both to the individual shortcomings of specific specimens (completely curable in capable hands). However, they can be used to indirectly judge the stability of quality and production culture. But the paint peeling off in shreds on the "elevators" and the falling out cotter pins at the "farm" are, alas, statistics that are repeated on almost every copy. If we talk about the convenience of work, then we did not notice much difference between the three models. Except that the effort on the handle when lifting the car by "our" hi-jack subjectively seemed a little more than that of the "Americans", and the work of the mechanism - a little harder.
Our measurements
* from the axis of attachment
** without rubber cover
The correctness of our feelings was also confirmed by an impartial technique ... Measurements in a special laboratory of NICIAMT showed that the lever mechanism of each of the hi-jacks transmits the effort developed by the handle to the lifting platform in a different way. The maximum gear ratio was found in the black (steel) Hi-Lift, the minimum - in the Sorokinsky. The difference was about 15%. At the same time, the characteristics of the red (cast-iron) "American" are located approximately in the middle. Along the way, some nonlinearity of the characteristics of the conversion of effort was revealed for all three jacks. The more you load the handle, the higher the gear ratio of the entire mechanism is. Most likely, this is due to the change in the force vector during the working stroke of the handle and levers.
Along the way, we took another measurement: what is the maximum effort a person can develop with the help of a jack. Tellingly, in each approach, different results were obtained even with the same tester. The lift proved to be very sensitive to how the “operator” stands, how he holds the handle, and even more so how he presses on it. However, no matter how hard we tried, no one managed to lift more than 2.5 tons. According to our calculations, taking this weight would require a hero with a mass of about a centner, and there was no such in our company that day ...
Now try to guess what a normal jeep will do if he needs to lift more than his own strength allows. There are two answers. He will either call another jeep for help and they will take the weight together, or simply lengthen the handle with a piece of pipe and win on his own. Yes, despite all the warnings in the instructions for the jacks that you can't do this, that's exactly what everyone does. And where to go if there is no other chance of salvation from the mud? We simulated such a situation by lengthening the handle to 190 cm. The laws of physics did not lie: it became several times easier to work. Now you can feel the lifting capacity of the jacks (in all cases declared by the manufacturers at the level of three tons) ...
Again we clamp the jacks in turn into a special stand with weights and now we press on the handle until something breaks. All three mechanisms are set at the same height - 1160 mm to the plane of the beak (in other words, in the upper part of the rail, a few clicks to the maximum), and the handles are lengthened. It is in such situations that the slats usually bend and mechanisms break off on the off-road ... Our laboratory experience differs from the jeep realities only in that we put each jack strictly vertically on a flat plane for a long time, simulating an ideal situation.
Black Hi-Lift was the first to hit the block. When the load on the beak approached the 2750 kg mark, the lateral deflection of the staff became visually noticeable. However, as the pressure on the handle increased, the lifting mass continued to increase, and soon the scale arrow crossed the three-ton mark. The deformation of the rail became more and more noticeable, the handle was slightly bent, but the jack continued to do its job. Only at around 3300 there was a crash, something flew near my ear, and the hi-jack collapsed. It turned out that the bolt, which performs the function of the supporting axis of the intermediate lever of the mechanism, could not stand. The lever, bent from a steel plate, simply cut it like scissors in two places (one of the pieces went free flight). At the same time, the mechanism flipped to the "descent" position, and the jack lost its balance. If he had a car, she would have fallen! As for the rail, despite a very noticeable bend during the ascent, it returned to its original state and again became perfectly straight ...
Now it's the turn of the red "elevator". On his account there was a suspicion that the thick cast lever would not be able to quickly cut the bolt and the jack would last longer (of course, if another part did not break). However, in terms of behavior under extreme loads, this specimen turned out to be similar to its black brother. At about the same figures, a lateral deformation of the rack appeared on the scales and began to gradually increase. However, we did not wait for the bend of the handle. But the already familiar bolt broke, but, as expected, a little later. Beyond the 3500 kg mark. At the same time, the mechanism flipped and fell down. What does a jeep in the forest do in such a situation? Finds the first hardened pin that matches the diameter, and again gets a workable hi-jack. However, the instruction for Hi-Lift explicitly prohibits such repairs, requiring only the original spare part from the repair kit to be installed. The fact is that the fracture of this bolt with the calculated strength is programmed by the manufacturers as a kind of fuse, preventing more serious damage to the jack during overload. In both cases, it worked. There are no other obvious defects that prevent the use of jacks.
Now it's the turn of Sorokinstrument. He has a thicker pin in place of the bolt. I wonder if he also serves as a fuse or will we see a different scenario? We push! After 2600 kg the rail bends slightly, but not across, but ... along the long side. We press it to almost 2800 kg - and here the handle becomes fluid. In this case, the load drops again by 2600 kg, but the jack maintains balance and continues to stand as if nothing had happened. The handle is bent in a half-ring, but not an ounce of sense. Had the jack sustained the declared three tons, this "overload" option would have been the best - the safest, at the same time visual and preserving further field operability of the instrument without any urgent need for repair (the rail, as in the two previous cases, straightened out after removing the load).
So, the first execution was tolerated by all three copies. After a minute of repair, the "Americans" are ready to return to service, "our", albeit with a crooked handle, is fully operational. So what kind of load is needed to make the "irreparable" happen?
The answer to the question asked was given by the last test. Weighty, rough and visible ... We decided to simply load the jacks with a mighty press, resting the heel on one plate, and the beak on the other. We bring the mechanisms almost to their full stroke - 1260 mm, and before starting the experiment, we fix each of the jacks in the press, strictly observing the vertical and horizontal position.
I must say, the results of this test puzzled us greatly. The black "lift" proved to be the most persistent. The rail was bent, but held for a very long time. Only at a load of 3600 kg there was a loud bang, like a shot, and the jack folded across the rail. We expected something like this. But the behavior of the cast-iron "elevator" puzzled us - it simply and softly folded when the load reached only ... 1700 kg. "Sorokinstrument" was not much stronger: its rail could not withstand the load of 1750 kg and also formed, but more sharply.
In an attempt to explain what happened, or rather, the sudden weakness of the two red competitors, we settled on two versions. The first is that during the previous test we practically overcame the stability limit of the rails, and irreversible deformation, which was imperceptible to the eye, occurred in them, possibly even with a change in the metal structure. Therefore, the fuse only worked correctly in the “combined” Hi-Lift. The second version - when the press moved in two cases, the position of the jack was violated and it moved relative to the position initially set in terms of level and plumb line. That is, it actually acquired a slope while continuing to increase the load, simulating a situation when the car is already starting to collapse, but it is still being raised. Such a significant decrease in carrying capacity in this case is explained by a change in the pressure vector.
What conclusions follow from this? In our opinion, the situation is quite obvious. Everything can be broken. But even if we take into account the likelihood of quality differences between different batches of the same brand, the strength of Hi-Lift is objectively higher than that of Sorokin. At the same time, for most SUVs, any of our three will work, just as we would not recommend one for pulling a truck. As for the features of the application, they are also similar: remember that the warnings about replacing safety bolts and lengthening the handles in the instructions are not written for the sake of an elegant style.
But it makes no sense to edit an already bent rail. It's like editing a bent nail. It is impossible to make it perfectly even the second time. In addition, during the appearance of irreversible deformation, the structure of the metal is disturbed and the carrying capacity becomes much less.
Chemical attack.
To comment on the results of the experiments and to conduct a spectral analysis of the material of the laths, we asked the metallurgists from the N.N. academician Bochvar. Experts considered both of our assumptions about the difference in loads sustained by each of the hi-jacks in the first and second experiments to be correct. The conclusion about the fatigue of the metal after the first test, according to the authoritative opinion, is more suitable for ideal laboratory conditions than the suspicion of displacement of the test sample, fixed in the press.
As for the material from which the slats are made, the result of the analysis surprised us. In terms of chemical composition, all three slats turned out to be very close, although not absolutely identical. But the material turned out to be steel. Moreover, the most ordinary, unalloyed. According to metallurgists, there can be no talk of any cast iron declared by both manufacturers with a carbon content of less than 0.5%. Cast irons should contain this element in the range of 2-4%. But this is good - a harder, but brittle cast iron would hardly withstand a much greater load, but if deformed, the rail would not bend, but broke in half, which, in our opinion, is much more dangerous in any case. In addition, in case of accidental strikes on the rail, inevitable during the operation of the jack, its metal could begin to crumble.
If we talk about the differences in withstanding load between jacks different manufacturers, then with a similar chemical composition the strength of the rail is determined by only one thing - the features of the material processing, during which the steel receives additional strength. It is in this that the secret of the ultimate hi-jack stability is hidden.
The chemical composition of the rails (mass fraction,%)
