NJ series backstopDetailed product description：

The NJ type contact wedge block backstop is a new type of backstop device used for belt conveyors. It is directly installed on the transmission drum shaft extension or the low-speed shaft extension of the reducer, and has strong anti reverse ability, allowing the maximum torsional rejection to usually reach hundreds of thousands of Newton meters or more. When a large belt conveyor loaded with materials suddenly stops running due to various reasons, the NJ type backstop can effectively prevent reverse sliding accidents caused by material gravity; And in the reverse state, the entire drive device is still in the unloaded state, which not only does not affect the maintenance and replacement of drive components such as motors and reducers, but also makes it safer and more reliable to prevent reverse accidents caused by damage to the drive system. Therefore, it is an ideal anti reverse safety protection device for large belt conveyors.

Model meaning
For example, the code NJ16-S-140 represents the NJ type contact type backstop, with a rated backstop torque of 16000N. m, the inner ring rotates clockwise, and the installation hole diameter is 140mm.

Structure and Working Principle
The wedge block, inner ring, and outer ring are the basic anti stop components of the wedge block anti stop, among which the wedge block (Figure 1) is the key part of the anti stop. The wedge block anti stop utilizes the unique cross-sectional shape of the wedge block, as well as its special geometric and mechanical relationships with the inner and outer rings, to achieve one-way braking.


In the manufacturing process of the backstop, advanced alloy steel materials are strictly selected for the basic backstop components, which are precision machined and rigorously heat-treated to ensure accurate backstop action, strong load-bearing capacity, easy release, and safe and reliable performance. The wedge block of the backstop is installed in the cage, and a certain number of rollers are arranged between the wedge blocks to form a wedge block device component (Figure 2). The rollers are used to maintain the concentricity of the inner and outer rings, while bearing radial loads. The structure is very compact.


The wedge assembly component is installed in the raceway formed by the inner and outer rings. When the backstop rotates freely, the roller will rotate with its own axis and drive the cage and wedge to revolve along the inner and outer rings. On the one hand, it evenly spreads lubricating oil (grease) in the raceway, improving the lubrication effect; On the other hand, it constantly changes the contact position between the wedge block and the inner and outer rings to ensure the reliable performance of the backstop during long-term use.

Technical characteristics and installation dimensions

Table 1 Main parameters of NJ type backstop

Specification	Maximum reverse torque N · m	Maximum speed of inner circle r/min	Idle resistance torque N · m	Maximum aperture mm	Maximum mass kg
NJ25	25000	100	35	160	112
NJ38	38000	100	45	200	183
NJ50	50000	80	75	220	355
NJ90	90000	50	95	250	644
NJ125	125000	50	100	270	755
NJ180	180000	50	110	300	1088
NJ270	270000	50	140	320	1426
NJ320	320000	50	160	350	1921
NJ520	520000	50	220	420	2945
NJ700	700000	50	250	450	3518

NJ25-NJ90 contact type backstop NJ125-NJ170 contact type backstop

Table 2 Installation dimensions of NJ type backstop

Specification	Structural dimensions (mm)
	d	A	B	C	D	E	F	H	h	L
NJ25	120-160	—-	140	80	360	—-	—-	800	—-	180
NJ38	160-200	—-	160	88	430	—-	—-	850	—-	210
NJ50	160-220	—-	200	100	500	—-	—-	1000	—-	240
NJ90	180-250	—-	250	120	600	—-	—-	1200	—-	290
NJ125	200-270	40	280	120	650	120	60	1100	80	290
NJ180	230-300	45	320	130	780	135	60	1300	80	320
NJ270	250-320	50	360	140	850	150	70	1500	100	340
NJ320	250-350	55	400	140	930	160	70	1600	100	360
NJ520	320-420	60	450	150	1030	180	80	1800	120	450
NJ700	350-450	70	500	160	1090	210	100	2000	120	480

Table 3 Diameter range of installation holes for NJ type backstop

Specification	Installation aperture range mm	Preferred installation hole diameter mm
NJ25	120-160	120,130,140,150,160
NJ38	160-200	160,170,180,190,200
NJ50	160-220	160,170,180,190,200,210,220
NJ90	180-250	180,190,200,210,220,230,230,240,250
NJ125	200-270	200,210,220,230,240,250,260,270
NJ180	230-300	230,240,250,260,270,280,290,300
NJ270	250-320	250,260,270,280,290,300,320
NJ320	250-350	250,260,270,280,290,300,320,340,350
NJ520	320-420	320,340,350,380,400,420
NJ700	350-450	350,380,400,420,450

Within a certain range, each specification of backstop has several different installation hole diameters for users to choose from. The range of installation hole diameters and the available preferred installation hole diameters are shown in Table 3. Unless otherwise specified by the user, the installation hole size and dimensional accuracy shall be supplied according to the user's requirements.
The installation hole of the backstop adopts a flat key form, and the keyway size is provided according to GB1095-79 standard.

Installation of backstop
Before installation, it should be checked whether the operating speed of the shaft where the backstop is installed is within the maximum speed range allowed by the backstop;
Due to the fact that the inner ring of the backstop can only rotate in one direction, the direction of rotation is indicated by the arrow on the steering indicator on the outer shell. Before installation, it is necessary to check whether the rotation direction of the shaft is consistent with the rotation direction of the inner ring of the backstop;
When installing the backstop, only apply pressure to the inner ring of the backstop. To avoid damaging the inner ring end, please use a wooden hammer to strike. Do not knock on the outer shell, sealing sleeve, dust cover and other parts of the backstop;
When assembling the backstop with the shaft, only flat keys can be used and wedge keys are not allowed.
⑸ For the check valve with thin oil lubrication, one of the four oil injection holes should be located at the bottom of the housing for future maintenance (refer to Figure 4);


After installation, press the inner ring of the backstop with an end cap at the end of the shaft;
The lower end of the anti rotation arm of the backstop should be fixed between two blocking irons, and it should be ensured that the backstop can move freely in the axial direction. There should be a gap of 5-10mm between the blocking iron and the force arm;
The anti rotation arm of the backstop should be installed vertically as much as possible, and can also be installed in a tilted or horizontal manner;
All shaft end cover plates, stoppers, etc. are not included in the supply scope of the backstop and are to be resolved by the user themselves.

Controlled by controls
Wedges, rollers, retainers, inner wheels, outer wheels.

vulnerable parts
Skeleton oil seal, rubber strip, bearing.

Lubrication and maintenance
⑴ The lubrication of NJ type contact wedge block backstop adopts thin oil lubrication, using No. 40 mechanical lubricating oil. The product is not equipped with lubricating oil at the factory and must be refilled before use;
There are four holes on the outer shell of the check valve for oil injection, oil level inspection, and oil discharge (see Figure 4). Remove the hole plug to inject oil and check the oil level, inject oil from the top until it overflows from the oil level, and then tighten the hole plug;
After the first 24 hours of operation, drain all the oil, clean the internal cavity of the check valve with clean oil, and then inject clean lubricating oil that meets the requirements.
After running the check valve for one month, drain all the oil and replace all the engine oil. Then, add some new oil every three months and replace all the engine oil every six months.
After one year of operation, the backstop should be disassembled, cleaned, and checked for any detachment or damage to the spring, as well as the integrity of the wedge, inner ring, outer ring, and rollers. If there are any defects, they should be replaced immediately.
Regularly check the fastening bolts of the anti rotation arm and anti transposition to ensure effective fastening.

Safety Warning and Precautions
When installing the backstop, pay attention to the rotation direction of the rotating label. The direction of rotation of the label should be consistent with the direction of operation of the backstop. Lubricating oil (grease) containing molybdenum disulfide, graphite, or any extreme pressure additive that improves lubrication performance cannot be used. These additives can reduce the coefficient of meshing friction and may cause the backstop to slip.

Fault analysis and troubleshooting

Fault phenomenon	Cause analysis	Exclusion method
The backstop does not work	The direction of rotation towards the label is reversed or the installation of the reverse stopper is reversed	Reverse the installation of the backstop
The check valve has leakage phenomenon	Hydraulic components are not tightly sealed, or the seals are deformed due to compression	Re tighten or replace the seal
Abnormal operation of the backstop	The oil is too dirty	Filter or replace working oil