In determining the size of the required elements of the frame and the cab cross beam rarely cause difficulties, because in most cases the calculations are quite simple. However with posts is not the case. Here, the cross section is more or less limited because the rack should occupy minimum space between the rail and the side wall of the cabin to cabin trim is not too wide. As a result, the bending strength of the rack in the plane of the car frame is limited, and therefore must be checked in the special conditions to ensure that they have sufficient strength and rigidity.
In both cases, the load frame is subjected to the cab tilting moment in its own plane, the value of which is equal to the product of the load on the amount of displacement from the center of the frame of the cab. The guide shoes in contact with the guide resist this tipping point. At the same forces act on the guide shoes and guide shoes. It is these forces cause a bending of the guide shoe racks. As a result, the rack flexes and sags platform on one side.
Although the side struts and trusses are a necessary adjunct car frame, they are usually treated as separate items of equipment of the elevator, since one and the other type of support platform under certain conditions can be used for the same type of car frame. If we talk about the forces acting on the frame of the cab, it is necessary to make a distinction, since the voltage caused by the farm, is different from the stress caused by the lateral struts. Generally, the farms cause more tension in the car frame than the side spacers. They will be discussed in the next section.
The following briefly told about the aspects to be taken into account to determine the required strength of the struts for the most common cases when loading the elevator during its movement.
It was noted earlier that the space below the cabin is highly valued because it is the area lost by to rent each floor. For this reason, the rack frame cabins are rotated so that they occupy minimum space next to the cab. However, we appreciably sacrificing toughness racks. In this position the rack is bent around its weak axis. Sometimes, at high nominal loads, causing large bending moments in the frame of the cab, and a small space in the elevator shaft need to use alternative means of enhancing the design, such as tendons. When the load becomes too great for these types of structures, as usually happens with cabins heavy-duty freight elevators, double racks do so that they bend around its strong axis. Normally, the space in the mine for such systems is sufficient.
Consider the simple case of a lift with lateral supports, with uniformly distributed load and four side struts.
This is the simplest case and the only one which fully known load conditions. The maximum bending moment in the racks occurs when half of the nominal (specified) load is evenly distributed over half the area of the platform from the side wall of the cab to the center line. Tipping mo-mentM equal to the product of the load P / E at a distance of 2/4, will be PE / 8.
Mathematically, this can be written as follows:
This overturning moment M causes a reaction in the guide shoe, which, in turn, create a bend in the direction of the low rack and bending the rails. In addition, the rack are under stress due to the weight of the nominal load, cabin and compensating cargo, if any. The ends of the platforms are supported by the side struts, which in turn are attached to the rack.
When using short struts, which is the standard layout for passenger elevators in the front there is an additional bending moment due to the load on the strut. However, these factors cause a bend around a strong axis rack and small in size. For long spacers such additional bend exists.
Cabins with corner towers used when needed adjacent openings. In this case, the cab frame is located approximately on a diagonal of the platform. Load, attributable to frame cabin with angled legs, usually higher than the load on the frame cabin with side supports.
In this case, more than any one of the preceding, it is necessary to know the precise load conditions, if we want to get economical construction car frame. Load point relative inputs and when loading and when unloading elevator and the position of the load about the center of the cab during the movement of the elevator have such a great influence on the dimensions of the frame members cab, that, in cases where the load is unknown, the calculations necessary to start from the extreme conditions, and this leads to heavier construction than might be required in practice.
For enclosures with corner bearing characterized by two bending points, namely, Pc, and of, each of which generates bending rack in two planes disposed at 90 ° to each other. Moment Pc acts via a coupler farm, from which, in turn, is transmitted to the farm. Then the farm receives a tendency to roll crossmember, which creates a point at the upper end of the bar. This causes a reaction in the guide shoes in contact with the guides. Twisting moment is distributed between the legs proportional to the distance to each of them, which means it is divided equally between the uprights for a square cabin, but the cabin is one of the rectangular rack takes on a more significant part of the bending moment.
If the length of the platform is significantly greater than its width or vice versa, if the load falls into the cab with the short-side turning point P ^ acting in the direction of a weak reception can become quite large. It depends on how close to the front is COG.
Total slack angle platform called cumulative effect of the following factors:
1. The vertical deflection of the cross because of the immediate burden on the farm.
2. The cross bar will twist, bringing the farm; the deflection at the end of ties increases.
3. The farm itself will sag.
4. Racks will sag due to curling cross.
5. The guide will sag.
6. Stretching the hoisting ropes.
For the above cases, the load should be noted that the generated voltage is caused by not only the dynamic loading, but its own weight of the cab. Unwanted deflection platform is only called dynamic load. The deflection caused by own weight of the platform, housing, farms, etc., can be taken into account by adjusting the truss screeds, if not exceeded the allowable stress in the elements of the system.
Some of the above-mentioned cases are most frequently encountered in practice, these include most of the problems with elements of car frame, as regards the conditions of load. In addition to designing car frame for normal usloviydvizheniya and load are considered as emergency conditions caused by, for example, the inclusion of protective systems, or buffer operation.
Frame cabin to withstand the forces acting on it when the catcher picks up and grips the rail. Since catchers are unique to each manufacturer, which give their approvals for these devices, and as there are no two alike greased rails, there is a difference in slowing the effort on both sides of the cabin. This difference forces has the same effect as an eccentric load. Accordingly, there is a tipping point. As already stated, it creates bend rack. Furthermore, racks are compressed because of the portion of the decelerating force which is transferred through the lateral struts.
When triggered buffers, channels timber subjected to considerable bending load. Racks also experience compression and bending, which depend on the position of the load in the cab.
For such emergency conditions, or when you want to test, it allowed much higher voltage than specified Rule 2.15.10 of ASME A17.1. This is justified, since the duration of action of these forces is very small, and besides, such situations are alert.
In the previous case it was assumed that the car frame suspended on ropes attached to the center cross member, which is the case of the ratio 1: 1, 2: 1 ratio to one pulley and the clutch 2: 1 when using two pulleys, if all the ropes go around two pulleys.
If the space in the upper part of the shaft is not enough, and requires a low cab frame, pulleys 2: 1 established under the cab. Depending on the layout, the pulleys can be located with the capture of the parallel bars with diagonal seizure or suspension.
The allowable stress fibers frame cabin and the hitch elements specified in Rule 2.15.10 of ASME A17.1, or other construction standards applicable in a particular case. Allowed deflection stipulated Rule 2.15.11. However, with ASME A17.1 does not specify the distance that may fall below the edge of the platform area in front of the elevator at the time the load in the cabin. Its value depends to some extent on the hardness car frame platforms and rails, as well as the elasticity of the hoisting ropes. Of course, it is impossible to attain absolute rigidity; accordingly, the permissible value is controlled by the appointment of a lift.
7.3. The load on the cab frame and its action — hydraulic lifts
Frames cabin for hydraulic elevators designed, in principle, as well as for traction elevators, with the exception that the lift is a piston fixed under the joists, the joists, usually more crossmembers and protective systems are generally not established. A typical layout is shown in Fig. 25.
Racks (vertical binding bars) exposed to the same bending moments that have been described for traction elevators, but they also experience a compressive load, as the load lying on the platform through the side spacers. Since the compressive load is quite possible to estimate the ratio of the free length of the rack to the radius of inertia must be kept small enough to ensure that the element will not lose stability. When using the long side struts ratio L / r (the ratio of the free length of the rack to the radius of inertia) is limited to ASME Code A17.1 value of 120; However, the use of short struts in passenger elevators allowed ratio L / r equal to 160 as a compressive load acts on spacers on rack over a shorter distance. L — the vertical distance from the bottom of the bolt hole in the crosspiece to the top bolt hole in the rod to attach the reception, as shown in Fig. 25.
8. The guide shoes
The guide shoes elevator and counterweight are sliding or roller type. Before the advent of roller-type passenger elevators are almost exclusively used articulated sliding shoes. In this case, the shoe is held in the bracket and can be rotated by adjusting its position so that it is smooth on the sides of the guide. In the direction against the front surface of the guide shoe is pressed by a spring mounted in the bracket, and is achieved by adjusting the desired gap or displacement in this direction.
The freight elevators, are generally used slide-type shoes with no hinges or automatic alignment guides on the sides. Accordingly, any deviation from the difference frame elements cabin should be adjusted with washers. The shoes are generally provided with removable clamping bars cast iron, usually in the form of a single element. Because of friction in the majority of this type of shoe is provided oiler. In some systems gibs successful non-metallic materials, such as naylatron.
In most passenger elevators nowadays roller guide shoes shoes replaced articulated. They provide smooth movement of the elevator car, even if the guide is not very smooth and straight. The offset is limited to the close proximity of safety guards to the side surfaces of the guide. Each roller is usually mounted on a spring-loaded arm which rotates around the slide.
Here are some advantages of roller guide shoes:
A. In the mine there is no lubrication, which reduces the need for maintenance, in particular, it is not necessary to clean the shaft wall and the pit, and also eliminated a major cause of fires.
B. Eliminates noise from bumps and gnashing associated with the guide.
B. It improves the quality of movement, especially for high-speed elevators.
G. reduce energy consumption of the elevator motor drive.
Each node of the roller guide shoe comprises at least three wheels with rubber tires, normally resiliently fixed by springs or other means. Thus, the elevator rides on wheels 12 coming into contact with the guide. It is important that the cabin was reasonably well balanced in the design phase so that the pressure guide shoes under its own weight, if possible, close to zero. The last twenty years with great success used roller guides with six rollers in the shoe. In this case, the elevator guide roller 24, which improves the quality of the car.
Runners perform the following functions:
A. To guide the vertical movement of the cab and, if possible, prevent its horizontal movement or roll.
B. Prevent tilt cab because the eccentric load, appearing, for example, when a group of passengers standing at one of the side walls or rear wall of the cab.
B. Stop and hold the cab when the protective mechanism.
9.1. Load rails in section 2.23 of ASME A17.1 specified form of guides, material strength and nominal load, but the representatives of lift building industry, users and consultants have long recognized that section 2.23 requires serious review and adjustment, reflecting modern approaches to design.
When you try to formulate a reasonable approach to the revision of section 2.23 there are two principal areas of design, each of which we will briefly examine below. The closest approach to the adjustment section is to develop a rational formula of stability of columns, which as far as possible the most suitable to the existing rails and curves that can be used to extrapolate the values are still not accounted for. You can include additional factors or modifying factors to take into account the effect of long stretches of rails on which there are two connection guide. Long-term approach should be to develop the specifications of the structural properties of the prescribing or otherwise determining the requirements for strength and stiffness, the corresponding static (non-moving) forces acting on the rails as a complex structure with respect to the moving car and counterweight in normal driving conditions and under emergency stop.
When the eccentric load in the cabin of the slope hinder guide shoes or rollers are pressed against the rails. Guide rail in this case acts as a beam support bracket, which must be of sufficient strength to withstand these forces, and sufficient rigidity to maintain the cutting edge of the platform at a playground in front of the lift when the load enters the elevator car or leave it . Now used as a guide section modulus and moment of inertia along both axes. For passenger elevator where the eccentric load is small, these properties are not so important as for freight, in which the eccentric load is usually very large.
Directing, from a security standpoint, it acts as a column, and the more it must bear the load, the larger cross-sectional area of the guide is required. In addition to cross-sectional area, the column should be maintained at a specified interval, otherwise it will tend to lose stability when the fulcrum spaced too far apart. The distance between the points of support preventing buckling depends on the magnitude of the moment of inertia and the minimum cross-sectional area of the guide.
In addition, the inclusion of such a pair of catchers to guide tends to stretch them, which is why one of the catchers can come off the guide. As mentioned earlier, the most important factor in the design of the guide and its supports, is the class of the load.
Allowed some form of guides, in addition to the T-shaped, if it complies with the rules of the ASME A17.1 2.23.3. To guide the other forms are round hollow tubular rails and omegoobraznye guides. Since the circular cross-sections have uniform properties, they are ideal for columns, since the moment of inertia is constant for each principal axis. Round guide is used for hydraulic lifts and balances that do not use safety gear.
What force K1 acting in the frame plane cockpit and R2 force acts on the guide from front to back in a plane perpendicular to the frame of the cab. They have the following effect on the guide:
A. Power of K1 guide bends in the same direction.
B. The strength of the R2 and bends and twists guide.
9.2. Supports guide
When the forces acting on the rails, is not too great, as in passenger elevators, usually fastened to the rail brackets.
If the support can not be set close enough to each other, or when such support are too numerous section of the guide between the brackets should be strengthened. This is done in different ways by U-sections or other structural elements attached to the rear side of the guide, in accordance with the requirements of the ASME rules 188.8.131.52 A17.1.
The strength and stiffness of the guide, with additional fittings or not, are important, but equally important strength and rigidity, which are attached to the rails. This can be a brick wall, the concrete wall, steel buildings, etc. Depending on the design of the building.
It often happens that the shaft wall on which you want to install support are at a considerable distance from the location of the desired track. In this case it may be necessary to install columns sufficiently strong to be resistant to bending and torsion due to the force acting side rail and having a tendency to twist by column torque.