Purification device based on melt crystallization
By using a baffle to separate the distillation tank and the balance pipe connection in the melt crystallization purification unit, the problems of large unit footprint and high nitrogen consumption are solved, achieving a highly efficient purification process and low emissions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- NINGXIA NINGDONG TAIHE CHEM TECH CO LTD
- Filing Date
- 2025-05-12
- Publication Date
- 2026-04-21
AI Technical Summary
Existing melt crystallization purification equipment occupies a large area and has high nitrogen consumption and exhaust gas emissions.
Multiple baffles are used to divide the distillation tank into multiple sub-distillation tanks, and the crystallization box, the material tank and the sub-distillation tanks are connected by a balance pipe. The temperature is controlled by a cooling and heating device to reduce the frequent introduction of nitrogen and the emission of exhaust gas.
This reduces the footprint of the equipment, lowers nitrogen consumption and exhaust emissions, and improves purification efficiency and equipment stability.
Smart Images
Figure CN224141506U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of refining and purification technology, and in particular to a purification apparatus based on melt crystallization. Background Technology
[0002] Melt crystallization is a highly efficient purification technology based on the difference in melting points of substances. By controlling the cooling process or temperature gradient of molten materials, the target substance is selectively crystallized, thereby achieving separation from impurities. This technology is widely used in high-value-added chemicals (such as electronic-grade chemicals, pharmaceutical intermediates, and fragrances), polymer materials, and metal refining, and is especially suitable for the production of heat-sensitive substances or high-purity products.
[0003] Current purification equipment typically has multiple distillation tanks arranged at intervals, which increases the overall footprint of the equipment. Furthermore, during the operation of the equipment, in order to prevent leakage or equipment damage caused by negative pressure, nitrogen needs to be frequently introduced to maintain pressure and exhaust gas to release pressure, resulting in a large consumption of nitrogen and a large amount of exhaust gas emissions.
[0004] Therefore, how to reduce the footprint of the device and reduce nitrogen consumption and exhaust emissions are problems that need to be solved by those skilled in the art. Utility Model Content
[0005] The purpose of this application is to provide a purification device based on melt crystallization to solve the problems of large footprint, large consumption of nitrogen, and large emissions of exhaust gas in current purification devices.
[0006] To solve the above-mentioned technical problems, this application provides a purification device based on melt crystallization, including: a crystallization box, a cooling and heating device, a material tank, a distillation tank, a balance pipe, and a delivery pump;
[0007] The distillation tank is equipped with multiple baffles to divide it into multiple sub-distillation tanks. The balance pipe is connected to the crystallization box, the chemical tank, and the sub-distillation tanks respectively. The cooling and heating device is connected to the crystallization box to regulate its temperature. The outlet of the crystallization box is connected to the chemical tank and the sub-distillation tanks respectively. The chemical tank is connected to the inlet of the crystallization box through the delivery pump.
[0008] In one feasible embodiment, the cooling and heating device includes a medium storage tank, a heating device, a cooling device, a circulating pump, a medium input pipe, and a medium output pipe. The medium input pipe is connected to the outlet of the medium storage tank and the inlet of the crystallization box, respectively. The medium output pipe is connected to the inlet of the medium storage tank and the outlet of the crystallization box, respectively. The heating device is used to heat the medium in the medium storage tank, and the cooling device is used to cool the medium in the medium storage tank. The circulating pump is installed on the medium input pipe or the medium output pipe.
[0009] In one feasible embodiment, a thermometer is installed on both the medium input tube and the medium output tube.
[0010] In one feasible embodiment, the outlet of the crystallization box is connected to a discharge pipe, which has multiple discharge ports. The discharge ports are connected to the inlet of the sub-distillation tank, and the discharge ports on the discharge pipe are higher than the inlet of the sub-distillation tank. The material purity in the sub-distillation tank connected to the upper discharge port is higher than the material purity in the sub-distillation tank connected to the lower discharge port.
[0011] In one feasible embodiment, the crystallization box is connected to a nitrogen input pipe and a tail gas emission pipe, respectively.
[0012] In one feasible embodiment, the discharge port of each of the sub-distillation tanks is connected to the delivery pump.
[0013] In one feasible embodiment, both ends of the distillation tank are provided with end caps, and the end caps are provided with heat preservation devices.
[0014] In one feasible embodiment, the top and bottom of the partition are provided with reinforcing plates, which are respectively connected to the partition and the inner wall of the distillation tank.
[0015] In one feasible embodiment, each of the sub-distillation tanks is provided with a level gauge on its sidewall, the level gauge being used to detect the material level in the sub-distillation tank.
[0016] In one feasible embodiment, the baffles are spaced apart along the length of the distillation tank, each sub-distillation tank has a nitrogen port, a feed port and a first spare port at the top, a second spare port and a discharge port at the bottom, and heating coils are provided on the top and bottom surfaces of each sub-distillation tank.
[0017] This application provides a purification apparatus based on melt crystallization, comprising: a crystallization tank, a cooling and heating device, a material processing tank, a distillation tank, a balance pipe, and a transfer pump. The distillation tank is equipped with multiple baffles to divide it into multiple sub-distillation tanks. The balance pipe connects to the crystallization tank, the material processing tank, and the sub-distillation tanks respectively. The cooling and heating device is connected to the crystallization tank for temperature control. The outlet of the crystallization tank is connected to both the material processing tank and the sub-distillation tanks. The material processing tank is connected to the inlet of the crystallization tank via the transfer pump. The balance pipe, connecting the crystallization tank, the material processing tank, and the sub-distillation tanks, balances the internal pressure of the apparatus, reducing frequent nitrogen injection and exhaust gas emissions. Dividing the distillation tank into multiple sub-distillation tanks by baffles avoids the requirement for spacing between the multiple sub-distillation tanks, reducing the footprint of the apparatus. Attached Figure Description
[0018] To more clearly illustrate the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 A structural diagram of a purification apparatus based on melt crystallization provided in an embodiment of this application;
[0020] Figure 2 This is a structural diagram of a distillation tank provided in an embodiment of this application.
[0021] The attached diagram is labeled as follows: 1-Crystallization box, 2-Cooling and heating device, 3-Chemical tank, 4-Distillation tank, 5-Balance pipe, 6-Transfer pump, 7-Baffle plate, 8-Nitrogen input pipe, 9-Tail exhaust pipe, 10-End cap, 11-Reinforcing plate, 12-Level gauge, 13-Nitrogen port, 14-Feed inlet, 15-First spare port, 16-Second spare port, 17-Discharge port, 18-Heating coil, 201-Circulation pump, 202-Media input pipe, 203-Media output pipe, 401-Sub-distillation tank. Detailed Implementation
[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this application.
[0023] The core of this application is to provide a purification device based on melt crystallization, which reduces the footprint of the device and reduces nitrogen consumption and exhaust emissions.
[0024] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0025] Figure 1 This is a structural diagram of a purification apparatus based on melt crystallization provided in an embodiment of this application. Figure 2 A structural diagram of a distillation tank 4 provided in an embodiment of this application is shown below. Figure 1 and Figure 2 As shown, the purification device based on melt crystallization includes: a crystallization box 1, a cooling and heating device 2, a material tank 3, a distillation tank 4, a balance pipe 5, and a transfer pump 6; the distillation tank 4 is provided with multiple baffles 7 to divide the distillation tank 4 into multiple sub-distillation tanks 401, the balance pipe 5 is connected to the crystallization box 1, the material tank 3, and the sub-distillation tanks 401 respectively, the cooling and heating device 2 is connected to the crystallization box 1 and is used to regulate the temperature of the crystallization box 1, the outlet of the crystallization box 1 is connected to the material tank 3 and the sub-distillation tanks 401 respectively, and the material tank 3 is connected to the inlet of the crystallization box 1 through the transfer pump 6.
[0026] This application embodiment does not specifically limit the shape and size of the crystallization box 1. The cooling and heating device 2 is connected to the crystallization box 1 and is used to regulate the temperature inside the crystallization box 1 to achieve the melting and crystallization process. The material tank 3 is used to store materials and input materials into the crystallization box 1 through the delivery pump 6. The top of the material tank 3 is provided with a material inlet for adding materials to the material tank 3. The distillation tank 4 is used to collect materials of different purities after crystallization and separation. The distillation tank 4 is provided with multiple baffles 7 to divide it into multiple sub-distillation tanks 401 so as to collect materials of different purities separately; the distillation tank 4 can be insulated as a whole. The balance pipe 5 connects the crystallization box 1, the material tank 3 and the sub-distillation tanks 401 to balance the pressure inside the device and avoid pressure fluctuations during the material transfer process. Without the balancing pipe 5, when the pressure in one container drops, nitrogen needs to be frequently introduced to maintain the pressure and prevent leakage or equipment damage caused by negative pressure. The balancing pipe 5 allows gas to flow between containers, thus avoiding this pressure drop and reducing the need for nitrogen replenishment. Without the balancing pipe 5, when the pressure in one container is too high, the system may need to release exhaust gas to relieve pressure and prevent equipment damage. The balancing pipe 5 allows gas to flow between containers, thus avoiding this excessive pressure and reducing exhaust gas emissions. The balancing pipe 5 can be a jacketed balancing pipe 5, consisting of an inner pipe and an outer pipe. The outer pipe forms a jacket space, and the medium circulates within the jacket space via a pump, maintaining a stable temperature within the jacket.
[0027] To facilitate understanding, the working principle of the purification device is described below. Raw materials are stored in the chemical tank 3 and transported to the crystallization tank 1 by the transfer pump 6. In the crystallization tank 1, the temperature is controlled by the cooling and heating device 2, allowing the raw materials to crystallize in a molten state. The crystallized material is distributed through the outlet of the crystallization tank 1 to the chemical tank 3 or the sub-distillation tank 401, with materials of different purities entering their respective sub-distillation tanks 401. Some material can be circulated back to the crystallization tank 1 through the chemical tank 3 for further purification to improve product purity.
[0028] This application provides a purification device based on melt crystallization, comprising: a crystallization tank 1, a cooling and heating device 2, a material processing tank 3, a distillation tank 4, a balance pipe 5, and a transfer pump 6. The distillation tank 4 is divided into multiple sub-distillation tanks 401 by multiple baffles 7. The balance pipe 5 connects to the crystallization tank 1, the material processing tank 3, and the sub-distillation tanks 401 respectively. The cooling and heating device 2 is connected to the crystallization tank 1 to regulate its temperature. The outlet of the crystallization tank 1 is connected to the material processing tank 3 and the sub-distillation tanks 401 respectively. The material processing tank 3 is connected to the inlet of the crystallization tank 1 via the transfer pump 6. The balance pipe 5, connecting the crystallization tank 1, the material processing tank 3, and the sub-distillation tanks 401, balances the internal pressure of the device, reducing frequent nitrogen injection and exhaust emissions. Dividing the distillation tank 4 into multiple sub-distillation tanks 401 by baffles 7 avoids the spacing requirements of the multiple distillation tanks 4, reducing the footprint of the device.
[0029] Based on the above embodiments, the cooling and heating device 2 of this application includes a medium storage tank, a heating device, a cooling device, a circulating pump 201, a medium input pipe 202, and a medium output pipe 203. The medium input pipe 202 is connected to the outlet of the medium storage tank and the inlet of the crystallization box 1, respectively. The medium output pipe 203 is connected to the inlet of the medium storage tank and the outlet of the crystallization box 1, respectively. The heating device is used to heat the medium in the medium storage tank, and the cooling device is used to cool the medium in the medium storage tank. The circulating pump 201 is installed on the medium input pipe 202 or the medium output pipe 203.
[0030] The crystallization tank 1 is equipped with a jacket. The inlet of the jacket is connected to the medium input pipe 202, and the outlet of the jacket is connected to the medium output pipe 203. A medium storage tank is used to store the medium, such as water or heat transfer oil. The outlet of the medium storage tank is connected to the jacket inlet of the crystallization tank 1 via the medium input pipe 202, and the inlet of the medium storage tank is connected to the jacket outlet of the crystallization tank 1 via the medium output pipe 203. A heating device is installed inside or connected to the medium storage tank to heat the medium within the tank. The heating device can be an electric heating element or a burner. A cooling device is installed inside or connected to the medium storage tank to cool the medium within the tank. The cooling device can consist of a cooler, a fan, an evaporator, etc. A circulating pump 201 is installed on the medium input pipe 202 to drive the medium to circulate between the medium storage tank and the crystallization tank 1. The cooling and heating device 2, by integrating heating, cooling, and circulation functions, can regulate the temperature within the crystallization tank 1 to meet various requirements during the melting and crystallization process.
[0031] Based on the above embodiments, thermometers are installed on both the medium input pipe 202 and the medium output pipe 203 in this application embodiment. The thermometer on the medium input pipe 202 is installed near the inlet of the crystallization chamber 1 to monitor the temperature of the medium entering the crystallization chamber 1 in real time. The thermometer on the medium output pipe 203 is installed near the outlet of the crystallization chamber 1 to monitor the temperature of the medium flowing out of the crystallization chamber 1 in real time. High-precision industrial temperature sensors, such as thermocouples or platinum resistance temperature sensors, can be selected as the thermometer type. These sensors can provide accurate and stable temperature readings. The thermometer readings can be fed back to the control system in real time. The control system automatically adjusts the operating status of the heating and cooling devices, as well as the flow rate of the circulating pump 201, based on this data, thereby achieving more precise temperature control. By monitoring the input temperature, it can be ensured that the medium has a suitable temperature when entering the crystallization chamber 1, thereby improving the efficiency of heat transfer. If the input temperature is too high, the temperature inside the crystallization chamber 1 may rise rapidly, affecting the stability of the crystallization process; if the input temperature is too low, it may not be able to provide sufficient heat. By monitoring the output temperature, we can understand the amount of heat absorbed or released by the medium in the crystallization box 1. If the output temperature is too high, it indicates that the heat transfer efficiency in the crystallization box 1 is low, and the power of the cooling device may need to be adjusted. If the output temperature is too low, it indicates that the heat transfer is too fast, and the power of the heating device may need to be adjusted.
[0032] Based on the above embodiments, the discharge port of the crystallization box 1 in this application embodiment is connected to a discharge pipe, and the discharge pipe is provided with multiple discharge ports. The discharge ports are connected to the inlet 14 of the sub-distillation tank 401, and the discharge ports on the discharge pipe are higher than the inlet 14 of the sub-distillation tank 401. The material purity in the sub-distillation tank 401 connected to the upper discharge port is higher than the material purity in the sub-distillation tank 401 connected to the lower discharge port.
[0033] For example, the distillation tank 4 includes three sub-distillation tanks 401, and four discharge ports arranged from highest to lowest as the first discharge port, the second discharge port, the third discharge port, and the fourth discharge port. The first discharge port is connected to the sub-distillation tank 401 containing the material with the highest purity, the second discharge port is connected to the sub-distillation tank 401 containing the material with medium purity, the third discharge port is connected to the sub-distillation tank 401 containing the material with the lowest purity, and the fourth discharge port is connected to the chemical tank 3. This design prevents low-purity materials from entering the sub-distillation tank 401 used to store high-purity materials.
[0034] Based on the above embodiments, in this application embodiment, the crystallization chamber 1 is connected to a nitrogen inlet pipe 8 and a tail gas outlet pipe 9. During the crystallization process, nitrogen enters the crystallization chamber 1 through the nitrogen inlet pipe 8, forming an inert gas environment. Nitrogen can prevent the material from contacting oxygen or moisture in the air, avoiding oxidation, decomposition, or moisture absorption, and ensuring the stability and purity of the material. Nitrogen can also be used to replace the air in the crystallization chamber 1, especially during equipment startup or material replacement, ensuring that the gas environment in the crystallization chamber 1 meets the process requirements. Gases generated during the crystallization process (such as volatile organic compounds, water vapor, etc.) are discharged from the crystallization chamber 1 through the tail gas outlet pipe 9. The safety valve on the tail gas outlet pipe 9 can regulate the flow rate of the tail gas discharge, ensuring stable pressure in the crystallization chamber 1. The safety valve can automatically open when the pressure is too high, preventing equipment damage due to excessive pressure. The nitrogen inlet pipe 8 and the tail gas outlet pipe 9 work together to ensure pressure balance in the crystallization chamber 1.
[0035] Based on the above embodiments, in this application embodiment, the discharge port 17 of each sub-distillation tank 401 is connected to the transfer pump 6. That is, the material in each sub-distillation tank 401 can enter the crystallization box 1. When the material in the sub-distillation tank 401 reaches a certain amount or the crystallization process is completed, the transfer pump 6 is started to transfer the material from the sub-distillation tank 401 to the crystallization box 1. After the material re-enters the crystallization box 1, it can undergo the melting and crystallization process again to further improve the purity of the material.
[0036] Based on the above embodiments, the distillation tank 4 of this application embodiment is provided with end caps 10 at both ends, and a heat insulation device is provided inside the end caps 10. The end caps 10 at both ends of the distillation tank 4 are used to seal both ends of the distillation tank 4 and prevent material leakage. The end caps 10 are typically made of robust materials, such as stainless steel or alloys, to ensure their strength and durability. The heat insulation device is installed inside the end caps 10 and can use various heat insulation materials, such as rock wool, glass wool, polyurethane foam, etc., which have good thermal insulation properties; it can also be a heating element such as a heating coil 18. During the crystallization process, the material in the distillation tank 4 needs to be maintained within a certain temperature range. The heat insulation device can effectively reduce heat loss to the outside through the end caps 10, ensuring temperature stability within the distillation tank 4.
[0037] Based on the above embodiments, in this application embodiment, the top and bottom of the partition 7 are provided with reinforcing plates 11, which are respectively connected to the inner walls of the partition 7 and the distillation tank 4. The reinforcing plates 11 can be made of stainless steel, carbon steel, or other high-strength alloy materials. Figure 2 As shown, the reinforcing plate 11, the partition plate 7, and the distillation tank 4 form a triangular structure. The triangular structure has extremely high stability and can effectively resist the action of external forces. When the partition plate 7 is subjected to material pressure and flow impact, the triangular fixing can significantly reduce the deformation and displacement of the partition plate 7, which meets the requirements for use under normal pressure.
[0038] Based on the above embodiments, each sub-distillation tank 401 in this application embodiment is equipped with a level gauge 12 on its side wall. The level gauge 12 is used to detect the material level in the sub-distillation tank 401. When the liquid level reaches the set high level, the control system triggers the start of the transfer pump 6 to transfer the material from the sub-distillation tank 401 to the crystallization box 1 or subsequent processing equipment; when the liquid level drops to the set low level, the transfer pump 6 stops running to avoid excessive material transfer or insufficient material in the tank.
[0039] Based on the above embodiments, in this application embodiment, the partition 7 is arranged at intervals along the length of the distillation tank 4. Each sub-distillation tank 401 is provided with a nitrogen port 13, a feed port 14 and a first spare port 15 at the top, and a second spare port 16 and a discharge port 17 at the bottom. Each sub-distillation tank 401 is provided with a heating coil 18 on both the top and bottom surfaces.
[0040] Partitions 7 are spaced along the length of the distillation tank 4, dividing it into multiple sub-distillation tanks 401. Each sub-distillation tank 401 can independently collect materials of different purities. A nitrogen inlet 13 is used to introduce nitrogen into the sub-distillation tank 401 to protect the material and prevent oxidation or contamination. The feed inlet 14 is connected to the discharge outlet of the crystallization box 1. The first spare inlet 15 and the second spare inlet 16 can be connected to other equipment or used for special operations as needed. The discharge outlet 17 is used to discharge the material from the sub-distillation tank 401. Each sub-distillation tank 401 has heating coils 18 on its top and bottom surfaces to heat the material within, ensuring it is stored at an appropriate temperature and preventing crystallization that adheres to the inner wall of the sub-distillation tank 401, thus reducing material loss during transfer.
[0041] The above provides a detailed description of a purification apparatus based on melt crystallization provided in this application. The various embodiments in the specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.
[0042] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
Claims
1. A purification apparatus based on melt crystallization, characterized in that include: Crystallization box (1), cooling and heating device (2), material tank (3), distillation tank (4), balance pipe (5) and transfer pump (6); The distillation tank (4) is provided with multiple baffles (7) to divide the distillation tank (4) into multiple sub-distillation tanks (401). The balance pipe (5) is connected to the crystallization box (1), the chemical tank (3) and the sub-distillation tank (401) respectively. The cooling and heating device (2) is connected to the crystallization box (1) and is used to regulate the temperature of the crystallization box (1). The outlet of the crystallization box (1) is connected to the chemical tank (3) and the sub-distillation tank (401) respectively. The chemical tank (3) is connected to the inlet of the crystallization box (1) through the conveying pump (6).
2. The purification apparatus based on melt crystallization according to claim 1, characterized in that The cooling and heating device (2) includes a medium storage tank, a heating device, a cooling device, a circulating pump (201), a medium input pipe (202), and a medium output pipe (203). The medium input pipe (202) is connected to the outlet of the medium storage tank and the inlet of the crystallization box (1), respectively. The medium output pipe (203) is connected to the inlet of the medium storage tank and the outlet of the crystallization box (1), respectively. The heating device is used to heat the medium in the medium storage tank, and the cooling device is used to cool the medium in the medium storage tank. The circulating pump (201) is installed on the medium input pipe (202) or the medium output pipe (203).
3. The purification apparatus based on melt crystallization according to claim 2, characterized in that Thermometers are installed on both the medium input pipe (202) and the medium output pipe (203).
4. The purification apparatus based on melt crystallization according to claim 1, characterized in that The outlet of the crystallization box (1) is connected to a discharge pipe, which is provided with multiple discharge ports. The discharge ports are connected to the inlet (14) of the sub-distillation tank (401), and the discharge ports on the discharge pipe are higher than the inlet (14) of the sub-distillation tank (401). The material purity in the sub-distillation tank (401) connected to the upper discharge port is higher than the material purity in the sub-distillation tank (401) connected to the lower discharge port.
5. The purification apparatus based on melt crystallization according to claim 1, characterized in that The crystallization box (1) is connected to the nitrogen input pipe (8) and the exhaust pipe (9) respectively.
6. The purification apparatus based on melt crystallization according to claim 1, characterized in that The discharge port (17) of each of the subdistillation tanks (401) is connected to the delivery pump (6).
7. The purification apparatus based on melt crystallization according to claim 1, characterized in that Both ends of the distillation tank (4) are provided with end caps (10), and the end caps (10) are provided with heat preservation devices.
8. The purification apparatus based on melt crystallization according to claim 1, characterized in that, The top and bottom of the partition (7) are provided with reinforcing plates (11), which are respectively connected to the inner wall of the partition (7) and the distillation tank (4).
9. The purification apparatus based on melt crystallization according to claim 1, characterized in that Each of the sub-distillation tanks (401) is provided with a level gauge (12) on its sidewall, the level gauge (12) being used to detect the material level in the sub-distillation tank (401).
10. The purification apparatus based on melt crystallization according to any one of claims 1 to 9, characterized in that The partition (7) is spaced apart along the length of the distillation tank (4). Each sub-distillation tank (401) has a nitrogen port (13), a feed port (14) and a first spare port (15) at the top. Each sub-distillation tank (401) has a second spare port (16) and a discharge port (17) at the bottom. Each sub-distillation tank (401) has a heating coil (18) on its top and bottom surfaces.